0001564590-21-013589 | 10-K | XBRL Viewer

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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2020	Mar. 09, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Registrant Name	PLIANT THERAPEUTICS, INC.
Entity Central Index Key	0001746473
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Well-known Seasoned Issuer	No
Entity Public Float			$ 855,889,147
ICFR Auditor Attestation Flag	false
Entity Common Stock, Shares Outstanding		35,738,192
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	PLRX
Security Exchange Name	NASDAQ
Entity File Number	001-39303
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	47-4272481
Entity Address, Address Line One	260 Littlefield Avenue
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	481-6770
Document Annual Report	true
Document Transition Report	false
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive Proxy Statement for the 2021 Annual Meeting of Stockholders to be filed with the U.S. Securities and Exchange Commission pursuant to Regulation 14A not later than 120 days after the end of the fiscal year covered by this Annual Report on Form 10-K are incorporated by reference in Part III, Items 10-14 of this Annual Report on Form 10-K

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 50,882	$ 85,807
Short-term investments	226,012	16,966
Accounts receivable	9,279	7,052
Tax credit receivable	83	333
Prepaid expenses and other current assets	4,498	1,742
Total current assets	290,754	111,900
Property and equipment, net	4,321	4,079
Other non-current assets	451	3,085
Total assets	295,526	119,064
Current liabilities
Accounts payable	2,023	1,250
Accrued liabilities (Note 5)	9,576	6,922
Total current liabilities	11,599	8,172
Other long-term liabilities (Note 5)	866	912
Total liabilities	12,465	9,084
Commitments and Contingencies (Note 13)
Stockholders’ equity (deficit)
Preferred stock, $0.0001 par value; 10,000,000 shares and 0 shares authorized at December 31, 2020 and 2019, respectively; 0 shares issued and outstanding at December 31, 2020 and 2019;	0	0
Common stock, $0.0001 par value; 300,000,000 and 181,000,000 shares authorized at December 31, 2020 and 2019; and 35,552,795 and 1,846,024 shares issued and outstanding at December 31, 2020 and 2019, respectively;	3	1
Additional paid-in capital	400,918	0
Accumulated deficit	(117,828)	(76,295)
Accumulated other comprehensive loss	(32)	(1)
Total stockholders’ equity (deficit)	283,061	(76,295)
Total liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit)	295,526	119,064
Series A Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock
Redeemable convertible preferred stock value	0	62,468
Series B Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock
Redeemable convertible preferred stock value	0	75,860
Series C Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock
Redeemable convertible preferred stock value	$ 0	$ 47,947

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	181,000,000
Common stock, shares issued	35,552,795	1,846,024
Common stock, shares outstanding	35,552,795	1,846,024
Series A Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, par value	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized	0	56,000,000
Redeemable convertible preferred stock, shares issued	0	56,000,000
Redeemable convertible preferred stock, shares outstanding	0	56,000,000
Redeemable convertible preferred stock. aggregate liquidation preference	$ 0	$ 62,468
Series B Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, par value	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized	0	49,501,221
Redeemable convertible preferred stock, shares issued	0	49,501,221
Redeemable convertible preferred stock, shares outstanding	0	49,501,221
Redeemable convertible preferred stock. aggregate liquidation preference	$ 0	$ 75,860
Series C Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, par value	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized	0	44,000,000
Redeemable convertible preferred stock, shares issued	0	26,360,745
Redeemable convertible preferred stock, shares outstanding	0	26,360,745
Redeemable convertible preferred stock. aggregate liquidation preference	$ 0	$ 47,947

Statements of Operations and Comprehensive Loss - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2020

Dec. 31, 2019

Income Statement [Abstract]

Revenue — related party

$ 41,817

$ 57,052

Operating expenses:

Research and development

(66,193)

(47,353)

General and administrative

(17,269)

(10,930)

Total operating expenses

(83,462)

(58,283)

Loss from operations

(41,645)

(1,231)

Interest income

478

816

Other expense, net

(366)

(216)

Net loss

(41,533)

(631)

Accretion to redemption value and dividends on redeemable convertible preferred stock

(6,225)

Net loss attributable to common stockholders

$ (41,533)

$ (6,856)

Net loss per share, attributable to common stockholders:

Basic

$ (1.95)

$ (4.22)

Diluted

$ (1.95)

$ (4.22)

Shares used in computing net loss per share attributable to common stockholders:

Basic

21,344,236

1,623,358

Diluted

21,344,236

1,623,358

Comprehensive loss:

Net loss

$ (41,533)

$ (631)

Other comprehensive loss:

Net unrealized loss on short-term investments

^[1]

(31)

(1)

Total other comprehensive loss

(31)

(1)

Comprehensive loss

$ (41,564)

$ (632)

[1]	Tax effect is nil for all periods presented.

Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($)
$ in Thousands

Total

Initial Public Offering

Private Placement

Series A Redeemable Convertible Preferred Stock

Series B Redeemable Convertible Preferred Stock

Series C Redeemable Convertible Preferred Stock

Common Stock

Initial Public Offering

Common Stock

Private Placement

Additional Paid-In Capital

Initial Public Offering

Additional Paid-In Capital

Private Placement

Accumulated Other Comprehensive Gain (Loss)

Accumulated Deficit

Beginning balance at Dec. 31, 2018

$ (71,469)

$ 1

$ (71,470)

Beginning balance, shares at Dec. 31, 2018

56,000,000

49,501,221

Beginning balance at Dec. 31, 2018

$ 61,516

$ 70,587

Beginning balance, shares at Dec. 31, 2018

1,363,000

Issuance of Series C redeemable preferred stock, shares

26,360,745

Issuance of Series C redeemable preferred stock

$ 47,947

Vesting of founders’ common stock and restricted stock awards

$ 28

Vesting of founders’ common stock and restricted stock awards, shares

440,964

Option exercises

174

Option exercises, shares

42,060

Accretion to redemption value and cumulative dividends on redeemable convertible preferred stock

$ 952

$ 5,273

Accretion to redemption value and cumulative dividends on redeemable convertible preferred stock

(6,225)

(2,031)

(4,194)

Stock-based compensation expense

1,829

Net unrealized loss on short-term investments

(1)

^[1]

$ (1)

Net loss

(631)

Ending balance at Dec. 31, 2019

$ (76,295)

$ 1

(1)

(76,295)

Ending balance, shares at Dec. 31, 2019

56,000,000

49,501,221

26,360,745

Ending balance at Dec. 31, 2019

$ 62,468

$ 75,860

$ 47,947

Ending balance, shares at Dec. 31, 2019

1,846,024

Issuance of common/preferred stock

$ 148,278

$ 10,000

$ 1

$ 148,277

$ 10,000

Issuance of Series C redeemable preferred stock, shares

28,527,313

Issuance of Series C redeemable preferred stock

$ 52,019

Issuance of common/preferred stock, shares

10,350,000

625,000

Conversion of Series A, B, C convertible preferred stock to common stock

$ 238,294

$ 1

238,293

Conversion of Series A, B, C convertible preferred stock to common stock, shares

(56,000,000)

(49,501,221)

(54,888,058)

Conversion of Series A, B, C convertible preferred stock to common stock

$ (62,468)

$ (75,860)

$ (99,966)

Conversion of Series A, B, C convertible preferred stock to common stock, shares

22,432,029

Vesting of restricted stock awards

Vesting of restricted stock awards, shares

163,544

Option exercises

442

Option exercises, shares

136,198

Stock-based compensation expense

3,895

Net unrealized loss on short-term investments

(31)

^[1]

(31)

Net loss

(41,533)

Ending balance at Dec. 31, 2020

$ 283,061

$ 3

$ 400,918

$ (32)

$ (117,828)

Ending balance, shares at Dec. 31, 2020

Ending balance at Dec. 31, 2020

$ 0

Ending balance, shares at Dec. 31, 2020

35,552,795

[1]	Tax effect is nil for all periods presented.

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (41,533)	$ (631)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	1,310	1,113
Stock-based compensation expense	3,895	1,829
Other losses	266	0
Changes in operating assets and liabilities:
Tax credit receivable	250	167
Accounts receivable	(2,227)	(7,052)
Prepaid expenses and other current assets	(2,756)	(1,458)
Other non-current assets	(70)	232
Accounts payable	922	(1,255)
Accrued liabilities	2,689	4,255
Deferred rent and other long-term liabilities	(17)	50
Net cash used in operating activities	(37,271)	(2,750)
Cash flows from investing activities:
Purchase of short-term investments	(322,605)	(51,713)
Accretion on short-term investments	0	(254)
Maturity of short-term investments	113,271	35,000
Purchase of property and equipment	(1,532)	(964)
Net cash used in investing activities	(210,866)	(17,931)
Cash flows from financing activities:
Proceeds from issuance of common stock upon initial public offering, net of issuance costs	150,751	0
Proceeds from issuance of common stock upon completion of private placement	10,000	0
Proceeds from issuance of Series C preferred stock, net of issuance costs	52,019	47,947
Proceeds from exercise of stock options	442	174
Payment of deferred offering costs	0	(2,582)
Net cash provided by financing activities	213,212	45,539
Net (decrease) increase in cash and cash equivalents	(34,925)	24,858
Cash and cash equivalents at beginning of period	85,807	60,949
Cash and cash equivalents at end of period	50,882	85,807
Supplemental disclosures of noncash investing and financing activities:
Purchase of property and equipment in accounts payable and accrued liabilities	188	159
Reclassification of restricted stock awards from liabilities to common stock upon vesting	11	30
Accretion to redemption value and dividends on redeemable convertible preferred stock	0	6,225
Deferred offering costs in accounts payable and accrued liabilities	0	230
Net unrealized loss on short-term investments	$ (31)	$ (1)

Description of Business

12 Months Ended

Dec. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Description of Business

1.	Description of Business

Pliant Therapeutics, Inc. (the “Company”) is a clinical stage biopharmaceutical company focused on discovering and developing novel therapies for the treatment of fibrosis with an initial focus on treating fibrosis by inhibiting integrin-mediated activation of TGF-ß. Fibrosis refers to the abnormal thickening and scarring of connective tissue due to the production and deposition of excess collagen in the extra-cellular matrix. Fibrosis can occur in many different tissues including lung, liver, kidney, muscle, skin and the GI tract, and often causes severe and debilitating disease leading to organ failure. The Company is located in South San Francisco, California, and was incorporated in the state of Delaware in June 2015.

Reverse Stock Split

In May 2020, the Company implemented a 1-for-7.15 reverse stock split of the Company’s common stock. Stockholders entitled to fractional shares as a result of the reverse stock split received a cash payment in lieu of receiving fractional shares. All share and per share data shown in the accompanying financial statements and related notes have been retroactively revised to reflect the reverse stock split. Shares of common stock underlying outstanding stock options and other equity instruments were proportionately reduced and the respective exercise prices, if applicable, were proportionately increased in accordance with the terms of the agreements governing such securities. Shares of common stock reserved for issuance upon the conversion of the Company’s Convertible Preferred Stock were proportionately reduced and the respective conversion prices were proportionately increased. As of June 3, 2020, all outstanding preferred stock have been converted into common stock.

Initial Public Offering

In June 2020, the Company completed its initial public offering (“IPO”), in which the Company issued and sold an aggregate of 10,350,000 shares of common stock, which included 9,000,000 shares of common stock and 1,350,000 shares of common stock sold pursuant to the underwriters’ exercise of their option to purchase additional shares, at a public offering price of $16.00 per share. The aggregate net proceeds received by the Company from the offering were $148.3 million, net of underwriting discounts, commissions and offering expenses of $5.7 million, of which $2.6 million were paid in 2019 and $3.1 million paid in the current year. Upon the closing of the IPO, 160,389,279 shares of the Company’s outstanding convertible preferred stock were automatically converted to common stock on a 7.15:1 basis and the related carrying amount of $238.3 million was reclassified to common stock and additional paid-in capital within stockholders’ equity (deficit). Concurrent with the completion of the IPO, the Company also issued 625,000 shares of its common stock to Novartis (“Novartis”), a strategic partner and existing stockholder of the Company, in a private placement at a price of $16.00 per share for proceeds of $10.0 million, which resulted in Novartis owning approximately 6.1% of the Company’s outstanding shares of common stock (Note 6).

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2.	Summary of Significant Accounting Policies

Policies Basis of Presentation

The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”).

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, and expenses as well as the disclosure of contingent assets and liabilities as of and during the reporting period. The Company bases its estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, useful lives assigned to property and equipment, the fair values of common and redeemable convertible preferred stock, stock-based compensation expense, accruals for research and development costs, income taxes and uncertain tax positions. The Company assesses estimates on an ongoing basis; however, actual results could materially differ from those estimates.

Revenue Recognition

Effective January 1, 2018 the Company adopted the provision of Accounting Standards Update or ASU, ASU 2014-09, Topic 606 Revenue from Contracts with Customers (“Topic 606”) using the full retrospective transition method. ASU 2014-09 provides a single, comprehensive revenue recognition model for all contracts with customers. This standard contains principles for the determination of the measurement of revenue and the timing of when such revenue is recognized. Revenue recognition will reflect the transfer of goods or services to customers at an amount that is expected to be earned in exchange for those goods or services. Subsequently, the FASB has issued the following guidance to amend ASU 2014-09: ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date; ASU 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net); ASU 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing; ASU 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients; and ASU 2016-20, Technical Corrections and Improvements to Topic 606, which clarifies narrow aspects of Topic 606 or corrects unintended application of the guidance. The Company must adopt ASU 2015-14, ASU 2016-08, ASU 2016-10, ASU 2016-12, and ASU 2016-20 with ASU 2014-09, which are referred to collectively as the “Topic 606”.

The FASB issued ASU 2018-18, “Collaborative Arrangements (Topic 808)” issued in November 2018. The Company assessed and concluded that they are not under Topic 808 and as the Novartis Agreement is not considered a collaboration under its provisions.

The Company’s revenue is generated solely from the Collaboration and License Agreement with Novartis (the “Novartis Agreement”). The Company’s licensing agreement includes upfront signing fees, cost reimbursements, research and development services, milestone payments and royalties on future licensee’s product sales. The Company has both fixed and variable consideration. Non-refundable upfront fees are considered fixed, while funding of research and development activities and milestone payments are identified as variable consideration. A contract liability is an obligation to transfer goods or services for which the Company has received consideration, or for which an amount of consideration is due from the customer. A contract asset is a right to consideration in exchange for goods or services that the Company has transferred to a customer when that right is conditional on something other than the passage of time. A receivable will be recorded on the balance sheet when the Company has unconditional rights to consideration (i.e., only the passage of time is required before payment becomes due). Receivables cannot be netted against contract liabilities and are presented separately from contract assets. Contract assets and contract liabilities are netted at the contract level and are then aggregated and presented separately each reporting period.

In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under its agreements, the Company performs the following steps: (i) identification of the contract with a customer; (ii) identification of the performance obligations in the contract; (iii) determination of the transaction price; (iv) allocation of the transaction price to the performance obligations in the contract; and (v) recognition of revenue when (or as) we satisfy each performance obligation.

A performance obligation is a promise in a contract to transfer a distinct good or service to the customer. The Company’s performance obligations include providing the worldwide license rights to compound PLN-1474, provide research and development services for PLN-1474 through Phase 1 of its development, achieving certain development or regulatory milestones and provide research and development services on initial candidate targets, which services are combined with a non-exclusive license to the initial candidate targets. The Company concluded that the worldwide license was distinct because the customer can benefit from the license on its own or together with other resources that are readily available, and the research and development services are not transformative in nature. The Company concluded the research and development services on initial candidate targets were not distinct from a non-exclusive license for the initial candidate targets, primarily as a result of (i) Pliant being unable to benefit on its own or together with other resources that are readily available as the license and (ii) the research and development services, including manufacturing in support of such services, were expected to significantly modify the initial license. Therefore, the promised goods and services were considered a single performance obligation. Significant management judgment is required in the identification of performance obligations and to determine the level of effort required under an arrangement and the period over which the Company expects to complete our performance obligations under the arrangement. If the Company cannot reasonably estimate when the performance obligations either are completed or become inconsequential, then revenue recognition is deferred until the Company can reasonably make such estimates. The Company estimates the transaction price and records revenue in the amount for which it is probable that a significant reversal of cumulative revenue recognized will not occur. At the end of each subsequent reporting period, we re-evaluate the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Revenue is then recognized over the remaining estimated period of performance using the cumulative catch-up method. The estimated period of performance and project costs are reviewed quarterly and adjusted, as needed, to reflect the Company’s current assumptions regarding the timing of our deliverables.

As part of the accounting for these arrangements, the Company must develop assumptions that require judgment to determine the stand-alone selling price of each performance obligation identified in the contract. The Company has never sold the performance obligations separately; therefore, an observable stand-alone selling price does not exist. Accordingly, the Company estimates a stand-alone selling price through maximizing the use of observable inputs such as market data, project cost estimates, and targeted margins. The Company determined that each of the performance obligations is priced and delivered at the stand-alone selling price. Therefore, no reallocations are needed since there is no material right and the license and services are provided at the stand-alone selling price.

During the years ended December 31, 2020 and 2019, the entirety of the Company’s revenue—related party is related to the Collaboration and License Agreement with Novartis. The Company did not have any prior revenue agreements and did not recognize revenue prior to 2019. Receivables from collaborations are typically unsecured and are concentrated in the biopharmaceutical industry. Accordingly, the Company may be exposed to credit risk generally associated with biopharmaceutical companies or specific to the Novartis Agreement. An allowance on the receivables will be recorded if circumstances indicate collection is doubtful for a particular receivables balance. To date, the Company has not experienced any losses related to these receivables.

Fair Value Measurements

The Company defines fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities which are required to be recorded at fair value, the Company considers the principal or most advantageous market in which to transact and the market-based risk. Fair value accounting is applied for all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. The carrying amount of the Company’s financial instruments, including cash and cash equivalents, short-term investments, tax credit receivable, accounts receivable, prepaid expenses and other current assets, accounts payable and accrued liabilities approximate fair value due to their short-term maturities.

Concentration of Credit Risk and Other Risks and Uncertainties

Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents, short-term investments and accounts receivable. The Company invests in money market funds, treasury bill and notes, government notes and corporate debt securities. The Company limits its credit risk associated with its cash and cash equivalents by placing them with banks and institutions it believes are highly credit worthy and in highly rated investments. However, the Company had deposits in excess of the Federal Deposit Insurance Corporation (“FDIC”) insured limit of $250,000. The Company performs credit evaluations of its customer, and the risk with respect to accounts receivable is further mitigated by the short duration of customer payment terms, generally within 60 days, and the pedigree of the customer base. During the year ended December 31, 2020, Novartis accounted for 100% of the Company’s revenue—related party and accounts receivable.

The Company’s future results of operations involve several other risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty of results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s product candidates, uncertainty of market acceptance of the Company’s product candidates, competition from substitute products, including those that may be developed or marketed by larger companies, securing and protecting intellectual property, strategic relationships and dependence on key individuals and sole source suppliers.

The Company’s product candidates require approvals from the U.S. Food and Drug Administration (“FDA”) and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company.

Segments

The Company operates and manages its business as one reportable and operating segment, which is the business of developing and commercializing novel therapies for fibrotic diseases. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for allocating and evaluating financial performance. All long-lived assets are maintained in the United States of America.

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents consist primarily of amounts invested in Money Market Funds, United States (“U.S.”) treasury securities, U.S. government agency securities and corporate debt securities and are stated at fair value.

Short-Term Investments

The Company’s short-term investments consist of U.S. Treasury securities, U.S. government agency securities and corporate debt securities with remaining maturities beyond three months at the date of purchase. The Company has classified and accounted for its short-term investments as available-for-sale securities as the Company may sell these securities at any time even prior to maturity and such investments represent cash available for current operations. As a result, short-term investments may include securities with maturities beyond twelve months that are classified within current assets in the Balance Sheets. As of December 31, 2020 and 2019, all of the Company’s short-term investments were classified as available-for-sale and were carried at fair market value with unrealized losses or income recorded in other comprehensive loss in the statements of operations and comprehensive loss. See Note 3 for further details.

Short-term investments are considered impaired when a decline in fair value is judged to be other-than-temporary. The Company consults with its investment managers and considers available quantitative and qualitative evidence in evaluating potential impairment of its short-term investments on a quarterly basis. If the cost of an individual investment exceeds its fair value, the Company evaluates, among other factors, general market conditions, the duration and extent to which the fair value is less than cost and its intent and ability to hold the investment. Once a decline in fair value is determined to be other-than-temporary, an impairment charge will be recorded to other expense, net, in the statements of operations and comprehensive loss and a new cost basis in the short-term investment will be established. As of December 31, 2020, the Company had not recorded any impairment related to other-than-temporary declines in the fair value of short-term investments.

Property and Equipment, Net

Property and equipment are recorded at cost net of accumulated depreciation and amortization. Property and equipment are depreciated using the straight-line method over the estimated useful lives of the assets. The useful lives of property and equipment are as follows:

Laboratory equipment		5 years
Computer equipment and software		3 years
Leasehold improvements		Shorter of remaining lease term or estimated useful life

Upon retirement or sale of the assets, the cost and related accumulated depreciation and amortization are removed from the balance sheets and the resulting gain or loss is recorded to the statements of operations and comprehensive loss. Repairs and maintenance are expensed as incurred.

Impairment of Long-Lived Assets

Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to future net cash flows expected to be generated by the asset. If the carrying amount of an asset exceeds its estimated future cash flows, an impairment charge is recognized by the amount by which the carrying amount of the asset exceeds the fair value of the asset. There was no impairment of long-lived assets during the years ended December 31, 2020 and 2019.

Redeemable Convertible Preferred Stock

All preferred stock was automatically converted into common stock upon the Company’s IPO in June 2020. Prior to this conversion, the Company classified redeemable convertible preferred stock outside of stockholders’ equity (deficit) because, upon the occurrence of certain change in control events that were outside the Company’s control, including liquidation, sale or transfer of the Company’s assets, holders of the redeemable convertible preferred stock could have caused redemption for cash. At any time on or after December 19, 2024, the holders of a majority of the outstanding redeemable convertible preferred stock could also have required the Company to redeem the redeemable convertible preferred stock by providing the Company a written notice requesting such redemption. The Company recognized changes in the redemption value immediately as they occurred, for example changes in fair value of preferred stock, and adjustments in the carrying amount of the redeemable convertible preferred stock to equal the redemption value at the end of each reporting period up through December 19, 2019, when the Company entered into the Series C Preferred Stock Purchase Agreement. See Note 9 for further details. In the absence of retained earnings these accretion charges were recorded against additional paid in capital, if any, and then to accumulated deficit. The Company analyzed all embedded derivatives and beneficial conversion features for its redeemable convertible preferred stock and concluded that none required bifurcation.

Research and Development Expenses

Research and development costs are expensed as incurred. Research and development expenses consist primarily of personnel costs for the Company’s research and product development employees. Also included are non-personnel costs such as fees paid to consultants and third parties for preclinical and clinical studies, research and development services, laboratory supplies and equipment maintenance costs, license costs, contract manufacturing costs and allocations of facility related costs.

The Company estimates preclinical and clinical studies and research expenses based on the services performed, pursuant to contracts with research institutions that conduct and manage preclinical and clinical studies and research services on its behalf. The Company estimates these expenses based on discussions with internal management personnel and external service providers as to the progress or stage of completion of services and the contracted fees to be paid for such services. If the actual timing of the performance of services or the level of effort varies from the original estimates, the Company will adjust the accrual accordingly. Payments made to third parties under these arrangements in advance of the performance of the related services are recorded as prepaid expenses and are expensed as services are rendered.

Payments associated with licensing agreements to acquire exclusive licenses to develop, use, manufacture and commercialize products that have not reached technological feasibility and do not have alternate commercial use are expensed as incurred.

Tax Credit Receivable

The Company was eligible for federal and California research and development credits for its research and development activities performed within the United States and California, respectively. The Company was eligible to apply up to $250,000 of the federal R&D credits to offset the Federal Insurance Contribution Act (“FICA”) portion of its payroll taxes each year prior to fiscal year 2019. Starting in the fourth quarter of 2019, the Company was no longer eligible to apply its federal R&D credits to offset its FICA taxes as it generated revenue in excess of $5 million of gross receipts during that year. The Company, however, is still eligible for future federal and California research and development credits for its research and development activities performed within the United States and California.

Stock-Based Compensation

The Company’s stock-based equity awards include restricted stock awards, stock options and shares that will be issued under the Company’s 2020 Employee Stock Purchase Plan (“ESPP”). Stock-based compensation for awards that are granted to employees is accounted at fair value on the award grant date and the expense is recognized over the period the employee is required to provide service in exchange for the award, which is generally on a straight-line basis over the vesting period of the award. The expense is recorded in either research and development or general and administrative expenses in the statements of operations and comprehensive loss based on the function to which the related services are provided. Forfeitures are accounted for as they occur.

The Black-Scholes option-pricing model, used to estimate fair value of stock-based awards, requires the use of the following assumptions:

•

Expected term—The expected term represents the period that the stock-based awards are expected to be outstanding. The expected term for the Company’s stock options was calculated based on the weighted-average vesting term of the awards and the contract period, or simplified method. The expected term for the ESPP is the offering period.

•

Expected volatility—Prior to the Company being public, the Company did not have any trading history for its common stock, the expected volatility was estimated based on the average historical volatilities of common stock of comparable publicly traded entities over a period equal to the expected term of the stock option grants. The comparable companies were chosen based on their size, stage in the life cycle or area of specialty. As the Company went public in June 2020, we will continue to apply this process for stock options and ESPP awards until enough historical information regarding the volatility of its stock price becomes available.

•

Risk-free interest rate—The risk-free interest rate is based on the U.S. Treasury yield in effect at the time of grant for zero-coupon U.S. Treasury notes with maturities approximately equal to the expected term of the awards.

•

Expected dividend—The Company has never paid dividends on the common stock and has no plans to pay dividends on the common stock. Therefore, the Company used an expected dividend yield of zero.

Prior to our IPO, the fair value of our common stock has been determined using independent third-party valuations based on relevant valuation methodologies as outlined in the American Institute of Certified Public Accountants (AICPA) Practice Aid, “Valuation of Privately-Held-Company Equity Securities Issued as Compensation”. The Company also considered the amount of time between the independent third-party valuation dates and the grant dates and used interpolation of the fair value between the two valuation dates to estimate common stock fair value at each grant date. This determination included an evaluation of whether the subsequent valuation indicated that any significant change in valuation had occurred between the previous valuation and the grant date. Following our IPO, we use our stock price traded on NASDAQ to determine its fair value.

Deferred Offering Costs

Deferred offering costs, consisting of direct legal, accounting, filing and other fees directly related to the Company’s IPO were capitalized and reclassified to additional paid in capital upon completion of the IPO in June 2020. As of December 31, 2019, $2.8 million in deferred offering costs were recorded as other non-current assets in the Balance Sheets.

Leases and Rent Expense

The Company records rent expense on a straight-line basis over the life of the lease. In cases where there is a free rent period or future fixed rent escalations, the Company records a deferred rent liability. Additionally, the receipt of any lease incentives is recorded as a deferred rent liability which is amortized over the lease term as a reduction of rent expense. Building improvements made with the lease incentives or tenant allowances are capitalized as leasehold improvements and included in property and equipment, net in the balance sheets.

Income Taxes

The Company provides for income taxes under the asset and liability method. Current income tax expense or benefit represents the amount of income taxes expected to be payable or refundable for the current year. Deferred income tax assets and liabilities are determined based on differences between the financial statement reporting and tax basis of assets and liabilities and net operating loss and credit carryforwards and are measured using the enacted tax rates and laws that will be in effect when such items are expected to reverse. Deferred income tax assets are reduced, as necessary, by a valuation allowance when management determines it is more likely than not that some or all the tax benefits will not be realized.

The Company accounts for uncertain tax positions in accordance with ASC No. 740, Income Taxes. The Company assesses all material positions taken in any income tax return, including all significant uncertain positions, in all tax years that are still subject to assessment or challenge by relevant taxing authorities. Assessing an uncertain tax position begins with the initial determination of the position’s sustainability and is measured at the largest amount of benefit that is greater than fifty percent likely of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed, and the Company will determine whether (i) the factors underlying the sustainability assertion have changed and (ii) the amount of the recognized tax benefit is still appropriate. The recognition and measurement of tax benefits requires significant judgment. Judgments concerning the recognition and measurement of a tax benefit might change as new information becomes available.

The Company includes any penalties and interest expense related to income taxes as a component of income tax expense, as necessary.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders.

Net Loss Per Share

Basic net loss per share is computed by dividing net loss attributed to common stockholders by the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share is computed using the weighted-average number of shares of common stock outstanding during the period and, if dilutive, the weighted-average number of potential shares of common stock.

Prior to the conversion of our preferred stock in our IPO, net loss or income per share attributable to common stockholders was calculated using the two-class method, which is based on an earnings allocation formula that determines net loss or income per share for the Company’s common stockholders and holders of participating securities. The holders of preferred stock were entitled to receive dividends prior and in preference to any declaration or payment of any dividend on the common stock. Under this method, net loss or income is increased or reduced by the amount of any dividends earned and accretion of redeemable convertible preferred stock to its redemption value, if any, during the period. The undistributed earnings are allocated to common stock and each series of redeemable convertible preferred stock to the extent that each preferred security may share in the earnings as if all of the earnings for the period had been distributed. Net loss or income attributable to common stockholders and participating preferred shares are allocated to each share on an as-converted basis as if all the earnings for the period had been distributed. The participating securities do not include a contractual obligation to share in losses of the Company and are not included in the calculation of net loss per share in the periods in which a net loss is recorded. Diluted net loss or income per share is computed using the more dilutive of (a) the two-class method or (b) the as-converted method. The Company allocated earnings first to redeemable convertible preferred shares stockholders based on dividend rights and then to common and preferred stockholders based on ownership interests. The weighted-average number of shares of common stock included in the computation of diluted net loss or income gives effect to all potentially dilutive common equivalent shares, including outstanding stock options and preferred stock.

Common stock equivalent shares are excluded from the computation of diluted net loss or income per share if their effect is antidilutive. In periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is generally the same as basic net loss per share attributable to common stockholders since dilutive common shares are not assumed to have been issued if their effect is antidilutive. The Company reported a net loss attributable to common stockholders for the years ended December 31, 2020 and 2019.

Recently Issued Accounting Pronouncements

In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) 2016-02, Leases (“Topic 842”), which requires an entity to recognize assets and liabilities arising from a lease for both finance and operating leases. For public entities, ASU 2016-02 is effective for fiscal years beginning after December 15, 2018. The ASU will also require new qualitative and quantitative disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. As a result of the Company having elected the extended transition period for complying with new or revised accounting standards pursuant to Section 107(b) of the JOBS Act, ASU 2016-02 is effective for the Company in the fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022, with early adoption permitted. The Company is currently in the process of evaluating the impact of the adoption of ASU 2016-02 on the Company’s financial statements.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The new standard amends guidance on measuring and reporting credit losses for financial assets held at amortized cost basis, including accounts receivable and investments classified as available for sale, such as our debt securities. This ASU requires a new forward-looking model based on expected credit losses rather than the current one based on incurred losses. In November 2019, the FASB issued ASU 2019-10, which deferred the effective date for certain ASUs including ASU 2016-13. This standard is effective for the Company’s fiscal year beginning after December 15, 2022. Early adoption is permitted for all entities. The Company does not expect the adoption of ASU 2016-13 to have a material impact on the Company’s financial statements.

In December 2019, the FASB issued Accounting Standards Update 2019-12 (“ASU 2019-12”), Income Taxes (topic 740): Simplifying the Accounting for Income Taxes. The amendments in ASU 2019-12 simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. ASU 2019-12 removes the exception for intraperiod tax allocations when there is a loss from continuing operations and income or a gain from other items (other comprehensive income). ASU 2019-12 is effective for fiscal years beginning after December 15, 2021. Early adoption of the amendments is permitted. The Company has early adopted the new standard effective January 1, 2020, and its adoption did not have a material impact on our condensed financial statements.

Financial Instruments

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Financial Instruments

3.	Financial Instruments

The Company’s short-term investments consist of U.S. Treasury securities, U.S. Government agency securities and corporate debt securities with remaining maturities beyond three months at the date of purchase. The Company has classified and accounted for its short-term investments as available-for-sale securities as the Company may sell these securities at any time even prior to maturity and such investments represent cash available for current operations. As a result, short-term investments may include securities with maturities beyond twelve months that are classified within current assets in the Balance Sheets. The Company’s short-term investments classified as available-for-sale are carried at fair market value with unrealized losses or income recognized in other comprehensive income (loss).

Assets and liabilities recorded at fair value on a recurring basis in the Balance Sheets and assets and liabilities measured at fair value on a non-recurring basis or disclosed at fair value, are categorized based upon the level of judgment associated with inputs used to measure their fair values. The accounting guidance for fair value provides a framework for measuring fair value and requires certain disclosures about how fair value is determined. Fair value is defined as the price that would be received upon the sale of an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. The accounting guidance also establishes a three-level valuation hierarchy that prioritizes the inputs to valuation techniques used to measure fair value based upon whether such inputs are observable or unobservable. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect market assumptions made by the reporting entity. The three-level hierarchy for the inputs to valuation techniques is briefly summarized as follows:

•

Level 1—Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date;

•

Level 2—Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and

•

Level 3—Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data.

The Company’s cash equivalent Money Market Funds are classified as Level 1 because they are valued using quoted market prices. The fair value of the Company’s U.S. Treasury securities, U.S. government agency securities and corporate debt securities are classified as Level 2 because they are valued using observable inputs to quoted market prices, benchmark yields, reported trades, broker/dealer quotes or alternative pricing sources with reasonable levels of price transparency and include U.S. government agency securities, U.S. Treasury securities and corporate debt securities. These Level 2 instruments require more management judgment and subjectivity compared to Level 1 instruments which include determining which instruments are most similar to the instrument being priced, determining whether the market is active and determining which model-derived valuations are to be used when calculating fair value. The Company performs its analysis with the assistance of investment advisors.

The following tables show the Company’s cash equivalents Money Market Funds and short-term investments by significant investment category (in thousands):

	As of December 31, 2020
	Adjusted Cost		Unrealized Gains		Unrealized Losses			Market Value
Level 1:
Money Market Funds	$	27,686	$	—	$	—		$	27,686
Level 2:
U.S. Treasury securities included in cash and cash equivalents and short-term investments		63,101		4		(1	)		63,104
U.S. government agency securities included in short-term investments		54,183		10		—			54,193
Corporate debt securities included in cash and cash equivalents and short-term investments		118,759		1		(46	)		118,714
Total financial assets	$	263,729	$	15	$	(47	)	$	263,697

	As of December 31, 2019
	Adjusted Cost		Unrealized Gains		Unrealized Losses			Market Value
Level 1:
Money Market Funds	$	16,366	$	—	$	—		$	16,366
Level 2:
U.S. Treasury securities included in short-term investments		2,998		—		—			2,998
U.S. government agency securities included in short-term investments		34,204		1		(2	)		34,203
Total financial assets	$	53,568	$	1	$	(2	)	$	53,567

The Company may sell certain of its short-term securities prior to their stated maturities for reasons including, but not limited to, managing liquidity, credit risk, duration and asset allocation.

The following summarizes the remaining contractual maturities of the Company’s short-term investments as of December 31, 2020:

	Adjusted Cost		Market Value
Mature in 1 year or less	$	220,980	$	220,946
Mature in 1 to 2 years		5,064		5,066
Total	$	226,044	$	226,012

There were no liabilities measured at fair value on a recurring basis as of December 31, 2020 and 2019. There have been no transfers between fair value measurement levels during the years ended December 31, 2020 and 2019. In addition, there were no assets or liabilities measured at fair value on a non-recurring basis as of December 31, 2020 and 2019.

As of December 31, 2020, the Company had not recorded any impairment related to other-than-temporary declines in the fair value of short-term investments. Short-term investments are considered impaired when a decline in fair value is judged to be other-than-temporary. The Company consults with its investment managers and considers available quantitative and qualitative evidence in evaluating potential impairment of its short-term investments on a quarterly basis. If the cost of an individual investment exceeds its fair value, the Company evaluates, among other factors, general market conditions, the duration and extent to which the fair value is less than cost and its intent and ability to hold the investment.

The Company records interest income and accretion income earned on Money Market Funds and U.S. Treasury, U.S. government agency and corporate debt securities to interest income in its statement of operations and comprehensive loss.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Property and Equipment, net

12 Months Ended

Dec. 31, 2020

Property Plant And Equipment [Abstract]

Property and Equipment, net

4.	Property and Equipment, net

Property and equipment, net consisted of the following (in thousands):

	December 31,
	2020			2019
Computer equipment and software	$	22		$	22
Laboratory equipment		6,540			5,580
Leasehold improvements		947			657
Construction-in-progress		300			8
Total property and equipment, gross		7,809			6,267
Less: Accumulated depreciation		(3,488	)		(2,188	)
Total property and equipment, net	$	4,321		$	4,079

Depreciation expense for the years ended December 31, 2020 and 2019 was $1.3 million and $1.1 million, respectively.

Accrued Liabilities and Other Long-Term Liabilities

12 Months Ended

Dec. 31, 2020

Accrued Liabilities And Other Liabilities [Abstract]

Accrued Liabilities and Other Long-Term Liabilities

5.	Accrued Liabilities and Other Long-Term Liabilities

Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	December 31,
	2020		2019
Accrued compensation and benefits	$	4,542	$	2,971
Accrued research and development expenses		3,274		2,624
Other accrued liabilities		1,675		1,263
Deferred rent/leasehold incentive obligation-current		85		64
Total accrued liabilities	$	9,576	$	6,922

Accrued compensation and benefits consist primarily of accrued bonuses and accrued vacation.

Other Long-Term Liabilities

Other long-term liabilities consisted of the following (in thousands):

	December 31,
	2020		2019
Deferred rent	$	581	$	458
Leasehold incentive obligation		283		444
Other liabilities — deposits		2		10
Total other long-term liabilities	$	866	$	912

Novartis Agreement

12 Months Ended

Dec. 31, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Novartis Agreement

6.	Novartis Agreement

In October 2019, the Company entered into a Collaboration and License Agreement with Novartis (the “Novartis Agreement”), for the development and commercialization of our preclinical product candidate, PLN-1474 and up to three additional integrin research targets. PLN-1474 is an internally discovered small molecule selective inhibitor of integrin αvß1, currently being developed for the treatment of liver fibrosis associated with nonalcoholic steatohepatitis (“NASH”). In accordance with the Novartis Agreement, on December 7, 2019, Novartis paid to Pliant an upfront non-refundable license fee of $50.0 million for the worldwide exclusive license to PLN-1474.

Novartis will fund the Company’s research and development services for PLN-1474 through Phase 1 after which Novartis will assume responsibility for all future development, manufacturing and commercialization costs of PLN-1474. Novartis will also fund the research and development services associated with integrin research targets as outlined in the Novartis Agreement. The Company is scheduled to receive up to $19.6 million in funding for PLN-1474 development services through Phase 1 and up to $13.4 million for optional research and development services on the integrin research targets. The Company is initially obligated to perform research and development services on the integrin research targets for sixty days. Novartis has the option to continue the research and development services through 2022, with the option to terminate the services with 60 days’ notice. If any of the targets achieves target validation and are deemed a research target, Novartis holds the rights to exercise its license options to obtain an exclusive license for those deemed research targets on a research target-by-research target basis by paying an option exercise fee for each target (up to three in total), including all license compounds that are the subject of the applicable research program. Novartis will also pay the Company a certain specified target validation fee of $4.0 million for each candidate target that achieves target validation and is deemed a research target, for up to three candidate targets. Upon exercise of an option, Novartis will be responsible for global clinical development and commercialization of each licensed research target.

Under the Novartis Agreement, the Company is eligible for developmental, regulatory and commercial milestone payments related to PLN-1474 and the integrin research targets of up to $416.0 million if defined development and commercialization milestones are achieved and tiered royalties ranging from the mid-single digits to low teens on product sales upon commercialization.

Upon execution of the Novartis Agreement, Pliant also entered into a Financing Side Letter with Novartis (the “Financing Side Letter”), whereby Novartis committed to provide up to $30.0 million in equity financing of which $20.0 million was satisfied by the issuance of 10,928,962 shares of Series C Redeemable Convertible Preferred Stock on December 19, 2019 and the remaining $10.0 million was satisfied by the issuance of shares of common stock through a concurrent private placement with the Company’s IPO. The Company determined that the Novartis Agreement and the Financing Side Letter are separate agreements and should not be combined as they were not entered into for a single commercial objective and the consideration in each agreement are tied to separate and different types of obligations. The Series C Redeemable Preferred Stock was issued to Novartis at fair value of $1.83 per share in conjunction with its issuance to other investors at the same price. In addition, the contingent issuance of shares upon an Initial Public Offering would also be at fair value. Further, Novartis became a related party to the Company following its purchase of 10.9 million shares of our Series C Redeemable Convertible Stock on December 19, 2019, representing holdings of 6.1% and 7.4% of our outstanding shares of common stock on a fully diluted basis as of December 31, 2020 and December 31, 2019, respectively. See Notes 9 and 14 to these financial statements for additional information.

The Company evaluated the Novartis Agreement under the revenue standard Topic 606 and concluded that Novartis is a customer. The Company identified the following performance obligations at the inception of the contract.

•

Provide Novartis worldwide license rights to PLN-1474.

•

Provide research and development services for PLN-1474 through Phase 1 of its development.

•

Provide non-exclusive license rights to integrin research targets and research and development services on integrin research targets, together as a single performance obligation.

The Company determined the transaction price at inception of the Novartis Agreement is the $69.6 million consisting of the license fee of $50.0 million and research and development funding of $19.6 million payment to be allocated to the various performance obligations. The Novartis Agreement includes variable consideration for the funding of research and development services and potential future milestones and royalties that were contingent on future success factors for development programs. The Company used the “most likely” method to determine the variable consideration. None of the regulatory or development milestones were included in the transaction price. The Company will re-evaluate the transaction price in each reporting period as uncertain events are resolved or other changes in circumstances occur.

The Company considered the license to PLN-1474 as functional intellectual property, as when control of the license was transferred to Novartis at the inception of the Novartis Agreement, Novartis had the right to access its technology and it was functional. The Company determined the $50.0 million was the standalone selling price PLN-1474 license and was recognized as revenue when control of the license transferred to Novartis, which was at or near inception of the Novartis Agreement.

The Company estimated the standalone selling price of each research program based on internal and external costs to perform the research plus a reasonable profit margin. The total estimated cost of the research and development services reflects the nature of the services to be performed and the Company’s best estimate of the length of time required to perform the services. The Company selected an input method of costs incurred to measure progress toward complete satisfaction of its performance obligation to provide research and development services as such method faithfully depicts the Company’s performance in transferring control of the research and development service to Novartis. Changes in estimates of total internal and external costs expected to be incurred are recognized in the period of change as a cumulative catch-up adjustment. There have been no changes to the Company’s estimates to date.

During the years ended December 31, 2020, the Company recognized revenue—related party of $41.8 million, which consists of $25.0 million of revenue from the achievement of the first patient dosing milestone of the Novartis agreement in the first quarter of 2020 and $16.8 million of revenue generated from research and development services performed during the year ended December 31, 2020. During the year ended December 31, 2019, Company recognized revenue - related party of $50.0 million related to the license fee and revenue - related party of $7.1 million generated from research and development services performed during 2019.

As of December 31, 2020 and 2019, there was a receivable of $9.3 million and $7.1 million, respectively, related to the Novartis Agreement. There were no contract assets or contract liabilities as of December 31, 2020 and 2019.

License Agreements

12 Months Ended

Dec. 31, 2020

License Agreements [Abstract]

License Agreements

7.	License Agreements

UC Regents

In August 2015, the Company entered into an exclusive, worldwide license agreement (the “UC Agreement”) with the Regents of the University of California (the “UC Regents”) relating to the use of certain patents and technology relating to αvß1 compound in fibrosis indications. Pursuant to the UC Agreement, the Company is obligated to (i) make a non-refundable upfront license fee payment of $0.4 million and annual license maintenance fee payments of $10,000 per year beginning on the first anniversary of the UC Agreement escalating to $25,000 per year thereafter (ii) make royalty payments to the UC Regents of 3% of net sales of a therapeutic licensed product or 1% of net sales of a method of use licensed product, subject to an annual minimum of $1.0 million, (iii) make milestone payments up to an aggregate of $18.2 million to the UC Regents upon the occurrence of certain events, (iv) make a milestone payment based on the number of outstanding shares and a price per share as defined in the UC Agreement within 30 days of the closing of an IPO or change of control, and (v) reimburse the UC Regents for prosecution and maintenance expenses of the licensed patents without limitation. As a result of the IPO in June 2020, the Company made a $2.4 million milestone payment to the UC Regents. The Company will expense any payments for milestones to research and development expenses prior to receiving FDA approval for any of its product candidates.

The UC Agreement can be terminated at any time upon the material breach of contract terms by either party to the agreement. The Company has the right to terminate the agreement at any time upon providing written notice to the UC Regents. Unless terminated early, the UC Agreement will remain in effect from the effective date until the later of (i) the expiration or abandonment of the patent rights licensed under the UC Agreement, or (ii) ten years from the date of the first commercial sale of the first licensed product under the agreement.

In November 2020, the technology licensed through the agreement was deemed to no longer be relevant to the Company’s product candidates and, therefore, the Company exercised its rights to terminate the UC Agreement with the termination taking effect in January 2021, which complied with the 60-day notice period specified under the agreement.

Research Agreement

12 Months Ended

Dec. 31, 2020

Research And Development [Abstract]

Research Agreement

8.	Research Agreement

Adimab Development and Option Agreement

In October 2018, the Company and Adimab LLC (“Adimab”) entered into a development and option agreement (the “Adimab Agreement”) for the discovery and optimization of proprietary antibodies as potential therapeutic product candidates. Under the Adimab Agreement, the Company will select biological targets against which Adimab will use its proprietary platform technology to research and develop antibody proteins using a mutually agreed upon research plan.

Upon the Company’s selection of a target, the Company and Adimab will initiate a research plan and the discovery term begins. During the discovery term, Adimab will grant the Company a non-exclusive, non-sublicensable license under its technology with respect to the target, to research, design and preclinically develop and use antibodies that were modified or derived using Adimab technology, solely to evaluate such antibodies, perform the Company’s responsibilities under the research plan and use such antibodies for certain diagnostic purposes. The Company will also grant to Adimab a non-exclusive, non-sublicensable and non-transferable license with respect to the target under the Company’s technology that covers or relates to such target, solely to perform its responsibilities under the research plan during the discovery period. The Company is required to pay Adimab at an agreed upon rate for its full-time employees during the discovery period while Adimab performs research on each target under the applicable research plan.

Adimab granted the Company an exclusive option to obtain a worldwide, royalty-bearing, sublicensable license under Adimab platform patents and other Adimab technology to research, develop and commercialize up to twenty-four antibodies selected by the Company (the “Program Antibodies”) against specific biological targets (the “Commercialization Option”). Upon the exercise of a Commercialization Option, and payment of the applicable option fee to Adimab, Adimab will assign the patents that cover the Program Antibodies to Company. The Company will be required to use commercially reasonable efforts to develop, seek market approval of, and commercialize at least one antibody against the target covered by the Commercialization Option in specified markets upon the exercise of a Commercialization Option.

Pursuant to the Adimab Agreement, the Company is obligated to (i) make a nonrefundable upfront license fee payment for access to Adimab’s technology; (ii) pay Adimab at an agreed upon rate for each full-time employee (“FTE”) during the research period; (iii) make additional payments upon the Company making other research related elections; (iv) pay up to a dollar amount in the low double digit millions for the achievement of certain research and development milestones for each research target program which can vary by target type; (v) make royalty payments to Adimab on Company net sales of its products covered under the Adimab Agreement, subject to varying royalty payments on certain product types. Currently, no product types have been selected by the Company.

During the years ended December 31, 2020, the Company recognized research and development expenses under the Adimab Agreement of $0.2 million related to FTE costs.

During the years ended December 31, 2019, the Company recognized research and development expense under the Adimab Agreement of $0.1 million related to antibody discovery fees and $0.2 million related to the FTE costs.

Redeemable Convertible Preferred Stock

12 Months Ended

Dec. 31, 2020

Temporary Equity Disclosure [Abstract]

Redeemable Convertible Preferred Stock

9.	Redeemable Convertible Preferred Stock

Under the Company’s Amended and Restated Certificate of Incorporation (“Certificate of Incorporation”), the Company is authorized to issue two classes of shares: preferred and common stock. The preferred stock may be issued in series, and the Company’s board of directors is authorized to determine the rights, preferences, and terms of each series.

Upon the closing of the Company’s IPO in June 2020, all outstanding convertible preferred stock was converted into common shares of the Company, as a result there was no authorized or outstanding redeemable convertible preferred stock as of December 31, 2020.

The following is a summary of the Company’s redeemable convertible preferred stock as of December 31, 2019 (in thousands except share amounts):

	Preferred Shares Authorized		Shares Issued and Outstanding		Redemption Value/ Liquidation Preference		Carrying Value
Series A		56,000,000		56,000,000	$	62,468	$	62,468
Series B		49,501,221		49,501,221		75,860		75,860
Series C		44,000,000		26,360,745		47,947		47,947
		149,501,221		131,861,966	$	186,275	$	186,275

Series A Preferred

In August 2015, the Company entered into a Series A Preferred Stock Purchase Agreement (the “Series A Purchase Agreement”) in which the Company agreed to sell up to $45.0 million of Series A Redeemable Convertible Preferred Stock (“Series A Preferred”) in three anticipated tranches. In March 2018, the Series A Purchase Agreement was amended to allow the Company to sell an additional $11.0 million of Series A Preferred. Under the Series A Purchase Agreements, the Company issued a total of 56.0 million shares of Series A Preferred for cash proceeds of approximately $56.0 million.

Series B Preferred

In July 2018, the Company entered into a Series B Preferred Stock Purchase Agreement (the “Series B Purchase Agreement”) in which the Company agreed to sell up to $70.0 million of Series B Redeemable Convertible Preferred Stock (“Series B Preferred”). Under the Series B Purchase Agreements, the Company issued a total of 49.5 million shares of Series B Preferred for cash proceeds of approximately $68.1 million.

Series C Preferred

In December 2019, the Company entered into a Series C Preferred Stock Purchase Agreement (the “Series C Purchase Agreement”) in which the Company agreed to sell up to $80.5 million of Series C Redeemable Convertible Preferred Stock (“Series C Preferred”). Under the Series C Purchase Agreements, the Company issued 26.4 million shares of Series C Preferred for cash proceeds of approximately $48.2 million. Novartis purchased 10.9 million shares of this allotment of Series C Preferred for cash proceeds of $20.0 million. Novartis became a related party following its purchase of our Series C Preferred. Novartis holdings represent of 6.1% and 7.4% of our outstanding shares of common stock on a fully diluted basis as of December 31, 2020 and December 31, 2019, respectively.

In February 2020, the Company issued an additional 28.5 million additional shares of Series C Preferred at $1.83 per share in exchange for gross cash proceeds of $52.2 million and incurred $0.2 million of issuance costs.

The Series A Preferred, Series B Preferred and Series C Preferred (collectively, the “Preferred Stock”) had the following rights and privileges prior to the Preferred Stock being converted to common stock:

Voting

Each holder of shares of Preferred Stock was entitled to the number of votes equal to the number of shares of common stock into which such shares could have been converted and had voting rights and powers equal to the voting rights and powers of the common stock, and except as provided by law or by other provisions of the Company’s Certificate of Incorporation, as amended, could have voted together with the common stock as a single class on an as-converted basis on all matters as to which holders of common stock have the right to vote.

Conversion

Shares of the Preferred Stock were convertible at any time at the option of the holder into such number of shares as is determined by dividing the original issuance price by the conversion price in effect at the time. The conversion price was the original issuance price for each series of Preferred Stock, as adjusted for the 1-for-7.15 reverse stock split of the Common Stock. Following such adjustment, the per-share conversion price was $7.15 for Series A Preferred, $9.843405 for Series B Preferred and $13.0845 for Series C Preferred, subject to certain adjustments. All outstanding shares of Preferred Stock converted to shares of common stock upon the completion of the Company’s IPO.

Dividends

The holders of Series A Preferred were originally entitled to receive cumulative dividends from their respective dates of issuance at the rate of 8.0% on their original issue price. In July 2018, in conjunction with the execution of the Series B Purchase Agreement, the Series A Preferred accreted dividends were cancelled. Under the Series B Purchase Agreement, the holders of both shares of Series A and Series B Preferred were entitled to receive cumulative dividends commencing on July 10, 2018, the issuance date of Series B Preferred, at an annual rate of 8.0% on their original issuance price. The Series A Preferred and Series B Preferred dividends accrue from day-to-day, whether declared or not, and were payable only when and if declared by the Company’s board of directors. As such, the Company recorded accretion charges to adjust the carrying values of the Series A Preferred and Series B Preferred to their redemption values up until the date the Series C Purchase Agreement was executed. In December 2019, in conjunction with the execution of the Series C Purchase agreement, the Series A preferred and Series B preferred accreted dividends were cancelled.

Under the Series C Purchase Agreement, the holders of Series A, Series B and Series C Preferred were entitled to receive non-cumulative dividends commencing on December 19, 2019 at an annual rate of 8.0% on their original issuance price. The Series A, Series B and Series C Preferred dividends accrue from day-to-day, whether declared or not, and were payable only when and if declared by the Company’s board of directors. The holders of all shares of preferred stock were entitled to receive dividends prior and in preference to any declaration or payment of any dividend on the common stock. Since inception, the Company has never declared or paid any dividends.

Liquidation Preferences

Upon liquidation, dissolution, or winding up of the Company or a deemed liquidation event as defined in the Company’s Certificate of Incorporation, the holders of shares of Series C and Series B Preferred Stock were entitled to receive, on a pari passu basis, a per share amount equal to the Series C purchase price of $1.83 (plus any declared but unpaid dividends) and equal to the original Series B purchase of $1.3767 (plus any declared but unpaid dividends), collectively (the “Series C and Series B Liquidation Preference”) or such amount per share as would have been payable had all shares of Series C and Series B been converted into common stock immediately prior to such liquidation event. The payment of Series C and Series B Liquidation Preference was to be made before any payment made to the holders of Series A Preferred Stock and Common Stock. Thereafter, the Series A Preferred holders were entitled to receive their liquidation preference before any distributions were made to common stockholders, a per share amount equal to $1.00 (plus any declared but unpaid dividends) (the “Series A Liquidation Preference”) or such amount per share as would have been payable had all shares of Series A had been converted into common stock immediately prior to such liquidation event. After payments of the full liquidation preferences of the Series C and Series B Liquidation Preference and the Series A Liquidation Preference described above, any remaining assets of the Company would have been distributed to the holders of the common stock in proportion to the number of shares of common stock that they held.

Redemption

In December 2019, in conjunction with the execution of the Series C Preferred Purchase Agreement, the Series A Preferred and Series B Preferred redemption provisions were modified as follows:

All outstanding shares of Preferred Stock shall be redeemed by the Company at a price equal to the original issuance price per share, plus any dividends declared but unpaid, in three annual installments commencing not more than sixty (60) days after receipt by the Company at any time on or after five years from the Series C Preferred original issuance date, December 19, 2019, a written notice from the holders of a majority of the shares of Preferred Stock. The Company accounted for the changes in Series A Preferred redemption and Series B Preferred redemption provisions as a modification as there was no significant difference in Series A Preferred and Series B Preferred fair values before and after the modification.

Common Stock

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Common Stock

10.	Common Stock

The voting, dividend, and liquidation rights of the holders of the common stock are subject to and qualified by the rights, powers, and preferences of the holders of the Preferred Stock. As of December 31, 2020 and 2019, the Company had 300,000,000 and 181,000,000 authorized shares of common stock, respectively, at a par value of $0.0001 per share. The common stock has the following rights and privileges:

Voting

The holders of shares of common stock are entitled to one vote for each share of common stock held at any meeting of stockholders and at the time of any written action in lieu of a meeting.

Dividends

The holders of shares of common stock are entitled to receive dividends, when declared by the Company’s board of directors. Cash dividends may not be declared or paid to holders of shares of common stock until all unpaid dividends on the Preferred Stock have been paid in accordance with their terms. No dividends have been declared or paid by the Company since its inception.

Liquidation

After payment of the respective liquidation preferences to the holders of shares of Preferred Stock, the holders of shares of common stock are entitled to share ratably in the Company’s remaining assets available for distribution to its stockholders in the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or upon occurrence of a deemed liquidation event.

Shares reserved for future issuance

	December 31,
	2020		2019
Conversion of redeemable convertible preferred stock		—		18,442,233
Exercises of outstanding stock option awards		2,993,855		1,337,501
Shares of common stock available for future grants under the 2015 Equity Incentive Plan, as amended		—		567,110
Shares of common stock available for future grants under the 2020 Equity Incentive Plan		3,644,459		—
Shares of common stock available for future issuance under the 2020 ESPP		700,000		—
Total shares reserved for future issuance		7,338,314		20,346,844

Founders’ Common Stock Awards

During 2015, the Company’s board of directors granted common stock awards to the Company’s founders in exchange for services provided to the Company. The purchase price of the common stock awards was the estimated fair value at the issuance date. The shares vest from one to four years and vesting could be accelerated upon a change in control. The vesting of certain performance-based grants of restricted stock awards were contingent upon the filing of an Investigational New Drug Application by the Company with the FDA.

If the holder of founders’ common stock award terminates their relationship with the Company during the vesting period, the Company may repurchase any unvested restricted common stock held by these individuals at their original purchase price. During the vesting term, holders of founders’ common stock awards are deemed to be common stockholders and have dividend and voting rights. The Company issued 745,244 shares of founders’ common stock during 2015. No founders’ common stock awards were granted in subsequent years. Total compensation expense was $25,000 for these founders’ common stock awards, which are recorded to operating expenses in the statements of operations over their respective vesting period. As of December 31, 2019, all shares of founders’ common stock awards were fully vested.

Equity Incentive Plans and Stock-Based Compensation

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Equity Incentive Plans and Stock-Based Compensation

11.	Equity Incentive Plans and Stock-Based Compensation

In August 2015, the board of directors adopted the 2015 Equity Incentive Plan, as amended (the “2015 Plan”), which provides for the grant of incentive stock options, nonqualified stock options or other awards including stock appreciation rights and restricted stock awards to the Company’s employees, officers, directors, advisors, and consultants for the purchase of up to 1.5 million shares of the Company’s common stock. In July 2018 and January 2019, the 2015 Plan was amended to increase the number of shares reserved thereunder by 1.0 million and 0.4 million shares, respectively. In March 2020, the Company’s board of directors and stockholders voted to increase the number of shares reserved for issuance under the 2015 Plan by 1.4 million shares. In May 2020, the board of directors adopted the 2020 Stock Options and Incentive Plan (the “2020 Plan”). The 2015 plan was suspended and no further grants may be issued under the 2015 Plan.

The 2020 Plan provides for the grant of incentive stock options, nonqualified stock options or other awards including stock appreciation rights, restricted stock awards and restricted stock units to the Company’s employees, officers, directors, advisors, and consultants for the purchase of up to 4.2 million shares of the Company’s common stock. In addition, to the extent that awards outstanding under the 2020 Plan or the 2015 Plan are cancelled, forfeited or held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by the registrant prior to vesting, satisfied without any issuance of stock, expire or are otherwise terminated (other than by exercise) subsequent to May 2020, the shares of common stock reserved for issuance pursuant to such awards will become available for issuance as shares of common stock under the 2020 Plan. The 2020 Plan provides that an additional number of shares will automatically be added to the shares authorized for issuance under the 2020 Plan on January 1 of each year beginning January 1, 2021. The number of shares added each January 1 will be equal to the lesser of: (i) 5% of the outstanding shares on the immediately preceding December 31 or (ii) such amount as determined by the administrator of the 2020 Plan, which is the compensation committee of the board of directors. As of December 31, 2020, 3.6 million shares remained available for issuance under the 2020 Plan.

Prior to the adoption of the 2020 Plan, options under the 2015 Plan could be granted for periods of up to 10 years and at prices no less than 100% of the estimated fair value of the shares on the date of grant as determined by the board of directors, provided, however, that the exercise price of an incentive stock option granted to a 10.0% shareholder could not be less than 110.0% of the estimated fair value of the shares on the date of grant and the option was not exercisable after the expiration of five years from the date of grant.

Options under the 2020 Plan may be granted for periods of up to 10 years and at prices no less than the market price of the Company’s common stock on the date of grant, provided, however, that the exercise price of an incentive stock option granted to a 10.0% shareholder shall not be less than 110.0% of the estimated fair value of the shares on the date of grant and the option is not exercisable after the expiration of five years from the date of grant.

Restricted Common Stock Awards

The Company granted restricted stock awards under the 2015 Plan. The purchase price of the restricted common stock awards was the estimated fair value as determined by the board of directors at the issuance date. The shares vest from one to four years and vesting could be accelerated upon a change in control. A holder of an award may pay a total purchase price or a part of the purchase price for granted shares at any time during the vesting periods. Upon termination of employment, the Company has the right to repurchase any unvested restricted shares. The repurchase price for unvested shares of common stock will be the lower of (i) the fair market value on the date of repurchase or (ii) their original purchase price. During the vesting term, holders of restricted stock awards are deemed to be a common stock shareholder and have dividends and voting rights.

The Company accounted for restricted stock awards as early exercised options and recognized a liability in other liabilities when cash was received for the purchase of shares of restricted stock. As shares of restricted stock vested, the Company reclassified the liability to common stock and additional paid in capital. As of December 31, 2020 and 2019, the Company recorded a liability included in accrued expenses and other liabilities of $10,000 and $22,000, respectively.

There have been no restricted stock awards granted during the years ended December 31, 2020 and 2019.

The following table summarizes restricted stock activity during the year ended December 31, 2020:

	Number of Shares			Weighted- Average Grant Date fair value
Outstanding and unvested, as of December 31, 2019		302,211		$	1.51
Issued		—		$	—
Vested		(163,568	)	$	1.30
Repurchases		(12,121	)	$	1.22
Outstanding and unvested, as of December 31, 2020		126,522		$	1.85

Restricted stock awards of 4,195 shares with a weighted-average grant date fair value of $0.08 per share, were not purchased by the award holders as of December 31, 2020. As these shares of the restricted common stock awards were not issued, they are not included in the table above.

The aggregate fair value of restricted stock awards vested during the years ended December 31, 2020 and 2019 was $0.2 million and $0.4 million, respectively. Total intrinsic value of outstanding unvested restricted stock awards as of December 31, 2020 and 2019 was $2.9 million and $2.1 million, respectively.

Incentive Stock Options and Nonqualified Stock Options

Stock options issued under either the 2015 Plan or the 2020 Plan generally vest over a four-year period and expire ten years from the date of grant. Certain options provide for accelerated vesting if there is a change in control, as defined in the respective plans.

The Company used Black-Scholes option pricing model to estimate stock-based compensation expense for stock option awards with the following assumptions:

	Year Ended December 31,
	2020		2019
Expected volatility	72.10% - 77.50%		74.80% - 82.53%
Risk-free interest rate	0.27% - 0.82%		1.43% - 2.59%
Expected dividend		—		—
Expected term (in years)	5.26 - 6.75		5.00 - 6.08
Underlying common stock fair value	6.22 - 28.79		5.15 - 7.08

A summary of option activity under the 2015 Plan and the 2020 Plan is as follows:

	Number of Options			Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2019		1,337,501		$	3.22		9.18	$	5,157
Granted		1,830,738		$	11.43
Exercised		(136,223	)	$	3.25
Forfeited		(38,161	)	$	8.13
Outstanding as of December 31, 2020		2,993,855		$	8.18		8.84	$	43,890
Exercisable as of December 31, 2020		736,601		$	4.19		8.22	$	13,664
Vested and expected to vest as of December 31, 2020		2,993,855		$	8.18		8.84	$	43,890

Aggregate intrinsic value represents the difference between the fair value of the underlying common stock and the exercise price as of December 31, 2020 and 2019. The weighted-average grant date fair value of options granted during years ended December 31, 2020 and 2019 was $7.27 per share and $4.37 per share, respectively.

As of December 31, 2020, there was $0.2 million of unrecognized compensation costs that is expected to be recognized over the weighted-average periods of 1.22 years related to restricted stock awards. As of December 31, 2020, there was $14.3 million of unrecognized compensation costs that is expected to be recognized over the weighted-average periods of 2.72 years related to stock options.

2020 Employee Stock Purchase Plan

In June 2020, the Company adopted the 2020 ESPP. The Company reserved 700,000 shares of common stock for future issuance under the plan. The 2020 ESPP provides that the number of shares reserved and available for issuance will automatically increase on January 1 of each calendar year, beginning January 1, 2021, by the least of (i) 1.0% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, (ii) 700,000 shares or (iii) such lesser amount as determined by the administrator of the 2020 ESPP, which is the compensation committee of the board of directors.

Under the 2020 ESPP, eligible employees may purchase shares of our common stock through payroll deductions that cannot exceed 15% of each employee’s salary. The 2020 ESPP provides for a six-month offering period. At the end of the purchase period, eligible employees are permitted to purchase shares of common stock at the lower of 85% of the fair market value at the beginning of the offering period or 85% of the fair market value at the end of the purchase period, subject to tax limitations on the total value of the purchase. The 2020 ESPP is considered a compensatory plan, and the Company recorded $0.5 million in stock-based compensation expense for year ended December 31, 2020. There was no stock-based compensation expense attributed to the 2020 ESPP for the year ended December 31, 2019 as the 2020 ESPP was adopted in 2020. As of December 31, 2020, no shares of common stock were issued under the 2020 ESPP. The Company used Black-Scholes option pricing model to estimate stock-based compensation expense for the 2020 ESPP with the following assumptions:

	Year Ended December 31,
	2020			2019
Risk-free interest rate		0.11	%		—
Expected term of options (in years)		0.58			—
Expected stock price volatility		83.72	%		—
Expected dividends		—			—

Stock-Based Compensation Expense

The following table presents the classification of stock-based compensation expense for the years ended December 31, 2020 and 2019 (in thousands):

	Year Ended December 31,
	2020		2019
Research and development expenses	$	1,719	$	584
General and administrative expenses		2,176		1,245
Total stock-based compensation expense	$	3,895	$	1,829

Income Taxes

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Income Taxes

12.	Income Taxes

The Company had a pre-tax U.S. book loss of $41.5 million and $0.6 million for the years ended December 31, 2020 and 2019, respectively. For the years ended December 31, 2020 and 2019, the Company did not record an income tax provision. The Company will continue to maintain a 100% valuation allowance on total deferred tax assets. The Company believes it is more likely than not that the related deferred tax asset will not be realized.

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2020			2019
Income tax computed at federal statutory rate		21.0	%		21.0	%
State taxes, net of federal tax benefit		7.4	%		2.7	%
General business credit—federal		5.3	%		295.9	%
Stock-based compensation		(1.0	)%		(50.0	)%
Other permanent differences		(0.1	)%		(2.4	)%
Change in valuation allowance		(32.6	)%		(267.7	)%
Effective income tax rate		0.0	%		(0.5	)%

Net deferred tax assets and liabilities consisted of the following (in thousands):

	December 31,
	2020			2019
Deferred tax assets:
Net operating losses	$	27,047		$	16,655
Research and development credits		7,617			4,949
Accrued expenses	291			130
Other	474			247
Deferred rent	266			124
Stock based compensation	428			73
Total deferred tax assets		36,123			22,178
Deferred tax liabilities:
Asset basis	$	(124	)	$	(110	)
Prepaid expenses		(558	)		(139	)
Total deferred tax liabilities		(682	)		(249	)
Valuation allowance		35,441			21,929
Net deferred taxes	$	—		$	—

Net operating losses and tax credit carryforwards were as follows (in thousands):

	December 31, 2020		Expiration Year
Net operating losses, federal (starting from January 1, 2018)	$	66,963	Does not expire
Net operating losses, federal (before January 1, 2018)	$	29,486	2035-2037
Net operating losses, state	$	97,273	2035-2040
Tax credits, federal	$	7,518	2036-2040
Tax credits, state	$	2,540	Does not expire

Utilization of the net operating loss carryforwards and research credit carryforwards may be subject to an annual limitation due to the ownership percentage change limitations provided by the Internal Revenue Code (“IRC”) and similar state provisions. Annual limitations may result in the expiration of the net operating losses and tax credit carryforwards before they are utilized. The Company performed a IRC Section 382 analysis through December 31, 2020 and does not expect any previous ownership changes to result in a limitation that will reduce the total amount of net operating loss and tax credit carryforwards disclosed that can be utilized. Subsequent ownership changes may affect the limitation in future years.

During the years ended December 31, 2020 and 2019, the Company recorded a full valuation allowance on federal and state deferred balances since management does not forecast the Company to be in a profitable position in the near future. Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2020 and 2019 related primarily to the increases in net operating loss carryforwards and research and development tax credit carryforwards and were as follows (in thousands):

	Year Ended December 31,
	2020		2019
Valuation allowance at the beginning of the year	$	21,929	$	20,240
Increases recorded to income tax provision		13,512		1,689
Valuation allowance at the end of the year	$	35,441	$	21,929

The Company’s U.S. federal and state income tax returns are generally subject to tax examinations for the tax years ended December 31, 2017 through December 31, 2020. There are currently no pending income tax examinations. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service and state tax authorities to the extent utilized in a future period.

The entire amount of the unrecognized tax benefits would not impact the Company’s effective tax rate if recognized. The Company has elected to include interest and penalties as a component of tax expense. During the years ended December 31, 2020 and 2019, the Company did not recognize accrued interest and penalties related to unrecognized tax benefits. The Company does not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease during the next 12 months.

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands):

	Year Ended December 31,
	2020		2019
January 1	$	1,355	$	855
Additions based on tax positions related to current year		513		570
Additions (reductions) for tax positions of prior year		139		(70	)
December 31	$	2,007	$	1,355

On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (the "Cares Act") was enacted. The CARES Act changed net loss carryforward and back provisions and the business interest expenses limitation. The Company has evaluated the impact of the CARES Act and determined that none of the changes would result in a material cash benefit to the Company.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Commitments and Contingencies

12 Months Ended

Dec. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

13.	Commitments and Contingencies

Purchase Commitments

The Company has contractual arrangements with research and development organizations and suppliers; however, these contracts are generally cancelable on 30 days’ notice and the obligations under these contracts are largely based on services performed.

License and Collaboration Agreements

Potential payments related to the Company’s license and research agreements, including milestone and royalty payments, are detailed in Notes 6 and 7.

Leases

In February 2018, the Company entered into a non-cancelable lease agreement (the “Lease”) for premises consisting of approximately 32,974 square feet located in South San Francisco, California (the “Premises”). The Company moved into the Premises in July 2018. The Premises is being used for the Company’s corporate headquarters and principal operating facility. The term of the Lease is eighty-four months, which commenced on July 1, 2018. Base rent was abated for the first two months of the lease term and thereafter is $0.2 million per month during the first year of the lease term, with specified annual increases thereafter. The Company paid a refundable security deposit of approximately $0.4 million, which is included in other non-current assets in the Balance Sheets at December 31, 2020 and 2019. The Company has the right to extend the lease term by seven years upon written notice not more than twelve months nor less than nine months prior to the expiration of the original lease term, with monthly payments equal to the “fair rental value” as defined in the Lease.

Rent expense, including common area maintenance expense, was $2.5 million for each of the year ended December 31, 2020 and 2019.

Future minimum lease payments under the Lease as of December 31, 2020 were as follows (in thousands):

Year ending December 31:	Operating Lease
2021	$	2,027
2022		2,098
2023		2,171
2024		2,247
2025		1,144
Total	$	9,687

Legal Proceedings

From time to time, we may become involved in legal proceedings arising from the ordinary course of business. We record a liability for such matters when it is probable that future losses will be incurred and that such losses can be reasonably estimated. Significant judgment by us is required to determine both probability and the estimated amount. Management is currently not aware of any legal matters that could have a material adverse effect on our financial position, results of operations or cash flows.

Indemnification

In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has never incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. The Company has also entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by Delaware corporate law. The Company currently has directors’ and officers’ insurance.

Related Party Transactions

12 Months Ended

Dec. 31, 2020

Related Party Transactions

14.	Related Party Transactions

In 2019, certain employees of Third Rock Ventures, a stockholder of the Company, provided consulting services to the Company. Commencing January 2020, Third Rock Ventures ceased providing management consulting services to the Company. The Company recorded no consulting expenses for consulting services provided by Third Rock Ventures during the year ended December 31, 2020. The Company recorded Third Rock Ventures consulting expenses to general and administrative expense of $36,000 for the year ended December 31, 2019.

In March 2020, the Company granted 26,573 stock options with a grant date fair value of $0.1 million to a partner at Third Rock Ventures, who is also serving as a non-employee director on the Company’s Board of Directors. The common shares subject to these options vest 1/12th on the last day of each calendar quarter over a three-year period and commenced vesting upon our IPO. In order to vest at each calendar quarter end date, the shareholder must be providing continuous service to the Company through such vesting date. The stock-based compensation expense related to these options was immaterial during the years ended December 31, 2020.

From time to time, the Company makes charitable contributions to the University of California, San Francisco Foundation (the “UCSF Foundation”), which are directed to support research performed in the laboratories of three of the Company’s scientific founders. The Company made charitable contributions to the UCSF Foundation in the amount of $0.7 million and $0.4 million during the years ended December 31, 2020 and 2019, respectively. The Company paid its scientific founders, who are members of the Company’s scientific advisory board, $0.2 million during the years ended December 31, 2020 and 2019.

In October 2019, the Company entered into the Novartis Agreement with Novartis covering the development and commercialization of Pliant’s preclinical product candidate, PLN-1474 and up to three additional targets. Upon execution of the Agreement, Pliant also entered into a financing side letter with Novartis, whereby Novartis committed to provide up to $30.0 million in equity financing of which $20.0 million was provided for preferred shares as a part of a Series C equity offering and the remaining $10.0 million was completed in a private placement for common shares upon the Company’s IPO. As of December 31, 2020 and 2019, Novartis owned approximately 6.1% and 7.4 %, respectively, of our outstanding shares of common stock on a fully diluted basis. See Notes 6 and Note 9 for additional information.

Defined Contribution Plan

12 Months Ended

Dec. 31, 2020

Compensation And Retirement Disclosure [Abstract]

Defined Contribution Plan

15.	Defined Contribution Plan

The Company sponsors a defined contribution plan under Section 401(k) of the Internal Revenue Code covering substantially all full-time U.S. employees. Employee contributions are voluntary and are determined on an individual basis subject to the maximum allowable under federal tax regulations. The Company made contributions to the plan of $0.4 million and $0.2 million for the years ended December 31, 2020 and 2019, respectively.

Net Loss Per Share Attributable to Common Stockholders

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Net Loss Per Share Attributable to Common Stockholders

16.	Net Loss Per Share Attributable to Common Stockholders

The following outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented, because including them would have been antidilutive:

	Year Ended December 31,
	2020		2019
Redeemable convertible preferred stock (on an as-converted basis)		—		18,442,233
Options to purchase common stock		2,993,855		1,337,501
Restricted stock awards granted and not purchased		4,195		4,195
Unvested restricted shares		126,522		302,211
Total		3,124,572		20,086,140

A reconciliation of the numerator and denominator used in the calculation of the basic and diluted net loss per share attributable to common stockholders is as follows (in thousands, except share and per share amounts):

	Year Ended December 31,
	2020			2019
Net loss per share:
Numerator
Net loss	$	(41,533	)	$	(631	)
Less: accretion to redemption value and dividends on redeemable convertible preferred shares		—			(6,225	)

Net loss attributable to common stockholders	$	(41,533	)	$	(6,856	)
Denominator
Weighted-average common shares outstanding used to calculate net loss per share attributable to common stockholders:
Basic		21,344,236			1,623,358
Diluted		21,344,236			1,623,358
Net loss per share attributable to common stockholders:
Basic	$	(1.95	)	$	(4.22	)
Diluted	$	(1.95	)	$	(4.22	)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Basis of Presentation

The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”).

Use of Estimates

Revenue Recognition

Fair Value Measurements

Concentration of Credit Risk and Other Risks and Uncertainties Policy

Concentration of Credit Risk and Other Risks and Uncertainties

Segments

Cash and Cash Equivalents

Short-Term Investments

Property and Equipment, Net

Laboratory equipment		5 years
Computer equipment and software		3 years
Leasehold improvements		Shorter of remaining lease term or estimated useful life

Impairment of Long-Lived Assets

Redeemable Convertible Preferred Stock

Research and Development Expenses

Tax Credit Receivable

Stock-Based Compensation

The Black-Scholes option-pricing model, used to estimate fair value of stock-based awards, requires the use of the following assumptions:

•

Expected dividend—The Company has never paid dividends on the common stock and has no plans to pay dividends on the common stock. Therefore, the Company used an expected dividend yield of zero.

Deferred Offering Costs

Leases and Rent Expense

Income Taxes

The Company includes any penalties and interest expense related to income taxes as a component of income tax expense, as necessary.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders.

Net Loss Per Share

Recently Issued Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Summary of Useful Lives of Property and Equipment

The useful lives of property and equipment are as follows:

Laboratory equipment		5 years
Computer equipment and software		3 years
Leasehold improvements		Shorter of remaining lease term or estimated useful life

Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Summary of Cash and Cash Equivalents, Money Market Funds and Short-term Investments by Significant Investment Category

The following tables show the Company’s cash equivalents Money Market Funds and short-term investments by significant investment category (in thousands):

	As of December 31, 2020
	Adjusted Cost		Unrealized Gains		Unrealized Losses			Market Value
Level 1:
Money Market Funds	$	27,686	$	—	$	—		$	27,686
Level 2:
U.S. Treasury securities included in cash and cash equivalents and short-term investments		63,101		4		(1	)		63,104
U.S. government agency securities included in short-term investments		54,183		10		—			54,193
Corporate debt securities included in cash and cash equivalents and short-term investments		118,759		1		(46	)		118,714
Total financial assets	$	263,729	$	15	$	(47	)	$	263,697

	As of December 31, 2019
	Adjusted Cost		Unrealized Gains		Unrealized Losses			Market Value
Level 1:
Money Market Funds	$	16,366	$	—	$	—		$	16,366
Level 2:
U.S. Treasury securities included in short-term investments		2,998		—		—			2,998
U.S. government agency securities included in short-term investments		34,204		1		(2	)		34,203
Total financial assets	$	53,568	$	1	$	(2	)	$	53,567

Summery of Remaining Contractual Maturities of Company’s Short-term Investments

The following summarizes the remaining contractual maturities of the Company’s short-term investments as of December 31, 2020:

	Adjusted Cost		Market Value
Mature in 1 year or less	$	220,980	$	220,946
Mature in 1 to 2 years		5,064		5,066
Total	$	226,044	$	226,012

Property and Equipment, net (Tables)

12 Months Ended

Dec. 31, 2020

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment, net consisted of the following (in thousands):

	December 31,
	2020			2019
Computer equipment and software	$	22		$	22
Laboratory equipment		6,540			5,580
Leasehold improvements		947			657
Construction-in-progress		300			8
Total property and equipment, gross		7,809			6,267
Less: Accumulated depreciation		(3,488	)		(2,188	)
Total property and equipment, net	$	4,321		$	4,079

Accrued Liabilities and Other Long-Term Liabilities (Tables)

12 Months Ended

Dec. 31, 2020

Accrued Liabilities And Other Liabilities [Abstract]

Schedule of Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):

	December 31,
	2020		2019
Accrued compensation and benefits	$	4,542	$	2,971
Accrued research and development expenses		3,274		2,624
Other accrued liabilities		1,675		1,263
Deferred rent/leasehold incentive obligation-current		85		64
Total accrued liabilities	$	9,576	$	6,922

Summary of Other Long-Term Liabilities

Other long-term liabilities consisted of the following (in thousands):

	December 31,
	2020		2019
Deferred rent	$	581	$	458
Leasehold incentive obligation		283		444
Other liabilities — deposits		2		10
Total other long-term liabilities	$	866	$	912

Redeemable Convertible Preferred Stock (Tables)

12 Months Ended

Dec. 31, 2020

Temporary Equity Disclosure [Abstract]

Summary of Redeemable Convertible Preferred Stock

The following is a summary of the Company’s redeemable convertible preferred stock as of December 31, 2019 (in thousands except share amounts):

	Preferred Shares Authorized		Shares Issued and Outstanding		Redemption Value/ Liquidation Preference		Carrying Value
Series A		56,000,000		56,000,000	$	62,468	$	62,468
Series B		49,501,221		49,501,221		75,860		75,860
Series C		44,000,000		26,360,745		47,947		47,947
		149,501,221		131,861,966	$	186,275	$	186,275

Common Stock (Tables)

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Schedule of Shares Reserved for Future Issuance

Shares reserved for future issuance

	December 31,
	2020		2019
Conversion of redeemable convertible preferred stock		—		18,442,233
Exercises of outstanding stock option awards		2,993,855		1,337,501
Shares of common stock available for future grants under the 2015 Equity Incentive Plan, as amended		—		567,110
Shares of common stock available for future grants under the 2020 Equity Incentive Plan		3,644,459		—
Shares of common stock available for future issuance under the 2020 ESPP		700,000		—
Total shares reserved for future issuance		7,338,314		20,346,844

Equity Incentive Plans and Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Restricted Stock Activity

The following table summarizes restricted stock activity during the year ended December 31, 2020:

	Number of Shares			Weighted- Average Grant Date fair value
Outstanding and unvested, as of December 31, 2019		302,211		$	1.51
Issued		—		$	—
Vested		(163,568	)	$	1.30
Repurchases		(12,121	)	$	1.22
Outstanding and unvested, as of December 31, 2020		126,522		$	1.85

Summary of Black-Scholes Option Pricing Model to Estimate Stock-based Compensation Expense for Stock Option Awards

The Company used Black-Scholes option pricing model to estimate stock-based compensation expense for stock option awards with the following assumptions:

	Year Ended December 31,
	2020		2019
Expected volatility	72.10% - 77.50%		74.80% - 82.53%
Risk-free interest rate	0.27% - 0.82%		1.43% - 2.59%
Expected dividend		—		—
Expected term (in years)	5.26 - 6.75		5.00 - 6.08
Underlying common stock fair value	6.22 - 28.79		5.15 - 7.08

Summary of Option Activity Under the 2015 Plan and 2020 Plan

A summary of option activity under the 2015 Plan and the 2020 Plan is as follows:

	Number of Options			Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2019		1,337,501		$	3.22		9.18	$	5,157
Granted		1,830,738		$	11.43
Exercised		(136,223	)	$	3.25
Forfeited		(38,161	)	$	8.13
Outstanding as of December 31, 2020		2,993,855		$	8.18		8.84	$	43,890
Exercisable as of December 31, 2020		736,601		$	4.19		8.22	$	13,664
Vested and expected to vest as of December 31, 2020		2,993,855		$	8.18		8.84	$	43,890

Summary of Black-Scholes Option Pricing Model to Estimate Stock-based Compensation Expense for 2020 Employee Stock Purchase Plan

The Company used Black-Scholes option pricing model to estimate stock-based compensation expense for the 2020 ESPP with the following assumptions:

	Year Ended December 31,
	2020			2019
Risk-free interest rate		0.11	%		—
Expected term of options (in years)		0.58			—
Expected stock price volatility		83.72	%		—
Expected dividends		—			—

Summary of Classification of Stock-based Compensation Expense

The following table presents the classification of stock-based compensation expense for the years ended December 31, 2020 and 2019 (in thousands):

	Year Ended December 31,
	2020		2019
Research and development expenses	$	1,719	$	584
General and administrative expenses		2,176		1,245
Total stock-based compensation expense	$	3,895	$	1,829

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Summary of Reconciliation of U.S. Federal Statutory Income Tax Rate to Company’s Effective Income Tax Rate

	Year Ended December 31,
	2020			2019
Income tax computed at federal statutory rate		21.0	%		21.0	%
State taxes, net of federal tax benefit		7.4	%		2.7	%
General business credit—federal		5.3	%		295.9	%
Stock-based compensation		(1.0	)%		(50.0	)%
Other permanent differences		(0.1	)%		(2.4	)%
Change in valuation allowance		(32.6	)%		(267.7	)%
Effective income tax rate		0.0	%		(0.5	)%

Summary of Deferred Tax Assets and Liabilities

Net deferred tax assets and liabilities consisted of the following (in thousands):

	December 31,
	2020			2019
Deferred tax assets:
Net operating losses	$	27,047		$	16,655
Research and development credits		7,617			4,949
Accrued expenses	291			130
Other	474			247
Deferred rent	266			124
Stock based compensation	428			73
Total deferred tax assets		36,123			22,178
Deferred tax liabilities:
Asset basis	$	(124	)	$	(110	)
Prepaid expenses		(558	)		(139	)
Total deferred tax liabilities		(682	)		(249	)
Valuation allowance		35,441			21,929
Net deferred taxes	$	—		$	—

Summary of Net Operating Losses and Tax Credit Carryforwards

Net operating losses and tax credit carryforwards were as follows (in thousands):

	December 31, 2020		Expiration Year
Net operating losses, federal (starting from January 1, 2018)	$	66,963	Does not expire
Net operating losses, federal (before January 1, 2018)	$	29,486	2035-2037
Net operating losses, state	$	97,273	2035-2040
Tax credits, federal	$	7,518	2036-2040
Tax credits, state	$	2,540	Does not expire

Summary of Changes in Valuation Allowance for Deferred Tax Assets

Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2020 and 2019 related primarily to the increases in net operating loss carryforwards and research and development tax credit carryforwards and were as follows (in thousands):

	Year Ended December 31,
	2020		2019
Valuation allowance at the beginning of the year	$	21,929	$	20,240
Increases recorded to income tax provision		13,512		1,689
Valuation allowance at the end of the year	$	35,441	$	21,929

Summary of Reconciliation of Unrecognized Tax Benefits

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands):

	Year Ended December 31,
	2020		2019
January 1	$	1,355	$	855
Additions based on tax positions related to current year		513		570
Additions (reductions) for tax positions of prior year		139		(70	)
December 31	$	2,007	$	1,355

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2020

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments

Future minimum lease payments under the Lease as of December 31, 2020 were as follows (in thousands):

Year ending December 31:	Operating Lease
2021	$	2,027
2022		2,098
2023		2,171
2024		2,247
2025		1,144
Total	$	9,687

Net Loss Per Share Attributable to Common Stockholders (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share

	Year Ended December 31,
	2020		2019
Redeemable convertible preferred stock (on an as-converted basis)		—		18,442,233
Options to purchase common stock		2,993,855		1,337,501
Restricted stock awards granted and not purchased		4,195		4,195
Unvested restricted shares		126,522		302,211
Total		3,124,572		20,086,140

Reconciliation of Numerator and Denominator Used in Calculation of Basic and Diluted Net Loss Per Share

	Year Ended December 31,
	2020			2019
Net loss per share:
Numerator
Net loss	$	(41,533	)	$	(631	)
Less: accretion to redemption value and dividends on redeemable convertible preferred shares		—			(6,225	)

Net loss attributable to common stockholders	$	(41,533	)	$	(6,856	)
Denominator
Weighted-average common shares outstanding used to calculate net loss per share attributable to common stockholders:
Basic		21,344,236			1,623,358
Diluted		21,344,236			1,623,358
Net loss per share attributable to common stockholders:
Basic	$	(1.95	)	$	(4.22	)
Diluted	$	(1.95	)	$	(4.22	)

Description of Business - Additional Information (Detail) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) $ / shares shares	May 31, 2020	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reverse stock split, description			1-for-7.15
Reverse stock split, conversion ratio		0.13986014	0.1399
Common stock, shares issued			35,552,795	1,846,024
Initial Public Offering
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reverse stock split, conversion ratio	7.15
Initial public offering, shares issued	10,350,000
Share price of shares issued in initial public offering \| $ / shares	$ 16.00
Proceeds from the initial public offering \| $	$ 148.3
Underwriting discounts, commissions and offering expenses \| $	$ 5.7		$ 3.1	$ 2.6
Convertible preferred stock converted into common shares	160,389,279
Reclassification of convertible preferred stock into additional paid in capital upon initial public offering \| $	$ 238.3
Initial Public Offering \| Underwriters
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Initial public offering, shares issued	1,350,000
Initial Public Offering \| Common Stock
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Initial public offering, shares issued	9,000,000
Private Placement \| Novartis
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Common stock, shares issued	625,000
Share price \| $ / shares	$ 16.00
Proceeds from issuance of common stock \| $	$ 10.0
Private Placement \| Pliant Therapeutics, Inc. \| Novartis
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Percentage of noncontrolling ownership	6.10%

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Accounting Policies [Line Items]
Revenue recognized		$ 0
Deposits, in excess of FDIC insured limit	$ 250,000
Number of reportable segments \| Segment	1
Number of operating segments \| Segment	1
Debt instrument remaining maturity period at date of purchase	3 months
Impairment of long-lived assets	$ 0	0
Amount of gross receipts during period		$ 5,000,000
Expected dividend yield	0.00%	0.00%
Deferred offering costs		$ 2,800,000
Maximum
Accounting Policies [Line Items]
Research and development arrangement with federal government, customer funding to offset costs incurred			$ 250,000
Novartis Agreement
Accounting Policies [Line Items]
Description of customer payment terms	The Company performs credit evaluations of its customer, and the risk with respect to accounts receivable is further mitigated by the short duration of customer payment terms, generally within 60 days, and the pedigree of the customer base.
Percentage of revenue contributed by related party	100.00%
Novartis Agreement \| Maximum
Accounting Policies [Line Items]
Customer payment terms	60 days

Summary of Significant Accounting Policies - Summary of Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2020
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	5 years
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property, plant and equipment, estimated useful lives	Shorter of remaining lease term or estimated useful life

Financial Instruments - Summary of Cash and Cash Equivalents, Money Market Funds and Short-term Investments by Significant Investment Category (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	$ 263,729	$ 53,568
Unrealized Gains	15	1
Unrealized Losses	(47)	(2)
Market Value	263,697	53,567
Level 1 \| Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	27,686	16,366
Market Value	27,686	16,366
Level 2 \| U.S. Treasury Securities Included in Cash and Cash Equivalents and Short-term Investments
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	63,101	2,998
Unrealized Gains	4
Unrealized Losses	(1)
Market Value	63,104	2,998
Level 2 \| U.S. Government Agency Securities Included in Short-term Investments
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	54,183	34,204
Unrealized Gains	10	1
Unrealized Losses		(2)
Market Value	54,193	$ 34,203
Level 2 \| Corporate Debt Securities Included in Cash and Cash Equivalents and Short-term Investments
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	118,759
Unrealized Gains	1
Unrealized Losses	(46)
Market Value	$ 118,714

Financial Instruments - Summery of Remaining Contractual Maturities of Company's Short-term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	$ 263,729	$ 53,568
Market Value	263,697	$ 53,567
Short Term Investments
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	226,044
Market Value	226,012
Short Term Investments \| Mature in 1 Year or Less
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	220,980
Market Value	220,946
Short Term Investments \| Mature in 1 to 2 Years
Schedule Of Available For Sale Securities [Line Items]
Adjusted Cost	5,064
Market Value	$ 5,066

Financial Instruments - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured at fair value	$ 0	$ 0
Transfers of assets between Level 1 and Level 2	0	0
Transfers of assets between Level 2 and Level 1	0	0
Transfers of liabilities between Level 1 and Level 2	0	0
Transfers of liabilities between Level 2 to Level 1	0	0
Transfer out of Level 3 measurement	0	0
Transfer in to Level 3 measurement	0	0
Fair Value Measurements, Non-recurring Basis
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities measured at fair value	0	0
Assets measured at fair value	$ 0	$ 0

Property and Equipment, net - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 7,809	$ 6,267
Less: Accumulated depreciation	(3,488)	(2,188)
Total property and equipment, net	4,321	4,079
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Total property and equipment, gross	22	22
Laboratory Equipment
Property Plant And Equipment [Line Items]
Total property and equipment, gross	6,540	5,580
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment, gross	947	657
Construction in Progress
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 300	$ 8

Property and Equipment, net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Depreciation expense	$ 1,310	$ 1,113

Accrued Liabilities and Other Long-Term Liabilities - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accrued Liabilities And Other Liabilities [Abstract]
Accrued compensation and benefits	$ 4,542	$ 2,971
Accrued research and development expenses	3,274	2,624
Other accrued liabilities	1,675	1,263
Deferred rent/leasehold incentive obligation-current	85	64
Total accrued liabilities	$ 9,576	$ 6,922

Accrued Liabilities and Other Long-Term Liabilities - Summary of Other Long-Term Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accrued Liabilities And Other Liabilities [Abstract]
Deferred rent	$ 581	$ 458
Leasehold incentive obligation	283	444
Other liabilities — deposits	2	10
Total other long-term liabilities	$ 866	$ 912

Novartis Agreement - Additional Information (Details)			1 Months Ended	3 Months Ended	12 Months Ended
Novartis Agreement - Additional Information (Details)	Dec. 19, 2019 USD ($) shares	Dec. 07, 2019 USD ($)	Oct. 31, 2019 USD ($) Research $ / shares	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares	Jun. 05, 2020 USD ($)
Series C Redeemable Convertible Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Redeemable convertible preferred stock, shares issued \| shares					0	26,360,745
Novartis \| Novartis Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from upfront non-refundable license fee		$ 50,000,000
Collaboration and license agreement, description					The Company is initially obligated to perform research and development services on the integrin research targets for sixty days. Novartis has the option to continue the research and development services through 2022, with the option to terminate the services with 60 days’ notice.
Collaboration and license agreement, target validation fee			$ 4,000,000
Committed to provide equity financing			30,000,000
Percentage of outstanding shares of common stock on fully diluted basis					6.10%	7.40%
Transaction price of Novartis agreement			69,600,000
Selling price of license			50,000,000
Revenue recognized from related party					$ 41,800,000
Receivable from related party transactions					9,300,000	$ 7,100,000
Contract assets					0	0
Contract liabilities					0	0
Novartis \| Novartis Agreement \| Achievement of First Patient Dosing Milestone
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized from related party				$ 25,000,000
Novartis \| Novartis Agreement \| License Fee
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price of Novartis agreement			50,000,000
Revenue recognized from related party						50,000,000
Novartis \| Novartis Agreement \| Research and Development
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transaction price of Novartis agreement			19,600,000
Revenue recognized from related party					$ 16,800,000	$ 7,100,000
Novartis \| Novartis Agreement \| Initial Public Offering
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Committed to provide equity financing			10,000,000				$ 10,000,000
Novartis \| Novartis Agreement \| Series C Redeemable Convertible Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Committed to provide equity financing	$ 20,000,000		$ 20,000,000
Redeemable convertible preferred stock, shares issued \| shares	10,928,962
Redeemable convertible preferred stock issued at fair value per share \| $ / shares			$ 1.83
Purchase of redeemable convertible preferred stock	$ 10,900,000
Novartis \| Novartis Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of Integrin research targets \| Research			3
Research and development future payments to be received			$ 19,600,000
Collaboration and license agreement, integrin research targets amount			416,000,000
Novartis \| Novartis Agreement \| Maximum \| Additional Funding Agreement Terms
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Research and development future payments to be received			$ 13,400,000

License Agreements - Additional Information (Details) - License Agreements - UC Regents - USD ($)	1 Months Ended	12 Months Ended
	Aug. 31, 2015	Dec. 31, 2020
License Agreements [Line Items]
Payment of non-refundable upfront license fee	$ 400,000
Payment of annual license maintenance fee	10,000
Payment of annual license maintenance fee after first year	$ 25,000
Percentage of royalty payments on net sales of licensed product	3.00%
Percentage of royalty payments on net sales of method use licensed product	1.00%
Annual minimum royalty payment on net sales	$ 1,000,000
Aggregate contingency payment on certain events milestones	$ 18,200,000
Milestone and annual royalty paid		$ 2,400,000

Research Agreement - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Oct. 31, 2018	Dec. 31, 2020	Dec. 31, 2019
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development expense		$ 66,193	$ 47,353
Adimab Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Development and option agreement date	2018-10
Adimab Agreement \| FTE costs
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development expense		$ 200	200
Adimab Agreement \| Antibody Discovery Fees
Research And Development Arrangement Contract To Perform For Others [Line Items]
Research and development expense			$ 100

Redeemable Convertible Preferred Stock - Additional Information (Details)			1 Months Ended				12 Months Ended
	Dec. 19, 2019	Jul. 10, 2018	May 31, 2020	Feb. 29, 2020 USD ($) $ / shares shares	Jul. 31, 2018 USD ($) shares	Aug. 31, 2015 USD ($) Tranche	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 shares	Mar. 31, 2018 USD ($)
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issuance costs \| $							$ 0	$ 2,582,000
Convertible stock, voting rights description							Each holder of shares of Preferred Stock was entitled to the number of votes equal to the number of shares of common stock into which such shares could have been converted and had voting rights and powers equal to the voting rights and powers of the common stock, and except as provided by law or by other provisions of the Company’s Certificate of Incorporation, as amended, could have voted together with the common stock as a single class on an as-converted basis on all matters as to which holders of common stock have the right to vote.
Convertible preferred stock, terms of conversion							Shares of the Preferred Stock were convertible at any time at the option of the holder into such number of shares as is determined by dividing the original issuance price by the conversion price in effect at the time.
Reverse stock split, conversion ratio			0.13986014				0.1399
Series C Preferred Stock Purchase Agreement
Temporary Equity [Line Items]
Redeemable convertible preferred stock redemption terms							All outstanding shares of Preferred Stock shall be redeemed by the Company at a price equal to the original issuance price per share, plus any dividends declared but unpaid, in three annual installments commencing not more than sixty (60) days after receipt by the Company at any time on or after five years from the Series C Preferred original issuance date, December 19, 2019, a written notice from the holders of a majority of the shares of Preferred Stock.
Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized							0
Redeemable convertible preferred stock, shares outstanding							0
Series A Preferred Stock
Temporary Equity [Line Items]
Redeembale convertaible preferred stock dividend rate		8.00%
Series A Preferred Stock \| Series A Preferred Stock Purchase Agreement
Temporary Equity [Line Items]
Redeemable convertible preferred stock, purchase amount \| $						$ 45,000,000				$ 11,000,000
Number of tranches \| Tranche						3
Redeemable convertible preferred stock, shares issued								56,000,000
Cash proceeds from redeemable convertible preferred stock \| $								$ 56,000,000
Series B Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized							0	49,501,221
Redeemable convertible preferred stock, shares outstanding							0	49,501,221	49,501,221
Redeemable convertible preferred stock, shares issued							0	49,501,221
Redeemable convertible preferred stock conversion price per share \| $ / shares							$ 9.843405
Redeemable convertible preferred stock liquidation price per share \| $ / shares							$ 1.3767
Series B Redeemable Convertible Preferred Stock \| Series B Preferred Stock Purchase Agreement
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issued					49,500,000
Cash proceeds from redeemable convertible preferred stock \| $					$ 68,100,000
Series B Redeemable Convertible Preferred Stock \| Series B Preferred Stock Purchase Agreement \| Maximum
Temporary Equity [Line Items]
Redeemable convertible preferred stock, purchase amount \| $					$ 70,000,000
Series B Redeemable Convertible Preferred Stock \| Series C Preferred Stock Purchase Agreement
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issued								26,400,000
Cash proceeds from redeemable convertible preferred stock \| $								$ 48,200,000
Series B Redeemable Convertible Preferred Stock \| Series C Preferred Stock Purchase Agreement \| Novartis
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized								10,900,000
Cash proceeds from redeemable convertible preferred stock \| $								$ 20,000,000
Percentage of outstanding shares of common stock on fully diluted basis							6.10%	7.40%
Series B Redeemable Convertible Preferred Stock \| Series C Preferred Stock Purchase Agreement \| Maximum
Temporary Equity [Line Items]
Redeemable convertible preferred stock, purchase amount \| $								$ 80,500,000
Series C Redeemable Convertible Preferred Stock \| Series C Preferred Stock Purchase Agreement
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares issued				28,500,000
Cash proceeds from redeemable convertible preferred stock \| $				$ 52,200,000
Redeemable convertible preferred stock, cash received price per share \| $ / shares				$ 1.83
Redeemable convertible preferred stock, shares issuance costs \| $				$ 200,000
Series A Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized							0	56,000,000
Redeemable convertible preferred stock, shares outstanding							0	56,000,000	56,000,000
Redeemable convertible preferred stock, shares issued							0	56,000,000
Redeemable convertible preferred stock conversion price per share \| $ / shares							$ 7.15
Redeemable convertible preferred stock liquidation price per share \| $ / shares							$ 1.00
Series C Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized							0	44,000,000
Redeemable convertible preferred stock, shares outstanding							0	26,360,745
Redeemable convertible preferred stock, shares issued							0	26,360,745
Redeemable convertible preferred stock conversion price per share \| $ / shares							$ 13.0845
Redeemable convertible preferred stock liquidation price per share \| $ / shares							$ 1.83
Series B Preferred Stock \| Series B Preferred Stock Purchase Agreement
Temporary Equity [Line Items]
Redeembale convertaible preferred stock dividend rate		8.00%
Series A, Series B and Series C Preferred \| Series C Preferred Stock Purchase Agreement
Temporary Equity [Line Items]
Redeembale convertaible preferred stock dividend rate	8.00%

Redeemable Convertible Preferred Stock - Summary of Redeemable Convertible Preferred Stock (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Series A Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized	0	56,000,000
Redeemable convertible preferred stock, shares issued	0	56,000,000
Redeemable convertible preferred stock, shares outstanding	0	56,000,000	56,000,000
Redeemable convertible preferred stock. aggregate liquidation preference	$ 0	$ 62,468
Redeemable convertible preferred stock value	$ 0	$ 62,468	$ 61,516
Series B Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized	0	49,501,221
Redeemable convertible preferred stock, shares issued	0	49,501,221
Redeemable convertible preferred stock, shares outstanding	0	49,501,221	49,501,221
Redeemable convertible preferred stock. aggregate liquidation preference	$ 0	$ 75,860
Redeemable convertible preferred stock value	$ 0	$ 75,860	$ 70,587
Series C Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized	0	44,000,000
Redeemable convertible preferred stock, shares issued	0	26,360,745
Redeemable convertible preferred stock, shares outstanding	0	26,360,745
Redeemable convertible preferred stock. aggregate liquidation preference	$ 0	$ 47,947
Redeemable convertible preferred stock value	$ 0	$ 47,947
Amended and Restated Certificate of Incorporation
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized		149,501,221
Redeemable convertible preferred stock, shares issued		131,861,966
Redeemable convertible preferred stock, shares outstanding		131,861,966
Redeemable convertible preferred stock. aggregate liquidation preference		$ 186,275
Redeemable convertible preferred stock value		$ 186,275
Amended and Restated Certificate of Incorporation \| Series A Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized		56,000,000
Redeemable convertible preferred stock, shares issued		56,000,000
Redeemable convertible preferred stock, shares outstanding		56,000,000
Redeemable convertible preferred stock. aggregate liquidation preference		$ 62,468
Redeemable convertible preferred stock value		$ 62,468
Amended and Restated Certificate of Incorporation \| Series B Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized		49,501,221
Redeemable convertible preferred stock, shares issued		49,501,221
Redeemable convertible preferred stock, shares outstanding		49,501,221
Redeemable convertible preferred stock. aggregate liquidation preference		$ 75,860
Redeemable convertible preferred stock value		$ 75,860
Amended and Restated Certificate of Incorporation \| Series C Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized		44,000,000
Redeemable convertible preferred stock, shares issued		26,360,745
Redeemable convertible preferred stock, shares outstanding		26,360,745
Redeemable convertible preferred stock. aggregate liquidation preference		$ 47,947
Redeemable convertible preferred stock value		$ 47,947

Common Stock - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended	48 Months Ended	67 Months Ended
	Dec. 31, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020
Class Of Stock [Line Items]
Common stock, shares authorized		300,000,000	181,000,000	300,000,000
Common stock, par value		$ 0.0001	$ 0.0001	$ 0.0001
Common stock, voting rights		The holders of shares of common stock are entitled to one vote for each share of common stock held at any meeting of stockholders and at the time of any written action in lieu of a meeting.
Dividends declared				0
Dividends paid				$ 0
Founders Common Stock Awards
Class Of Stock [Line Items]
Number of shares granted during period	745,244		0
Total compensation expense	$ 25,000
Minimum \| Founders Common Stock Awards
Class Of Stock [Line Items]
Vesting period		1 year
Maximum \| Founders Common Stock Awards
Class Of Stock [Line Items]
Vesting period		4 years

Common Stock - Schedule of Shares Reserved for Future Issuance (Details) - shares	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Jan. 31, 2019	Jul. 31, 2018
Class Of Stock [Line Items]
Total shares reserved for future issuance	7,338,314		20,346,844
Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Total shares reserved for future issuance			18,442,233
Exercises of Outstanding Stock Option Awards
Class Of Stock [Line Items]
Total shares reserved for future issuance	2,993,855		1,337,501
Shares of Common Stock Available for Future Grants under the 2015 Equity Incentive Plan, as Amended
Class Of Stock [Line Items]
Total shares reserved for future issuance	0	1,400,000	567,110	400,000	1,000,000
Shares of Common Stock Available for Future Grants under the 2020 Equity Incentive Plan
Class Of Stock [Line Items]
Total shares reserved for future issuance	3,644,459
Shares of Common Stock Available for Future Issuance under the 2020 ESPP
Class Of Stock [Line Items]
Total shares reserved for future issuance	700,000

Equity Incentive Plans and Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2020	Jan. 31, 2019	Jul. 31, 2018	Aug. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares reserved for future issuance		7,338,314	20,346,844
Number of shares, not purchased		4,195
Weighted-average grant date fair value, not purchased		$ 0.08
2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares reserved for future issuance		0	567,110	1,400,000	400,000	1,000,000
Exercise price as a percentage of estimated grant date fair value of shares		10.00%
Expiration period from date of grant		5 years
Two Thousand And Twenty Stock Options And Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares reserved for future issuance		3,600,000
Common stock shares outstanding percentage	5.00%
Exercise price as a percentage of estimated grant date fair value of shares		10.00%
Expiration period from date of grant		5 years
Restricted Common Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting rights		The repurchase price for unvested shares of common stock will be the lower of (i) the fair market value on the date of repurchase or (ii) their original purchase price.
Number of shares granted		0	0
Restricted Common Stock Awards \| Accrued Expenses and Other Liabilities
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Accrued expenses and other liabilities		$ 10,000	$ 22,000
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate fair value of restricted stock awards vested		200	400
Total intrinsic value of outstanding unvested restricted stock awards		$ 2,900	$ 2,100
2015 Equity and 2020 Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expiration period from date of grant		10 years
Vesting period		4 years
Maximum \| 2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options under plan could be granted for periods		10 years
Percentage of estimated fair value of shares on date of grant		100.00%
Exercise price as a percentage of estimated grant date fair value of shares		110.00%
Maximum \| Two Thousand And Twenty Stock Options And Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price as a percentage of estimated grant date fair value of shares		110.00%
Options under plan may be granted for periods		10 years
Maximum \| Restricted Common Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		4 years
Minimum \| Restricted Common Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		1 year
Common Stock \| Maximum \| 2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for future grant							1,500,000
Common Stock \| Maximum \| Two Thousand And Twenty Stock Options And Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for future grant	4,200,000

Equity Incentive Plans and Stock-Based Compensation - Summary of Restricted Stock Activity (Details) - Restricted Common Stock Awards	12 Months Ended
	Dec. 31, 2020 $ / shares shares	Dec. 31, 2019 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Shares, Outstanding and unvested, beginning balance	302,211
Number of Shares, Issued	0	0
Number of Shares, Vested	(163,568)
Number of Shares, Repurchases	(12,121)
Number of Shares, Outstanding and unvested, ending balance	126,522	302,211
Weighted-Average Grant Date fair value, Outstanding and unvested, beginning balance \| $ / shares	$ 1.85	$ 1.51
Weighted-Average Grant Date fair value, Vested \| $ / shares	1.30
Weighted-Average Grant Date fair value, Repurchases \| $ / shares	$ 1.22

Equity Incentive Plans and Stock-Based Compensation - Summary of Black-Scholes Option Pricing Model to Estimate Stock-based Compensation Expense for Stock Option Awards (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%
Incentive Stock Options and Nonqualified Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	72.10%	74.80%
Expected volatility, maximum	77.50%	82.53%
Risk-free interest rate, minimum	0.27%	1.43%
Risk-free interest rate, maximum	0.82%	2.59%
Incentive Stock Options and Nonqualified Stock Options \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 3 months 3 days	5 years
Underlying common stock fair value	$ 6.22	$ 5.15
Incentive Stock Options and Nonqualified Stock Options \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 9 months	6 years 29 days
Underlying common stock fair value	$ 28.79	$ 7.08

Equity Incentive Plans and Stock-Based Compensation - Summary of Option Activity Under the 2015 Plan and 2020 Plan (Details) - 2015 Equity and 2020 Incentive Plan - Incentive Stock Options and Nonqualified Stock Options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, Outstanding, Beginning balance	1,337,501
Number of Options, Granted	1,830,738
Number of Options, Exercised	(136,223)
Number of Options, Forfeited	(38,161)
Number of Options, Outstanding, Ending balance	2,993,855	1,337,501
Number of Options, Exercisable	736,601
Number of Options, Vested and expected to vest	2,993,855
Weighted- Average Exercise Price per Share, Outstanding, Beginning balance	$ 3.22
Weighted- Average Exercise Price per Share, Granted	11.43
Weighted- Average Exercise Price per Share, Exercised	3.25
Weighted- Average Exercise Price per Share, Forfeited	8.13
Weighted- Average Exercise Price per Share, Outstanding, Ending balance	8.18	$ 3.22
Weighted- Average Exercise Price per Share, Exercisable	4.19
Weighted- Average Exercise Price per Share, Vested and expected to vest	$ 8.18
Weighted- Average Remaining Contractual Term (in Years), Outstanding	8 years 10 months 2 days	9 years 2 months 4 days
Weighted- Average Remaining Contractual Term (in Years), Exercisable	8 years 2 months 19 days
Weighted- Average Remaining Contractual Term (in Years), Vested and expected to vest	8 years 10 months 2 days
Aggregate Intrinsic Value, Outstanding balance	$ 43,890	$ 5,157
Aggregate Intrinsic Value, Exercisable	13,664
Aggregate Intrinsic Value, Vested and expected to vest	$ 43,890

Equity Incentive Plans and Stock-Based Compensation - Incentive Stock Options and Nonqualified Stock Options - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Incentive Stock Options and Nonqualified Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Grant date fair value of stock option	$ 7.27	$ 4.37
Restricted Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost	$ 0.2
Unrecognized compensation expense, weighted average period	1 year 2 months 19 days
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense, weighted average period	2 years 8 months 19 days
Unrecognized compensation cost	$ 14.3

Equity Incentive Plans and Stock-Based Compensation - 2020 Employee Stock Purchase Plan - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares reserved for future issuance		7,338,314	20,346,844
Stock-based compensation expense		$ 3,895,000	$ 1,829,000
Shares of Common Stock Available for Future Issuance under the 2020 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares reserved for future issuance	700,000
Employee stock purchase plan, description		The 2020 ESPP provides that the number of shares reserved and available for issuance will automatically increase on January 1 of each calendar year, beginning January 1, 2021, by the least of (i) 1.0% of the total number of shares of common stock outstanding on December 31 of the preceding calendar year, (ii) 700,000 shares or (iii) such lesser amount as determined by the administrator of the 2020 ESPP, which is the compensation committee of the board of directors.
Common stock shares outstanding percentage	1.00%
Percentage of payroll deductions		15.00%
Employee stock purchase plan offering period		6 months
Stock-based compensation expense		$ 500,000	$ 0
Common stock fair market value percentage		85.00%
Number of common stock issued		0

Equity Incentive Plans and Stock-Based Compensation - 2020 Employee Stock Purchase Plan - Summary of Black-Scholes Option Pricing Model to Estimate Stock-based Compensation Expense for 2020 Employee Stock Purchase Plan (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%
Shares of Common Stock Available for Future Issuance under the 2020 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	0.11%
Expected term of options (in years)	6 months 29 days
Expected stock price volatility	83.72%

Equity Incentive Plans and Stock-Based Compensation - Summary of Classification of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 3,895	$ 1,829
Research and Development Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	1,719	584
General and Administrative Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 2,176	$ 1,245

Income Taxes - Additional Information (Details)	12 Months Ended
Income Taxes - Additional Information (Details)	Dec. 31, 2020 USD ($) Examination	Dec. 31, 2019 USD ($)
Income Tax Disclosure [Abstract]
Pre-tax U.S. book loss	$ 41,500,000	$ 600,000
Income tax provision	$ 0	$ 0
Valuation allowance as a percentage on total deferred tax assets	100.00%
Effective tax rate	0.00%	(0.50%)
Income tax examination, description	The Company’s U.S. federal and state income tax returns are generally subject to tax examinations for the tax years ended December 31, 2017 through December 31, 2020.
Number of income tax examinations pending \| Examination	0

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Income Taxes - Summary of Reconciliation of U.S. Federal Statutory Income Tax Rate to Company’s Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income tax computed at federal statutory rate	21.00%	21.00%
State taxes, net of federal tax benefit	7.40%	2.70%
General business credit—federal	5.30%	295.90%
Stock-based compensation	(1.00%)	(50.00%)
Other permanent differences	(0.10%)	(2.40%)
Change in valuation allowance	(32.60%)	(267.70%)
Effective income tax rate	0.00%	(0.50%)

Income Taxes - Summary of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating losses	$ 27,047	$ 16,655
Research and development credits	7,617	4,949
Accrued expenses	291	130
Other	474	247
Deferred rent	266	124
Stock based compensation	428	73
Total deferred tax assets	36,123	22,178
Deferred tax liabilities:
Asset basis	(124)	(110)
Prepaid expenses	(558)	(139)
Total deferred tax liabilities	(682)	(249)
Valuation allowance	$ 35,441	$ 21,929	$ 20,240

Income Taxes - Summary of Net Operating Losses and Tax Credit Carry Forwards (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Federal
Operating Loss Carryforwards [Line Items]
Tax credits	$ 7,518
Federal \| Starting from January 1, 2018
Operating Loss Carryforwards [Line Items]
Net operating losses	66,963
Federal \| Before January 1, 2018
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 29,486
Federal \| Earliest Tax Year
Operating Loss Carryforwards [Line Items]
Net operating losses, Expiration year	2035
Federal \| Latest Tax Year
Operating Loss Carryforwards [Line Items]
Net operating losses, Expiration year	2037
State
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 97,273
Tax credits	$ 2,540
State \| Earliest Tax Year
Operating Loss Carryforwards [Line Items]
Net operating losses, Expiration year	2035
Tax credits Expiration year	2036
State \| Latest Tax Year
Operating Loss Carryforwards [Line Items]
Net operating losses, Expiration year	2040
Tax credits Expiration year	2040

Income Taxes - Summary of Changes in Valuation Allowance for Deferred Tax Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Valuation Allowance [Abstract]
Valuation allowance at the beginning of the year	$ 21,929	$ 20,240
Increases recorded to income tax provision	13,512	1,689
Valuation allowance at the end of the year	$ 35,441	$ 21,929

Income Taxes - Summary of Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Unrecognized Tax Benefits Income Tax Penalties And Interest Expense [Abstract]
January 1	$ 1,355	$ 855
Additions based on tax positions related to current year	513	570
Additions (reductions) for tax positions of prior year	139	(70)
December 31	$ 2,007	$ 1,355

Commitments and Contingencies - Additional Information (Details) $ in Millions	1 Months Ended	12 Months Ended
	Feb. 28, 2018 USD ($) ft²	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Commitments [Line Items]
Contractual arrangements cancellation period		30 days
Rent expenses and common area maintenance charges		$ 2.5	$ 2.5
California
Commitments [Line Items]
Leased premises under non cancelable operating lease \| ft²	32,974
Lease term	84 months
Operating lease description		Base rent was abated for the first two months of the lease term and thereafter is $0.2 million per month during the first year of the lease term, with specified annual increases thereafter.
Base rent abated amount	$ 0.2
Lease term extension period		7 years
California \| Minimum
Commitments [Line Items]
Lease term extension notice period		12 months
California \| Maximum
Commitments [Line Items]
Lease term extension notice period		9 months
California \| Other Non-current Assets
Commitments [Line Items]
Refundable security deposit		$ 0.4	$ 0.4

Commitments and Contingencies - Schedule of Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Leases [Abstract]
2021	$ 2,027
2022	2,098
2023	2,171
2024	2,247
2025	1,144
Total	$ 9,687

Related Party Transactions - Additional Information (Details)	1 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($) shares	Oct. 31, 2019 USD ($) Research	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 05, 2020 USD ($)	Dec. 19, 2019 USD ($)
Novartis \| Novartis Agreement
Related Party Transaction [Line Items]
Payment to related party		$ 69,600,000
Committed to provide equity financing		$ 30,000,000
Percentage of outstanding equity on fully diluted basis			6.10%	7.40%
Maximum \| Novartis \| Novartis Agreement
Related Party Transaction [Line Items]
Number of Integrin research targets \| Research		3
IPO \| Novartis \| Novartis Agreement
Related Party Transaction [Line Items]
Committed to provide equity financing		$ 10,000,000			$ 10,000,000
Series C Redeemable Convertible Preferred Stock \| Novartis \| Novartis Agreement
Related Party Transaction [Line Items]
Committed to provide equity financing		$ 20,000,000				$ 20,000,000
Third Rock Ventures \| Non-employee Director \| Stock Options
Related Party Transaction [Line Items]
Option granted \| shares	26,573
Grant date fair value of stock option	$ 100,000
Vesting rights			The common shares subject to these options vest 1/12th on the last day of each calendar quarter over a three-year period and commenced vesting upon our IPO.
Vesting period			3 years
UCSF Foundation
Related Party Transaction [Line Items]
Payment to related party			$ 700,000	$ 400,000
Scientific Founders
Related Party Transaction [Line Items]
Payment to related party			200,000	200,000
General and Administrative Expenses \| Third Rock Ventures
Related Party Transaction [Line Items]
Consulting service expenses			$ 0	$ 36,000

Defined Contribution Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Payment made under defined contribution plan	$ 0.4	$ 0.2
Defined Contribution Plan, Plan Name [Extensible List]	plrx:FourZeroOneKPlansMember	plrx:FourZeroOneKPlansMember

Net Loss Per Share Attributable to Common Stockholders - Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted net loss per share	3,124,572	20,086,140
Redeemable Convertible Preferred Stock (on an As-converted Basis)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted net loss per share	0	18,442,233
Exercises of Outstanding Stock Option Awards
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted net loss per share	2,993,855	1,337,501
Restricted Stock Awards Granted and Not Purchased
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted net loss per share	4,195	4,195
Unvested Restricted Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted net loss per share	126,522	302,211

Net Loss Per Share Attributable to Common Stockholders - Reconciliation of Numerator and Denominator Used in Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Numerator
Net loss	$ (41,533)	$ (631)
Less: accretion to redemption value and dividends on redeemable convertible preferred shares	0	(6,225)
Net loss attributable to common stockholders	$ (41,533)	$ (6,856)
Weighted-average common shares outstanding used to calculate net loss per share attributable to common stockholders:
Basic	21,344,236	1,623,358
Diluted	21,344,236	1,623,358
Net loss per share, attributable to common stockholders:
Basic	$ (1.95)	$ (4.22)
Diluted	$ (1.95)	$ (4.22)