Kronos Bio (KRON) 10-Q 11 May 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	May 10, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-39592
Entity Registrant Name	Kronos Bio, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-1895605
Entity Address, Address Line One	1300 So. El Camino Real
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	San Mateo
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94402
City Area Code	650
Local Phone Number	781-5200
Title of 12(b) Security	Common stock, $0.001 par value per share
Trading Symbol	KRON
Security Exchange Name	NASDAQ
Entity Current Reporting Status	No
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		56,069,854
Entity Central Index Key	0001741830
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false

Condensed Balance Sheets (Unaud

Condensed Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	[1]
Current assets:
Cash and cash equivalents	$ 141,448	$ 248,009
Short-term investments	257,476	165,052
Prepaid expenses and other current assets	6,347	6,741
Total current assets	405,271	419,802
Long-term investments	41,684	49,001
Total property and equipment, net	14,021	13,646
Operating lease right-of-use assets	24,845	27,322
Restricted cash	2,026	2,027
Other noncurrent assets	114	166
Total assets	487,961	511,964
Current liabilities:
Accounts payable	3,586	4,550
Accrued expenses	4,275	4,974
Current portion of operating lease liabilities	822	937
Current portion of other liabilities	2,602	2,395
Total current liabilities	11,285	12,856
Noncurrent operating lease liabilities	29,394	31,120
Other noncurrent liabilities	2,025	2,469
Total liabilities	42,704	46,445
Commitments and contingencies (Note 11)
Stockholders’ equity:
Common stock, $0.001 par value, 200,000,000 and 200,000,000 shares authorized as of March 31, 2021 and December 31, 2020 respectively; 54,385,963 and 54,073,901 shares issued and outstanding as of March 31, 2021 and December 31, 2020, respectively.	54	54
Preferred stock, $0.001 par value; 10,000,000 authorized; no shares issued and outstanding.	0	0
Additional paid-in capital	583,218	577,390
Accumulated deficit	(137,992)	(111,906)
Accumulated other comprehensive loss	(23)	(19)
Total stockholders' equity	445,257	465,519
Total liabilities, convertible preferred stock and stockholders’ equity	$ 487,961	$ 511,964
[1]	The balance sheet as of December 31, 2020 is derived from the audited financial statements as of that date.

Condensed Balance Sheets (Una_2

Condensed Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	54,385,963	54,073,901
Common stock, shares outstanding (in shares)	54,385,963	54,073,901

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating expenses:
Research and development	$ 17,594	$ 6,195
General and administrative	8,584	1,154
Total operating expenses	26,178	7,349
Loss from operations	(26,178)	(7,349)
Other Income and Expenses [Abstract]
Interest expense	0	(1)
Interest and other income, net	92	355
Total other income (expense), net	92	354
Net loss	(26,086)	(6,995)
Other comprehensive income (loss):
Net unrealized gain (loss) on available-for-sale securities	(4)	158
Net comprehensive loss	$ (26,090)	$ (6,837)
Net loss per share, basic and diluted (in dollars per share)	$ (0.48)	$ (1.23)
Weighted-average shares of common stock, basic and diluted (in shares)	54,152,656	5,694,832

Condensed Statements of Convert

Condensed Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total		Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Convertible preferred stock, beginning balance (in shares) at Dec. 31, 2019	21,504,893
Convertible preferred stock, beginning balance at Dec. 31, 2019	$ 122,907
Convertible preferred stock, ending balance (in shares) at Mar. 31, 2020	21,504,893
Convertible preferred stock, ending balance at Mar. 31, 2020	$ 122,907
Common stock, beginning balance (in shares) at Dec. 31, 2019			5,660,391
Beginning balance at Dec. 31, 2019	(23,203)		$ 6	$ 271	$ (18)	$ (23,462)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon vesting and exercise of options and vesting of restricted stock (in shares)			119,939
Issuance of common stock upon vesting and exercise of options and vesting of restricted stock	20			20
Stock-based compensation expense	188			188
Net unrealized gain (loss) on available-for-sale securities	158				158
Net loss	(6,995)					(6,995)
Common stock, ending balance (in shares) at Mar. 31, 2020			5,780,330
Beginning balance at Mar. 31, 2020	$ (29,832)		$ 6	479	140	(30,457)
Convertible preferred stock, beginning balance (in shares) at Dec. 31, 2020	0
Convertible preferred stock, beginning balance at Dec. 31, 2020	$ 0
Convertible preferred stock, ending balance (in shares) at Mar. 31, 2021	0
Convertible preferred stock, ending balance at Mar. 31, 2021	$ 0
Common stock, beginning balance (in shares) at Dec. 31, 2020			54,073,901
Beginning balance at Dec. 31, 2020	465,519	[1]	$ 54	577,390	(19)	(111,906)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon vesting and exercise of options and vesting of restricted stock (in shares)			312,062
Issuance of common stock upon vesting and exercise of options and vesting of restricted stock	590			590
Stock-based compensation expense	5,238			5,238
Net unrealized gain (loss) on available-for-sale securities	(4)				(4)
Net loss	(26,086)					(26,086)
Common stock, ending balance (in shares) at Mar. 31, 2021			54,385,963
Beginning balance at Mar. 31, 2021	$ 445,257		$ 54	$ 583,218	$ (23)	$ (137,992)
[1]	The balance sheet as of December 31, 2020 is derived from the audited financial statements as of that date.

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		46 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2021	Dec. 31, 2020		Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ (26,086)	$ (6,995)	$ (138,000)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	444	160
Net amortization/accretion on available-for-sale securities	943	17
Change in accrued interest on available-for-sale securities	16	(68)
Stock-based compensation expense	5,238	188
Noncash lease expense	461	68
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	971	(150)
Other long-term assets	52	0
Accounts payable	(1,199)	(244)
Accrued expenses	228	(286)
Right-of-use operating assets and liabilities, net	175	271
Other liabilities	(241)	(27)
Net cash used in operating activities	(18,998)	(7,066)
Cash flows from investing activities:
Purchase of property and equipment	(1,505)	(626)
Purchase of available-for-sale securities	(126,060)	(2,309)
Maturities of available-for-sale securities	39,416	8,245
Net cash provided by (used in) investing activities	(88,149)	5,310
Cash flows from financing activities:
Principal payments on finance lease	(5)	(8)
Proceeds from issuance of common stock	590	20
Net cash provided by financing activities	585	12
Net decrease in cash and cash equivalents	(106,562)	(1,744)
Cash, cash equivalents and restricted cash at beginning of period	250,036	32,570
Cash, cash equivalents and restricted cash at end of period	143,474	30,826	143,474
Supplemental disclosures of non-cash activities:
Property and equipment additions included in accounts payable and accrued expenses	588	686
Reduction of right-of-use asset due to modification	(1,741)	0
Cash and cash equivalents				$ 141,448	$ 248,009	[1]	$ 28,800
Restricted cash				2,026	2,027	[1]	2,026
Cash, cash equivalents and restricted cash at end of period	$ 143,474	$ 30,826	$ 143,474	$ 143,474	$ 250,036		$ 30,826
[1]	The balance sheet as of December 31, 2020 is derived from the audited financial statements as of that date.

Nature of Operations and Basis

Nature of Operations and Basis of Presentation	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations and Basis of Presentation	NATURE OF OPERATIONS AND BASIS OF PRESENTATION Kronos Bio, Inc. (Kronos or the Company), a Delaware corporation, was incorporated on June 2, 2017. The Company is a clinical-stage biopharmaceutical company dedicated to the discovery and development of novel cancer therapeutics designed to transform patient outcomes through a precision medicine strategy by targeting dysregulated transcription. The Company operates in one business segment: the development of biopharmaceutical products. Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP) for interim financial information and pursuant to Form 10-Q and Article 10 of Regulation S-X of the Securities and Exchange Commission (SEC). Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. Initial Public Offering In October 2020, the Company completed an initial public offering (IPO) of its common stock. In connection with its IPO, the Company issued and sold 15,131,579 shares of its common stock, which included 1,973,684 shares of its common stock issued and sold pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a price to the public of $19.00 per share. As a result of the IPO, the Company received approximately $263.7 million in net proceeds, after deducting underwriting discounts and commissions of $20.1 million and offering expenses of approximately $3.7 million payable by the Company. At the closing of the IPO, all then outstanding convertible preferred stock were automatically converted into 22,687,625 shares of common stock and the then outstanding 2020 Notes were automatically converted into 9,610,713 shares of common stock. At the closing of the IPO, the then outstanding Gilead Note (See Note 11) was also converted into 188,567 shares of common stock. Following the IPO, there were no shares of convertible preferred stock outstanding. Forward Stock Split On October 2, 2020, the Company filed an amendment to the Company’s amended and restated certificate of incorporation to effect a forward split of shares of the Company’s common stock on a 1.055-for-1 basis (the Forward Stock Split). In connection with the Forward Stock Split, the conversion ratio for the Company’s outstanding convertible preferred stock was proportionally adjusted such that the common stock issuable upon conversion of such preferred stock was increased in proportion to the Forward Stock Split. The par value of the common stock was not adjusted as the result of the Forward Stock Split. All references to common stock, options to purchase common stock, early exercised options, share data, per share data, convertible preferred stock (to the extent presented on an as-converted to common stock basis) and related information contained in these condensed financial statements have been retrospectively adjusted to reflect the effect of the Forward Stock Split for all periods presented. Need for Additional Capital The Company has incurred net operating losses since its inception of $138.0 million as of March 31, 2021. The Company expects that its cash, cash equivalents and investments as of March 31, 2021, in addition to its approximate net cash proceeds of $263.7 million from the Company’s IPO, which closed on October 14, 2020, will enable it to fund its planned operating expenses and capital expenditure requirements for at least one year from the date of issuance of these condensed financial statements. Management expects to incur additional losses in the future to fund its operations and conduct product research and development and recognizes the need to raise additional capital to fully implement its business plan. The Company intends to raise additional capital through the issuance of equity securities, debt financings or other sources in order to further implement its business plan. However, if such financing is not available when needed and at adequate levels, the Company will need to reevaluate its operating plan and may be required to delay the development of its product candidates. The Company expects that its cash and cash equivalents and investments will be sufficient to fund its operations for a period of at least one year from the date the accompanying financial statements are filed with the Securities and Exchange Commission (SEC). The Company cannot at this time predict the specific extent, duration, or full impact that the COVID-19 pandemic will have on its financial condition and operations, including ongoing and planned clinical trials. The impact of the COVID-19 pandemic on the financial performance of the Company will depend on future developments, including the duration and spread of the pandemic and related governmental advisories and restrictions. These developments and the impact of the COVID-19 pandemic on the financial markets and the overall economy are highly uncertain. If the financial markets and/or the overall economy are impacted for an extended period, the Company’s results may be adversely affected. The future viability of the Company is dependent on its ability to generate cash from operating activities or to raise additional capital to finance its operations. The Company’s failure to raise capital as and when needed could have a material adverse effect on its financial condition and ability to pursue business strategies. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into collaboration arrangements or obtain government grants. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce, or eliminate its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects. In the event that the Company requires additional funding, there can be no assurance that it will be successful in obtaining sufficient funding on terms acceptable to the Company to fund its continuing operations, if at all.

Significant Accounting Policies

Significant Accounting Policies, Estimates and Judgments	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Significant Accounting Policies, Estimates and Judgments	SIGNIFICANT ACCOUNTING POLICIES, ESTIMATES AND JUDGMENTS Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP) for interim financial information and pursuant to Form 10-Q and Article 10 of Regulation S-X of the Securities and Exchange Commission (SEC). Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. Unaudited Interim Financial Information The accompanying balance sheet as of March 31, 2021, the statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020, the statements of convertible preferred stock and stockholders’ equity (deficit) as of March 31, 2021 and 2020, the statements of cash flows for the three months ended March 31, 2021 and 2020, and the financial data and other financial information disclosed to in the notes to the condensed financial statements are unaudited. The unaudited interim financial statements have been prepared on a basis consistent with the Company’s audited annual financial statements and, in the opinion of management, reflect all adjustments, consisting solely of normal recurring adjustments, necessary for the fair presentation of the Company’s financial position as of March 31, 2021 and the results of its operations the three months ended March 31, 2021 and 2020. The results for the three months ended March 31, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021, any other interim periods, or any future year or period. These financial statements should be read in conjunction with the Company's audited financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on March 23, 2021. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed financial statements include, but are not limited to, the accrual of research and development expenses, the fair value of convertible notes and investments, income tax uncertainties, the valuation of equity instruments and the incremental borrowing rate for determining the operating lease assets and liabilities. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including expenses, clinical trials and research and development costs, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain or treat COVID-19, as well as the economic impact on local, regional, national and international markets. Significant Accounting Policies There have been no significant changes to the accounting policies during the three months ended March 31, 2021, as compared to the significant accounting policies described in Note 2 of the “Notes to Financial Statements” of the Company’s audited financial statements included in its Annual Report. Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses: Measurement of Credit Losses on Financial Instruments and also issued subsequent amendments to the initial guidance: ASU 2018-19, ASU 2019-04, ASU 2019-05, and ASU 2019-11. The standard requires measurement and recognition of expected credit losses for financial assets by requiring an allowance to be recorded as an offset to the amortized cost of such assets. For available-for-sale debt securities, expected credit losses should be estimated when the fair value of the debt securities is below their associated amortized costs. The standard will become effective for the Company in the first quarter of 2020, with early adoption permitted beginning the first quarter of 2019. The modified retrospective approach should be applied upon adoption of this new guidance. The Company’s financial instruments that are in the scope of ASU 2016-13 include available-for-sale debt securities. The Company adopted this standard on January 1, 2020 and this amendment did not have a material impact on its financial statements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12), which simplifies the accounting for income taxes, eliminates certain exceptions within ASC 740, Income Taxes

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	FAIR VALUE MEASUREMENTS The Company follows authoritative accounting guidance, which among other things, defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. The Company measures and reports its cash equivalents, investments, and convertible notes at fair value. Money market funds are measured at fair value on a recurring basis using quoted prices and are classified as Level 1. Investments measured at fair value based on inputs other than quoted prices that are derived from observable market data are classified as Level 2. Financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements by major security type as of March 31, 2021 and December 31, 2020 were as follows: March 31, 2021 Level 1 Level 2 Level 3 Fair Value (in thousands) Financial Assets: Money market funds $ 125,053 $ — $ — $ 125,053 Certificates of deposit 491 — — 491 Corporate bonds — 97,500 — 97,500 U.S. agency securities — 10,001 — 10,001 U.S. treasury securities 202,266 — — 202,266 Total financial assets $ 327,810 $ 107,501 $ — $ 435,311 December 31, 2020 Level 1 Level 2 Level 3 Fair Value (in thousands) Financial Assets: Money market funds $ 114,184 $ — $ — $ 114,184 Certificates of deposit 1,229 — — 1,229 Corporate bonds — 40,736 — 40,736 U.S. agency securities — 10,001 — 10,001 U.S. treasury securities 284,721 — — 284,721 Total financial assets $ 400,134 $ 50,737 $ — $ 450,871 The carrying amounts of accounts payable and accrued expenses approximate their fair values due to their short-term maturities. The Company’s Level 2 securities are valued using third-party pricing sources. The pricing services utilize industry standard valuation models, including both income- and market-based approaches, for which all significant inputs are observable, either directly or indirectly. The Company did not have any financial assets or liabilities as of March 31, 2021 and December 31, 2020 that required Level 3 inputs. There were no transfers of assets between the fair value measurement levels during any of the periods presented in the accompanying financial statements.

Investments

Investments	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Investments	INVESTMENTS The fair value and amortized cost of available-for-sale securities by major security type as of March 31, 2021 and December 31, 2020 were as follows: March 31, 2021 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Money market funds $ 125,053 $ — $ — $ 125,053 Certificates of deposit 491 1 — 492 Corporate bonds 97,541 3 (44) 97,500 U.S. agency securities 9,999 1 — 10,000 U.S. treasury securities 202,250 22 (6) 202,266 Total cash equivalents and investments $ 435,334 $ 27 $ (50) $ 435,311 December 31, 2020 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Money market funds $ 114,184 $ — $ — $ 114,184 Certificates of deposit 1,225 4 — 1,229 Corporate bonds 40,743 9 (16) 40,736 U.S. agency securities 9,999 2 — 10,001 U.S. treasury securities 284,739 3 (21) 284,721 Total cash equivalents and investments $ 450,890 $ 18 $ (37) $ 450,871 These available-for-sale securities were classified on the Company’s balance sheets as of March 31, 2021 and December 31, 2020 as: Fair Value March 31, 2021 December 31, 2020 (in thousands) Cash equivalents $ 136,151 $ 236,818 Short-term investments 257,476 165,052 Long-term investments 41,684 49,001 Total cash equivalents and investments $ 435,311 $ 450,871 The fair values of available-for-sale securities by contractual maturity as of March 31, 2021 and December 31, 2020 were as follows: March 31, 2021 December 31, 2020 (in thousands) Due in 1 year or less $ 268,574 $ 287,686 Due in 1 to 2 years 41,684 49,001 Instruments not due at a single maturity date 125,053 114,184 Total cash equivalents and investments $ 435,311 $ 450,871 As of March 31, 2021 and December 31, 2020, the remaining contractual maturities of available-for-sale securities were less than two years, respectively. There have been no significant realized losses on available-for-sale securities for any of the periods presented in the accompanying financial statements. Based on the Company’s review of its available-for-sale securities, the Company believes that it had no other-than-temporary impairments on these securities as of March 31, 2021 and December 31, 2020 because the Company does not intend to sell these securities nor does it believe that it will be required to sell these securities before the recovery of their amortized cost basis. Gross realized gains and gross realized losses were immaterial for any of the periods presented in the accompanying financial statements. As of March 31, 2021 and December 31, 2020, unrealized losses on available-for-sale investments are not attributed to credit risk. The Company believes that an allowance for credit losses is unnecessary because the unrealized losses on certain of the Company’s marketable securities are due to market factors.

Prepaid Expenses And Other Curr

Prepaid Expenses And Other Current Assets	3 Months Ended
	Mar. 31, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses And Other Current Assets	PREPAID EXPENSES AND OTHER CURRENT ASSETS Prepaid expenses and other current assets consisted of the following as of March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 (in thousands) Accrued interest on short-term available-for-sale securities $ 1,274 $ 612 Prepaid equipment service contracts 343 383 Prepaid external research and development and outside services 1,287 1,889 Prepaid software 742 736 Prepaid insurance 1,958 2,881 Prepaid rent and other 743 240 Total prepaid expenses and other current assets $ 6,347 $ 6,741

Property and Equipment, Net

Property and Equipment, Net	3 Months Ended
	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	PROPERTY AND EQUIPMENT, NET Property and equipment, net consisted of the following as of March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 (in thousands) Property and equipment: Lab equipment $ 6,497 $ 5,619 Leasehold improvements 9,033 8,957 Furniture and fixtures 217 216 Finance lease on R&D equipment — 139 Total property and equipment 15,747 14,931 Less: Accumulated depreciation and amortization (1,726) (1,285) Total property and equipment, net $ 14,021 $ 13,646 Depreciation and amortization expense was $0.4 million and $0.2 million for the three months ended March 31, 2021 and 2020, respectively.

Accrued Expenses and Current Po

Accrued Expenses and Current Portion of Other Liabilities	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Accrued Expenses and Current Portion of Other Liabilities	ACCRUED EXPENSES AND CURRENT PORTION OF OTHER LIABILITIES Accrued expenses consisted of the following as of March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 (in thousands) Accrued compensation $ 841 $ 2,274 Accrued taxes 4 558 External research and development 2,530 1,017 Accrued outside services 714 — Accrued leasehold improvements — 927 Other accrued expenses 186 198 Total accrued expenses $ 4,275 $ 4,974 March 31, 2021 December 31, 2020 (in thousands) Current portion of finance lease liability $ — $ 5 Current portion of unvested early exercised share liability 2,063 2,174 ESPP withholdings 539 216 Total current portion of other current liabilities $ 2,602 $ 2,395

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	STOCK-BASED COMPENSATION 2020 Equity Incentive Plan In October 2020, the Company adopted its 2020 Equity Incentive Plan (the 2020 Plan) which replaced the 2017 Equity Incentive Plan (Prior Plan) upon completion of the IPO. The 2020 Plan provides for the grant of incentive stock options or nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock units, performance awards and other forms of awards to employees, directors, and consultants of the Company. The number of shares of common stock reserved for issuance under the 2020 Plan will automatically increase each year for a period of ten years, beginning in 2021 and continuing through 2030, in an amount equal to (1) 5.0% of the total numbers of shares of the Company’s common stock outstanding on December 31 of the immediately preceding year, or (2) a lesser number of shares determined by the Board of Directors no later than December 31 of the immediately preceding year. As of March 31, 2021, the maximum number of shares of common stock that may be issued increased to 14,739,827 shares. The Company recognizes the impact of forfeitures on stock-based compensation expense as forfeitures occur. The Company applies the straight-line method of expense recognition to all awards with only service-based vesting conditions. Vesting periods are determined at the discretion of the Board of Directors. Stock options typically vest over four years. The maximum contractual term is 10 years. As of March 31, 2021, there were 5,373,328 shares reserved by the Company under the 2020 Plan for the future issuance of equity awards. Stock Options Stock option activity under the 2020 Plan as of March 31, 2021 is summarized as follows: Number of Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term Aggregate Intrinsic Value (in years) (in thousands) Balance, December 31, 2020 6,251,159 $ 8.95 Granted 785,287 29.38 Forfeited — — Exercised (285,160) 2.07 Balance, March 31, 2021 6,751,286 $ 11.62 9.15 $ 121,472 The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the closing price of the Company’s common stock on the Nasdaq Global Select Market on March 31, 2021. The intrinsic value of options exercised for the three months ended March 31, 2021 and 2020 was $7.6 million a nd $0.2 million, respectively, determined as of the applicable date of exercise. There was no future tax benefit related to options exercised, as the Company had accumulated net operating losses as of March 31, 2021 and December 31, 2020. The weighted-average grant-date fair value per share of stock options granted, using the Black-Scholes option pricing model, was $21.11 and $1.59 during the three months ended March 31, 2021 and 2020, respectively. The weighted-average grant-date fair value per share of stock options vested was $3.37 and $0.33 during the three months ended March 31, 2021 and 2020, respectively. For the three months ended March 31, 2021 and 2020, total stock-based compensation related to options was classified in the Company’s statements of operations and comprehensive loss as follows: Three Months Ended March 31, 2021 2020 (in thousands) Research and development expenses $ 1,425 $ 130 General and administrative expenses 1,612 57 Total stock-based compensation expense $ 3,037 $ 187 As of March 31, 2021 and December 31, 2020, there was $49.9 million and $36.3 million of unrecognized stock-based compensation related to stock options, respectively, which is expected to be recognized over a weighted-average period of 3.53 and 3.70 years, respectively. 2020 Employee Stock Purchase Plan In October 2020, the Company adopted its 2020 Employee Stock Purchase Plan (ESPP), which initially reserved 688,000 shares of the Company’s common stock for employee purchase under terms and provisions established by the Board of Directors. The number of shares of our common stock reserved for issuance under the ESPP automatically increases in 2021 and continuing through 2030, by the lesser of (i) 1.0% of the total number of shares of common stock outstanding on December 31 of the immediately preceding year, and (ii) 1,376,000 shares, except before the date of any increase, the Board of Directors may determine that such increase will be less than the amount set forth in clauses (i) and (ii). The Company has 1,248,335 shares reserved for future issuance as of March 31, 2021. For the three months ended March 31, 2021, total stock-based compensation related to the ESPP was $0.3 million, with $0.1 million recorded in general and administrative expenses and $0.2 million recorded in research and development expenses in the statements of operations and comprehensive loss. Restricted Stock Restricted stock awards and units as of March 31, 2021 are summarized as follows: Number of Restricted Stock Weighted-Average Grant Date Fair Value Weighted-Average Remaining Vesting Life Aggregate Intrinsic Value (in years) (in thousands) Unvested, December 31, 2020 810,197 $ 22.26 Granted - restricted stock awards and units 339,430 29.32 Vested and converted to shares (26,902) 0.05 Unvested, March 31, 2021 1,122,725 $ 24.93 2.69 $ 32,862 In February 2021, the Company issued 339,430 restricted stock units (RSUs) to certain employees pursuant to the 2020 Plan. These RSUs have a three year vest period and in order to vest, the holder is required to provide service to the Company. The Company recognized $1.8 million of stock-based compensation expense related to the RSUs for the three months ended March 31, 2021, of which $0.9 million and $0.9 million are recorded in research and development and general and administrative expenses, respectively, in the current year statement of operations and comprehensive loss. As of March 31, 2021 and December 31, 2020, there was $25.2 million and $17.1 million, respectively, of unrecognized stock-based compensation related to RSUs, which is expected to be recognized over a weighted average period of 2.76 and 2.94 years, respectively. No RSUs have vested as of March 31, 2021. The Company recorded stock-based compensation expense for its restricted stock awards (RSAs) of $35,000 in general and administrative expenses in the statements of operations and comprehensive loss for the three months ended March 31, 2021 for RSAs granted to a certain executive officer in July 2020. The stock-based compensation recorded for RSAs in the three months ended March 31, 2020 was not material. As of March 31, 2021 and December 31, 2020, there was $0.5 million and $0.5 million, respectively, of unrecognized stock-based compensation related to RSAs, which is expected to be recognized over a weighted average period of 3.33 and 3.58 years, respectively. The RSAs are subject to lapsing repurchase rights and in order to vest, are subject to the holder’s service to the Company. There were no RSAs granted during the three months ended March 31, 2021. Stock-Based Compensation Summary Stock-based compensation expense was classified in the Company’s statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020 as follows: Three Months Ended March 31, 2021 2020 (in thousands) Research and development expenses $ 2,554 $ 131 General and administrative expenses 2,684 57 Total stock-based compensation expense $ 5,238 $ 188 Early Exercised Options The Company allows certain of its employees and its consultants to exercise options granted under the Prior Plan prior to vesting. The shares related to early exercised stock options are subject to the Company’s lapsing repurchase right upon termination of employment or service on the Board of Directors at the lesser of the original purchase price or fair market value at the time of repurchase. In order to vest, the holders are required to provide continued service to the Company. The early exercise by an employee or consultant of a stock option is not considered to be a substantive exercise for accounting purposes, and therefore the payment received by the employer for the exercise price is recognized as a liability. For accounting purposes, unvested early exercised shares are not considered issued and outstanding and therefore not reflected as issued and outstanding in the accompanying statements of convertible preferred stock and stockholders' equity (deficit) until the awards vest. The deposits received are initially recorded in current portion of other liabilities and other noncurrent liabilities for the noncurrent portion. The liabilities are reclassified to common stock and paid-in capital as the repurchase right lapses. At March 31, 2021 and December 31, 2020, there was $2.1 million and $2.2 million recorded in current portion of other liabilities, and $2.0 million and $2.5 million recorded in other noncurrent liabilities, respectively, related to shares held by employees and nonemployees that were subject to repurchase.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXESThe Company did not record any income tax expense for the three months ended March 31, 2021 and 2020. The Company has incurred net operating losses for all the periods presented and has not reflected any benefit of such net operating loss carryforwards in the accompanying financial statements. The Company has recorded a full valuation allowance against all of its deferred tax assets as it is not more likely than not that such assets will be realized in the near future.It is the Company’s policy to record penalties and interest related to income taxes as a component of income tax expense. The Company has not recorded any interest or penalties related to income taxes during the three months ended March 31, 2021 and 2020. The Company has not identified any new uncertain tax positions as of March 31, 2021. Unrecognized tax benefits are not expected to change during the next 12 months. The reversal of the unrecognized tax benefits would not affect the effective tax rate. The Company is subject to examination by U.S. federal and state tax authorities for all years since its inception.

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	NET LOSS PER SHARE The following table summarizes the computation of basic and diluted net loss per share of the Company for the three months ended March 31, 2021 and 2020: Three Months Ended March 31, 2021 2020 (in thousands, except share and per share amounts) Net loss $ (26,086) $ (6,995) Weighted-average common stock outstanding, basic and diluted 54,152,656 5,694,832 Net loss per share, basic and diluted $ (0.48) $ (1.23) The Company’s potentially dilutive securities, which include options to purchase shares of the Company's common stock and restricted stock subject to future vesting, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of shares of common stock outstanding used to calculate both basic and diluted net loss per share is the same. The Company excluded the following potential shares of common stock, presented based on amounts outstanding at each stated period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: March 31, 2021 March 31, 2020 Stock options to purchase common stock 5,307,444 2,642,509 Early exercised stock options subject to future vesting 1,443,842 681,894 Restricted stock awards subject to future vesting 217,877 188,318 Restricted stock units subject to future vesting 904,847 — Total 7,874,010 3,512,721

Commitment and Contingencies

Commitment and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	COMMITMENTS AND CONTINGENCIES Asset Purchase Agreement In July 2020, the Company entered into an asset purchase agreement (Gilead Asset Purchase Agreement) with Gilead Sciences, Inc. (Gilead), pursuant to which the Company acquired certain assets from Gilead related to entospletinib (ENTO) and lanraplenib (LANRA), and patents and other intellectual property covering or related to the development, manufacture and commercialization of ENTO and LANRA. In consideration for such assets, on the date of the Gilead Asset Purchase Agreement, the Company made a $3.0 million upfront cash payment and issued a $3.0 million principal amount convertible promissory note to Gilead (Gilead Note)The Company also made a $0.7 million payment to reimburse Gilead for certain liabilities assumed by the Company pursuant to the Gilead Asset Purchase Agreement. In addition, the Company is required to make milestone payments upon successful achievement of certain regulatory and sales milestones for ENTO, LANRA and other selective spleen tyrosine kinase inhibitor compounds covered by the patent rights acquired pursuant to the Gilead Asset Purchase Agreement and developed by the Company as a back-up to ENTO or LANRA (Other Compounds). Upon initiation of the Company’s planned registrational Phase 3 clinical trial of ENTO in combination with induction chemotherapy in acute myeloid leukemia patients with NPM1 mutations, the Company will be required to pay a milestone to Gilead of $29.0 million, and upon successful completion of certain other regulatory milestones in the United States, European Union and United Kingdom for ENTO, LANRA and any Other Compounds, across up to two distinct indications, the Company will be required to pay to Gilead an aggregate total of $51.3 million. Upon achieving certain thresholds for the aggregate annual net sales of ENTO, LANRA and any Other Compounds combined, the Company would owe to Gilead potential milestone payments totaling $115.0 million. Gilead is also eligible to receive (i) tiered marginal royalties ranging from the very low-teens to high-teens on annual worldwide net sales of ENTO, (ii) tiered marginal royalties ranging from high-single digits to the mid-teens on annual worldwide net sales of LANRA and (iii) tiered marginal royalties ranging from low single digits to mid-single digits on annual worldwide net sales of any Other Compounds. The royalties in the foregoing clauses are subject to reduction, on a country-by-country basis, for products not covered by certain claims within the assigned patents, for generic entry and, in the case of ENTO and LANRA, for any royalties paid for future licenses of third party intellectual property required to develop or commercialize ENTO or LANRA. The Company’s royalty obligation with respect to a given product in a given country begins upon the first commercial sale of such product in such country and ends on the latest of (i) expiration of the last claim of a defined set of the assigned patent rights covering such product in such country; (ii) loss of exclusive data or marketing rights to such product in such country; or (iii) 10 years from the first commercial sale of such product in such country. Under the Gilead Asset Purchase Agreement, the Company is required to use commercially reasonable efforts to develop, obtain regulatory approval for and commercialize either ENTO or LANRA. The Gilead Note settled upon the completion of the Company’s IPO in October 2020. Purchase Commitments In the normal course of business, the Company enters into contracts with CROs for preclinical studies and other vendors for other services and products for operating purposes. These agreements generally provide for termination or cancellation, other than for costs already incurred. Contingencies In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnifications. The Company’s exposure under these agreements is unknown, because it involves claims that may be made against the Company in the future, but have not yet been made. The Company accrues a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated. Indemnification In accordance with the Company’s amended and restated certificate of incorporation and amended and restated bylaws, the Company has indemnification obligations to its officers and directors for certain events or occurrences, subject to certain limits, while they are serving in such capacity. There have been no claims to date, and the Company has a directors and officers liability insurance policy that may enable it to recover a portion of any amounts paid for future claims.

Leases

Leases	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Leases	LEASES In November 2020, the Company entered into a lease termination for its lab space in Cambridge, Massachusetts to terminate the lease as of January 31, 2021, rather than May 31, 2021. The cost for early termination was a payment of $0.1 million. The Company accounted for this change in lease term as a modification of the originally amended lease. As a result of the modification, the operating right-of-use asset and lease liability were remeasured as of the modification date. As of March 31, 2021, there was no remaining lease liability or right-of-use asset related to this lease. In March 2020, the Company entered into an 11-year lease agreement to move its research and development operations from 21 Erie Street, Cambridge, Massachusetts, to a 40,514 square-feet facility at 301 Binney Street, Cambridge, Massachusetts (new Cambridge facility). The new lease commenced on February 28, 2020 with an initial annual base rent of $4.1 million. The initial rent payment was paid as of September 30, 2020, with rent payments escalating 3.0% annually after the initial 12 payments. As discussed in Note 2, the Company executed a letter of credit for $2.0 million in connection with the lease. The lease includes $3.7 million in certain tenant improvement allowances, which the Company included in its calculation of the right-of-use asset in the lease at commencement. As of March 31, 2021, $3.3 million in improvement costs incurred by the Company were reimbursed by the lessor and are now included within the total lease liability. In connection with the lease, the Company recognized an operating lease right-of-use asset of $24.7 million and $25.1 million and an aggregate lease liability of $30.1 million and $30.1 million on the March 31, 2021 and December 31, 2020 balance sheets, respectively. The remaining lease term is 9 years and 11 months, and the estimated incremental borrowing rate is 8.50%. In July 2018, the Company entered into a lease agreement for a 4,661 square-foot office space to be used for general and administrative activities in San Mateo, California. The lease commenced on August 1, 2018 and had a 37-month initial term expiring on August 31, 2021. The lease also contained an option for the Company to extend the lease upon its initial expiration. In connection with the lease, the Company made a one-time cash security deposit in the amount of $28,000. In May 2020, the Company amended its agreement to extend the lease for its office in San Mateo, California through April 2025. The initial annual base rent was $0.3 million, and such amount was to increase by 3% annually on each anniversary of the commencement date. The Company expanded to an adjacent suite in July 2020, which was treated as a separate lease for accounting purposes. The additional space was approximately 3,414 square feet and was similarly be used for general and administrative activities. The lease commenced on July 1, 2020 and with an initial expiration date of April 30, 2025. In connection with the additional space leased, the Company made a one-time additional cash security deposit in the amount of $25,000. The initial annual base rent for the expansion was $0.2 million, and such amount will increase by 3% annually on each anniversary of the commencement date. In February 2021, the Company entered into a new lease agreement for its office space in San Mateo, California to move from its current suites, totaling 8,075 square-feet, to a larger suite totaling 17,340 square-feet, with a target move date of July 1, 2021. The Company accounted for this change in lease term of the original suites as a modification of the originally amended lease. As a result of the modification, the operating right-of-use asset and lease liability were remeasured as of the modification date. In connection with the lease of the 4,661 square foot suite, the Company recognized an operating lease right-of-use asset of $59,000 and an aggregate lease liability of $53,000 on the March 31, 2021 balance sheet, after the modification adjustment. The operating lease right-of-use asset and aggregate lease liability for this suite were $1.1 million and $1.1 million, respectively, as of December 31, 2020. In connection with the lease of the 3,414 square foot suite, the Company recognized an operating lease right-of-use asset of $43,000 and an aggregate lease liability of $38,000 on the March 31, 2021 balance sheet, after the modification adjustment. The operating lease right-of-use asset and aggregate lease liability for this suite were $0.8 million and $0.8 million, respectively, as of December 31, 2020. The remaining lease term for both spaces is 3 months and the estimated incremental borrowing rate is 12.07%. The new 17,340 square foot suite will be treated as a separate lease for accounting purposes. The initial annual base rent for the new space will be $1.2 million, and such amount will increase by 3% annually on each anniversary of the new premises commencement date. In connection with the larger space leased, the Company has also made an additional one-time cash security deposit in the amount of $59,000. The new lease commenced in April 2021 while tenant improvements are being made and the new lease agreement extends the termination date from April 30, 2025 to April 30, 2026. The following table summarizes the presentation of the Company’s operating leases in its balance sheets as of March 31, 2021 and December 31, 2020: Balance Sheet Caption March 31, 2021 December 31, 2020 (in thousands) Assets: Operating lease assets $ 24,845 $ 27,322 Liabilities: Current portion of operating lease liabilities $ 822 $ 937 Noncurrent operating lease liabilities 29,394 31,120 Total operating lease liabilities $ 30,216 $ 32,057 The following table summarizes the effect of finance lease costs in the Company’s statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020: Statement of Operations and Three Months Ended March 31, 2021 2020 (in thousands) Research and development $ 3 $ 5 Interest income (expense), net — 1 Total finance lease cost $ 3 $ 6 The following table summarizes the effect of operating lease costs in the Company’s statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020 : Statement of Operations and Three Months Ended March 31, 2021 2020 (in thousands) Research and development $ 1,008 $ 256 General and administrative 376 163 Total operating lease cost $ 1,384 $ 419 The Company made cash payments of $1.2 million and $0.1 million under the lease agreements during the three months ended March 31, 2021 and 2020, respectively. The undiscounted future non-cancellable lease payments under the Company's operating leases as of March 31, 2021 for the next five years and thereafter is expected to be as follows: Period Ending December 31, Amount (in thousands) Remaining nine months of 2021 $ 3,207 2022 4,204 2023 4,330 2024 4,460 2025 and thereafter 30,624 Total undiscounted lease payments 46,825 Less: Present value adjustment (16,241) Less: Tenant improvement allowance (368) Present value of operating lease liabilities $ 30,216
Leases	LEASES In November 2020, the Company entered into a lease termination for its lab space in Cambridge, Massachusetts to terminate the lease as of January 31, 2021, rather than May 31, 2021. The cost for early termination was a payment of $0.1 million. The Company accounted for this change in lease term as a modification of the originally amended lease. As a result of the modification, the operating right-of-use asset and lease liability were remeasured as of the modification date. As of March 31, 2021, there was no remaining lease liability or right-of-use asset related to this lease. In March 2020, the Company entered into an 11-year lease agreement to move its research and development operations from 21 Erie Street, Cambridge, Massachusetts, to a 40,514 square-feet facility at 301 Binney Street, Cambridge, Massachusetts (new Cambridge facility). The new lease commenced on February 28, 2020 with an initial annual base rent of $4.1 million. The initial rent payment was paid as of September 30, 2020, with rent payments escalating 3.0% annually after the initial 12 payments. As discussed in Note 2, the Company executed a letter of credit for $2.0 million in connection with the lease. The lease includes $3.7 million in certain tenant improvement allowances, which the Company included in its calculation of the right-of-use asset in the lease at commencement. As of March 31, 2021, $3.3 million in improvement costs incurred by the Company were reimbursed by the lessor and are now included within the total lease liability. In connection with the lease, the Company recognized an operating lease right-of-use asset of $24.7 million and $25.1 million and an aggregate lease liability of $30.1 million and $30.1 million on the March 31, 2021 and December 31, 2020 balance sheets, respectively. The remaining lease term is 9 years and 11 months, and the estimated incremental borrowing rate is 8.50%. In July 2018, the Company entered into a lease agreement for a 4,661 square-foot office space to be used for general and administrative activities in San Mateo, California. The lease commenced on August 1, 2018 and had a 37-month initial term expiring on August 31, 2021. The lease also contained an option for the Company to extend the lease upon its initial expiration. In connection with the lease, the Company made a one-time cash security deposit in the amount of $28,000. In May 2020, the Company amended its agreement to extend the lease for its office in San Mateo, California through April 2025. The initial annual base rent was $0.3 million, and such amount was to increase by 3% annually on each anniversary of the commencement date. The Company expanded to an adjacent suite in July 2020, which was treated as a separate lease for accounting purposes. The additional space was approximately 3,414 square feet and was similarly be used for general and administrative activities. The lease commenced on July 1, 2020 and with an initial expiration date of April 30, 2025. In connection with the additional space leased, the Company made a one-time additional cash security deposit in the amount of $25,000. The initial annual base rent for the expansion was $0.2 million, and such amount will increase by 3% annually on each anniversary of the commencement date. In February 2021, the Company entered into a new lease agreement for its office space in San Mateo, California to move from its current suites, totaling 8,075 square-feet, to a larger suite totaling 17,340 square-feet, with a target move date of July 1, 2021. The Company accounted for this change in lease term of the original suites as a modification of the originally amended lease. As a result of the modification, the operating right-of-use asset and lease liability were remeasured as of the modification date. In connection with the lease of the 4,661 square foot suite, the Company recognized an operating lease right-of-use asset of $59,000 and an aggregate lease liability of $53,000 on the March 31, 2021 balance sheet, after the modification adjustment. The operating lease right-of-use asset and aggregate lease liability for this suite were $1.1 million and $1.1 million, respectively, as of December 31, 2020. In connection with the lease of the 3,414 square foot suite, the Company recognized an operating lease right-of-use asset of $43,000 and an aggregate lease liability of $38,000 on the March 31, 2021 balance sheet, after the modification adjustment. The operating lease right-of-use asset and aggregate lease liability for this suite were $0.8 million and $0.8 million, respectively, as of December 31, 2020. The remaining lease term for both spaces is 3 months and the estimated incremental borrowing rate is 12.07%. The new 17,340 square foot suite will be treated as a separate lease for accounting purposes. The initial annual base rent for the new space will be $1.2 million, and such amount will increase by 3% annually on each anniversary of the new premises commencement date. In connection with the larger space leased, the Company has also made an additional one-time cash security deposit in the amount of $59,000. The new lease commenced in April 2021 while tenant improvements are being made and the new lease agreement extends the termination date from April 30, 2025 to April 30, 2026. The following table summarizes the presentation of the Company’s operating leases in its balance sheets as of March 31, 2021 and December 31, 2020: Balance Sheet Caption March 31, 2021 December 31, 2020 (in thousands) Assets: Operating lease assets $ 24,845 $ 27,322 Liabilities: Current portion of operating lease liabilities $ 822 $ 937 Noncurrent operating lease liabilities 29,394 31,120 Total operating lease liabilities $ 30,216 $ 32,057 The following table summarizes the effect of finance lease costs in the Company’s statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020: Statement of Operations and Three Months Ended March 31, 2021 2020 (in thousands) Research and development $ 3 $ 5 Interest income (expense), net — 1 Total finance lease cost $ 3 $ 6 The following table summarizes the effect of operating lease costs in the Company’s statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020 : Statement of Operations and Three Months Ended March 31, 2021 2020 (in thousands) Research and development $ 1,008 $ 256 General and administrative 376 163 Total operating lease cost $ 1,384 $ 419 The Company made cash payments of $1.2 million and $0.1 million under the lease agreements during the three months ended March 31, 2021 and 2020, respectively. The undiscounted future non-cancellable lease payments under the Company's operating leases as of March 31, 2021 for the next five years and thereafter is expected to be as follows: Period Ending December 31, Amount (in thousands) Remaining nine months of 2021 $ 3,207 2022 4,204 2023 4,330 2024 4,460 2025 and thereafter 30,624 Total undiscounted lease payments 46,825 Less: Present value adjustment (16,241) Less: Tenant improvement allowance (368) Present value of operating lease liabilities $ 30,216

Related Parties

Related Parties	3 Months Ended
	Mar. 31, 2021
Related Party Transactions [Abstract]
Related Parties	RELATED PARTIES On December 1, 2017, the Company entered into a three-year services agreement with Two River Consulting, LLC (Two River) to provide various clinical development, operational, managerial, accounting and financial, and administrative services to the Company. Arie Belldegrun, M.D., FACS, the Chairman of the Board of Directors, is the Chairman of Two River. Mr. Joshua Kazam and Mr. David Tanen, each a director of the Company, are each partners of Two River. Mr. Tanen additionally serves as our Corporate Secretary. Mr. Christopher Wilfong, a strategic advisor to the Company, is an Operating Partner of Two River and Mr. Sean Algeo, serving as the Company’s Financial Consultant, is the Chief Financial Officer of Two River. During the three months ended March 31, 2021 and 2020, the Company incurred expense of $0.2 million and $0.2 million respectively, for these services. Some of the Company’s expenses are periodically paid by Two River. The Company reimburses Two River for these expenses and no interest is charged on the outstanding balance. These reimbursable expenses were not material for the three months ended March 31, 2021 and 2020, respectively. As of March 31, 2021 and December 31, 2020, the Company had payables to Two River of $63,000 and $182,000, respectively. In 2019, the Company entered into a consulting agreement with Bellco Capital, LLC (Bellco) to provide various executive services to the Company. Arie Belldegrun, M.D., FACS, the Chairman of the Board of Directors, is the Chairman of Bellco. Rebecka Belldegrun, M.D., who served as a director of the Company through January 25, 2021, is the President and Chief Executive Officer of Bellco. During the three months ended March 31, 2021 and 2020, the Company incurred expense of $6,300 and $6,300, respectively, for these services.

Significant Accounting Polici_2

Significant Accounting Policies, Estimates and Judgments (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (GAAP) for interim financial information and pursuant to Form 10-Q and Article 10 of Regulation S-X of the Securities and Exchange Commission (SEC). Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. Unaudited Interim Financial Information The accompanying balance sheet as of March 31, 2021, the statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020, the statements of convertible preferred stock and stockholders’ equity (deficit) as of March 31, 2021 and 2020, the statements of cash flows for the three months ended March 31, 2021 and 2020, and the financial data and other financial information disclosed to in the notes to the condensed financial statements are unaudited. The unaudited interim financial statements have been prepared on a basis consistent with the Company’s audited annual financial statements and, in the opinion of management, reflect all adjustments, consisting solely of normal recurring adjustments, necessary for the fair presentation of the Company’s financial position as of March 31, 2021 and the results of its operations the three months ended March 31, 2021 and 2020. The results for the three months ended March 31, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021, any other interim periods, or any future year or period. These financial statements should be read in conjunction with the Company's audited financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on March 23, 2021.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses: Measurement of Credit Losses on Financial Instruments and also issued subsequent amendments to the initial guidance: ASU 2018-19, ASU 2019-04, ASU 2019-05, and ASU 2019-11. The standard requires measurement and recognition of expected credit losses for financial assets by requiring an allowance to be recorded as an offset to the amortized cost of such assets. For available-for-sale debt securities, expected credit losses should be estimated when the fair value of the debt securities is below their associated amortized costs. The standard will become effective for the Company in the first quarter of 2020, with early adoption permitted beginning the first quarter of 2019. The modified retrospective approach should be applied upon adoption of this new guidance. The Company’s financial instruments that are in the scope of ASU 2016-13 include available-for-sale debt securities. The Company adopted this standard on January 1, 2020 and this amendment did not have a material impact on its financial statements. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12), which simplifies the accounting for income taxes, eliminates certain exceptions within ASC 740, Income Taxes

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	Financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used in such measurements by major security type as of March 31, 2021 and December 31, 2020 were as follows: March 31, 2021 Level 1 Level 2 Level 3 Fair Value (in thousands) Financial Assets: Money market funds $ 125,053 $ — $ — $ 125,053 Certificates of deposit 491 — — 491 Corporate bonds — 97,500 — 97,500 U.S. agency securities — 10,001 — 10,001 U.S. treasury securities 202,266 — — 202,266 Total financial assets $ 327,810 $ 107,501 $ — $ 435,311 December 31, 2020 Level 1 Level 2 Level 3 Fair Value (in thousands) Financial Assets: Money market funds $ 114,184 $ — $ — $ 114,184 Certificates of deposit 1,229 — — 1,229 Corporate bonds — 40,736 — 40,736 U.S. agency securities — 10,001 — 10,001 U.S. treasury securities 284,721 — — 284,721 Total financial assets $ 400,134 $ 50,737 $ — $ 450,871

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Investments Classified by Contractual Maturity Date	The fair value and amortized cost of available-for-sale securities by major security type as of March 31, 2021 and December 31, 2020 were as follows: March 31, 2021 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Money market funds $ 125,053 $ — $ — $ 125,053 Certificates of deposit 491 1 — 492 Corporate bonds 97,541 3 (44) 97,500 U.S. agency securities 9,999 1 — 10,000 U.S. treasury securities 202,250 22 (6) 202,266 Total cash equivalents and investments $ 435,334 $ 27 $ (50) $ 435,311 December 31, 2020 Amortized Cost Unrealized Gains Unrealized Losses Fair Value (in thousands) Money market funds $ 114,184 $ — $ — $ 114,184 Certificates of deposit 1,225 4 — 1,229 Corporate bonds 40,743 9 (16) 40,736 U.S. agency securities 9,999 2 — 10,001 U.S. treasury securities 284,739 3 (21) 284,721 Total cash equivalents and investments $ 450,890 $ 18 $ (37) $ 450,871 These available-for-sale securities were classified on the Company’s balance sheets as of March 31, 2021 and December 31, 2020 as: Fair Value March 31, 2021 December 31, 2020 (in thousands) Cash equivalents $ 136,151 $ 236,818 Short-term investments 257,476 165,052 Long-term investments 41,684 49,001 Total cash equivalents and investments $ 435,311 $ 450,871 The fair values of available-for-sale securities by contractual maturity as of March 31, 2021 and December 31, 2020 were as follows: March 31, 2021 December 31, 2020 (in thousands) Due in 1 year or less $ 268,574 $ 287,686 Due in 1 to 2 years 41,684 49,001 Instruments not due at a single maturity date 125,053 114,184 Total cash equivalents and investments $ 435,311 $ 450,871

Prepaid Expenses And Other Cu_2

Prepaid Expenses And Other Current Assets (Tables)	3 Months Ended
	Mar. 31, 2021
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses and Other Assets	Prepaid expenses and other current assets consisted of the following as of March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 (in thousands) Accrued interest on short-term available-for-sale securities $ 1,274 $ 612 Prepaid equipment service contracts 343 383 Prepaid external research and development and outside services 1,287 1,889 Prepaid software 742 736 Prepaid insurance 1,958 2,881 Prepaid rent and other 743 240 Total prepaid expenses and other current assets $ 6,347 $ 6,741

Property, Plant, and Equipment

Property, Plant, and Equipment (Tables)	3 Months Ended
	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Property and Equipment [Table Text Block]	Property and equipment, net consisted of the following as of March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 (in thousands) Property and equipment: Lab equipment $ 6,497 $ 5,619 Leasehold improvements 9,033 8,957 Furniture and fixtures 217 216 Finance lease on R&D equipment — 139 Total property and equipment 15,747 14,931 Less: Accumulated depreciation and amortization (1,726) (1,285) Total property and equipment, net $ 14,021 $ 13,646

Accrued Expenses And Current _2

Accrued Expenses And Current Portion Of Other Liabilities (Tables)	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued expenses consisted of the following as of March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 (in thousands) Accrued compensation $ 841 $ 2,274 Accrued taxes 4 558 External research and development 2,530 1,017 Accrued outside services 714 — Accrued leasehold improvements — 927 Other accrued expenses 186 198 Total accrued expenses $ 4,275 $ 4,974
Other Current Liabilities	Current portion of other liabilities consist of the following as of March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 (in thousands) Current portion of finance lease liability $ — $ 5 Current portion of unvested early exercised share liability 2,063 2,174 ESPP withholdings 539 216 Total current portion of other current liabilities $ 2,602 $ 2,395

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock Option Activity	Stock option activity under the 2020 Plan as of March 31, 2021 is summarized as follows: Number of Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term Aggregate Intrinsic Value (in years) (in thousands) Balance, December 31, 2020 6,251,159 $ 8.95 Granted 785,287 29.38 Forfeited — — Exercised (285,160) 2.07 Balance, March 31, 2021 6,751,286 $ 11.62 9.15 $ 121,472
Stock-based Compensation, Classified in Statements of Operations	For the three months ended March 31, 2021 and 2020, total stock-based compensation related to options was classified in the Company’s statements of operations and comprehensive loss as follows: Three Months Ended March 31, 2021 2020 (in thousands) Research and development expenses $ 1,425 $ 130 General and administrative expenses 1,612 57 Total stock-based compensation expense $ 3,037 $ 187 Stock-based compensation expense was classified in the Company’s statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020 as follows: Three Months Ended March 31, 2021 2020 (in thousands) Research and development expenses $ 2,554 $ 131 General and administrative expenses 2,684 57 Total stock-based compensation expense $ 5,238 $ 188
Schedule of Nonvested Share Activity	Restricted Stock Restricted stock awards and units as of March 31, 2021 are summarized as follows: Number of Restricted Stock Weighted-Average Grant Date Fair Value Weighted-Average Remaining Vesting Life Aggregate Intrinsic Value (in years) (in thousands) Unvested, December 31, 2020 810,197 $ 22.26 Granted - restricted stock awards and units 339,430 29.32 Vested and converted to shares (26,902) 0.05 Unvested, March 31, 2021 1,122,725 $ 24.93 2.69 $ 32,862

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following table summarizes the computation of basic and diluted net loss per share of the Company for the three months ended March 31, 2021 and 2020: Three Months Ended March 31, 2021 2020 (in thousands, except share and per share amounts) Net loss $ (26,086) $ (6,995) Weighted-average common stock outstanding, basic and diluted 54,152,656 5,694,832 Net loss per share, basic and diluted $ (0.48) $ (1.23)
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The Company excluded the following potential shares of common stock, presented based on amounts outstanding at each stated period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: March 31, 2021 March 31, 2020 Stock options to purchase common stock 5,307,444 2,642,509 Early exercised stock options subject to future vesting 1,443,842 681,894 Restricted stock awards subject to future vesting 217,877 188,318 Restricted stock units subject to future vesting 904,847 — Total 7,874,010 3,512,721

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Assets And Liabilities, Operating Leases, Lessee	The following table summarizes the presentation of the Company’s operating leases in its balance sheets as of March 31, 2021 and December 31, 2020: Balance Sheet Caption March 31, 2021 December 31, 2020 (in thousands) Assets: Operating lease assets $ 24,845 $ 27,322 Liabilities: Current portion of operating lease liabilities $ 822 $ 937 Noncurrent operating lease liabilities 29,394 31,120 Total operating lease liabilities $ 30,216 $ 32,057
Summary of Lease Costs	The following table summarizes the effect of finance lease costs in the Company’s statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020: Statement of Operations and Three Months Ended March 31, 2021 2020 (in thousands) Research and development $ 3 $ 5 Interest income (expense), net — 1 Total finance lease cost $ 3 $ 6 The following table summarizes the effect of operating lease costs in the Company’s statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020 : Statement of Operations and Three Months Ended March 31, 2021 2020 (in thousands) Research and development $ 1,008 $ 256 General and administrative 376 163 Total operating lease cost $ 1,384 $ 419
Schedule of Maturities on Lease Liabilities	The undiscounted future non-cancellable lease payments under the Company's operating leases as of March 31, 2021 for the next five years and thereafter is expected to be as follows: Period Ending December 31, Amount (in thousands) Remaining nine months of 2021 $ 3,207 2022 4,204 2023 4,330 2024 4,460 2025 and thereafter 30,624 Total undiscounted lease payments 46,825 Less: Present value adjustment (16,241) Less: Tenant improvement allowance (368) Present value of operating lease liabilities $ 30,216

Nature of Operations and Basi_2

Nature of Operations and Basis of Presentation (Details) $ / shares in Units, $ in Thousands	Oct. 14, 2020USD ($)	Oct. 02, 2020	Oct. 31, 2020USD ($)$ / sharesshares	Mar. 31, 2021USD ($)segmentshares	Mar. 31, 2020USD ($)shares	Mar. 31, 2021USD ($)shares	Dec. 31, 2020shares	Dec. 31, 2019shares
Subsidiary, Sale of Stock [Line Items]
Number of operating segments | segment				1
Convertible preferred stock, shares outstanding (in shares)				0	21,504,893	0	0	21,504,893
Net loss | $				$ 26,086	$ 6,995	$ 138,000
Common Stock
Subsidiary, Sale of Stock [Line Items]
Forward stock split ratio		1.055
IPO
Subsidiary, Sale of Stock [Line Items]
Shares issued in private placement (in shares)			15,131,579
Shares issued in private placement, price per share (in dollars per share) | $ / shares			$ 19
Net proceeds from stock offering | $	$ 263,700
Payments of underwriting discounts and commissions | $			$ (20,100)
Payments of offering costs | $			$ 3,700
Convertible preferred stock, shares outstanding (in shares)			0
IPO | Common Stock
Subsidiary, Sale of Stock [Line Items]
Shares issued upon conversion of convertible preferred stock (in shares)			22,687,625
IPO | Common Stock | 2020 Convertible Notes
Subsidiary, Sale of Stock [Line Items]
Shares issued upon conversion of convertible preferred stock (in shares)			9,610,713
IPO | Common Stock | 2020 Gilead Notes
Subsidiary, Sale of Stock [Line Items]
Shares issued upon conversion of convertible preferred stock (in shares)			188,567
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Shares issued in private placement (in shares)			1,973,684

Fair Value Measurements (Detail

Fair Value Measurements (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	$ 435,311	$ 450,871
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	125,053	114,184
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	491	1,229
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	97,500	40,736
U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	10,001	10,001
U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	202,266	284,721
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	327,810	400,134
Level 1 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	125,053	114,184
Level 1 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	491	1,229
Level 1 | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 1 | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 1 | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	202,266	284,721
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	107,501	50,737
Level 2 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	0	0
Level 2 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 2 | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	97,500	40,736
Level 2 | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	10,001	10,001
Level 2 | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total financial assets	0	0
Level 3 | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	0	0
Level 3 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 3 | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 3 | U.S. agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	0	0
Level 3 | U.S. treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments, fair value	$ 0	$ 0

Investments - Fair Value and Am

Investments - Fair Value and Amortized Cost (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Money market funds, amortized cost	$ 136,151	$ 236,818
Total cash equivalents and investments, amortized cost	435,334	450,890
Total cash equivalents and investments, unrealized gains	27	18
Total cash equivalents and investments, unrealized losses	(50)	(37)
Total cash equivalents and investments, fair value	435,311	450,871
Money market funds
Schedule of Held-to-maturity Securities [Line Items]
Money market funds, amortized cost	125,053	114,184
Certificates of deposit
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	491	1,225
Unrealized Gains	1	4
Unrealized Losses	0	0
Fair Value	492	1,229
Corporate bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	97,541	40,743
Unrealized Gains	3	9
Unrealized Losses	(44)	(16)
Fair Value	97,500	40,736
U.S. agency securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	9,999	9,999
Unrealized Gains	1	2
Unrealized Losses	0	0
Fair Value	10,000	10,001
U.S. treasury securities
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	202,250	284,739
Unrealized Gains	22	3
Unrealized Losses	(6)	(21)
Fair Value	$ 202,266	$ 284,721

Investments - Balance Sheet (De

Investments - Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Cash equivalents	$ 136,151	$ 236,818
Short-term investments	257,476	165,052	[1]
Long-term investments	41,684	49,001	[1]
Total cash equivalents and investments	$ 435,311	$ 450,871
[1]	The balance sheet as of December 31, 2020 is derived from the audited financial statements as of that date.

Investments - Contractual Matur

Investments - Contractual Maturity (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Due in 1 year or less	$ 268,574,000		$ 287,686,000
Due in 1 to 2 years	41,684,000		49,001,000
Instruments not due at a single maturity date	125,053,000		114,184,000
Total cash equivalents and investments	435,311,000		$ 450,871,000
Other-than-temporary impairments on available-for-sale securities	$ 0	$ 0

Prepaid Expenses And Other Cu_3

Prepaid Expenses And Other Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Accrued interest on short-term available-for-sale securities	$ 1,274	$ 612
Prepaid equipment service contracts	343	383
Prepaid external research and development and outside services	1,287	1,889
Prepaid software	742	736
Prepaid insurance	1,958	2,881
Prepaid rent and other	743	240
Prepaid expenses and other current assets	$ 6,347	$ 6,741	[1]
[1]	The balance sheet as of December 31, 2020 is derived from the audited financial statements as of that date.

Property, Plant, and Equipmen_2

Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Finance Lease, Right-of-Use Asset, before Accumulated Amortization	$ 0		$ 139
Total property and equipment	15,747		14,931
Less: Accumulated depreciation and amortization	(1,726)		(1,285)
Total property and equipment, net	14,021		13,646	[1]
Depreciation and amortization	444	$ 160
Lab equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,497		5,619
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,033		8,957
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 217		$ 216
[1]	The balance sheet as of December 31, 2020 is derived from the audited financial statements as of that date.

Accrued Expenses And Current _3

Accrued Expenses And Current Portion Of Other Liabilities - Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued compensation	$ 841	$ 2,274
Accrued taxes	4	558
External research and development	2,530	1,017
Accrued outside services	714	0
Accrued leasehold improvements	0	927
Other accrued expenses	186	198
Total accrued expenses	$ 4,275	$ 4,974	[1]
[1]	The balance sheet as of December 31, 2020 is derived from the audited financial statements as of that date.

Accrued Expenses And Current _4

Accrued Expenses And Current Portion Of Other Liabilities - Current Other Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Current portion of finance lease liability	$ 0	$ 5
Current portion of unvested early exercised share liability	2,063	2,174
ESPP withholdings	539	216
Total current portion of other current liabilities	$ 2,602	$ 2,395	[1]
[1]	The balance sheet as of December 31, 2020 is derived from the audited financial statements as of that date.

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Oct. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options exercised, intrinsic value		$ 7,600	$ 200
Weighted-average grant-date fair value, options granted (in dollars per share)		$ 21.11	$ 1.59
Weighted-average grant-date fair value, options vested (in dollars per share)		$ 3.37	$ 0.33
Stock options, unrecognized cost		$ 49,900		$ 36,300
Current liabilities related to shares that were subject to repurchase		2,063		2,174
Current portion of other liabilities
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Current liabilities related to shares that were subject to repurchase		2,100		2,200
Other noncurrent liabilities
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-current liabilities related to shares that were subject to repurchase		$ 2,000		$ 2,500
2020 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period	10 years
Shares that may be issued, percent increase as total of common stock outstanding	5.00%
Number of shares that may have been issued (in shares)		14,739,827
Number of shares reserved for future issuance (in shares)		5,373,328
2020 Equity Incentive Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
2020 Equity Incentive Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		10 years
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options recognized, weighted average period		3 years 6 months 10 days		3 years 8 months 12 days

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)$ / sharesshares
Stock Option Activity Under the 2017 Plan [Roll Forward]
Beginning Balance (in shares) | shares	6,251,159
Granted (in shares) | shares	785,287
Forfeited (in shares) | shares	0
Exercised (in shares) | shares	(285,160)
Ending Balance (in shares) | shares	6,751,286
Stock Options, Weighted Average Exercise Price [Roll Forward]
Beginning Balance (dollars per share) | $ / shares	$ 8.95
Granted (dollars per share) | $ / shares	29.38
Forfeited (dollars per share) | $ / shares	0
Exercised (dollars per share) | $ / shares	2.07
Ending Balance (dollars per share) | $ / shares	$ 11.62
Stock Option Activity, Additional Disclosures [Abstract]
Balance, Weighted-Average Remaining Contractual Term	9 years 1 month 24 days
Balance, Aggregate Intrinsic Value | $	$ 121,472

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5,238	$ 188
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	3,037	187
Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,554	131
Research and development expenses | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,425	130
General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,684	57
General and administrative expenses | Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,612	$ 57

Stock-Based Compensation - ESPP

Stock-Based Compensation - ESPP (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Oct. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 5,238	$ 188
General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		2,684	57
Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 2,554	$ 131
The ESPP | Stock options to purchase common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares that may have been issued (in shares)	688,000
Number of shares that may be issued, increase percentage	1.00%
Number of shares that may be issued, increase (in shares)	1,376,000
Number of shares reserved for future issuance (in shares)		1,248,335
Stock-based compensation expense		$ 300
The ESPP | Stock options to purchase common stock | General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		100
The ESPP | Stock options to purchase common stock | Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 200

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Awards Activity (Details) - Restricted Stock $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)$ / sharesshares
Number of Restricted Stock
Unvested Beginning Balance (in shares) | shares	810,197
Granted - restricted stock awards and units (in shares) | shares	339,430
Vested and converted to shares (in shares) | shares	(26,902)
Unvested Ending Balance (in shares) | shares	1,122,725
Weighted-Average Grant Date Fair Value
Unvested Beginning Balance (in dollars per share) | $ / shares	$ 22.26
Granted - restricted stock awards and units (in dollars per share) | $ / shares	29.32
Vested and converted to shares (in dollars per share) | $ / shares	0.05
Unvested Ending Balance (in dollars per share) | $ / shares	$ 24.93
Unvested, Weighted Average Remaining Vesting Life	2 years 8 months 8 days
Unvested, Aggregate Intrinsic Value | $	$ 32,862

Stock-Based Compensation - Re_2

Stock-Based Compensation - Restricted Stock Awards (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5,238	$ 188
Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,554	131
General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,684	$ 57
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock awards issued (in shares)	339,430
Unrecognized stock based compensation	$ 500		$ 500
Awards weighted average recognition period	3 years 3 months 29 days		3 years 6 months 29 days
Restricted Stock | General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 35
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,800
Unrecognized stock based compensation	$ 25,200		$ 17,100
Awards weighted average recognition period	2 years 9 months 3 days		2 years 11 months 8 days
Restricted Stock Units (RSUs) | Executive Employee | Research and development expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 900
Restricted Stock Units (RSUs) | Executive Employee | General and administrative expenses
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 900

Income Taxes (Details)

Income Taxes (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Income tax expense	$ 0	$ 0

Net Loss Per Share (Details)

Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		46 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021
Earnings Per Share [Abstract]
Net loss	$ (26,086)	$ (6,995)	$ (138,000)
Weighted-average shares of common stock, basic and diluted (in shares)	54,152,656	5,694,832
Net loss per share, basic and diluted (in dollars per share)	$ (0.48)	$ (1.23)

Net Loss Per Share - Antidiluti

Net Loss Per Share - Antidilutive Securities Excluded from Computation of Earnings Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	7,874,010	3,512,721,000
Stock options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	5,307,444	2,642,509,000
Early exercised stock options subject to future vesting
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	1,443,842	681,894,000
Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	217,877	188,318,000
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	904,847	0

Commitment and Contingencies -

Commitment and Contingencies - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jul. 31, 2020	Mar. 31, 2021
Schedule Of Asset Acquisition [Line Items]
Royalty obligation, termination, period from first commercial sale		10 years
Asset Purchase Agreement
Schedule Of Asset Acquisition [Line Items]
Sales milestone payment	$ 29
Regulatory milestone payment	51.3
Aggregate sales milestone payment	115
Gilead Asset Purchase
Schedule Of Asset Acquisition [Line Items]
Upfront cash payment	3
Convertible promissory note issued	3
Payments for reimbursements	$ 0.7

Leases - Additional Information

Leases - Additional Information (Details)

Sep. 30, 2020

Jul. 01, 2020USD ($)ft²

Feb. 28, 2020USD ($)

Aug. 01, 2018USD ($)

Feb. 28, 2021USD ($)ft²

Mar. 31, 2021USD ($)

Mar. 31, 2020USD ($)ft²

Dec. 31, 2020USD ($)

Nov. 30, 2020USD ($)

Mar. 01, 2020USD ($)

Jul. 31, 2018ft²

Lessee, Lease, Description [Line Items]

Operating lease right-of-use assets

$ 24,845,000

$ 27,322,000

[1]

Lease liabilities

30,216,000

32,057,000

Lease payments

1,200,000

$ 100,000

21 Erie Street, Cambridge, Massachusetts | Cambridge, Massachusetts

Lessee, Lease, Description [Line Items]

Cost for early lease termination

$ 100,000

Operating lease right-of-use assets

0

Lease liabilities

0

301 Binney Street, Cambridge, Massachusetts

Lessee, Lease, Description [Line Items]

Operating lease right-of-use assets

24,700,000

25,100,000

Lease liabilities

$ 30,100,000

30,100,000

Remaining lease term

9 years 10 months 24 days

Incremental borrowing rate

8.50%

Lease term

11 years

Facility size | ft²

40,514

Escalating rent payments, percent

3.00%

Letter of credit

$ 2,000,000

Tenant improvement allowances

$ 3,700,000

Improvement costs incurred, reimbursed by lessor

3,300,000

Initial annual base rent

$ 4,100,000

San Mateo, California

Lessee, Lease, Description [Line Items]

Lease term

37 months

Facility size | ft²

4,661

Escalating rent payments, percent

3.00%

Security deposit

$ 28,000

Initial annual base rent

$ 300,000

San Mateo, California, Adjacent Space

Lessee, Lease, Description [Line Items]

Facility size | ft²

3,414

Escalating rent payments, percent

3.00%

Security deposit

$ 25,000

Initial annual base rent

$ 200,000

San Mateo, California. Original Lease

Lessee, Lease, Description [Line Items]

Facility size | ft²

8,075

San Mateo, California. February 2021 Lease Agreement

Lessee, Lease, Description [Line Items]

Remaining lease term

3 months

Incremental borrowing rate

12.07%

Facility size | ft²

17,340

Escalating rent payments, percent

3.00%

Security deposit

$ 59,000

Initial annual base rent

$ 1,200,000

San Mateo, California. February 2021 Lease Agreement, 4,661 Square Foot Suite

Lessee, Lease, Description [Line Items]

Operating lease right-of-use assets

59,000

1,100,000

Lease liabilities

53,000

1,100,000

Facility size | ft²

4,661

San Mateo, California. February 2021 Lease Agreement, 3,414 Square Foot Suite

Lessee, Lease, Description [Line Items]

Operating lease right-of-use assets

43,000

800,000

Lease liabilities

$ 38,000

$ 800,000

Facility size | ft²

3,414

[1]

The balance sheet as of December 31, 2020 is derived from the audited financial statements as of that date.

Leases - Supplemental Balance S

Leases - Supplemental Balance Sheet Information - Operating Leases (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets:
Operating lease assets	$ 24,845	$ 27,322	[1]
Liabilities:
Current portion of operating lease liabilities	822	937	[1]
Noncurrent operating lease liabilities	29,394	31,120	[1]
Total operating lease liabilities	$ 30,216	$ 32,057
[1]	The balance sheet as of December 31, 2020 is derived from the audited financial statements as of that date.

Leases - Summary of Lease Costs

Leases - Summary of Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Lessee, Lease, Description [Line Items]
Finance lease cost	$ 3	$ 6
Interest income (expense), net	0	1
Operating lease cost	1,384	419
Research and development
Lessee, Lease, Description [Line Items]
Finance lease cost	3	5
Operating lease cost	1,008	256
General and administrative expenses
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 376	$ 163

Leases - Schedule of Maturities

Leases - Schedule of Maturities on Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Remaining nine months of 2021	$ 3,207
2022	4,204
2023	4,330
2024	4,460
2025 and thereafter	30,624
Total undiscounted lease payments	46,825
Less: Present value adjustment	(16,241)
Less: Tenant improvement allowance	(368)
Present value of operating lease liabilities	$ 30,216	$ 32,057

Related Party Disclosures (Deta

Related Party Disclosures (Details) - Affiliated Entity - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Payables to related parties	$ 63,000		$ 182,000
Two River Consulting, LLC
Related Party Transaction [Line Items]
Services agreement term	3 years
Expenses from transaction with related party	$ 200,000	$ 200,000
Bellco Capital, LLC
Related Party Transaction [Line Items]
Expenses from transaction with related party	$ 6,300	$ 6,300