Atreca Inc - Ordinary Shares (BCEL) 10-Q 2 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 02, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2021
Entity File Number	001-38935
Entity Registrant Name	ATRECA, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-3723255
Entity Address, Address Line One	835 Industrial Road, Suite 400
Entity Address, City or Town	San Carlos
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94070
City Area Code	650
Local Phone Number	595-2595
Title of 12(b) Security	Class A Common Stock
Trading Symbol	BCEL
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001532346
Amendment Flag	false
Class A common stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		30,435,167
Class B common stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		6,715,441

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current Assets
Cash and cash equivalents	$ 113,189	$ 60,789
Investments	39,697	179,296
Prepaid expenses and other current assets	9,180	9,037
Total current assets	162,066	249,122
Property and equipment, net	44,291	19,831
Long-term investments	10,824
Deposits and other	3,080	3,111
Total assets	220,261	272,064
Current Liabilities
Accounts payable	5,238	5,216
Accrued expenses	9,286	10,302
Other current liabilities	1,631	1,900
Total current liabilities	16,155	17,418
Capital lease obligations, net of current portion		4
Deferred rent	28,677	12,585
Total liabilities	44,832	30,007
Commitment and contingencies (Note 8)
Stockholders' equity
Additional paid-in capital	505,680	492,436
Accumulated other comprehensive income (loss)	(6)	58
Accumulated deficit	(330,249)	(250,441)
Total stockholders' equity	175,429	242,057
Total liabilities and stockholders' equity	220,261	272,064
Class A common stock
Stockholders' equity
Common stock	3	3
Class B common stock
Stockholders' equity
Common stock	$ 1	$ 1

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Class A common stock
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	650,000,000	650,000,000
Common stock, shares issued	30,249,727	30,089,162
Common stock, shares outstanding	30,249,727	30,089,162
Class B common stock
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	6,715,441	6,715,441
Common stock, shares outstanding	6,715,441	6,715,441

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Expenses
Research and development	$ 18,721	$ 16,808	$ 56,145	$ 45,198
General and administrative	8,796	6,614	24,648	20,195
Total expenses	27,517	23,422	80,793	65,393
Interest and other income (expense)
Other income	158	353	851	987
Interest income	36	142	183	1,082
Interest expense	(1)	(1)	(3)	(3)
Loss on disposal of property and equipment	(34)		(45)
Loss before income tax expense	(27,358)	(22,928)	(79,807)	(63,327)
Income tax expense		(1)	(1)	(1)
Net loss	$ (27,358)	$ (22,929)	$ (79,808)	$ (63,328)
Net loss per share, basic	$ (0.74)	$ (0.66)	$ (2.16)	$ (2.09)
Net loss per share, diluted	$ (0.74)	$ (0.66)	$ (2.16)	$ (2.09)
Weighted-average shares used in computing net loss per share, basic	36,918,255	34,723,888	36,884,665	30,313,047
Weighted-average shares used in computing net loss per share, diluted	36,918,255	34,723,888	36,884,665	30,313,047

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Loss and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net loss	$ (27,358)	$ (22,929)	$ (79,808)	$ (63,328)
Other comprehensive income:
Unrealized gain(loss) on available-for-sale debt securities	(22)	(99)	(64)	101
Comprehensive loss	$ (27,380)	$ (23,028)	$ (79,872)	$ (63,227)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Balances at beginning at Dec. 31, 2019	$ 3	$ 351,039	$ 16	$ (164,106)	$ 186,952
Balances at beginning (in shares) at Dec. 31, 2019	27,970,167
Issuance of common stock upon initial public offering, net	$ 1	126,054			126,055
Issuance of common stock upon initial public offering, net (in shares)	8,423,375
Issuance of common stock upon exercise of options		1,131			1,131
Issuance of common stock upon exercise of options (in shares)	223,143
Vesting of early exercised stock options		4			4
Issuance of common stock under the Employee Stock Purchase Plan		1,012			1,012
Issuance of common stock under the Employee Stock Purchase Plan (shares)	76,164
Stock-based compensation		9,353			9,353
Unrealized gain(loss) on available-for-sale debt securities			101		101
Net loss				(63,328)	(63,328)
Balances at end at Sep. 30, 2020	$ 4	488,593	117	(227,434)	261,280
Balances at end (in shares) at Sep. 30, 2020	36,692,849
Balances at beginning at Jun. 30, 2020	$ 3	358,401	216	(204,505)	154,115
Balances at beginning (in shares) at Jun. 30, 2020	28,192,733
Issuance of common stock upon initial public offering, net	$ 1	126,054			126,055
Issuance of common stock upon initial public offering, net (in shares)	8,423,375
Issuance of common stock upon exercise of options		172			172
Issuance of common stock upon exercise of options (in shares)	37,133
Issuance of common stock under the Employee Stock Purchase Plan		479			479
Issuance of common stock under the Employee Stock Purchase Plan (shares)	39,608
Stock-based compensation		3,487			3,487
Unrealized gain(loss) on available-for-sale debt securities			(99)		(99)
Net loss				(22,929)	(22,929)
Balances at end at Sep. 30, 2020	$ 4	488,593	117	(227,434)	261,280
Balances at end (in shares) at Sep. 30, 2020	36,692,849
Balances at beginning at Dec. 31, 2020	$ 4	492,436	58	(250,441)	242,057
Balances at beginning (in shares) at Dec. 31, 2020	36,804,603
Issuance of common stock upon exercise of options		272			272
Issuance of common stock upon exercise of options (in shares)	46,793
Issuance of common stock under the Employee Stock Purchase Plan		837			837
Issuance of common stock under the Employee Stock Purchase Plan (shares)	113,772
Stock-based compensation		12,135			12,135
Unrealized gain(loss) on available-for-sale debt securities			(64)		(64)
Net loss				(79,808)	(79,808)
Balances at end at Sep. 30, 2021	$ 4	505,680	(6)	(330,249)	175,429
Balances at end (in shares) at Sep. 30, 2021	36,965,168
Balances at beginning at Jun. 30, 2021	$ 4	501,474	16	(302,891)	198,603
Balances at beginning (in shares) at Jun. 30, 2021	36,894,414
Issuance of common stock under the Employee Stock Purchase Plan		353			353
Issuance of common stock under the Employee Stock Purchase Plan (shares)	70,754
Stock-based compensation		3,853			3,853
Unrealized gain(loss) on available-for-sale debt securities			(22)		(22)
Net loss				(27,358)	(27,358)
Balances at end at Sep. 30, 2021	$ 4	$ 505,680	$ (6)	$ (330,249)	$ 175,429
Balances at end (in shares) at Sep. 30, 2021	36,965,168

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash Flows from Operating Activities
Net loss	$ (79,808)	$ (63,328)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,184	1,805
Loss on disposal of property and equipment	45
Stock-based compensation	12,135	9,353
Amortization (accretion) of investments	1,311	(63)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(307)	(1,170)
Accounts payable	(358)	38
Accrued expenses	3,128	(93)
Other current liabilities	(1,111)	932
Deferred rent	16,967	3,952
Net cash used in operating activities	(44,814)	(48,574)
Cash Flows from Investing Activities
Purchase of property and equipment	(31,453)	(3,726)
Purchase of investments	(30,529)	(163,881)
Proceeds from maturities of investments	157,929	63,110
Change in deposits		127
Net cash provided by (used in) investing activities	95,947	(104,370)
Cash Flows from Financing Activities
Proceeds from the issuance of common stock under the Employee Stock Purchase Plan	837	1,012
Proceeds from exercise of stock options	272	1,131
Proceeds from public offering, net		126,688
Principal payments on capital lease obligations	(36)	(35)
Payments of initial offering costs		(364)
Net cash provided by financing activities	1,073	128,432
Net change in cash, cash equivalents and restricted cash	52,206	(24,512)
Cash, cash equivalents and restricted cash, beginning of period	62,441	159,236
Cash, cash equivalents and restricted cash, end of period	114,647	134,724
Supplemental Disclosure of Cash Flow Information
Cash paid for interest	3	3
Cash paid for income taxes	1	1
Supplemental Schedule of Non-Cash Investing and Financing Activities
Costs related to public offering included in accounts payable and accrued liabilities		269
Vesting of early exercised common stock options		4
Purchases of property and equipment included in accounts payable and accrued liabilities	$ 3,548	$ 91

Business

Business	9 Months Ended
	Sep. 30, 2021
Business
Business	1. Business Nature of Business Atreca, Inc. (the “Company”) was incorporated in the State of Delaware on June 11, 2010 (“inception date”), and is located in San Carlos, California. The Company is a biopharmaceutical company utilizing its differentiated platform to discover and develop novel antibody-based immunotherapeutics to treat a range of solid tumor types. The Company's lead product candidate, ATRC-101, is a monoclonal antibody in clinical development with a novel mechanism of action and target derived from an antibody identified using its discovery platform. The Company operates in a single

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and include the accounts of the Company and its wholly owned subsidiary. Certain information and note disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to the applicable rules and regulations of the Securities and Exchange Commission (“SEC”). Therefore, these unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related footnotes included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2020 (the “2020 Form 10-K”). Principles of Consolidation The condensed consolidated financial statements include accounts of the Company and its wholly owned subsidiary. All significant intercompany accounts and transactions are eliminated upon consolidation. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities, and reported amounts of income and expenses in the condensed consolidated financial statements and accompanying notes. Changes in facts and circumstances may result in revised estimates and actual results could differ from those estimates. Key estimates in the condensed consolidated financial statements include estimated useful lives of property and equipment, impairment of long-lived assets, accrued expenses, valuation of deferred income tax assets, fair value of warrants issued to purchasers of shares of common stock and fair value of options granted under the Company's stock option plan. Unaudited Interim Condensed Consolidated Financial Statements The accompanying condensed consolidated financial statements are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the annual consolidated financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair statement of the Company’s financial position as of September 30, 2021 and its results of operations and cash flows for the three months and nine months ended September 30, 2021 and 2020. The financial data and the other financial information contained in these notes to the condensed consolidated financial statements related to the three-month and nine-months periods are also unaudited. The condensed results of operations for the three months and nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or for any other future annual or interim period. The consolidated balance sheet as of December 31, 2020 included herein was derived from the audited consolidated financial statements as of that date. ​ Collaborations Historically, we have entered into a number of discovery collaborations as we developed our discovery platform. These collaborations have generally focused on identifying novel antibodies in areas of significant unmet medical need. In July 2020, the Company entered into a Collaboration and License Agreement with Xencor, Inc. (“Xencor Agreement”), to research, develop and commercialize novel CD3 bispecific antibodies as potential therapeutics in oncology. Under the Xencor Agreement, the Company and Xencor, Inc. will engage in a three-year research program in which the Company will provide antibodies against novel tumor targets through its discovery platform from which Xencor, Inc. will engineer XmAb bispecific antibodies that also bind to the CD3 receptor on T cells. Up to two joint programs are eligible to be mutually selected for further development and commercialization, with each partner sharing 50% of costs and profits. Each company has the option to lead development, regulatory and commercialization activities for one of the joint programs. In addition, the Xencor Agreement allows each partner the option to pursue up to two programs independently, with a mid-to high-single digit percent royalty payable on net sales to the other partner. For the cost-sharing related to the research program, the Company will follow the presentation and disclosure guidance of Accounting Standard Codification (“ASC”) 808, Collaboration Agreements The Company evaluated the Xencor Agreement under the provisions of Accounting Standard Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers Collaborative Arrangements (Topic 808) Clarifying the Interaction between Topic 808 and Topic 606 Other Income Other income is comprised of amounts earned from services performed under service agreements. Beginning January 1, 2018, the Company follows the provisions of Accounting Standards Update 2014-09 ASC Topic 606, Revenue from Contracts with Customers (“Topic 606”). In determining the appropriate amount of other income to be recognized as it fulfills its obligations under the agreements, the Company performs the following steps: (i) identifies the promised goods or services in the contract; (ii) determines whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measures the transaction price, including the constraint on variable consideration; (iv) allocates the transaction price to the performance obligations based on estimated selling prices; and (v) recognizes other income when (or as) the Company satisfies each performance obligation. Upon adoption of Topic 606, there was no change to the units of accounting previously identified with respect to existing service agreements under legacy Generally Accepted Accounting Principles (“GAAP”), which are now considered performance obligations under Topic 606, and there was no change to the revenue recognition pattern for the performance obligations. Accordingly, the adoption of the new standard resulted in no cumulative effect change to the Company's opening accumulated deficit balance. The Company generally allocates the transaction price to distinct performance obligations at their stand-alone selling prices, determined by their estimated costs plus some margin. Performance obligations are generally delivered over time and recognized based upon observable inputs as the related research services are performed, which are recorded as research and development expenses. Amounts due under service agreements are generally billed monthly as services are delivered and do not generally result in contract liabilities or assets. Receivables under service agreements of $0 and $13,000 are included in prepaid expenses and other current assets as of September 30, 2021 and December 31, 2020, respectively. In February 2020, the Company entered into an agreement with an external partner for a research project to identify the antigenic targets of select antibodies discovered by the Company with potential utility in oncology. The nonrefundable upfront payment from this agreement was classified as a contract liability and the Company fully recognized the amount as other income over the service period of 18 months. Contract liabilities of $0 and $0.8 million related to the agreement are included in other current liabilities as of September 30, 2021 and December 31, 2020, respectively. Cash, Cash Equivalents and Restricted Cash Cash and cash equivalents include all cash balances and highly liquid investments purchased with an original maturity of three months or less. The Company maintained restricted cash of $1.5 million and $1.7 million as of September 30, 2021 and December 31, 2020, respectively. This amount is included in deposits and other in the accompanying condensed consolidated balance sheets and is comprised solely of letters of credit required pursuant to leases for Company facilities. The Company’s reconciliation of cash and cash equivalents and restricted cash reported within the condensed consolidated balance sheets that sum to the total of the same amounts shown in the condensed consolidated statements of cash flows were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, ​ ​ ​ 2021 2020 ​ Cash and cash equivalents ​ $ 113,189 ​ $ 60,789 ​ Restricted cash ​ ​ 1,458 ​ ​ 1,652 ​ Cash, cash equivalents and restricted cash shown in the consolidated statements of cash flows ​ $ 114,647 ​ $ 62,441 ​ ​ Investments The Company considers securities purchased with original maturities greater than three months to be investments. The Company’s policy is to protect the value of its investment portfolio and minimize principal risk by earning returns based on current interest rates. The Company’s intent is to convert all investments into cash to be used for operations and has classified them as available for sale. For purposes of determining realized gains and losses, the cost of securities sold is based on specific identification. Interest and dividends on securities classified as available-for-sale are included in interest income. Risks and Uncertainties The Company is subject to a number of risks associated with companies at a similar stage, including COVID-19, dependence on key individuals, competition from similar services and larger companies, volatility of the industry, ability to obtain regulatory clearance, ability to obtain adequate financing to support growth, the ability to attract and retain additional qualified personnel to manage the anticipated growth of the Company and general economic conditions. Concentration of Credit Risk Financial instruments that potentially subject the Company to concentration of credit risk consist of cash and cash equivalents, investments and other receivables. Cash and cash equivalents are held at two financial institutions and were in excess of the Federal Deposit Insurance Corporation insurable limit at September 30, 2021 and December 31, 2020. Additionally, cash and cash equivalents and investments are maintained at brokerage firms for which amounts are insured by the Securities Investor Protection Corporation subject to legal limits. The Company has not experienced any losses on its deposits to date. The Company does not require collateral or other security for other receivables; however, credit risk is mitigated by the Company’s ongoing evaluations of its debtors’ credit worthiness. Research and Development Costs Research and development costs are expensed as incurred. Research and development costs consist primarily of salaries and benefits, consultant fees, stock-based compensation, certain facility costs, legal costs and other costs associated with preclinical and clinical development. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers in connection with preclinical and clinical development activities and contract manufacturing organizations in connection with the production of materials for clinical trials. At the end of the reporting period, the Company compares payments made to third-party service providers to the estimated progress toward completion of the research or development objectives. Such estimates are subject to change as additional information becomes available. Depending on the timing of payments to the service providers and the progress that the Company estimates has been made as a result of the service provided, the Company may record net prepaid or accrued expense relating to these costs. Stock-Based Compensation The Company generally grants stock options to its employees for a fixed number of shares with an exercise price equal to the fair value of the underlying shares at the date of grant. The Company accounts for stock option grants using the fair value method. The fair value of options is calculated using the Black-Scholes option pricing model. For restricted stock units, fair value is based on the closing price of the Company’s Class A common stock on the grant date. Stock-based compensation is recognized as the underlying options vest using the straight-line attribution approach, and forfeitures are recorded as they occur. Emerging Growth Company Status The Company is an “emerging growth company,” (“EGC”) as defined in the Jumpstart Our Business Startups Act, (“JOBS Act”), and may take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not EGCs. The Company may take advantage of these exemptions until it is no longer an EGC under Section 107 of the JOBS Act, which provides that an EGC can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. The Company has elected to use the extended transition period for complying with new or revised accounting standards, and as a result of this election, the Company’s condensed consolidated financial statements may not be comparable to companies that comply with public company Financial Accounting Standards Board (“FASB”) standards’ effective dates. The Company may take advantage of these exemptions up until the last day of the fiscal year following the fifth anniversary of the IPO or such earlier time that the Company is no longer an EGC. Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes - Simplifying the Accounting for Income Taxes (“Topic 740”) The new guidance, effective January 1, 2021, did not have an impact on the Company’s condensed consolidated financial statements. Recent Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU 2016-02 and subsequent amendments to the initial guidance under ASU 2017-13, ASU 2018-10, ASU 2018-11, and ASU 2019-01 (collectively, “Topic 842” accounting by lessees for all leases with a term greater than 12 months. This standard will require lessees to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. Topic 842 In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses “Topic 326” Measurement of Credit Losses on Financial Instruments Topic 326

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2021
Fair Value of Financial Instruments
Fair Value of Financial Instruments	3. Fair Value of Financial Instruments ​ The fair value of the Company's assets and liabilities, which qualify as financial instruments under FASB ASC 820, Fair Value Measurements and Disclosures ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 ​ Level 1 Level 2 Level 3 Total Assets ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 108,046 ​ $ — ​ $ — ​ $ 108,046 Certificates of deposit ​ ​ 1,670 ​ ​ — ​ ​ — ​ ​ 1,670 Corporate debt securities ​ ​ — ​ ​ 6,118 ​ ​ — ​ ​ 6,118 U.S. Treasury securities ​ ​ 42,733 ​ ​ — ​ ​ — ​ ​ 42,733 Total ​ $ 152,449 ​ $ 6,118 ​ $ — ​ $ 158,567 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ Level 1 Level 2 Level 3 Total Assets ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 57,951 ​ $ — ​ $ — ​ $ 57,951 U.S. Agency Bonds ​ ​ — ​ ​ 10,706 ​ ​ — ​ ​ 10,706 Certificates of deposit ​ ​ 941 ​ ​ — ​ ​ — ​ ​ 941 Corporate debt securities ​ ​ — ​ ​ 16,667 ​ ​ — ​ ​ 16,667 U.S. Treasury securities ​ ​ 150,982 ​ ​ — ​ ​ — ​ ​ 150,982 Total ​ $ 209,874 ​ $ 27,373 ​ $ — ​ $ 237,247 ​ The Company utilized the market approach and Level 1 valuation inputs to value its money market funds and U.S. government treasury securities because published fair market values were readily available. The Company measured the fair value of corporate debt securities and U.S. agency bonds using Level 2 valuation inputs, which are based on quoted prices and market observable data of similar instruments. As of September 30, 2021 and December 31, 2020, gross unrealized gains and unrealized losses for cash equivalents and investments were not material, and the remaining contractual maturity of all marketable securities was less than two years.

Cash, Cash Equivalents and Inve

Cash, Cash Equivalents and Investments	9 Months Ended
	Sep. 30, 2021
Cash, Cash Equivalents and Investments
Cash, Cash Equivalents and Investments	4. Cash, Cash Equivalents and Investments ​ The fair value and the amortized cost of cash, cash equivalents and available-for-sale investments by major security type consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ Cash and ​ ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cash ​ Short-term ​ Long-term September 30, 2021 Cost Gains Losses Value Equivalents ​ Investment ​ Investment Cash, cash equivalents and money market funds ​ $ 113,189 ​ $ — ​ $ — ​ $ 113,189 ​ $ 113,189 ​ $ — ​ $ — ​ U.S. Treasury securities ​ 42,739 ​ ​ — ​ ​ (6) ​ ​ 42,733 ​ ​ — ​ ​ 32,644 ​ ​ 10,089 ​ Corporate debt securities ​ ​ 6,118 ​ ​ — ​ ​ — ​ ​ 6,118 ​ ​ — ​ ​ 6,118 ​ ​ — ​ Certificates of deposit ​ ​ 1,669 ​ 1 ​ — ​ 1,670 ​ — ​ 935 ​ ​ 735 ​ Total ​ $ 163,715 ​ $ 1 ​ $ (6) ​ $ 163,710 ​ $ 113,189 ​ $ 39,697 ​ $ 10,824 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ Cash and ​ ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cash ​ Short-term ​ Long-term December 31, 2020 Cost Gains Losses Value Equivalents ​ Investment ​ Investment Cash, cash equivalents and money market funds ​ $ 60,789 ​ $ — ​ $ — ​ $ 60,789 ​ $ 60,789 ​ $ — ​ $ — ​ U.S. Treasury securities ​ 150,929 ​ ​ 53 ​ ​ — ​ ​ 150,982 ​ ​ — ​ ​ 150,982 ​ ​ — ​ Corporate debt securities ​ ​ 16,668 ​ ​ — ​ ​ (1) ​ ​ 16,667 ​ ​ — ​ ​ 16,667 ​ ​ — ​ U.S. Agency bonds ​ ​ 10,704 ​ ​ 2 ​ ​ — ​ ​ 10,706 ​ ​ — ​ ​ 10,706 ​ ​ — ​ Certificates of deposit ​ ​ 937 ​ 4 ​ — ​ 941 ​ — ​ 941 ​ — ​ Total ​ $ 240,027 ​ $ 59 ​ $ (1) ​ $ 240,085 ​ $ 60,789 ​ $ 179,296 ​ $ — ​ ​

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	9 Months Ended
	Sep. 30, 2021
Prepaid Expenses and Other Current Assets.
Prepaid Expenses and Other Current Assets	5. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2021 2020 Prepaid insurance ​ $ 2,307 ​ $ 1,453 ​ Vendor prepayments and deposits ​ ​ 3,092 ​ ​ 1,557 ​ Prepaid rent ​ 807 ​ 1,397 ​ Tenant improvement receivables ​ ​ 2,589 ​ ​ 3,732 ​ Non-trade receivables ​ 48 ​ 336 ​ Interest receivable and other current assets ​ ​ 337 ​ ​ 562 ​ Total prepaid expenses and other current assets ​ $ 9,180 ​ $ 9,037 ​ ​

Property and Equipment, net

Property and Equipment, net	9 Months Ended
	Sep. 30, 2021
Property and Equipment, net
Property and Equipment, net	6. Property and Equipment, net Property and equipment consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, ​ ​ 2021 2020 Laboratory equipment ​ $ 13,090 ​ $ 11,287 ​ Furniture and fixtures ​ 1,968 ​ 242 ​ Computer hardware and software ​ 1,423 ​ 919 ​ Leasehold improvements ​ 37,841 ​ 667 ​ Construction in process ​ — ​ 14,379 ​ ​ ​ 54,322 ​ 27,494 ​ Less accumulated depreciation and amortization ​ (10,031) ​ (7,663) ​ Total property and equipment, net ​ $ 44,291 ​ $ 19,831 ​ ​ Depreciation expense was $1.4 million and $0.6 million for the three months ended September 30, 2021 and 2020, respectively, and $3.2 million and $1.8 million for the nine months ended September 30, 2021 and 2020, respectively. The net book value of property and equipment under capital leases was $15,000 and $49,000 at September 30, 2021 and December 31, 2020, respectively.

Accrued Expenses

Accrued Expenses	9 Months Ended
	Sep. 30, 2021
Accrued Expenses
Accrued Expenses	7. Accrued Expenses Accrued expenses consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, ​ ​ 2021 2020 Compensation and related benefits ​ $ 3,876 ​ $ 4,954 Accrued construction costs ​ ​ 11 ​ ​ 4,145 Professional fees ​ ​ 357 ​ ​ 82 Contract research fees ​ ​ 3,440 ​ ​ 809 Accrued cease-use liabilities ​ ​ 1,285 ​ ​ — Other ​ ​ 317 ​ ​ 312 Total accrued expenses ​ $ 9,286 ​ $ 10,302 ​

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies
Commitments and Contingencies	8. Commitments and Contingencies Leases The Company leases its office facilities under non-cancellable operating lease agreements that expire at various dates through April 2033. Under the terms of the leases, the Company is responsible for certain insurance, property taxes and maintenance expenses. The office facilities lease agreements contain scheduled increases over the lease term. The related rent expense is calculated on a straight-line basis with the difference recorded as deferred rent. Rent expense was $1.9 million and $2.9 million for the three months ended September 30, 2021 and 2020, respectively, and $8.2 million and $6.7 million for the nine months ended September 30, 2021 and 2020, respectively. The Company leases certain property and equipment under capital leases. In 2017, the Company financed purchases of $226,000 under a capital lease agreement. Outstanding amounts under the capital lease agreements are generally secured by liens on the related property and equipment. The Company vacated its former office space in September 2021, prior to the expiration of the lease in March 2022. The remaining rent payable, deferred rent and associated prepaid rent for the former office space were expensed in full on September 30, 2021 and resulted in a charge of $1.5 million, recorded as a general and administrative operating expense in the Company’s unaudited condensed consolidated statement of operations. As of September 30, 2021, there was an associated cease-use liability of $1.3 million, which the Company expects to be settled by March 2022. ​ Future minimum lease payments under non-cancelable operating and capital lease agreements consisted of the following at September 30, 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Capital Operating ​ ​ Leases ​ Leases Years ending December 31: ​ ​ ​ ​ ​ ​ 2021 (remaining 3 months) ​ $ 13 ​ $ 2,408 2022 ​ 4 ​ 7,944 2023 ​ — ​ 7,644 2024 ​ ​ — ​ ​ 7,855 2025 ​ ​ — ​ ​ 8,072 Thereafter ​ ​ — ​ ​ 66,453 Total minimum lease payments ​ 17 ​ $ 100,376 Less: amount representing interest ​ — ​ ​ ​ Present value of capital lease obligation ​ 17 ​ ​ ​ Less: current portion ​ (17) ​ ​ ​ Non-current portion ​ $ — ​ ​ ​ ​ Litigation The Company is not aware of any asserted or unasserted claims against it where it believes that an unfavorable resolution would have an adverse material impact on the operations or financial position of the Company.

Capital Stock

Capital Stock	9 Months Ended
	Sep. 30, 2021
Capital Stock
Capital Stock	9. Capital Stock Class A and Class B Common Stock On June 2, 2019 the board of directors of the Company authorized the issuance of 650,000,000 shares of Class A common stock, $0.0001 par value per share, 50,000,000 shares of Class B common stock, $0.0001 par value per share and 300,000,000 shares of preferred stock, $0.0001 par value per share, upon the filing of the Company’s Amended and Restated Certificate of Incorporation in connection with the reverse stock split. Each holder of Class A common stock is entitled to one vote and each holder of Class B common stock is not entitled to vote except as may be required by law and shall not be entitled to vote on the election of directors at any time. Sales Agreement In August 2020, the Company entered into a sales agreement (“Sales Agreement”) with Cowen and Company, LLC (“Cowen”), pursuant to which the Company may, upon the terms and subject to the conditions set forth therein, issue and sell through Cowen, acting as the Company’s sales agent and/or principal, shares of the Company’s Class A common stock, having an aggregate offering price of up to $100.0 million (the “ATM Shares”). The Company has no obligations to sell any ATM Shares under the Sales Agreement. The Sales Agreement provides that Cowen will be entitled to compensation for its services in an amount equal to up to 3.0% of gross proceeds for each time we issue and sell ATM Shares under the Sales Agreement. The ATM Shares will be sold based on prevailing market prices at the time of the sale, and, as a result, prices may vary. Unless otherwise terminated earlier, the Sales Agreement continues until all shares available under the Sales Agreement have been sold. As of September 30, 2021, no ATM Shares have been sold under the Sales Agreement. ​

Equity Incentive Plans

Equity Incentive Plans	9 Months Ended
	Sep. 30, 2021
Equity Incentive Plans
Equity Incentive Plans	10. Equity Incentive Plans 2019 Equity Incentive Plan The Company’s board of directors adopted and our stockholders approved our 2019 Equity Incentive Plan (the “2019 Plan”) on June 2, 2019, and June 7, 2019, respectively. The 2019 Plan became effective on June 19, 2019, and no further grants will be made under the Company’s 2010 Equity Incentive Plan (the “2010 Plan”). The purpose of the 2019 Plan, through the grant of stock awards including stock options and other stock-based awards, including restricted stock units (“RSUs”), is to help the Company secure and retain the services of eligible award recipients, provide incentives for such persons to exert maximum efforts for our success and that of the Company’s affiliates, and provide a means by which the eligible recipients may benefit from increases in the value of the Company’s Class A common stock. Under the 2019 Plan, 6,141,842 shares of the Company’s Class A common stock have been reserved for issuance to employees, directors and consultants. Additionally, the number of shares of the Company’s Class A common stock reserved for issuance under the 2019 Plan will automatically increase on January 1 of each year, beginning on January 1, 2020 and continuing through and including January 1, 2029, by 4% of the total number of shares of our capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors. Stock Options Stock option activity under the 2019 Plan and the Company’s 2010 Plan is as follow: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options Outstanding ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ Aggregate ​ ​ ​ ​ Weighted- ​ Remaining ​ Intrinsic ​ ​ Number ​ Average ​ Contractual ​ Value ​ of Shares ​ Exercise Price ​ Life (years) ​ (in thousands) Balances, December 31, 2020 4,812,223 ​ $ 13.33 ​ 8.2 ​ $ 21,493 Granted 1,829,770 ​ 13.29 ​ ​ ​ Exercised (46,793) ​ 5.82 ​ ​ ​ Cancelled (580,209) ​ 15.12 ​ ​ ​ Balances, September 30, 2021 6,014,991 ​ $ 13.20 ​ 8.0 ​ $ 1,377 Vested and expected to vest at September 30, 2021 6,014,991 ​ $ 13.20 ​ 8.0 ​ $ 1,377 Exercisable at September 30, 2021 3,144,958 ​ $ 11.40 ​ 7.3 ​ $ 1,376 Vested at September 30, 2021 3,011,904 ​ $ 11.68 ​ 7.4 ​ $ 1,233 ​ The weighted-average grant date fair value of options granted to employees and non-employees in the nine months ended September 30, 2021 and 2020 was $9.85 and $13.55, respectively. The fair value of each option is estimated on the date of grant using the Black-Scholes option pricing model, assuming no expected dividends and the following weighted average assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ ​ Nine Months Ended September 30, ​ ​ ​ 2021 2020 2021 2020 Expected life (in years) 6.01 6.01 ​ 5.97 5.85 ​ ​ Volatility 90.0 % 88.5 % 91.4 % 85.6 % ​ Risk-free interest rate 1.0 % 0.4 % 0.6 % 1.1 % ​ ​ Expected volatility is based on volatilities of public companies operating in the Company’s industry. The expected life of the options is estimated using the simplified method detailed in SEC Staff Accounting Bulletin No. 107. The simplified method calculates the expected term as the mid-point between the weighted-average time to vesting and the contractual maturity. The risk-free rate is based on the U.S. Treasury yield curve in effect at the time of grant. The Company has elected to account for forfeitures as they occur, rather than estimate expected forfeitures. Restricted Stock Units The 2019 Plan provides for the issuance of RSU to employees, directors and consultants. RSUs vest over a period of two years with 50% vesting on the one year anniversary of the award and the remainder The following table summarizes RSU activity for the nine months ended September 30, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ Number ​ Grant Date ​ of Shares ​ Fair Value per RSU Unvested Balances, December 31, 2020 — ​ $ — RSUs Granted 884,820 ​ 6.15 RSUs Vested ​ — ​ ​ — RSUs Cancelled (3,330) ​ 6.15 Unvested Balances, September 30, 2021 881,490 ​ $ 6.15 ​ 2019 Employee Stock Purchase Plan The Company’s board of directors adopted the 2019 Employee Stock Purchase Plan (“ESPP”) on June 2, 2019, and the Company’s stockholders approved the ESPP on June 7, 2019. The ESPP became effective on June 19, 2019. The Company’s board of directors authorized 283,333 shares of Class A common stock to be reserved for future issuance under the ESPP. The number of shares of our Class A common stock reserved for issuance will automatically increase on January 1 of each calendar year, from January 1, 2020 through January 1, 2029, by the lesser of (1) 1% of the total number of shares of our Class A common stock outstanding on December 31 of the preceding calendar year, and (2) 416,666 shares; provided, that prior to the date of any such increase, the Company’s board of directors may determine that such increase will be less than the amount set forth in clauses (1) and (2). During the three months ended September 30, 2021 and 2020, the expense related to the ESPP was $204,000 and $194,000, respectively. During the nine months ended September 30, 2021 and 2020, the expense related to the ESPP was $608,000 and $525,000, respectively. The fair value of each ESPP is estimated on the date of grant using the Black-Scholes option pricing model, assuming no expected dividends and the following range of assumptions: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ ​ Nine Months Ended September 30, ​ ​ ​ 2021 2020 2021 2020 Expected life (in years) 0.5 - 2.0 0.5 - 2.0 ​ 0.5 - 2.0 0.5 - 2.0 ​ ​ Volatility 91.1 - 98.5 % 103.4 - 114.6 % 91.1 - 107.6 % 91.4 - 114.6 % ​ Risk-free interest rate 0.1 - % 0.1 % 0.1 - % 0.1 - % ​ ​ The Company recognized $3.9 million and $3.5 million of stock-based compensation expense related to the 2019 Plan, 2010 Plan, and ESPP for the three months ended September 30, 2021 and 2020, respectively. The Company recognized $12.1 million and $9.4 million of stock-based compensation expense related to the 2019 Plan, 2010 Plan, and ESPP for the nine months ended September 30, 2021 and 2020, respectively. The compensation expense is allocated on a departmental basis, based on the classification of the option holder, as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ ​ 2021 2020 2021 2020 Research and development ​ $ 1,946 ​ $ 1,628 ​ $ 6,080 ​ $ 4,490 ​ General and administrative ​ 1,907 ​ 1,859 ​ 6,055 ​ 4,863 ​ ​ ​ $ 3,853 ​ $ 3,487 ​ $ 12,135 ​ $ 9,353 ​ ​ No income tax benefits have been recognized in the statements of operations for stock-based compensation arrangements and no stock-based compensation costs have been capitalized as property and equipment as of September 30, 2021. Unrecognized compensation expense as of September 30, 2021 totaled $30.0 million related to non-vested stock options with a remaining weighted-average requisite service period of 2.5 years and $5.3 million related to non-vested RSUs with a remaining weighted-average requisite service period of 1.9 years.

401(k) Plan

401(k) Plan	9 Months Ended
	Sep. 30, 2021
401 (k) Plan
401 (k) Plan	11. 401(k) Plan The Company has a 401(k) plan that qualifies as a deferred compensation arrangement under Section 401 of the Code. Eligible employees may elect to defer a portion of their pretax earnings subject to certain statutory limits. Beginning January 1, 2021, the Company matches 100% up to the first $5,000 contributed by a participant. All matching contributions are immediately vested. Total matching contributions to the 401(k) Plan were $0.1 million for the three months ended September 30, 2021, and $0.6 million for the nine months ended September 30, 2021. ​

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Net Loss Per Share
Net Loss Per Share	12. Net Loss Per Share The following outstanding potentially dilutive common shares were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because the impact of including them would have been antidilutive: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ 2021 2020 2021 2020 Common stock options ​ ​ 6,014,991 ​ ​ 4,920,857 ​ ​ 6,014,991 ​ ​ 4,920,857 Unvested restricted stock units ​ ​ 881,490 ​ ​ — ​ ​ 881,490 ​ ​ — Common stock warrants ​ 49,997 ​ 49,997 ​ 49,997 ​ 49,997 ​ ​ ​ 6,946,478 ​ ​ 4,970,854 ​ ​ 6,946,478 ​ ​ 4,970,854 ​

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Taxes
Income Taxes	13. Income Taxes On March 27, 2020, the Coronavirus Aid, Relief and Economic Security (“CARES”) Act was enacted and signed into law. GAAP requires recognition of the tax effects of new legislation during the reporting period that includes the enactment date. The CARES Act, includes changes to the tax provisions that benefits business entities, and makes certain technical corrections to the 2017 Tax Cuts and Jobs Act. The tax relief measures for businesses include a five-year net operating loss carryback, suspension of annual deduction limitation of 80% of taxable income from net operating losses generated in a tax year beginning after December 31, 2017, changes in the deductibility of interest, acceleration of alternative minimum tax credit refunds, payroll tax relief, and a technical correction to allow accelerated deductions for qualified improvement property. The CARES Act also provides other non-tax benefits to assist those impacted by the pandemic. The Company has evaluated the impact of the CARES Act and determined there was no material impact to the income tax provision for the quarter. ​

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2021
Related Party Transactions
Related Party Transactions	14. Related Party Transactions The Company recorded other income of $0 and $2,000 for the three months ended September 30, 2021 and 2020, respectively, and $1,000 and $187,000 for the nine months ended September 30, 2021 and 2020, respectively, under service contracts with a stockholder. The Company had a receivable from the stockholder at September 30, 2021 and December 31, 2020 of $0 and $13,000, respectively. The Company recorded expense of $0.3 million during both the three months ended September 30, 2021 and 2020, and $1.0 million during both the nine months ended September 30, 2021 and 2020, related to intellectual property and other legal services performed by a related party. The Company owed $91,000 and $69,000 to the related party at September 30, 2021 and December 31, 2020, respectively. The Company recorded expense of $0.2 million and $0.4 million during the three months ended September 30, 2021 and 2020, respectively, and $0.6 million and $1.3 million during the nine months ended September 30, 2021 and 2020, respectively, related to legal services performed by a related party. The Company owed $248,000 and $250,000 to the related party at September 30, 2021 and December 31, 2020, respectively. The Company recorded research and development expense of $63,000 and $61,000 during the three months ended September 30, 2021 and 2020, respectively, and $188,000 during both the nine months ended September 30, 2021 and 2020, under consulting agreements with a member of the Company’s board of directors. The Company owed $74,000 to the member of the Company’s board of directors as of both September 30, 2021 and December 31, 2020. ​

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and include the accounts of the Company and its wholly owned subsidiary. Certain information and note disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to the applicable rules and regulations of the Securities and Exchange Commission (“SEC”). Therefore, these unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related footnotes included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2020 (the “2020 Form 10-K”).
Principles of Consolidation	Principles of Consolidation The condensed consolidated financial statements include accounts of the Company and its wholly owned subsidiary. All significant intercompany accounts and transactions are eliminated upon consolidation.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities, and reported amounts of income and expenses in the condensed consolidated financial statements and accompanying notes. Changes in facts and circumstances may result in revised estimates and actual results could differ from those estimates. Key estimates in the condensed consolidated financial statements include estimated useful lives of property and equipment, impairment of long-lived assets, accrued expenses, valuation of deferred income tax assets, fair value of warrants issued to purchasers of shares of common stock and fair value of options granted under the Company's stock option plan.
Unaudited Interim Condensed Financial Statements	Unaudited Interim Condensed Consolidated Financial Statements The accompanying condensed consolidated financial statements are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the annual consolidated financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair statement of the Company’s financial position as of September 30, 2021 and its results of operations and cash flows for the three months and nine months ended September 30, 2021 and 2020. The financial data and the other financial information contained in these notes to the condensed consolidated financial statements related to the three-month and nine-months periods are also unaudited. The condensed results of operations for the three months and nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or for any other future annual or interim period. The consolidated balance sheet as of December 31, 2020 included herein was derived from the audited consolidated financial statements as of that date. ​
Collaborations	Collaborations Historically, we have entered into a number of discovery collaborations as we developed our discovery platform. These collaborations have generally focused on identifying novel antibodies in areas of significant unmet medical need. In July 2020, the Company entered into a Collaboration and License Agreement with Xencor, Inc. (“Xencor Agreement”), to research, develop and commercialize novel CD3 bispecific antibodies as potential therapeutics in oncology. Under the Xencor Agreement, the Company and Xencor, Inc. will engage in a three-year research program in which the Company will provide antibodies against novel tumor targets through its discovery platform from which Xencor, Inc. will engineer XmAb bispecific antibodies that also bind to the CD3 receptor on T cells. Up to two joint programs are eligible to be mutually selected for further development and commercialization, with each partner sharing 50% of costs and profits. Each company has the option to lead development, regulatory and commercialization activities for one of the joint programs. In addition, the Xencor Agreement allows each partner the option to pursue up to two programs independently, with a mid-to high-single digit percent royalty payable on net sales to the other partner. For the cost-sharing related to the research program, the Company will follow the presentation and disclosure guidance of Accounting Standard Codification (“ASC”) 808, Collaboration Agreements The Company evaluated the Xencor Agreement under the provisions of Accounting Standard Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers Collaborative Arrangements (Topic 808) Clarifying the Interaction between Topic 808 and Topic 606
Other Income	Other Income Other income is comprised of amounts earned from services performed under service agreements. Beginning January 1, 2018, the Company follows the provisions of Accounting Standards Update 2014-09 ASC Topic 606, Revenue from Contracts with Customers (“Topic 606”). In determining the appropriate amount of other income to be recognized as it fulfills its obligations under the agreements, the Company performs the following steps: (i) identifies the promised goods or services in the contract; (ii) determines whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measures the transaction price, including the constraint on variable consideration; (iv) allocates the transaction price to the performance obligations based on estimated selling prices; and (v) recognizes other income when (or as) the Company satisfies each performance obligation. Upon adoption of Topic 606, there was no change to the units of accounting previously identified with respect to existing service agreements under legacy Generally Accepted Accounting Principles (“GAAP”), which are now considered performance obligations under Topic 606, and there was no change to the revenue recognition pattern for the performance obligations. Accordingly, the adoption of the new standard resulted in no cumulative effect change to the Company's opening accumulated deficit balance. The Company generally allocates the transaction price to distinct performance obligations at their stand-alone selling prices, determined by their estimated costs plus some margin. Performance obligations are generally delivered over time and recognized based upon observable inputs as the related research services are performed, which are recorded as research and development expenses. Amounts due under service agreements are generally billed monthly as services are delivered and do not generally result in contract liabilities or assets. Receivables under service agreements of $0 and $13,000 are included in prepaid expenses and other current assets as of September 30, 2021 and December 31, 2020, respectively. In February 2020, the Company entered into an agreement with an external partner for a research project to identify the antigenic targets of select antibodies discovered by the Company with potential utility in oncology. The nonrefundable upfront payment from this agreement was classified as a contract liability and the Company fully recognized the amount as other income over the service period of 18 months. Contract liabilities of $0 and $0.8 million related to the agreement are included in other current liabilities as of September 30, 2021 and December 31, 2020, respectively.
Fair Value of Financial Instruments	The Company utilized the market approach and Level 1 valuation inputs to value its money market funds and U.S. government treasury securities because published fair market values were readily available. The Company measured the fair value of corporate debt securities and U.S. agency bonds using Level 2 valuation inputs, which are based on quoted prices and market observable data of similar instruments.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash Cash and cash equivalents include all cash balances and highly liquid investments purchased with an original maturity of three months or less. The Company maintained restricted cash of $1.5 million and $1.7 million as of September 30, 2021 and December 31, 2020, respectively. This amount is included in deposits and other in the accompanying condensed consolidated balance sheets and is comprised solely of letters of credit required pursuant to leases for Company facilities. The Company’s reconciliation of cash and cash equivalents and restricted cash reported within the condensed consolidated balance sheets that sum to the total of the same amounts shown in the condensed consolidated statements of cash flows were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, ​ ​ ​ 2021 2020 ​ Cash and cash equivalents ​ $ 113,189 ​ $ 60,789 ​ Restricted cash ​ ​ 1,458 ​ ​ 1,652 ​ Cash, cash equivalents and restricted cash shown in the consolidated statements of cash flows ​ $ 114,647 ​ $ 62,441 ​
Investments	Investments The Company considers securities purchased with original maturities greater than three months to be investments. The Company’s policy is to protect the value of its investment portfolio and minimize principal risk by earning returns based on current interest rates. The Company’s intent is to convert all investments into cash to be used for operations and has classified them as available for sale. For purposes of determining realized gains and losses, the cost of securities sold is based on specific identification. Interest and dividends on securities classified as available-for-sale are included in interest income.
Risks and Uncertainties	Risks and Uncertainties The Company is subject to a number of risks associated with companies at a similar stage, including COVID-19, dependence on key individuals, competition from similar services and larger companies, volatility of the industry, ability to obtain regulatory clearance, ability to obtain adequate financing to support growth, the ability to attract and retain additional qualified personnel to manage the anticipated growth of the Company and general economic conditions.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to concentration of credit risk consist of cash and cash equivalents, investments and other receivables. Cash and cash equivalents are held at two financial institutions and were in excess of the Federal Deposit Insurance Corporation insurable limit at September 30, 2021 and December 31, 2020. Additionally, cash and cash equivalents and investments are maintained at brokerage firms for which amounts are insured by the Securities Investor Protection Corporation subject to legal limits. The Company has not experienced any losses on its deposits to date. The Company does not require collateral or other security for other receivables; however, credit risk is mitigated by the Company’s ongoing evaluations of its debtors’ credit worthiness.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development costs consist primarily of salaries and benefits, consultant fees, stock-based compensation, certain facility costs, legal costs and other costs associated with preclinical and clinical development. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers in connection with preclinical and clinical development activities and contract manufacturing organizations in connection with the production of materials for clinical trials. At the end of the reporting period, the Company compares payments made to third-party service providers to the estimated progress toward completion of the research or development objectives. Such estimates are subject to change as additional information becomes available. Depending on the timing of payments to the service providers and the progress that the Company estimates has been made as a result of the service provided, the Company may record net prepaid or accrued expense relating to these costs.
Stock Based Compensation	Stock-Based Compensation The Company generally grants stock options to its employees for a fixed number of shares with an exercise price equal to the fair value of the underlying shares at the date of grant. The Company accounts for stock option grants using the fair value method. The fair value of options is calculated using the Black-Scholes option pricing model. For restricted stock units, fair value is based on the closing price of the Company’s Class A common stock on the grant date. Stock-based compensation is recognized as the underlying options vest using the straight-line attribution approach, and forfeitures are recorded as they occur.
Emerging Growth Company Status	Emerging Growth Company Status The Company is an “emerging growth company,” (“EGC”) as defined in the Jumpstart Our Business Startups Act, (“JOBS Act”), and may take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not EGCs. The Company may take advantage of these exemptions until it is no longer an EGC under Section 107 of the JOBS Act, which provides that an EGC can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. The Company has elected to use the extended transition period for complying with new or revised accounting standards, and as a result of this election, the Company’s condensed consolidated financial statements may not be comparable to companies that comply with public company Financial Accounting Standards Board (“FASB”) standards’ effective dates. The Company may take advantage of these exemptions up until the last day of the fiscal year following the fifth anniversary of the IPO or such earlier time that the Company is no longer an EGC.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes - Simplifying the Accounting for Income Taxes (“Topic 740”) The new guidance, effective January 1, 2021, did not have an impact on the Company’s condensed consolidated financial statements.
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU 2016-02 and subsequent amendments to the initial guidance under ASU 2017-13, ASU 2018-10, ASU 2018-11, and ASU 2019-01 (collectively, “Topic 842” accounting by lessees for all leases with a term greater than 12 months. This standard will require lessees to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. Topic 842 In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses “Topic 326” Measurement of Credit Losses on Financial Instruments Topic 326

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2021
Summary of Significant Accounting Policies
Schedule of reconciliation of cash and cash equivalents and restricted cash	The Company’s reconciliation of cash and cash equivalents and restricted cash reported within the condensed consolidated balance sheets that sum to the total of the same amounts shown in the condensed consolidated statements of cash flows were as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, ​ ​ ​ 2021 2020 ​ Cash and cash equivalents ​ $ 113,189 ​ $ 60,789 ​ Restricted cash ​ ​ 1,458 ​ ​ 1,652 ​ Cash, cash equivalents and restricted cash shown in the consolidated statements of cash flows ​ $ 114,647 ​ $ 62,441 ​

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value of Financial Instruments
Summary of financial assets and liabilities subject to fair value measurements on a recurring basis	The fair value of the Company's assets and liabilities, which qualify as financial instruments under FASB ASC 820, Fair Value Measurements and Disclosures ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 ​ Level 1 Level 2 Level 3 Total Assets ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 108,046 ​ $ — ​ $ — ​ $ 108,046 Certificates of deposit ​ ​ 1,670 ​ ​ — ​ ​ — ​ ​ 1,670 Corporate debt securities ​ ​ — ​ ​ 6,118 ​ ​ — ​ ​ 6,118 U.S. Treasury securities ​ ​ 42,733 ​ ​ — ​ ​ — ​ ​ 42,733 Total ​ $ 152,449 ​ $ 6,118 ​ $ — ​ $ 158,567 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ Level 1 Level 2 Level 3 Total Assets ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 57,951 ​ $ — ​ $ — ​ $ 57,951 U.S. Agency Bonds ​ ​ — ​ ​ 10,706 ​ ​ — ​ ​ 10,706 Certificates of deposit ​ ​ 941 ​ ​ — ​ ​ — ​ ​ 941 Corporate debt securities ​ ​ — ​ ​ 16,667 ​ ​ — ​ ​ 16,667 U.S. Treasury securities ​ ​ 150,982 ​ ​ — ​ ​ — ​ ​ 150,982 Total ​ $ 209,874 ​ $ 27,373 ​ $ — ​ $ 237,247

Cash, Cash Equivalents and In_2

Cash, Cash Equivalents and Investments (Tables)	9 Months Ended
	Sep. 30, 2021
Cash, Cash Equivalents and Investments
Summary of fair value and the amortized cost of cash, cash equivalents and available-for-sale investments by major security type	The fair value and the amortized cost of cash, cash equivalents and available-for-sale investments by major security type consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ Cash and ​ ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cash ​ Short-term ​ Long-term September 30, 2021 Cost Gains Losses Value Equivalents ​ Investment ​ Investment Cash, cash equivalents and money market funds ​ $ 113,189 ​ $ — ​ $ — ​ $ 113,189 ​ $ 113,189 ​ $ — ​ $ — ​ U.S. Treasury securities ​ 42,739 ​ ​ — ​ ​ (6) ​ ​ 42,733 ​ ​ — ​ ​ 32,644 ​ ​ 10,089 ​ Corporate debt securities ​ ​ 6,118 ​ ​ — ​ ​ — ​ ​ 6,118 ​ ​ — ​ ​ 6,118 ​ ​ — ​ Certificates of deposit ​ ​ 1,669 ​ 1 ​ — ​ 1,670 ​ — ​ 935 ​ ​ 735 ​ Total ​ $ 163,715 ​ $ 1 ​ $ (6) ​ $ 163,710 ​ $ 113,189 ​ $ 39,697 ​ $ 10,824 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ Cash and ​ ​ ​ ​ ​ ​ Amortized ​ Unrealized ​ Unrealized ​ Fair ​ Cash ​ Short-term ​ Long-term December 31, 2020 Cost Gains Losses Value Equivalents ​ Investment ​ Investment Cash, cash equivalents and money market funds ​ $ 60,789 ​ $ — ​ $ — ​ $ 60,789 ​ $ 60,789 ​ $ — ​ $ — ​ U.S. Treasury securities ​ 150,929 ​ ​ 53 ​ ​ — ​ ​ 150,982 ​ ​ — ​ ​ 150,982 ​ ​ — ​ Corporate debt securities ​ ​ 16,668 ​ ​ — ​ ​ (1) ​ ​ 16,667 ​ ​ — ​ ​ 16,667 ​ ​ — ​ U.S. Agency bonds ​ ​ 10,704 ​ ​ 2 ​ ​ — ​ ​ 10,706 ​ ​ — ​ ​ 10,706 ​ ​ — ​ Certificates of deposit ​ ​ 937 ​ 4 ​ — ​ 941 ​ — ​ 941 ​ — ​ Total ​ $ 240,027 ​ $ 59 ​ $ (1) ​ $ 240,085 ​ $ 60,789 ​ $ 179,296 ​ $ — ​

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	9 Months Ended
	Sep. 30, 2021
Prepaid Expenses and Other Current Assets.
Summary of Prepaid expenses and other current assets	Prepaid expenses and other current assets consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ 2021 2020 Prepaid insurance ​ $ 2,307 ​ $ 1,453 ​ Vendor prepayments and deposits ​ ​ 3,092 ​ ​ 1,557 ​ Prepaid rent ​ 807 ​ 1,397 ​ Tenant improvement receivables ​ ​ 2,589 ​ ​ 3,732 ​ Non-trade receivables ​ 48 ​ 336 ​ Interest receivable and other current assets ​ ​ 337 ​ ​ 562 ​ Total prepaid expenses and other current assets ​ $ 9,180 ​ $ 9,037 ​

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	9 Months Ended
	Sep. 30, 2021
Property and Equipment, net
Summary of property and equipment	Property and equipment consists of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, ​ ​ 2021 2020 Laboratory equipment ​ $ 13,090 ​ $ 11,287 ​ Furniture and fixtures ​ 1,968 ​ 242 ​ Computer hardware and software ​ 1,423 ​ 919 ​ Leasehold improvements ​ 37,841 ​ 667 ​ Construction in process ​ — ​ 14,379 ​ ​ ​ 54,322 ​ 27,494 ​ Less accumulated depreciation and amortization ​ (10,031) ​ (7,663) ​ Total property and equipment, net ​ $ 44,291 ​ $ 19,831 ​

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2021
Accrued Expenses
Summary of accrued expenses	Accrued expenses consist of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ September 30, December 31, ​ ​ 2021 2020 Compensation and related benefits ​ $ 3,876 ​ $ 4,954 Accrued construction costs ​ ​ 11 ​ ​ 4,145 Professional fees ​ ​ 357 ​ ​ 82 Contract research fees ​ ​ 3,440 ​ ​ 809 Accrued cease-use liabilities ​ ​ 1,285 ​ ​ — Other ​ ​ 317 ​ ​ 312 Total accrued expenses ​ $ 9,286 ​ $ 10,302

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies
Schedule of future minimum lease payments under non-cancelable operating and capital lease agreements	​ Future minimum lease payments under non-cancelable operating and capital lease agreements consisted of the following at September 30, 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ Capital Operating ​ ​ Leases ​ Leases Years ending December 31: ​ ​ ​ ​ ​ ​ 2021 (remaining 3 months) ​ $ 13 ​ $ 2,408 2022 ​ 4 ​ 7,944 2023 ​ — ​ 7,644 2024 ​ ​ — ​ ​ 7,855 2025 ​ ​ — ​ ​ 8,072 Thereafter ​ ​ — ​ ​ 66,453 Total minimum lease payments ​ 17 ​ $ 100,376 Less: amount representing interest ​ — ​ ​ ​ Present value of capital lease obligation ​ 17 ​ ​ ​ Less: current portion ​ (17) ​ ​ ​ Non-current portion ​ $ — ​ ​ ​

Equity Incentive Plans (Tables)

Equity Incentive Plans (Tables)	9 Months Ended
	Sep. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of stock option activity	Stock option activity under the 2019 Plan and the Company’s 2010 Plan is as follow: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options Outstanding ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Average ​ Aggregate ​ ​ ​ ​ Weighted- ​ Remaining ​ Intrinsic ​ ​ Number ​ Average ​ Contractual ​ Value ​ of Shares ​ Exercise Price ​ Life (years) ​ (in thousands) Balances, December 31, 2020 4,812,223 ​ $ 13.33 ​ 8.2 ​ $ 21,493 Granted 1,829,770 ​ 13.29 ​ ​ ​ Exercised (46,793) ​ 5.82 ​ ​ ​ Cancelled (580,209) ​ 15.12 ​ ​ ​ Balances, September 30, 2021 6,014,991 ​ $ 13.20 ​ 8.0 ​ $ 1,377 Vested and expected to vest at September 30, 2021 6,014,991 ​ $ 13.20 ​ 8.0 ​ $ 1,377 Exercisable at September 30, 2021 3,144,958 ​ $ 11.40 ​ 7.3 ​ $ 1,376 Vested at September 30, 2021 3,011,904 ​ $ 11.68 ​ 7.4 ​ $ 1,233
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ ​ Nine Months Ended September 30, ​ ​ ​ 2021 2020 2021 2020 Expected life (in years) 6.01 6.01 ​ 5.97 5.85 ​ ​ Volatility 90.0 % 88.5 % 91.4 % 85.6 % ​ Risk-free interest rate 1.0 % 0.4 % 0.6 % 1.1 % ​
Schedule of summarizes RSU activity	The following table summarizes RSU activity for the nine months ended September 30, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-Average ​ ​ Number ​ Grant Date ​ of Shares ​ Fair Value per RSU Unvested Balances, December 31, 2020 — ​ $ — RSUs Granted 884,820 ​ 6.15 RSUs Vested ​ — ​ ​ — RSUs Cancelled (3,330) ​ 6.15 Unvested Balances, September 30, 2021 881,490 ​ $ 6.15
Schedule of stock-based compensation expense	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ ​ 2021 2020 2021 2020 Research and development ​ $ 1,946 ​ $ 1,628 ​ $ 6,080 ​ $ 4,490 ​ General and administrative ​ 1,907 ​ 1,859 ​ 6,055 ​ 4,863 ​ ​ ​ $ 3,853 ​ $ 3,487 ​ $ 12,135 ​ $ 9,353 ​
2019 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ ​ Nine Months Ended September 30, ​ ​ ​ 2021 2020 2021 2020 Expected life (in years) 0.5 - 2.0 0.5 - 2.0 ​ 0.5 - 2.0 0.5 - 2.0 ​ ​ Volatility 91.1 - 98.5 % 103.4 - 114.6 % 91.1 - 107.6 % 91.4 - 114.6 % ​ Risk-free interest rate 0.1 - % 0.1 % 0.1 - % 0.1 - % ​

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Net Loss Per Share
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, ​ Nine Months Ended September 30, ​ 2021 2020 2021 2020 Common stock options ​ ​ 6,014,991 ​ ​ 4,920,857 ​ ​ 6,014,991 ​ ​ 4,920,857 Unvested restricted stock units ​ ​ 881,490 ​ ​ — ​ ​ 881,490 ​ ​ — Common stock warrants ​ 49,997 ​ 49,997 ​ 49,997 ​ 49,997 ​ ​ ​ 6,946,478 ​ ​ 4,970,854 ​ ​ 6,946,478 ​ ​ 4,970,854

Business (Details)

Business (Details)	9 Months Ended
	Sep. 30, 2021segment
Business
Number of Operating Segments	1

Summary of Significant Accoun_4

Summary of Significant Accounting Policies (Details)	1 Months Ended
	Jul. 31, 2020	Feb. 29, 2020	Sep. 30, 2021USD ($)Institution	Dec. 31, 2020USD ($)Institution	Sep. 30, 2020USD ($)	Dec. 31, 2019USD ($)
Other Income
Expected service period		18 months
Cash and cash equivalents and restricted cash reported within the condensed balance sheets
Cash and cash equivalents			$ 113,189,000	$ 60,789,000
Restricted cash			$ 1,458,000	1,652,000
Restricted Cash, Asset, Statement of Financial Position [Extensible List]			Deposits and Others
Cash, cash equivalents and restricted cash shown in the consolidated statements of cash flows			$ 114,647,000	$ 62,441,000	$ 134,724,000	$ 159,236,000
Concentration of credit risk
Number of financial institutions holding cash and cash and cash equivalents | Institution			2	2
Research cost sharing provision receivable			$ 1,000
Prepaid expenses and other current assets
Other Income
Receivables under service agreements			0	$ 13,000
Other current liabilities
Other Income
Contract liabilities			$ 0	$ 800,000
Xencor Inc [Member] | Collaboration And License Agreement
Concentration of credit risk
Percentage of costs and profit shared by partners	50.00%

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Financial assets and liabilities (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Maximum
Company's financial assets and liabilities subject to fair value measurements on a recurring basis
Remaining contractual maturity of marketable securities (in years)	2 years	2 years
Recurring basis
Assets
Total assets	$ 158,567	$ 237,247
Recurring basis | Cash, cash equivalents and money market funds
Assets
Total assets	108,046	57,951
Recurring basis | Certificates of deposit
Assets
Total assets	1,670	941
Recurring basis | Corporate debt securities
Assets
Total assets	6,118	16,667
Recurring basis | U.S. Treasury securities
Assets
Total assets	42,733	150,982
Recurring basis | U.S. Agency bonds
Assets
Total assets		10,706
Recurring basis | Level 1
Assets
Total assets	152,449	209,874
Recurring basis | Level 1 | Cash, cash equivalents and money market funds
Assets
Total assets	108,046	57,951
Recurring basis | Level 1 | Certificates of deposit
Assets
Total assets	1,670	941
Recurring basis | Level 1 | Corporate debt securities
Assets
Total assets	0	0
Recurring basis | Level 1 | U.S. Treasury securities
Assets
Total assets	42,733	150,982
Recurring basis | Level 1 | U.S. Agency bonds
Assets
Total assets		0
Recurring basis | Level 2
Assets
Total assets	6,118	27,373
Recurring basis | Level 2 | Cash, cash equivalents and money market funds
Assets
Total assets	0	0
Recurring basis | Level 2 | Certificates of deposit
Assets
Total assets	0	0
Recurring basis | Level 2 | Corporate debt securities
Assets
Total assets	6,118	16,667
Recurring basis | Level 2 | U.S. Treasury securities
Assets
Total assets	$ 0	0
Recurring basis | Level 2 | U.S. Agency bonds
Assets
Total assets		$ 10,706

Cash, Cash Equivalents and In_3

Cash, Cash Equivalents and Investments - Fair value and Amortized cost (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents	$ 113,189	$ 60,789
Short-term Investment	39,697	179,296
Long-term Investment	10,824
Cash, cash equivalents and money market funds
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents	113,189	60,789
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	113,189	60,789
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	113,189	60,789
U.S. Treasury securities
Cash and Cash Equivalents [Line Items]
Short-term Investment	32,644	150,982
Long-term Investment	10,089
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	42,739	150,929
Gross Unrealized Gains	0	53
Gross Unrealized Losses	(6)	0
Estimated Fair Value	42,733	150,982
Corporate debt securities
Cash and Cash Equivalents [Line Items]
Short-term Investment	6,118	16,667
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	6,118	16,668
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(1)
Estimated Fair Value	6,118	16,667
U.S. Agency bonds
Cash and Cash Equivalents [Line Items]
Short-term Investment		10,706
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost		10,704
Gross Unrealized Gains		2
Gross Unrealized Losses		0
Estimated Fair Value		10,706
Certificates of deposit
Cash and Cash Equivalents [Line Items]
Short-term Investment	935	941
Long-term Investment	735
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	1,669	937
Gross Unrealized Gains	1	4
Gross Unrealized Losses	0	0
Estimated Fair Value	1,670	941
Total
Cash and Cash Equivalents [Line Items]
Cash and Cash Equivalents	113,189	60,789
Short-term Investment	39,697	179,296
Total
Cash and Cash Equivalents [Line Items]
Long-term Investment	10,824
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	163,715	240,027
Gross Unrealized Gains	1	59
Gross Unrealized Losses	(6)	(1)
Estimated Fair Value	$ 163,710	$ 240,085

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Prepaid Expenses and Other Current Assets.
Prepaid Insurance	$ 2,307	$ 1,453
Vendor prepayments and deposits	3,092	1,557
Prepaid rent	807	1,397
Tenant improvement receivables	2,589	3,732
Non-trade receivables	48	336
Interest receivables and other current assets	337	562
Total prepaid expenses and other current assets	$ 9,180	$ 9,037

Property and Equipment, net (De

Property and Equipment, net (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 54,322,000		$ 54,322,000		$ 27,494,000
Less accumulated depreciation and amortization	(10,031,000)		(10,031,000)		(7,663,000)
Total property and equipment, net	44,291,000		44,291,000		19,831,000
Depreciation expense	1,400,000	$ 600,000	3,200,000	$ 1,800,000
Net book value of property and equipment under capital leases	15,000		15,000		49,000
Laboratory equipment
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	13,090,000		13,090,000		11,287,000
Furniture and fixtures
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	1,968,000		1,968,000		242,000
Computer hardware and software
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	1,423,000		1,423,000		919,000
Leasehold improvements
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	37,841,000		37,841,000		667,000
Construction-in-process
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 0		$ 0		$ 14,379,000

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accrued Expenses
Compensation and related benefits	$ 3,876	$ 4,954
Accrued construction costs	11	4,145
Professional fees	357	82
Contract research fees	3,440	809
Accrued cease-use liabilities	1,285	0
Other	317	312
Total accrued expenses	$ 9,286	$ 10,302

Commitments and Contingencies_2

Commitments and Contingencies (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2017
Operating leases
Rent expenses	$ 1,900,000	$ 2,900,000	$ 8,200,000	$ 6,700,000
Gain (loss) on termination of lease			(1,500,000)
Lease termination, cease use lease liability	$ 1,300,000		$ 1,300,000
Capital lease
Purchases under capital lease					$ 226,000

Commitments and Contingencies -

Commitments and Contingencies - Future Minimum Lease Payments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Future minimum capital leases:
2021 (remaining 3 months)	$ 13
2022	4
Total minimum lease payments	17
Present value of capital lease obligation	17
Less: current portion	(17)
Non-current portion		$ 4
Future minimum operating leases:
2021 (remaining 3 months)	2,408
2022	7,944
2023	7,644
2024	7,855
2025	8,072
Thereafter	66,453
Total minimum lease payments	$ 100,376

Capital Stock (Details)

Capital Stock (Details) $ / shares in Units, $ in Millions	Jun. 02, 2019Vote$ / sharesshares	Aug. 31, 2020USD ($)	Sep. 30, 2021$ / sharesshares	Dec. 31, 2020$ / sharesshares
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	300,000,000
Preferred stock par value | $ / shares	$ 0.0001
At The Market Offering [Member]
Class of Stock [Line Items]
Percentage of gross proceeds as compensation for services		3.00%
Shares sold			0
Class A common stock
Class of Stock [Line Items]
Common stock, shares authorized	650,000,000		650,000,000	650,000,000
Common stock, par value | $ / shares	$ 0.0001		$ 0.0001	$ 0.0001
Number of votes entitled per share | Vote	1
Class A common stock | At The Market Offering [Member]
Class of Stock [Line Items]
Share offering price | $		$ 100
Class B common stock
Class of Stock [Line Items]
Common stock, shares authorized	50,000,000		50,000,000	50,000,000
Common stock, par value | $ / shares	$ 0.0001		$ 0.0001	$ 0.0001

Equity Incentive Plan - Narrati

Equity Incentive Plan - Narrative (Details) - 2019 Plan	Jun. 19, 2019shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance	6,141,842
Percentage of additional number of shares authorized annually	4.00%

Equity Incentive Plan - Stock o

Equity Incentive Plan - Stock option (Details) - 2019 Plan - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Number of Shares
Balance at beginning of period (in shares)	4,812,223
Granted (in shares)	1,829,770
Exercised (in shares)	(46,793)
Cancelled (in shares)	(580,209)
Balance at end of period (in shares)	6,014,991	4,812,223
Vested and expected to vest at end of period (in shares)	6,014,991
Exercisable at end of period (in shares)	3,144,958
Vested at end of period (in shares)	3,011,904
Weighted-Average Exercise Price
Balance at beginning of period (in dollars per share)	$ 13.33
Granted (in dollars per share)	13.29
Exercised (in dollars per share)	5.82
Cancelled (in dollars per share)	15.12
Balance at end of period (in dollars per share)	13.20	$ 13.33
Vested and expected to vest at end of period (in dollars per share)	13.20
Exercisable at end of period (in dollars per share)	11.40
Vested at end of period (in dollars per share)	$ 11.68
Weighted-Average Remaining Contractual Life
Weighted-Average Remaining Contractual Life	8 years	8 years 2 months 12 days
Vested and expected to vest at end of period (in years)	8 years
Exercisable at end of period (in years)	7 years 3 months 18 days
Vested at end of period (in years)	7 years 4 months 24 days
Aggregate Intrinsic Value
Balance at beginning of period	$ 21,493
Balance at end of period	1,377	$ 21,493
Vested and expected to vest at end of period	1,377
Exercisable at end of period	1,376
Vested at end of period	$ 1,233

Equity Incentive Plan - Weighte

Equity Incentive Plan - Weighted-average grant date fair value (Details) - 2019 Plan - $ / shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value (in dollars per share)	$ 9.85	$ 13.55
Expected dividend	0.00%	0.00%

Equity Incentive Plan - Weigh_2

Equity Incentive Plan - Weighted average assumptions (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
2019 Plan
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected life (in years)	6 years 3 days	6 years 3 days	5 years 11 months 19 days	5 years 10 months 6 days
Volatility	90.00%	88.50%	91.40%	85.60%
Risk-free interest rate	1.00%	0.40%	0.60%	1.10%
2019 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate		0.10%
2019 Employee Stock Purchase Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected life (in years)	6 months	6 months	6 months	6 months
Volatility	91.10%	103.40%	91.10%	91.40%
Risk-free interest rate	0.10%		0.10%	0.10%
2019 Employee Stock Purchase Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected life (in years)	2 years	2 years	2 years	2 years
Volatility	98.50%	114.60%	107.60%	114.60%
Risk-free interest rate	0.20%		0.20%	1.10%

Equity Incentive Plan - Restric

Equity Incentive Plan - Restricted Stock Units (Details) - Unvested restricted stock units	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Number of Shares
RSUs Granted (in shares) | shares	884,820
RSUs Cancelled (in shares) | shares	(3,330)
Unvested balance, at end of period (in shares) | shares	881,490
Weighted-Average Grant Date Fair Value per RSU
RSUs Granted (in dollars per share) | $ / shares	$ 6.15
RSUs Cancelled (in dollars per share) | $ / shares	6.15
Weighted-Average Grant Date Fair Value per RSU Unvested balance, at end of period (in dollars per share) | $ / shares	$ 6.15
2019 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	2 years
Vesting on the one year anniversary | 2019 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	50.00%
Vesting on the two year anniversary | 2019 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	50.00%

Equity Incentive Plan - 2019 Em

Equity Incentive Plan - 2019 Employee Stock Purchase Plan (Details) - USD ($)	Jun. 19, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 3,853,000	$ 3,487,000	$ 12,135,000	$ 9,353,000
Class A common stock | 2019 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance	283,333
Stock-based compensation expense		$ 204,000	$ 194,000	$ 608,000	$ 525,000
Expected dividend				0.00%
Class A common stock | 2019 Employee Stock Purchase Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of additional number of shares authorized annually	1.00%
Additional number of shares authorized annually	416,666

Equity Incentive Plan - Stock-b

Equity Incentive Plan - Stock-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,853	$ 3,487	$ 12,135	$ 9,353
Income tax benefits for stock-based compensation			0
Stock-based compensation costs capitalized			0
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,946	1,628	6,080	4,490
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,907	$ 1,859	$ 6,055	$ 4,863

Equity Incentive Plan - Unrecog

Equity Incentive Plan - Unrecognized compensation (Details) - 2019 Plan $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)
Common stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 30
Remaining weighted-average requisite service period	2 years 6 months
Unvested restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 5.3
Remaining weighted-average requisite service period	1 year 10 months 24 days

401(k) Plan (Details)

401(k) Plan (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
401 (k) Plan
Employer contribution (as a percent)		100.00%
Amount up to which the employer matches 100 percent contribution		$ 5,000
Total matching contributions	$ 100,000	$ 600,000

Net Loss Per Share - Antidiluti

Net Loss Per Share - Antidilutive securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the diluted net loss per share calculation	6,946,478	4,970,854	6,946,478	4,970,854
Common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the diluted net loss per share calculation	6,014,991	4,920,857	6,014,991	4,920,857
Unvested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the diluted net loss per share calculation	881,490		881,490
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the diluted net loss per share calculation	49,997	49,997	49,997	49,997

Income Taxes (Details)

Income Taxes (Details)	Mar. 27, 2020
Income Taxes
Percentage of taxable income limitation of net operating loss carryforwards	80.00%
Period of operating loss carryback	5 years

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Other income	$ 0	$ 2,000	$ 1,000	$ 187,000
Receivable from stockholders	0		0		$ 13,000
Due to related party	74,000		74,000		74,000
Research and development expense	63,000	61,000	188,000	188,000
Intellectual property related legal fees
Related Party Transaction [Line Items]
Expense	300,000	300,000	1,000,000	1,000,000
Due to related party	91,000		91,000		69,000
Other legal fees
Related Party Transaction [Line Items]
Expense	200,000	$ 400,000	600,000	$ 1,300,000
Due to related party	$ 248,000		$ 248,000		$ 250,000