Atreca Inc - Ordinary Shares (BCEL) 10-Q 13 Aug 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Aug. 13, 2019
Document Type	10-Q
Document Period End Date	Jun. 30, 2019
Entity Registrant Name	ATRECA, INC.
Entity Current Reporting Status	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Shell Company	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Entity Central Index Key	0001532346
Amendment Flag	false
Entity Ex Transition Period	false
Class A common stock
Entity Common Stock, Shares Outstanding		22,013,578
Class B common stock
Entity Common Stock, Shares Outstanding		5,934,191

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current Assets
Cash and cash equivalents	$ 154,959	$ 114,504
Investments	64,703
Prepaid expenses and other current assets	2,589	2,721
Total current assets	222,251	117,225
Property and equipment, net	4,155	4,143
Deposits and other	974	316
Total assets	227,380	121,684
Current Liabilities
Accounts payable	3,942	1,307
Accrued expenses	4,299	3,008
Other current liabilities	158	247
Capital lease obligations, current portion	45
Total current liabilities	8,399	4,562
Capital lease obligations, net of current portion	77	100
Deferred rent	22	6
Preferred stock warrant liability		380
Total liabilities	8,498	5,048
Stockholders’ equity (deficit)
Additional paid-in capital	346,915	3,593
Accumulated other comprehensive loss	86	(4)
Accumulated deficit	(128,122)	(96,622)
Total stockholders’ equity (deficit)	218,882	(93,033)
Total liabilities and stockholders’ equity (deficit)	227,380	121,684
Series A convertible preferred stock
Current Liabilities
Convertible preferred stock		55,030
Series B convertible preferred stock
Current Liabilities
Convertible preferred stock		34,333
Series C1 convertible preferred stock
Current Liabilities
Convertible preferred stock		65,691
Series C2 convertible preferred stock
Current Liabilities
Convertible preferred stock		$ 54,615
Class A common stock
Stockholders’ equity (deficit)
Common stock	2
Class B common stock
Stockholders’ equity (deficit)
Common stock	$ 1

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Series A convertible preferred stock
Convertible preferred stock, par value	$ 0.0001	$ 0.0001
Convertible preferred stock, shares authorized	100,000,000	32,133,287
Convertible preferred stock, shares issued	0	5,305,513
Convertible preferred stock, shares outstanding	0	5,305,513
Convertible preferred stock, aggregate liquidation preference	$ 58,892	$ 58,892
Series B convertible preferred stock
Convertible preferred stock, par value	$ 0.0001	$ 0.0001
Convertible preferred stock, shares authorized	100,000,000	18,008,749
Convertible preferred stock, shares issued	0	3,001,421
Convertible preferred stock, shares outstanding	0	3,001,421
Convertible preferred stock, aggregate liquidation preference	$ 35,000	$ 35,000
Series C1 convertible preferred stock
Convertible preferred stock, par value	$ 0.0001	$ 0.0001
Convertible preferred stock, shares authorized	50,000,000	54,184,549
Convertible preferred stock, shares issued	0	5,007,134
Convertible preferred stock, shares outstanding	0	5,007,134
Convertible preferred stock, aggregate liquidation preference	$ 70,000	$ 70,000
Series C2 convertible preferred stock
Convertible preferred stock, par value	$ 0.0001	$ 0.0001
Convertible preferred stock, shares authorized	50,000,000	23,605,150
Convertible preferred stock, shares issued	0	3,934,191
Convertible preferred stock, shares outstanding	0	3,934,191
Convertible preferred stock, aggregate liquidation preference	$ 55,000	$ 55,000
Class A common stock
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	650,000,000	191,398,492
Common stock, shares issued	22,013,010	2,119,872
Common stock, shares outstanding	22,013,010	2,119,872
Class B common stock
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	50,000,000	23,605,150
Common stock, shares issued	5,934,191	0
Common stock, shares outstanding	5,934,191	0

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Expenses
Research and development	$ 15,922	$ 7,419	$ 27,635	$ 14,062
General and administrative	3,537	1,632	6,055	2,932
Total expenses	19,459	9,051	33,690	16,994
Interest and other income (expense)
Other income	1,021	347	1,186	560
Interest income	594	33	1,139	90
Interest expense	(2)	(2)	(4)	(5)
Preferred stock warrant liability revaluation	(73)	7	(123)	27
Loss on disposal of property and equipment	(2)	(1)	(7)	(1)
Loss before income tax expense	(17,921)	(8,667)	(31,499)	(16,323)
Income tax expense		(1)	(1)	(1)
Net loss	$ (17,921)	$ (8,668)	$ (31,500)	$ (16,324)
Net loss per share, basic and diluted	$ (3.67)	$ (4.13)	$ (8.97)	$ (7.79)
Weighted-average shares used in computing net loss per share, basic and diluted	4,888,987,000	2,097,296,000	3,512,606	2,095,363

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net loss	$ (17,921)	$ (8,668)	$ (31,500)	$ (16,324)
Other comprehensive income (loss);
Unrealized gain (loss) on fair value of investments	61	16	89	21
Unrealized gain on currency translation	2	(17)	1	(24)
Comprehensive loss	$ (17,858)	$ (8,669)	$ (31,410)	$ (16,327)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit - USD ($)	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Convertible preferred stock (as converted)	Total
Balances at beginning at Dec. 31, 2017					$ 89,362,000
Balances at beginning (in shares) at Dec. 31, 2017					8,306,934
Balances at beginning at Dec. 31, 2017		$ 2,130,000	$ (14,000)	$ (58,682,000)		$ (56,566,000)
Balances at beginning (in shares) at Dec. 31, 2017	2,092,040
Issuance of common stock upon initial public offering, net (in shares)	18,500
Issuance of common stock upon exercise of options		9,000				9,000
Stock-based compensation		490,000				490,000
Unrealized gain (loss) on fair value of investments			21,000			21,000
Unrealized gain on currency translation			(24,000)			(24,000)
Net loss				(16,324,000)		(16,324,000)
Balances at end at Jun. 30, 2018					$ 89,362,000
Balances at end (in shares) at Jun. 30, 2018					8,306,934
Balances at end at Jun. 30, 2018		2,629,000	(17,000)	(75,006,000)		(72,394,000)
Balances at end (in shares) at Jun. 30, 2018	2,110,540
Balances at beginning at Mar. 31, 2018					$ 89,362,000
Balances at beginning (in shares) at Mar. 31, 2018					8,306,934
Balances at beginning at Mar. 31, 2018		2,243,000	(16,000)	(66,338,000)		(64,111,000)
Balances at beginning (in shares) at Mar. 31, 2018	2,093,473
Issuance of common stock upon exercise of options	$ 17,067	9,000				9,000
Stock-based compensation		377,000				377,000
Unrealized gain (loss) on fair value of investments			16,000			16,000
Unrealized gain on currency translation			(17,000)			(17,000)
Net loss				(8,668,000)		(8,668,000)
Balances at end at Jun. 30, 2018					$ 89,362,000
Balances at end (in shares) at Jun. 30, 2018					8,306,934
Balances at end at Jun. 30, 2018		2,629,000	(17,000)	(75,006,000)		(72,394,000)
Balances at end (in shares) at Jun. 30, 2018	2,110,540
Balances at beginning at Dec. 31, 2018					$ 209,668,000
Balances at beginning (in shares) at Dec. 31, 2018					17,248,259
Balances at beginning at Dec. 31, 2018		3,593,000	(4,000)	(96,622,000)		(93,033,000)
Balances at beginning (in shares) at Dec. 31, 2018	2,119,872
Conversion of convertible preferred stock					$ (209,668,000)	209,669,000
Conversion of convertible preferred stock (in shares)					(17,248,259)
Conversion of convertible preferred stock	$ 2,000	209,666,000				209,668,000
Conversion of convertible preferred stock (in shares)	17,248,259
Issuance of common stock upon initial public offering, net	$ 1,000	130,785,000				130,786,000
Issuance of common stock upon initial public offering, net (in shares)	8,452,500
Exercise of warrants (in shares)	62,936
Issuance of common stock upon exercise of options		231,000				231,000
Issuance of common stock upon exercise of options (in shares)	63,634
Vesting of early exercised stock options		2,000				2,000
Reclassification of redeemable convertible preferred stock warrant liability to additional paid-in capital		503,000				503,000
Stock-based compensation		2,135,000				2,135,000
Unrealized gain (loss) on fair value of investments			89,000			89,000
Unrealized gain on currency translation			1,000			1,000
Net loss				(31,500,000)		(31,500,000)
Balances at end at Jun. 30, 2019	$ 3,000	346,915,000	86,000	(128,122,000)		218,882,000
Balances at end (in shares) at Jun. 30, 2019	27,947,201
Balances at beginning at Mar. 31, 2019					$ 209,668,000
Balances at beginning (in shares) at Mar. 31, 2019					17,248,259
Balances at beginning at Mar. 31, 2019		4,383,000	23,000	(110,201,000)		(105,795,000)
Balances at beginning (in shares) at Mar. 31, 2019	2,123,257
Conversion of convertible preferred stock					$ (209,668,000)
Conversion of convertible preferred stock (in shares)					(17,248,259)
Conversion of convertible preferred stock	$ 2,000	209,666,000				209,668,000
Conversion of convertible preferred stock (in shares)	17,248,259
Issuance of common stock upon initial public offering, net	$ 1,000	130,785,000				130,786,000
Issuance of common stock upon initial public offering, net (in shares)	8,452,500
Exercise of warrants (in shares)	62,936
Issuance of common stock upon exercise of options		217,000				217,000
Issuance of common stock upon exercise of options (in shares)	60,249
Vesting of early exercised stock options		2,000				2,000
Reclassification of redeemable convertible preferred stock warrant liability to additional paid-in capital		503,000				503,000
Stock-based compensation		1,359,000				1,359,000
Unrealized gain (loss) on fair value of investments			61,000			61,000
Unrealized gain on currency translation			2,000			2,000
Net loss				(17,921,000)		(17,921,000)
Balances at end at Jun. 30, 2019	$ 3,000	$ 346,915,000	$ 86,000	$ (128,122,000)		$ 218,882,000
Balances at end (in shares) at Jun. 30, 2019	27,947,201

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash Flows from Operating Activities
Net loss	$ (31,500)	$ (16,324)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	792	667
Loss on disposal of property and equipment	7	1
Stock-based compensation	2,135	490
Preferred stock warrant liability revaluation	123	(27)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	160	(400)
Accounts payable	1,935	43
Accrued expenses	(231)	(598)
Other current liabilities	(136)
Deferred rent	(13)	24
Net cash used in operating activities	(26,728)	(16,124)
Cash Flows from Investing Activities
Purchase of property and equipment	(810)	(618)
Purchase of investments	(84,613)
Proceeds from maturities of investments	20,000	14,899
Change in deposits	66	9
Net cash provided by (used in) investing activities	(65,357)	14,290
Cash Flows from Financing Activities
Proceeds from exercise of stock options	248	9
Proceeds from the initial public offering, net	133,618
Principal payments on capital lease obligations	(25)	(23)
Payments of initial offering costs	(577)
Net cash provided by (used in) financing activities	133,264	(14)
Net change in cash, cash equivalents and restricted stock	41,179	(1,848)
Cash, cash equivalents and restricted cash, beginning of period	114,504	8,242
Cash, cash equivalents and restricted cash, end of period	155,683	6,394
Supplemental Disclosure of Cash Flow Information
Cash paid for interest	3	$ 4
Cash paid for income taxes	1
Supplemental Schedule of Non-Cash Investing and Financing Activities
Costs related to initial public offering included in accounts payable and accrued liabilities	2,271
Conversion of redeemable convertible preferred stock to common stock	209,669
Reclassification of redeemable convertible preferred stock warrant liability to additional paid-in capital	(503)
Vesting of early exercised common stock options	$ 2

Business

Business	6 Months Ended
	Jun. 30, 2019
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 Redwood City, California. In April 2016, the Company formed a wholly owned subsidiary, Atreca Pte. Ltd., in Singapore. 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 preclinical development with a novel mechanism of action and target derived from an antibody identified using its discovery platform. The Company operates in a single segment. Since inception, the Company has been primarily engaged in research and development, raising capital, building its management team and building its intellectual property portfolio. Reverse Stock Split On June 7, 2019, the Company effected a 1-for-6 reverse stock split of all classes of its capital stock. Upon the effectiveness of the reverse stock split, (i) every one share of the Company’s outstanding capital stock was combined into one-sixth of one share of the same class and series of capital stock, (ii) the number of shares of its Class A common stock and its Series A preferred stock for which each outstanding option or warrant, to purchase its Class A common stock and its Series A preferred stock is exercisable was proportionally decreased on a 1-for-6 basis and (iii) the exercise price of each outstanding option or warrant to purchase its Class A common stock and its Series A preferred stock was proportionately increased on a 1-for-6 basis. The par value per share of its common stock and preferred stock were not adjusted as a result of the reverse stock split. Initial Public Offering In June 2019, the Company closed its initial public offering (“IPO”) of 6,452,500 shares of its Class A common stock and 2,000,000 shares of its Class B common stock at an offering price of $17.00 per share, including 1,102,500 shares pursuant to the underwriters’ option to purchase additional shares of the Company’s Class A common stock. The Company received net proceeds of $130.8 million, after deducting underwriting discounts and commissions of $10.1 million and offering expenses of $2.8 million. Immediately prior to the closing of the IPO, all outstanding shares of the Company’s convertible Series A preferred stock, convertible Series B preferred stock and convertible Series C1 preferred stock automatically converted into 13,314,068 shares of the Company’s Class A common stock and all outstanding shares of the Company’s convertible Series C2 preferred stock automatically converted into 3,934,191 shares of the Company’s Class B common stock. Immediately prior to the closing of the IPO, the Company issued 62,936 shares of Class A common stock upon the exercise of an outstanding warrant. The Company reclassified $209.7 million from temporary equity to Class A common stock, Class B common stock, and additional paid-in-capital on its consolidated balance sheet. Deferred Offering Cost Deferred offering cost of $2.8 million, consisting of legal, accounting and other fees and costs related to the IPO, were reclassified to additional paid-in capital as a reduction of the proceeds upon the closing of the IPO in June 2019. During the six months ended June 30, 2019, $0.6 million of the deferred offering costs were paid.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2019
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The 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 subsidiaries. All intercompany transactions and accounts have been eliminated. 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 final prospectus for its IPO dated as of June 19, 2019 and filed with the SEC pursuant to Rule 424(b)(4) under the Securities Act of 1933, as amended, on June 20, 2019. Prior period reclassification An immaterial reclassification of prior period amounts has been made to conform to the current period presentation. 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 consolidated financial statements and accompanying notes. Actual results could differ from those estimates. Key estimates in the 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 preferred stock and 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 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 June 30, 2019 and its results of operations and cash flows for the six months ended June 30, 2018 and 2019. The financial data and the other financial information contained in these notes to the condensed consolidated financial statements related to the three-month and six-month periods are also unaudited. The condensed results of operations for the three months ended and six months ended June 30, 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or for any other future annual or interim period. The condensed consolidated balance sheet as of December 31, 2018 included herein was derived from the audited consolidated financial statements as of that date. 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 Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“Topic 606”). The guidance provides a unified model to determine how income is recognized. 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 $440,000 and $282,000 are included in prepaid expenses and other current assets as of June 30, 2019 and December 31, 2018, respectively. Contract liabilities of $64,000 and $200,000 are included in other current liabilities as of June 30, 2019 and December 31, 2018, 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 $724,000 and $0 as of June 30, 2019 and December 31, 2018, respectively. This amount as of June 30, 2019 is included in deposits and other in the accompanying condensed consolidated balance sheets and is comprised solely of a letter of credit required pursuant to a lease for Company facilities. The following table provides a 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. June 30, December 31, 2019 2018 Cash and cash equivalents $ 154,959 $ 114,504 Restricted cash 724 — Cash, cash equivalents and restricted cash shown in the condensed consolidated statements of cash flows $ 155,683 $ 114,504 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. Convertible Preferred Stock Warrants The Company issued convertible preferred stock warrants, which were exercisable into series A preferred stock with liquidation preference. The conversion feature was evaluated under ASC Topic 480 Distinguishing liabilities from equity and the warrants were determined to be debt instruments and classified prior to the IPO as liabilities on the consolidated balance sheets. The Company recorded these warrant liabilities at fair value and adjusted the carrying value to their estimated fair value at each reporting date with the increases or decreases in the fair value recorded as a gain (loss) on revaluation of the warrant liability in the consolidated statements of operations. Upon the IPO, t he 49,997 preferred stock warrants were converted to common stock warrants of Class A shares and the warrant liability of $0.5 million was reclassified to additional paid-in capital as a result of the conversion. The warrants were not subject to further remeasurement for fair value. Risks and Uncertainties The Company is subject to a number of risks associated with companies at a similar stage, including 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 one financial institution and were in excess of the Federal Deposit Insurance Corporation insurable limit at June 30, 2019 and December 31, 2018. Additionally, cash and cash equivalents and investments are maintained at a brokerage firm 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 development. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers in connection with preclinical 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. 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. Recent Accounting Pronouncements In February 2016, the FASB issued ASU 2016‑02 and subsequent amendments to the initial guidance under ASU 2017-13, ASU 2018-10 and ASU 2018-11 (collectively, “Topic 842” ), which modifies the 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 is effective for the Company as of January 1, 2020. Early adoption is permitted. The Company’s most significant lease is its operating lease for its corporate headquarters, and, while the Company has not yet estimated the amounts by which its financial statements will be affected by the adoption of this guidance, it expects that the overall recognition of expense will be similar to current guidance, but that there will be a significant change in the balance sheet due to the recognition of right of use assets and the corresponding lease liabilities. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses ( “Topic 326” ): Measurement of Credit Losses on Financial Instruments and subsequent amendments to the initial guidance under ASU 2018-19, ASU 2019-04 and ASU 2019-05, which amends the current approach to estimate credit losses on certain financial assets, including trade and other receivables. The amendment replaces the existing incurred loss impairment model with an expected loss methodology, which will result in more timely recognition of credit losses. For available-for-sale debt securities, credit losses should be recorded through an allowance for credit losses. The Company is currently evaluating the impact the adoption of this standard will have on its consolidated financial statements and related disclosures. In August 2016, the FASB issued ASU 2016‑15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments ( “Topic 230” ). The standard clarifies how certain cash receipts and cash payments will be presented and classified in the statement of cash flows. Topic 230 is effective for the Company as of January 1, 2019. The adoption of this update had no material effect on the Company’s consolidated financial statements.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 2019
Fair Value of Financial Instruments
Fair Value of Financial Instruments	3. Fair Value of Financial Instruments The Company’s financial assets and liabilities subject to fair value measurements on a recurring basis and the level of inputs used for such measurements were as follows: June 30, 2019 Level 1 Level 2 Level 3 Total Assets Money market funds 150,477 — — 150,477 U.S. Treasury securities 64,703 — — 64,703 Total $ 215,180 $ — $ — $ 215,180 December 31, 2018 Level 1 Level 2 Level 3 Total Assets Money market funds $ 109,630 $ — $ — $ 109,630 Total $ 109,630 $ — $ — $ 109,630 Liabilities Warrant liability $ — $ — $ $ Total $ — $ — $ $ 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 net asset values were readily available. As of June 30, 2019 and December 31, 2018, gross unrealized gains and unrealized losses for cash equivalents and short-term investments were not material, and the contractual maturity of all marketable securities was less than one year. The fair value of the warrants was calculated using the Black-Scholes option pricing model and was revalued to fair value at the end of each reporting period until the warrants were converted to common stock warrants effective with the closing of the IPO on June 24, 2019. The liability was valued using the following assumptions: December 31, 2018 Exercise price (1) $ 14.46 Stock price (2) $ 13.20 Time to maturity (in years) 3.64 Volatility (3) 83.7 % Risk-free interest rate (4) 2.50 % Expected dividend $ — (1) Based upon terms provided in the warrant agreement. (2) Based upon an independently prepared valuation as of December 31, 2018, adjusted for the one-for-six reverse stock split . (3) Based upon the historical daily volatility of a group of peer public company closing prices. (4) Based upon interest rate for U.S. Treasury Bonds, as published by the U.S. Federal Reserve. The preferred stock warrants were previously valued at Level 3 as there were no observable inputs supported by market activity. The Company estimated the fair value of the preferred stock warrants using the Black-Scholes model which considers various potential liquidity outcomes and assigned probabilities to each to arrive at the weighted equity value. Upon the IPO, t he 49,997 preferred stock warrants were revalued and converted to common stock warrants of Class A shares and the warrant liability of $0.5 million was reclassified to additional paid-in capital as a result of the conversion. Revaluation upon IPO was performed using the following assumptions: expected life of 3.17 years; fair value of Series A of $17.00 per share; risk-free interest rate of 1.69%; volatility of 83.61% and no expected dividends. For further information regarding convertible preferred stock warrants, refer to Note 9, Capital Stock .

Cash, Cash Equivalents and Inve

Cash, Cash Equivalents and Investments	6 Months Ended
	Jun. 30, 2019
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): As of June 30, 2019 Gross Gross Estimated Amortized Unrealized Unrealized Fair Cash and cash equivalents and investments Cost Gains Losses Value Cash and money market funds $ 154,959 $ — $ — $ 154,959 U.S. Treasury securities 64,613 90 — 64,703 Total 219,572 90 — 219,662 Less amounts classified as cash and cash equivalents (154,959) — — (154,959) Total available-for-sale investments $ 64,613 $ 90 $ — $ 64,703 As of December 31, 2018 Gross Gross Estimated Amortized Unrealized Unrealized Fair Cash and cash equivalents and investments Cost Gains Losses Value Cash and money market funds $ 114,504 $ — $ — $ 114,504 Total 114,504 — — 114,504 Less amounts classified as cash and cash equivalents (114,504) — — (114,504) Total available-for-sale investments $ — $ — $ — $ —

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	6 Months Ended
	Jun. 30, 2019
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): June 30, December 31, 2019 2018 Vendor prepayments and deposits $ 1,238 $ 2,045 Prepaid rent 626 394 Non-trade receivables 519 282 Interest receivables and other current assets 206 — Total prepaid expenses and other current assets $ 2,589 $ 2,721

Property and Equipment, net

Property and Equipment, net	6 Months Ended
	Jun. 30, 2019
Property and Equipment, net
Property and Equipment, net	6. Property and Equipment, net Property and equipment consists of the following (in thousands): June 30, December 31, 2019 2018 Laboratory equipment $ 8,304 $ 7,561 Furniture and fixtures 389 386 Computer hardware and software 559 580 Leasehold improvements 236 236 9,488 8,763 Less accumulated depreciation and amortization (5,333) (4,620) Total property and equipment, net $ 4,155 $ 4,143 Depreciation expense was $792,000 and $667,000 for the six months ended June 30, 2019 and 2018, respectively. The net book value of property and equipment under capital leases was $117,000 and $142,000 at June 30, 2019 and December 31, 2018, respectively.

Accrued Expenses

Accrued Expenses	6 Months Ended
	Jun. 30, 2019
Accrued Expenses
Accrued Expenses	7. Accrued Expenses Accrued expenses consist of the following (in thousands): June 30, December 31, 2019 2018 Compensation and related benefits $ 1,741 $ 2,568 Professional fees 1,173 183 Contract research fees 707 43 Other 678 214 Total accrued expenses $ 4,299 $ 3,008

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2019
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 2022. 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 $1,260,000 and $625,000 for the six months ended June 30, 2019 and 2018, 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. Future minimum lease payments under non-cancelable operating and capital lease agreements consisted of the following at June 30, 2019 (in thousands): Capital Operating Leases Leases Years ending December 31: 2019 (remaining 6 months) $ 25 $ 1,752 2020 51 2,436 2021 51 2,310 2022 4 504 Total minimum lease payments 131 $ 7,002 Less: amount representing interest (9) Present value of capital lease obligation 122 Less: current portion (45) Non-current portion $ 77 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	6 Months Ended
	Jun. 30, 2019
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 will be 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. Convertible Preferred Stock Warrant Upon the IPO, t he 49,997 preferred stock warrants were revalued and converted to common stock warrants of Class A common stock shares and the warrant liability of $0.5 million was reclassified to additional paid-in capital as a result of the conversion. The warrants were not subject to further remeasurement for fair value. The balances of the preferred stock warrant liabilities were zero and $0.4 million, respectively, as of June 30, 2019 and December 31, 2018. Common Stock Warrant In connection with the issuance of Series A in August 2015, the Company issued a warrant to purchase an aggregate of 62,936 shares of common stock at $0.0001 per share. The warrant was immediately exercisable and expires, if not exercised, in August 2025. At issuance, the fair value of the warrant was determined to be $41,509, which was recorded as a Series A preferred stock issuance cost and additional paid-in capital. The warrant was exercised in full during the three months ended June 30, 2019 and the Company issued 62,936 shares of Class A common stock upon such exercise.

Equity Incentive Plan

Equity Incentive Plan	6 Months Ended
	Jun. 30, 2019
Stock Option Plan
Stock Option Plan	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 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 us secure and retain the services of eligible award recipients, provide incentives for such persons to exert maximum efforts for our success and that of our affiliates, and provide a means by which the eligible recipients may benefit from increases in the value of our 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 our Class A common stock reserved for issuance under our 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 our board of directors. Stock option activity under the 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, 2018 2,136,291 $ 6.06 $ 12,881 Granted 1,526,838 13.48 Exercised (63,633) 3.90 Cancelled (18,755) 10.56 Balances, June 30, 2019 3,580,741 $ 9.22 $ 34,447 Vested and expected to vest at June 30, 2019 3,580,741 $ 9.22 $ 34,447 Exerciseable at June 30, 2019 1,647,094 $ 5.26 $ 22,368 Vested at June 30, 2019 817,423 $ 5.45 $ 10,945 The weighted‑average grant date fair value of options granted to employees and non‑employees in the six months ended June 30, 2019 and 2018 was $10.37 and $3.57, 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 June 30, Six Months Ended June 30, 2019 2018 2019 2018 Expected life (in years) 6.02 6.02 6.02 6.01 Volatility 80.8 % 78.3 % 80.8 % % Risk-free interest rate 2.12 % 2.84 % 2.22 % % 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. The Company recognized $1,359,000 and $377,000 of stock‑based compensation expense related to options granted to employees and non‑employees for the three months ended June 30, 2019 and 2018, respectively. The Company recognized $2,135,000 and $490,000 of stock‑based compensation expense related to options granted to employees and non‑employees for the six months ended June 30, 2019 and 2018, 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 June 30, Six Months Ended June 30, 2019 2018 2019 2018 Research and development $ 754 $ 133 $ 1,171 $ 210 General and administrative 605 244 964 280 $ 1,359 $ 377 $ 2,135 $ 490 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 June 30, 2019 (in thousands, except share and per share data). Unrecognized estimated compensation expense as of June 30, 2019 totaled $21.3 million related to non‑vested stock options with a remaining requisite service period of 3.5 years. 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 and six months ended June 30, 2019, the expense related to the 2019 ESPP was immaterial due to the short period since the effective of the plan.

401(k) Plan

401(k) Plan	6 Months Ended
	Jun. 30, 2019
Net Loss Per Share
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. The Company has not made any matching contributions to date.

Net Loss Per Share

Net Loss Per Share	6 Months Ended
	Jun. 30, 2019
Net Loss Per Share
Earnings Per Share [Text Block]	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 June 30, Six Months Ended June 30, 2019 2018 2019 2018 Convertible preferred stock (as converted) — 8,306,934 — 8,306,934 Common stock options 3,580,741 1,645,109 3,580,741 1,645,109 Common stock warrants 49,997 62,936 49,997 62,936 Convertible preferred stock warrants — 49,997 — 49,997 Early exercised stock options 3,655 — 3,655 — 3,634,393 10,064,976 3,634,393 10,064,976

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2019
Related Party Transactions
Related Party Transactions	13. The Company recorded other income of $319,000 and $347,000 for the three months ended June 30, 2019 and 2018, respectively, and $484,000 and $495,000 for the six months ended June 30, 2019 and 2018, respectively, under service contracts with a stockholder. The Company had a receivable from the stockholder at June 30, 2019 and December 31, 2018 of $99,000 and $89,000, respectively. The Company recorded expense of $351,000 and $325,000 during the three months ended June 30, 2019 and 2018, respectively, and $732,000 and $613,000 during the six months ended June 30, 2019 and 2018, respectively, related to intellectual property and other legal services performed by a related party. The Company owed $410,000 and $134,000 to the related party at June 30, 2019 and December 31, 2018, respectively. The Company recorded expense of $1.6 million and $102,000 during the three months ended June 30, 2019 and 2018, respectively, and $2.0 million and $212,000 during the six months ended June 30, 2019 and 2018, respectively, related to legal services performed by a related party. The Company owed $1.6 million and $40,000 to the related party at June 30, 2019 and December 31, 2018, respectively. The Company recorded research and development expense of $106,000 and $100,000 during three months ended June 30, 2019 and 2018, respectively, and $213,000 and $200,000 during six months ended June 30, 2019 and 2018, respectively, under consulting agreements with two members of the Company’s board of directors . The Company owed $106,000 and zero to the members of the Company at June 30, 2019 and December 31, 2018, respectively.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2019
Subsequent Events
Subsequent Events	14. Subsequent Events The Company has evaluated subsequent events that may require adjustments to or disclosure in the unaudited interim condensed consolidated financial statements through August 13, 2019, the date on which the unaudited interim condensed consolidated financial statements were available to be issued. In July 2019 the Company entered into a lease agreement, or the San Carlos Lease, for the lease of approximately 99,557 rentable square feet of office space located in San Carlos, California that is intended to serve as the Company’s permanent headquarters, office and laboratory space following the completion of construction and certain tenant improvements. The term of the San Carlos Lease will commence on the date that the landlord delivers the premises to the Company for construction of certain tenant improvements, which is estimated to be August 2020, and will end on the date that is 144 months from the first day of the first full month after rent commences. Base rent for the San Carlos Lease is $557,519 per month, with annual increases of 3%. The Company is obligated to provide a security deposit of $1.1 million in the form of a letter of credit. In July 2019, concurrently with the execution and delivery of the San Carlos Lease, the Company also entered into a lease agreement, or the Temporary Lease, for the lease of approximately 74,788 rentable square feet of office space located in South San Francisco, California, which is intended to serve as its temporary headquarters, office and laboratory space while the Company’s permanent headquarters is under construction. The Temporary Lease is expected to commence August 1, 2019 and is expected to end 90 days following the substantial completion of certain tenant improvements and construction on the space covered by the San Carlos Lease. Base rent for the Temporary Lease is $280,455 per month, with annual increases of 3%.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2019
Summary of Significant Accounting Policies
Principles of Consolidation	Basis of Presentation The 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 subsidiaries. All intercompany transactions and accounts have been eliminated. 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 final prospectus for its IPO dated as of June 19, 2019 and filed with the SEC pursuant to Rule 424(b)(4) under the Securities Act of 1933, as amended, on June 20, 2019. Prior period reclassification An immaterial reclassification of prior period amounts has been made to conform to the current period presentation. 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 consolidated financial statements and accompanying notes. Actual results could differ from those estimates. Key estimates in the 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 preferred stock and 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 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 June 30, 2019 and its results of operations and cash flows for the six months ended June 30, 2018 and 2019. The financial data and the other financial information contained in these notes to the condensed consolidated financial statements related to the three-month and six-month periods are also unaudited. The condensed results of operations for the three months ended and six months ended June 30, 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or for any other future annual or interim period. The condensed consolidated balance sheet as of December 31, 2018 included herein was derived from the audited consolidated financial statements as of that date.
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 Accounting Standards Codification (“ASC”) Topic 606, Revenue from Contracts with Customers (“Topic 606”). The guidance provides a unified model to determine how income is recognized. 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 $440,000 and $282,000 are included in prepaid expenses and other current assets as of June 30, 2019 and December 31, 2018, respectively. Contract liabilities of $64,000 and $200,000 are included in other current liabilities as of June 30, 2019 and December 31, 2018, respectively.
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.
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. Convertible Preferred Stock Warrants The Company issued convertible preferred stock warrants, which were exercisable into series A preferred stock with liquidation preference. The conversion feature was evaluated under ASC Topic 480 Distinguishing liabilities from equity and the warrants were determined to be debt instruments and classified prior to the IPO as liabilities on the consolidated balance sheets. The Company recorded these warrant liabilities at fair value and adjusted the carrying value to their estimated fair value at each reporting date with the increases or decreases in the fair value recorded as a gain (loss) on revaluation of the warrant liability in the consolidated statements of operations. Upon the IPO, t he 49,997 preferred stock warrants were converted to common stock warrants of Class A shares and the warrant liability of $0.5 million was reclassified to additional paid-in capital as a result of the conversion. The warrants were not subject to further remeasurement for fair value.
Risks and Uncertainties	Risks and Uncertainties The Company is subject to a number of risks associated with companies at a similar stage, including 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 one financial institution and were in excess of the Federal Deposit Insurance Corporation insurable limit at June 30, 2019 and December 31, 2018. Additionally, cash and cash equivalents and investments are maintained at a brokerage firm 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 development. A substantial portion of the Company’s ongoing research and development activities are conducted by third-party service providers in connection with preclinical 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.
Preferred Stock Warrant Liability	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. Stock‑based compensation is recognized as the underlying options vest using the straight‑line attribution approach, and forfeitures are recorded as they occur.
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 June 30, Six Months Ended June 30, 2019 2018 2019 2018 Convertible preferred stock (as converted) — 8,306,934 — 8,306,934 Common stock options 3,580,741 1,645,109 3,580,741 1,645,109 Common stock warrants 49,997 62,936 49,997 62,936 Convertible preferred stock warrants — 49,997 — 49,997 Early exercised stock options 3,655 — 3,655 — 3,634,393 10,064,976 3,634,393 10,064,976
Recent Accounting Pronouncements	Recent Accounting Pronouncements In February 2016, the FASB issued ASU 2016‑02 and subsequent amendments to the initial guidance under ASU 2017-13, ASU 2018-10 and ASU 2018-11 (collectively, “Topic 842” ), which modifies the 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 is effective for the Company as of January 1, 2020. Early adoption is permitted. The Company’s most significant lease is its operating lease for its corporate headquarters, and, while the Company has not yet estimated the amounts by which its financial statements will be affected by the adoption of this guidance, it expects that the overall recognition of expense will be similar to current guidance, but that there will be a significant change in the balance sheet due to the recognition of right of use assets and the corresponding lease liabilities. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses ( “Topic 326” ): Measurement of Credit Losses on Financial Instruments and subsequent amendments to the initial guidance under ASU 2018-19, ASU 2019-04 and ASU 2019-05, which amends the current approach to estimate credit losses on certain financial assets, including trade and other receivables. The amendment replaces the existing incurred loss impairment model with an expected loss methodology, which will result in more timely recognition of credit losses. For available-for-sale debt securities, credit losses should be recorded through an allowance for credit losses. The Company is currently evaluating the impact the adoption of this standard will have on its consolidated financial statements and related disclosures. In August 2016, the FASB issued ASU 2016‑15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments ( “Topic 230” ). The standard clarifies how certain cash receipts and cash payments will be presented and classified in the statement of cash flows. Topic 230 is effective for the Company as of January 1, 2019. The adoption of this update had no material effect on the Company’s consolidated financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2019
Summary of Significant Accounting Policies
Schedule of reconciliation of cash and cash equivalents and restricted cash	June 30, December 31, 2019 2018 Cash and cash equivalents $ 154,959 $ 114,504 Restricted cash 724 — Cash, cash equivalents and restricted cash shown in the condensed consolidated statements of cash flows $ 155,683 $ 114,504
Summary of unaudited pro forma net loss per share	Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Convertible preferred stock (as converted) — 8,306,934 — 8,306,934 Common stock options 3,580,741 1,645,109 3,580,741 1,645,109 Common stock warrants 49,997 62,936 49,997 62,936 Convertible preferred stock warrants — 49,997 — 49,997 Early exercised stock options 3,655 — 3,655 — 3,634,393 10,064,976 3,634,393 10,064,976

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2019
Fair Value of Financial Instruments
Summary of financial assets and liabilities subject to fair value measurements on a recurring basis	June 30, 2019 Level 1 Level 2 Level 3 Total Assets Money market funds 150,477 — — 150,477 U.S. Treasury securities 64,703 — — 64,703 Total $ 215,180 $ — $ — $ 215,180 December 31, 2018 Level 1 Level 2 Level 3 Total Assets Money market funds $ 109,630 $ — $ — $ 109,630 Total $ 109,630 $ — $ — $ 109,630 Liabilities Warrant liability $ — $ — $ $ Total $ — $ — $ $
Summary of fair value of the warrants were calculated using the Black-Scholes option pricing model	December 31, 2018 Exercise price (1) $ 14.46 Stock price (2) $ 13.20 Time to maturity (in years) 3.64 Volatility (3) 83.7 % Risk-free interest rate (4) 2.50 % Expected dividend $ — (1) Based upon terms provided in the warrant agreement. (2) Based upon an independently prepared valuation as of December 31, 2018, adjusted for the one-for-six reverse stock split . (3) Based upon the historical daily volatility of a group of peer public company closing prices. Based upon interest rate for U.S. Treasury Bonds, as published by the U.S. Federal Reserve.

Cash, Cash Equivalents and In_2

Cash, Cash Equivalents and Investments (Tables)	6 Months Ended
	Jun. 30, 2019
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	As of June 30, 2019 Gross Gross Estimated Amortized Unrealized Unrealized Fair Cash and cash equivalents and investments Cost Gains Losses Value Cash and money market funds $ 154,959 $ — $ — $ 154,959 U.S. Treasury securities 64,613 90 — 64,703 Total 219,572 90 — 219,662 Less amounts classified as cash and cash equivalents (154,959) — — (154,959) Total available-for-sale investments $ 64,613 $ 90 $ — $ 64,703 As of December 31, 2018 Gross Gross Estimated Amortized Unrealized Unrealized Fair Cash and cash equivalents and investments Cost Gains Losses Value Cash and money market funds $ 114,504 $ — $ — $ 114,504 Total 114,504 — — 114,504 Less amounts classified as cash and cash equivalents (114,504) — — (114,504) Total available-for-sale investments $ — $ — $ — $ —

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	6 Months Ended
	Jun. 30, 2019
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): June 30, December 31, 2019 2018 Vendor prepayments and deposits $ 1,238 $ 2,045 Prepaid rent 626 394 Non-trade receivables 519 282 Interest receivables and other current assets 206 — Total prepaid expenses and other current assets $ 2,589 $ 2,721

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	6 Months Ended
	Jun. 30, 2019
Property and Equipment, net
Summary of property and equipment	Property and equipment consists of the following (in thousands): June 30, December 31, 2019 2018 Laboratory equipment $ 8,304 $ 7,561 Furniture and fixtures 389 386 Computer hardware and software 559 580 Leasehold improvements 236 236 9,488 8,763 Less accumulated depreciation and amortization (5,333) (4,620) Total property and equipment, net $ 4,155 $ 4,143

Accrued Expenses (Tables)

Accrued Expenses (Tables)	6 Months Ended
	Jun. 30, 2019
Accrued Expenses
Summary of accrued expenses	Accrued expenses consist of the following (in thousands): June 30, December 31, 2019 2018 Compensation and related benefits $ 1,741 $ 2,568 Professional fees 1,173 183 Contract research fees 707 43 Other 678 214 Total accrued expenses $ 4,299 $ 3,008

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2019
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 June 30, 2019 (in thousands): Capital Operating Leases Leases Years ending December 31: 2019 (remaining 6 months) $ 25 $ 1,752 2020 51 2,436 2021 51 2,310 2022 4 504 Total minimum lease payments 131 $ 7,002 Less: amount representing interest (9) Present value of capital lease obligation 122 Less: current portion (45) Non-current portion $ 77

Equity Incentive Plan (Tables)

Equity Incentive Plan (Tables)	6 Months Ended
	Jun. 30, 2019
Stock Option Plan
Schedule of stock-based compensation expense	The compensation expense is allocated on a departmental basis, based on the classification of the option holder as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Research and development $ 754 $ 133 $ 1,171 $ 210 General and administrative 605 244 964 280 $ 1,359 $ 377 $ 2,135 $ 490
Schedule of stock option activity	Options Outstanding Weighted- Average Aggregate Weighted- Remaining Intrinsic Number Average Contractual Value of Shares Exercise Price Life (years) (in thousands) Balances, December 31, 2018 2,136,291 $ 6.06 $ 12,881 Granted 1,526,838 13.48 Exercised (63,633) 3.90 Cancelled (18,755) 10.56 Balances, June 30, 2019 3,580,741 $ 9.22 $ 34,447 Vested and expected to vest at June 30, 2019 3,580,741 $ 9.22 $ 34,447 Exerciseable at June 30, 2019 1,647,094 $ 5.26 $ 22,368 Vested at June 30, 2019 817,423 $ 5.45 $ 10,945
Schedule of weighted average assumptions	Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Expected life (in years) 6.02 6.02 6.02 6.01 Volatility 80.8 % 78.3 % 80.8 % % Risk-free interest rate 2.12 % 2.84 % 2.22 % %

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	6 Months Ended
	Jun. 30, 2019
Net Loss Per Share
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Convertible preferred stock (as converted) — 8,306,934 — 8,306,934 Common stock options 3,580,741 1,645,109 3,580,741 1,645,109 Common stock warrants 49,997 62,936 49,997 62,936 Convertible preferred stock warrants — 49,997 — 49,997 Early exercised stock options 3,655 — 3,655 — 3,634,393 10,064,976 3,634,393 10,064,976

Business (Details)

Business (Details) $ / shares in Units, $ in Thousands	Jun. 07, 2019	Jun. 30, 2019USD ($)$ / sharesshares	Jun. 30, 2019USD ($)$ / sharesshares	Dec. 31, 2018
Business
Reverse stock split	0.167			0.167
Proceeds from Issuance Initial Public Offering | $			$ 133,618
underwriting discounts and commissions | $		$ 10,100
Offering expenses | $		$ 2,800
Warrants to purchase (in shares) | shares		49,997	49,997
Conversion of redeemable convertible preferred stock to common stock | $		$ 209,700	$ 209,669
Deferred offering cost | $		$ 2,800	2,800
Payment of deferred offering cost | $			$ 577
IPO
Business
Offering price | $ / shares		$ 17	$ 17
Proceeds from Issuance Initial Public Offering | $		$ 130,800
Class A common stock
Business
Number of shares issued up on conversion | shares		13,314,068
Warrants to purchase (in shares) | shares		62,936	62,936
Class A common stock | IPO
Business
Shares issued | shares		6,452,500
Class A common stock | underwriters option
Business
Shares issued | shares		1,102,500
Class B common stock
Business
Number of shares issued up on conversion | shares		3,934,191
Class B common stock | IPO
Business
Shares issued | shares		2,000,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Cash and cash equivalents and restricted cash reported within the condensed balance sheets
Cash and cash equivalents	$ 154,959,000	$ 154,959,000	$ 114,504,000
Restricted cash	724,000	724,000	0
Cash, cash equivalents and restricted cash shown in the condensed consolidated statements of cash flows	$ 155,683,000	$ 155,683,000	114,504,000	$ 6,394,000	$ 8,242,000
Convertible Preferred Stock Warrants
Warrants to purchase (in shares)	49,997	49,997
Reclassification of redeemable convertible preferred stock warrant liability to additional paid-in capital	$ 503,000	$ 503,000
Prepaid expenses and other current assets
Other Income
Receivables under service agreements	440,000	440,000	282,000
Other current liabilities
Other Income
Contract liabilities	$ 64,000	$ 64,000	$ 200,000

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Financial assets and liabilities (Details) - Recurring basis - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets
Total assets	$ 215,180	$ 109,630
Liabilities
Total liabilities		380
Common stock warrants
Liabilities
Total liabilities		380
Cash and money market funds
Assets
Total assets	150,477	109,630
U.S. Treasury securities
Assets
Total assets	64,703
Level 1
Assets
Total assets	215,180	109,630
Level 1 | Cash and money market funds
Assets
Total assets	150,477	109,630
Level 1 | U.S. Treasury securities
Assets
Total assets	$ 64,703
Level 3
Liabilities
Total liabilities		380
Level 3 | Common stock warrants
Liabilities
Total liabilities		$ 380

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Fair value of the warrants (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019USD ($)itemshares	Jun. 30, 2019USD ($)itemshares	Dec. 31, 2018item
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant liability, measurement input	17	17
Warrants to purchase (in shares) | shares	49,997	49,997
Reclassification of redeemable convertible preferred stock warrant liability to additional paid-in capital | $	$ 503	$ 503
Expected life	3 years 2 months 1 day	3 years 2 months 1 day	3 years 7 months 21 days
Exercise price (1)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant liability, measurement input			14.46
Stock price (2)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant liability, measurement input			13.20
Volatility (3)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant liability, measurement input	0.8361	0.8361	0.837
Risk-free interest rate (4)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant liability, measurement input	0.0169	0.0169	0.0250
Expected dividend
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrant liability, measurement input	0	0

Cash, Cash Equivalents and In_3

Cash, Cash Equivalents and Investments - Fair value and Amortized cost (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Cash and money market funds
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	$ 154,959	$ 114,504
Estimated Fair Value	154,959	114,504
U.S. Treasury securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	64,613
Gross Unrealized Gains	90
Estimated Fair Value	64,703
Total
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	219,572	114,504
Gross Unrealized Gains	90
Estimated Fair Value	219,662	114,504
Less amounts classified as cash and cash equivalents
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	154,959	114,504
Estimated Fair Value		$ 114,504
Total available-for-sale investments
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Amortized Cost	64,613
Gross Unrealized Gains	90
Estimated Fair Value	$ 64,703

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Prepaid expenses and other current assets (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Prepaid Expenses and Other Current Assets
Vendor prepayments and deposits	$ 1,238	$ 2,045
Prepaid rent	626	394
Non-trade receivables	519	282
Interest receivables and other current assets	206
Prepaid expenses and other current assets	$ 2,589	$ 2,721

Property and Equipment, net (De

Property and Equipment, net (Details) - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 9,488,000		$ 8,763,000
Less accumulated depreciation and amortization	(5,333,000)		(4,620,000)
Property and equipment, net	4,155,000		4,143,000
Depreciation expense	792,000	$ 667,000
Net book value of property and equipment under capital leases	117,000		142,000
Laboratory equipment
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	8,304,000		7,561,000
Furniture and fixtures
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	389,000		386,000
Computer hardware and software
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	559,000		580,000
Leasehold improvements
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 236,000		$ 236,000

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accrued Expenses
Compensation and related benefits	$ 1,741	$ 2,568
Professional fees	1,173	183
Contract research fees	707	43
Other	678	214
Total accrued expenses	$ 4,299	$ 3,008

Commitments and Contingencies_2

Commitments and Contingencies (Details) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2017
Operating leases
Rent expenses	$ 1,260,000	$ 625,000
Capital lease
Purchases under capital lease			$ 226,000

Commitments and Contingencies -

Commitments and Contingencies - Future Minimum Lease Payments (Details) - K - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Future minimum capital leases:
2019 (remaining 6 months)	$ 25
2020	51
2021	51
2022	4
Total minimum lease payments	131
Less: amount representing interest	(9)
Present value of capital lease obligation	122
Capital lease obligations, current portion	45
Capital Lease Obligations, Noncurrent	77	$ 100
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019 (remaining 6 months)	1,752
2020	2,436
2021	2,310
2022	504
Total minimum lease payments	$ 7,002

Capital Stock - Class A and Cla

Capital Stock - Class A and Class B Common Stock (Details)	Jun. 02, 2019Vote$ / sharesshares	Jun. 30, 2019$ / sharesshares	Dec. 31, 2018$ / sharesshares
Class of Stock [Line Items]
Preferred Stock, Shares Authorized | shares	300,000,000
Preferred stock par value | $ / shares	$ 0.0001
Class A common stock
Class of Stock [Line Items]
Common stock, shares authorized | shares	650,000,000	650,000,000	191,398,492
Common stock, par value | $ / shares	$ 0.0001	$ 0.0001	$ 0.0001
Number of votes entitled per share | Vote	1
Class B common stock
Class of Stock [Line Items]
Common stock, shares authorized | shares	50,000,000	50,000,000	23,605,150
Common stock, par value | $ / shares	$ 0.0001	$ 0.0001	$ 0.0001

Capital Stock - Convertible Pre

Capital Stock - Convertible Preferred Stock Warrant (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Class of Warrant or Right [Line Items]
Warrants to purchase (in shares)	49,997	49,997
Reclassification of redeemable convertible preferred stock warrant liability to additional paid-in capital	$ 503	$ 503
Preferred stock warrant liability			$ 380
Preferred Stock Warrants
Class of Warrant or Right [Line Items]
Warrants to purchase (in shares)	49,997	49,997
Reclassification of redeemable convertible preferred stock warrant liability to additional paid-in capital		$ 500
Preferred stock warrant liability	$ 400	$ 400	$ 0

Capital Stock - Common Stock Wa

Capital Stock - Common Stock Warrants (Details) - USD ($)	1 Months Ended	3 Months Ended
	Aug. 31, 2015	Jun. 30, 2019
Class of Warrant or Right [Line Items]
Warrants to purchase (in shares)		49,997
Class A common stock
Class of Warrant or Right [Line Items]
Warrants to purchase (in shares)		62,936
Common Stock Warrants | Class A common stock
Class of Warrant or Right [Line Items]
Exercise of warrants		62,936
Common Stock Warrants | Series A convertible preferred stock
Class of Warrant or Right [Line Items]
Warrants to purchase (in shares)	62,936
Price per share (in dollars per share)	$ 0.0001
Fair value of warrants	$ 41,509

Equity Incentive Plan - Narrati

Equity Incentive Plan - Narrative (Details) - 2019 Equity Incentive 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 - Stock-based

Equity Incentive - Stock-based compensation expense (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,359,000	$ 377,000	$ 2,135,000	$ 490,000
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	754,000	133,000	1,171,000	210,000
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 605,000	$ 244,000	$ 964,000	$ 280,000

Equity Incentive Plan - Stock o

Equity Incentive Plan - Stock option (Details) - 2019 Equity Incentive Plan	6 Months Ended	12 Months Ended
	Jun. 30, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares
Number of Shares
Balance at beginning of period (in shares) | shares	2,136,291
Granted (in shares) | shares	1,526,838
Exercised (in shares) | shares	(63,633)
Cancelled (in shares) | shares	(18,755)
Balance at end of period (in shares) | shares	3,580,741	2,136,291
Vested and expected to vest at end of period (in shares) | shares	3,580,741
Exercisable at end of period (in shares) | shares	1,647,094
Vested at end of period (in shares) | shares	817,423
Weighted-Average Exercise Price
Balance at beginning of period (in dollars per share) | $ / shares	$ 6.06
Granted (in dollars per share) | $ / shares	13.48
Exercised (in dollars per share) | $ / shares	3.90
Cancelled (in dollars per share) | $ / shares	10.56
Balance at end of period (in dollars per share) | $ / shares	9.22	$ 6.06
Vested and expected to vest at end of period (in dollars per share) | $ / shares	9.22
Exercisable at end of period (in dollars per share) | $ / shares	5.26
Vested at end of period (in dollars per share) | $ / shares	$ 5.45
Weighted-Average Remaining Contractual Life
Weighted-Average Remaining Contractual Life	9 years	8 years 10 months 24 days
Vested and expected to vest at end of period (in years)	9 years
Exercisable at end of period (in years)	8 years 2 months 12 days
Vested at end of period (in years)	7 years 9 months 18 days
Weighted-Average Exercise Price
Balance at end of period | $	$ 34,447	$ 12,881
Vested and expected to vest at end of period | $	34,447
Exercisable at end of period | $	22,368
Vested at end of period | $	$ 10,945

Equity Incentive - Weighted-ave

Equity Incentive - Weighted-average grant date fair value (Details) - $ / shares	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant date fair value (in dollars per share)	$ 10.37	$ 3.57

Equity Incentive - Weighted ave

Equity Incentive - Weighted average assumptions (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected life (in years)	6 years 7 days	6 years 7 days
Volatility	80.80%	78.30%
Risk-free interest rate	2.12%	2.84%
2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected dividend			0.00%	0.00%
Expected life (in years)			6 years 7 days	6 years 4 days
Volatility			80.80%	78.30%
Risk-free interest rate			2.22%	2.88%

Equity Incentive - Unrecognized

Equity Incentive - Unrecognized compensation (Details) - 2019 Equity Incentive Plan $ in Millions	6 Months Ended
	Jun. 30, 2019USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized estimated compensation expense	$ 21.3
Remaining requisite service period	3 years 6 months

Equity Incentive - 2019 Employe

Equity Incentive - 2019 Employee Stock Purchase Plan (Details) - Class A common stock - 2019 Employee Stock Purchase Plan	Jun. 19, 2019shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance	283,333
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

Net Loss Per Share (Details)

Net Loss Per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the diluted net loss per share calculation	3,634,393	10,064,976	3,634,393	10,064,976
Convertible preferred stock (as converted)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities not included in the diluted net loss per share calculation		8,306,934		8,306,934
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	3,580,741	1,645,109	3,580,741	1,645,109
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	62,936	49,997	62,936
Convertible preferred 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
Early exercised 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	3,655		3,655

Related Party Transactions (Det

Related Party Transactions (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019USD ($)director	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Related Party Transaction [Line Items]
Other income	$ 319,000	$ 347,000	$ 484,000	$ 495,000
Receivable from stockholders	99,000		99,000		$ 89,000
Due to related party	106,000		106,000		0
Research and development expense	$ 106,000	100,000	213,000	200,000
Number of members under consulting agreements | director	2
Intellectual property related legal fees
Related Party Transaction [Line Items]
Legal fees	$ 351,000	325,000	732,000	613,000
Due to related party	410,000		410,000		134,000
Other legal fees
Related Party Transaction [Line Items]
Legal fees	1,600,000	$ 102,000	2,000,000	$ 212,000
Due to related party	$ 1,600,000		$ 1,600,000		$ 40,000

Subsequent Events (Details)

Subsequent Events (Details) - Subsequent event	1 Months Ended
	Jul. 31, 2019USD ($)ft²
Office space located in San Carlos
Subsequent Event [Line Items]
Rentable square footage | ft²	99,557
Lease term	144 months
Base rent	$ 557,519
Security deposit	$ 1,100,000
Percentage of annual increase of lease rent	3.00%
Office space located in South San Francisco
Subsequent Event [Line Items]
Rentable square footage | ft²	74,788
Base rent	$ 280,455
Lease term after expiration of permanent lease	90 days
Percentage of annual increase of lease rent	3.00%