Karuna Therapeutics (KRTX) 10-Q 8 Aug 19 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2019	Aug. 08, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Trading Symbol	KRTX
Entity Registrant Name	Karuna Therapeutics, Inc.
Entity Central Index Key	0001771917
Current Fiscal Year End Date	--12-31
Entity File Number	001-38958
Entity Tax Identification Number	270605902
Entity Address, Address Line One	33 Arch Street
Entity Address, Address Line Two	Suite 3110
Entity Address, City or Town	Boston
Entity Address, State or Province	Massachusetts
Entity Address, Postal Zip Code	02110
City Area Code	857
Local Phone Number	449-2244
Entity Current Reporting Status	No
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		23,412,754

BALANCE SHEETS (Unaudited)

BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 10,495	$ 8,904
Short-term investments	64,804	4,983
Deferred offering costs	2,032
Prepaid expenses and other current assets	1,717	1,709
Total current assets	79,048	15,596
Restricted cash	123	123
Property and equipment, net	186	138
Total assets	79,357	15,857
Current liabilities:
Accounts payable (includes $8 and $112 at June 30, 2019 and December 31, 2018, respectively, due to related parties)	960	269
Accrued expenses	1,260	538
Deferred lease obligation, short term portion	55
Derivative liability		389
Total current liabilities	2,275	1,196
Non-current convertible notes, net of discount		2,516
Deferred lease obligation, long term portion	179	102
Total liabilities	2,454	3,814
Commitments and Contingencies (Note 10)
Stockholders’ equity (deficit):
Additional paid-in capital	11,640	1,633
Accumulated deficit	(58,700)	(31,555)
Accumulated other comprehensive income	71
Total stockholders’ equity (deficit)	(46,989)	(29,922)
Total liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit)	79,357	15,857
Series Seed Redeemable Convertible Preferred Stock
Current liabilities:
Redeemable convertible preferred stock	1	1
Series A Redeemable Convertible Preferred Stock
Current liabilities:
Redeemable convertible preferred stock	41,964	$ 41,964
Series B Redeemable Convertible Preferred Stock
Current liabilities:
Redeemable convertible preferred stock	$ 81,927

BALANCE SHEETS (Unaudited) (Par

BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accounts payable to related party	$ 8	$ 112
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	20,779,200	12,337,650
Common stock, shares issued	164,122	12
Common stock, shares outstanding	164,122	12
Series Seed Redeemable Convertible Preferred Stock
Temporary Equity, par value	$ 0.0001	$ 0.0001
Temporary Equity, shares authorized	4,412,500	4,412,500
Temporary Equity, shares outstanding	4,412,500	4,412,500
Temporary Equity, liquidation preference	$ 4,413	$ 4,413
Series A Redeemable Convertible Preferred Stock
Temporary Equity, par value	$ 0.0001	$ 0.0001
Temporary Equity, shares authorized	3,126,700	3,126,700
Temporary Equity, shares outstanding	3,126,700	3,126,700
Temporary Equity, liquidation preference	$ 42,085	$ 42,085
Series B Redeemable Convertible Preferred Stock
Temporary Equity, par value	$ 0.0001	$ 0.0001
Temporary Equity, shares authorized	5,422,845	0
Temporary Equity, shares outstanding	5,422,845	0
Temporary Equity, liquidation preference	$ 80,016

STATEMENTS OF OPERATIONS (Unaud

STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating expenses:
Research and development	$ 6,784	$ 2,175	$ 13,751	$ 3,399
General and administrative	8,286	256	12,892	492
Total operating expenses	15,070	2,431	26,643	3,891
Loss from operations	(15,070)	(2,431)	(26,643)	(3,891)
Other income (expense):
Interest income (expense) (Note 4)		(307)	11	(588)
Interest income	452		567
Accretion of debt discount	(522)	(85)	(945)	(672)
Change in fair value of derivative		2,284	(135)	2,204
Total other income (expense), net	(70)	1,892	(502)	944
Net loss before income taxes	(15,140)	(539)	(27,145)	(2,947)
Net loss attributable to common stockholders	$ (15,140)	$ (539)	$ (27,145)	$ (2,947)
Net loss per share, basic and diluted (Note 7)	$ (146.02)		$ (507.76)
Weighted average common shares outstanding used in computing net loss per share, basic and diluted	103,684		53,460

STATEMENTS OF COMPREHENSIVE LOS

STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (15,140)	$ (539)	$ (27,145)	$ (2,947)
Other comprehensive income:
Unrealized gains on short-term investments	71		71
Comprehensive loss	$ (15,069)	$ (539)	$ (27,074)	$ (2,947)

STATEMENTS OF REDEEMABLE CONVER

STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income	Series Seed Redeemable Convertible Preferred Stock	Series A Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock
Temporary Equity, beginning balance at Dec. 31, 2017						$ 1
Temporary Equity, beginning balance, shares at Dec. 31, 2017						4,412,500
Beginning balance at Dec. 31, 2017	$ (13,368)		$ 675	$ (14,043)
Shared-based compensation expense	54		54
Net loss	(2,408)			(2,408)
Temporary Equity, ending balance at Mar. 31, 2018						$ 1
Temporary Equity, ending balance, shares at Mar. 31, 2018						4,412,500
Ending balance at Mar. 31, 2018	(15,722)		729	(16,451)
Temporary Equity, beginning balance at Dec. 31, 2017						$ 1
Temporary Equity, beginning balance, shares at Dec. 31, 2017						4,412,500
Beginning balance at Dec. 31, 2017	(13,368)		675	(14,043)
Net loss	(2,947)
Temporary Equity, ending balance at Jun. 30, 2018						$ 1
Temporary Equity, ending balance, shares at Jun. 30, 2018						4,412,500
Ending balance at Jun. 30, 2018	(16,187)		803	(16,990)
Temporary Equity, beginning balance at Mar. 31, 2018						$ 1
Temporary Equity, beginning balance, shares at Mar. 31, 2018						4,412,500
Beginning balance at Mar. 31, 2018	(15,722)		729	(16,451)
Shared-based compensation expense	74		74
Net loss	(539)			(539)
Temporary Equity, ending balance at Jun. 30, 2018						$ 1
Temporary Equity, ending balance, shares at Jun. 30, 2018						4,412,500
Ending balance at Jun. 30, 2018	(16,187)		803	(16,990)
Temporary Equity, beginning balance at Dec. 31, 2018						$ 1	$ 41,964
Temporary Equity, beginning balance, shares at Dec. 31, 2018						4,412,500	3,126,700	0
Beginning balance at Dec. 31, 2018	(29,922)		1,633	(31,555)
Beginning balance, shares at Dec. 31, 2018		12
Temporary Equity, Issuance of Series B redeemable convertible preferred stock, net of issuance costs								$ 79,841
Temporary Equity, Issuance of Series B redeemable convertible preferred stock, net of issuance cost, shares								5,285,102
Exercise of common warrants	58		58
Exercise of common warrants, shares		19,986
Shared-based compensation expense	3,104		3,104
Net loss	(12,005)			(12,005)
Temporary Equity, ending balance at Mar. 31, 2019						$ 1	$ 41,964	$ 79,841
Temporary Equity, ending balance, shares at Mar. 31, 2019						4,412,500	3,126,700	5,285,102
Ending balance at Mar. 31, 2019	(38,765)		4,795	(43,560)
Ending balance, shares at Mar. 31, 2019		19,998
Temporary Equity, beginning balance at Dec. 31, 2018						$ 1	$ 41,964
Temporary Equity, beginning balance, shares at Dec. 31, 2018						4,412,500	3,126,700	0
Beginning balance at Dec. 31, 2018	$ (29,922)		1,633	(31,555)
Beginning balance, shares at Dec. 31, 2018		12
Exercise of common options, shares	38,961
Net loss	$ (27,145)
Temporary Equity, ending balance at Jun. 30, 2019						$ 1	$ 41,964	$ 81,927
Temporary Equity, ending balance, shares at Jun. 30, 2019						4,412,500	3,126,700	5,422,845
Ending balance at Jun. 30, 2019	(46,989)		11,640	(58,700)	$ 71
Ending balance, shares at Jun. 30, 2019		164,122
Temporary Equity, beginning balance at Mar. 31, 2019						$ 1	$ 41,964	$ 79,841
Temporary Equity, beginning balance, shares at Mar. 31, 2019						4,412,500	3,126,700	5,285,102
Beginning balance at Mar. 31, 2019	(38,765)		4,795	(43,560)
Beginning balance, shares at Mar. 31, 2019		19,998
Temporary Equity, Issuance of Series B redeemable convertible preferred stock, net of issuance costs								$ 2,086
Temporary Equity, Issuance of Series B redeemable convertible preferred stock, net of issuance cost, shares								137,743
Exercise of common options	4		4
Exercise of common options, shares		38,961
Vesting of restricted stock units, shares		105,163
Shared-based compensation expense	6,841		6,841
Other comprehensive income	71				71
Net loss	(15,140)			(15,140)
Temporary Equity, ending balance at Jun. 30, 2019						$ 1	$ 41,964	$ 81,927
Temporary Equity, ending balance, shares at Jun. 30, 2019						4,412,500	3,126,700	5,422,845
Ending balance at Jun. 30, 2019	$ (46,989)		$ 11,640	$ (58,700)	$ 71
Ending balance, shares at Jun. 30, 2019		164,122

STATEMENTS OF REDEEMABLE CONV_2

STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Unaudited) (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Statement Of Stockholders Equity [Abstract]
Issuance of redeemable convertible preferred stock, net of issuance costs	$ 175

STATEMENTS OF CASH FLOWS (Unaud

STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Cash flows from operating activities
Net loss				$ (27,145)		$ (2,947)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense				22		2
Stock-based compensation expense				9,945		110
Warrant expense						18
Non-cash interest expense (income)		$ 307		(11)		588
Non-cash interest income				(282)
Accretion of debt discount	$ 522	85		945		672
Change in fair value of derivative liability		(2,284)		135		(2,204)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets				(8)		(1,969)
Accounts payable				253		(778)
Accrued expenses				327		126
Deferred lease obligation				132
Net cash used in operating activities				(15,687)		(6,382)
Cash flows from investing activities
Acquisition of property and equipment				(70)
Purchases of short-term investments				(64,468)
Maturities of short-term investments				5,000
Net cash used in investing activities				(59,538)
Cash flows from financing activities
Proceeds from exercise of warrant				58
Payment of deferred offering costs				(1,199)
Proceeds from issuance of convertible notes		4,000	$ 3,000	3,128		7,000
Proceeds from exercise of stock options				4
Net cash provided by financing activities				76,816		7,000
Net increase in cash, cash equivalents and restricted cash				1,591		618
Cash, cash equivalents and restricted cash at beginning of period			$ 1,942	9,027	$ 2,560	1,942
Cash, cash equivalents and restricted cash at end of period	$ 10,618	$ 2,560		10,618	9,027	$ 2,560
Supplemental disclosures of cash flows information
Conversion of convertible notes, accrued interest and discount upon conversion to preferred stock				7,102	$ 15,784
Deferred offering costs included in accrued expenses and accounts payable				833
Series B Redeemable Convertible Preferred Stock
Cash flows from financing activities
Proceeds from issuance of Series B redeemable convertible preferred stock, net of issuance cost				$ 74,825

Nature of the Business

Nature of the Business	6 Months Ended
	Jun. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business	Note 1. Nature of the Business Karuna Therapeutics, Inc. (the “Company”) was incorporated under the laws of the State of Delaware in July 2009 as Karuna Pharmaceuticals, Inc. and is headquartered in Boston, Massachusetts. In March 2019, the Company changed its name to Karuna Therapeutics, Inc. The Company is focused on the development of novel therapies to address disabling neuropsychiatric conditions characterized by significant unmet medical need. Since the Company’s inception, it has focused substantially all of its efforts and financial resources on organizing and staffing the Company, acquiring and developing its technology, raising capital, building its intellectual property portfolio, undertaking preclinical studies and clinical trials and providing general and administrative support for these activities. The Company has not generated any product revenue related to its primary business purpose to date and is subject to a number of risks similar to those of other early stage companies, including dependence on key individuals, regulatory approval of products, uncertainty of market acceptance of products, competition from substitute products and larger companies, compliance with government regulations, protection of proprietary technology, dependence on third parties, product liability and the need to obtain adequate additional financing to fund the development of its product candidates. Forward Stock Split On June 14, 2019, the Company effected a one-for-1.2987 stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s redeemable convertible preferred stock (see Note 5). Accordingly, all share and per share amounts for all periods presented in the accompanying financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this stock split and adjustment of the redeemable convertible preferred stock conversion ratios. Initial Public Offering On June 27, 2019, the Company’s registration statement on Form S-1 relating to its initial public offering of its common stock (“IPO”) was declared effective by the Securities and Exchange Commission (“SEC”). In the IPO, which closed on July 2, 2019, the Company issued and sold 6,414,842 Liquidity The Company’s financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. The Company experienced negative operating cash flows of $15.7 million for the six months ended June 30, 2019 and had an accumulated deficit of $58.7 million as of June 30, 2019. The Company expects to continue to generate operating losses for the foreseeable future. The Company expects that its cash and cash equivalents and short-term investments of $75.3 million as of June 30, 2019, together with the $93.2 million aggregate net proceeds received from the Company’s IPO on July 2, 2019, will be sufficient to fund its operating expenses and capital expenditure requirements through at least 12 months from the date of issuance of these financial statements. The future viability of the Company beyond that point is dependent on its ability to raise additional capital to fund its operations. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects, or the Company may be unable to continue operations. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	NOTE 2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation and Use of Estimates The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”). The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, the accrual for research and development expenses, derivative liabilities, the valuation of stock-based awards and prior to the IPO, the valuation of common stock. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates. Unaudited Interim Financial Information The accompanying balance sheet as of June 30, 2019, the statements of operations, comprehensive loss, and cash flows for the three and six months ended June 30, 2019 and 2018, and the statements of redeemable convertible preferred stock and stockholders’ equity (deficit) for the three and six months ended June 30, 2019 and 2018 are unaudited. The unaudited interim financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of June 30, 2019 and the results of its operations and its cash flows for the three and six months ended June 30, 2019 and 2018. Certain information and footnote disclosures typically included in annual financial statements prepared in accordance with have been condensed or omitted. Accordingly, these unaudited interim financial statements should be read in conjunction with the Company’s financial statements as of and for the year ended December 31, 2018, which are included in the Company’s prospectus related to the Company’s IPO, filed June 28, 2019 (File No. 333-231863) with the SEC, pursuant to Rule 424(b) under the Securities Act of 1933, as amended. Cash and Cash Equivalents The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Short-term Investments The Company’s short-term investments are classified as available-for-sale and are carried at fair value with the unrealized gains and losses reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other income (expense), net based on the specific identification method. Concentration of Manufacturing Risk The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the statements of operations. $2.0 million As of December 31, 2018, the Company had not recorded any deferred offering costs. As of June 30, 2019, the Company recorded deferred offering costs of $XX in connection with its IPO. Fair Value of Financial Instruments The Company’s financial instruments consist of cash equivalents, short-term investments, accounts payable, accrued expenses, convertible notes and derivatives embedded within the convertible notes. The carrying amount of accounts payable and accrued expenses are considered a reasonable estimate of their fair value, due to the short-term maturity of these instruments. The Company’s cash equivalents, short-term investments and derivative liabilities are carried at fair value, determined according to the fair value hierarchy described below (see Note 9). The Company follows the guidance in FASB ASC 820, Fair Value Measurements and Disclosures Level 1: Quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2: Valuations based on quoted prices in markets that are not active or for which all significant inputs are observable, either directly or indirectly. Level 3: Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Fair value is a market-based measure considered from the perspective of a market participant rather than an entity-specific measure. Therefore, even when market assumptions are not readily available, the Company’s own assumptions reflect those that market participants would use in pricing the asset or liability at the measurement date. The Company uses prices and inputs that are current as of the measurement date, including during periods of market dislocation. In periods of market dislocation, the observability of prices and inputs may be reduced for many instruments. This condition could cause an instrument to be reclassified from Level 1 to Level 2 or Level 2 to Level 3. Convertible Notes and Derivative Liabilities In connection with the issuance of the Wellcome Trust Convertible Notes and the Convertible Notes (see Note 4), the Company has identified embedded derivatives, which are recorded as liabilities on the Company’s balance sheets and are remeasured to fair value at each reporting date until the derivative is settled. Changes in the fair value of the derivative liabilities are recognized as change in fair value of derivative in the statements of operations. The fair value of the derivative liabilities are determined at each period end using a with and without method, which assesses the likelihood and timing of events that would result in either a conversion or change-of-control feature being triggered, as well as changes in the market conditions. Upon issuance of the notes, each note was recorded at cost, net of the derivative liability. The discount on each note is amortized as interest expense to the date such note is expected to convert using the effective interest rate method and is reflected in the statements of operations as accretion of debt discount. The Company classifies its derivative liabilities in the balance sheet as current or non-current based on its expectation of when the derivative will be settled, consistent with the assumptions used when determining the fair value of the derivative liabilities. Redeemable Convertible Preferred Stock The Company records all shares of redeemable convertible preferred stock at their respective fair values on the dates of issuance, net of issuance costs. The redeemable convertible preferred stock is recorded outside of permanent equity because upon the occurrence of certain deemed liquidation events, the majority of the holders can opt to redeem the shares at the liquidation preference and these events, including a merger, acquisition or sale of substantially all of the assets, are considered not solely within the Company’s control. The Company has not adjusted the carrying values of the redeemable convertible preferred stock to its redemption value because it is uncertain whether or when a deemed liquidation event would occur. If a deemed liquidation event becomes probable, the carrying value will be adjusted to the redemption value at that time. Leases Leases are classified at their inception as either operating or capital leases based on the economic substance of the agreement. The Company recognizes rent expense for its operating leases, inclusive of rent escalation provisions and rent holidays, on a straight-line basis over the respective lease term. Additionally, the Company recognizes tenant improvement allowances under the operating leases as a deferred lease obligation and amortizes the tenant improvement allowances as a reduction to rent expense on a straight-line basis over the respective lease term. At June 30, 2019 and December 31, 2018, no capital leases were recorded in the balance sheets. Research and Development Costs Research and development costs are expensed as incurred. Research and development costs include salaries and bonuses, stock compensation, employee benefits, consulting costs and external contract research and development and manufacturing expenses. Upfront payments and milestone payments made for the licensing of technology are expensed as research and development in the period in which they are incurred. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed. Research Contract Costs and Accruals The Company accrues for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of preclinical studies and clinical trials, and contract manufacturing activities. The Company records the estimated costs of research and development activities based upon the estimated amount of services provided and includes these costs in accrued liabilities in the balance sheets and within research and development expense in the statements of operations. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the research studies or clinical trials and manufacturing activities, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. Stock-Based Compensation The Company measures all stock options and other stock-based awards based on the date of the grant and recognizes compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. The Company has mainly issued stock options with service-based vesting conditions and records the expense for these awards using the straight-line method. The Company has also issued stock options with performance-based vesting conditions and records the expense for these awards at the time that the achievement of the performance becomes highly probable or complete. The Company recognizes adjustments to stock-based compensation expense for forfeitures as they occur. The Company classifies stock-based compensation expense in its statements of operations in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified. The Company recognizes adjustments to stock-based compensation expense for forfeitures as they occur. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company historically has been a private company and lacked company-specific historical and implied volatility information. Therefore, it estimated its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to do so until such time as it has adequate historical data regarding the volatility of its own publicly traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The fair value for each restricted common stock award is estimated on the date of grant based on the fair value of the Company’s common stock on that same date. Net Loss Per Share The Company follows the two-class method when computing net income (loss) per share, as the Company has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting income (loss) attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities, including outstanding stock options. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of outstanding stock options. The Company’s outstanding redeemable convertible preferred stock contractually entitle the holders of such shares to participate in distributions but contractually does not require the holders of such shares to participate in losses of the Company. As the Company reported a net loss attributable to common stockholders for the three and six months ended June 30, 2019, there is no income allocation required under the two-class method. In addition, there is no dilution attributed to weighted average shares outstanding in the calculation of diluted loss per share, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the three and six months ended June 30, 2019, the Company’s only element of other comprehensive income was unrealized gains on available for sale securities. There was no difference between net loss and comprehensive loss for the six months ended June 30, 2018. Recently Adopted Accounting Pronouncements In May 2014, the Financial Accounting Standards Board issued Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers In June 2018, the FASB issued Accounting Standards Update 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. This guidance addresses specific cash flow issues with the objective of reducing the diversity in practice for the treatment of these issues. The areas identified include: debt prepayment or debt extinguishment costs; settlement of zero-coupon debt instruments; contingent consideration payments made after a business combination; proceeds from the settlement of insurance claims; proceeds from the settlement of corporate-owned life insurance policies; distributions received from equity method investees; beneficial interests in securitization transactions; and application of the predominance principle with respect to separately identifiable cash flows. The Company adopted this new guidance beginning January 1, 2017, on a retrospective basis, which did not result in a material impact on its financial statements and related disclosures. In November 2016, the FASB issued ASU 2016-18, Restricted Cash In May 2017, the FASB issued ASU No. 2017-09, Compensation—Stock Compensation Scope of Modification Accounting Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”). ASU 2016-02 will require lessees to recognize most leases on their balance sheet as a right-of-use asset and a lease liability. Leases will be classified as either operating or finance, and classification will be based on criteria similar to current lease accounting, but without explicit bright lines. For public entities, the guidance is effective for annual reporting periods beginning after December 15, 2018 and for interim periods within those fiscal years. For non-public entities, the guidance is effective for annual reporting periods beginning after December 15, 2019. Early adoption is permitted for all entities. The Company is currently evaluating the impact that the adoption of ASU 2016-02 will have on its financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820) (“ASU 2018-13”). ASU 2018-13 modifies fair value disclosure requirements, specifically around level transfers and valuation of Level 3 assets and liabilities. ASU 2018-13 is effective for financial statements issued for annual and interim periods beginning after December 15, 2019 for all entities. Early adoption of all or part of ASU No. 2018-13 is permitted. The Company does not expect that the adoption of this new standard will have a material impact on its disclosures.

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets and Accrued Expenses	6 Months Ended
	Jun. 30, 2019
Prepaid Expenses And Other Current Assets And Accrued Expenses [Abstract]
Prepaid Expenses and Other Current Assets and Accrued Expenses	Note 3. Prepaid Expenses and Other Current Assets and Accrued Expenses Prepaid expenses and other current assets consisted of the following (in thousands): June 30, 2019 December 31, 2018 Prepaid research and development expenses $ 1,654 $ 1,686 Other 63 23 Total prepaid expenses and other current assets $ 1,717 $ 1,709 Accrued expenses consisted of the following (in thousands): June 30, 2019 December 31, 2018 Accrued payroll and related expenses $ 540 $ 311 Accrued research and development expenses 145 100 Professional fees 530 75 Other 45 52 Total accrued expenses $ 1,260 $ 538

Convertible Notes Payable

Convertible Notes Payable	6 Months Ended
	Jun. 30, 2019
Convertible Debt Disclosure [Abstract]
Convertible Notes Payable	Note 4. Convertible Notes Payable Wellcome Trust Convertible Notes In June 2018, the Company entered into a second Company Funding Agreement with The Wellcome Trust, LLC (“Wellcome Trust”) to receive up to $8.0 million in gross proceeds from the issuance of a convertible note (the “2018 Convertible Note”). The Company received $2.0 million of proceeds in July 2018, $2.7 million in November 2018, $1.6 million in March 2019, and $1.6 million in April 2019. The Company is eligible to receive up to an aggregate of approximately $0.1 million in future funding under the terms of the 2018 Wellcome Funding Agreement, which would be payable by Wellcome Trust at the Company’s option upon the achievement of a specified clinical milestone The 2018 Convertible Note has a stated interest rate of 2% per annum above the three-month Dollar LIBOR rate, which is not payable until settlement of the principal. The note is subject to redemption upon written demand by Wellcome Trust any time after the fifth anniversary of the effective date, resulting in their classification as long-term liabilities as of December 31, 2018. The principal due under the 2018 Convertible Note converts into the class of the Company’s stock issued in the Company’s next qualified financing or upon event of default at a discounted conversion price between 0% and 25% of the purchase price per share of such securities issued. The accrued interest in such a circumstance would be forgiven. At inception, the Company concluded that the 2018 Convertible Note contained a conversion option at a significant discount that was deemed to be an embedded derivative, which is required to be bifurcated and accounted for separately from the debt host. There were no debt issuance costs associated with the 2018 Convertible Note. The Company recognized the following changes in the debt related to the 2018 Convertible Note during the year ended December 31, 2018 as well as the six months ended June 30, 2018 and 2019 (in thousands): Financial statement impacted Balance, December 31, 2017 $ 3,985 Accretion to settlement value 25 Statement of operations Accrued interest 39 Statement of operations Balance March 31, 2018 4,049 Accretion to settlement value 3 Statement of operations Accrued interest 44 Statement of operations Balance June 30, 2018 4,096 Issuance of 2018 Convertible Note 2,000 Balance sheet Accretion to settlement value 23 Statement of operations Accrued interest 19 Statement of operations Interest forgiven upon conversion (289 ) Statement of operations Conversion of Wellcome Trust Convertible Notes to redeemable convertible preferred stock (5,849 ) Balance sheet Balance, August 1, 2018 (date of conversion) — Issuance of 2018 Convertible Note 2,700 Balance sheet Allocation of proceeds to derivative liability (375 ) Balance sheet Accretion to settlement value 180 Statement of operations Accrued interest 11 Statement of operations Balance, December 31, 2018 2,516 Issuance of 2018 Convertible Note 1,564 Balance sheet Allocation of proceeds to derivative liability (228 ) Balance sheet Accretion to settlement value 423 Statement of operations Accrued interest 29 Statement of operations Interest forgiven upon conversion (40 ) Statement of operations Conversion of Wellcome Trust Convertible Notes to redeemable convertible preferred stock (4,264 ) Balance sheet Balance, March 31, 2019 $ — Issuance of 2018 Convertible Note 1,564 Balance sheet Allocation of proceeds to derivative liability (522 ) Balance sheet Accretion to settlement value 522 Statement of operations Conversion of Wellcome Trust Convertible Notes to redeemable convertible preferred stock (1,564 ) Balance sheet Balance, June 30, 2019 $ — Convertible Notes Since inception, the Company has issued $14.0 million of convertible notes (the “Convertible Notes”), of which $13.5 million was issued to PureTech Health LLC (“PureTech Health”), a related party (see Note 11). There were no debt issuance costs associated with the Convertible Notes. The Company concluded that the Convertible Notes contained a conversion option at a significant premium that was deemed to be an embedded derivative, which is required to be bifurcated and accounted for separately from the debt host. In August 2018, the then outstanding Convertible Notes were converted to Series A Preferred Stock. The Company recognized the following changes in the debt related to the Convertible Notes during the six months ended June 30, 2018 (in thousands): Financial statement impacted Balance, December 31, 2017 $ 7,674 Issuance of new notes 3,000 Balance sheet Allocation of proceeds to derivative liability (722 ) Balance sheet Accretion to settlement value 562 Statement of operations Accrued interest 242 Statement of operations Balance, March 31, 2018 10,756 Issuance of new notes 4,000 Balance sheet Allocation of proceeds to derivative liability (696 ) Balance sheet Accretion to settlement value 82 Statement of operations Accrued interest 263 Statement of operations Balance, June 30, 2018 14,405 Accretion to settlement value 1,301 Statement of operations Accrued interest 125 Statement of operations Interest forgiven upon conversion (47 ) Statement of operations Conversion of Convertible Notes to redeemable convertible preferred stock (15,784 ) Balance sheet Balance, December 31, 2018 $ — There were no Convertible Notes issued during the six months ended June 30, 2019.

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	6 Months Ended
	Jun. 30, 2019
Temporary Equity Disclosure [Abstract]
Redeemable Convertible Preferred Stock	Note 5. Redeemable Convertible Preferred Stock Series Seed Redeemable Convertible Preferred Stock Between 2009 and 2011, the Company authorized and issued 4,412,500 shares of Series Seed Preferred Stock at an issuance price of $0.0001 per share, for total proceeds of less than $0.1 million. There were no issuance costs in connection with the Series Seed Preferred Stock issuance. Series A Redeemable Convertible Preferred Stock In August 2018, the Company authorized 3,126,700 shares of Series A Preferred Stock. The Company then issued 1,188,707 shares of Series A Preferred Stock at an issuance price of $13.46 per share resulting in gross proceeds of approximately $16.0 million. There were $0.1 million of issuance costs associated with the Series A Preferred Stock. In conjunction with the August 2018 issuance of Series A Preferred Stock, all outstanding principal and accrued interest under the Wellcome Trust Notes and Convertible Notes converted to 1,937,993 shares of Series A Preferred Stock. Series B Redeemable Convertible Preferred Stock In March 2019, the Company authorized 5,422,845 shares of Series B Preferred Stock. The Company then issued 4,953,758 shares of Series B Preferred Stock at an issuance price of $15.14 per share resulting in gross proceeds of approximately $75.0 million. There were $0.2 million of issuance costs associated with the Series B Preferred Stock. In conjunction with the March 2019 issuance of Series B Preferred Stock, all outstanding principal and accrued interest under the Wellcome Trust Notes converted to 331,344 shares of Series B Preferred Stock. In April 2019, the Company received $1.6 million from the issuance of the Wellcome Trust Notes, which were subsequently converted into 137,743 shares of Series B redeemable convertible preferred stock. The Series Seed, Series A and Series B redeemable convertible preferred stock (together as “Preferred Stock”) have the following rights and preferences: Voting: On any matter presented to the stockholders of the Company for their action or consideration at any meeting of stockholders of the Company, each holder of outstanding shares of Preferred Stock shall be entitled to cast the number of votes equal to the number of whole shares of common stock into which the shares of Preferred Stock held by such holder are convertible as of the record date for determining stockholders entitled to vote on such matter. Dividends: Prior to and in preference of any dividends declared for common stock of the Company, the Board of Directors may elect to declare dividends on each share of Preferred Stock. Liquidation preference: In the event of any liquidation, dissolution or winding-up of the Company, the Preferred Stock shall be entitled to receive an amount per share equal to the greater of (i) the original issue price, plus any dividends declared but unpaid thereon, or (ii) such amount per share as would have been payable had all shares of such class or series of Preferred Stock been converted into common stock, prior to any distributions being made to common stock. If upon liquidation, dissolution or winding up of the Company, the assets available for distribution are insufficient to pay the holders of Preferred Stock the full amount to which they are entitled, the Preferred Stockholders share ratably in any distribution of the assets. Conversion: Each share of Preferred Stock is convertible at the option of the holder at any time after issuance into the number of fully paid and non-assessable shares of common stock as determined by dividing the original issue price of each series of Preferred Stock by the conversion price of each series in effect at time of the conversion. The initial conversion price is the respective original issue price, subject to adjustment in accordance with the anti-dilution provisions of the stock. Each share of Preferred Stock will automatically be converted into one share of common stock at the then effective conversion rate in the event of either (i) a qualified initial public offering that results in minimum gross proceeds to the Company of $50.0 million or (ii) the election of the holders of the then outstanding Preferred Stock. As of June 30, 2019, none of the outstanding shares of Preferred Stock had been converted into common stock. Redemption: The Preferred Stock may be redeemed upon a Deemed Liquidation Event as defined in the Company’s Certificate of Incorporation. The Preferred Stock may be redeemed at the greater of (i) the original issue price per share, plus any dividends declared but unpaid thereon, or (ii) such amount per share as would have been payable had all shares of such class or series of Preferred Stock been converted into common stock prior to the Deemed Liquidation Event. At June 30, 2019, the shares of Preferred Stock were not redeemable and the likelihood of an occurrence of a Deemed Liquidation Event was not deemed to be probable. Reissuance: Shares of any Preferred Stock that are redeemed or converted will be retired or canceled and may not be reissued by the Company. The original issuance price of the Preferred Stock was $1.00 per share, $13.46 per share and $15.14 per share for the Series Seed Preferred Stock, Series A Preferred Stock and Series B Preferred Stock, respectively.

Common Stock

Common Stock	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Common Stock	Note 6. Common Stock As of June 30, 2019, the Company’s Certificate of Incorporation authorized the Company to issue 20,779,200 shares of common stock, $0.0001 par value per share. The voting, dividend and liquidation rights of the holders of common stock are subject to and qualified by the rights, powers, and preferences of the holders of the shares of Preferred Stock. Holders of the common stock are entitled to one vote for each share of common stock held at all meetings of stockholders and written actions in lieu of meetings, provided, however, that except as otherwise required by law, holders of common stock as such shall not be entitled to vote on any amendment to the Company’s Certificate of Incorporation that relates solely to the terms of one or more outstanding series of Preferred Stock if the holders of such affected series are entitled, either separately or together with the holders of one or more other such series, to vote thereon pursuant to the Company’s Certificate of Incorporation or pursuant to Delaware General Corporation Law. Subject to the payment in full of all preferential dividends to which the holders of the Preferred Stock are entitled, the holders of common stock shall be entitled to receive dividends out of funds legally available. In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company, after the payment or provision for payment of all debts and liabilities of the Company and all preferential amounts to which the holders of Preferred Stock are entitled with respect to the distribution of assets in liquidation, the holders of common stock shall be entitled to share ratably in the remaining assets of the Company available for distribution. As of June 30, 2019, there were 164,122 shares of common stock outstanding.

Net Loss per Share

Net Loss per Share	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Net Loss per Share	Note 7. Net Loss per Share The following table sets forth the computation of basic and diluted net loss per share of common stock for the three and six months ended June 30, 2019 (in thousands, except share and per share data): Three Months Ended June 30, Six Months Ended June 30, 2019 2019 Net Loss $ (15,140 ) $ (27,145 ) Weighted-average shares used in computing net loss per share 103,684 53,460 Net loss per share, basic and diluted $ (146.02 ) $ (507.76 ) As of June 30, 2018, there were no shares of common stock outstanding. As of December 31, 2018, the Company had 12 shares of common stock outstanding. The Company’s potentially dilutive securities, which include stock options and convertible preferred stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company’s outstanding shares of Preferred Stock contractually entitle the holders of such shares to participate in distributions but contractually does not require the holders of such shares to participate in losses of the Company. Accordingly, these shares have not been included in the denominator used to calculate net loss per share. Common Stock Equivalents The following common stock equivalents presented based on amounts outstanding at each period end, have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive impact: June 30, 2019 2018 Redeemable convertible preferred stock (as converted to common stock) 16,833,790 5,730,513 Stock options to purchase common stock 4,702,906 1,230,512 Warrants to purchase common stock — 19,998 21,536,696 6,981,023

Stock-based Compensation

Stock-based Compensation	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	Note 8. Stock-based Compensation Stock Options In September 2009, the Company’s board of directors approved the 2009 Stock Incentive Plan (the “2009 Plan”) which provided for the grant of incentive stock options to employees and non-statutory stock options to directors, consultants, and non-employees of the Company. The aggregate common shares issuable were 3,911,138 under the 2009 Plan, as amended. The 2009 Plan terminated in July 2019 effective upon the completion of the Company’s IPO. No additional options will be granted under the 2009 Plan. At June 30, 2019, there were 3,839,545 options and restricted stock units (“RSUs”) outstanding under the 2009 Plan. In May 2019, the board of directors approved the 2019 Stock Option and Incentive Plan (the “2019 Plan”) which became effective on June 26, 2019, the date immediately prior to the date on which the registration statement related to the IPO was declared effective by the SEC Options under the 2019 Plan generally vest based on the grantee’s continued service with the Company during a specified period following a grant as determined by the board of directors and expire ten years from the grant date. In general, awards typically vest in four years, but vesting conditions can vary based on the discretion of the Company’s board of directors. A summary of the Company’s stock option activity and related information is as follows: Number of Shares Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2018 2,310,369 $ 4.49 7.1 $ 6,420 Granted 2,554,146 11.93 Exercised (38,961 ) 0.11 Forfeited (122,648 ) 2.22 Outstanding as of June 30, 2019 4,702,906 8.63 8.5 53,571 Options vested and expected to vest as of June 30, 2019 4,702,906 $ 8.63 8.5 $ 53,571 Options exercisable as of June 30, 2019 2,776,727 $ 7.80 7.7 $ 33,939 The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock as of June 30, 2019. As of June 30, 2019, there was $7.9 million of unrecognized compensation cost, which is expected to be recognized over a weighted-average period of 2.5 years. The fair value of all option activity was estimated at the date of grant using the Black-Scholes model with the following assumptions: Six Months Ended June 30, 2019 Fair value of options $ 3.83 - 8.05 Fair value of common stock $ 9.20 - 20.02 Expected term (in years) 5.02 - 6.16 Expected volatility 43.57% - 44.41% Risk-free interest rate 1.76% - 2.44% Expected dividend yield 0.00% On May 16, 2019, we issued 105,163 fully vested restricted stock units with respect to 105,163 shares of common stock. The average grant date fair value was $10.97 per share. As of June 30, 2019, there was no unrecognized compensation expense related to unvested RSUs. Warrants In October 2016, PureTech Health, a related party, agreed to provide management services to the Company in exchange for a warrant to purchase up to 19,998 shares of the Company’s common stock. The warrant vests monthly as services are performed over a 24-month period and has a purchase price of $2.92 per share. The total expense for the three and six months ended June 30, 2018 for the warrant was less than $0.1 million. The warrant was fully vested as of October 2018. In August 2018, PureTech Health exercised the warrant to purchase 12 shares resulting in proceeds to the Company of less than $0.1 million. In March 2019, PureTech Health exercised the warrant to purchase the remaining 19,986 shares resulting in proceeds to the Company of $0.1 million. There are no outstanding warrants as of June 30, 2019. Stock-based Compensation Expense Stock-based compensation expense is classified in the statements of operations for the three and six months ended June 30, 2019 and 2018 as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Research and development $ 144 $ 18 $ 224 $ 43 General and administrative 6,697 48 9,721 68 Total stock based compensation expense $ 6,841 $ 66 $ 9,945 $ 111

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	6 Months Ended
	Jun. 30, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]
Fair Value of Financial Assets and Liabilities	Note 9. Fair Value of Financial Assets and Liabilities The following tables present information about the Company’s assets and liabilities as of June 30, 2019 and December 31, 2018 that are measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values (in thousands): Fair Value Measurement at June 30, 2019 Using Level 1 Level 2 Level 3 Total Assets: Cash equivalents (Money Market Fund) $ 7,291 $ — $ — $ 7,291 Short-term investments (US Treasuries) 64,804 — — 64,804 Total $ 72,095 $ — $ — $ 72,095 Fair Value Measurement at December 31, 2018 Using Level 1 Level 2 Level 3 Total Assets: Cash equivalents (US Treasuries) $ 5,042 $ — $ — $ 5,042 Short-term investments (US Treasuries) 4,983 — — 4,983 Total $ 10,025 $ — $ — $ 10,025 Liabilities: Derivative instrument $ — $ — $ 389 $ 389 Total $ — $ — $ 389 $ 389 The estimated fair value and amortized cost of the Company’s short-term investments by contractual maturity are summarized as follows (in thousands): June 30, 2019 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Due in one year or less $ 64,733 $ 71 $ — $ 64,804 Total $ 64,733 $ 71 $ — $ 64,804 December 31, 2018 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Due in one year or less $ 4,984 $ — $ (1 ) $ 4,983 Total $ 4,984 $ — $ (1 ) $ 4,983 The derivative liability is considered a Level 3 liability because its fair value measurement is based, in part, on significant inputs not observed in the market. Any reasonable changes in the assumptions used in the valuation could materially affect the financial results of the Company. The Company recognized the following changes in the fair value of derivative liabilities during the year ended December 31, 2018 and the six months ended June 30, 2019 (in thousands): Balance, December 31, 2017 $ 2,606 Allocation of note issuance proceeds to derivative 722 Change in fair value of derivative 80 Balance, March 31, 2018 3,408 Allocation of note issuance proceeds to derivative 696 Change in fair value of derivative (2,283 ) Balance, June 30, 2018 1,821 Change in fair value of derivative 2,633 Conversion of convertible debt to Series A preferred stock (4,454 ) Balance, August 1, 2018 (date of conversion) — Allocation of note issuance proceeds to derivative 375 Change in fair value of derivative 14 Balance, December 31, 2018 389 Allocation of note issuance proceeds to derivative 228 Change in fair value of derivative 135 Conversion of convertible debt to Series B preferred stock (752 ) Balance, March 31, 2019 $ — Allocation of note issuance proceeds to derivative 522 Conversion of convertible debt to Series B preferred stock (522 ) Balance, June 30, 2019 $ —

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 10. Commitments and Contingencies Leases The Company entered into a 51-month lease for office space in Boston, Massachusetts that began in December 2018 and expires in February 2023. The Company is required to maintain a cash balance of $0.1 million to secure a letter of credit associated with this lease. The amount was classified as restricted cash in the balance sheet at December 31, 2018 and June 30, 2019. The Company recorded rent expense of $0.2 million during the six months ended June 30, 2019. Future minimum lease payments under non-cancelable operating lease agreements as of June 30, 2019, are as follows (in thousands): As of June 30, Minimum Lease Payments Less than 1 year $ 496 1 to 2 years 503 2 to 3 years 510 3 to 4 years 343 4 to 5 years — Total $ 1,852 Intellectual Property License with PureTech Health In March 2011, the Company entered into a royalty-bearing exclusive patent license agreement with PureTech Health, a related party, granting the Company rights to research, develop, make, use, sell, and lease technology covered by two then-pending patent applications (the “Patent License”). The two patents pending related to methods and compositions for treatment of disorders ameliorated by muscarinic receptor activation. The Company paid no initial upfront costs upon signing the agreement. Under the agreement, of products covered by the patents, the Company will owe PureTech Health a low single digit percentage running royalty of annual net sales by the Company. Additionally, upon certain clinical and regulatory approval events, the Company will owe PureTech amounts in the form of milestone payments, totaling $10.0 million. The Company incurred no expenses related to the Patent License provided by PureTech Health during the six months ended June 30, 2018 and 2019. The Company had no outstanding liabilities to PureTech Health related to the Patent License at December 31, 2018 and June 30, 2019. Intellectual Property License with Eli Lilly and Company In May 2012, the Company entered into an agreement with Eli Lilly and Company to obtain rights to data, regulatory filings and patents (now expired) related to xanomeline. The Company paid an initial upfront payment of $0.1 million upon signing of the agreement, which was expensed when incurred. Upon certain regulatory approval events and other sales achievements, the Company will owe Eli Lilly and Company additional amounts in the form of milestone payments of up to $70.0 million and tiered royalties ranging from the low to mid single digits on sales. As of June 30, 2019, no milestones have been reached, and accordingly, no milestone payments have been made. Indemnification In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnifications. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future but have not yet been made. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. However, the Company may incur charges in the future as a result of these indemnification obligations. Contingencies From time to time, the Company may have certain contingent liabilities that arise in the ordinary course of its business activities. The Company accrues a liability for such matters when it is probable that future expenditures will be made, and such expenditures can be reasonably estimated. Litigation The Company is not a party to any litigation and does not have contingency reserves established for any litigation liabilities as of June 30, 2019.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2019
Related Party Transactions [Abstract]
Related Party Transactions	Note 11. Related Party Transactions PureTech Health Management Consulting Services and Overhead Agreement The Company engages PureTech Health, a related party, to provide, among other things, management expertise, strategic advice, administrative support, computer and telecommunications services and office infrastructure. In exchange for providing such services, the Company pays PureTech Health a monthly fee. In addition, PureTech Health periodically invoices the Company for out-of-pocket expenses reasonably incurred in connection with providing such business services. The Company incurred general and administrative costs for management services provided by PureTech Health totaling less than $0.1 million in the six months ended June 30, 2019, and totaling $0.1 million in the six months ended June 30, 2018. The Company had outstanding current liabilities to PureTech Health of less than $0.1 million and $0.1 million at June 30, 2019 and December 31, 2018, respectively, which are recorded as accounts payable in the balance sheet.

401(k) Savings Plan

401(k) Savings Plan	6 Months Ended
	Jun. 30, 2019
Compensation And Retirement Disclosure [Abstract]
401(k) Savings Plan	Note 12. 401(k) Savings Plan The Company has a 401(k) retirement plan in which substantially all U.S. employees are eligible to participate. Eligible employees may elect to contribute up to the maximum limits, as set by the Internal Revenue Service, of their eligible compensation. The total contribution matching expense for the Company was less than $0.1 million for each of the six months ended June 30, 2019 and 2018.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2019
Subsequent Events [Abstract]
Subsequent Events	Note 13. Subsequent Events Amended and Restated Certificate of Incorporation In May 2019 and June 2019, the Company’s board of directors and stockholders, respectively, approved an amended and restated certificate of incorporation that, effective simultaneous with the closing of the IPO (see Note 1), increased the total number of shares of capital stock which the Company shall have authority to issue to 160,000,000 shares, par value $0.0001 per share, of which 150,000,000 shares shall be shares of common stock and 10,000,000 shares shall be undesignated preferred stock.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation and Use of Estimates	Basis of Presentation and Use of Estimates The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) of the Financial Accounting Standards Board (“FASB”). The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, the accrual for research and development expenses, derivative liabilities, the valuation of stock-based awards and prior to the IPO, the valuation of common stock. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The accompanying balance sheet as of June 30, 2019, the statements of operations, comprehensive loss, and cash flows for the three and six months ended June 30, 2019 and 2018, and the statements of redeemable convertible preferred stock and stockholders’ equity (deficit) for the three and six months ended June 30, 2019 and 2018 are unaudited. The unaudited interim financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of June 30, 2019 and the results of its operations and its cash flows for the three and six months ended June 30, 2019 and 2018. Certain information and footnote disclosures typically included in annual financial statements prepared in accordance with have been condensed or omitted. Accordingly, these unaudited interim financial statements should be read in conjunction with the Company’s financial statements as of and for the year ended December 31, 2018, which are included in the Company’s prospectus related to the Company’s IPO, filed June 28, 2019 (File No. 333-231863) with the SEC, pursuant to Rule 424(b) under the Securities Act of 1933, as amended.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents.
Short-term Investments	Short-term Investments The Company’s short-term investments are classified as available-for-sale and are carried at fair value with the unrealized gains and losses reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other income (expense), net based on the specific identification method.
Concentration of Manufacturing Risk	Concentration of Manufacturing Risk The Company is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering. Should the in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the statements of operations. $2.0 million As of December 31, 2018, the Company had not recorded any deferred offering costs. As of June 30, 2019, the Company recorded deferred offering costs of $XX in connection with its IPO.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company’s financial instruments consist of cash equivalents, short-term investments, accounts payable, accrued expenses, convertible notes and derivatives embedded within the convertible notes. The carrying amount of accounts payable and accrued expenses are considered a reasonable estimate of their fair value, due to the short-term maturity of these instruments. The Company’s cash equivalents, short-term investments and derivative liabilities are carried at fair value, determined according to the fair value hierarchy described below (see Note 9). The Company follows the guidance in FASB ASC 820, Fair Value Measurements and Disclosures Level 1: Quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2: Valuations based on quoted prices in markets that are not active or for which all significant inputs are observable, either directly or indirectly. Level 3: Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Fair value is a market-based measure considered from the perspective of a market participant rather than an entity-specific measure. Therefore, even when market assumptions are not readily available, the Company’s own assumptions reflect those that market participants would use in pricing the asset or liability at the measurement date. The Company uses prices and inputs that are current as of the measurement date, including during periods of market dislocation. In periods of market dislocation, the observability of prices and inputs may be reduced for many instruments. This condition could cause an instrument to be reclassified from Level 1 to Level 2 or Level 2 to Level 3.
Convertible Notes and Derivative Liabilities	Convertible Notes and Derivative Liabilities In connection with the issuance of the Wellcome Trust Convertible Notes and the Convertible Notes (see Note 4), the Company has identified embedded derivatives, which are recorded as liabilities on the Company’s balance sheets and are remeasured to fair value at each reporting date until the derivative is settled. Changes in the fair value of the derivative liabilities are recognized as change in fair value of derivative in the statements of operations. The fair value of the derivative liabilities are determined at each period end using a with and without method, which assesses the likelihood and timing of events that would result in either a conversion or change-of-control feature being triggered, as well as changes in the market conditions. Upon issuance of the notes, each note was recorded at cost, net of the derivative liability. The discount on each note is amortized as interest expense to the date such note is expected to convert using the effective interest rate method and is reflected in the statements of operations as accretion of debt discount. The Company classifies its derivative liabilities in the balance sheet as current or non-current based on its expectation of when the derivative will be settled, consistent with the assumptions used when determining the fair value of the derivative liabilities.
Redeemable Convertible Preferred Stock	Redeemable Convertible Preferred Stock The Company records all shares of redeemable convertible preferred stock at their respective fair values on the dates of issuance, net of issuance costs. The redeemable convertible preferred stock is recorded outside of permanent equity because upon the occurrence of certain deemed liquidation events, the majority of the holders can opt to redeem the shares at the liquidation preference and these events, including a merger, acquisition or sale of substantially all of the assets, are considered not solely within the Company’s control. The Company has not adjusted the carrying values of the redeemable convertible preferred stock to its redemption value because it is uncertain whether or when a deemed liquidation event would occur. If a deemed liquidation event becomes probable, the carrying value will be adjusted to the redemption value at that time.
Leases	Leases Leases are classified at their inception as either operating or capital leases based on the economic substance of the agreement. The Company recognizes rent expense for its operating leases, inclusive of rent escalation provisions and rent holidays, on a straight-line basis over the respective lease term. Additionally, the Company recognizes tenant improvement allowances under the operating leases as a deferred lease obligation and amortizes the tenant improvement allowances as a reduction to rent expense on a straight-line basis over the respective lease term. At June 30, 2019 and December 31, 2018, no capital leases were recorded in the balance sheets.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development costs include salaries and bonuses, stock compensation, employee benefits, consulting costs and external contract research and development and manufacturing expenses. Upfront payments and milestone payments made for the licensing of technology are expensed as research and development in the period in which they are incurred. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed.
Research Contract Costs And Accruals	Research Contract Costs and Accruals The Company accrues for estimated costs of research and development activities conducted by third-party service providers, which include the conduct of preclinical studies and clinical trials, and contract manufacturing activities. The Company records the estimated costs of research and development activities based upon the estimated amount of services provided and includes these costs in accrued liabilities in the balance sheets and within research and development expense in the statements of operations. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the research studies or clinical trials and manufacturing activities, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.
Share-Based Compensation	Stock-Based Compensation The Company measures all stock options and other stock-based awards based on the date of the grant and recognizes compensation expense of those awards over the requisite service period, which is generally the vesting period of the respective award. The Company has mainly issued stock options with service-based vesting conditions and records the expense for these awards using the straight-line method. The Company has also issued stock options with performance-based vesting conditions and records the expense for these awards at the time that the achievement of the performance becomes highly probable or complete. The Company recognizes adjustments to stock-based compensation expense for forfeitures as they occur. The Company classifies stock-based compensation expense in its statements of operations in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified. The Company recognizes adjustments to stock-based compensation expense for forfeitures as they occur. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company historically has been a private company and lacked company-specific historical and implied volatility information. Therefore, it estimated its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to do so until such time as it has adequate historical data regarding the volatility of its own publicly traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The fair value for each restricted common stock award is estimated on the date of grant based on the fair value of the Company’s common stock on that same date.
Net Loss Per Share	Net Loss Per Share The Company follows the two-class method when computing net income (loss) per share, as the Company has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting income (loss) attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities, including outstanding stock options. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of outstanding stock options. The Company’s outstanding redeemable convertible preferred stock contractually entitle the holders of such shares to participate in distributions but contractually does not require the holders of such shares to participate in losses of the Company. As the Company reported a net loss attributable to common stockholders for the three and six months ended June 30, 2019, there is no income allocation required under the two-class method. In addition, there is no dilution attributed to weighted average shares outstanding in the calculation of diluted loss per share, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the three and six months ended June 30, 2019, the Company’s only element of other comprehensive income was unrealized gains on available for sale securities. There was no difference between net loss and comprehensive loss for the six months ended June 30, 2018.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In May 2014, the Financial Accounting Standards Board issued Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers In June 2018, the FASB issued Accounting Standards Update 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. This guidance addresses specific cash flow issues with the objective of reducing the diversity in practice for the treatment of these issues. The areas identified include: debt prepayment or debt extinguishment costs; settlement of zero-coupon debt instruments; contingent consideration payments made after a business combination; proceeds from the settlement of insurance claims; proceeds from the settlement of corporate-owned life insurance policies; distributions received from equity method investees; beneficial interests in securitization transactions; and application of the predominance principle with respect to separately identifiable cash flows. The Company adopted this new guidance beginning January 1, 2017, on a retrospective basis, which did not result in a material impact on its financial statements and related disclosures. In November 2016, the FASB issued ASU 2016-18, Restricted Cash In May 2017, the FASB issued ASU No. 2017-09, Compensation—Stock Compensation Scope of Modification Accounting Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”). ASU 2016-02 will require lessees to recognize most leases on their balance sheet as a right-of-use asset and a lease liability. Leases will be classified as either operating or finance, and classification will be based on criteria similar to current lease accounting, but without explicit bright lines. For public entities, the guidance is effective for annual reporting periods beginning after December 15, 2018 and for interim periods within those fiscal years. For non-public entities, the guidance is effective for annual reporting periods beginning after December 15, 2019. Early adoption is permitted for all entities. The Company is currently evaluating the impact that the adoption of ASU 2016-02 will have on its financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820) (“ASU 2018-13”). ASU 2018-13 modifies fair value disclosure requirements, specifically around level transfers and valuation of Level 3 assets and liabilities. ASU 2018-13 is effective for financial statements issued for annual and interim periods beginning after December 15, 2019 for all entities. Early adoption of all or part of ASU No. 2018-13 is permitted. The Company does not expect that the adoption of this new standard will have a material impact on its disclosures.

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets and Accrued Expenses (Tables)	6 Months Ended
	Jun. 30, 2019
Prepaid Expenses And Other Current Assets And Accrued Expenses [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): June 30, 2019 December 31, 2018 Prepaid research and development expenses $ 1,654 $ 1,686 Other 63 23 Total prepaid expenses and other current assets $ 1,717 $ 1,709
Schedule of Accrued Expenses	Accrued expenses consisted of the following (in thousands): June 30, 2019 December 31, 2018 Accrued payroll and related expenses $ 540 $ 311 Accrued research and development expenses 145 100 Professional fees 530 75 Other 45 52 Total accrued expenses $ 1,260 $ 538

Convertible Notes Payable (Tabl

Convertible Notes Payable (Tables)	6 Months Ended
	Jun. 30, 2019
Convertible Notes Payable [Line Items]
Schedule of Changes in Convertible Debt	The Company recognized the following changes in the debt related to the Convertible Notes during the six months ended June 30, 2018 (in thousands): Financial statement impacted Balance, December 31, 2017 $ 7,674 Issuance of new notes 3,000 Balance sheet Allocation of proceeds to derivative liability (722 ) Balance sheet Accretion to settlement value 562 Statement of operations Accrued interest 242 Statement of operations Balance, March 31, 2018 10,756 Issuance of new notes 4,000 Balance sheet Allocation of proceeds to derivative liability (696 ) Balance sheet Accretion to settlement value 82 Statement of operations Accrued interest 263 Statement of operations Balance, June 30, 2018 14,405 Accretion to settlement value 1,301 Statement of operations Accrued interest 125 Statement of operations Interest forgiven upon conversion (47 ) Statement of operations Conversion of Convertible Notes to redeemable convertible preferred stock (15,784 ) Balance sheet Balance, December 31, 2018 $ —
2018 Convertible Note
Convertible Notes Payable [Line Items]
Schedule of Changes in Convertible Debt	The Company recognized the following changes in the debt related to the 2018 Convertible Note during the year ended December 31, 2018 as well as the six months ended June 30, 2018 and 2019 (in thousands): Financial statement impacted Balance, December 31, 2017 $ 3,985 Accretion to settlement value 25 Statement of operations Accrued interest 39 Statement of operations Balance March 31, 2018 4,049 Accretion to settlement value 3 Statement of operations Accrued interest 44 Statement of operations Balance June 30, 2018 4,096 Issuance of 2018 Convertible Note 2,000 Balance sheet Accretion to settlement value 23 Statement of operations Accrued interest 19 Statement of operations Interest forgiven upon conversion (289 ) Statement of operations Conversion of Wellcome Trust Convertible Notes to redeemable convertible preferred stock (5,849 ) Balance sheet Balance, August 1, 2018 (date of conversion) — Issuance of 2018 Convertible Note 2,700 Balance sheet Allocation of proceeds to derivative liability (375 ) Balance sheet Accretion to settlement value 180 Statement of operations Accrued interest 11 Statement of operations Balance, December 31, 2018 2,516 Issuance of 2018 Convertible Note 1,564 Balance sheet Allocation of proceeds to derivative liability (228 ) Balance sheet Accretion to settlement value 423 Statement of operations Accrued interest 29 Statement of operations Interest forgiven upon conversion (40 ) Statement of operations Conversion of Wellcome Trust Convertible Notes to redeemable convertible preferred stock (4,264 ) Balance sheet Balance, March 31, 2019 $ — Issuance of 2018 Convertible Note 1,564 Balance sheet Allocation of proceeds to derivative liability (522 ) Balance sheet Accretion to settlement value 522 Statement of operations Conversion of Wellcome Trust Convertible Notes to redeemable convertible preferred stock (1,564 ) Balance sheet Balance, June 30, 2019 $ —

Net Loss per Share (Tables)

Net Loss per Share (Tables)	6 Months Ended
	Jun. 30, 2019
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Net Loss Per Share of Common Stock	The following table sets forth the computation of basic and diluted net loss per share of common stock for the three and six months ended June 30, 2019 (in thousands, except share and per share data): Three Months Ended June 30, Six Months Ended June 30, 2019 2019 Net Loss $ (15,140 ) $ (27,145 ) Weighted-average shares used in computing net loss per share 103,684 53,460 Net loss per share, basic and diluted $ (146.02 ) $ (507.76 )
Schedule of Anti-Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share	The following common stock equivalents presented based on amounts outstanding at each period end, have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive impact: June 30, 2019 2018 Redeemable convertible preferred stock (as converted to common stock) 16,833,790 5,730,513 Stock options to purchase common stock 4,702,906 1,230,512 Warrants to purchase common stock — 19,998 21,536,696 6,981,023

Stock-based Compensation (Tabl

Stock-based Compensation (Tables)	6 Months Ended
	Jun. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Option Activity	A summary of the Company’s stock option activity and related information is as follows: Number of Shares Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2018 2,310,369 $ 4.49 7.1 $ 6,420 Granted 2,554,146 11.93 Exercised (38,961 ) 0.11 Forfeited (122,648 ) 2.22 Outstanding as of June 30, 2019 4,702,906 8.63 8.5 53,571 Options vested and expected to vest as of June 30, 2019 4,702,906 $ 8.63 8.5 $ 53,571 Options exercisable as of June 30, 2019 2,776,727 $ 7.80 7.7 $ 33,939
Summary of Fair Value of Option Activity Estimated at Date of Grant Using Black-Scholes Model	The fair value of all option activity was estimated at the date of grant using the Black-Scholes model with the following assumptions: Six Months Ended June 30, 2019 Fair value of options $ 3.83 - 8.05 Fair value of common stock $ 9.20 - 20.02 Expected term (in years) 5.02 - 6.16 Expected volatility 43.57% - 44.41% Risk-free interest rate 1.76% - 2.44% Expected dividend yield 0.00%
Summary of Stock-based Compensation Expense	Stock-based compensation expense is classified in the statements of operations for the three and six months ended June 30, 2019 and 2018 as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2019 2018 2019 2018 Research and development $ 144 $ 18 $ 224 $ 43 General and administrative 6,697 48 9,721 68 Total stock based compensation expense $ 6,841 $ 66 $ 9,945 $ 111

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	6 Months Ended
	Jun. 30, 2019
Schedule of Fair Value Measurement on Recurring Basis and Indicates the level of Fair Value Hierarchy Utilized	The following tables present information about the Company’s assets and liabilities as of June 30, 2019 and December 31, 2018 that are measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values (in thousands): Fair Value Measurement at June 30, 2019 Using Level 1 Level 2 Level 3 Total Assets: Cash equivalents (Money Market Fund) $ 7,291 $ — $ — $ 7,291 Short-term investments (US Treasuries) 64,804 — — 64,804 Total $ 72,095 $ — $ — $ 72,095 Fair Value Measurement at December 31, 2018 Using Level 1 Level 2 Level 3 Total Assets: Cash equivalents (US Treasuries) $ 5,042 $ — $ — $ 5,042 Short-term investments (US Treasuries) 4,983 — — 4,983 Total $ 10,025 $ — $ — $ 10,025 Liabilities: Derivative instrument $ — $ — $ 389 $ 389 Total $ — $ — $ 389 $ 389
Summary of Estimated Fair Value and Amortized Cost of Short term Investments by Contractual Maturity	The estimated fair value and amortized cost of the Company’s short-term investments by contractual maturity are summarized as follows (in thousands): June 30, 2019 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Due in one year or less $ 64,733 $ 71 $ — $ 64,804 Total $ 64,733 $ 71 $ — $ 64,804 December 31, 2018 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Due in one year or less $ 4,984 $ — $ (1 ) $ 4,983 Total $ 4,984 $ — $ (1 ) $ 4,983
Derivative Financial Instruments, Liabilities
Schedule of Changes in Fair Value Derivative Liabilities	The derivative liability is considered a Level 3 liability because its fair value measurement is based, in part, on significant inputs not observed in the market. Any reasonable changes in the assumptions used in the valuation could materially affect the financial results of the Company. The Company recognized the following changes in the fair value of derivative liabilities during the year ended December 31, 2018 and the six months ended June 30, 2019 (in thousands): Balance, December 31, 2017 $ 2,606 Allocation of note issuance proceeds to derivative 722 Change in fair value of derivative 80 Balance, March 31, 2018 3,408 Allocation of note issuance proceeds to derivative 696 Change in fair value of derivative (2,283 ) Balance, June 30, 2018 1,821 Change in fair value of derivative 2,633 Conversion of convertible debt to Series A preferred stock (4,454 ) Balance, August 1, 2018 (date of conversion) — Allocation of note issuance proceeds to derivative 375 Change in fair value of derivative 14 Balance, December 31, 2018 389 Allocation of note issuance proceeds to derivative 228 Change in fair value of derivative 135 Conversion of convertible debt to Series B preferred stock (752 ) Balance, March 31, 2019 $ — Allocation of note issuance proceeds to derivative 522 Conversion of convertible debt to Series B preferred stock (522 ) Balance, June 30, 2019 $ —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments Under Non-Cancelable Operating Lease Agreements	Future minimum lease payments under non-cancelable operating lease agreements as of June 30, 2019, are as follows (in thousands): As of June 30, Minimum Lease Payments Less than 1 year $ 496 1 to 2 years 503 2 to 3 years 510 3 to 4 years 343 4 to 5 years — Total $ 1,852

Nature of the Business - Additi

Nature of the Business - Additional Information (Details) $ / shares in Units, $ in Thousands	Jul. 02, 2019USD ($)$ / sharesshares	Jun. 14, 2019	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Subsidiary Sale Of Stock [Line Items]
Stock split ratio, description			one-for-1.2987
Stock split, conversion ratio		1.2987
Cash flows from operating activities			$ 15,687	$ 6,382
Accumulated deficit			58,700		$ 31,555
Cash and cash equivalents and short-term			$ 75,300
Subsequent Event | Redeemable Convertible Preferred Stock
Subsidiary Sale Of Stock [Line Items]
Temporary Equity, shares outstanding | shares	12,962,045
Subsequent Event | Redeemable Convertible Preferred Stock | Common Stock
Subsidiary Sale Of Stock [Line Items]
Conversion of stock, shares issued | shares	16,833,790
Subsequent Event | Initial Public Offering | Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold | shares	6,414,842
Public offering price pre share | $ / shares	$ 16
Net proceeds from initial public offering	$ 93,200
Underwriting discounts and commissions	7,200
Estimated offering expenses	$ 2,300
Subsequent Event | Underwriters' Over-Allotment Option | Common Stock
Subsidiary Sale Of Stock [Line Items]
Shares issued and sold | shares	836,718

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018	Jan. 01, 2017
Summary Of Significant Accounting Policies [Line Items]
Deferred offering costs	$ 2,032,000
Capital leases	0	$ 0
Maximum
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect of change on retained earnings for awards granted to non-employees			$ 100,000
Initial Public Offering
Summary Of Significant Accounting Policies [Line Items]
Deferred offering costs	$ 2,000,000	$ 0

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets and Accrued Expenses - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid research and development expenses	$ 1,654	$ 1,686
Other	63	23
Total prepaid expenses and other current assets	$ 1,717	$ 1,709

Prepaid Expenses and Other Cu_4

Prepaid Expenses and Other Current Assets and Accrued Expenses - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued payroll and related expenses	$ 540	$ 311
Accrued research and development expenses	145	100
Professional fees	530	75
Other	45	52
Total accrued expenses	$ 1,260	$ 538

Convertible Notes Payable - Add

Convertible Notes Payable - Additional Information (Detail) - USD ($)

1 Months Ended

3 Months Ended

5 Months Ended

6 Months Ended

12 Months Ended

120 Months Ended

Apr. 30, 2019

Mar. 31, 2019

Nov. 30, 2018

Jul. 31, 2018

Jun. 30, 2018

Jun. 30, 2019

Mar. 31, 2019

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2018

Jun. 30, 2019

Jun. 30, 2018

Dec. 31, 2018

Jun. 30, 2019

Debt Instrument [Line Items]

Proceeds from issuance of convertible notes

$ 4,000,000

$ 3,000,000

$ 3,128,000

$ 7,000,000

2018 Convertible Note

Debt Instrument [Line Items]

Gross proceeds from the issuance of a convertible note

$ 2,000,000

$ 1,564,000

$ 1,564,000

$ 2,700,000

Interest on unpaid principal balance of convertible notes

2.00%

2.00%

Debt issuance cost

0

0

$ 0

2018 Convertible Note | Wellcome Trust

Debt Instrument [Line Items]

Gross proceeds from the issuance of a convertible note

$ 1,600,000

$ 1,600,000

$ 2,700,000

$ 2,000,000

Convertible Notes

Debt Instrument [Line Items]

Debt issuance cost

$ 0

0

0

Proceeds from issuance of convertible notes

0

14,000,000

Convertible Notes | PureTech Health

Debt Instrument [Line Items]

Proceeds from issuance of convertible notes

$ 13,500,000

Maximum | 2018 Convertible Note

Debt Instrument [Line Items]

Percentage of debt discount conversion price

25.00%

Maximum | 2018 Convertible Note | Wellcome Trust

Debt Instrument [Line Items]

Gross proceeds from the issuance of a convertible note

$ 8,000,000

$ 100,000

Minimum [Member] | 2018 Convertible Note

Debt Instrument [Line Items]

Percentage of debt discount conversion price

0.00%

Convertible Notes Payable - Sch

Convertible Notes Payable - Schedule of Changes in Convertible Debt (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended				5 Months Ended	6 Months Ended
	Jul. 31, 2018	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Debt Instrument [Line Items]
Beginning balance	$ 14,405		$ 2,516	$ 10,756	$ 7,674		$ 2,516	$ 14,405	$ 7,674
Issuance of new notes				4,000	3,000		3,128		7,000
Allocation of proceeds to derivative liability				(696)	(722)
Accretion to settlement value				82	562			1,301
Accrued interest				263	242			125
Interest forgiven upon conversion								(47)
Conversion of Wellcome Trust Convertible Notes to redeemable convertible preferred stock							(7,102)	(15,784)
Ending balance				14,405	10,756	$ 2,516		2,516	14,405
2018 Convertible Note
Debt Instrument [Line Items]
Beginning balance	4,096		2,516	4,049	3,985		$ 2,516	4,096	3,985
Issuance of 2018 Convertible Note	2,000	$ 1,564	1,564			2,700
Allocation of proceeds to derivative liability		(522)	(228)			(375)
Accretion to settlement value	23	522	423	3	25	180
Accrued interest	19		29	44	39	11
Interest forgiven upon conversion	(289)		(40)
Conversion of Wellcome Trust Convertible Notes to redeemable convertible preferred stock	$ (5,849)	$ (1,564)	$ (4,264)
Ending balance				$ 4,096	$ 4,049	$ 2,516		$ 2,516	$ 4,096

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock - Additional Information (Details) - USD ($)	1 Months Ended			3 Months Ended		6 Months Ended		36 Months Ended
	Apr. 30, 2019	Mar. 31, 2019	Aug. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2011	Dec. 31, 2018
Temporary Equity [Line Items]
Payments of stock issuance costs						$ 1,199,000
Proceeds from issuance of convertible notes				$ 4,000,000	$ 3,000,000	$ 3,128,000	$ 7,000,000
Common Stock
Temporary Equity [Line Items]
Number of shares issued upon conversion						0
Wellcome Trust Notes
Temporary Equity [Line Items]
Proceeds from issuance of convertible notes	$ 1,600,000
Series Seed Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized						4,412,500		4,412,500	4,412,500
Redeemable convertible preferred stock, shares issued								4,412,500
Stock issuance price per share						$ 1		$ 0.0001
Payments of stock issuance costs								$ 0
Series Seed Redeemable Convertible Preferred Stock | Maximum
Temporary Equity [Line Items]
Proceeds from issuance of redeemable convertible preferred stock								$ 100,000
Series A Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized			3,126,700			3,126,700			3,126,700
Redeemable convertible preferred stock, shares issued			1,188,707
Stock issuance price per share			$ 13.46
Proceeds from issuance of redeemable convertible preferred stock			$ 16,000,000
Payments of stock issuance costs			$ 100,000
Number of shares issued upon conversion of debt			1,937,993
Series B Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized		5,422,845				5,422,845			0
Redeemable convertible preferred stock, shares issued		4,953,758
Stock issuance price per share		$ 15.14
Proceeds from issuance of redeemable convertible preferred stock		$ 75,000,000
Payments of stock issuance costs		$ 200,000
Number of shares issued upon conversion of debt	137,743	331,344
Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Convertible preferred stock, description						Each share of Preferred Stock will automatically be converted into one share of common stock at the then effective conversion rate in the event of either (i) a qualified initial public offering that results in minimum gross proceeds to the Company of $50.0 million or (ii) the election of the holders of the then outstanding Preferred Stock.
Convertible preferred stock, conversion rate						100.00%
Redeemable Convertible Preferred Stock | Minimum [Member]
Temporary Equity [Line Items]
Gross proceeds from qualified initial public offering for automatic conversion of preferred stock						$ 50,000,000

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - $ / shares	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Equity [Abstract]
Common stock, shares authorized	20,779,200	12,337,650
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares outstanding	164,122	12	0

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Computation of Basic and Diluted Net Loss Per Share of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Earnings Per Share Basic And Diluted [Abstract]
Net Loss	$ (15,140)	$ (27,145)
Weighted average common shares outstanding used in computing net loss per share, basic and diluted	103,684	53,460
Net loss per share, basic and diluted	$ (146.02)	$ (507.76)

Net Loss Per Share - Additional

Net Loss Per Share - Additional Information (Details) - shares	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Earnings Per Share [Abstract]
Common stock, shares outstanding	164,122	12	0

Net Loss Per Share - Schedule_2

Net Loss Per Share - Schedule of Anti-Dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	21,536,696	6,981,023
Redeemable convertible preferred stock (as converted to common stock)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	16,833,790	5,730,513
Stock Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	4,702,906	1,230,512
Warrants to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	0	19,998

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details) - USD ($)	May 16, 2019	Mar. 31, 2019	Aug. 31, 2018	Oct. 31, 2016	Sep. 30, 2009	Jun. 30, 2019	Jun. 30, 2019	May 30, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding						4,702,906	4,702,906		2,310,369
Unrecognized compensation cost						$ 7,900,000	$ 7,900,000
Unrecognized compensation costs, weighted average recognition period							2 years 6 months
Proceeds from exercise of warrant							$ 58,000
PureTech Health
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exchange for a warrant to purchase shares of common stock				19,998
Warrant vests monthly as service performance, period				24 months
Warrant purchase price, per share				$ 2.92
Exercise of warrant to purchase shares of common stock		19,986	12
Proceeds from exercise of warrant		$ 100,000
Outstanding warrants						0	0
PureTech Health | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total expense of warrant						$ 100,000	$ 100,000
Proceeds from exercise of warrant			$ 100,000
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units, shares vested with respective common stock	105,163
Average grant date fair value, per share	$ 10.97
Unrecognized compensation expense related to unvested RSUs						$ 0	$ 0
Restricted Stock Units | Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock units, shares vested with respective common stock	105,163
2009 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate common shares issuable					3,911,138
Share based compensation arrangement by share based payment award termination date					Jul. 31, 2019
2009 Plan | Options and Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding						3,839,545	3,839,545
2019 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate common shares issuable						741,308	741,308
Number of shares outstanding						968,524	968,524
Common stock reserved for future issuance								1,709,832
Automatic increase in stock issuance as percentage on outstanding stock							4.00%
Stock option and incentive plan expiration date							May 31, 2029
Expiration period							10 years
Vesting period							4 years

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares
Compensation Related Costs [Abstract]
Number of Shares, Outstanding, beginning of period | shares	2,310,369
Number of Shares, Granted | shares	2,554,146
Number of Shares, Exercised | shares	(38,961)
Number of Shares, Forfeited | shares	(122,648)
Number of Shares, Outstanding, end of period | shares	4,702,906	2,310,369
Number of Shares, Options vested and expected to vest | shares	4,702,906
Number of Shares, Options exercisable | shares	2,776,727
Weighted-Average Exercise Price Per Share, Outstanding, beginning of period | $ / shares	$ 4.49
Weighted-Average Exercise Price Per Share, Outstanding, Granted | $ / shares	11.93
Weighted-Average Exercise Price Per Share, Outstanding, Exercised | $ / shares	0.11
Weighted-Average Exercise Price Per Share, Outstanding, Forfeited | $ / shares	2.22
Weighted-Average Exercise Price Per Share, Outstanding, end of period | $ / shares	8.63	$ 4.49
Weighted-Average Exercise Price Per Share, Options vested and expected to vest | $ / shares	8.63
Weighted-Average Exercise Price Per Share, Options exercisable | $ / shares	$ 7.80
Weighted-Average Remaining Contractual Term, Outstanding (Years)	8 years 6 months	7 years 1 month 6 days
Weighted-Average Remaining Contractual Term, Options vested and expected to vest	8 years 6 months
Weighted-Average Remaining Contractual Term, Options exercisable	7 years 8 months 12 days
Aggregate Intrinsic Value, Outstanding | $	$ 53,571	$ 6,420
Aggregate Intrinsic Value, Options vested and expected to vest | $	53,571
Aggregate Intrinsic Value, Options exercisable | $	$ 33,939

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Fair Value of Option Activity Estimated at Date of Grant Using Black-Scholes Model (Details)	6 Months Ended
	Jun. 30, 2019$ / shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	43.57%
Expected volatility, maximum	44.41%
Risk-free interest rate, minimum	1.76%
Risk-free interest rate, maximum	2.44%
Expected dividend yield	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of options	$ 3.83
Fair value of common stock	$ 9.20
Expected term (in years)	5 years 7 days
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of options	$ 8.05
Fair value of common stock	$ 20.02
Expected term (in years)	6 years 1 month 28 days

Stock-based Compensation - Su_3

Stock-based Compensation - Summary of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	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 [Line Items]
Total stock based compensation expense	$ 6,841	$ 66	$ 9,945	$ 111
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock based compensation expense	144	18	224	43
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock based compensation expense	$ 6,697	$ 48	$ 9,721	$ 68

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities - Schedule of Fair Value Measurement on Recurring Basis and Indicates the level of Fair Value Hierarchy Utilized (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Assets:
Short-term investments	$ 64,804	$ 4,983
Liabilities:
Derivative instrument		389
Recurring
Assets:
Total fair value assets	72,095	10,025
Liabilities:
Derivative instrument		389
Total fair value liabilities		389
Recurring | Money Market Fund
Assets:
Cash equivalents	7,291
Recurring | US Treasuries
Assets:
Cash equivalents		5,042
Short-term investments	64,804	4,983
Recurring | Level 1
Assets:
Total fair value assets	72,095	10,025
Recurring | Level 1 | Money Market Fund
Assets:
Cash equivalents	7,291
Recurring | Level 1 | US Treasuries
Assets:
Cash equivalents		5,042
Short-term investments	$ 64,804	4,983
Recurring | Level 3
Liabilities:
Derivative instrument		389
Total fair value liabilities		$ 389

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Summary of Estimated Fair Value and Amortized Cost of Short term Investments by Contractual Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Abstract]
Due in one year or less, Amortized cost	$ 64,733	$ 4,984
Due in one year or less, Unrealized gains	71
Due in one year or less, Unrealized losses		(1)
Due in one year or less, Fair value	64,804	4,983
Amortized Cost	64,733	4,984
Unrealized Gains	71
Unrealized Losses		(1)
Fair Value	$ 64,804	$ 4,983

Fair Value of Financial Asset_5

Fair Value of Financial Assets and Liabilities - Schedule of Changes in Fair Value Derivative Liabilities (Details) - Derivative Financial Instruments, Liabilities - USD ($) $ in Thousands	1 Months Ended	3 Months Ended				5 Months Ended
	Jul. 31, 2018	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Derivatives Fair Value [Line Items]
Balance	$ 0	$ 0	$ 0	$ 1,821	$ 3,408	$ 389	$ 2,606
Allocation of note issuance proceeds to derivative		522	228	696	722	375
Change in fair value of derivative	2,633		135	$ (2,283)	$ 80	$ 14
Series A Preferred Stock
Derivatives Fair Value [Line Items]
Conversion of convertible debt	$ (4,454)
Series B Preferred Stock
Derivatives Fair Value [Line Items]
Conversion of convertible debt		$ (522)	$ (752)

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	1 Months Ended		6 Months Ended
	May 31, 2012USD ($)	Mar. 31, 2011USD ($)Patent	Jun. 30, 2019USD ($)Milestone	Jun. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Commitments And Contingencies [Line Items]
Rent expense			$ 200,000
Contingency reserves for litigation			$ 0
Intellectual Property License Agreement | Eli Lilly and Company
Commitments And Contingencies [Line Items]
Initial upfront payment	$ 100,000
Number of milestones reached | Milestone			0
Milestone payments			$ 0
Intellectual Property License Agreement | Eli Lilly and Company | Maximum
Commitments And Contingencies [Line Items]
Milestone payments payable	$ 70,000,000
PureTech Health | Patent License Agreement
Commitments And Contingencies [Line Items]
Number of patents pending related to methods and compositions | Patent		2
Initial upfront payment		$ 0
Contingent milestone payments payable		$ 10,000,000
Expenses incurred			0	$ 0
Outstanding liabilities			$ 0		$ 0
Office Space | Massachusetts
Commitments And Contingencies [Line Items]
Lease term					51 months
Lease commencement period			2018-12
Lease expiration period			2023-02
Restricted cash			$ 100,000		$ 100,000

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-Cancelable Operating Lease Agreements (Details) $ in Thousands	Jun. 30, 2019USD ($)
Commitments And Contingencies Disclosure [Abstract]
Less than 1 year	$ 496
1 to 2 years	503
2 to 3 years	510
3 to 4 years	343
Total	$ 1,852

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - PureTech Health - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
General and administrative expenses incurred		$ 100,000
Outstanding current liabilities due to related party			$ 100,000
Maximum
Related Party Transaction [Line Items]
General and administrative expenses incurred	$ 100,000
Outstanding current liabilities due to related party	$ 100,000

401(k) Savings Plan - Additiona

401(k) Savings Plan - Additional Information (Details) - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, plan name	401(k)
Maximum
Defined Benefit Plan Disclosure [Line Items]
Total contribution matching expense	$ 100,000	$ 100,000

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - $ / shares	Jul. 02, 2019	Jun. 30, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Common stock, par value		$ 0.0001	$ 0.0001
Common stock, shares authorized to issue		20,779,200	12,337,650
Initial Public Offering | Subsequent Event
Subsequent Event [Line Items]
Authority to issue shares	160,000,000
Common stock, par value	$ 0.0001
Common stock, shares authorized to issue	150,000,000
Initial Public Offering | Subsequent Event | Undesignated Preferred Stock
Subsequent Event [Line Items]
Preferred stock, shares authorized to issue	10,000,000
Preferred stock, par value	$ 0.0001