Rein Therapeutics (RNTX) 10-Q10 Aug 172017 Q2 Quarterly reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jun. 30, 2017	Aug. 10, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q2
Trading Symbol	ALRN
Entity Registrant Name	AILERON THERAPEUTICS INC
Entity Central Index Key	1,420,565
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		14,714,816

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 9,397	$ 20,715
Investments	1,946	0
Prepaid expenses and other current assets	561	333
Restricted cash	88	25
Total current assets	11,992	21,073
Property and equipment, net	109	107
Restricted cash		63
Other assets	782	778
Deferred offering costs	2,222
Total assets	15,105	22,021
Current liabilities:
Accounts payable	2,212	1,971
Accrued expenses and other current liabilities	3,259	2,100
Total current liabilities	5,471	4,071
Deferred rent		11
Total liabilities	5,471	4,082
Commitments and contingencies (Note 10)
Redeemable convertible preferred stock (Series A, A-1, B, C-1, C-2, D, D-1, E, E-1, E-2, E-3 and F), $0.01 par value; 151,557,293 shares authorized at June 30, 2017 and December 31, 2016; 106,114,520 and 105,631,019 shares issued and outstanding at June 30, 2017 and December 31, 2016, respectively; aggregate liquidation preference of $130,711 and $130,053 at June 30, 2017 and December 31, 2016, respectively; no shares issued and outstanding, pro forma at June 30, 2017	130,412	129,745
Stockholders' equity (deficit):
Common stock, $0.001 par value; 143,500,000 shares authorized at June 30, 2017 and December 31, 2016; 450,937 and 432,413 shares issued and outstanding at June 30, 2017 and December 31, 2016, respectively; 10,960,711 shares issued and outstanding, pro forma at June 30, 2017	0	0
Additional paid-in capital	3,044	2,536
Accumulated deficit	(123,822)	(114,342)
Total stockholders' equity (deficit)	(120,778)	(111,806)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	15,105	$ 22,021
Pro Forma [Member]
Current assets:
Cash and cash equivalents	9,397
Investments	1,946
Prepaid expenses and other current assets	561
Restricted cash	88
Total current assets	11,992
Property and equipment, net	109
Other assets	782
Deferred offering costs	2,222
Total assets	15,105
Current liabilities:
Accounts payable	2,212
Accrued expenses and other current liabilities	3,259
Total current liabilities	5,471
Total liabilities	5,471
Commitments and contingencies (Note 10)
Stockholders' equity (deficit):
Common stock, $0.001 par value; 143,500,000 shares authorized at June 30, 2017 and December 31, 2016; 450,937 and 432,413 shares issued and outstanding at June 30, 2017 and December 31, 2016, respectively; 10,960,711 shares issued and outstanding, pro forma at June 30, 2017	11
Additional paid-in capital	133,445
Accumulated deficit	(123,822)
Total stockholders' equity (deficit)	9,634
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 15,105

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Redeemable convertible preferred stock, authorized (in shares)	151,557,293	151,557,293
Redeemable convertible preferred stock, issued (in shares)	106,114,520	105,631,019
Redeemable convertible preferred stock, outstanding (in shares)	106,114,520	105,631,019
Redeemable convertible preferred stock,liquidation preference	$ 130,711	$ 130,053
Redeemable convertible preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	143,500,000	143,500,000
Common stock, shares issued	450,937	432,413
Common stock, shares outstanding	450,937	432,413
Pro Forma [Member]
Redeemable convertible preferred stock, issued (in shares)	0
Redeemable convertible preferred stock, outstanding (in shares)	0
Common stock, shares issued	10,960,711
Common stock, shares outstanding	10,960,711

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Revenue	$ 0	$ 0	$ 0	$ 0
Operating expenses:
Research and development	3,161	2,086	6,103	4,579
General and administrative	1,791	3,464	3,438	4,910
Total operating expenses	4,952	5,550	9,541	9,489
Loss from operations	(4,952)	(5,550)	(9,541)	(9,489)
Interest and other income	29	16	61	30
Net loss	(4,923)	(5,534)	(9,480)	(9,459)
Accretion of redeemable convertible preferred stock to redemption value	(21)	(19)	(41)	(37)
Net loss attributable to common stockholders	$ (4,944)	$ (5,553)	$ (9,521)	$ (9,496)
Net loss per share attributable to common stockholders-basic and diluted	$ (10.98)	$ (12.95)	$ (21.56)	$ (22.21)
Weighted average common shares outstanding-basic and diluted	450,495	428,870	441,661	427,679
Other comprehensive loss:
Unrealized loss on investments, net of tax of $0		$ (5)
Total other comprehensive loss		(5)
Comprehensive loss	$ (4,923)	$ (5,539)	$ (9,480)	$ (9,459)

Condensed Statements of Operat5

Condensed Statements of Operations and Comprehensive Loss (Parenthetical) $ in Thousands	3 Months Ended
	Jun. 30, 2016USD ($)
Income Statement [Abstract]
Unrealized loss on investments, tax	$ 0

Condensed Statement of Redeemab

Condensed Statement of Redeemable Convertible Preferred Stock and Stockholders' Deficit - 6 months ended Jun. 30, 2017 - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Redeemable convertible preferred stock, beginning balance at Dec. 31, 2016	$ 129,745
Redeemable convertible preferred stock, beginning balance, shares at Dec. 31, 2016	105,631,019
Issuance of Series F redeemable convertible preferred stock, net of issuance costs of $32	$ 626
Issuance of Series F redeemable convertible preferred stock, net of issuance costs, Shares	483,501
Accretion of redeemable convertible preferred stock to redemption value	$ 41
Redeemable convertible preferred stock, ending balance at Jun. 30, 2017	$ 130,412
Redeemable convertible preferred stock, ending balance, shares at Jun. 30, 2017	106,114,520
Beginning balance at Dec. 31, 2016	$ (111,806)		$ 2,536	$ (114,342)
Beginning balance, shares at Dec. 31, 2016	432,413	432,413
Exercise of stock options	$ 80		80
Exercise of stock options, shares	18,524	18,524
Stock-based compensation expense	$ 469		469
Accretion of redeemable convertible preferred stock to redemption value	(41)		(41)
Net loss	(9,480)			(9,480)
Ending balance at Jun. 30, 2017	$ (120,778)		$ 3,044	$ (123,822)
Ending balance, shares at Jun. 30, 2017	450,937	450,937

Condensed Statement of Redeema7

Condensed Statement of Redeemable Convertible Preferred Stock and Stockholders' Deficit (Parenthetical) $ in Thousands	6 Months Ended
	Jun. 30, 2017USD ($)
Statement of Stockholders' Equity [Abstract]
Issuance of Series F redeemable convertible preferred stock, Issuance costs	$ 32

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
Condensed Statements of Cash Flows - USD ($) $ in Thousands	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net loss	$ (9,480)	$ (9,459)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	45	132
Stock-based compensation expense	469	330
Change in deferred rent	(11)	(29)
Loss on disposal of property and equipment		12
Write-off of deferred offering costs		1,500
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(291)	(128)
Other assets	59
Accounts payable	(500)	229
Accrued expenses and other current liabilities	252	558
Net cash used in operating activities	(9,457)	(6,855)
Cash flows from investing activities:
Purchases of property and equipment	(47)
Purchases of investments	(8,747)	(11,887)
Proceeds from sales or maturities of investments	6,800	5,841
Net cash used in investing activities	(1,994)	(6,046)
Cash flows from financing activities:
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	472	13,183
Proceeds from exercise of stock options	80	15
Payments of initial public offering costs	(419)	(180)
Net cash provided by financing activities	133	13,018
Net increase (decrease) in cash and cash equivalents	(11,318)	117
Cash and cash equivalents at beginning of period	20,715	3,768
Cash and cash equivalents at end of period	9,397	3,885
Supplemental disclosure of non-cash financing activities:
Accretion of redeemable convertible preferred stock to redemption value	41	$ 37
Deferred offering costs included in accounts payable and accrued expenses	$ 1,803

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	6 Months Ended
Nature of the Business and Basis of Presentation	Jun. 30, 2017
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Aileron Therapeutics, Inc. (“Aileron” or the “Company”) is a clinical-stage biopharmaceutical company that is focused on developing and commercializing a novel class of therapeutics called stapled peptides. The Company’s lead product candidate, ALRN-6924, targets the tumor suppressor p53 for the treatment of a wide variety of cancers. ALRN-6924 reactivates p53-mediated The Company was incorporated under the laws of the State of Delaware in August 2001 as Renegade Therapeutics, Inc. and commenced its principal operations in 2006. In February 2007, the Company amended its certificate of incorporation to change its name to Aileron Therapeutics, Inc. The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure, and extensive compliance-reporting capabilities. The Company’s product candidates are in development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that any products developed will obtain necessary governmental regulatory approval or that any approved products will be commercially viable. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants. Reverse Stock Split On June 16, 2017, the Company effected a one-for-9.937 Initial Public Offering On June 28, 2017, the Company’s registration statement on Form S-1 Pro Forma Information The accompanying pro forma condensed balance sheet as of June 30, 2017 has been prepared to give effect to the automatic conversion of all outstanding shares of redeemable convertible preferred stock into 10,509,774 shares of common stock as if the Company’s closing of the IPO had occurred on June 30, 2017. Going Concern In accordance with Accounting Standards Update (“ASU”) No. 2014-15, 205-40), 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. Through June 30, 2017, the Company has funded its operations with proceeds from the sale of redeemable convertible preferred stock and, to a lesser extent, payments received in connection with a collaboration agreement. The Company has incurred losses and negative cash flows from operations and had an accumulated deficit of $123,822 as of June 30, 2017 and $114,342 as of December 31, 2016. The Company expects to continue to generate losses for the foreseeable future. As of August 10, 2017, the date of issuance of these unaudited interim condensed financial statements, the Company expects that its cash, cash equivalents and investments of $11,343 as of June 30, 2017 together with the $50,091 of net cash proceeds received from the Company’s IPO, will be sufficient to fund its operating expenses and capital expenditure requirements through the second quarter of 2019. The future viability of the Company beyond that point is dependent on its ability to raise additional capital to finance its operations. Although the Company has been successful in raising capital in the past, there is no assurance that it will be successful in obtaining such additional financing on terms acceptable to the Company, if at all. To execute its business plans, the Company will need substantial funding to support its continuing operations and pursue its growth strategy. Until such time as the Company can generate significant revenue from product sales, if ever, it expects to finance its operations through the sale of common stock in public offering and/or private placements, debt financings or other capital sources, including collaborations with other companies or other strategic transactions. The Company may not be able to obtain financing on acceptable terms or at all. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion plans or commercialization efforts, which could adversely affect its business prospects. The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
Summary of Significant Accounting Policies	Jun. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of 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 of research and development expenses and the valuation of common stock and stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates. Unaudited Interim Financial Information The accompanying unaudited condensed financial statements as of June 30, 2017 and for the six months ended June 30, 2017 and 2016 have been prepared by the Company, pursuant to the rules and regulations of the SEC for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2016 included in the Company’s prospectus that forms a part of the Company’s Registration Statement on Form S-1 No. 333-218474). The accompanying balance sheet as of June 30, 2017, the statements of operations and comprehensive loss for the three and six months ended June 30, 2017 and 2016, the statements of cash flows for the six months ended June 30, 2017 and 2016, and the statement of redeemable convertible preferred stock and stockholders’ deficit for the six months ended June 30, 2017 are unaudited. The unaudited interim condensed 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, 2017, the results of its operations and cash flows for the three and six months ended June 30, 2017 and 2016 and its cash flows for the six months ended June 30, 2017 and 2016. The financial data and other information disclosed in these notes related to the three and six months ended June 30, 2017 and 2016 are unaudited. The results for the six months ended June 30, 2017 are not necessarily indicative of results to be expected for the year ending December 31, 2017, any other interim periods, or any future year or period. The accompanying balance sheet as of December 31, 2016 has been derived from the Company’s audited financial statements for the year ended December 31, 2016 previously filed with the Securities and Exchange Commission. 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. Cash equivalents, which consist of money market accounts, government sponsored enterprises and commercial paper, are stated at fair value. Restricted Cash As of June 30, 2017, current restricted cash of $88 consisted of $25 of cash deposited in a separate restricted bank account as a security deposit for the Company’s corporate credit cards and $63 of cash deposited in a separate restricted bank account as a security deposit for the lease of the Company’s facilities. As of December 31, 2016, current restricted cash consisted of $25 of cash deposited in a separate restricted bank account as a security deposit for the Company’s corporate credit cards and non-current Investments The Company classifies its available-for-sale The Company classifies all of its investments as available-for-sale available-for-sale The Company evaluates its investments with unrealized losses for other-than-temporary impairment. When assessing investments for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary”, the Company reduces the investment to fair value through a charge to the statements of operations and comprehensive loss. No such adjustments were necessary during the periods presented. Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable. • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and investments are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair value due to the short-term nature of these liabilities. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process paid-in As of June 30, 2017 and December 31, 2016 the Company recorded $2,222 and $0, respectively, of deferred offering costs in contemplation of the IPO. Such costs were transferred to additional paid-in-capital write-off Net Income (Loss) per Share The Company follows the two-class two-class two-class 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) per share attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. 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 shares of common stock outstanding for the period, including potential dilutive common shares. For purpose of this calculation, outstanding options to purchase common stock and shares of redeemable convertible preferred stock are considered potential dilutive common shares. The Company’s redeemable convertible preferred stock contractually entitles the holders of such shares to participate in dividends but contractually does not require the holders of such stock to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. Recently Issued Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606) 2014-09”), 2014-09 No. 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date 2014-09 No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations 2016-08”), 2014-09. No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing 2016-10”), No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”), non-cash 2014-09 2016-08, 2016-10 2016-12 2014-09. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments-Overall: Recognition and Measurement of Financial Assets and Financial Liabilities available-for-sale In February 2016, the FASB issued ASU No. 2016-02, Leases 2016-02”), right-of-use 2016-02 Leases 2016-02 In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation 2016-09”), Compensation—Stock Compensation 2016-09 ASU 2016-09 In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments 2016-15”). 2016-15 In November 2016, the FASB issued ASU No. 2016-18, Restricted Cash 2016-18”). The 2016-18 In May 2017, the FASB issued ASU No. 2017-09, Compensation – Stock Compensation 2017-09”), Scope of Modification Accounting 2017-09

Fair Value of Financial Assets

Fair Value of Financial Assets	6 Months Ended
Fair Value of Financial Assets	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets	3. Fair Value of Financial Assets The following tables present information about the Company’s assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair Value Measurements as of June 30, 2017 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 5,027 $ — $ — $ 5,027 Government sponsored enterprises — 500 — 500 Commercial paper — 2,897 — 2,897 Investments: — Commercial paper — 1,946 — 1,946 $ 5,027 $ 5,343 $ — $ 10,370 Fair Value Measurements as of December 31, 2016 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 20,016 $ — $ — $ 20,016 $ 20,016 $ — $ — $ 20,016 As of June 30, 2017, the Company’s cash equivalents and investments were invested in money market funds, government sponsored enterprises and commercial paper and were valued based on Level 1 and Level 2 inputs. As of December 31, 2016, the Company’s cash equivalents were invested in money market funds and were valued based on Level 1 inputs. In determining the fair value of its government sponsored enterprises and commercial paper at each date presented above, the Company relied on quoted prices for similar securities in active markets or using other inputs that are observable or can be corroborated by observable market data. The Company’s cash equivalents have original maturities of less than 90 days from the date of purchase. All available-for-sale

Investments

Investments	6 Months Ended
Investments	Jun. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Investments	4. Investments As of December 31, 2016, the Company had no available-for-sale available-for-sale June 30, 2017 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Commercial paper $ 1,946 $ — $ — $ 1,946 $ 1,946 $ — $ — $ 1,946

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	6 Months Ended
Accrued Expenses and Other Current Liabilities	Jun. 30, 2017
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	5. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following: June 30, 2017 December 31, 2016 Payroll and payroll-related costs $ 502 $ 899 External research and development services 985 723 Professional fees 1,345 322 Other 427 156 $ 3,259 $ 2,100

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	6 Months Ended
Redeemable Convertible Preferred Stock	Jun. 30, 2017
Equity [Abstract]
Redeemable Convertible Preferred Stock	6. Redeemable Convertible Preferred Stock As of June 30, 2017 and December 31, 2016, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 151,557,293 shares of $0.01 par value preferred stock. The Company has issued Series A, Series A-1, C-1 C-2 D-1, Series E-1, E-2, E-3 In October 2014, the Company issued 14,558,823 shares of Series E-1 E-1 In January 2016, the Company issued 9,705,882 shares of Series E-1 In December 2016, the Company issued 13,949,357 shares of Series F redeemable convertible preferred stock (the “Series F preferred stock”) at a price of $1.36 per share, resulting in proceeds of $18,806, net of issuance costs of $165. As part of the Series F preferred stock purchase agreement, the investors agreed to purchase an additional 8,192,477 shares of Series F preferred stock at a price of $1.36 per share upon the Company achieving specified clinical milestones (the “second tranche closing”) for an aggregate purchase price of $11,142. In February 2017, the Company amended the Series F preferred stock purchase agreement to permit the sale of up to 758,458 additional shares of Series F preferred stock. In February 2017, pursuant to the amended Series F preferred stock purchase agreement, the Company issued 483,501 shares of Series F preferred stock at a price of $1.36 per share, resulting in proceeds of $626, net of issuance costs of $32. The purchasers of Series F preferred stock in this February 2017 closing agreed to purchase an additional 274,957 shares of Series F preferred stock at a price of $1.36 per share in the second tranche closing, which increased the aggregate number of shares of Series F preferred stock to be purchased in the second tranche closing to 8,467,434 shares for an aggregate purchase price of $11,516. The Company determined that the future tranche obligations of the Series F preferred stock purchase agreement, as amended, do not meet the definition of a freestanding financial instrument because, while separately exercisable, they were not legally detachable. Further, the Company determined that the embedded future tranche obligations did not require bifurcation for accounting purposes as they are clearly and closely related to the economic characteristics and risks of the initial preferred shares and would not qualify as a derivative on a standalone basis. In December 2016, pursuant to the Series F preferred stock purchase agreement, holders of 8,927,582 shares of Series E redeemable convertible preferred stock (the “Series E preferred stock”) that participated in the Series F preferred stock financing elected to convert their shares of Series E preferred stock into 8,927,582 shares of Series E-2 E-1 E-1 E-3 E-3 E-1 E-2 E-3 E-1 E-1 E-3 The Company determined that the conversion of shares of preferred stock that occurred in December 2016 and February 2017 represented modifications of these securities for accounting purposes; however, the modifications did not result in the recognition of a deemed dividend for accounting purposes because the modifications did not result in a transfer of value from common stockholders to preferred stockholders. Pursuant to the terms of the amended Series F preferred stock purchase agreement, if the second tranche closing has not occurred prior to the closing of the Company’s initial public offering of common stock, then, immediately prior to such closing, the purchasers of the Series F preferred stock will be required to purchase a number of shares of the Company’s common stock equal to $11,516 divided by the price per share paid by the public in the initial public offering in a concurrent private offering. This requirement to purchase shares immediately prior to the closing of the Company’s initial public offering may be waived in whole or in part by the Company’s board of directors. As of December 31, 2016, the specified clinical milestones had not been achieved and the second tranche closing had not occurred. On June 15, 2017, the Company’s board of directors waived in whole, effective immediately prior to the closing of the Company’s IPO, the requirement of the purchasers of Series F preferred stock to purchase shares of the Company’s common stock in a concurrent private offering in connection with the Company’s initial public offering. Upon the completion of the Company’s IPO on July 5, 2017, all shares of the Redeemable Preferred Stock converted to common stock. As of each balance sheet date, Redeemable Preferred Stock consisted of the following: June 30, 2017 Preferred Shares Authorized Preferred Shares Issued and Outstanding Carrying Value Liquidation Preference Common Stock Issuable Upon Conversion Series A preferred stock 1,250,000 1,250,000 $ 1,250 $ 1,250 12,579 Series A-1 615,384 615,384 800 800 6,192 Series B preferred stock 3,706,056 3,706,056 1,506 1,506 372,955 Series C-1 5,934,050 5,934,050 6,997 7,000 597,167 Series C-2 8,689,144 8,689,144 10,248 10,250 874,423 Series D preferred stock 34,142,865 34,142,865 40,265 40,276 3,435,932 Series D-1 363,636 363,636 2,000 2,000 36,594 Series E preferred stock 12,715,822 3,788,240 4,455 4,469 381,225 Series E-1 24,264,705 3,285,832 4,460 4,469 330,666 Series E-2 9,226,082 8,927,582 10,498 10,531 898,418 Series E-3 21,237,785 20,978,873 28,478 28,531 2,111,187 Series F preferred stock 29,411,764 14,432,858 19,455 19,629 1,452,436 151,557,293 106,114,520 $ 130,412 $ 130,711 10,509,774 December 31, 2016 Preferred Shares Authorized Preferred Shares Issued and Outstanding Carrying Value Liquidation Preference Common Stock Issuable Upon Conversion Series A preferred stock 1,250,000 1,250,000 $ 1,250 $ 1,250 12,579 Series A-1 615,384 615,384 800 800 6,192 Series B preferred stock 3,706,056 3,706,056 1,506 1,506 372,955 Series C-1 5,934,050 5,934,050 6,997 7,000 597,167 Series C-2 8,689,144 8,689,144 10,248 10,250 874,423 Series D preferred stock 34,142,865 34,142,865 40,263 40,276 3,435,932 Series D-1 363,636 363,636 2,000 2,000 36,594 Series E preferred stock 12,715,822 3,788,240 4,453 4,469 381,225 Series E-1 24,264,705 7,697,597 10,446 10,469 774,639 Series E-2 9,226,082 8,927,582 10,493 10,531 898,418 Series E-3 21,237,785 16,567,108 22,483 22,531 1,667,214 Series F preferred stock 29,411,764 13,949,357 18,806 18,971 1,403,779 151,557,293 105,631,019 $ 129,745 $ 130,053 10,461,117 The holders of the Redeemable Preferred Stock had the following rights and preferences prior to conversion: Voting Rights The holders of the Redeemable Preferred Stock are entitled to vote, together with the holders of common stock, on all matters submitted to stockholders for a vote and have the right to vote the number of shares equal to the number of whole shares of common stock into which such holders of Redeemable Preferred Stock could convert on the record date for determination of stockholders entitled to vote. In addition, holders of the Senior Preferred Stock, voting as a single class, are entitled to elect three directors of the Company. The holders of the Junior Preferred Stock, voting as a single class, are entitled to elect two directors of the Company. Dividends The holders of the Redeemable Preferred Stock, in order of preference, are entitled to receive noncumulative dividends when and if declared by the Company’s board of directors. The Company may not declare, pay or set aside any dividends on shares of any other class or series of capital stock of the Company unless the holders of the Redeemable Preferred Stock then outstanding shall first receive, or simultaneously receive, a dividend on each outstanding share of Redeemable Preferred Stock in an amount at least equal to the greater of (i) $0.08 per share for Series A redeemable convertible preferred stock (“Series A preferred stock”), $0.104 per share for Series A-1 A-1 C-1 C-1 C-2 C-2 E-2 D-1 D-1 E-1 E-3 The Original Issue Price per share is $1.00 for Series A, $1.30 for Series A-1, C-1, Series C-2, D-1, E-1, E-2, E-3 Liquidation Preference In the event of any liquidation event, voluntary or involuntary, dissolution or winding up of the Company or Deemed Liquidation Event (as defined below), the holders of the then outstanding Series F preferred stock will be entitled to receive, prior and in preference to any distributions to the holders of the common stock and other preferred stock, $1.36 per share, plus any dividends declared but unpaid on the Series F preferred stock. After the payment of all preferential amounts to the holders of Series F preferred stock, then, to the extent available, the holders of the Series E-2 E-3 E-2 Series E-3 E-1, D-1 After the payment of all preferential amounts to the holders of Series E-2 E-3 E-1 E-1 D-1 After the payment of all preferential amounts to the holders of Series E and Series E-1 D-1 Series D-1 After the payment of all preferential amounts to the holders of the Senior Preferred Stock, then, to the extent available, the holders of Series C-1 C-2 C-1 C-2 A-1 After the payment of all preferential amounts to the holders of the Senior Preferred Stock and the Series C-1 C-2 A-1 After the payment of all preferential amounts to the holders of the Senior Preferred Stock, Series C-1, C-2 A-1 A-1 After payments have been made in full to the holders of the Redeemable Preferred Stock, then, to the extent available, the remaining amounts will be distributed among the holders of the shares of preferred stock and common stock, pro rata based on the number of shares held by each holder, treating for this purpose all such securities as if they had been converted to common stock immediately prior to such dissolution, liquidation or winding up of the Company. Unless 55% of the holders of the Senior Preferred Stock, voting together as a single class, elect otherwise, a Deemed Liquidation Event shall include a merger or consolidation (other than one in which stockholders of the Company own a majority by voting power of the outstanding shares of the surviving or acquiring corporation) or a sale, lease, transfer, exclusive license, or other disposition of substantially all of the assets of the Company. Conversion Each share of Redeemable Preferred Stock is convertible, at the option of the holder, at any time, and without the payment of additional consideration, or will automatically be converted into shares of common stock at the applicable conversion ratio then in effect (i) upon the closing of a firm commitment underwritten public offering at a price per share to the public, which when multiplied by the total number of shares of common stock then outstanding or then issuable upon conversion of outstanding Redeemable Preferred Stock immediately prior to the consummation of the offering, exceeds $150,000 and with at least $50,000 of gross proceeds to the Company or (ii) upon the vote or written consent of the holders of at least 55% of the outstanding shares of the Senior Preferred Stock, voting together as a single class. All shares that are required to be surrendered per the provisions above will be deemed to have been retired and canceled and may not be reissued as shares of preferred stock. The conversion ratio of each series of Redeemable Preferred Stock is determined by dividing the Original Issue Price of each series of preferred stock by the Conversion Price of each series, except for Series D-1 D-1 A-1, C-1, C-2, E-2, E-1, E-3 Redemption Rights At the written election of at least 55% of the holders of the Senior Preferred Stock, voting together as a single class, the shares of Redeemable Preferred Stock outstanding are redeemable, at any time on or after December 22, 2020, in three equal annual installments commencing 60 days after receipt of the required vote, in an amount equal to the Original Issue Price per share of each series of Redeemable Preferred Stock plus all declared but unpaid dividends thereon.

Common Stock

Common Stock	6 Months Ended
Common Stock	Jun. 30, 2017
Equity [Abstract]
Common Stock	7. Common Stock As of June 30, 2017 and December 31, 2016, the Company’s certificate of incorporation, as amended and restated, authorized the Company to issue 143,500,000 shares of $0.001 par value common stock. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive dividends, as may be declared by the Company’s board of directors, if any, subject to the preferential dividend rights of the Redeemable Preferred Stock. When dividends are declared on shares of common stock, the Company must declare at the same time a dividend payable to the holders of Redeemable Preferred Stock equivalent to the dividend amount they would receive if each preferred share were converted into common stock. The Company may not pay dividends to common stockholders until all dividends accrued or declared but unpaid on the Redeemable Preferred Stock have been paid in full. As of June 30, 2017 and December 31, 2016, no dividends had been declared. As of June 30, 2017 and December 31, 2016, the Company had reserved 13,631,297 and 12,206,216 shares, respectively, for the conversion of outstanding shares of Redeemable Preferred Stock (see Note 6), the exercise of outstanding stock options and the number of shares remaining available for future grant under the Company’s stock incentive plans (see Note 8). Upon completion of the Company’s IPO on July 5, 2017, all shares of Redeemable Preferred Stock converted to common stock.

Stock-Based Awards

Stock-Based Awards	6 Months Ended
Stock-Based Awards	Jun. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Awards	8. Stock-Based Awards 2017 Stock Incentive Plan The Company’s 2017 Stock Incentive Plan (the “2017 Plan”) was approved by the Company’s stockholders on June 16, 2017 and became effective on June 28, 2017. Under the 2017 Plan, the Company may grant incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, awards of restricted stock units and other stock-based awards. The Company’s employees, officers, directors, consultants and advisors are eligible to receive awards under the 2017 Plan; however, incentive stock options may only be granted to employees. The 2017 Plan is administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The number of shares of common stock covered by options and the date those options become exercisable, type of options to be granted, exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or its committee if so delegated. Stock options granted under the 2017 Plan with service-based vesting conditions generally vest over four years and may not have a duration in excess of ten years. The total number of shares of common stock that may be issued under the 2017 Plan was (1) 1,244,816; plus (2) the number of shares equal to the sum of the number of shares of our common stock then available for issuance under the 2016 plan, which was 424,601 shares, and the number of shares of common stock subject to outstanding awards under the 2006 plan and the 2016 plan that expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by us at their original issuance price pursuant to a contractual repurchase right. During the three months ended June 30, 2017, pursuant to the terms of our 2017 Stock Incentive Plan, we granted options to employees to purchase 147,428 shares of common stock at a price of $15.00 per share. Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards. The exercise price for stock options granted may not be less than the fair market value of the common stock as of the date of grant. 2017 Employee Stock Purchase Plan On June 16, 2017, the Company’s stockholders approved the 2017 Employee Stock Purchase Plan (the “2017 ESPP”), which became effective on June 28, 2017. A total of 150,000 shares of common stock were initially reserved for issuance under this plan. The number of shares of common stock that may be issued under the 2017 ESPP will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2018 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2027, equal to the least of (i) 622,408 shares, (ii) 1% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors. 2016 Stock Incentive Plan The Company’s 2016 Stock Incentive Plan (the “2016 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock, restricted stock units and other equity awards to employees, directors and consultants of the Company. The 2016 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The exercise prices, vesting and other restrictions were determined at the discretion of the board of directors, or its committee if so delegated. Stock options granted under the 2016 Plan with service-based vesting conditions vest over four years and expire after ten years. The 2016 Plan terminated in 2017. No shares remained available for future issuance as of June 30, 2017. Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards under the 2017 Plan. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards under the 2017 Plan. 2006 Stock Incentive Plan The Company’s 2006 Stock Incentive Plan, as amended, (the “2006 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock, restricted stock units and other equity awards to employees, directors and consultants of the Company. The 2006 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The exercise prices, vesting and other restrictions were determined at the discretion of the board of directors, or its committee if so delegated. Stock options granted under the 2006 Plan with service-based vesting conditions generally vest over four years and expire after ten years, although options have been granted with vesting terms of less than four years. The 2006 Plan expired in 2016. No shares remained available for future issuance as of December 31, 2016. Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards under the 2017 Plan. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards under the 2017 Plan. Stock Option Valuation The assumptions that the Company used to determine the grant-date fair value of the stock options granted to employees and directors during the six months ended June 30, 2017 and 2016 were as follows, presented on a weighted average basis: Six Months Six Months Risk-free interest rate 2.19 % 1.37 % Expected term (in years) 6.1 6.1 Expected volatility 80.2 % 80.5 % Expected dividend yield 0 % 0 % Stock Options The following table summarizes the Company’s stock option activity since January 1, 2017: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding at December 31, 2016 920,731 $ 4.36 6.4 $ 1,297 Granted 588,701 8.08 Exercised (18,524 ) 4.33 Forfeited (46,594 ) 5.14 Outstanding at June 30, 2017 1,444,314 $ 5.85 7.7 $ 8,220 Options exercisable at June 30, 2017 636,409 $ 4.00 5.8 $ 4,550 Options vested and expected to vest at June 30, 2017 1,408,747 $ 5.81 7.6 $ 8,063 Options exercisable at December 31, 2016 585,959 $ 3.78 5.2 $ 1,136 Options vested and expected to vest at December 31, 2016 904,010 $ 4.37 6.3 $ 1,289 The weighted average grant-date fair value of stock options granted during the six months ended June 30, 2017 and 2016 was $5.98 and $3.24, respectively. The aggregate fair value of stock options that vested during the six months ended June 30, 2017 and 2016 was $412 and $545, respectively. The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. The aggregate intrinsic value of stock options exercised during the six months ended June 30, 2017 and 2016 was $126 and $6, respectively. Stock-Based Compensation The Company recorded stock-based compensation expense related to stock options in the following expense categories of its statements of operations and comprehensive loss: Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Research and development expenses $ 131 $ 53 $ 205 $ 104 General and administrative expenses 142 114 264 226 $ 273 $ 167 $ 469 $ 330 As of June 30, 2017, the Company had an aggregate of $14,232 of unrecognized stock-based compensation expense, which is expected to be recognized over a weighted average period of 3.4 years.

Net Loss per Share

Net Loss per Share	6 Months Ended
Net Loss per Share	Jun. 30, 2017
Earnings Per Share [Abstract]
Net Loss per Share	9. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows : Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Numerator: Net loss $ (4,923 ) $ (5,534 ) $ (9,480 ) $ (9,459 ) Accretion of redeemable convertible preferred stock to redemption value (21 ) (19 ) (41 ) (37 ) Net loss attributable to common stockholders $ (4,944 ) $ (5,553 ) $ (9,521 ) $ (9,496 ) Denominator: Weighted average common shares outstanding— basic and diluted 450,495 428,870 441,661 427,679 Net loss per share attributable to common stockholders—basic and diluted $ (10.98 ) $ (12.95 ) $ (21.56 ) $ (22.21 ) The Company’s potential dilutive securities, which include stock options and redeemable convertible preferred stock, have been excluded from the computation of diluted net loss per share attributable to common stockholders whenever the effect of including them would be to reduce the net loss per share. In periods where there is a net loss, 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 following potential common shares, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Three Months and Six Months Ended June 30, 2017 2016 Stock options to purchase common stock 1,444,314 993,844 Redeemable convertible preferred stock (as converted to common stock) 10,509,774 9,057,339 11,954,088 10,051,183

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
Commitments and Contingencies	Jun. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and Contingencies Operating Leases In February 2010, the Company entered into an operating lease agreement for office and laboratory space, which, as amended, expires in May 2018. Upon entering into the agreement, the Company was required to maintain a security deposit of $776, which was recorded as restricted cash in the Company’s balance sheet. In connection with an amendment to the operating lease agreement in January 2015, the required security deposit was reduced from $776 to $63, and $713 of restricted cash was released to the Company. In connection with an amendment to the operating lease agreement in June 2011, the landlord agreed to fund up to $752 in improvements to the leased facility, which was recorded as a liability and is being recognized as a reduction of rent expense over the remaining lease term. The agreement requires future minimum lease payments for the years ending December 31, 2017 (remaining six months) and 2018 of $270 and $202, respectively. The Company recognizes rent expense on a straight-line basis over the lease period and has recorded deferred rent for rent expense incurred but not yet paid. Rental expense under operating leases totaled $120 and $105 for the three months ended June 30, 2017 and 2016, respectively, and $239 and $211 for the six months ended June 30, 2017 and 2016, respectively. Intellectual Property Licenses Harvard and Dana-Farber Agreement In August 2006, the Company entered into an exclusive license agreement with President and Fellows of Harvard College (“Harvard”) and Dana-Farber Cancer Institute (“DFCI”). The agreement granted the Company an exclusive worldwide license, with the right to sublicense, under specified patents and patent applications to develop, obtain regulatory approval for and commercialize specified product candidates based on stapled peptides. Under the agreement, the Company is obligated to use commercially reasonable efforts to develop and commercialize one or more licensed products and to achieve specified milestone events by specified dates. In connection with entering into the agreement, the Company paid an upfront license fee and issued to Harvard and DFCI shares of its common stock. In February 2010, the agreement was amended and restated (the “Harvard/DFCI agreement”) under which additional patent rights were added to the scope of the license agreement and the annual license maintenance fees were increased. Under the Harvard/DFCI agreement, the Company is obligated to make aggregate milestones payments of up to $7,700 per licensed therapeutic product upon the Company’s achievement of specified clinical, regulatory and sales milestones with respect to such product and up to $700 per licensed diagnostic product upon the Company’s achievement of specified regulatory and sales milestones with respect to such product. In addition, the Company is obligated to pay royalties of low single-digit percentages on annual net sales of licensed products sold by the Company, its affiliates or its sublicensees. The royalties are payable on a product-by-product country-by-country mid-twenties, The Harvard/DFCI agreement requires the Company to pay annual license maintenance fees of $145 each year. Any payments made in connection with the annual license maintenance fees will be credited against any royalties due. The Company did not incur any license fees during the three months ended June 30, 2017 and 2016 and incurred license fees of $145 during each of the six months ended June 30, 2017 and 2016. In addition, the Company did not make any milestone payments during the three and six month periods ended June 30, 2017 and 2016. As of June 30, 2017, no additional milestones had been achieved and no liabilities for additional milestone payments had been recorded in the Company’s financial statements. Through June 30, 2017 and December 31, 2016, the Company had made non-refundable As of June 30, 2017, the Company had not developed a commercial product using the licensed technologies and no royalties under the agreement had been paid or were due. Under the Harvard/DFCI agreement, the Company is responsible for all patent expenses related to the prosecution and maintenance of the licensed patents and applications in-licensed product-by-product country-by-country Materia Agreement In December 2006, the Company entered into a license agreement (the “Materia agreement”) with Materia, Inc. (“Materia”), under which it was granted a non-exclusive Under the Materia agreement, the Company is obligated to make aggregate milestone payments to Materia of up to $6,400 upon the Company’s achievement of specified clinical, regulatory and sales milestones with respect to each licensed product. In addition, the Company is obligated to pay tiered royalties ranging in the low single-digit percentages on annual net sales of licensed products sold by the Company or its sublicensees. The royalties are payable on a product-by-product country-by-country The Materia agreement requires the Company to pay annual license fees of $50. The Company did not incur any license fees during the three and six month periods ended June 30, 2017 and 2016, respectively. In addition, the Company did not make any milestone payments during the three and six month periods ended June 30, 2017 and 2016. As of June 30, 2017, no additional milestones had been achieved and no liabilities for additional milestone payments had been recorded in the Company’s financial statements. The agreement expires upon the expiration of the Company’s obligation to pay royalties in each territory covered under the agreement. Scripps Agreement In October 2010, the Company entered into a patent license agreement (the “Scripps agreement”) with The Scripps Research Institute (“Scripps”) under which it was granted a license, with the right to sublicense, for the exclusive worldwide rights to utilize Scripps’ “Click” chemistry for therapeutics and non-exclusive Under the agreement, the Company is obligated to make aggregate milestone payments to Scripps of up to $1,900 for each licensed peptide product and up to $950 for each licensed protein product upon achieving of specified clinical, regulatory and commercial milestones. In addition, the Company is obligated to pay tiered royalties ranging in the low single-digit percentages on annual net sales of licensed products sold by the Company or its sublicensees. The royalties are payable on a product-by-product country-by-country As of June 30, 2017, no milestones had been achieved and no liabilities for milestone payments had been recorded in the Company’s financial statements. As of June 30, 2017, the Company had not developed a commercial product using the licensed technologies and no royalties under the agreement had been paid or were due. The agreement expires upon expiration of the last of any patent rights covered under the agreement. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it had not accrued any liabilities related to such obligations in its financial statements as of June 30, 2017 or December 31, 2016.

Income Taxes

Income Taxes	6 Months Ended
Income Taxes	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes The Company did not provide for any income taxes for the three month or six month periods ended June 30, 2017 or 2016 and it did not record any deferred income tax assets for the operating losses incurred in each period, due to its uncertainty of realizing a benefit from those items.

Subsequent Events

Subsequent Events	6 Months Ended
Subsequent Events	Jun. 30, 2017
Subsequent Events [Abstract]
Subsequent Events	12. Subsequent Events For the unaudited financial statements as of June 30, 2017, and for the six months then ended, the Company evaluated subsequent events through August 10, 2017, the date on which those financial statements were available to be issued. Initial Public Offering On June 28, 2017, the Company’s registration statement on Form S-1 Increase in Authorized Shares On July 5, 2017, the Company amended and restated its certificate of incorporation to change authorized capital stock to 150,000,000 shares of common stock and 5,000,000 shares of preferred stock, all with a par value of $0.001 per share. Unaudited Pro Forma Financial Data The unaudited pro forma condensed balance sheet data in the table below reflects the sale of common stock in the IPO and the net proceeds of $50,091 that the Company received, after deducting the underwriting discounts and commissions of $3,938, and estimated offering expenses of $2,222, of which $433 were paid as of June 30, 2017 and therefore are not included in the pro forma adjustment to cash below. In addition, the unaudited pro forma condensed balance sheet reflects the automatic conversion of all of our outstanding shares of redeemable convertible preferred stock into 10,509,774 shares of common stock, which occurred upon the closing of our IPO on July 5, 2017. Historical as of 2017 Pro Forma Pro Forma as of 2017 Assets Current assets: Cash and cash equivalents $ 9,397 $ 50,510 $ 59,907 Investments 1,946 — 1,946 Prepaid expenses and other current assets 561 — 561 Restricted cash 88 — 88 Total current assets 11,992 50,510 62,502 Property and equipment, net 109 — 109 Restricted cash — — — Other assets 782 — 782 Deferred offering costs 2,222 (2,222 ) — Total assets $ 15,105 $ 48,288 $ 63,393 Liabilities, Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) Total liabilities $ 5,471 $ (1,803 ) $ 3,668 Redeemable convertible preferred stock 130,412 (130,412 ) — Stockholders’ equity (deficit): Common stock — 15 15 Additional paid-in 3,044 180,488 183,532 Accumulated deficit (123,822 ) — (123,822 ) Total stockholders’ equity (deficit) (120,778 ) 180,503 59,725 Total liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit) $ 15,105 $ 48,288 $ 63,393

Summary of Significant Accoun21

Summary of Significant Accounting Policies (Policies)	6 Months Ended
Summary of Significant Accounting Policies (Policies)	Jun. 30, 2017
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of 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 of research and development expenses and the valuation of common stock and stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The accompanying unaudited condensed financial statements as of June 30, 2017 and for the six months ended June 30, 2017 and 2016 have been prepared by the Company, pursuant to the rules and regulations of the SEC for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2016 included in the Company’s prospectus that forms a part of the Company’s Registration Statement on Form S-1 No. 333-218474). The accompanying balance sheet as of June 30, 2017, the statements of operations and comprehensive loss for the three and six months ended June 30, 2017 and 2016, the statements of cash flows for the six months ended June 30, 2017 and 2016, and the statement of redeemable convertible preferred stock and stockholders’ deficit for the six months ended June 30, 2017 are unaudited. The unaudited interim condensed 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, 2017, the results of its operations and cash flows for the three and six months ended June 30, 2017 and 2016 and its cash flows for the six months ended June 30, 2017 and 2016. The financial data and other information disclosed in these notes related to the three and six months ended June 30, 2017 and 2016 are unaudited. The results for the six months ended June 30, 2017 are not necessarily indicative of results to be expected for the year ending December 31, 2017, any other interim periods, or any future year or period. The accompanying balance sheet as of December 31, 2016 has been derived from the Company’s audited financial statements for the year ended December 31, 2016 previously filed with the Securities and Exchange Commission.
Cash Equivalents	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. Cash equivalents, which consist of money market accounts, government sponsored enterprises and commercial paper, are stated at fair value.
Restricted Cash	Restricted Cash As of June 30, 2017, current restricted cash of $88 consisted of $25 of cash deposited in a separate restricted bank account as a security deposit for the Company’s corporate credit cards and $63 of cash deposited in a separate restricted bank account as a security deposit for the lease of the Company’s facilities. As of December 31, 2016, current restricted cash consisted of $25 of cash deposited in a separate restricted bank account as a security deposit for the Company’s corporate credit cards and non-current
Investments	Investments The Company classifies its available-for-sale The Company classifies all of its investments as available-for-sale available-for-sale The Company evaluates its investments with unrealized losses for other-than-temporary impairment. When assessing investments for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary”, the Company reduces the investment to fair value through a charge to the statements of operations and comprehensive loss. No such adjustments were necessary during the periods presented.
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable. • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and investments are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair value due to the short-term nature of these liabilities.
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 paid-in As of June 30, 2017 and December 31, 2016 the Company recorded $2,222 and $0, respectively, of deferred offering costs in contemplation of the IPO. Such costs were transferred to additional paid-in-capital write-off
Net Income (Loss) per Share	Net Income (Loss) per Share The Company follows the two-class two-class two-class 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) per share attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. 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 shares of common stock outstanding for the period, including potential dilutive common shares. For purpose of this calculation, outstanding options to purchase common stock and shares of redeemable convertible preferred stock are considered potential dilutive common shares. The Company’s redeemable convertible preferred stock contractually entitles the holders of such shares to participate in dividends but contractually does not require the holders of such stock to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606) 2014-09”), 2014-09 No. 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date 2014-09 No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations 2016-08”), 2014-09. No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing 2016-10”), No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”), non-cash 2014-09 2016-08, 2016-10 2016-12 2014-09. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments-Overall: Recognition and Measurement of Financial Assets and Financial Liabilities available-for-sale In February 2016, the FASB issued ASU No. 2016-02, Leases 2016-02”), right-of-use 2016-02 Leases 2016-02 In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation 2016-09”), Compensation—Stock Compensation 2016-09 ASU 2016-09 In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows: Classification of Certain Cash Receipts and Cash Payments 2016-15”). 2016-15 In November 2016, the FASB issued ASU No. 2016-18, Restricted Cash 2016-18”). The 2016-18 In May 2017, the FASB issued ASU No. 2017-09, Compensation – Stock Compensation 2017-09”), Scope of Modification Accounting 2017-09

Fair Value of Financial Assets

Fair Value of Financial Assets (Tables)	6 Months Ended
Fair Value of Financial Assets (Tables)	Jun. 30, 2017
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value on Recurring Basis	The following tables present information about the Company’s assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair Value Measurements as of June 30, 2017 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 5,027 $ — $ — $ 5,027 Government sponsored enterprises — 500 — 500 Commercial paper — 2,897 — 2,897 Investments: — Commercial paper — 1,946 — 1,946 $ 5,027 $ 5,343 $ — $ 10,370 Fair Value Measurements as of December 31, 2016 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 20,016 $ — $ — $ 20,016 $ 20,016 $ — $ — $ 20,016

Investments (Tables)

Investments (Tables)	6 Months Ended
Investments (Tables)	Jun. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Summary of Fair Value of Available for Sale Investments	As of December 31, 2016, the Company had no available-for-sale available-for-sale June 30, 2017 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Commercial paper $ 1,946 $ — $ — $ 1,946 $ 1,946 $ — $ — $ 1,946

Accrued Expenses and Other Cu24

Accrued Expenses and Other Current Liabilities (Tables)	6 Months Ended
Accrued Expenses and Other Current Liabilities (Tables)	Jun. 30, 2017
Payables and Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: June 30, 2017 December 31, 2016 Payroll and payroll-related costs $ 502 $ 899 External research and development services 985 723 Professional fees 1,345 322 Other 427 156 $ 3,259 $ 2,100

Redeemable Convertible Prefer25

Redeemable Convertible Preferred Stock (Tables)	6 Months Ended
Redeemable Convertible Preferred Stock (Tables)	Jun. 30, 2017
Equity [Abstract]
Schedule of Redeemable Preferred Stock	As of each balance sheet date, Redeemable Preferred Stock consisted of the following: June 30, 2017 Preferred Shares Authorized Preferred Shares Issued and Outstanding Carrying Value Liquidation Preference Common Stock Issuable Upon Conversion Series A preferred stock 1,250,000 1,250,000 $ 1,250 $ 1,250 12,579 Series A-1 615,384 615,384 800 800 6,192 Series B preferred stock 3,706,056 3,706,056 1,506 1,506 372,955 Series C-1 5,934,050 5,934,050 6,997 7,000 597,167 Series C-2 8,689,144 8,689,144 10,248 10,250 874,423 Series D preferred stock 34,142,865 34,142,865 40,265 40,276 3,435,932 Series D-1 363,636 363,636 2,000 2,000 36,594 Series E preferred stock 12,715,822 3,788,240 4,455 4,469 381,225 Series E-1 24,264,705 3,285,832 4,460 4,469 330,666 Series E-2 9,226,082 8,927,582 10,498 10,531 898,418 Series E-3 21,237,785 20,978,873 28,478 28,531 2,111,187 Series F preferred stock 29,411,764 14,432,858 19,455 19,629 1,452,436 151,557,293 106,114,520 $ 130,412 $ 130,711 10,509,774 December 31, 2016 Preferred Shares Authorized Preferred Shares Issued and Outstanding Carrying Value Liquidation Preference Common Stock Issuable Upon Conversion Series A preferred stock 1,250,000 1,250,000 $ 1,250 $ 1,250 12,579 Series A-1 615,384 615,384 800 800 6,192 Series B preferred stock 3,706,056 3,706,056 1,506 1,506 372,955 Series C-1 5,934,050 5,934,050 6,997 7,000 597,167 Series C-2 8,689,144 8,689,144 10,248 10,250 874,423 Series D preferred stock 34,142,865 34,142,865 40,263 40,276 3,435,932 Series D-1 363,636 363,636 2,000 2,000 36,594 Series E preferred stock 12,715,822 3,788,240 4,453 4,469 381,225 Series E-1 24,264,705 7,697,597 10,446 10,469 774,639 Series E-2 9,226,082 8,927,582 10,493 10,531 898,418 Series E-3 21,237,785 16,567,108 22,483 22,531 1,667,214 Series F preferred stock 29,411,764 13,949,357 18,806 18,971 1,403,779 151,557,293 105,631,019 $ 129,745 $ 130,053 10,461,117

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	6 Months Ended
Stock-Based Awards (Tables)	Jun. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Valuation Assumptions of Stock Options Granted	The assumptions that the Company used to determine the grant-date fair value of the stock options granted to employees and directors during the six months ended June 30, 2017 and 2016 were as follows, presented on a weighted average basis: Six Months Six Months Risk-free interest rate 2.19 % 1.37 % Expected term (in years) 6.1 6.1 Expected volatility 80.2 % 80.5 % Expected dividend yield 0 % 0 %
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity since January 1, 2017: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding at December 31, 2016 920,731 $ 4.36 6.4 $ 1,297 Granted 588,701 8.08 Exercised (18,524 ) 4.33 Forfeited (46,594 ) 5.14 Outstanding at June 30, 2017 1,444,314 $ 5.85 7.7 $ 8,220 Options exercisable at June 30, 2017 636,409 $ 4.00 5.8 $ 4,550 Options vested and expected to vest at June 30, 2017 1,408,747 $ 5.81 7.6 $ 8,063 Options exercisable at December 31, 2016 585,959 $ 3.78 5.2 $ 1,136 Options vested and expected to vest at December 31, 2016 904,010 $ 4.37 6.3 $ 1,289
Summary of Stock Based Compensation Expense	The Company recorded stock-based compensation expense related to stock options in the following expense categories of its statements of operations and comprehensive loss: Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Research and development expenses $ 131 $ 53 $ 205 $ 104 General and administrative expenses 142 114 264 226 $ 273 $ 167 $ 469 $ 330

Net Loss per Share (Tables)

Net Loss per Share (Tables)	6 Months Ended
Net Loss per Share (Tables)	Jun. 30, 2017
Earnings Per Share [Abstract]
Basic and Diluted Net Loss per Share Attributable to Common Stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows : Three Months Ended June 30, Six Months Ended June 30, 2017 2016 2017 2016 Numerator: Net loss $ (4,923 ) $ (5,534 ) $ (9,480 ) $ (9,459 ) Accretion of redeemable convertible preferred stock to redemption value (21 ) (19 ) (41 ) (37 ) Net loss attributable to common stockholders $ (4,944 ) $ (5,553 ) $ (9,521 ) $ (9,496 ) Denominator: Weighted average common shares outstanding— basic and diluted 450,495 428,870 441,661 427,679 Net loss per share attributable to common stockholders—basic and diluted $ (10.98 ) $ (12.95 ) $ (21.56 ) $ (22.21 )
Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share	The following potential common shares, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Three Months and Six Months Ended June 30, 2017 2016 Stock options to purchase common stock 1,444,314 993,844 Redeemable convertible preferred stock (as converted to common stock) 10,509,774 9,057,339 11,954,088 10,051,183

Subsequent Events (Tables)

Subsequent Events (Tables)	6 Months Ended
Subsequent Events (Tables)	Jun. 30, 2017
IPO [Member]
Summary of Unaudited Pro Forma Financial Data	The unaudited pro forma condensed balance sheet data in the table below reflects the sale of common stock in the IPO and the net proceeds of $50,091 that the Company received, after deducting the underwriting discounts and commissions of $3,938, and estimated offering expenses of $2,222, of which $433 were paid as of June 30, 2017 and therefore are not included in the pro forma adjustment to cash below. In addition, the unaudited pro forma condensed balance sheet reflects the automatic conversion of all of our outstanding shares of redeemable convertible preferred stock into 10,509,774 shares of common stock, which occurred upon the closing of our IPO on July 5, 2017. Historical as of 2017 Pro Forma Pro Forma as of 2017 Assets Current assets: Cash and cash equivalents $ 9,397 $ 50,510 $ 59,907 Investments 1,946 — 1,946 Prepaid expenses and other current assets 561 — 561 Restricted cash 88 — 88 Total current assets 11,992 50,510 62,502 Property and equipment, net 109 — 109 Restricted cash — — — Other assets 782 — 782 Deferred offering costs 2,222 (2,222 ) — Total assets $ 15,105 $ 48,288 $ 63,393 Liabilities, Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit) Total liabilities $ 5,471 $ (1,803 ) $ 3,668 Redeemable convertible preferred stock 130,412 (130,412 ) — Stockholders’ equity (deficit): Common stock — 15 15 Additional paid-in 3,044 180,488 183,532 Accumulated deficit (123,822 ) — (123,822 ) Total stockholders’ equity (deficit) (120,778 ) 180,503 59,725 Total liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit) $ 15,105 $ 48,288 $ 63,393

Nature of the Business and Ba29

Nature of the Business and Basis of Presentation - Additional Information (Detail) $ / shares in Units, $ in Thousands	Jul. 05, 2017USD ($)$ / sharesshares	Jun. 16, 2017	Jun. 30, 2017USD ($)shares	Jun. 30, 2016USD ($)	Aug. 10, 2017shares	Dec. 31, 2016USD ($)shares
Class of Stock [Line Items]
Offering expenses \| $			$ 419	$ 180
Redeemable convertible preferred stock, outstanding (in shares)			106,114,520			105,631,019
Number of common shares issued on conversion of redeemable convertible preferred stock			10,509,774			10,461,117
Common stock, shares outstanding			450,937			432,413
Accumulated deficit \| $			$ (123,822)			$ (114,342)
Cash, cash equivalents and investments \| $			11,343
IPO [Member]
Class of Stock [Line Items]
Accumulated deficit \| $			$ (123,822)
Redeemable Convertible Preferred Stock [Member] \| IPO [Member] \| Subsequent Event [Member]
Class of Stock [Line Items]
Redeemable convertible preferred stock, outstanding (in shares)	106,114,520
Common Stock [Member]
Class of Stock [Line Items]
Reverse stock split description			One-for-9.937 reverse stock split
Reverse stock split ratio		0.100634
Common stock, shares outstanding			450,937			432,413
Common Stock [Member] \| IPO [Member] \| Subsequent Event [Member]
Class of Stock [Line Items]
Stock issued and sold	3,750,000
Share price \| $ / shares	$ 15
Net proceeds from issuance of initial public offering \| $	$ 50,090
Underwriting discounts and commissions incurred \| $	3,938
Offering expenses \| $	$ 2,222
Number of common shares issued on conversion of redeemable convertible preferred stock	10,509,774
Common stock, shares outstanding	14,714,816				14,714,816

Summary of Significant Accoun30

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, current	$ 88		$ 88		$ 25
Restricted cash, non-current					63
Deferred offering costs	2,222		2,222		0
General and administrative expense	1,791	$ 3,464	3,438	$ 4,910
2016 Equity Financing [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred offering costs						$ 1,500
Write-off of Deferred Financing Costs [Member]
Summary Of Significant Accounting Policies [Line Items]
General and administrative expense			1,500
Security Deposit Related to Credit Card Accounts [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, current	25		25		25
Security Deposit Related to Lease Facilities [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, current	$ 63		$ 63
Restricted cash, non-current					$ 63

Fair Value of Financial Asset31

Fair Value of Financial Assets - Summary of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	$ 10,370	$ 20,016
Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	5,027	20,016
Government Sponsored Enterprises [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	500
Commercial Paper [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	2,897
Commercial Paper [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	1,946
Recurring [Member] \| Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	5,027	20,016
Recurring [Member] \| Level 1 [Member] \| Money Market Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	5,027	$ 20,016
Recurring [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total assets	5,343
Recurring [Member] \| Level 2 [Member] \| Government Sponsored Enterprises [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	500
Recurring [Member] \| Level 2 [Member] \| Commercial Paper [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	2,897
Recurring [Member] \| Level 2 [Member] \| Commercial Paper [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments	$ 1,946

Fair Value of Financial Asset32

Fair Value of Financial Assets - Additional Information (Detail) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair value, assets transfers from Level 1 to Level 2	$ 0	$ 0
Fair value, assets transfers from Level 2 to Level 1	0	0
Fair Value, assets transfers into (out of) Level 3	$ 0	$ 0

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Investments, Fair Value	$ 1,946	$ 0

Investments - Summary of Fair V

Investments - Summary of Fair Value of Available for Sale Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	$ 1,946
Investments, Gross Unrealized Gain	0
Investments, Gross Unrealized Loss	0
Investments, Fair Value	1,946	$ 0
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	1,946
Investments, Gross Unrealized Gain	0
Investments, Gross Unrealized Loss	0
Investments, Fair Value	$ 1,946

Accrued Expenses and Other Cu35

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Payroll and payroll-related costs	$ 502	$ 899
External research and development services	985	723
Professional fees	1,345	322
Other	427	156
Total accrued expenses and other current liabilities	$ 3,259	$ 2,100

Redeemable Convertible Prefer36

Redeemable Convertible Preferred Stock - Additional Information (Detail)	1 Months Ended				3 Months Ended	6 Months Ended
	Feb. 28, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Jan. 31, 2016USD ($)$ / sharesshares	Oct. 31, 2014USD ($)$ / sharesshares	Jun. 30, 2017USD ($)Installment$ / sharesshares	Jun. 30, 2017USD ($)InstallmentDirectors$ / sharesshares	Jun. 30, 2016USD ($)
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		151,557,293			151,557,293	151,557,293
Redeemable convertible preferred stock, par value (in dollars per share)		$ 0.01			$ 0.01	$ 0.01
Preferred stock shares issued \| shares						483,501
Proceeds from issuance of redeemable convertible preferred stock \| $						$ 472,000	$ 13,183,000
Preferred stock issuance costs, paid \| $						$ 419,000	180,000
Preferred stock, voting rights description						The holders of the Redeemable Preferred Stock are entitled to vote, together with the holders of common stock, on all matters submitted to stockholders for a vote and have the right to vote the number of shares equal to the number of whole shares of common stock into which such holders of Redeemable Preferred Stock could convert on the record date for determination of stockholders entitled to vote. In addition, holders of the Senior Preferred Stock, voting as a single class, are entitled to elect three directors of the Company. The holders of the Junior Preferred Stock, voting as a single class, are entitled to elect two directors of the Company.
Dividends declared \| $					$ 0		0
Dividends paid \| $					$ 0		$ 0
Percentage of voting to be held by holders of senior preferred stock for deemed liquidation event						55.00%
Redemption date of redeemable preferred stock						Dec. 22, 2020
Number of annual installments for redemption \| Installment					3	3
IPO [Member]
Temporary Equity [Line Items]
Initial public offering completion date						Jul. 5, 2017
Series E-1 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock shares issued \| shares			9,705,882	14,558,823
Preferred stock shares issued, price per share			$ 1.36	$ 1.36
Proceeds from issuance of redeemable convertible preferred stock \| $			$ 13,183,000	$ 19,674,000
Preferred stock issuance costs, paid \| $			$ 17,000	$ 126,000
Preferred stock shares converted \| shares	4,411,765	16,567,108
Series F Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock shares issued \| shares	483,501	13,949,357
Preferred stock shares issued, price per share	$ 1.36	$ 1.36
Proceeds from issuance of redeemable convertible preferred stock \| $	$ 626,000	$ 18,806,000
Preferred stock issuance costs, paid \| $	$ 32,000	$ 165,000
Stock purchase agreement, additional shares agreed to purchase \| shares	274,957	8,192,477
Stock purchase agreement, price per share	$ 1.36	$ 1.36
Stock purchase agreement, aggregate purchase price \| $	$ 11,516,000	$ 11,142,000
Stock purchase agreement, shares authorized \| shares	758,458
Stock purchase agreement, aggregate number of shares agreed to purchase \| shares	8,467,434
Series E- Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock shares converted \| shares		8,927,582
Series E-2 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock shares issued on conversion \| shares		8,927,582
Series E-3 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock shares issued on conversion \| shares	4,411,765	16,567,108
Junior Preferred Stock [Member]
Temporary Equity [Line Items]
Number of directors entitled to be elected \| Directors						2
Senior Preferred Stock [Member]
Temporary Equity [Line Items]
Number of directors entitled to be elected \| Directors						3
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		1,250,000			1,250,000	1,250,000
Noncumulative dividends entitled to receive by redeemable preferred stock holders						$ 0.08
Original issue price per share						1
Liquidation preference per share					$ 1	1
Conversion price of Redeemable Preferred					$ 99.37	$ 99.37
Series A-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		615,384			615,384	615,384
Noncumulative dividends entitled to receive by redeemable preferred stock holders						$ 0.104
Original issue price per share						1.30
Liquidation preference per share					$ 1.30	1.30
Conversion price of Redeemable Preferred					$ 129.181	$ 129.181
Series B Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		3,706,056			3,706,056	3,706,056
Noncumulative dividends entitled to receive by redeemable preferred stock holders						$ 0.03251
Original issue price per share						0.4064
Liquidation preference per share					$ 0.4064	0.4064
Conversion price of Redeemable Preferred					$ 4.038397	$ 4.038397
Series C-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		5,934,050			5,934,050	5,934,050
Noncumulative dividends entitled to receive by redeemable preferred stock holders						$ 0.09437
Original issue price per share						1.179633
Liquidation preference per share					$ 1.179633	1.179633
Conversion price of Redeemable Preferred					$ 11.722013	$ 11.722013
Series C-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		8,689,144			8,689,144	8,689,144
Noncumulative dividends entitled to receive by redeemable preferred stock holders						$ 0.09437
Original issue price per share						1.179633
Liquidation preference per share					$ 1.179633	1.179633
Conversion price of Redeemable Preferred					$ 11.722013	$ 11.722013
Series D Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		34,142,865			34,142,865	34,142,865
Noncumulative dividends entitled to receive by redeemable preferred stock holders						$ 0.09437
Original issue price per share						1.179633
Liquidation preference per share					$ 1.179633	1.179633
Conversion price of Redeemable Preferred					$ 11.722013	$ 11.722013
Series D-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		363,636			363,636	363,636
Noncumulative dividends entitled to receive by redeemable preferred stock holders						$ 0.40
Original issue price per share						5.50
Liquidation preference per share					$ 5.50	$ 5.50
Series E-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		24,264,705			24,264,705	24,264,705
Noncumulative dividends entitled to receive by redeemable preferred stock holders						$ 0.1088
Original issue price per share						1.36
Liquidation preference per share					$ 1.36	1.36
Conversion price of Redeemable Preferred					$ 13.51432	$ 13.51432
Series E Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		12,715,822			12,715,822	12,715,822
Original issue price per share						$ 1.179633
Liquidation preference per share					$ 1.179633	1.179633
Conversion price of Redeemable Preferred					$ 11.722013	$ 11.722013
Series E-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		9,226,082			9,226,082	9,226,082
Original issue price per share						$ 1.179633
Liquidation preference per share					$ 1.179633	1.179633
Conversion price of Redeemable Preferred					$ 11.722013	$ 11.722013
Series E-3 Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		21,237,785			21,237,785	21,237,785
Original issue price per share						$ 1.36
Liquidation preference per share					$ 1.36	1.36
Conversion price of Redeemable Preferred					$ 13.51432	$ 13.51432
Series F Preferred Stock [Member]
Temporary Equity [Line Items]
Redeemable convertible preferred stock, authorized (in shares) \| shares		29,411,764			29,411,764	29,411,764
Original issue price per share						$ 1.36
Liquidation preference per share					$ 1.36	1.36
Conversion price of Redeemable Preferred					$ 13.51432	$ 13.51432
Redeemable Convertible Preferred Stock [Member] \| Maximum [Member]
Temporary Equity [Line Items]
Underwritten public offering costs \| $						$ 150,000,000
Redeemable Convertible Preferred Stock [Member] \| Minimum [Member]
Temporary Equity [Line Items]
Gross proceeds from issuance of redeemable convertible preferred stock \| $						$ 50,000,000

Redeemable Convertible Prefer37

Redeemable Convertible Preferred Stock - Schedule of Redeemable Preferred Stock (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Temporary Equity [Line Items]
Preferred Shares Authorized	151,557,293	151,557,293
Preferred Shares Issued	106,114,520	105,631,019
Preferred Shares Outstanding	106,114,520	105,631,019
Carrying Value	$ 130,412	$ 129,745	$ 129,745
Liquidation Preference	$ 130,711	$ 130,053
Common Stock Issuable Upon Conversion	10,509,774	10,461,117
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	1,250,000	1,250,000
Preferred Shares Issued	1,250,000	1,250,000
Preferred Shares Outstanding	1,250,000	1,250,000
Carrying Value	$ 1,250	$ 1,250
Liquidation Preference	$ 1,250	$ 1,250
Common Stock Issuable Upon Conversion	12,579	12,579
Series A-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	615,384	615,384
Preferred Shares Issued	615,384	615,384
Preferred Shares Outstanding	615,384	615,384
Carrying Value	$ 800	$ 800
Liquidation Preference	$ 800	$ 800
Common Stock Issuable Upon Conversion	6,192	6,192
Series B Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	3,706,056	3,706,056
Preferred Shares Issued	3,706,056	3,706,056
Preferred Shares Outstanding	3,706,056	3,706,056
Carrying Value	$ 1,506	$ 1,506
Liquidation Preference	$ 1,506	$ 1,506
Common Stock Issuable Upon Conversion	372,955	372,955
Series C-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	5,934,050	5,934,050
Preferred Shares Issued	5,934,050	5,934,050
Preferred Shares Outstanding	5,934,050	5,934,050
Carrying Value	$ 6,997	$ 6,997
Liquidation Preference	$ 7,000	$ 7,000
Common Stock Issuable Upon Conversion	597,167	597,167
Series C-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	8,689,144	8,689,144
Preferred Shares Issued	8,689,144	8,689,144
Preferred Shares Outstanding	8,689,144	8,689,144
Carrying Value	$ 10,248	$ 10,248
Liquidation Preference	$ 10,250	$ 10,250
Common Stock Issuable Upon Conversion	874,423	874,423
Series D Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	34,142,865	34,142,865
Preferred Shares Issued	34,142,865	34,142,865
Preferred Shares Outstanding	34,142,865	34,142,865
Carrying Value	$ 40,265	$ 40,263
Liquidation Preference	$ 40,276	$ 40,276
Common Stock Issuable Upon Conversion	3,435,932	3,435,932
Series D-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	363,636	363,636
Preferred Shares Issued	363,636	363,636
Preferred Shares Outstanding	363,636	363,636
Carrying Value	$ 2,000	$ 2,000
Liquidation Preference	$ 2,000	$ 2,000
Common Stock Issuable Upon Conversion	36,594	36,594
Series E Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	12,715,822	12,715,822
Preferred Shares Issued	3,788,240	3,788,240
Preferred Shares Outstanding	3,788,240	3,788,240
Carrying Value	$ 4,455	$ 4,453
Liquidation Preference	$ 4,469	$ 4,469
Common Stock Issuable Upon Conversion	381,225	381,225
Series E-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	24,264,705	24,264,705
Preferred Shares Issued	3,285,832	7,697,597
Preferred Shares Outstanding	3,285,832	7,697,597
Carrying Value	$ 4,460	$ 10,446
Liquidation Preference	$ 4,469	$ 10,469
Common Stock Issuable Upon Conversion	330,666	774,639
Series E-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	9,226,082	9,226,082
Preferred Shares Issued	8,927,582	8,927,582
Preferred Shares Outstanding	8,927,582	8,927,582
Carrying Value	$ 10,498	$ 10,493
Liquidation Preference	$ 10,531	$ 10,531
Common Stock Issuable Upon Conversion	898,418	898,418
Series E-3 Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	21,237,785	21,237,785
Preferred Shares Issued	20,978,873	16,567,108
Preferred Shares Outstanding	20,978,873	16,567,108
Carrying Value	$ 28,478	$ 22,483
Liquidation Preference	$ 28,531	$ 22,531
Common Stock Issuable Upon Conversion	2,111,187	1,667,214
Series F Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred Shares Authorized	29,411,764	29,411,764
Preferred Shares Issued	14,432,858	13,949,357
Preferred Shares Outstanding	14,432,858	13,949,357
Carrying Value	$ 19,455	$ 18,806
Liquidation Preference	$ 19,629	$ 18,971
Common Stock Issuable Upon Conversion	1,452,436	1,403,779

Common Stock - Additional Infor

Common Stock - Additional Information (Detail) - $ / shares	6 Months Ended	12 Months Ended
Common Stock - Additional Information (Detail) - $ / shares	Jun. 30, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Common stock, shares authorized	143,500,000	143,500,000
Common stock, par value	$ 0.001	$ 0.001
Common stock, dividends declared	$ 0	$ 0
Stock reserved for conversion of redeemable preferred stock	13,631,297	12,206,216
IPO [Member]
Class of Stock [Line Items]
Initial public offering completion date	Jul. 5, 2017

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jun. 16, 2017	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized for issuance		13,631,297	13,631,297		12,206,216
Weighted average grant-date fair value of stock options			$ 5.98	$ 3.24
Aggregate fair value of stock options vested			$ 412	$ 545
Aggregate intrinsic value of stock options exercised			126	$ 6
Aggregate unrecognized stock-based compensation expense		$ 14,232	$ 14,232
Unrecognized stock-based compensation expense, expected weighted average period for recognition			3 years 4 months 24 days
2017 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period			4 years
Number of shares, available for grant		1,244,816	1,244,816
Options to purchase		147,428
Common stock, price per share		$ 15	$ 15
2017 Stock Incentive Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option expiration period			10 years
2017 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized for issuance	150,000
Stock incentive plan description			On June 16, 2017, the Company’s stockholders approved the 2017 Employee Stock Purchase Plan (the “2017 ESPP”), which became effective on June 28, 2017. A total of 150,000 shares of common stock were initially reserved for issuance under this plan. The number of shares of common stock that may be issued under the 2017 ESPP will automatically increase on each January 1, beginning with the fiscal year ending December 31, 2018 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2027, equal to the least of (i) 622,408 shares, (ii) 1% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors.
Maximum annual increase in common stock reserved for future issuance	622,408
Percentage of common stock shares outstanding	1.00%
2016 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period			4 years
Stock option expiration period			10 years
Common stock, shares authorized for issuance		0	0
Stock incentive plan termination year			2,017
Stock incentive plan termination year					2,016
2016 Stock Incentive Plan [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized for issuance		424,601	424,601
2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period					4 years
Stock option expiration period					10 years
2006 Stock Incentive Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period					4 years

Stock-Based Awards - Valuation

Stock-Based Awards - Valuation Assumptions of Stock Options Granted (Detail)	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rate	2.19%	1.37%
Expected term	6 years 1 month 6 days	6 years 1 month 6 days
Expected volatility	80.20%	80.50%
Expected dividend yield	0.00%	0.00%

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of Shares, Beginning balance	920,731
Aggregate Intrinsic Value, Beginning balance		$ 1,297
Number of Shares, Granted	588,701
Number of Shares, Exercised	(18,524)
Number of Shares, Forfeited	(46,594)
Number of Shares, Ending balance	1,444,314	920,731
Number of Shares, Options exercisable	636,409	585,959
Number of Shares, Options vested and expected to vest	1,408,747	904,010
Weighted Average Exercise Price, Beginning balance	$ 4.36
Weighted Average Exercise Price, Granted	8.08
Weighted Average Exercise Price, Exercised	4.33
Weighted Average Exercise Price, Forfeited	5.14
Weighted Average Exercise Price, Ending balance	5.85	$ 4.36
Weighted Average Exercise Price, Options exercisable	4	3.78
Weighted Average Exercise Price, Options vested and expected to vest	$ 5.81	$ 4.37
Weighted-Average Remaining Contractual Term, Outstanding	7 years 8 months 12 days	6 years 4 months 24 days
Weighted Average Remaining Contractual Term, Options exercisable	5 years 9 months 18 days	5 years 2 months 12 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	7 years 7 months 6 days	6 years 3 months 19 days
Aggregate Intrinsic Value, Ending balance	$ 8,220
Aggregate Intrinsic Value, Options exercisable	4,550	$ 1,136
Aggregate Intrinsic Value, Options vested and expected to vest	$ 8,063	$ 1,289

Stock-Based Awards - Summary 42

Stock-Based Awards - Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 273	$ 167	$ 469	$ 330
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	131	53	205	104
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 142	$ 114	$ 264	$ 226

Net Loss per Share - Basic and

Net Loss per Share - Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net loss	$ (4,923)	$ (5,534)	$ (9,480)	$ (9,459)
Accretion of redeemable convertible preferred stock to redemption value	(21)	(19)	(41)	(37)
Net loss attributable to common stockholders	$ (4,944)	$ (5,553)	$ (9,521)	$ (9,496)
Denominator:
Weighted average common shares outstanding- basic and diluted	450,495	428,870	441,661	427,679
Net loss per share attributable to common stockholders-basic and diluted	$ (10.98)	$ (12.95)	$ (21.56)	$ (22.21)

Net Loss per Share - Summary of

Net Loss per Share - Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	11,954,088	10,051,183	11,954,088	10,051,183
Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	10,509,774	9,057,339	10,509,774	9,057,339
Stock Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	1,444,314	993,844	1,444,314	993,844

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Feb. 28, 2010USD ($)	Jun. 30, 2017USD ($)	Jan. 31, 2015USD ($)	Jun. 30, 2017USD ($)Milestone	Jun. 30, 2016USD ($)Milestone	Jun. 30, 2017USD ($)Milestone	Jun. 30, 2016USD ($)Milestone	Dec. 31, 2016USD ($)	Jun. 30, 2011USD ($)	Oct. 31, 2010USD ($)	Dec. 31, 2006USD ($)
Other Commitments [Line Items]
Restricted cash								$ 63,000
Rental expense under operating leases				$ 120,000	$ 105,000	$ 239,000	$ 211,000
Operating Lease Agreement [Member]
Other Commitments [Line Items]
Operating lease expiration		2018-05
Restricted cash	$ 776,000		$ 63,000
Restricted cash released			$ 713,000
Improvements to leased facility									$ 752,000
Future minimum lease payments, 2017		$ 270,000		270,000		270,000
Future minimum lease payments, 2018		202,000		202,000		202,000
Harvard and Dana-Farber Agreement [Member]
Other Commitments [Line Items]
Annual license maintenance fees	145,000
License fees				$ 0	$ 0	$ 145,000	$ 145,000
Milestones achieved \| Milestone				0	0	0	0
Additional liabilities for milestone payments		0		$ 0		$ 0
Non-refundable cash payment						4,428,000		$ 4,283,000
Payments for royalties						0
Harvard and Dana-Farber Agreement [Member] \| Therapeutic Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments	7,700,000
Harvard and Dana-Farber Agreement [Member] \| Diagnostic Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments	$ 700,000
Materia Agreement [Member]
Other Commitments [Line Items]
Aggregate milestones payments											$ 6,400,000
License fees				$ 0	$ 0	$ 0	$ 0
Milestones achieved \| Milestone				0	0	0	0
Additional liabilities for milestone payments		0		$ 0	$ 0	$ 0	$ 0
Annual license fees											$ 50,000
Scripps Agreement [Member]
Other Commitments [Line Items]
License fees				0	$ 0	$ 0	$ 0
Milestones achieved \| Milestone						0
Payments for royalties						$ 0
Annual license fees										$ 50,000
Additional liabilities for milestone payments		$ 0		$ 0		$ 0
Scripps Agreement [Member] \| Peptide Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments										1,900,000
Scripps Agreement [Member] \| Protein Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments										$ 950,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
Income Taxes - Additional Information (Detail) - USD ($)	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Tax Disclosure [Abstract]
Income tax expense (benefit)	$ 0	$ 0	$ 0	$ 0
Deferred income tax assets, operating losses	$ 0	$ 0	$ 0	$ 0

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jul. 05, 2017	Jun. 30, 2017	Jun. 30, 2016	Aug. 10, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Offering expenses		$ 419	$ 180
Number of common shares issued on conversion of redeemable convertible preferred stock		10,509,774			10,461,117
Common stock, shares outstanding		450,937			432,413
Common stock, shares authorized		143,500,000			143,500,000
Common stock, par value		$ 0.001			$ 0.001
Payment of offering expenses		$ 433
Subsequent Event [Member]
Subsequent Event [Line Items]
Common stock, shares authorized	150,000,000
Preferred stock, shares authorized	5,000,000
Common stock, par value	$ 0.001
Preferred stock, par value	$ 0.001
Pro Forma [Member]
Subsequent Event [Line Items]
Common stock, shares outstanding		10,960,711
Pro Forma [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Number of common shares issued on conversion of redeemable convertible preferred stock	10,509,774
Common Stock [Member]
Subsequent Event [Line Items]
Common stock, shares outstanding		450,937			432,413
IPO [Member] \| Pro Forma [Member]
Subsequent Event [Line Items]
Net proceeds from issuance of initial public offering		$ 50,091
Underwriting discounts and commissions incurred		3,938
Offering expenses		$ 2,222
IPO [Member] \| Common Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Stock issued and sold	3,750,000
Share price	$ 15
Net proceeds from issuance of initial public offering	$ 50,090
Underwriting discounts and commissions incurred	3,938
Offering expenses	$ 2,222
Number of common shares issued on conversion of redeemable convertible preferred stock	10,509,774
Common stock, shares outstanding	14,714,816			14,714,816

Subsequent Events - Summary of

Subsequent Events - Summary of Unaudited Pro Forma Financial Data (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 9,397	$ 20,715	$ 3,885	$ 3,768
Investments	1,946	0
Prepaid expenses and other current assets	561	333
Restricted cash	88	25
Total current assets	11,992	21,073
Property and equipment, net	109	107
Restricted cash		63
Other assets	782	778
Deferred offering costs	2,222
Total assets	15,105	22,021
Liabilities, Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit)
Total liabilities	5,471	4,082
Redeemable convertible preferred stock	130,412	129,745		$ 129,745
Stockholders' equity (deficit):
Common stock	0	0
Additional paid-incapital	3,044	2,536
Accumulated deficit	(123,822)	(114,342)
Total stockholders' equity (deficit)	(120,778)	(111,806)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	15,105	$ 22,021
Scenario, Previously Reported [Member]
Current assets:
Cash and cash equivalents	9,397
Investments	1,946
Prepaid expenses and other current assets	561
Restricted cash	88
Total current assets	11,992
Property and equipment, net	109
Restricted cash	0
Other assets	782
Deferred offering costs	2,222
Total assets	15,105
Liabilities, Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit)
Total liabilities	5,471
Redeemable convertible preferred stock	130,412
Stockholders' equity (deficit):
Additional paid-incapital	3,044
Accumulated deficit	(123,822)
Total stockholders' equity (deficit)	(120,778)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	15,105
Scenario, Adjustment [Member]
Current assets:
Cash and cash equivalents	50,510
Total current assets	50,510
Restricted cash	0
Deferred offering costs	(2,222)
Total assets	48,288
Liabilities, Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit)
Total liabilities	(1,803)
Redeemable convertible preferred stock	(130,412)
Stockholders' equity (deficit):
Common stock	15
Additional paid-incapital	180,488
Total stockholders' equity (deficit)	180,503
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	48,288
IPO [Member]
Current assets:
Cash and cash equivalents	59,907
Investments	1,946
Prepaid expenses and other current assets	561
Restricted cash	88
Total current assets	62,502
Property and equipment, net	109
Restricted cash	0
Other assets	782
Total assets	63,393
Liabilities, Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit)
Total liabilities	3,668
Stockholders' equity (deficit):
Common stock	15
Additional paid-incapital	183,532
Accumulated deficit	(123,822)
Total stockholders' equity (deficit)	59,725
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 63,393