Kineta (KANT) 10-Q 9 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	May 07, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Trading Symbol	PTI
Entity Registrant Name	PROTEOSTASIS THERAPEUTICS, INC.
Entity Central Index Key	1,445,283
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		36,081,032

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 19,457	$ 29,724
Short-term investments	43,874	44,738
Restricted cash	294	294
Prepaids and other current assets	1,982	1,377
Total current assets	65,607	76,133
Operating lease, right-of-use asset	15,261	472
Property and equipment, net	376	424
Deferred offering costs	160
Other assets	24	33
Restricted cash, net of current portion	828	1,656
Total assets	82,256	78,718
Current liabilities:
Accounts payable	1,222	2,098
Accrued expenses	5,222	6,120
Deferred revenue		1,108
Operating lease liabilities	1,671	559
Total current liabilities	8,115	9,885
Derivative liability	13	25
Operating lease liabilities, net of current portion	13,999
Total liabilities	22,127	9,910
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized as of March 31, 2018 and December 31, 2017, respectively; no shares issued and outstanding as of March 31, 2018 and December 31, 2017
Common stock, $0.001 par value; 125,000,000 shares authorized as of March 31, 2018 and December 31, 2017, respectively; 34,482,574 and 34,416,088 shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively	35	35
Additional paid-in capital	286,851	285,583
Accumulated other comprehensive loss	(28)	(2)
Accumulated deficit	(226,729)	(216,808)
Total stockholders’ equity	60,129	68,808
Total liabilities and stockholders’ equity	$ 82,256	$ 78,718

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	34,482,574	34,416,088
Common stock, shares outstanding	34,482,574	34,416,088

Condensed Statements of Operati

Condensed Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenue	$ 942	$ 1,021
Operating expenses:
Research and development	8,400	13,108
General and administrative	3,823	3,170
Total operating expenses	12,223	16,278
Loss from operations	(11,281)	(15,257)
Interest income	165	191
Other income (expense), net	90	(30)
Net loss	$ (11,026)	$ (15,096)
Net loss per share attributable to common stockholders—basic and diluted	$ (0.32)	$ (0.60)
Weighted average common shares outstanding—basic and diluted	34,474,004	25,020,337

Condensed Statements of Compreh

Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (11,026)	$ (15,096)
Other comprehensive loss:
Unrealized loss on investments	(26)	(16)
Comprehensive loss	$ (11,052)	$ (15,112)

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net loss	$ (11,026)	$ (15,096)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	563	340
Premium on short-term investments		(100)
Amortization of premium on short-term investments	(55)	78
Stock-based compensation expense	914	486
Stock issued for consulting services	308	258
Change in fair value of derivative liability	(12)	(54)
Changes in operating assets and liabilities:
Accounts receivable		(42)
Prepaids and other current assets	(605)	311
Other assets	9	9
Accounts payable	(876)	(595)
Accrued expenses	(1,058)	(313)
Deferred revenue	(3)	(311)
Operating lease liabilities	(193)	(316)
Net cash used in operating activities	(12,034)	(15,345)
Cash flows from investing activities:
Purchases of short-term investments	(7,957)	(11,393)
Proceeds received from maturities of short-term investments	8,850	23,550
Purchases of property and equipment		(10)
Net cash provided by investing activities	893	12,147
Cash flows from financing activities:
Proceeds from exercise of stock options	21	4
Net cash provided by financing activities	46	4
Net decrease in cash, cash equivalents, and restricted cash	(11,095)	(3,194)
Cash, cash equivalents, and restricted cash at beginning of period	31,674	18,907
Cash, cash equivalents, and restricted cash at end of period	20,579	15,713
Supplemental disclosure of non-cash investing and financing activities:
Deferred offering costs included in accrued expenses	160
Addition of Operating Lease Right-Of-Use Asset [Member]
Supplemental disclosure of non-cash investing and financing activities:
Capital expenditures incurred but not yet paid	15,304
Accounts Payable [Member]
Supplemental disclosure of non-cash investing and financing activities:
Capital expenditures incurred but not yet paid		$ 25
Employee Stock Purchase Plan [Member]
Cash flows from financing activities:
Proceeds from issuance of common stock pursuant to employee stock purchase plan	$ 25

Nature of the Business

Nature of the Business	3 Months Ended
	Mar. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Proteostasis Therapeutics, Inc. (the “Company”) was incorporated in Delaware on December 13, 2006. The Company is a clinical stage biopharmaceutical company developing small molecule therapeutics to treat cystic fibrosis (“CF”) and other diseases caused by dysfunctional protein processing. The Company focuses on identifying therapies that restore protein function. CF is a disease caused by defects in the cystic fibrosis transmembrane conductance regulator (“CFTR”) protein and insufficient CFTR protein function. The Company’s lead product candidates, PTI-428, an amplifier, PTI-801, a third generation corrector, and PTI-808, a potentiator, as well as a dual combination consisting of PTI-801 and PTI-808, and a triple combination consisting of PTI-428, PT-801, and PTI-808 are in clinical development. The Company’s other drug candidates are in the preclinical development and discovery phases. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and ability to secure additional capital to fund operations. 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 and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales In accordance with ASC 205-40, Going Concern, the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date the financial statements are issued . As of March 31, 2018, the Company had an accumulated deficit of $226.7 million. During the three months ended March 31, 2018, the Company incurred losses of $11.0 million and used $12.0 million of cash in operations. $63.3 million will be sufficient to fund its operating expenses and capital requirements, based upon its current operating plan, into early 2019.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Unaudited Interim Financial Information The condensed balance sheet at December 31, 2017 was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed financial statements as of March 31, 2018 and for the three months ended March 31, 2018 are unaudited. The accompanying unaudited interim financial statements have been prepared by the Company, pursuant to the rules and regulations of the Securities and Exchange Commission (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 unaudited condensed financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2017 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 14, 2018. In the opinion of management, all adjustments, consisting only of normal recurring adjustments as necessary, for the fair statement of the Company’s condensed financial position as of March 31, 2018 and condensed results of its operations and cash flows for the three months ended March 31, 2018 have been made. The results of operations for the three months ended March 31, 2018 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2018. 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, revenue recognition, the accrual for research and development expenses and the valuation of common stock, and the derivative liability. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates. Concentrations of Credit Risk and Significant Customers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, short-term investments and accounts receivable. The Company mitigates its risk with respect to cash, cash equivalents and short-term investments by maintaining its balances at two accredited financial institutions, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company’s accounts receivable balances are due from the counterparty to its collaboration agreements (see Note 8) that the Company believes to be creditworthy. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity as a reduction of additional paid-in capital generated as a result of the offering. As of March 31, 2018, a deferred offering cost of $0.2 million related to the Company’s at-the-market common stock offering program sales agreement that was entered into with Leerink Partners LLC in March 2018 remains an asset on the Company’s financial statements. Restricted Cash As of March 31, 2018 and December 31, 2017, the current portion of restricted cash consisted of a certificate of deposit in the amount of $0.3 million collateralizing a letter of credit issued as a security deposit in connection with the Company’s lease of its corporate facilities at 200 Technology Square, Cambridge, MA. On September 19, 2017, the Company entered into a lease agreement for a new corporate headquarters at 80 Guest Street, Boston, MA (see Note 11). As of March 31, 2018, restricted cash, net of current portion, consisted of a money market account in the amount of $0.8 million collateralizing a letter of credit issued as a security deposit for this lease agreement. The restricted cash amount decreased by $0.8 million from December 31, 2017 as the Company was entitled to reduce the amount of the letter of credit and the corresponding restricted cash upon meeting certain conditions noted within the lease agreement. Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of March 31, 2018 and December 31, 2017, the Company’s cash equivalents consisted of money market funds. Short-term Investments Short-term investments represent holdings of available-for-sale marketable securities in accordance with the Company’s investment policy and cash management strategy. Short-term investments mature within one-year from the balance sheet date. Investments in marketable securities are recorded at fair value, with any unrealized gains and losses, net of taxes, reported as a component of stockholders’ equity until realized or until a determination is made that an other-than-temporary decline in market value has occurred. The cost of marketable securities sold is determined based on the specific identification method and any realized gains or losses on the sale of investments are reflected as a component of other expense, net. Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance are charged to expense as incurred. Leases In February 2016, the FASB issued ASU No. 2016-02, Leases At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received. The Company has elected to combine lease and non-lease components as a single component. The lease expense is recognized over the expected term on a straight-line basis. Operating leases are recognized on the balance sheet as right-of-use assets, operating lease liabilities current and operating lease liabilities non-current. Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets. 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 derivative liability, short-term investments and cash equivalents are carried at fair value determined according to the fair value hierarchy described above (see Note 4). The carrying value of cash and cash equivalents, accounts receivable, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities Revenue Recognition Effective January 1, 2018, the Company adopted Accounting Standards Codification ASC Topic 606, Revenue from Contracts with Customers modified retrospective transition method. Under this method, results for reporting periods beginning after January 1, 2018 are presented under ASC 606, while prior period amounts are not adjusted and continue to be reported in accordance The Company enters into licensing agreements which are within the scope of ASC 606, under which it may exclusively license rights to research, develop, manufacture and commercialize its product candidates to third parties. The terms of these arrangements typically include payment to the Company of one or more of the following: non-refundable, upfront license fees; reimbursement of certain costs; customer option exercise fees; development, regulatory and commercial milestone payments; and royalties on net sales of licensed products. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for these arrangements, the Company must use significant judgment to determine: a) the number of performance obligations based on the determination under step (ii) above; b) the transaction price under step (iii) above; and c) the stand-alone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above. The Company uses judgment to determine whether milestones or other variable consideration, except for royalties, should be included in the transaction price as described further below. The transaction price is allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. In developing the stand-alone price for a performance obligation, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validates the stand-alone selling price for performance obligations by evaluating whether changes in the key assumptions used to determine the stand-alone selling prices will have a significant effect on the allocation of transaction price between multiple performance obligations. The Company records as deferred revenue any amounts received prior to satisfying the revenue recognition criteria. Amounts recognized as revenue, but not yet received or invoiced are generally recorded as current assets. Exclusive Licenses If the license to the Company’s intellectual property is determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. In assessing whether a promise or performance obligation is distinct from the other promises, the Company considers factors such as the research, development, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can benefit from a promise for its intended purpose without the receipt of the remaining promise, whether the value of the promise is dependent on the unsatisfied promise, whether there are other vendors that could provide the remaining promise, and whether it is separately identifiable from the remaining promise. For licenses that are combined with other promises, the Company assesses the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The measure of progress, and thereby periods over which revenue should be recognized, are subject to estimates by management and may change over the course of the research and development and licensing agreement. Such a change could have a material impact on the amount of revenue the Company records in future periods. Research and Development Services The promises under the Company’s collaboration and license agreements generally include research and development services to be performed by the Company on behalf of the collaboration partner. As the provision of research and development services is a part of the Company’s central operations, when the Company is principally responsible for the performance of these services under the agreements, the Company recognizes revenue on a gross basis for research and development services in accordance with the ASC 606 framework described above. Customer Options If an arrangement is determined to contain customer options that allow the customer to acquire additional goods or services, the goods and services underlying the customer options are not considered to be performance obligations at the outset of the arrangement, as they are contingent upon option exercise. The Company evaluates the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. The Company allocates the transaction price to material rights based on the relative standalone selling price, which is determined based on the identified discount and the probability that the customer will exercise the option. Amounts allocated to a material right are not recognized as revenue until, at the earliest, the option is exercised. Milestone Payments At the inception of each arrangement that includes development milestone payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. Royalties For arrangements that include sales-based royalties, including milestone payments based on a level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements. For a complete discussion of accounting for collaboration revenues, see Note 8, Collaboration Agreement. Segment Information The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is developing therapeutics to treat protein conformational diseases. All of the Company’s tangible assets are held in the United States. To date, all of the Company’s revenue has been generated in the United States. Embedded Derivatives Embedded derivatives that are required to be bifurcated from the underlying host instrument are accounted for and valued as a separate financial instrument. An embedded derivative exists associated with an alternate payment option upon change of control within the research, development and commercialization agreement with Cystic Fibrosis Foundation Therapeutics, Inc.. The embedded derivative has been bifurcated and is classified as a liability on the balance sheet and separately accounted for at its fair value. The derivative liability is marked-to-market every reporting period. Changes in fair value of the derivative liability are recognized as a component of other income (expense), net in the accompanying statement of operations and comprehensive loss. Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries, stock-based compensation and benefits, facilities costs, depreciation, third-party license fees, and external costs of outside vendors engaged to conduct preclinical development activities and clinical trials. Research and development expenses include the Company’s costs of performing services in connection with its collaboration agreements and research grant. Nonrefundable prepayments for goods or services that will be used or rendered for future research and development activities are deferred and capitalized. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered or the services rendered. Research Contract Costs and Accruals The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the United States. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses. Preferred Stock Warrant Liability Through February 2016, the Company classified a warrant to purchase shares of its Series A preferred stock as a liability on its balance sheets as this warrant was a free-standing financial instrument could have required the Company to transfer assets upon exercise. The warrant was initially recorded at fair value on date of grant and subsequently remeasured to fair value at each balance sheet date. Changes in fair value of the warrant were recognized as a component of other income (expense), net in the statement of operations. Following the reverse stock split of the common stock of the Company and the completion of the Company’s IPO in February 2016, the warrant became a warrant to purchase 14,800 shares of common stock. At that time, the warrant was reclassified to a component of stockholder’s equity and is no longer subject to remeasurement. The Company used the Black-Scholes option-pricing model, which incorporates assumptions and estimates, to value the preferred stock warrant. The Company has assessed these assumptions and estimates on a quarterly basis as additional information impacting the assumptions is obtained. Estimates and assumptions impacting the fair value measurement include the fair value per share of the underlying Series A preferred stock, the remaining contractual term of the warrant, risk-free interest rate, expected dividend yield and expected volatility of the price of the underlying preferred stock. The Company determined the fair value per share of the underlying preferred stock by taking into consideration the most recent sales of its convertible preferred stock, results obtained from third-party valuations and additional factors that are deemed relevant. Up until February 2016, the Company was a private company and therefore lacks company-specific historical and implied volatility information of its stock. Therefore, it estimates its expected stock volatility based on the historical volatility of publicly traded peer companies for a term equal to the remaining contractual term of the warrant. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve for time periods approximately equal to the remaining contractual term of the warrant. Expected dividend yield is determined considering that the underlying Series A preferred stock is entitled to dividends of 8.0% per year, whether or not declared. Stock-Based Compensation The Company measures all stock options and other stock-based awards granted to employees and directors based on the fair value on the date of the grant and recognizes compensation expense of those awards, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues stock options and restricted stock awards to employees with only service- based vesting conditions and records the expense for these awards using the straight-line method. The Company measures stock-based awards granted to consultants and non-employees based on the fair value of the award on the date on which the related service is complete. Compensation expense is recognized over the period during which services are rendered by such consultants and non-employees until completed. At the end of each financial reporting period prior to completion of the service, the fair value of these awards is remeasured using the then-current fair value of the Company’s common stock and updated assumption inputs in the Black-Scholes option-pricing model. The Company does not recognize compensation expense for awards with performance-based vesting conditions granted to consultants and non-employees for which satisfaction of the performance conditions is not solely within the control of the holder until the performance conditions have been met. The Company classifies stock-based compensation expense in its statement of operations in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified. Prior to January 1, 2017, the Company recognized compensation expense for only the portion of awards that are expected to vest. In developing a forfeiture rate estimate, the Company has considered its historical experience to estimate pre- vesting forfeitures for service-based awards. Effective January 1, 2017, the company adopted ASU No. 2016-09 on a modified retrospective basis. As a result, the Company has made an accounting policy election to account for forfeitures as they occur. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option- pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends on common stock and does not expect to pay any cash dividends in the foreseeable future. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the three months ended March 31, 2018 and 2017, comprehensive loss included less than $0.1 million of unrealized loss on short term investments. Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. Net Loss per Share Basic net income (loss) per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of common shares, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common shares, as determined using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. For any period in which the Company has reported net income, basic net income per common share attributable to common stockholders is adjusted for certain amounts to calculate diluted net loss per common share attributable to common stockholders, since dilutive common shares are assumed to have been issued if their effect is dilutive and not to have been issued if their effect is anti-dilutive. Recently Issued Accounting Pronouncements Revenues In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, which amends the guidance for accounting for revenue from contracts with customers. This ASU supersedes the revenue recognition requirements in ASC Topic 605, Revenue Recognition Revenue from Contracts with Customers As a result of adopting ASC 606 on January 1, 2018, the Company has recorded a cumulative-effect decrease to opening accumulated deficit of $1.1 million as of January 1, 2018 and a corresponding decrease to deferred revenue. The total impact to revenue for the three months ended March 31, 2018 as a result of the adoption of ASC 606 was $0.8 million. Total revenue recorded in the three months ended March 31,

Short-Term Investments

Short-Term Investments	3 Months Ended
	Mar. 31, 2018
Cash Cash Equivalents And Short Term Investments [Abstract]
Short-Term Investments	3. Short-Term Investments The following table summarizes the Company’s short-term investments as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S government-sponsored enterprise securities $ 9,479 $ — $ (9 ) $ 9,470 U.S. treasury securities 34,423 0 (19 ) 34,404 $ 43,902 $ 0 $ (28 ) $ 43,874 December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S government-sponsored enterprise securities $ 9,817 $ — $ (1 ) $ 9,816 U.S. treasury securities 34,923 1 (2 ) 34,922 $ 44,740 $ 1 $ (3 ) $ 44,738 The Company did not have any realized gains or losses on its short-term investments for the three months ended March 31, 2018 and 2017 2017

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	4. Fair Value of Financial Assets and Liabilities The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): Fair Value Measurements as of March 31, 2018 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 18,137 $ — $ — $ 18,137 Short-term investments: U.S. government-sponsored enterprise securities — 9,470 — 9,470 U.S. treasury securities — 34,404 — 34,404 $ 18,137 $ 43,874 $ — $ 62,011 Liabilities: Derivative liability $ — $ — $ 13 $ 13 $ — $ — $ 13 $ 13 Fair Value Measurements as of December 31, 2017 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 13,871 $ — $ — $ 13,871 U.S. government-sponsored enterprise securities — 8,960 — 8,960 U.S. treasury securities — 3,497 — 3,497 Short-term investments: U.S. government-sponsored enterprise securities — 9,816 — 9,816 U.S. treasury securities — 34,922 — 34,922 $ 13,871 $ 57,195 $ — $ 71,066 Liabilities: Derivative liability $ — $ — $ 25 $ 25 $ — $ — $ 25 $ 25 During the periods ended March 31, 2018 and December 31, 2017, there were no transfers between Level 1, Level 2 and Level 3. Derivative Liability The derivative liability relates to a cash settlement option associated with the change of control provision in the Company’s Cystic Fibrosis Foundation Therapeutics, Inc. (“CFFT”) agreement, which meets the definition of a derivative. The fair value of the derivative liability is based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. The fair value of the derivative instrument was determined using the Monte-Carlo simulation analysis. In determining the fair value of the derivative liability, the inputs impacting fair value include the fair value of the Company’s common stock, expected term of the derivative instrument, expected volatility of the common stock price, risk-free interest rate, expected sales-based milestone payments, discount rate, probability of a change of control event, and the probability that the counterparty would elect to accept the alternative cash payment in lieu of its right to the future sales-based milestone payments. As of March 31, 2018 and December 31, 2017, the Company determined the per share common stock price available based on the closing price of its common stock on the NASDAQ Global Market as of March 29, 2018 and December 29, 2017, respectively. The Company determined the expected term of the instrument to be 1.75 years and 2.00 years as of March 31, 2018 and December 31, 2017, respectively. The Company estimated its expected stock volatility to be 80.0% and 80.0% as of March 31, 2018 and December 31, 2017, respectively, based on the historical volatility of publicly traded peer companies for terms matching the expected term of the instrument for each respective period. The risk-free interest rate was determined to be 2.20% and 1.87% as of March 31, 2018 and December 31, 2017, respectively, by reference to the U.S. Treasury yield curve for terms matching the expected term of the instrument for each respective period. Changes in the values of the derivative liability are summarized below (in thousands): Derivative Liability Fair value at December 31, 2017 $ 25 Change in fair value (12 ) Fair value at March 31, 2018 $ 13

Prepaids and Other Current Asse

Prepaids and Other Current Assets	3 Months Ended
	Mar. 31, 2018
Prepaid Expense And Other Assets Current [Abstract]
Prepaids and Other Current Assets	5. Prepaids and Other Current Assets Prepaids and other current assets consisted of the following (in thousands): March 31, December 31, 2018 2017 Prepaid clinical, manufacturing and scientific expenses $ 753 $ 568 Prepaid insurance expenses 569 55 Other prepaid expenses and other current assets 660 754 $ 1,982 $ 1,377

Accrued Expenses

Accrued Expenses	3 Months Ended
	Mar. 31, 2018
Text Block [Abstract]
Accrued Expenses	6. Accrued Expenses Accrued expenses consisted of the following (in thousands): March 31, December 31, 2018 2017 Accrued payroll and related expenses $ 973 $ 1,542 Accrued research and development expenses 3,282 3,930 Accrued professional fees 928 556 Accrued other 39 92 $ 5,222 $ 6,120

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	7. Stock-Based Compensation 2016 Stock Option and Incentive Plan On February 3, 2016, the Company’s stockholders approved the 2016 Stock Option and Incentive Plan (the “2016 Plan”), which became effective on February 9, 2016. The 2016 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock units, restricted stock awards and other stock-based awards. The number of shares initially reserved for issuance under the 2016 Plan is 1,581,839 shares. The number of shares of common stock that may be issued under the 2016 Plan will automatically increase on each January 1, beginning on January 1, 2017, by the lesser of 3% of the shares of the Company’s common stock outstanding on the immediately preceding December 31 or an amount determined by the Company’s board of directors or the compensation committee of the board of directors. The shares of common stock underlying any awards that are forfeited, canceled, repurchased or are otherwise terminated by the Company under the 2016 Plan and the 2008 Equity Incentive Plan, as amended (the “2008 Plan”) will be added back to the shares of common stock available for issuance under the 2016 Plan. As of March 31, 2018, the total number of shares reserved under the 2016 Plan and 2008 Plan was 4,446,676 and the Company had 701,140 shares available for future issuance under the 2016 Plan. 2016 Employee Stock Purchase Plan On February 3, 2016, the Company’s stockholders approved the 2016 Employee Stock Purchase Plan (the “2016 ESPP”), which became effective in connection with the completion of the Company’s initial public offering. A total of 138,757 shares of common stock were reserved for issuance under this plan. In addition, the number of shares of common stock that may be issued under the 2016 ESPP will automatically increase on each January 1, beginning on January 1, 2017 and ending on January 1, 2026, by the least of (i) 138,757 shares of common stock, (ii) 1% of the Company’s shares of common stock outstanding on the immediately preceding December 31 and (iii) an amount determined by the Company’s board of directors or the compensation committee of the board of directors. During the three months ended March 31, 2018, 6,114 shares of common stock were issued pursuant to the 2016 ESPP. As of March 31, 2018, the total number of shares reserved under the 2016 ESPP was 399,328 shares. The Company recognized less than $0.1 million of stock-based compensation during the three month period ended March 31, 2018 related to this plan. Stock Option Grants and Shares to Non-employees Prior to 2013, the Company issued options to purchase 203,964 shares of common stock to non-employees, primarily members of the Company’s scientific advisory board, that vest upon the achievement of specified development and clinical milestones. As of March 31, 2018, options for the purchase of 83,250 shares held by non-employees remained unvested, pending achievement of the specified milestones, and had an aggregate fair value of $0.3 million. Bonus Restricted Stock Units (RSU’s) On February 1, 2018, the Company’s board approved the executive bonuses for the year ended December 31, 2017 and elected payment to be made through grant of an equivalent number of RSU’s based on the February 1, 2018 closing share price. The requisite service period for the awards is from February 1, 2018 through February 1, 2019 (the vesting period). The Company measures employee stock-based compensation based on the grant date fair value of the stock-based compensation award. In addition, the Company grants RSU’s at prices equal to the fair value of the Company’s common stock on the date of grant, based on observable market prices. The Company will recognize employee stock-based compensation expense for the bonus RSU grants on a straight-line basis over the requisite service period of the awards which is from February 1, 2018 through February 1, 2019. The Company will account for these grants in Q1 2018. Specifically, the grants do not meet the criteria for liability classification as there is a fixed number of shares to be issued and there is no variability in the number of shares which have been granted. As of the three month period ended March 31, 2018, 197,625 RSU’s had been granted with a total expense of $0.1 million being recognized. Stock-Based Compensation Stock-based compensation expense, including shares issued to a non-employee for consulting services, was classified in the statements of operations as follows (in thousands): Three Months Ended March 31, 2018 2017 Research and development $ 363 $ 255 General and administrative 859 489 $ 1,222 $ 744

Collaboration Agreement

Collaboration Agreement	3 Months Ended
	Mar. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration Agreement	8. Collaboration Agreement Astellas In November 2014, the Company entered into the Collaborative Research, Development, Commercialization and License Agreement (the “Astellas Agreement” with Astellas Pharma Inc. (“Astellas”). The focus of the Astellas Agreement is to identify, develop and commercialize therapeutic candidates relating to the Unfolded Protein Response (“UPR”) pathway. Financial Terms Under terms of the Astellas Agreement, Astellas purchased from the Company convertible promissory notes totaling $5.0 million with terms consistent with those of other investors that purchased convertible promissory notes issued during 2014. In addition, the Company will be eligible to receive research funding support, based on the establishment of an annual research budget, and future research, development and sales milestone payments of up to $398.5 million, as well as tiered royalty payments ranging in the mid single-digit to low double-digit percentages of net sales, as defined in the agreement. Under the agreement, the companies will conduct research during the initial research term, which is approximately three and a half years, to identify lead compounds for clinical development. The Company will provide Astellas with a report of the actual expenses incurred within 30 days after the end of the quarter, which Astellas will provide payment to the Company within 30 days of receiving of the report. At the end of the research term, Astellas, in its sole discretion, may designate a development compound and make a milestone payment to the Company. The Company has the right, but not the obligation, to co-develop the compound. If the Company does not exercise its option to co-develop the compound, Astellas will have an exclusive right to the compound and sole right and responsibility for the development of the compound. Term and Termination The term of the Astellas Agreement commenced in November 2014 and will continue in full force and effect, unless terminated under the conditions described below, until expiration of all applicable royalty terms with respect to all licensed products in all countries in the territory defined as per the agreement. The agreement was set to automatically terminate at the end of the three and a half year research term, in the second quarter of 2018, if Astellas has not designated at least one development compound, unless mutually agreed to be extended. On April 20, 2018, the Company and Astellas entered into Amendment No. 6 (“Amendment No. 6”) to the “Astellas Agreement”. Amendment No. 6, effective as of April 23, 2018, extends the research term for the initial project under the Astellas Agreement to December 4, 2018. Astellas has the unilateral right to terminate the agreement on a project-by-project basis by providing written notice to the Company. Reciprocal termination rights under the agreement include termination for breach and termination for bankruptcy. Accounting Analysis The Company assessed this arrangement in accordance with ASC 606 and concluded that the contract counterparty, Astellas, is a customer. The Company identified the following material promises as of the most recent amendment in July 2016: (1) the research license; (2) the research services to be provided over the research term; and (3) participation in the Joint Research Committee (the “Committee”) to be provided over the initial three and a half year research term of the agreement. The Company determined that the license and research services were not distinct from one another, as the license has limited value without the performance of the research and development activities. Participation in the Committee to oversee the research activities was determined to be quantitatively and qualitatively immaterial and therefore is excluded from performance obligations. As such, the Company determined that these promises should be combined into a single performance obligation. The Company evaluated the Astellas option right to designate a development compound, as described above, to determine whether it provides Astellas with a material right. The Company concluded that the option was not issued at a significant and incremental discount and Astellas has only the right to pursue negotiations for additional projects, and therefore does not provide a material right. As such, they are excluded from performance obligations at the inception of the arrangement. Under the Astellas Agreement, in order to evaluate the appropriate transaction price as of the adoption of ASC 606, the Company determined that the payments received to date for research funding support and reimbursement of third-party costs, the estimated payments that will be received for research funding support and reimbursement of third-party costs over the remaining research term, and the milestone payments received to date represent the transaction price, which was allocated to the single performance obligation. The transaction price as of the adoption of ASC 606 and March 31, 2018 was $12.8 million, of which $0.9 million is yet to be completed as of March 31, 2018. The option exercise fee that may be received is excluded from the transaction price until the customer option is exercised. Future potential milestone payments were excluded from the transaction price, as all milestone amounts were fully constrained due to Astellas having only the right to pursue negotiations for additional projects. The Company will reevaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, if necessary, adjust its estimate of the transaction price. Revenue associated with the performance obligation is being recognized as revenue as the research and development services are provided using an input method, according to the costs incurred as related to the research and development activities and the costs expected to be incurred in the future to satisfy the performance obligation. The transfer of control occurs over this time period and, in management’s judgment, is the best measure of progress towards satisfying the performance obligation. The research and development services related to this performance obligation are expected to be performed over a period ending on December 4, 2018 as noted above. The amounts received that have not yet been recognized as revenue are recorded in deferred revenue on the Company’s condensed balance sheet. The Company recognized revenue of $0.9 million and $1.0 million for the three months ended March 31, 2018 and 2017, respectively. Amounts recorded as a contract asset under the Astellas Agreement totaled less than $0.1 million as of March 31, 2018. Amounts recorded as deferred revenue under the Astellas Agreement totaled $1.1 million as of December 31, 2017

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The Company did not record a federal or state income tax benefit for its losses for the three months ended March 31, 2018 and 2017 due to the conclusion that a full valuation allowance is required against the Company’s deferred tax assets. All of the Company’s losses before income taxes were generated in the United States.

Net Loss per Share

Net Loss per Share	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Net Loss per Share	10. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Three Months Ended March 31, 2018 2017 Numerator: Net loss $ (11,026 ) $ (15,096 ) Denominator: Weighted average number of common shares outstanding—basic 34,474,004 25,020,337 Net loss per share attributable to common stockholders—basic and diluted $ (0.32 ) $ (0.60 ) The Company’s potential dilutive securities, which include stock options and a warrant to purchase common stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company has reported a net loss for all periods presented. Therefore, diluted net loss per common share is the same as basic net loss per common share. The following potentially dilutive securities outstanding, prior to the use of the treasury stock method or if-converted method, have been excluded from the computation of diluted weighted-average shares outstanding, because such securities had an antidilutive impact due to the losses reported March 31, 2018 2017 Options to purchase common stock 3,548,271 2,086,453 Restricted stock units 197,265 — Potentially dilutive securities outstanding 3,745,536 2,086,453

Leases

Leases	3 Months Ended
	Mar. 31, 2018
Leases [Abstract]
Leases	11. Leases The Company has operating leases of office and laboratory space. The lease of the Company’s principal facilities in Cambridge, Massachusetts, which, as amended expires in May 2018. This lease was used as the Company’s corporate headquarters, and was located at 200 Technology Square, 4 th In September 2017, the Company entered into a new lease of office and laboratory space in Boston, Massachusetts which will become the new corporate headquarters. The new lease commenced on January 19, 2018. This lease has a 10-year initial term with an option to extend for 7 additional years. The lessee has the right to terminate the lease cause in case of the inability to use the space due to substantial damage while the lessor has the right to terminate the lease for tenant’s default of lease financial obligations. Per the terms of the agreement, the Company does not have any residual value guarantees. In calculating the present value of the lease payments, the Company has elected to utilize its incremental borrowing rate based on the original lease term and not the remaining lease term. The Company has elected to account for each lease component and its associated non-lease components as a single lease component, and has allocated all of the contract consideration across lease components only. This will potentially result in the initial and subsequent measurement of the balances of the right-of-use asset and lease liability for leases being greater than if the policy election was not applied. The Company’s existing real estate leases in Cambridge and Boston are net leases as their non-lease components (i.e. common area maintenance) are paid separately from rent based on actual costs incurred and therefore were not included in the right-of-use asset and liability and are reflected as an expense in the period incurred. As of March 31, 2018, and December 31, 2017 assets under operating lease were $15.3 million and $0.5 million, respectively. The elements of lease expense were as follows: Three Months Ended March 31, 2018 2017 Lease cost Operating lease cost $ 660 $ 286 Total lease cost $ 660 $ 286 Other information Operating cash flows used for operating leases $ 338 $ 333 Operating lease liabilities arising from obtaining right-of-use assets $ 15,304 $ — Weighted average remaining lease term 10 years 1 years Weighted average discount rate 4.50 % 4.06 % Future lease payments under no n-cancelable leases as of March 31, 2018: Future Operating Lease Payments 2018 $ 1,824 2019 1,686 2020 1,733 2021 1,780 2022 1,829 Thereafter 10,636 Total lease payments 19,488 Less: imputed interest 3,920 Total operating lease liabilities $ 15,568

Summary of Significant Accoun18

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Unaudited Interim Financial Information	Unaudited Interim Financial Information The condensed balance sheet at December 31, 2017 was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed financial statements as of March 31, 2018 and for the three months ended March 31, 2018 are unaudited. The accompanying unaudited interim financial statements have been prepared by the Company, pursuant to the rules and regulations of the Securities and Exchange Commission (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 unaudited condensed financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2017 included in the Company’s Annual Report on Form 10-K filed with the SEC on March 14, 2018. In the opinion of management, all adjustments, consisting only of normal recurring adjustments as necessary, for the fair statement of the Company’s condensed financial position as of March 31, 2018 and condensed results of its operations and cash flows for the three months ended March 31, 2018 have been made. The results of operations for the three months ended March 31, 2018 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2018.
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, revenue recognition, the accrual for research and development expenses and the valuation of common stock, and the derivative liability. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.
Concentrations of Credit Risk and Significant Customers	Concentrations of Credit Risk and Significant Customers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, short-term investments and accounts receivable. The Company mitigates its risk with respect to cash, cash equivalents and short-term investments by maintaining its balances at two accredited financial institutions, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company’s accounts receivable balances are due from the counterparty to its collaboration agreements (see Note 8) that the Company believes to be creditworthy.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity as a reduction of additional paid-in capital generated as a result of the offering. As of March 31, 2018, a deferred offering cost of $0.2 million related to the Company’s at-the-market common stock offering program sales agreement that was entered into with Leerink Partners LLC in March 2018 remains an asset on the Company’s financial statements.
Restricted Cash	Restricted Cash As of March 31, 2018 and December 31, 2017, the current portion of restricted cash consisted of a certificate of deposit in the amount of $0.3 million collateralizing a letter of credit issued as a security deposit in connection with the Company’s lease of its corporate facilities at 200 Technology Square, Cambridge, MA. On September 19, 2017, the Company entered into a lease agreement for a new corporate headquarters at 80 Guest Street, Boston, MA (see Note 11). As of March 31, 2018, restricted cash, net of current portion, consisted of a money market account in the amount of $0.8 million collateralizing a letter of credit issued as a security deposit for this lease agreement. The restricted cash amount decreased by $0.8 million from December 31, 2017 as the Company was entitled to reduce the amount of the letter of credit and the corresponding restricted cash upon meeting certain conditions noted within the lease agreement.
Cash Equivalents	Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. As of March 31, 2018 and December 31, 2017, the Company’s cash equivalents consisted of money market funds.
Short-Term Investments	Short-term Investments Short-term investments represent holdings of available-for-sale marketable securities in accordance with the Company’s investment policy and cash management strategy. Short-term investments mature within one-year from the balance sheet date. Investments in marketable securities are recorded at fair value, with any unrealized gains and losses, net of taxes, reported as a component of stockholders’ equity until realized or until a determination is made that an other-than-temporary decline in market value has occurred. The cost of marketable securities sold is determined based on the specific identification method and any realized gains or losses on the sale of investments are reflected as a component of other expense, net.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the estimated useful life of each asset. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is included in loss from operations. Expenditures for repairs and maintenance are charged to expense as incurred.
Leases	Leases In February 2016, the FASB issued ASU No. 2016-02, Leases At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received. The Company has elected to combine lease and non-lease components as a single component. The lease expense is recognized over the expected term on a straight-line basis. Operating leases are recognized on the balance sheet as right-of-use assets, operating lease liabilities current and operating lease liabilities non-current.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets.
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 derivative liability, short-term investments and cash equivalents are carried at fair value determined according to the fair value hierarchy described above (see Note 4). The carrying value of cash and cash equivalents, accounts receivable, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities
Revenue Recognition	Revenue Recognition Effective January 1, 2018, the Company adopted Accounting Standards Codification ASC Topic 606, Revenue from Contracts with Customers modified retrospective transition method. Under this method, results for reporting periods beginning after January 1, 2018 are presented under ASC 606, while prior period amounts are not adjusted and continue to be reported in accordance The Company enters into licensing agreements which are within the scope of ASC 606, under which it may exclusively license rights to research, develop, manufacture and commercialize its product candidates to third parties. The terms of these arrangements typically include payment to the Company of one or more of the following: non-refundable, upfront license fees; reimbursement of certain costs; customer option exercise fees; development, regulatory and commercial milestone payments; and royalties on net sales of licensed products. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for these arrangements, the Company must use significant judgment to determine: a) the number of performance obligations based on the determination under step (ii) above; b) the transaction price under step (iii) above; and c) the stand-alone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above. The Company uses judgment to determine whether milestones or other variable consideration, except for royalties, should be included in the transaction price as described further below. The transaction price is allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. In developing the stand-alone price for a performance obligation, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validates the stand-alone selling price for performance obligations by evaluating whether changes in the key assumptions used to determine the stand-alone selling prices will have a significant effect on the allocation of transaction price between multiple performance obligations. The Company records as deferred revenue any amounts received prior to satisfying the revenue recognition criteria. Amounts recognized as revenue, but not yet received or invoiced are generally recorded as current assets. Exclusive Licenses If the license to the Company’s intellectual property is determined to be distinct from the other promises or performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. In assessing whether a promise or performance obligation is distinct from the other promises, the Company considers factors such as the research, development, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can benefit from a promise for its intended purpose without the receipt of the remaining promise, whether the value of the promise is dependent on the unsatisfied promise, whether there are other vendors that could provide the remaining promise, and whether it is separately identifiable from the remaining promise. For licenses that are combined with other promises, the Company assesses the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The measure of progress, and thereby periods over which revenue should be recognized, are subject to estimates by management and may change over the course of the research and development and licensing agreement. Such a change could have a material impact on the amount of revenue the Company records in future periods. Research and Development Services The promises under the Company’s collaboration and license agreements generally include research and development services to be performed by the Company on behalf of the collaboration partner. As the provision of research and development services is a part of the Company’s central operations, when the Company is principally responsible for the performance of these services under the agreements, the Company recognizes revenue on a gross basis for research and development services in accordance with the ASC 606 framework described above. Customer Options If an arrangement is determined to contain customer options that allow the customer to acquire additional goods or services, the goods and services underlying the customer options are not considered to be performance obligations at the outset of the arrangement, as they are contingent upon option exercise. The Company evaluates the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the outset of the arrangement. The Company allocates the transaction price to material rights based on the relative standalone selling price, which is determined based on the identified discount and the probability that the customer will exercise the option. Amounts allocated to a material right are not recognized as revenue until, at the earliest, the option is exercised. Milestone Payments At the inception of each arrangement that includes development milestone payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. Royalties For arrangements that include sales-based royalties, including milestone payments based on a level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements. For a complete discussion of accounting for collaboration revenues, see Note 8, Collaboration Agreement.
Segment Information	Segment Information The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is developing therapeutics to treat protein conformational diseases. All of the Company’s tangible assets are held in the United States. To date, all of the Company’s revenue has been generated in the United States.
Embedded Derivatives	Embedded Derivatives Embedded derivatives that are required to be bifurcated from the underlying host instrument are accounted for and valued as a separate financial instrument. An embedded derivative exists associated with an alternate payment option upon change of control within the research, development and commercialization agreement with Cystic Fibrosis Foundation Therapeutics, Inc.. The embedded derivative has been bifurcated and is classified as a liability on the balance sheet and separately accounted for at its fair value. The derivative liability is marked-to-market every reporting period. Changes in fair value of the derivative liability are recognized as a component of other income (expense), net in the accompanying statement of operations and comprehensive loss.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries, stock-based compensation and benefits, facilities costs, depreciation, third-party license fees, and external costs of outside vendors engaged to conduct preclinical development activities and clinical trials. Research and development expenses include the Company’s costs of performing services in connection with its collaboration agreements and research grant. Nonrefundable prepayments for goods or services that will be used or rendered for future research and development activities are deferred and capitalized. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered or the services rendered.
Research Contract Costs and Accruals	Research Contract Costs and Accruals The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the United States. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.
Patent Costs	Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.
Preferred Stock Warrant Liability	Preferred Stock Warrant Liability Through February 2016, the Company classified a warrant to purchase shares of its Series A preferred stock as a liability on its balance sheets as this warrant was a free-standing financial instrument could have required the Company to transfer assets upon exercise. The warrant was initially recorded at fair value on date of grant and subsequently remeasured to fair value at each balance sheet date. Changes in fair value of the warrant were recognized as a component of other income (expense), net in the statement of operations. Following the reverse stock split of the common stock of the Company and the completion of the Company’s IPO in February 2016, the warrant became a warrant to purchase 14,800 shares of common stock. At that time, the warrant was reclassified to a component of stockholder’s equity and is no longer subject to remeasurement. The Company used the Black-Scholes option-pricing model, which incorporates assumptions and estimates, to value the preferred stock warrant. The Company has assessed these assumptions and estimates on a quarterly basis as additional information impacting the assumptions is obtained. Estimates and assumptions impacting the fair value measurement include the fair value per share of the underlying Series A preferred stock, the remaining contractual term of the warrant, risk-free interest rate, expected dividend yield and expected volatility of the price of the underlying preferred stock. The Company determined the fair value per share of the underlying preferred stock by taking into consideration the most recent sales of its convertible preferred stock, results obtained from third-party valuations and additional factors that are deemed relevant. Up until February 2016, the Company was a private company and therefore lacks company-specific historical and implied volatility information of its stock. Therefore, it estimates its expected stock volatility based on the historical volatility of publicly traded peer companies for a term equal to the remaining contractual term of the warrant. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve for time periods approximately equal to the remaining contractual term of the warrant. Expected dividend yield is determined considering that the underlying Series A preferred stock is entitled to dividends of 8.0% per year, whether or not declared.
Stock-Based Compensation	Stock-Based Compensation The Company measures all stock options and other stock-based awards granted to employees and directors based on the fair value on the date of the grant and recognizes compensation expense of those awards, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective award. Generally, the Company issues stock options and restricted stock awards to employees with only service- based vesting conditions and records the expense for these awards using the straight-line method. The Company measures stock-based awards granted to consultants and non-employees based on the fair value of the award on the date on which the related service is complete. Compensation expense is recognized over the period during which services are rendered by such consultants and non-employees until completed. At the end of each financial reporting period prior to completion of the service, the fair value of these awards is remeasured using the then-current fair value of the Company’s common stock and updated assumption inputs in the Black-Scholes option-pricing model. The Company does not recognize compensation expense for awards with performance-based vesting conditions granted to consultants and non-employees for which satisfaction of the performance conditions is not solely within the control of the holder until the performance conditions have been met. The Company classifies stock-based compensation expense in its statement of operations in the same manner in which the award recipient’s payroll costs are classified or in which the award recipients’ service payments are classified. Prior to January 1, 2017, the Company recognized compensation expense for only the portion of awards that are expected to vest. In developing a forfeiture rate estimate, the Company has considered its historical experience to estimate pre- vesting forfeitures for service-based awards. Effective January 1, 2017, the company adopted ASU No. 2016-09 on a modified retrospective basis. As a result, the Company has made an accounting policy election to account for forfeitures as they occur. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option- pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends on common stock and does not expect to pay any cash dividends in the foreseeable future.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the three months ended March 31, 2018 and 2017, comprehensive loss included less than $0.1 million of unrealized loss on short term investments.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the financial statements or in the Company’s tax returns. Deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.
Net Loss per Share	Net Loss per Share Basic net income (loss) per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of common shares outstanding for the period. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of common shares, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common shares, as determined using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. For any period in which the Company has reported net income, basic net income per common share attributable to common stockholders is adjusted for certain amounts to calculate diluted net loss per common share attributable to common stockholders, since dilutive common shares are assumed to have been issued if their effect is dilutive and not to have been issued if their effect is anti-dilutive.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements Revenues In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, which amends the guidance for accounting for revenue from contracts with customers. This ASU supersedes the revenue recognition requirements in ASC Topic 605, Revenue Recognition Revenue from Contracts with Customers As a result of adopting ASC 606 on January 1, 2018, the Company has recorded a cumulative-effect decrease to opening accumulated deficit of $1.1 million as of January 1, 2018 and a corresponding decrease to deferred revenue. The total impact to revenue for the three months ended March 31, 2018 as a result of the adoption of ASC 606 was $0.8 million. Total revenue recorded in the three months ended March 31, 2018 under ASC 606 was $0.9 million, as compared to $1.7 million that would have been recorded under ASC 605. As of March 31, 2018, the Company recorded less than $0.1 million as a contract asset under ASC 606 which is included in other current assets, as compared to a deferred revenue balance of $0.3 million in current liabilities, which would have resulted under ASC 605. The most significant change relates to the Company’s determination of transaction price at inception and each reporting period as well as the revenue recognition pattern under step (v) above for the Collaborative Research, Development, Commercialization and License Agreement (the “Astellas Agreement”) with Astellas Pharma Inc. (“Astellas”) as well as treatment of variable consideration in the form of milestone payments. Under ASC 605, the research funding support payments, reimbursement of third-party costs, and milestone payments were being recognized by the Company as revenue on a straight-line basis over the three and a half year research term of the agreement, which commenced in January 2015, with a cumulative catch-up for the elapsed portion of the research term being recognized at the time any such payments are earned. Under ASC 606, the Company is recognizing the revenue allocated to the one performance obligation measuring progress using the proportional performance method. Leases: In February 2016, the FASB issued ASU No. 2016-02, Leases Due to the Company commencing a new lease in Boston, Massachusetts on January 19, 2018, the Company elected to early adopt the standard effective January 1, 2018, as permitted by the guidance in order to enhance overall transparency within financial reporting. The Company has implemented the standard using the required modified retrospective approach and have also elected to utilize the package of practical expedients. The expedients used by the Company are as follows: (1) allowing an entity to not reassess the lease classification for any expired or existing leases, (2) allowing an entity to not reassess the treatment of initial direct costs as they related to existing leases, and (3) allowing an entity to not reassess whether expired or existing contracts are or contain leases. The company also elected the practical expedient to use hindsight in determining the appropriate lease term and in assessing impairment of its right-of-use assets. In using the modified retrospective approach, the Company is required to recognize and measure leases existing at, or entered into after, the beginning of the earliest comparative period presented. During 2017, the Company was deemed the accounting owner of the construction project for the build-to-suit lease in Boston, Massachusetts because of the Company’s involvement in the build-out of the space. Under the new standard, the Company is no longer considered the accounting owner due to (1) not having the right to obtain or control the leased premises during the construction period, (2) having no right of payment for the partially constructed assets, and the leased premises are not of a specialized nature and, thus, could be potentially leased to another tenant, and (3) not legally owning or controlling the land on which the property improvements will be constructed. As such, upon transition, the existing construction-in-progress balance within property and equipment, and the corresponding build-to-suit facility lease financing obligation balance within other liabilities, current and non-current, have been derecognized. Prior period results have been restated to this effect through to the earliest period presented. The adoption of this standard has had a material impact on the Company’s financial position but did not significantly affect the Company’s results of operations. See below for Impacts on Previously Reported Results. Impacts to Previously Reported Results The impact of the adoption of the new leasing standard on the December 31, 2017 balance sheet is as follows: December 31, 2017 As Previously Reported New Lease Standard Adjustment As restated Operating lease right-of-use assets, net $ — $ 472 $ 472 Property and equipment, net 16,567 (16,143 ) 424 Deferred rent, current 87 (87 ) — Operating lease liabilities, current — 559 559 Other liabilities, current 902 (902 ) — Other liabilities, net of current 15,315 (15,315 ) — Accumulated deficit (216,882 ) 74 (216,808 ) Cash Flow: In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230) - Restricted Cash (“ASU 2016-18”). ASU 2016-18 requires a statement of cash flows to explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. Amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of- period total amounts shown on the statement of cash flows. This resulted in the $1.1 million and $2.0 million of restricted cash for the three months ended March 31, 2018 and March 31, 2017 being displayed within the overall change in the cash balance on the statement of cash flows. Stock Compensation In May 2017, the FASB issued ASU 2017-09, Compensation – Stock Compensation (Topic 719): Scope of Modification Accounting
Derivative Liability	Derivative Liability The derivative liability relates to a cash settlement option associated with the change of control provision in the Company’s Cystic Fibrosis Foundation Therapeutics, Inc. (“CFFT”) agreement, which meets the definition of a derivative. The fair value of the derivative liability is based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. The fair value of the derivative instrument was determined using the Monte-Carlo simulation analysis. In determining the fair value of the derivative liability, the inputs impacting fair value include the fair value of the Company’s common stock, expected term of the derivative instrument, expected volatility of the common stock price, risk-free interest rate, expected sales-based milestone payments, discount rate, probability of a change of control event, and the probability that the counterparty would elect to accept the alternative cash payment in lieu of its right to the future sales-based milestone payments. As of March 31, 2018 and December 31, 2017, the Company determined the per share common stock price available based on the closing price of its common stock on the NASDAQ Global Market as of March 29, 2018 and December 29, 2017, respectively. The Company determined the expected term of the instrument to be 1.75 years and 2.00 years as of March 31, 2018 and December 31, 2017, respectively. The Company estimated its expected stock volatility to be 80.0% and 80.0% as of March 31, 2018 and December 31, 2017, respectively, based on the historical volatility of publicly traded peer companies for terms matching the expected term of the instrument for each respective period. The risk-free interest rate was determined to be 2.20% and 1.87% as of March 31, 2018 and December 31, 2017, respectively, by reference to the U.S. Treasury yield curve for terms matching the expected term of the instrument for each respective period. Changes in the values of the derivative liability are summarized below (in thousands): Derivative Liability Fair value at December 31, 2017 $ 25 Change in fair value (12 ) Fair value at March 31, 2018 $ 13

Summary of Significant Accoun19

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Schedule of Impact of Adoption of New Leasing Standard	The impact of the adoption of the new leasing standard on the December 31, 2017 balance sheet is as follows: December 31, 2017 As Previously Reported New Lease Standard Adjustment As restated Operating lease right-of-use assets, net $ — $ 472 $ 472 Property and equipment, net 16,567 (16,143 ) 424 Deferred rent, current 87 (87 ) — Operating lease liabilities, current — 559 559 Other liabilities, current 902 (902 ) — Other liabilities, net of current 15,315 (15,315 ) — Accumulated deficit (216,882 ) 74 (216,808 )

Short-Term Investments (Tables)

Short-Term Investments (Tables)	3 Months Ended
	Mar. 31, 2018
Cash Cash Equivalents And Short Term Investments [Abstract]
Summary of Short-Term Investments	The following table summarizes the Company’s short-term investments as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S government-sponsored enterprise securities $ 9,479 $ — $ (9 ) $ 9,470 U.S. treasury securities 34,423 0 (19 ) 34,404 $ 43,902 $ 0 $ (28 ) $ 43,874 December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S government-sponsored enterprise securities $ 9,817 $ — $ (1 ) $ 9,816 U.S. treasury securities 34,923 1 (2 ) 34,922 $ 44,740 $ 1 $ (3 ) $ 44,738

Fair Value of Financial Asset21

Fair Value of Financial Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): Fair Value Measurements as of March 31, 2018 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 18,137 $ — $ — $ 18,137 Short-term investments: U.S. government-sponsored enterprise securities — 9,470 — 9,470 U.S. treasury securities — 34,404 — 34,404 $ 18,137 $ 43,874 $ — $ 62,011 Liabilities: Derivative liability $ — $ — $ 13 $ 13 $ — $ — $ 13 $ 13 Fair Value Measurements as of December 31, 2017 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 13,871 $ — $ — $ 13,871 U.S. government-sponsored enterprise securities — 8,960 — 8,960 U.S. treasury securities — 3,497 — 3,497 Short-term investments: U.S. government-sponsored enterprise securities — 9,816 — 9,816 U.S. treasury securities — 34,922 — 34,922 $ 13,871 $ 57,195 $ — $ 71,066 Liabilities: Derivative liability $ — $ — $ 25 $ 25 $ — $ — $ 25 $ 25
Summary of Changes in Values of Derivative Liability	Changes in the values of the derivative liability are summarized below (in thousands): Derivative Liability Fair value at December 31, 2017 $ 25 Change in fair value (12 ) Fair value at March 31, 2018 $ 13

Prepaids and Other Current As22

Prepaids and Other Current Assets (Tables)	3 Months Ended
	Mar. 31, 2018
Prepaid Expense And Other Assets Current [Abstract]
Schedule of Prepaids and Other Current Assets	Prepaids and other current assets consisted of the following (in thousands): March 31, December 31, 2018 2017 Prepaid clinical, manufacturing and scientific expenses $ 753 $ 568 Prepaid insurance expenses 569 55 Other prepaid expenses and other current assets 660 754 $ 1,982 $ 1,377

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2018
Text Block [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following (in thousands): March 31, December 31, 2018 2017 Accrued payroll and related expenses $ 973 $ 1,542 Accrued research and development expenses 3,282 3,930 Accrued professional fees 928 556 Accrued other 39 92 $ 5,222 $ 6,120

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock-Based Compensation Expense, Including Shares Issued to Non-Employee for Consulting Services	Stock-based compensation expense, including shares issued to a non-employee for consulting services, was classified in the statements of operations as follows (in thousands): Three Months Ended March 31, 2018 2017 Research and development $ 363 $ 255 General and administrative 859 489 $ 1,222 $ 744

Net Loss per Share (Tables)

Net Loss per Share (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Schedule of 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 (in thousands, except share and per share amounts): Three Months Ended March 31, 2018 2017 Numerator: Net loss $ (11,026 ) $ (15,096 ) Denominator: Weighted average number of common shares outstanding—basic 34,474,004 25,020,337 Net loss per share attributable to common stockholders—basic and diluted $ (0.32 ) $ (0.60 )
Schedule of Antidilutive Securities Excluded from Computation of Diluted Weighted-average Shares Outstanding	The following potentially dilutive securities outstanding, prior to the use of the treasury stock method or if-converted method, have been excluded from the computation of diluted weighted-average shares outstanding, because such securities had an antidilutive impact due to the losses reported : March 31, 2018 2017 Options to purchase common stock 3,548,271 2,086,453 Restricted stock units 197,265 — Potentially dilutive securities outstanding 3,745,536 2,086,453

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2018
Lessee Disclosure [Abstract]
Elements of Lease Expense	The elements of lease expense were as follows: Three Months Ended March 31, 2018 2017 Lease cost Operating lease cost $ 660 $ 286 Total lease cost $ 660 $ 286 Other information Operating cash flows used for operating leases $ 338 $ 333 Operating lease liabilities arising from obtaining right-of-use assets $ 15,304 $ — Weighted average remaining lease term 10 years 1 years Weighted average discount rate 4.50 % 4.06 %
Schedule of Future Lease Payments under Non-Cancelable Leases	Future lease payments under no n-cancelable leases as of March 31, 2018: Future Operating Lease Payments 2018 $ 1,824 2019 1,686 2020 1,733 2021 1,780 2022 1,829 Thereafter 10,636 Total lease payments 19,488 Less: imputed interest 3,920 Total operating lease liabilities $ 15,568

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ (226,729)		$ (216,808)
Cash, cash equivalents and short-term investments	63,300
Net loss	(11,026)	$ (15,096)
Cash in operations	$ 12,034	$ 15,345

Summary of Significant Accoun28

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)FinancialInstitution	Mar. 31, 2017USD ($)	Jan. 01, 2018USD ($)	Dec. 31, 2017USD ($)	Feb. 28, 2016shares
Significant Accounting Policies [Line Items]
Number of accredited financial institutions | FinancialInstitution	2
Deferred offering costs	$ 160
Restricted cash	294			$ 294
Restricted cash, net of current portion	828			1,656
Decrease in restricted cash	800
Unrealized gains (loss) on short-term investments included in comprehensive loss	(26)	$ (16)
Accumulated deficit	(226,729)			(216,808)
Revenue	900
ASU 2016-18 [Member]
Significant Accounting Policies [Line Items]
Change in restricted cash	1,100	2,000
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | ASC 606 [Member]
Significant Accounting Policies [Line Items]
Accumulated deficit			$ 1,100
Revenue	(800)
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | ASC 606 [Member]
Significant Accounting Policies [Line Items]
Revenue	1,700
Deferred revenue	300
Maximum [Member] | ASC 606 [Member]
Significant Accounting Policies [Line Items]
Contract asset	100
Maximum [Member] | Short-term Investments [Member]
Significant Accounting Policies [Line Items]
Unrealized gains (loss) on short-term investments included in comprehensive loss	$ (100)	$ (100)
Warrants to Purchase Convertible Preferred Stock [Member]
Significant Accounting Policies [Line Items]
Number of warrants to purchase | shares					14,800
Series A Preferred Stock [Member]
Significant Accounting Policies [Line Items]
Dividends percentage	8.00%
Certificate of Deposit [Member]
Significant Accounting Policies [Line Items]
Restricted cash	$ 300			$ 300
Money Market Funds [Member]
Significant Accounting Policies [Line Items]
Restricted cash, net of current portion	800
At-the-market Common Stock Offering Program Sales Agreement [Member] | Leerink Partners LLC [Member]
Significant Accounting Policies [Line Items]
Deferred offering costs	$ 200

Summary of Significant Accoun29

Summary of Significant Accounting Policies - Schedule of Impact of Adoption of New Leasing Standard (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Operating lease right-of-use assets, net	$ 15,261	$ 472
Property and equipment, net	376	424
Operating lease liabilities, current	1,671	559
Accumulated deficit	$ (226,729)	(216,808)
As Previously Reported [Member] | ASU 2016-02 [Member]
Significant Accounting Policies [Line Items]
Property and equipment, net		16,567
Deferred rent, current		87
Other liabilities, current		902
Other liabilities, net of current		15,315
Accumulated deficit		(216,882)
New Lease Standard Adjustment [Member] | ASU 2016-02 [Member]
Significant Accounting Policies [Line Items]
Operating lease right-of-use assets, net		472
Property and equipment, net		(16,143)
Deferred rent, current		(87)
Operating lease liabilities, current		559
Other liabilities, current		(902)
Other liabilities, net of current		(15,315)
Accumulated deficit		$ 74

Short-Term Investments - Summar

Short-Term Investments - Summary of Short-Term Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 43,902	$ 44,740
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(28)	(3)
Fair Value	43,874	44,738
U.S Government-Sponsored Enterprise Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,479	9,817
Gross Unrealized Losses	(9)	(1)
Fair Value	9,470	9,816
U.S. Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	34,423	34,923
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(19)	(2)
Fair Value	$ 34,404	$ 34,922

Short-Term Investments - Additi

Short-Term Investments - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Investments Debt And Equity Securities [Abstract]
Realized gains (losses) on short-term investments	$ 0	$ 0
Other-than-temporary impairments recognized	$ 0	$ 0

Fair Value of Financial Asset32

Fair Value of Financial Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Liabilities:
Derivative liability	$ 13	$ 25
Fair Value, Measurements, Recurring [Member]
Assets:
Total assets	62,011	71,066
Liabilities:
Derivative liability	13	25
Total liabilities	13	25
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	18,137	13,871
Fair Value, Measurements, Recurring [Member] | U.S Government-Sponsored Enterprise Securities [Member]
Assets:
Cash equivalents		8,960
Short-term investments	9,470	9,816
Fair Value, Measurements, Recurring [Member] | U.S. Treasury Securities [Member]
Assets:
Cash equivalents		3,497
Short-term investments	34,404	34,922
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets:
Total assets	18,137	13,871
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Money Market Funds [Member]
Assets:
Cash equivalents	18,137	13,871
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets:
Total assets	43,874	57,195
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S Government-Sponsored Enterprise Securities [Member]
Assets:
Cash equivalents		8,960
Short-term investments	9,470	9,816
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Treasury Securities [Member]
Assets:
Cash equivalents		3,497
Short-term investments	34,404	34,922
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Liabilities:
Derivative liability	13	25
Total liabilities	$ 13	$ 25

Fair Value of Financial Asset33

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Transfer of assets from level 1 to level 2	$ 0	$ 0
Transfer of assets from level 2 to level 1	0	0
Transfer of liabilities from level 1 to level 2	0	0
Transfer of liabilities from level 2 to level 1	$ 0	$ 0
Fair value determination model	Monte-Carlo simulation analysis
Expected term	1 year 9 months	2 years
Expected volatility	80.00%	80.00%
Risk-free interest rate	2.20%	1.87%

Fair Value of Financial Asset34

Fair Value of Financial Assets and Liabilities - Summary of Changes in Values of Derivative Liability (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Derivative Liability, Fair value, Beginning Balance	$ 25
Derivative Liability, Change in fair value	(12)
Derivative Liability, Fair value, Ending Balance	$ 13

Prepaids and Other Current As35

Prepaids and Other Current Assets - Schedule of Prepaids and Other Current Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Prepaid Expense And Other Assets Current [Abstract]
Prepaid clinical, manufacturing and scientific expenses	$ 753	$ 568
Prepaid insurance expenses	569	55
Other prepaid expenses and other current assets	660	754
Prepaids and other current assets	$ 1,982	$ 1,377

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued payroll and related expenses	$ 973	$ 1,542
Accrued research and development expenses	3,282	3,930
Accrued professional fees	928	556
Accrued other	39	92
Total accrued expenses	$ 5,222	$ 6,120

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	Feb. 01, 2018	Feb. 03, 2016	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation			$ 1,222,000	$ 744,000
Bonus Restricted Stock Units (RSU’s) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation			$ 100,000
RSUs granted			197,625
Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options unvested			83,250
Fair value of option			$ 300,000
Non-Employees [Member] | Prior to 2013 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option issued to purchase common stock			203,964
Maximum [Member] | Bonus Restricted Stock Units (RSU’s) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards requisite service period date	Feb. 1, 2019
Minimum [Member] | Bonus Restricted Stock Units (RSU’s) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards requisite service period date	Feb. 1, 2018
2016 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance		1,581,839	701,140
Common stock reserved for issuance, percentage of number of shares of common stock outstanding		3.00%
2016 Plan and 2008 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance			4,446,676
2016 ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance		138,757	399,328
Common stock reserved for issuance, percentage of number of shares of common stock outstanding		1.00%
Common stock available for issuance			138,757
Number of shares issued			6,114
2016 ESPP [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation			$ 100,000

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-Based Compensation Expense, Including Shares Issued to Non-Employee for Consulting Services (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 1,222	$ 744
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	363	255
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Stock-based compensation expense	$ 859	$ 489

Collaboration Agreement - Addit

Collaboration Agreement - Additional Information (Detail) - USD ($) $ in Thousands	Apr. 23, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue		$ 942	$ 1,021
Maximum [Member] | ASC 606 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue recorded as contract asset		$ 100
Astellas Collaboration Agreement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Convertible promissory notes					$ 5,000
Initial research term		3 years 6 months
Maximum period to submit actual expenses report after quarter end		30 days
Maximum period to receive payments for expenses after submit of report		30 days
Description of material promises under agreement		(1) the research license; (2) the research services to be provided over the research term; and (3) participation in the Joint Research Committee (the “Committee”) to be provided over the initial three and a half year research term of the agreement.
Performance obligation, expected performance period		Dec. 4, 2018
Revenue		$ 900	$ 1,000
Deferred revenue				$ 1,100
Astellas Collaboration Agreement [Member] | ASC 606 [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction price		12,800
Yet to be completed transaction value		900
Astellas Collaboration Agreement [Member] | Subsequent Event [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Extended research term	Dec. 4, 2018
Astellas Collaboration Agreement [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development and sales milestone payments		398,500
Deferred revenue recorded as contract asset		$ 100

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Federal income tax benefit	$ 0	$ 0
State income tax benefit	$ 0	$ 0

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net loss	$ (11,026)	$ (15,096)
Denominator:
Weighted average number of common shares outstanding—basic	34,474,004	25,020,337
Net loss per share attributable to common stockholders—basic and diluted	$ (0.32)	$ (0.60)

Net Loss per Share - Schedule42

Net Loss per Share - Schedule of Antidilutive Securities Excluded from Computation of Diluted Weighted-average Shares Outstanding (Detail) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding	3,745,536	2,086,453
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding	3,548,271	2,086,453
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding	197,265

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($) $ in Thousands	Jan. 19, 2018	Mar. 31, 2018	Dec. 31, 2017
Leases [Abstract]
Operating lease expiration date		2018-05
Operating lease, initial term	10 years
Operating lease, option to extend additional term	7 years
Operating lease assets		$ 15,261	$ 472

Leases - Elements of Lease Expe

Leases - Elements of Lease Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Lease cost
Operating lease cost	$ 660	$ 286
Total lease cost	660	286
Other information
Operating cash flows used for operating leases	338	$ 333
Operating lease liabilities arising from obtaining right-of-use assets	$ 15,304
Weighted average remaining lease term	10 years	1 year
Weighted average discount rate	4.50%	4.06%

Leases - Schedule of Future Lea

Leases - Schedule of Future Lease Payments under Non-Cancelable Leases (Detail) $ in Thousands	Mar. 31, 2018USD ($)
Leases [Abstract]
2,018	$ 1,824
2,019	1,686
2,020	1,733
2,021	1,780
2,022	1,829
Thereafter	10,636
Total lease payments	19,488
Less: imputed interest	3,920
Total operating lease liabilities	$ 15,568