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CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Cash flows from operating activities: |  |  |  |  |
Net loss | $ (10,644) | $ (6,411) | $ (39,886) | $ (32,641) | $ (13,153)
Adjustments to reconcile net loss to net cash used in operating activities: |  |  |  |  |
Non-cash research and development expense |  |  |  | 4,595 | 3,517
Depreciation and amortization | 95 | 87 | 363 | 279 | 11
Change in fair value of derivative liabilities |  | (1,199) | (1,541) | (580) | (174)
Share-based compensation | 614 | 62 | 1,427 | 180 | 21
Unrealized foreign currency transaction (gain) loss | 8 |  | 83 |  |
Accretion of discount on marketable securities | (45) |  |  |  |
Changes in operating assets and liabilities: |  |  |  |  |
Other receivables | (208) | 190 | (707) | (294) | (10)
Prepaid expenses and other current assets | 604 | 131 | (575) | (966) | (280)
Tax incentive receivables | (45) | (159) | (1,811) | (144) |
Deposits |  |  |  | (53) | (150)
Accounts payable | (2,469) | (82) | 2,349 | (644) | 671
Accrued expenses and other current liabilities | 165 | 434 | 1,315 | 2,322 | 409
Deferred rent | (36) | (497) | (128) | (84) |
Advance payments from collaborator |  | 465 |  | (929) | (470)
Net cash used in operating activities | (11,961) | (6,979) | (39,111) | (28,959) | (9,608)
Cash flows from investing activities: |  |  |  |  |
Purchases of property and equipment |  |  | (27) | (830) | (232)
Purchases of marketable securities | (22,825) |  |  |  |
Net cash used in investing activities | (22,825) |  | (27) | (830) | (232)
Cash flows from financing activities: |  |  |  |  |
Proceeds from initial public offering of common stock, net of commissions and underwriting discounts |  |  | 77,749 |  |
Payment of initial public offering costs |  |  | (3,574) |  |
Changes in restricted cash |  |  |  |  | (30)
Cash payment for non-controlling interests |  |  | (1,175) |  |
Net cash provided by financing activities |  | 43,001 | 116,111 | 34,413 | 15,275
Net increase in cash and cash equivalents | (34,786) | 36,022 | 76,973 | 4,624 | 5,435
Cash and cash equivalents at beginning of period | 87,288 | 10,315 | 10,315 | 5,691 | 256
Cash, cash equivalents and restricted cash at beginning of period | 87,338 | 10,365 | 10,365 |  |
Cash and cash equivalents at end of period | 52,552 |  | 87,288 | 10,315 | 5,691
Cash, cash equivalents and restricted cash at end of period | $ 52,552 | 46,387 | 87,338 | 10,365 |
Supplemental disclosure of non-cash investing and financing activities: |  |  |  |  |
Conversion of bridge units into preferred units |  | 8,500 | 8,500 |  | 8,000
Conversion of preferred stock to common stock |  |  | 107,018 |  |
Settlement of derivative liabilities upon issuance of preferred units |  | 944 | 944 |  | 888
Issuance of tranche rights with preferred units |  |  |  | 909 | 2,401
Deemed contribution of capital |  |  |  | 2,408 | 1,419
Settlement of derivative liability upon issuance of bridge units |  |  |  | 305 |
Issuance of contingent prepayment option with bridge units |  |  |  | 908 |
Cumulative dividends on redeemable convertible preferred shares |  | 1,236 | 6,146 | 3,441 | 932
Accretion of redeemable convertible preferred units and stock to redemption value |  |  | 632 | 969 | 34
Accretion of redeemable convertible preferred units to redemption value |  | 18 |  |  |
Accretion of bridge units to redemption value |  | 576 | 576 | 27 | 2,307
Issuance of additional shares of common stock to minority investors under anti-dilution rights |  |  |  | 980 | 1,459
Purchases of property and equipment included in accounts payable, accrued expenses and deferred rent |  |  |  |  | 728
Deferred offering costs included in accounts payable and accrued expenses |  |  |  |  | 11
Series A Preferred Stock [Member] |  |  |  |  |
Cash flows from financing activities: |  |  |  |  |
Proceeds from issuance of preferred units, net of issuance costs |  |  |  |  | 7,330
Bridge Units [Member] |  |  |  |  |
Cash flows from financing activities: |  |  |  |  |
Proceeds from issuance of bridge units |  |  |  | 8,500 | 8,000
Series B Preferred Stock [Member] |  |  |  |  |
Cash flows from financing activities: |  |  |  |  |
Payment of initial public offering costs |  |  |  |  | $ (25)
Proceeds from issuance of preferred units, net of issuance costs |  |  |  | $ 25,913 |
Series C Preferred Stock [Member] |  |  |  |  |
Cash flows from financing activities: |  |  |  |  |
Payment of initial public offering costs |  |  | (176) |  |
Proceeds from issuance of preferred units, net of issuance costs |  | $ 43,001 | $ 43,111 |  |

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- Definition The cash outflow for cost incurred directly with the issuance of an equity security. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585 + Details
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- Definition Cash outflow for purchase of trading, available-for-sale securities and held-to-maturity securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26853-111562 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585 + Details
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- Definition The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585 + Details
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- Definition Amount of cash outflow to a noncontrolling interest. Includes, but not limited to, reduction of noncontrolling interest ownership. Excludes dividends paid to the noncontrolling interest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585 + Details
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- Definition The cash inflow associated with the amount received from entity's first offering of stock to the public. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585 + Details
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- Definition The cash inflow from issuance of callable preferred stock which is identified as being convertible to another type of financial security at the option of the issuer or the holder. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585 + Details
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- Definition The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 55 -Paragraph 4K -URI http://asc.fasb.org/extlink&oid=84234705&loc=SL4591552-111686 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=96868048&loc=SL4569616-111683 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84161450&loc=SL4573702-111684 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 55 -Paragraph 4J -URI http://asc.fasb.org/extlink&oid=84234705&loc=SL4591551-111686 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=84161450&loc=SL4573702-111684 + Details
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- Definition Dividends paid to preferred stock holders that is redeemable solely at the option of the issuer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=96947427&loc=d3e1377-109256 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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- Definition The aggregate amount of noncash, equity-based employee remuneration. This may include the value of stock or unit options, amortization of restricted stock or units, and adjustment for officers' compensation. As noncash, this element is an add back when calculating net cash generated by operating activities using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
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