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CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Income Statement [Abstract] |  |  |  |  |
Grant revenue | $ 1,153 | $ 140 | $ 1,979 | $ 335 |
Operating expenses: |  |  |  |  |
Research and development | 8,925 | 5,999 | 32,869 | 26,333 | $ 11,125
General and administrative | 3,044 | 1,740 | 10,840 | 7,223 | 2,202
Total operating expenses | 11,969 | 7,739 | 43,709 | 33,556 | 13,327
Loss from operations | (10,816) | (7,599) | (41,730) | (33,221) | (13,327)
Other income (expense): |  |  |  |  |
Change in fair value of derivative liabilities |  | 1,199 | 1,541 | 580 | 174
Interest income and other income (expense), net | 172 | (11) | 303 |  |
Total other income (expense), net | 172 | 1,188 | 1,844 | 580 | 174
Net loss | (10,644) | (6,411) | (39,886) | (32,641) | (13,153)
Less: Net loss attributable to non-controlling interest |  | (535) | (1,143) | (7,150) | (2,999)
Net loss attributable to Spero Therapeutics, Inc. | (10,644) | (5,876) | (38,743) | (25,491) | (10,154)
Cumulative dividends on redeemable convertible preferred shares |  | (1,236) | (6,146) | (3,441) | (932)
Accretion of redeemable bridge units and redeemable convertible preferred shares to redemption value |  | (18) | (1,208) | (996) | (2,341)
Net loss attributable to common shareholders of Spero Therapeutics, Inc. | $ (10,644) | $ (7,130) | $ (46,097) | $ (29,928) | $ (13,427)
Net loss per share attributable to common shareholders per share, basic and diluted | $ (0.74) | $ (21.60) | $ (17.82) | $ (95.87) | $ (53.11)
Weighted average common shares outstanding, basic and diluted: | 14,369,182 | 330,075 | 2,586,865 | 312,169 | 252,807
Comprehensive loss: |  |  |  |  |
Net loss | $ (10,644) | $ (6,411) | $ (39,886) | $ (32,641) | $ (13,153)
Other comprehensive loss: |  |  |  |  |
Unrealized gain (loss) on marketable securities | (29) |  |  |  |
Total other comprehensive loss | (29) |  |  |  |
Total comprehensive loss | $ (10,673) | $ (6,411) |  |  |

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