CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 29,730	$ 34,080
Marketable securities	52,315	81,363
Other receivables	7,760	376
Tax incentive receivable, current	786	922
Prepaid expenses and other current assets	4,823	7,478
Total current assets	95,414	124,219
Property and equipment, net	2,273	2,893
Tax incentive receivable	21	233
Operating lease right of use assets	4,875
Other assets	3,520	1,661
Total assets	106,103	129,006
Current liabilities:
Accounts payable	4,147	3,603
Accrued expenses and other current liabilities	21,588	8,263
Derivative liabilities		223
Deferred rent		229
Operating lease liabilities	928
Total current liabilities	26,663	12,318
Deferred rent, net of current portion		833
Non-current operating lease liabilities	4,617
Other long-term liabilities	249
Total liabilities	31,529	13,151
Commitments and contingencies (Note 12)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized, 2,720 shares issued and outstanding as of December 31, 2019 and 3,220 shares issued and outstanding as of December 31, 2018
Common stock, $0.001 par value; 60,000,000 shares authorized as of December 31, 2019 and December 31, 2018;19,190,695 shares issued and outstanding as of December 31, 2019 and 17,205,962 shares issued and outstanding as of December 31, 2018	19	17
Additional paid-in capital	273,966	254,013
Accumulated deficit	(199,427)	(138,502)
Accumulated other comprehensive gain (loss)	16	(28)
Total Spero Therapeutics, Inc. stockholders' equity	74,574	115,500
Non-controlling interests		355
Total stockholders' equity	74,574	115,855
Total liabilities and stockholders' equity	$ 106,103	$ 129,006