CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 52,552	$ 87,288
Marketable securities	22,841
Other receivables	1,219	1,011
Tax incentive receivable, current	1,902	1,932
Prepaid expenses and other current assets	1,224	1,828
Total current assets	79,738	92,059
Tax incentive receivable	45
Property and equipment, net	1,070	1,164
Deposits	206	206
Restricted cash		50
Total assets	81,059	93,479
Current liabilities:
Accounts payable	982	3,470
Accrued expenses and other current liabilities	4,484	4,321
Derivative liabilities	223	223
Deferred rent	145	143
Total current liabilities	5,834	8,157
Deferred rent, net of current portion	327	365
Total liabilities	6,161	8,522
Commitments and contingencies (Note 7)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized as of March 31, 2018 and December 31, 2017
Common stock, $0.001 par value; 60,000,000 shares authorized as of March 31, 2018 and December 31, 3017; 14,369,182 shares issued and outstanding as of March 31, 2018 and December 31, 2017	14	14
Additional paid-in capital	182,042	181,428
Accumulated deficit	(107,484)	(96,840)
Accumulated other comprehensive loss	(29)
Total Spero Therapeutics, Inc. stockholders' equity	74,543	84,602
Non-controlling interests	355	355
Total stockholders' equity	74,898	84,957
Total liabilities and stockholders' equity	$ 81,059	$ 93,479