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Each RSU represents the right, upon achievement of certain pre-established performance criteria, to receive one share of the Issuer's common stock, subject to vesting conditions.  On June 12, 2023, the Board of Directors of the Issuer determined that 100% of the performance-based conditions were met resulting in 140,000 RSUs earned by the Reporting Person. The RSUs vest in two equal annual installments on September 12, 2023 and September 12, 2024, subject to the Reporting Person's continued service through the applicable vesting date."},{"field":"balance_after","element":"sharesOwnedFollowingTransaction","label":"F2","text":"Consists of RSUs held by the Reporting Person."}],"balance_after":615957,"source":{"system":"sec-edgar","filing":"0000950170-23-027860","document":"ownership.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1701108/000095017023027860/ownership.xml","form_type":"4"}},{"id":2030629,"issuer":{"id":7014,"kind":"organization","name":"Spero Therapeutics, Inc."},"owners":[{"id":75825,"kind":"person","name":"Mahadevia Ankit","position":1,"cik":"0001720974","reported_name":"Mahadevia Ankit","relationship":{"director":true,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"CEO and President"}}],"security":"Common Stock","published_at":"2023-02-06T21:15:11.000Z","date":"2023-02-03","kind":"sale","acquired":false,"shares":12286,"price":1.81,"value":22237.66,"ownership":{"direct":true},"footnotes":[{"field":"kind","element":"transactionCoding","label":"F1","text":"The reported transaction is a sale of common stock effected to cover tax withholding obligations in connection with the vesting of restricted stock units (\"RSUs\") that were granted to the Reporting Person on February 1, 2022 pursuant to a \"sell to cover\" provision included in the RSU Agreement."},{"field":"balance_after","element":"sharesOwnedFollowingTransaction","label":"F2","text":"Amount includes 65,817 shares of common stock held by the Mahadevia-Mehta Family Trust, of which the Reporting Person is a trustee. Amount also includes 691,205 RSUs held by the Reporting Person."}],"balance_after":797832,"source":{"system":"sec-edgar","filing":"0000899243-23-004039","document":"doc4.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1701108/000089924323004039/doc4.xml","form_type":"4"}},{"id":2033067,"issuer":{"id":7014,"kind":"organization","name":"Spero Therapeutics, Inc."},"owners":[{"id":67253,"kind":"person","name":"Keutzer Timothy","position":1,"cik":"0001798155","reported_name":"Keutzer Timothy","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Chief Operating Officer"}}],"security":"Common Stock","published_at":"2023-02-04T00:43:51.000Z","date":"2023-02-02","kind":"sale","acquired":false,"shares":3394,"price":1.86,"value":6312.84,"ownership":{"direct":true},"footnotes":[{"field":"kind","element":"transactionCoding","label":"F3","text":"The reported transaction is a sale of common stock effected to cover tax withholding obligations in connection with the vesting of RSUs that were granted to the Reporting Person on February 1, 2022 pursuant to a \"sell to cover\" provision included in the RSU Agreement."},{"field":"balance_after","element":"sharesOwnedFollowingTransaction","label":"F2","text":"Includes 312,518 RSUs held by the Reporting Person."}],"balance_after":327144,"source":{"system":"sec-edgar","filing":"0000899243-23-003948","document":"doc4.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/1701108/000089924323003948/doc4.xml","form_type":"4"}},{"id":2033066,"issuer":{"id":7014,"kind":"organization","name":"Spero Therapeutics, Inc."},"owners":[{"id":67253,"kind":"person","name":"Keutzer Timothy","position":1,"cik":"0001798155","reported_name":"Keutzer Timothy","relationship":{"director":false,"officer":true,"ten_percent_owner":false,"other":false,"officer_title":"Chief Operating Officer"}}],"security":"Common Stock","published_at":"2023-02-04T00:43:51.000Z","date":"2023-02-01","kind":"grant","acquired":true,"shares":265957,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"shares","element":"transactionShares","label":"F1","text":"Consists of restricted stock units (\"RSUs\"). Each RSU represents the right to receive one share of common stock upon vesting. The RSUs vest in four equal annual installments beginning on February 1, 2024, subject to the Reporting Person's continued service through the applicable vesting date."},{"field":"balance_after","element":"sharesOwnedFollowingTransaction","label":"F2","text":"Includes 312,518 RSUs held by the Reporting Person."}],"balance_after":330538,"source":{"system":"sec-edgar","filing":"0000899243-23-003948","document":"doc4.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1701108/000089924323003948/doc4.xml","form_type":"4"}}],"next_cursor":"2023-02-04T00:43:51.000000Z,2033066"}