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These shares were purchased at prices ranging from $2.245 to $2.32, inclusive. The reporting person has provided to the Issuer, and undertakes to provide any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the range set forth in this footnote."}],"balance_after":147205,"source":{"system":"sec-edgar","filing":"0001193125-26-018317","document":"ownership.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000119312526018317/ownership.xml","form_type":"4"}},{"id":1118000,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Stock Option (Right to Buy)","published_at":"2025-06-10T00:28:01.000Z","date":"2025-06-09","kind":"grant","planned":false,"acquired":true,"shares":22000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_date","element":"exerciseDate","label":"F1","text":"This option shall vest in full upon the earlier of (i) June 9, 2026 or (ii) the date of the next annual meeting of the Corporation's stockholders."}],"balance_after":22000,"derivative":{"exercise_price":2.37,"expiration_date":"2035-06-08","underlying":"Common Stock","underlying_shares":22000},"source":{"system":"sec-edgar","filing":"0000950170-25-084022","document":"ownership.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000095017025084022/ownership.xml","form_type":"4"}},{"id":1142848,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Stock Option (Right to Buy)","published_at":"2025-05-20T01:36:46.000Z","date":"2025-05-19","kind":"grant","planned":false,"acquired":true,"shares":22000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_price","element":"conversionOrExercisePrice","label":"F3","text":"The exercise price of the option is $1.92 per share, representing the fair market value per share of the Issuer's Common Stock on the Repricing Date.  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Such transactions were exempt pursuant to Rule 16b-6(d) and Rule 16b-3 of the Exchange Act, as applicable."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F2","text":"This stock option award was issued pursuant to the Cabaletta Bio, Inc. 2018 Stock Option and Incentive Plan, as amended (the \"2018 Plan\") or the Cabaletta Bio, Inc. 2019 Stock Option and Incentive Plan, as amended (the \"2019 Plan\"), as applicable, and becomes exercisable in accordance with the vesting schedule specified in the award agreement and as previously reported on applicable Form 4, subject to the Reporting Person's continued service with the Issuer as of the applicable vesting date."}],"balance_after":22000,"derivative":{"exercise_price":1.92,"expiration_date":"2034-06-02","underlying":"Common Stock","underlying_shares":22000},"source":{"system":"sec-edgar","filing":"0000950170-25-074817","document":"ownership.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":8,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000095017025074817/ownership.xml","form_type":"4"}},{"id":1142847,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Stock Option (Right to Buy)","published_at":"2025-05-20T01:36:46.000Z","date":"2025-05-19","kind":"disposition_to_issuer","planned":false,"acquired":false,"shares":22000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"kind","element":"transactionCoding","label":"F1","text":"On May 15, 2025, the Issuer's board of directors approved an option repricing (the \"Repricing\"), to be effective May 19, 2025 (the \"Repricing Date\"). All of the other terms of the options remain unchanged. Such transactions were exempt pursuant to Rule 16b-6(d) and Rule 16b-3 of the Exchange Act, as applicable."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F2","text":"This stock option award was issued pursuant to the Cabaletta Bio, Inc. 2018 Stock Option and Incentive Plan, as amended (the \"2018 Plan\") or the Cabaletta Bio, Inc. 2019 Stock Option and Incentive Plan, as amended (the \"2019 Plan\"), as applicable, and becomes exercisable in accordance with the vesting schedule specified in the award agreement and as previously reported on applicable Form 4, subject to the Reporting Person's continued service with the Issuer as of the applicable vesting date."}],"balance_after":0,"derivative":{"exercise_price":10.01,"expiration_date":"2034-06-02","underlying":"Common Stock","underlying_shares":22000},"source":{"system":"sec-edgar","filing":"0000950170-25-074817","document":"ownership.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":7,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000095017025074817/ownership.xml","form_type":"4"}},{"id":1142846,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Stock Option (Right to Buy)","published_at":"2025-05-20T01:36:46.000Z","date":"2025-05-19","kind":"grant","planned":false,"acquired":true,"shares":22000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_price","element":"conversionOrExercisePrice","label":"F3","text":"The exercise price of the option is $1.92 per share, representing the fair market value per share of the Issuer's Common Stock on the Repricing Date.  Under the terms of the stock option award repricing, a repriced stock option award will revert to its original exercise price if exercised during the Retention Period. The \"Retention Period\", through which the Reporting Person must remain in service to the Issuer, commenced on the Repricing Date and ends upon the earliest of (i) the one-year anniversary of the Repricing Date, (ii) a Sale Event (as defined in the 2018 Plan and 2019 Plan, as applicable) and (iii) the termination of the Reporting Person's Service Relationship (as defined in the 2018 Plan and 2019 Plan, as applicable) due to the Reporting Person's death or disability."},{"field":"kind","element":"transactionCoding","label":"F1","text":"On May 15, 2025, the Issuer's board of directors approved an option repricing (the \"Repricing\"), to be effective May 19, 2025 (the \"Repricing Date\"). All of the other terms of the options remain unchanged. 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All of the other terms of the options remain unchanged. Such transactions were exempt pursuant to Rule 16b-6(d) and Rule 16b-3 of the Exchange Act, as applicable."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F2","text":"This stock option award was issued pursuant to the Cabaletta Bio, Inc. 2018 Stock Option and Incentive Plan, as amended (the \"2018 Plan\") or the Cabaletta Bio, Inc. 2019 Stock Option and Incentive Plan, as amended (the \"2019 Plan\"), as applicable, and becomes exercisable in accordance with the vesting schedule specified in the award agreement and as previously reported on applicable Form 4, subject to the Reporting Person's continued service with the Issuer as of the applicable vesting date."}],"balance_after":0,"derivative":{"exercise_price":11.18,"expiration_date":"2033-05-31","underlying":"Common Stock","underlying_shares":22000},"source":{"system":"sec-edgar","filing":"0000950170-25-074817","document":"ownership.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":5,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000095017025074817/ownership.xml","form_type":"4"}},{"id":1142844,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Stock Option (Right to Buy)","published_at":"2025-05-20T01:36:46.000Z","date":"2025-05-19","kind":"grant","planned":false,"acquired":true,"shares":22000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_price","element":"conversionOrExercisePrice","label":"F3","text":"The exercise price of the option is $1.92 per share, representing the fair market value per share of the Issuer's Common Stock on the Repricing Date.  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All of the other terms of the options remain unchanged. 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Under the terms of the stock option award repricing, a repriced stock option award will revert to its original exercise price if exercised during the Retention Period. The \"Retention Period\", through which the Reporting Person must remain in service to the Issuer, commenced on the Repricing Date and ends upon the earliest of (i) the one-year anniversary of the Repricing Date, (ii) a Sale Event (as defined in the 2018 Plan and 2019 Plan, as applicable) and (iii) the termination of the Reporting Person's Service Relationship (as defined in the 2018 Plan and 2019 Plan, as applicable) due to the Reporting Person's death or disability."},{"field":"kind","element":"transactionCoding","label":"F1","text":"On May 15, 2025, the Issuer's board of directors approved an option repricing (the \"Repricing\"), to be effective May 19, 2025 (the \"Repricing Date\"). All of the other terms of the options remain unchanged. Such transactions were exempt pursuant to Rule 16b-6(d) and Rule 16b-3 of the Exchange Act, as applicable."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F2","text":"This stock option award was issued pursuant to the Cabaletta Bio, Inc. 2018 Stock Option and Incentive Plan, as amended (the \"2018 Plan\") or the Cabaletta Bio, Inc. 2019 Stock Option and Incentive Plan, as amended (the \"2019 Plan\"), as applicable, and becomes exercisable in accordance with the vesting schedule specified in the award agreement and as previously reported on applicable Form 4, subject to the Reporting Person's continued service with the Issuer as of the applicable vesting date."}],"balance_after":18460,"derivative":{"exercise_price":1.92,"expiration_date":"2029-02-18","underlying":"Common Stock","underlying_shares":18460},"source":{"system":"sec-edgar","filing":"0000950170-25-074817","document":"ownership.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000095017025074817/ownership.xml","form_type":"4"}},{"id":1142841,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Stock Option (Right to Buy)","published_at":"2025-05-20T01:36:46.000Z","date":"2025-05-19","kind":"disposition_to_issuer","planned":false,"acquired":false,"shares":18460,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"kind","element":"transactionCoding","label":"F1","text":"On May 15, 2025, the Issuer's board of directors approved an option repricing (the \"Repricing\"), to be effective May 19, 2025 (the \"Repricing Date\"). All of the other terms of the options remain unchanged. Such transactions were exempt pursuant to Rule 16b-6(d) and Rule 16b-3 of the Exchange Act, as applicable."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F2","text":"This stock option award was issued pursuant to the Cabaletta Bio, Inc. 2018 Stock Option and Incentive Plan, as amended (the \"2018 Plan\") or the Cabaletta Bio, Inc. 2019 Stock Option and Incentive Plan, as amended (the \"2019 Plan\"), as applicable, and becomes exercisable in accordance with the vesting schedule specified in the award agreement and as previously reported on applicable Form 4, subject to the Reporting Person's continued service with the Issuer as of the applicable vesting date."}],"balance_after":0,"derivative":{"exercise_price":6.3,"expiration_date":"2029-02-18","underlying":"Common Stock","underlying_shares":18460},"source":{"system":"sec-edgar","filing":"0000950170-25-074817","document":"ownership.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000095017025074817/ownership.xml","form_type":"4"}},{"id":1492467,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Stock Option (Right to Buy)","published_at":"2024-06-04T23:21:39.000Z","date":"2024-06-03","kind":"grant","planned":false,"acquired":true,"shares":22000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_date","element":"exerciseDate","label":"F1","text":"This option shall vest in full upon the earlier of (i) June 3, 2025 or (ii) the date of the next annual meeting of the Corporation's stockholders."}],"balance_after":22000,"derivative":{"exercise_price":10.01,"expiration_date":"2034-06-02","underlying":"Common Stock","underlying_shares":22000},"source":{"system":"sec-edgar","filing":"0000950170-24-068993","document":"ownership.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000095017024068993/ownership.xml","form_type":"4"}},{"id":1870081,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Stock Option (Right to Buy)","published_at":"2023-06-02T11:30:13.000Z","date":"2023-06-01","kind":"grant","planned":false,"acquired":true,"shares":22000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_date","element":"exerciseDate","label":"F1","text":"This option shall vest in full upon the earlier of (i) June 1, 2024 or (ii) the date of the next annual meeting of the Corporation's stockholders."}],"balance_after":22000,"derivative":{"exercise_price":11.18,"expiration_date":"2033-05-31","underlying":"Common Stock","underlying_shares":22000},"source":{"system":"sec-edgar","filing":"0000899243-23-014333","document":"doc4.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000089924323014333/doc4.xml","form_type":"4"}},{"id":2135612,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Common Stock","published_at":"2022-10-19T01:50:40.000Z","date":"2022-10-18","kind":"purchase","acquired":true,"shares":7000,"price":0.9764,"value":6834.8,"ownership":{"direct":false,"nature":"By Spouse"},"footnotes":[{"field":"price","element":"transactionPricePerShare","label":"F2","text":"The price reported in Column 4 is a weighted average price. These shares were purchased at prices ranging from $0.9375 to $0.9899, inclusive."}],"balance_after":7000,"source":{"system":"sec-edgar","filing":"0000899243-22-033781","document":"doc4.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000089924322033781/doc4.xml","form_type":"4"}},{"id":2135611,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Common Stock","published_at":"2022-10-19T01:50:40.000Z","date":"2022-10-18","kind":"purchase","acquired":true,"shares":118000,"price":0.977,"value":115286.0,"ownership":{"direct":true},"footnotes":[{"field":"price","element":"transactionPricePerShare","label":"F1","text":"The price reported in Column 4 is a weighted average price. These shares were purchased at prices ranging from $0.9315 to $0.99, inclusive. The reporting person has provided to the Issuer, and undertakes to provide any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the ranges set forth in footnotes (1) and (2) to this Form 4."}],"balance_after":136144,"source":{"system":"sec-edgar","filing":"0000899243-22-033781","document":"doc4.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000089924322033781/doc4.xml","form_type":"4"}},{"id":2244925,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Stock Option (Right to buy)","published_at":"2022-06-03T20:46:36.000Z","date":"2022-06-01","kind":"grant","acquired":true,"shares":22000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_date","element":"exerciseDate","label":"F1","text":"This option shall vest in full upon the earlier of (1) June 1, 2023 or (2) the date of the next annual meeting of the Corporation's stockholders."}],"balance_after":22000,"derivative":{"exercise_price":1.28,"expiration_date":"2032-05-31","underlying":"Common Stock","underlying_shares":22000},"source":{"system":"sec-edgar","filing":"0000899243-22-020998","document":"doc4.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000089924322020998/doc4.xml","form_type":"4"}},{"id":2683512,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Stock Option (Right to buy)","published_at":"2021-06-03T20:31:00.000Z","date":"2021-06-01","kind":"grant","acquired":true,"shares":22000,"price":0,"value":0.0,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_date","element":"exerciseDate","label":"F1","text":"This option shall vest in full upon the earlier of (1) June 1, 2022 or (2) the date of the next annual meeting of the Corporation's stockholders."}],"balance_after":22000,"derivative":{"exercise_price":11,"expiration_date":"2031-05-31","underlying":"Common Stock","underlying_shares":22000},"source":{"system":"sec-edgar","filing":"0000899243-21-021795","document":"doc4.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000089924321021795/doc4.xml","form_type":"4"}},{"id":3385426,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Series A-1 Preferred Stock","published_at":"2019-10-30T20:12:45.000Z","date":"2019-10-29","kind":"exercise","acquired":false,"shares":27217,"ownership":{"direct":true},"footnotes":[{"field":"derivative.exercise_price","element":"conversionOrExercisePrice","label":"F1","text":"Upon the closing of the Issuer's initial public offering, all shares of Series A-1 Preferred Stock automatically converted into shares of Common Stock of the Issuer on a one-for-1.5 basis. The Series A-1 Preferred Stock had no expiration date."},{"field":"price","element":"transactionPricePerShare","label":"F1","text":"Upon the closing of the Issuer's initial public offering, all shares of Series A-1 Preferred Stock automatically converted into shares of Common Stock of the Issuer on a one-for-1.5 basis. The Series A-1 Preferred Stock had no expiration date."},{"field":"derivative.exercise_date","element":"exerciseDate","label":"F1","text":"Upon the closing of the Issuer's initial public offering, all shares of Series A-1 Preferred Stock automatically converted into shares of Common Stock of the Issuer on a one-for-1.5 basis. The Series A-1 Preferred Stock had no expiration date."},{"field":"derivative.expiration_date","element":"expirationDate","label":"F1","text":"Upon the closing of the Issuer's initial public offering, all shares of Series A-1 Preferred Stock automatically converted into shares of Common Stock of the Issuer on a one-for-1.5 basis. The Series A-1 Preferred Stock had no expiration date."}],"balance_after":0,"derivative":{"underlying":"Common Stock","underlying_shares":18144},"source":{"system":"sec-edgar","filing":"0000899243-19-026346","document":"doc4.xml","document_sequence":1,"table":"derivative","row_type":"transaction","position":2,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000089924319026346/doc4.xml","form_type":"4"}},{"id":3385425,"issuer":{"id":5418,"kind":"organization","name":"Cabaletta Bio, Inc."},"owners":[{"id":39683,"kind":"person","name":"Simon Mark","position":1,"cik":"0001400717","reported_name":"Simon Mark","relationship":{"director":true,"officer":false,"ten_percent_owner":false,"other":false}}],"security":"Common Stock","published_at":"2019-10-30T20:12:45.000Z","date":"2019-10-29","kind":"exercise","acquired":true,"shares":18144,"ownership":{"direct":true},"footnotes":[{"field":"price","element":"transactionPricePerShare","label":"F1","text":"Upon the closing of the Issuer's initial public offering, all shares of Series A-1 Preferred Stock automatically converted into shares of Common Stock of the Issuer on a one-for-1.5 basis. The Series A-1 Preferred Stock had no expiration date."}],"balance_after":18144,"source":{"system":"sec-edgar","filing":"0000899243-19-026346","document":"doc4.xml","document_sequence":1,"table":"nonDerivative","row_type":"transaction","position":1,"url":"https://www.sec.gov/Archives/edgar/data/1759138/000089924319026346/doc4.xml","form_type":"4"}}]}