Additional Information and Where to Find It The tender offer described in this document has not yet commenced. This document is for informational purposes only and is neither an offer to purchase nor a solicitation of an offer to sell any shares of the common stock of 2seventy bio or any other securities, nor is it a substitute for the tender offer materials described herein. At the time the planned tender offer is commenced, a tender offer statement on Schedule TO, including an offer to purchase, a letter of transmittal and related documents, will be filed by BMS ("BMS") and Daybreak Merger Sub Inc., a wholly owned indirect subsidiary of BMS, with the Securities and Exchange Commission ("SEC"), and a solicitation/recommendation statement on Schedule 14D-9 will be filed by 2seventy bio with the SEC. The offer to purchase shares of 2seventy bio common stock will only be made pursuant to the offer to purchase, the letter of transmittal and related documents filed as a part of the Schedule TO.