-BMS CONFIDENTIAL-

From: Lynelle Hoch

To: 2seventy bio employees

Date: Thursday, 3/13

Subject: Continuing our work together to bring Abecma to patients

Dear 2seventy bio colleagues,

Monday was an important day with the announcement that Bristol Myers Squibb (BMS) has entered into an agreement to acquire 2seventy bio. As the president of BMS' Cell Therapy Organization, I have had a front row seat to witness the commitment and important work we have done together to ensure Abecma reaches patients who need it.

Your team has played a significant role in bringing Abecma from bench to bedside, and this asset has set a high bar in the industry for what is possible with cell therapy in multiple myeloma (MM) as the first cell therapy to target BCMA and the first to treat MM. Thank you to everyone at 2seventy bio for your incredible dedication and partnership with Celgene/BMS since 2013.

I believe the acquisition of 2seventy bio not only gives us an opportunity to continue on the important journey we have started for Abecma, but as one company, further strengthens our position to deliver transformational outcomes for patients.

As you're aware, until the transaction closes, which is expected in Q2 2025, BMS and 2seventy bio will continue to operate as separate and independent companies; in other words, it's "business as usual." During this period, we will be forming our integration plans and are committed to expediting the transition after closing and communicating quickly and transparently throughout this process.

In the meantime, I look forward to visiting you in Cambridge on Tuesday, March 25 at 10:30 a.m. Thomas Potgieter, senior vice president, BMS Cell Therapy Development and Operations, and Paul Staid, vice president, Cell Therapy Product Strategy, will join me so we can have a dialogue with you and answer your questions.

BMS is well positioned in cell therapy with its two approved CAR T cell therapies against two distinct targets; deep clinical, manufacturing and translational capabilities; best-in-class pipeline, and exceptional, passionate individuals who bring our commitment to patients to life every day. Together with 2seventy bio, we have delivered many transformational firsts, and I believe this transaction will allow our list of achievements to keep growing.

We are excited to continue on this journey because we believe in the incredible potential of this transformational treatment modality. See you soon!

Sincerely,

/s/ Lynelle Hoch

Lynelle Hoch

President, Cell Therapy Organization

Bristol Myers Squibb

-BMS CONFIDENTIAL-