ArsenalBio Sheds Most of Staff, Pivots Entirely to In Vivo CAR T

ArsenalBio announced a strategic shift to focus the company entirely on in vivo CAR T-cell therapy, ending development of its ex vivo autologous cell therapy programs for solid tumors.¹ The transition draws on the company's existing investment in T-cell biology, synthetic biology, computation, and cell engineering, and will pursue a broader range of diseases, including hematologic malignancies and autoimmune conditions, beyond the solid-tumor focus that defined ArsenalBio's earlier pipeline.¹ To align its organization with the new direction, the company is cutting the substantial majority of its workforce: a spokesperson confirmed to Fierce Biotech that the reduction affects 99 of ArsenalBio's 127 employees, with a core team remaining to advance the in vivo strategy.²

Ken Drazan, MD, co-founder, chairman, and chief executive officer of ArsenalBio, said, "We founded ArsenalBio with the belief that deeply understanding and engineering T cell biology could unlock entirely new possibilities for medicine. The standard we have always set at ArsenalBio is that the science and the data must guide our decisions, particularly when developing potential therapies for people living with serious chronic diseases. Over the past several years, we have built an extraordinary foundation of technology, scientific capabilities and knowledge through our work in solid tumors. However, we now believe this technology is enabling outside of solid tumors. We plan to apply our foundational understanding of T cell biology and compositions to in vivo, where we believe our technology will advance the field and help patients win."¹

Why is ArsenalBio moving away from ex vivo solid-tumor CAR T?

ArsenalBio had raised $325 million with backing from Bristol Myers Squibb and Regeneron, and held a partnership with Roche's Genentech, to pursue CAR T therapies for solid tumors.² No CAR T therapy has yet been approved for a solid tumor; all six approved CAR T products in the US target blood cancers, and reaching solid tumors has remained one of the field's most persistent technical obstacles, owing to antigen heterogeneity, poor tumor penetration, and an immunosuppressive tumor microenvironment.³ ArsenalBio's lead asset, AB-2100, targeted clear-cell renal cell carcinoma; it no longer appears on the company's pipeline following the restructuring. Data from the company's autologous solid-tumor programs will still be presented at a future medical meeting.¹

How does in vivo CAR T differ from the ex vivo approach ArsenalBio is leaving behind?

Conventional, or ex vivo, CAR T manufacturing requires collecting a patient's T cells through leukapheresis, genetically modifying them outside the body, expanding the modified cells, and reinfusing them after chemotherapy-based lymphodepletion, a process that typically takes weeks and carries substantial manufacturing complexity and cost. In vivo approaches instead aim to generate CAR T cells directly inside the patient. Luke Walker, MD, chief medical officer of Umoja Biopharma, described the appeal of that shift in BioPharm International© coverage of Umoja's own in vivo CAR T program: "Generating CAR T cells within a patient's body would have the potential to transform clinical practice."⁴

Why is in vivo CAR T drawing so much industry investment right now?

Ryan Larson, PhD, SVP, head of research at Umoja BioPharma, addressed the broader significance of in vivo approaches in a video interview with BioPharm International at the 2025 American Society of Gene and Cell Therapy annual meeting. "We're seeing the continued transformative nature of cell therapies, in particular in hematologic malignancies, where you're seeing deep and durable responses continue in diffuse large B-cell lymphoma and other B-cell malignancies, as well as in multiple myeloma," Larson said. "Yet access to ex vivo autologous cell therapies continues to be a challenge wherein a large fraction of patients that may be eligible for those therapies are not able to gain access to them for a variety of reasons."⁵

That access gap is a central argument driving the field's shift toward in vivo delivery, and ArsenalBio is entering an increasingly crowded arena. Johnson & Johnson struck a collaboration with Sail Biomedicines that includes an exclusive option to acquire the company for $2.58 billion. Eli Lilly, AstraZeneca, and Gilead Sciences' Kite Pharma all have in vivo CAR T programs of their own.²

What happens next?

ArsenalBio said it will provide additional information on its strategy and programs as appropriate, and is evaluating strategic opportunities for its existing technologies and assets as it makes the transition.¹

References

1. Arsenal Biosciences, Inc. ArsenalBio Announces New Focus on In Vivo CAR T Programs to Leverage Investment in T cell Engineering. Press release. Published August 31, 2026. Accessed September 2, 2026.
2. Incorvaia D. ArsenalBio Sheds Most of Staff in Pivot to In Vivo CAR-T. Fierce Biotech. Published September 1, 2026. Accessed September 2, 2026.
3. Challenges of Expanding CAR-T Cell Therapy into Solid Tumors. BioPharm International. Published May 1, 2023. Accessed September 2, 2026.
4. Umoja Biopharma Wins FDA IND Clearance for First CD22-Directed In Vivo CAR T Therapy. BioPharm International. Published July 16, 2026. Accessed September 2, 2026.
5. Haigney S. ASGCT 2025: Emerging Modalities for Cancer Treatments. BioPharm International. Published May 12, 2025. Accessed September 2, 2026.