After the Pivot: What In Vivo Cell Therapy Offers, and What It Still Has to Prove

Several cell therapy developers have scaled back ex vivo programs in recent weeks to focus on engineering immune cells directly inside the patient. On August 31, 2026, ArsenalBio announced a significant strategic shift toward in vivo CAR-T programs for hematologic malignancies and autoimmune diseases, with a substantial reduction in its workforce.¹ "We now believe this technology is enabling outside of solid tumors," said Ken Drazan, MD, co-founder, chairman, and chief executive officer of ArsenalBio.¹ Two days later, TScan Therapeutics paused further enrollment in its Phase 3 ALLOHA-2 study of the ex vivo TCR-T therapy TSC-101, citing insufficient capital to complete the trial, and redirected resources to in vivo TCR-T candidates targeting PRAME and MAGE-A4 in solid tumors.² The company cut approximately 75% of its workforce.²