RE: Vlad posting10 Apr 2026 19:06
In Vivo CAR-T: A Promising Concept Meets Clinical Reality
Results from a Phase 1 trial of ESO-T01 — EsoBiotec’s lentiviral in vivo BCMA-directed CAR-T candidate for relapsed/refractory multiple myeloma were published last week in Nature Medicine, and they deserve a careful read.
The premise was elegant: skip the complex ex vivo manufacturing entirely and generate CAR-T cells directly inside the patient — no leukapheresis, no lymphodepletion, potentially a fraction of the cost of current approved therapies. A genuinely transformative idea.
The efficacy signal was real. Four of five patients achieved objective responses, including three stringent complete remissions, with MRD negativity in all evaluable responders by day 60.
But the safety data should give the field pause. All five patients developed grade 3 or higher adverse events, and CRS occurred in four patients, reaching grade 3 in three of them. One patient died, and while the authors attributed the death to disease progression, the timing, coinciding with peak CAR-T expansion and immune activation raises unresolved questions.
Perhaps most sobering is a point the article raises directly: once the therapy is administered, it cannot be easily controlled or withdrawn. That loss of reversibility is a fundamentally different risk calculus compared to ex vivo approaches.
The authors noted that the timing and sequence of toxicities suggest different underlying biology from traditional CAR-T which means we cannot simply apply the management playbook we’ve developed over the past decade.
The trial was stopped in 2025 with no further patients enrolled. AstraZeneca, which had acquired EsoBiotec, has stated it intends to continue development and the field at large is clearly not stepping back, with Lilly, Orna, and others accelerating their own in vivo programs.
The vision remains compelling. But this data is a reminder that bypassing ex vivo manufacturing does not mean bypassing biology. The immune system still has to contend with a systemically delivered viral vector, uncontrolled CAR expression kinetics, and an activation cascade that we don’t yet fully understand how to tune.
In vivo CAR-T is not a shortcut. It’s a different problem.
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