In vivo generation of anti-BCMA CAR-T cells in relapsed or refractory multiple myeloma: a phase 1 study

In vivo chimeric antigen receptor (CAR)-T cell generation can bypass ex vivo manufacturing and lymphodepletion, potentially simplifying and accelerating access to cellular therapy; preliminary clinical experience supports feasibility and suggests preliminary efficacy. This phase 1, single-arm, open-label trial evaluated the safety and tolerability of ESO-T01, a nanobody-directed, immune-shielded lentiviral vector encoding a humanized anti-B cell maturation antigen (BCMA) CAR, in adults with relapsed or refractory multiple myeloma. ESO-T01 was administered as a single intravenous infusion of 0.2 × 10⁹ transduction units without leukapheresis, ex vivo manufacturing or lymphodepleting chemotherapy. Five heavily pretreated male patients (median three prior lines) were consecutively enrolled and followed for a median of 6.0 months. The trial was stopped early in 2025, and no further enrollment was performed. The primary endpoint was safety and tolerability, and secondary endpoints included efficacy, pharmacokinetics and pharmacodynamics of ESO-T01. No dose-limiting toxicities occurred. All patients developed grade 3 or higher adverse events. Cytokine release syndrome occurred in four patients (three grade 3 and one grade 2) and was managed with corticosteroids, tocilizumab, or supportive care. The most frequent toxicities were transient cytopenias and reversible hepatic enzyme elevations, and three patients experienced grade 2 infections. One patient developed grade 1 immune effector cell-associated neurotoxicity and died from extramedullary lesion-related spinal cord compression. Preliminary antimyeloma activity was observed: four of five patients achieved objective responses, including three stringent complete remissions, with minimal residual disease negativity (10^-5) in all evaluable responders (4/4) by day 60. These findings provide preliminary evidence on the feasibility and safety of in vivo CAR-T generation using an immune-shielded vector. ClinicalTrials.gov registration: NCT06791681 .