A phase 1 study investigated the in vivo generation of anti-BCMA CAR-T cells in patients with relapsed or refractory multiple myeloma. CAR-T cells were generated by administering lentivirus directly into the patient's body. This method was feasible in five patients. No dose-limiting toxicity was observed. The study was published in Nature Medicine on March 25, 2026. The main finding is the safety of the procedure without serious side effects. This is the first attempt at the in vivo production of CAR-T cells targeting the BCMA antigen.