Low-Dose TBI Plus CAR T-Cell Therapy for Relapsed/Refractory DLBCL and Multiple Myeloma

This is a single-center, open-label, non-randomized, Phase Ib trial evaluating dose escalation of low-dose total body irradiation (LD-TBI) combined with standard-of-care CAR T-cell therapy in patients with relapsed or refractory large B-cell lymphoma (LBCL) or multiple myeloma (MM). The study includes two disease-specific cohorts: Cohort 1 (LBCL) receives commercial CD19-directed CAR T-cell therapy (axicabtagene ciloleucel or lisocabtagene maraleucel), and Cohort 2 (MM) receives commercial BCMA-directed CAR T-cell therapy (ciltacabtagene autoleucel). In CAR T-cell therapy, T-cells are removed via apheresis, modified to target the tumor, and infused back into the patient after lymphodepleting chemotherapy. On the same day as CAR T-cell infusion, prior to infusion, patients receive a single dose of LD-TBI. Each cohort follows a standard 3+3 dose-escalation design (Part 1) to identify the maximum tolerated dose (MTD) across three planned dose levels (0.5 Gy, 1.0 Gy starting dose, and 2.0 Gy), based on dose-limiting toxicities occurring within 28 days of treatment. Once the MTD is identified, an expansion cohort (Part 2) of up to 10 additional participants per cohort will be randomized 1:1 to the MTD or a dose level below it to further evaluate safety and activity. Approximately 16-22 participants are anticipated per disease cohort. Participants will be followed for up to 2 years after treatment.