Bispecific antibodies as bridging to BCMA CAR-T cell therapy for relapsed/refractory multiple myeloma

Establishing a strategy for sequencing of T cell redirecting therapies for relapsed/refractory multiple myeloma (RRMM) is a pressing clinical need. We longitudinally tracked the clinical and immunological impact of bispecific T cell engaging antibodies (BsAb) as bridging therapy (BT) to subsequent BCMA-directed CAR-T cell therapies in 52 RRMM patients. BsAbs were a potent and safe option for BT, achieving the highest overall response rate (100%) to BT compared to chemotherapy, anti-CD38 or anti-SLAMF7 antibody based regimens (46%). We observed early CD4+CAR+ and delayed CD8+CAR+ T cell expansion in patients receiving BsAb as BT. In vitro cytotoxicity of CAR-T cells was comparable amongst BT options. Single-cell analyses revealed increased clonality in the CD4+ and CD8+ T cell compartments in patients with previous exposure to BsAbs at leukapheresis and on day 30 after CAR-T infusion. This study demonstrates the feasibility and efficacy of BT with BsAbs for CAR-T cell therapy in RRMM.