Arne Van der Vreken, Fien Meeus, Chenggong Tu, Lauren van den Broecke, Vincenzo Raimondi, Rosanna Vescovini, Heleen Hanssens, Fenja Watté, Dorien Autaers, Marta Marco Aragon, Janne Billiau, Kim De Veirman, Karin Vanderkerken, Yannick De Vlaeminck, Lorenzo Franceschini, Holly Lee, Paola Neri, Elke De Bruyne, Paola Storti, Nicola Giuliani, Karine Breckpot, Eline Menu
BACKGROUND: CAR T cell therapy targeting BCMA has shown remarkable efficacy in multiple myeloma (MM), but relapses occur due to T cell exhaustion and the emergence of BCMA-negative subpopulations. Novel targets are needed to overcome antigen escape. METHODS: B7-H3 (CD276) expression was assessed on primary MM patient samples. We engineered nanobody-based CAR T cells (nanoCARs) targeting B7-H3 and evaluated their cytotoxicity and cytokine production in vitro, including against patient-derived myeloma cells. Anti-tumor activity was tested in two different MM xenograft models. Dual CAR T cells (BCMA/B7-H3) and CARpooling (mix of BCMA and B7-H3 CAR T cells) were also tested for efficacy in antigen escape models. RESULTS: B7-H3 expression was detected on plasma cells in 60% of MM patients. B7-H3 nanoCAR T cells exhibited strong antigen-specific cytotoxicity and effector cytokine secretion, including against primary MM cells. In vivo, they reduced tumor burden and improved survival. Dual (BCMA/B7-H3) CAR T cells and CARpooling effectively eliminated heterogeneous tumor populations with mutually exclusive BCMA or B7-H3 expression. These findings show that BCMA/B7-H3 targeting may be a strategy to overcome antigen escape mechanisms. CONCLUSION: B7-H3 is a promising immunotherapy target in MM. B7-H3-specific and dual-targeting nanoCAR T cells could offer a strategy to prevent antigen escape and improve treatment durability.