CAR-T and nanoCAR-T for multiple myeloma: Does smaller mean smarter ?

Multiple myeloma (MM) is an incurable hematologic malignancy of plasma cells. Chimeric antigen receptor T lymphocyte (CART) immunotherapy has shown remarkable results in relapse patients. Single-domain antibody (sdAb) offers an excellent alternative to scFv, due to its simple, small, and stable folding structure, therefore avoiding tonic signaling. Despite the development of numerous nanoCARTs, there is limited data demonstrating direct differences and their mechanisms. We aim to characterize the activity of a nanoCART compared to a standard CART and elucidate mechanisms driving these differences. These findings may reveal new potential targets for novel CART designs. An anti-BCMA sdAb was generated and tested for BCMA binding on MM cell lines before incorporating it into a CAR sequence. A nanoCART and standard CART were generated by lentiviral transduction on primary T cells, and their killing capacity, cytokine production, exhaustion, and memory properties compared in coculture with MM cell lines. sdAb17 binds excellently to BCMA expressed on MM cells and was integrated in a NanoCART, that could exhibit superior or the same killing capacity and cytokine production (IL-2, TFNa, IFNg) compared to an scFv-based CART. Morevoer, nanoCART and this CART differentiated faster and exhausted less than untransduced T cells upon rechallenge with MM cells. However, we observed NanoCART proliferated less compared to CART, but their proliferation could be boosted upon repeated antigen exposure. Our nanoCART demonstrates excellent anticancer efficacy but less persistence compared to CAR T. Further investigation at transcriptomic level may reveal the mechanistic difference and potentially suggest new targets to improve CART therapy.