Abstract
Background: Chimeric antigen receptor (CAR) engineered T cells directed B cell maturation antigen (BCMA) showed transient recovery to multiple myeloma (MM). However, the expression of CD19 on immature plasma cell may escape the recognition by BCMA-CAR T, which restrict the efficacy and facilitate to relapse. The purpose of this study is to characterize a novel CAR structure with a tandem orientation of scFv-BCMA and scFv-CD19, tandem CAR (tan-CAR), to provide an effective solution for killing both BCMA and/or CD19 expression MM cells.Method: Single-chain variable fragment (scFv) sequences from the anti-CD19 antibody FMC63 and the anti-BCMA antibody C11D5.3 were ligated in tandem with transmembrane and T cell signaling domains to achieve tan-CAR construct. The therapeutic specificity and efficiency were analyzed for tan-CAR T cells activation, proliferation, cytokine release and cytolytic toxicity in vitro. Also, in vivo efficacy evaluation conducted in xenograft mouse models with the combination of two corresponding target tumor cells, in comparison with conventional CAR.Results: The in vitro studies demonstrated specific activation of tan-CAR T cells to the K562 tumor cell overexpressing CD19, BCMA, or both. Besides, it also elicits the comparable immunoreactivities, in terms of proliferation, cytokine release and cytolytic activity compared to single scFv modified CAR T cells. Importantly, the in vivo studies of tan-CAR-transduced T cells results specific inhibition of tumor growth in xenograft model that express combined tumor antigen i.e. CD19 and BCMA. Moreover, systemic administration of tan-CAR resulted in complete tumor remission, whilst neither BCMA-CAR T nor CD19-CAR-T could. Conclusion: A novel tan-CAR T was successfully designed and showed the significant antitumor efficacy for combined antigen-positive tumor cells in vitro and in vivo. However, the single CAR T cells with targeting one antigen didn’t achieve similar potency. The data from this study suggest a novel strategy to help reduce relapse due to existing CD19-expressing multiple myeloma cells or downregulation of the BCMA antigen after CAR-based treatment of multiple myeloma.