Reconstitution of the Multiple Myeloma Microenvironment Following Lymphodepletion with BCMA CAR-T Therapy

Despite the acknowledged effectiveness of BCMA chimeric antigen receptor T (CAR-T) cells in killing multiple myeloma (MM) cells, predicting treatment responsivity to BCMA CAR-T therapy remains a challenge. In this study, we demonstrated that the best overall responses (BORs) of patients over the 15-month follow-up are positively correlated with the abundance and targeted cytotoxic activity of CD8+ effector CAR-T cells on day 28 after CAR-T cell infusion. Additionally, favorable responses are associated with attenuated immunosuppression mediated by regulatory T cells (Tregs), enhanced CD8+ effector T cell cytotoxic activity, and elevated type 1 conventional dendritic cell (cDC1) antigen presentation ability. Our study sheds light on MM microenvironment dynamics after BCMA CAR-T therapy, offering clues for predicting treatment responsivity. The collected paired bone marrow (BM) specimens from MM patients before and after BCMA CAR-T therapy were isolated into single cell suspensions, and 3'-scRNA-seq (Chromium Single Cell 3' v3 Libraries) analysis was performed on each sample.