Macrophage and IL-6 signaling modulate multiple myeloma progression and response to metformin and CAR-T cell therapy

The tumor microenvironment (TME) plays a crucial role in tumor progression and therapeutic response. Monocytes and macrophages, depending on their phenotype, can either enhance anti-tumor immunity or promote tumor growth by regulating cytokines such as IL-6. Multiple myeloma (MM), a hematologic malignancy, expresses the IL-6 receptor CD126 on its surface. Chimeric antigen receptor (CAR)-T cells targeting CD126 have been developed and shown to effectively eliminate CD126-positive tumor cells. However, interactions between macrophages, myeloma cells, and CAR-T cells require further investigation to optimize treatment strategies and minimize adverse effects. In this study, THP-1-derived macrophages, CD126 CAR-T cells, and MM cells, especially RPMI 8226 cells, were used to explore these interactions. A reduced cell population and an increased apoptosis of RPMI 8226 cells were observed in the presence of M1 macrophages. Metformin, known to influence IL-6 production, reduced the viability of RPMI 8226 cells with decreased CD126 expression. However, the killing activity of CD126 CAR-T cells against RPMI 8226 cells decreased after co-culture with macrophages, likely due to interactions between the CAR-T cells and the macrophages. These findings highlight the significant role of macrophages and inflammatory responses in MM progression and in modulating the efficacy of CAR-T cell therapy, providing valuable insights for the optimization of immunotherapeutic strategies.