miR‐34a promotes the immunosuppressive function of multiple myeloma‐associated macrophages by dampening the TLR‐9 signaling

Abstract

Abstract Background Promising outcomes have been observed in multiple myeloma (MM) with the use of immunotherapies, specifically chimeric antigen receptor T (CAR‐T) cell therapy. However, a portion of MM patients do not respond to CAR‐T therapy, and the reasons for this lack of response remain unclear. The objective of this study was to investigate the impact of miR‐34a on the immunosuppressive polarization of macrophages obtained from MM patients. Methods The levels of miR‐34a and TLR9 (Toll‐like receptor 9) were examined in macrophages obtained from both healthy individuals and patients with MM. ELISA was employed to investigate the cytokine profiles of the macrophage samples. Co‐culture experiments were conducted to evaluate the immunomodulatory impact of MM‐associated macrophages on CAR‐T cells. Results There was an observed suppressed activation of macrophages and CD4+ T lymphocytes in the blood samples of MM patients. Overexpression of miR‐34a in MM‐associated macrophages dampened the TLR9 expression and impaired the inflammatory polarization. In both the co‐culture system and an animal model, MM‐associated macrophages suppressed the activity and tumoricidal effect of CAR‐T cells in a miR‐34a‐dependent manner. Conclusion The findings imply that targeting the macrophage miR‐34a/TLR9 axis could potentially alleviate the immunosuppression associated with CAR‐T therapy in MM patients.

Keywords

• CAR‐T
• macrophages
• miR‐34a
• multiple myeloma
• TLR9