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Background: Chimeric antigen receptor T (CAR‐T) cell therapy has emerged as a potent treatment for relapsed or refractory multiple myeloma, demonstrating significant clinical efficacy. Despite these advances, treatment‐related toxicities, particularly infections, pose a significant challenge to patient safety. Methods: This review synthesizes current knowledge on the mechanisms underlying post‐CAR‐T therapy infections, focusing on the interplay between immune dysfunction, host factors, and treatment‐induced toxicity. It provides a comprehensive analysis of the temporal and individual variability in infection characteristics and the confounding clinical presentation of cytokine release syndrome. Results: The review identifies that patients receiving CAR‐T cells are at increased risk of concurrent infections due to the heterogeneity in infection characteristics across different time periods, individuals, and patient groups. It highlights the diagnostic and therapeutic complexities introduced by the overlapping symptoms of infection and cytokine release syndrome. Conclusion: To enhance the infection control post‐CAR‐T therapy, this review proposes preventive strategies tailored to the early and long‐term management of patients. It underscores the need for a nuanced understanding of infection mechanisms and the importance of personalized prevention plans to improve clinical outcomes in multiple myeloma treatment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]