Mechanisms of Resistance to CAR T-Cells and How to Overcome Them

In the last few decades, chimeric antigen receptor (CAR) T-cell therapy has led to a paradigm shift in the treatment of hematological malignancies, including various subtypes of B-cell non-Hodgkin's lymphoma, B-cell acute lymphoblastic leukemia, and multiple myeloma. However, most patients experience refractoriness to CAR T-cells or relapse after treatment. Many efforts are underway to understand the mechanisms behind CAR T-cell failure, which are mainly related to CAR T-cell dysfunction, tumor-intrinsic resistance, an immunosuppressive tumor microenvironment, manufacturing issues, or patient-related factors. Several strategies are being developed to overcome these resistance mechanisms, including the engineering of more functional allogeneic CAR T-cell products, the targeting of alternative tumor antigens, and combination therapies with other drugs such as checkpoint inhibitors or small molecules to enhance CAR T-cell efficacy. In this review, we will provide an updated overview of the mechanisms of CAR T-cell failure and the therapeutic advances currently under development to address them.