Triple knockdown of CD11a , CD49d , and PSGL1 in T cells reduces CAR-T cell toxicity but preserves activity against solid tumors in mice

Chimeric antigen receptor (CAR)–T cell therapies have revolutionized the landscape of cancer treatment, in particular in the context of hematologic malignancies. However, for solid tumors that lack tumor-specific antigens, CAR-T cells can infiltrate and attack nonmalignant tissues expressing the CAR target antigen, leading to on-target, off-tumor toxicity. Severe on-target, off-tumor toxicities have been observed in clinical trials of CAR-T therapy for solid tumors, highlighting the need to address this issue. Here, we demonstrated that targeting the cell adhesion and migration molecules lymphocyte function–associated antigen 1 (LFA-1; CD11a/CD18) and very late activation antigen 4 (VLA-4; CD49d/CD29) with blocking antibodies reduced the on-target, off-tumor toxicity of CAR-T cells in mice. To translate this observation into improved CAR-T cell therapy, we either knocked out both CD11a and CD49d or knocked down CD11a and CD49d along with PSGL1 , another cell adhesion molecule, in CAR-T cells. We found that these modified CAR-T cells exhibited reduced on-target, off-tumor toxicity in vivo without affecting CAR-T cell efficacy. Furthermore, we showed that this approach promoted T cell memory formation and decreased tonic signaling. On the basis of these data, we engineered a human version of these low-toxicity CAR-T cells and further validated the feasibility of this approach in vitro and in vivo. Together, these results provide a potential solution to address the clinical challenge of on-target, off-tumor toxicity in CAR-T therapy.