Collagen-binding IL-12-armoured STEAP1 CAR-T cells reduce toxicity and treat prostate cancer in mouse models

Immunosuppressive microenvironments, the lack of immune infiltration, and antigen heterogeneity pose challenges for chimaeric antigen receptor (CAR)-T cell therapies applied to solid tumours. Previously, CAR-T cells were armoured with immunostimulatory molecules, such as interleukin 12 (IL-12), to overcome this issue, but faced high toxicity. Here we show that collagen-binding domain-fused IL-12 (CBD-IL-12) secreted from CAR-T cells to target human six transmembrane epithelial antigen of prostate 1 (STEAP1) is retained within murine prostate tumours. This leads to high intratumoural interferon-γ levels, without hepatotoxicity and infiltration of T cells into non-target organs compared with unmodified IL-12. Both innate and adaptive immune compartments are activated and recognize diverse tumour antigens after CBD-IL-12-armoured CAR-T cell treatment. A combination of CBD-IL-12-armoured CAR-T cells and immune checkpoint inhibitors eradicated large tumours in an established prostate cancer mouse model. In addition, human CBD-IL-12-armoured CAR-T cells showed potent anti-tumour efficacy in a 22Rv1 xenograft while reducing circulating IL-12 levels compared with unmodified IL-12-armoured CAR-T cells. CBD fusion to potent payloads for CAR-T therapy may remove obstacles to their clinical translation towards elimination of solid tumours.