PVR Mediates Resistance to IL21.CD276.CAR-T Therapy in Esophageal Squamous Cell Carcinoma.

Chimeric antigen receptor (CAR)-T therapy has achieved partial therapeutic efficacy in solid tumors, but its overall effectiveness remains limited. IL-21-armored CD276.CAR-T (IL21.CD276.CAR-T) represents a promising strategy to enhance anti-tumor activity against esophageal squamous cell carcinoma (ESCC). However, resistance mechanisms remain unclear. We generated IL21.CD276.CAR-T cells and evaluated their cytotoxicity in vitro and in B-NDG xenograft models. Poliovirus receptor (PVR) expression on ESCC cells was analyzed, and shRNA-mediated PVR knockdown was performed to validate its role in resistance. IL-21R expression on ESCC cells was examined to exclude direct IL-21 signaling. IL-21 enhances the cytotoxicity of CD276.CAR-T cells against ESCC. Although IL21.CD276.CAR-T exhibited potent cytotoxicity in vitro, it failed to achieve complete tumor regression, and resistant cells still emerged. Mechanistically, resistance was not caused by CD276 antigen loss or IL-21R expression, but by upregulation of PVR on cancer cell membrane after IL21.CAR-T exposure. PVR knockdown restored CAR-T sensitivity in vitro, enhanced the anti-tumor capacity of IL21.CD276.CAR-T cells, and partially improved anti-tumor efficacy in vivo without systemic toxicity. PVR may act as a mediator of resistance to IL21.CD276.CAR-T in ESCC. Targeting PVR represents a novel strategy to overcome IL21.CAR-T resistance and improve therapeutic outcomes in ESCC.