Programmed death 1 (PD-1) blockade has great effect in the prevention of oral precancerous lesions, but the drug resistance has also been observed. The determinants of immune resistance during the malignant transformation are poorly understood.

Our findings identified a novel mechanism that T cell dysfunction contributes to the immune resistance during the malignant transformation of the oral mucosa. This study provides new targets for improving the efficacy of immunotherapy for early stage of tumorigenesis.

Anti-PD-1 antibody was administered in the 4NQO-induced carcinogenesis mouse models. The mice were then subdivided into PD-1 resistance(PD-1R) group and PD-1 sensitive(PD-1S) group according to the efficacy. The expression of PD-1 and PD-L1, and the abundance of CD3+ T cells in tumor microenvironment between the two groups was tested by immunohistochemistry. In addition, the activation and effector functions, as well as the accumulation of immunosuppressive cells and expression of immune checkpoints of T cells in the draining lymph nodes and spleen between PD-1R and PD-1S group were analyzed by flow cytometry.

Our results showed that T cell infiltration in tumor microenvironment, effector T cell cytokine secretion and central memory T cell accumulation in peripheral lymphoid organs were all inhibited in the anti-PD-1 resistance group. Furthermore, we found that an increase of regulatory T cell (Treg) population contributed to the resistance of the anti-PD-1 therapy. Notably, TIM-3 was found to be the only immunosuppressive molecule that mediated the resistance to anti-PD-1 therapy in the oral malignant transformation model. Conclusions: Our findings identified a novel mechanism that T cell dysfunction contributes to the immune resistance during the malignant transformation of the oral mucosa. This study provides new targets for improving the efficacy of immunotherapy for early stage of tumorigenesis.