PD-1 blockade prevents the development and progression of carcinogen-induced oral premalignant lesions

Oral squamous cell carcinoma (OSCC) is preceded by progressive oral premalignant lesions (OPL). Therefore, therapeutic strategies that prevent malignant progression of OPLs are expected to reduce the incidence of OSCC development. Immune checkpoint inhibitors that target the interaction of programmed death receptor 1 (PD-1) on T cells with the PD-1 ligand PD-L1 on cancer cells have been shown to extend the survival of patients with advanced OSCC. Here, we used the 4-nitroquinoline-1-oxide (4-NQO) mouse model of oral carcinogenesis to test the hypothesis that PD-1 blockade may control the progression of OPLs. Mice were exposed to 4-NQO in their drinking water and then randomly assigned to two treatment groups that received either a blocking antibody for PD-1 or a control IgG. We found that anti–PD-1 treatment significantly reduced the number of oral lesions that developed in these mice and prevented malignant progression. Low-grade dysplastic lesions responded to PD-1 blockade with a significant increase in the recruitment of CD8^þ and CD4^þ T cells and the accumulation of CTLA-4^þ T cells in their microenvironment. Notably, PD-1 inhibition was accompanied by induction of IFNg, STAT1 activation and the production of the T-cell effector granzyme B in infiltrating cells, and by the induction of apoptosis in the epithelial cells of the oral lesions, suggesting that T-cell activation mediates the immunopreventive effects of anti–PD-1. These results support the potential clinical benefit of PD-1 immune checkpoint blockade to prevent OSCC development and progression and suggest that CTLA-4 inhibitors may enhance the preventive effects of anti–PD-1.