PD-1 blockade prevents the progression of oral carcinogenesis.

Oral squamous cell carcinoma (OSCC) is one of the most common malignancies in the head and neck with a poor prognosis. Oral cancer development is a multistep process involving carcinogenesis. Though significant advances in cancer immunotherapy over the years, there is lack of evidence for T cell exhaustion during oral carcinogenesis. Clinical specimens from healthy donors and patients diagnosed with oral leukoplakia (OLK) or OSCC were collected for immunohistochemical staining with PD-L1, CD86, CD8, PD-1 and CTLA-4 antibodies. Meanwhile, chemically induced mouse models of oral carcinogenesis were constructed with 4-NQO induction. Exhaustion status of T cells was measured by flow cytometry for spleens and by multiplex immunohistochemistry (mIHC) for formalin-fixed paraffin-embedded lesions in multiple stages of oral carcinogenesis. The efficacy of PD-1 blockade with or without cisplatin treatment was evaluated on the mice in precancerous and OSCC stages. We observed higher expression of PD-1 in the human OLK and OSCC tissues compared with the normal, while low expression CTLA-4 in all oral mucosa tissues. Animal experiments showed that the exhausted CD4 + T cells existed much earlier than exhausted CD8 + T cells, and an increased ratio of stem-like exhausted T cells and partially exhausted T cells were detected in the experimental groups. Besides, the expression of immune checkpoint markers (PDCD1, CTLA4, HAVCR2) were strongly positively correlated with cytokines (IFNG, IL-2). In summary, T cell exhaustion plays a vital role in oral carcinogenesis, and PD-1 blockade can prevent the progression of oral carcinogenesis.