In this article, we review the involvement of CTLA-4 and PD-1/PD-1 in tumor immunity, the mechanism by which anti-CTLA-4, anti-PD-1, and anti-PD-L1 antibodies exhibit anti-tumor effects and induce irAEs, the types of irAEs in ICI-treated HNSCC patients, and ICI-induced Sicca syndrome, oral lichenoid reaction (OLR), and oral pemphigoid lesions. Here, CTLA4 is linked to Sjogren syndrome.