CTLA4 and head and neck squamous cell carcinoma: Currently, the ICIs that have been tested on HNSCC include PD-1 (nivolumab and pembrolizumab), PD-L1 (atezolizumab, durvalumab, and avelumab), and CTLA-4 (ipilimumab and tremelimumab) (Alsaab et al., 2017; Szturz and Vermorken, 2017; Dogan et al., 2018; Gong et al., 2018).