CTLA4 and head and neck squamous cell carcinoma: We observed significant but weak inverse correlations between CTLA4 promoter methylation and presence of CD3+ (Spearman’s ρ =  − 0.19, p = 0.029), CD4+ (ρ =  − 0.23, p = 0.006), CD8+ (ρ =  − 0.17, p = 0.048), and CD45+ (ρ =  − 0.21, p = 0.014; all N = 138) immune cells within the HNSCC microenvironment.