(A) Single-sample gene set enrichment analysis for 280 HNSCC tumor samples identifying relative expression of immune cell populations clustered into immune-high and -low phenotypes. (B) Relative cytolytic (CYT) activity, IFN-γ expression, and CD8+/Treg ratios between immune-high and -low tumors clustered by overall immune cell infiltration. (C) Correlations between relative IFN-γ expression and immune infiltration characterized by T cell infiltration score (TIS) and immune cell infiltration score (IIS) in HPV-positive and -negative tumors. (D) Relative TIS, Treg, and CD8+/Treg ratios stratified by head and neck tumor subsite. (E) Relative TIS, IIS, IFN-γ expression, and CYT activity between HNSCC gene expression subtypes. All box-and-whisker plots represent values within the interquartile range (IQR) (boxes) and 1.5 × IQR (whiskers). Outliers are plotted as values > 1.5 × IQR (circles) and > 3 × IQR (stars). All P values for significance (<0.05) represent comparisons via 2-tailed t tests and 1-way ANOVA for continuous comparisons. All r values represent Pearson correlation coefficients. n = 280. APM, antigen-processing machinery.