CTLA4 and head and neck squamous cell carcinoma: The majority of CTLA-4+ T cells was CD8+ in PBMC HC (55.9 ± 19.1%), with significantly lower percentages of CD8+ T cells in the CTLA-4+ T-cell subset in PBMC HNSCC (18.2 ± 11.4%; p < 0.0001).