CTLA4 and head and neck squamous cell carcinoma: However, CTLA-4+ T cells were significantly decreased in the microenvironment of late stage HNSCC compared to early stage (18.9 ± 11.3% vs. 8.2 ± 5.2%; p < 0.05; Figure 5C), which was attributable to lower percentages of CTLA-4 expressing CD4+ T cells (10.6 ± 6.2% vs. 26.1 ± 17.2%; p < 0.05), but not to altered expression of CTLA-4 in CD8+ T cells (6.5 ± 6.7% vs. 12.2 ± 7.5%; p = 0.14; Figure 5D, right plot).