CTLA4 and head and neck squamous cell carcinoma: The DP CD4+ Th TILs expressed higher levels of HLA-DR, CD39, and CTLA-4 compared with levels in the DN and SP CD4+ Th TILs (Figure 2A), in both HNSCC and CRC samples (Figure 2, B and C, respectively), indicative of an activated phenotype.