CD8A and neoplasm: TILs represent the major component of the adaptive immune system in the TME and can be classified into two main categories: 1) CD4-expressing T cells (CD4 + T cells), which can differentiate into the T helper1 (Th1) or T helper2 (Th2) phenotype, and 2) CD8-expressing T cells (CD8 + T cells), which are able to eliminate tumor cells after differentiation into cytotoxic effector T lymphocytes.