CD8A and neoplasm: For example, tumour and virally infected cells are killed by the action of cytotoxic CD8 T Cells and their subtypes; CD4 T cell modulate the action of innate and adaptive cells (B and T cells) by secreting different types of cytokines that are necessary for the proliferation and differentiation of CD4 T cells into subsets of helper T (Th) cells: Th1, Th2, Th17, and Treg cells.