CD4 and neoplasm: Tumour-infiltrating innate and adaptive immune cells are a prominent feature of the tumour microenvironment (TME), and consist of different subpopulations, including cytotoxic CD8 + and helper CD4 + T cells, regulatory T and B cells (Tregs and Bregs), natural killer (NK) cells, macrophages, and myeloid-derived suppressor cells (MDSCs; [115, 116]).