CD4 and neoplasm: Differentiated T cells have an important role in adaptive immunity and are subdivided into (i) CD8+ T cells that have cytotoxic activity, able to kill infected or tumor cells; (ii) CD4+ T cells, or "helper cells”, that release cytokines and activate indirectly regulatory B cells; and (iii) regulatory T cells (Treg) usually activated by tumor cells to prevent their killing.