CD8⁺ regulatory T cells, their suppressive mechanisms, and regulation in cancer

Regulatory T (Treg) cells induce immune tolerance by suppressing host immune responses against self- or nonself-antigens, thus playing critical roles in the prevention of autoimmune diseases, but they may inhibit antitumor immunity and promote tumor growth. Increasing evidence demonstrates that elevated proportions of CD4⁺ Treg cells are present in various types of cancers and suppress antitumor immunity. However, less is known about CD8⁺ Treg cells and their detrimental effects on immunotherapy directed toward cancer. Toll-like receptor (TLR)-8 signaling may directly regulate the suppressive function of CD4⁺ and CD8⁺ Treg cells. Linking TLR signaling to the functional control of Treg cells opens the potential for intriguing opportunities to manipulate TLR signaling to control the suppressive function of different subsets of Treg cells for effective immunotherapy of cancer.