CD4 and cancer: Treg cells represent a minor heterogenic subsite of CD4+ T cells with the potential to induce suppression of CD8+ T cells and may contribute to carcinogenesis and cancer progression by two mechanisms; first, by limiting immune function upon tumor recognition; and second, by suppressing the cellular activity of cytotoxic T cells (Dayan et al., 2012; Hadler-Olsen and Wirsing, 2019; Perri et al., 2020).