CCL4 and cancer: Another conserved feature of cytotoxic CD4+ T cells across these cancer and non-cancer contexts is the co-expression of chemokines, usually CCL4 and CCL5, although the biological importance of this production is unknown; in some studies, expression of the chemokine receptor CX3CR1 (fractalkine receptor) is characteristic of GZMB+ CD4+ T cells in both dengue viral infection and colorectal cancer (Patil et al., 2018; Zhang et al., 2018).