CD4 and cancer: Th2 cells and double-positive CD4+CD8αβ+αβ T cells, in conjunction with cancer-initiating cells, represent important sources of secreted IL-4 in CRC.[39,40] The in vitro coculture of IL-4-secreting colorectal cancer-derived tumor-initiating cells with peripheral blood mononuclear cells resulted in the inhibition of peripheral blood mononuclear cell proliferation, which the introduction of IL-4-blocking antibodies could reverse.