In IL-30 conditional knockout (KO) mice (EIIa-p28f/f) [94], the lack of IL-30 production by the host leukocytes, essentially myeloid cells that are its main source, not only prevents expansion of CD4+CD25hiFoxp3+ Tregs and IL-10 production in both spleen and TME, following PC–SLC engraftment, but also favors the intratumoral influx of perforin+ cytotoxic T lymphocytes (CTLs), with a moderate cancer cell apoptosis. This evidence concerns the gene CD4 and cancer.