The proposed anti-cancer activity mechanisms of IL-10 include the activation of NK cells, enhancement of the surface expression of the MHC antigen to maintain the susceptibility of cancer cells to NK cells, the synergistic activation of CTL for maintenance of the CD8+ and CD4+ mediated anti-tumor response, the modulation of angiogenesis and invasiveness through the inhibition of metalloproteinase, and finally, the enhancement of tumor infiltration by neutrophils and macrophages. This evidence concerns the gene CD4 and cancer.