We have previously demonstrated that MPA/DMBA-driven mammary tumors develop with an accelerated kinetic in Rag2−/−Il2rg−/− mice (which lack T cells, B cells and NK cells), as well as in mice receiving an antibody specific for NKG2D (which depletes NK cells and a subpopulation of CD8+ T cells), but not in Rag2−/− mice (which lack T and B cells) or in mice receiving CD4- and CD8-targeting antibodies (which are depleted of T cells), globally pointing to NK cells as to central mediators of natural immunosurveillance in this model [13, 50]. This evidence concerns the gene CD4 and breast cancer.