Inguinal mammary fat pads of 3-week-old nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice were cleared of endogenous mammary epithelium and humanized with SVF cells expressing empty vector (SVF/EV) or CCL2 (SVF/CCL2) (Figure 1A). Here, CCL2 is linked to severe combined immunodeficiency.