CD4 and breast cancer: Taken together, in both PyMT and MMTV-RON models, RON signaling loss within the mammary epithelium or myeloid cell populations (see below) hinders breast cancer progression by overcoming an immunosuppressive tumor microenvironment to a more immune-enriched environment with increased M1 macrophage, NK cell, and cytotoxic CD8+ T cells or CD4+ T cells anti-tumor responses.