In this context, EPO therapy given at doses used for the treatment of anemia inhibits proliferation of naïve and memory murine and human CD4+ and CD8+ T cells (3); prevents CD4+ TH1, TH17, and TFH cell differentiation and expansion (3–5); facilitates regulatory T-cell (Treg) generation and expansion (6, 7); and promotes differentiation of regulatory macrophages (7). The gene discussed is CD4; the disease is anemia.