Although MS and EAE have been described as T-helper type 1 (TH1) cell–mediated autoimmune diseases, CD4+ CD25+ regulatory T (Treg) cells have recently received a great deal of attention as negative regulators of MS pathogenesis (Kohm et al. 2002; Baecher-Allan & Hafler 2004; Viglietta et al. 2004; Matarese et al. 2005). Here, CD4 is linked to myeloid sarcoma.