In two different germ-free multiple sclerosis (MS), mouse models induced either by expressing a transgenic myelin oligodendrocyte glycoprotein (MOG)-specific T cell receptor in most CD4+ T cells [28] or by immunization with a fragment of MOG (MOG 35–55) [29], colonization of the germ-free mice with MS patient- vs. healthy donor-derived microbiota can significantly exacerbate experimental autoimmune encephalomyelitis symptoms. The gene discussed is CD4; the disease is myeloid sarcoma.