These include the strongest MS-associated genetic risk factor, the human leukocyte antigen (HLA) DRB1*15, specifically the HLA-DRB1*15:01 variant, of the major histocompatibility complex (MHC) class II that restricts CD4+ T cells (Sawcer et al., 2011; Beecham et al., 2013). This evidence concerns the gene CD4 and myeloid sarcoma.