The human leukocyte antigen (HLA) class II DRB1 locus with a DR15 haplotype, carrying the DRB1*15: 01 and DRB5*01:01 alleles, is the strongest genetic risk factor for MS, with an approximately threefold increased risk of disease, and implicates a central role for CD4+ T cells in disease development (3). Here, CD4 is linked to myeloid sarcoma.