Extensive flow cytometric immunophenotyping of peripheral blood lymphocytes from untreated and persistently IFN-β-treated MS patients revealed that the long-term usage of IFN-β increased the percentages of Vδ1−Vδ2−Vγ9− γδ T cells and decreased the percentages of class-switched memory B cells without a major influence on other T and B lymphocyte subsets, which may contribute to the attenuation of disease activity. Here, IFNB1 is linked to myeloid sarcoma.