Functional impairment of Treg cells is commonly reported in MS studies; however, conventional analyses have failed to describe corresponding phenotypic characteristics.5 In light of the work by Sakaguchi and colleagues,11 it was our hypothesis that conventional definitions, such as those used in previous MS studies, obfuscate the functional heterogeneity of FoxP3+ Treg cells and that the CD45RA/FoxP3 fraction approach to analysis would yield more informative results. This evidence concerns the gene FOXP3 and myeloid sarcoma.