CD4 and myeloid sarcoma: Although let-7 is one of the most highly expressed miRNA families in CD4+ T cells (26) and it has been shown to play regulatory roles in helper T cell responses (31–33, 35, 36), published reports have yielded conflicting conclusions regarding the contribution of let-7 miRNAs to Th17 cell pathogenicity during MS and EAE, and have remained unresolved (25).