Surprisingly, CD39 expression on CD4+ T cells and increased proportions of this cell population can also be induced by polysaccharide A (PSA), a molecule derived from Bacteroides fragilis, a commensal microorganism that inhabits the gut (54–56), which highlights the important role of the gut microbiota in the pathophysiology of MS (57, 58), especially in the context of ADO signaling. Here, ADO is linked to myeloid sarcoma.