Potently Immunosuppressive 5-Fluorouracil–Resistant Mesenchymal Stromal Cells Completely Remit an Experimental Autoimmune Disease

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We treated mice with 5-fluorouracil (5-FU) to isolate a quiescent and undifferentiated mesenchymal stromal cell (MSC) population from the bone marrow. We examined these 5-FU-resistant MSCs (5-FU-MSCs) free from hematopoietic components for CFU fibroblasts (CFU-Fs) and assessed their immunosuppressive potential in vitro and in vivo. We differentiated fibroblastic CFU-Fs (Fibro-CFU-Fs) from mixed CFU-Fs, based on the absence of in situ expression of CD11b and CD45 hematopoietic markers, as well as on their differentiation capacity. Fibro-CFU-Fs were associated with increased numbers of large-sized Fibro-CFU-Fs (≥9 mm(2)) that displayed enhanced capacity for differentiation into adipogenic and osteogenic mesenchymal lineages. Administration of these 5-FU-resistant CD11b(-)CD45(-) MSCs 6 d after myelin oligodendrocyte glycoprotein (MOG) immunization completely remitted MOG-induced experimental autoimmune encephalomyelitis after initial development of mild disease. The remission was accompanied by reduced CNS cellular infiltration and demyelination, as well as a significant reduction in anti-MOG Ab and splenocyte proliferation to MOG. MOG-stimulated splenocytes from these mice showed elevated levels of Th2 cytokines (IL-4, IL-5, and IL-6) and decreased IL-17. Compared with untreated MSCs, 5-FU-MSCs demonstrated potent immunosuppression of Con A-stimulated splenocytes in vitro, even at a 1:320 MSC/splenocyte ratio. Immunosuppression was accompanied by elevated IL-1ra, IL-10, and PGE(2). Blocking IL-1ra, IL-10, and PGE(2), but not IL-6, heme oxygenase-1, and NO, attenuated 5-FU-MSC-induced immunosuppression. Together, our findings suggested that immunosuppression by 5-FU-MSC is mediated by a combination of elevated IL-1ra, IL-10, and PGE(2), anti-inflammatory Th2 cytokines, and decreased IL-17. Our findings suggested that 5-FU treatment identifies a population of potently immunosuppressive 5-FU-MSCs that have the potential to be exploited to remit autoimmune diseases.