As shown in Fig. 4, co-culture of both naïve- and memory-phenotype CD4+ T cells with a low ratio of MSCs was associated with a moderate anti-proliferative

effect under Th17-skewing conditions using CFSE labelling (Fig. 4A) and a reduced proportion of IL-17A+ cells within each generation of cell division using intracellular staining for IL-17A (Fig. 4B and C). It was concluded that the presence of low numbers of MSCs during a Th17-biased activation culture of either naïve or memory CD4+ T cells resulted in separate effects on T-cell proliferation and on induction of high-level IL-17A production. In additional experiments the specificity and direct nature of MSC suppression of Th17 differentiation was demonstrated. Inhibition of IL-17A secretion upon re-stimulation of Th17-skewed Nivolumab chemical structure naïve- and memory-phenotype CD4+ cells was not apparent following co-culture with primary fibroblasts (Supplemental Fig. S4A). The possibility that monocyte/macrophages or DCs were responsible for indirectly mediating MSC suppressive Tyrosine Kinase Inhibitor Library datasheet effects on T-cell responders was eliminated by experiments in which primary CD4+ T-cell/MSC co-cultures were initiated with anti-CD3/anti-CD28-coated beads rather than splenic APCs. In this case, the Th-17-suppressive effect of MSCs for both naïve

and memory CD4+T cells persisted (Supplemental Fig. S4B). In order to identify potential mediators Celecoxib of MSC-induced Th17 suppression, experiments were carried out in which FACS-purified naïve CD4+ T cells were Th17-skewed in APC-free culture (anti-CD3/anti-CD28 beads) in the presence or absence of MSCs (1:200 ratio) with or without blocking/inhibiting factors for candidate mediators. The primary experimental read-out was secretion of IL-17A following overnight stimulation of re-purified CD4+ T cells. As shown in Fig. 5A, the non-specific COX

inhibitor indomethacin reversed the MSC suppressive effect and, in some experiments, was associated with a paradoxical increase. The observation was consistent with induction, via T-cell–MSC contact, of a COX-dependent soluble mediator. To test this further, culture supernatants were removed from 4-day, APC-free Th17 cultures generated with and without indomethacin in the presence or absence of MSCs. These supernatants were applied to newly initiated Th17 cultures along with unconditioned medium and MSC-conditioned medium containing equivalent concentrations of Th17 inducing factors with and without indomethacin (Fig. 5B). CD4+ T cells were then re-purified from each culture and stimulated overnight, after which IL-17A production was measured. As shown, MSC-conditioned medium was associated with a modest reduction in IL-17A compared with unconditioned medium.