Therapeutic anti-psoriatic effects of myeloid-derived suppressor cells in combination with systemic tacrolimus (FK-506) in an imiquimod-induced mouse model of psoriasis

Although tacrolimus (FK-506) has been shown to be an effective monotherapy for psoriasis, it does not always work well. Currently, combination therapy is frequently used to manage psoriasis because clinical trials have shown it may provide additive or synergistic benefits and reduce risks of adverse effects. Myeloid-derived suppressor cells (MDSCs) have potent immunomodulatory and anti-inflammatory properties in autoimmune diseases. We previously reported that MDSCs had protective effects in a murine model of imiquimod (IMQ)-induced psoriasis. The present study was undertaken to investigate the systemic immunomodulatory and therapeutic efficacy effects of MDSC plus FK-506 in an IMQ-induced mouse model of psoriasis and to investigate the immunomodulatory mechanisms involved. Systemic MDSC plus FK-506 therapy was found to have a significant anti-psoriatic effect in the murine model, to reduce levels of pro-inflammatory cytokines Th1 cytokines (TNF-alpha and IFN-gamma) and Th17 cytokines (IL-17A and IL-23) in serum and skin. However, treatment with MDSCs or FK-506 alone had little impact. Furthermore, the anti-psoriatic effects of MDSC plus FK-506 were associated with histopathological reductions in inflammatory infiltration, epidermal hyperplasia, and hyperkeratosis. In addition, this combined treatment also attenuated IMQ-induced splenomegaly, and increased the proportion of CD4(+)CD25(+)FoxP3(+) regulatory T (Treg) cells and decreased the proportions of CD4(+)IFN-gamma(+) Th1 cells and CD4(+)IL-17(+) Th17 cells in spleen. Taken together, our results show systemic combination therapy with MDSCs and FK-506 had a better therapeutic effect in our IMQ-induced psoriasis model than either agent alone, and suggest that this combinatorial therapy might be useful for the management of autoimmune skin diseases like psoriasis.