Immunosuppressive therapy after solid organ transplantation and the gut microbiota: bidirectional interactions with clinical consequences.

Our understanding of the involvement of the gut microbiota (GM) in human health has expanded exponentially over the last decades, particularly in the fields of metabolism, inflammation and immunology. Immunosuppressive treatment (IST) prescribed to solid organ transplant (SOT) recipients produce GM changes that affect these different processes. This review aims at describing the current knowledge of how IST change the GM. Overall, SOT followed by IST results in persistent changes in the GM, with a consistent increase in proteobacteria including opportunistic pathobionts. In mice, Tacrolimus induces dysbiosis, metabolic disorders, and alters the intestinal barrier. The transfer of the GM from Tacrolimus-treated hosts confers immunosuppressive properties, suggesting a contributary role for the GM in this drug's efficacy. Steroids induce a dysbiosis and intestinal barrier alterations, and also seem to depend partly on the GM for their immunosuppressive and metabolic effects. Mycophenolate Mofetil, frequently responsible for digestive side effects such as diarrhea and colitis, is associated with pro-inflammatory dysbiosis and increased endotoxemia. Alemtuzumab, m-TOR inhibitors and belatacept have shown more marginal impacts on the GM. Most of these observations are descriptive. Future studies should explore the underlying mechanism of IST-induced dysbiosis in order to better understand their efficacy and safety characteristics.