RESUMEN
Given their capacity to modulate the immune response, adipose mesenchymal stem or stromal cells (ASCs) have been used as therapeutic tools to treat chronic inflammatory and autoimmune diseases both in preclinical and clinical studies. Patients enrolled in such clinical trials are often concomitantly treated with immunomodulatory drugs such as methotrexate (MTX) or azathioprine (AZA). Therefore it is necessary to investigate the possible impact of these drugs on ASC function to learn if there are any interactions that would affect the therapeutic effects of either component and thus the clinical outcome of the trials. ASCs were cultured in the absence or presence of MTX or AZA and the effects on viability, proliferation, immunomodulatory properties, and immunogenic features were studied in vitro. The drugs did not affect the viability and proliferative capacity of ASCs. When the drugs and the ASCs were concomitantly used to inhibit lymphocyte proliferation, no synergistic or antagonizing inhibitory effects were found. MTX and AZA did not impair the capacity of ASCs to induce the generation of regulatory T cells in vitro. These data confirm that the immunomodulating features of ASCs are fully functional after exposure to these drugs. Interestingly, whereas MTX did not affect the capacity of natural killer (NK) cells to lyse allogeneic ASCs in vitro, AZA protected allogeneic ASCs from NK cell lysis.
RESUMEN
Human adipose-derived mesenchymal stem cells (hASCs) are mesenchymal stem cells (MSCs) with reduced immunogenicity and capability to modulate immune responses. Whereas the immunosuppressive activity of bone marrow-MSCs has received considerable attention during the last few years, the specific mechanisms underlying hASC-mediated immunosuppression have been poorly studied. Recent studies comparing both cell types have reported differences at transcriptional and proteomic levels, suggesting that hASCs and bone marrow-MSCs, while having similarities, are quite different. This suggests that different mechanisms of immunosuppression may apply. Here, we report that hASCs inhibit peripheral blood mononuclear cells (PBMCs), and CD4(+) and CD8(+) T cell proliferation in both cell-cell contact and transwell conditions, which is accompanied by a reduction of proinflammatory cytokines. We demonstrate that hASCs do not constitutively express immunomodulatory factors. Conditioned supernatants from hASCs stimulated by IFN-gamma, PBMCs, or activated PBMCs highly inhibited PBMC proliferation, indicating that inhibitory factors are released upon hASC activation. Many factors have been involved in MSC-mediated immunosuppression, including IFN-gamma, IL-10, hepatocyte growth factor, prostaglandin E2, transforming growth factor-beta1, indoleamine 2,3-dioxygenase (IDO), nitric oxide, and IL-10. Using pharmacological inhibitors, neutralizing antibodies, and genetically modified hASCs that constitutively express or silence IDO enzyme, we demonstrate that, in the case of hASCs, the IFN-gamma/IDO axis is essential. Taken together, our data support the key role of IDO in the therapeutic use of hASC on immunomediated diseases.