Microenvironmental cues enhance mesenchymal stem cell-mediated immunomodulation and regulatory T-cell expansion

Abstract

Mesenchymal stem cells (MSCs) are known to both have powerful immunosuppressive properties and promote allograft tolerance. Determining the environmental oxygen tension and inflammatory conditions under which MSCs are optimally primed for this immunosuppressive function is essential to their utilization in promoting graft tolerance. Of particular interest is the mechanisms governing the interaction between MSCs and regulatory T cells (Tregs), which is relatively unknown. We performed our experiments utilizing rat bone marrow derived MSCs. We observed that priming MSCs in hypoxia promotes maintenance of stem-like characteristics, with greater expression of typical MSC cell-surface markers, increased proliferation, and maintenance of differentiation potential. Addition of autologous MSCs to CD4+/allogeneic endothelial cell (EC) co-culture increases regulatory T cell (Treg) proliferation, which is further enhanced when MSCs are primed in hypoxia. Furthermore, MSC-mediated Treg expansion does not require direct cell-cell contact. The expression of indolamine 2,3-dioxygenase, a mediator of MSC immunomodulation, increases when MSCs are primed in hypoxia, and inhibition of IDO significantly decreases the expansion of Tregs. Priming with inflammatory cytokines IFNγ and TNFα increases also expression of markers associated with MSC immunomodulatory function, but decreases MSC proliferation. The expression of IDO also increases when MSCs are primed with inflammatory cytokines. However, there is no increase in Treg expansion when MSCs are primed with IFNγ, suggesting an alternate mechanism for inflammatory-stimulated MSC immunomodulation. Overall, these results suggest that MSCs primed in hypoxia or inflammatory conditions are optimally primed for immunosuppressive function. These results provide a clearer picture of how to enhance MSC immunomodulation for clinical use.

CD146+CD107a+ Mesenchymal Stem/Stromal Cells with Signature Attributes Correlate to Therapeutic Potency as “First Responders” to Injury and Inflammation

“…The results obtained with UNF Naïve and Primed cohorts built the foundation for the subsequent evaluation of the CD146+ (POS) and CD146-(NEG) subpopulations, where correlative evidence suggested the contribution of each subpopulation within the whole UNF preparation. Cell priming has been used as a strategic method to incite an analyzable response by the cells or to pre-condition them to augment a desired trait or effect (Kadle et al, 2018;Silva et al, 2018). Moreover, priming BM-MSC prior to performing immunopotency assays using target cells better recapitulates the in vivo pathologic events involving active secretion of inflammatory molecules followed by cellular infiltration of immune cells (e.g., T cells and whole PBMC) and activation of resident cells (e.g., macrophages) typical of tissue damage (Julier et al, 2017).…”

Mesenchymal stem cells: a promising way in therapies of graft-versus-host disease

“…IFN-γ generated from T cells suppress the proliferation of T cells, activating rat BM-MSCs by low concentrations of IFN-γ. While high concentrations of IFN-γ won't take effect as mentioned above [52]. Moreover, transforming growth factor-β (TGF-β) and Prostaglandin E2 (PGE2) were further correlated to the function of MSCs.…”

Mesenchymal stromal cell-derived extracellular vesicles for regenerative therapy and immune modulation: Progress and challenges toward clinical application

“…13,14 Hypoxia can also enhance immune modulation by MSCs through increased secretion of indoleamine-pyrrole 2,3-dioxygenase (IDO) and increased Treg induction. 15 Inflammatory conditions, meanwhile, were associated with increased IDO secretion by MSCs, but Treg induction was unchanged. 15 Other signaling pathways can also be influenced by exogenous signals introduced during the culture phase of EVproducing cells.…”

“…15 Inflammatory conditions, meanwhile, were associated with increased IDO secretion by MSCs, but Treg induction was unchanged. 15 Other signaling pathways can also be influenced by exogenous signals introduced during the culture phase of EVproducing cells. Adipose-derived MSC treated with platelet-derived growth factor release EVs with enhanced levels of stem cell factor F I G U R E 1 Method of extracellular vesicle isolation.…”