Priming Mesenchymal Stem/Stromal Cells with a Combination of a Low Dose of IFN-γ and Bortezomib Results in Potent Suppression of Pathogenic Th17 Immunity Through the IDO1-AHR Axis

Abstract

Preconditioning of mesenchymal stem/stromal cells (MSCs) with the inflammatory cytokine IFN-γ enhances not only their immunosuppressive activity but also their expression of HLA and proinflammatory genes. We hypothesized that prevention of the upregulation of inflammatory cytokines and HLA molecules in IFN-γ-primed MSCs would render these cells more immunosuppressive and less immunogenic. In this study, we discovered the following findings supporting this hypothesis: 1) activated human T cells induced the expression of IDO1 in MSCs via IFN-γ secretion and those MSCs in turn inhibited T-cell proliferation in an AHR-dependent fashion; 2) there was no difference in the expression of IDO1 and HLA-DR in MSCs after priming with a low dose (25 IU/ml) versus a high dose (100 IU/ml) of IFN-γ; 3) the transient addition of bortezomib, a proteasome inhibitor, to culture MSCs after IFN-γ priming decreased the expression of HLA-DR, inflammatory cytokine genes and Vcam1 while increasing the expression of IDO1 and the production of L-kynurenine; finally, MSCs primed with a combination of a low dose of IFN-γ and bortezomib were more effective in inhibiting Th17-mediated idiopathic pneumonia syndrome (IPS) and chronic colitis than unprimed MSCs. Our results suggest that bortezomib significantly eliminates the unfavorable effects of IFN-γ priming of MSCs (increased expression of MHC molecules and inflammatory cytokines and cell aggregation genes) and simultaneously increases their immunosuppressive activity by upregulating IDO1. Taken together, our newly established MSC priming method may contribute to MSC-based cell therapy for inflammatory diseases.

A novel role of CD73-IFNγ signalling axis in human mesenchymal stromal cell mediated inflammatory macrophage suppression

“…The endowment of immune modulatory behaviour to MSCs upon exposure to pro-inflammatory cytokines is termed as inflammatory licensing. IFNγ, either alone or in combination with other pro-inflammatory cytokines, immune licenses MSCs in vitro and enhances their therapeutic outcomes [ 3 , 21 ]. In fact, blocking IFNγ reception or deficiency of IFNγR1 in MSCs has been shown to annul MSC mediated immunosuppression [ 6 , 20 , 21 ].…”

“…IFNγ, either alone or in combination with other pro-inflammatory cytokines, immune licenses MSCs in vitro and enhances their therapeutic outcomes [ 3 , 21 ]. In fact, blocking IFNγ reception or deficiency of IFNγR1 in MSCs has been shown to annul MSC mediated immunosuppression [ 6 , 20 , 21 ]. To evaluate whether CD73-KDN MSCs are receptive to IFNγ-mediated immune-licensing, CD73-KDN cells were treated with IFNγ and induction of IDO, a prototypic interferon gamma stimulated gene (ISG), and an immunomodulatory molecule was assessed as a readout of IFNγ-sensing ability.…”

Unveiling the functional heterogeneity of cytokine-primed human umbilical cord mesenchymal stem cells through single-cell RNA sequencing

“…An increase in the level of HLA-DR on IFN-γ-primed MSCs can elicit transplant rejection after cell transplantation, which can lead to increased MSC death and the induction of allogeneic immune reactions [ 37 , 38 ]. Methods for reducing the rejection of allogeneic IFN-γ-primed MSCs may be necessary for overcoming the limitations of MSCs in clinical translation [ 39 ]. No reports associated with the biological functions of IL-4 in MSCs have been published, and our study is the first to uncover the functions of IL-4.…”

Immune regulation through tryptophan metabolism

“…IFN-γ has been widely tested for priming mesenchymal stem cells (MSCs) to enhance their immunosuppressive activity; however, this priming approach has side effects. We devised a method to reduce the side effects of IFN-γ in MSCs: priming with a low dose of IFN-γ followed by bortezomib, a proteasome inhibitor, lowered the expression of class II MHC molecules, inflammatory cytokines and the cell adhesion molecule VCAM1 with intact IDO1 expression 107 . Transplantation of primed MSCs efficiently prevents acute graftversus-host disease (GVHD) and IPS.…”