IFNγ Licensed Human Bone Marrow Derived Mesenchymal Stromal Cells Inhibit T Cell Cytokine Production by a Mechanism Independent of Indoleamine 2 3-Dioxygenase (IDO) Activity

Abstract 1255

Human Bone marrow derived Mesenchymal Stromal Cells (MSCs) inhibit activation-mediated T cell proliferation. This functional interaction serves nearly universally as a surrogate assay for immune suppressive activity and potency of MSCs in vitro. However the role of MSCs in inhibiting T cell function, cytokine production in particular, has not been investigated thoroughly. In the present study we have compared resting MSCs with IFNγ licensed MSCs for their ability to inhibit activated T cell function such as cytokine secretion and degranulation through intracellular cytokine staining assays. PBMCs cocultured with resting or inflammatory cytokine licensed MSCs were stimulated with the super antigen Stephylococcal Enterotoxin B (SEB) for 12–14hours in the presence of Brefeldin A. Intracellular cytokine staining was performed on the T cells to detect the Interferon gamma (IFNγ), Tumor Necrosis Alpha (TNFα) and Interleukin-2 (IL-2). Our results demonstrate that resting MSCs do not inhibit T cell cytokine secreting function. However, IFNγ and IFNγ plus TNFα licensed MSCs dose dependently inhibit IFNγ secretion by T cells. Our results also show that IFNγ and IFNγ plusTNFα licensed MSCs not only inhibit cytokine secretion but also inhibit dregranulation of activated T cells. Boolean gating analysis demonstrates that IFNγ and IFNγ plusTNFα licensed MSCs inhibit triple cytokine producing highly inflammatory IFNγ +TNFα +IL2+T cells. Phenotypic analysis of MSCs demonstrates that IFNγ licensing upregulate indoleamine 2 3-dioxygenase (IDO) and B7-H1. Blocking of IDO activity with 1-Methyl D,L Tryptophan (1MT) will abolish MSC-mediated blockade of T cell proliferation. However, 1MT does not reverse the MSC blockade of T cell cytokine secretion. Phenotypical analysis of T cells demonstrate that PD1+ cells are inhibited while PD1- cells are not inhibited suggesting the role of B7-H1 and PD-1 inhibitory pathway is involved in the inhibitory potential of IFNγ licensed MSCs. Interestingly, the inhibitory potential of IFNγ licensed MSCs has been observed only with the SEB stimulation but not with anti-CD3, CD28 stimulation. This suggests that MHC-TCR interaction is necessary for the inhibitory effect of IFNγ licensed MSCs. Our results demonstrate the superiority of IFNγ licensed MSCs in inhibiting multiple cytokine producing T cell function independent of IDO activity. Our results also provide the rationale for use of IFNγ licensed MSCs in autologous immunosuppressive cell therapy.