Immunosuppression of Human Adipose-Derived Stem Cells on T Cell Subsets via the Reduction of NF-kappaB Activation Mediated by PD-L1/PD-1 and Gal-9/TIM-3 Pathways

Adipose-derived stem cells (ADSCs) are a type of multipotent mesenchymal stem cells with immunosuppressive capacities. However, the underlying mechanisms involved in the inhibitory effects of ADSCs on T cells are not completely elucidated. In this study, human peripheral blood mononuclear cells (PBMCs) stimulated with anti-CD3/CD28 antibody-coated beads were cultured with or without allogeneic ADSCs (ADSC-to-PBMC ratio, 1:5). Surface marker levels, violet-labeled cell proliferation, apoptosis, interferon-gamma (IFN-gamma) production, and nuclear factor-kappaB (NF-kappaB) phosphorylation of CD4(+) and CD8(+) T cells were detected using flow cytometry. It was observed that ADSCs significantly suppressed the proliferation and IFN-gamma production but enhanced apoptosis of both CD4(+) and CD8(+) T cells in T cell receptor (TCR)-stimulated PBMCs. The expressions of programmed death-ligand 1 (PD-L1) and galectin 9 (Gal-9) on ADSCs were significantly upregulated and induced during coculture with PBMCs. TCR-stimulated CD4(+) and CD8(+) T cells cultured with ADSCs had higher expression levels of programmed death-1 (PD-1) and T cell immunoglobulin and mucin-containing protein-3 (TIM-3) than those in cells cultured without ADSCs. Moreover, the suppressive effects of ADSCs on T cells in terms of proliferation and IFN-gamma production were significantly reversed in the presence of anti-PD-L1 and anti-Gal-9 antibodies. Importantly, the phosphorylation of NF-kappaB in CD4(+) and CD8(+) T cells cocultured with ADSCs was significantly inhibited, and this inhibition was significantly attenuated via the PD-L1 and Gal-9 blockades. In conclusion, human ADSCs perform immunoregulatory functions partially through the inhibition of NF-kappaB activation in T cells via the PD-L1/PD-1 and Gal-9/TIM-3 pathways, which provide new insights into the mechanism of human ADSC-mediated immunomodulation.