Interferon-gamma and Interleukin-17 Modified Mesenchymal Stem Cells (MSC) Directly or Indirectly Modulate T Cell Responses By Expressing Inhibitory Factors, Downregulating T Cell Activation and Inducing Regulatory T Cells.

Abstract

MSC have immunosuppressive properties beneficial for transplantation cellular therapy. We modified human bone marrow-derived MSC with inflammatory cytokines as a strategy to enhance MSC immunosuppression on T cells. MSC were preconditioned with inflammatory cytokines IFN-γ, TNF-α, IL-1β, IL-2, IL-12 and IL-17 for 5d and were co-cultured with T cells activated by the mitogen phytohemagglutinin (PHA). Modified MSC displayed greater immunosuppression on T cell proliferation compared to unmodified-MSC (UT:MSC). IL-6 gene expression significantly increased in TNF-α and IL-1β-modified MSC following 5d of preconditioning. MSCγ and TNF-α-modified MSC upregulated cyclooxygenase gene expression relative to UT:MSC while only IFN-γ induced indoleamine 2,3-dioxygenase expression in MSC. TGF-β1 gene expression was unaffected following cytokine modification of MSC and IL-10 was undetectable. Mechanistically, only IFN-γ modified MSC (MSCγ) increased the T cell negative co-stimulatory molecule B7-H1. Neutralization of B7-H1 failed to restore T cell proliferative responses suggesting a partial but non-exclusive role of B7-H1 in MSCγ immunosuppression. Furthermore, UT:MSC, MSCγ and IL-17 preconditioned MSC (MSC17) downregulated the T cell activation marker CD25 on CD4+ and CD8+ T cells to a similar extent but does not affect CD69 on T cells. Additionally, an increase in proportion of CD4+CD25hiCD127loFoxp3+ regulatory T cells (Tregs) was observed in PHA-activated T cells co-cultured with MSCγ (1.8 to 4.2-fold) and MSC17 (2.3 to 3-fold) relative to UT:MSC; an effect dependent on the MSC donor and responder T cells. In subsequent experiments, MSCγ and MSC17 that were co-cultured with PHA-activated CD4+CD25- T cells showed greater induction of Tregs (iTregs) compared to UT:MSC, with MSC17 showing highest iTregs up to 8.2-fold increase relative to UT:MSC. In 2 of 3 MSC donors, prostaglandin-2 protein levels were highest in MSC17 suggesting a possible involvement of prostaglandin-2 in MSC17-mediated Treg induction. In conclusion, proinflammatory cytokine preconditioning enhances immunosuppression in MSC.