Induction of Regulatory T Cells and Its Regulation with Insulin-like Growth Factor/Insulin-like Growth Factor Binding Protein-4 by Human Mesenchymal Stem Cells

Human mesenchymal stem cells (MSCs) are multipotent and exert anti-inflammatory effects, but the underlying mechanism remains to be elucidated. In the current study, we investigated the regulatory mechanism of regulatory T cell (Treg) induction through the growth factors released by human MSCs. Human naive CD4(+) T cells were stimulated with anti-CD3/28 Abs and cocultured with human MSC culture supernatant for 48 h. The proliferation and cytokine production of CD4(+) T cells and surface molecule expression on CD4(+) T cells were evaluated. The proliferation of anti-CD3/28 Abs-stimulated CD4(+) T cells was suppressed by the addition of human MSC culture supernatant; in addition, the production of IL-10 and IL-4 increased. The human MSC culture supernatant induced CD4(+)FOXP3(+) Tregs that expressed CD25, CTLA-4, glucocorticoid-induced TNFR-related protein, insulin-like growth factor (IGF)-1R, and IGF-2R, showing antiproliferative activity against CD4(+) T cells. In addition, the induction of Tregs by human MSC culture supernatant was enhanced by the addition of IGF and suppressed by the inhibition of IGF-1R. In contrast, a significant amount of IGF binding protein (IGFBP)-4, an inhibitor of IGF action, was detected in the human MSC culture supernatant. After neutralization of IGFBP-4 in the human MSC culture supernatant by anti-IGFBP-4 Ab, Treg numbers increased significantly. Thus, our results raise the possibility that human MSC actions also involve a negative-regulatory mechanism that suppresses Treg proliferation by releasing IGFBP-4. The results of this study suggest that regulation of IGF may be important for treatments using human MSCs.