Background Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by synovitis and subsequent joint destruction. Biological agents and Janus kinase inhibitors have proven to be more effective than conventional treatments. However, no effective treatment for repairing damaged joints has yet been established. Human mesenchymal stem cells (hMSCs) are multipotent and are expected as potential therapeutic tools for promoting tissue repair at various sites, including joints in RA. Human MSCs also have the capacity to modulate immune responses, but the underlying mechanism remains elucidated.

Objectives In the present study, we investigated the regulatory mechanism of induce regulatory T cells (Treg cells) induction through the growth factors released by hMSCs.

Methods Human naïve CD4⁺T cells were stimulated with anti-CD3/28 antibodies and co-cultured with hMSC culture supernatant for 48 hours. The proliferation and cytokine production of CD4⁺T cells and surface molecule expressions on CD4⁺T cells were evaluated.

Results The proliferation of anti-CD3/28 antibody-stimulated CD4⁺T cells was suppressed by the addition of hMSCs culture supernatant, but production of IL-10 and IL-4 from CD4⁺T cells were induced the supernatant. The hMSCs supernatant induced CD4⁺FoxP3⁺Treg cells. The induced CD4⁺FoxP3⁺Treg cells expressed CD25, CTLA-4, GITR, and IGF (insulin-like growth factor)-1R and IGF-2R and revealed anti-proliferative activity against CD4⁺T cells. In addition, the induction of Treg cells by the hMSCs supernatant was enhanced by addition of rhIGF-1/2 and suppressed by inhibition of IGF-1R. The MSCs supernatant include not only IGF-1 and IGF-2 but also a significant amount of IGFBP-4, an inhibitor of IGF action. After neutralization of IGFBP-4 in the hMSCs culture supernatant by anti-IGFBP-4 antibodies, the number of the Treg cells increased significantly as compared to the neutralization of IGFBP-3.

Conclusions Human MSCs induced CD4⁺IGF1R⁺IGF2R⁺FoxP3⁺Treg cells responsive to IGF signaling thorough the secretion of soluble factors. On the other hand, hMSCs are also involved in a negative regulatory mechanism, which suppresses Treg cells proliferation by releasing IGFBP-4, indicating differential regulation of Treg cells by the MSCs: positive regulation by IGF and negative regulation by IGFBP-4. The present results also suggest that the inhibition of IGFBP-4 may be necessary for the efficient application of MSC therapy in the context of joint repair in RA

Disclosure of Interest I. Miyagawa: None declared, S. Nakayamada: None declared, K. Nakano: None declared, K. Yamagata: None declared, K. Sakata Employee of: Mitsubishi Tanabe pharma corporation, K. Yamaoka: None declared, Y. Tanaka Grant/research support from: Mitsubishi-Tanabe, Takeda, Chugai, Astellas, Eisai, Taisho-Toyama, Kyowa-Kirin, Abbvie, Bristol-Myers, Consultant for: Abbvie, Daiichi-Sankyo, Chugai, Takeda, Mitsubishi-Tanabe, Bristol-Myers, Astellas, Eisai, Janssen, Pfizer, Asahi-kasei, Eli Lilly, GlaxoSmithKline, UCB, Teijin, MSD, Santen