Mesenchymal stem cells empower T cells in the lymph nodes via MCP-1/PD-L1 axis.

Mesenchymal stem cells (MSCs) are a type of immunosuppressive stromal cell found in multiple tissues and organs. However, whether MSCs possess immunosupportive characteristics remains unclear. In this study, we showed that the lymph nodes contain immunosupportive MSCs. They produce and secrete a high level of MCP-1 to promote T-cell proliferation and differentiation, in contrast to bone marrow MSCs (BMMSCs), which repress T-cell activation. Unlike BMMSCs, lymph node MSCs (LNMSCs) fail to respond to activated T-cell-induced production of PD-L1 to induce T-cell apoptosis. Mechanistically, MCP-1 activates phospho-Erk to sustain T-cell proliferation and activation while it represses NF-κB/PD-L1 pathway to avoid induction of T-cell apoptosis. Interestingly, inflammatory lymph node-derived LNMSCs abolish their immunosupportive function due to reduction of MCP-1 expression. Finally, we show that systemic infusion of LNMSCs rescues immunosuppression in cytoxan (CTX)-treated mice. This study reveals a previously unrecognized mechanism underlying MSC-based immunoregulation using the MCP-1/PD-L1 axis to energize T cells and suggests a potential to use MSCs to treat immunosuppressive disorders.