Bone marrow mesenchymal stromal cells protect allograft lung transplants from acute rejection via the PD-L1/IL-17A axis

Purpose Using a rat model of allograft lung transplantation, we investigated the effectiveness of mesenchymal stromal cells (MSCs) as prophylactic and therapeutic agents against the acute rejection of lung grafts. Methods Lung grafts were harvested from donor rats and transplanted orthotopically into major histocompatibility complex-mismatched rats. MSCs were administered to the recipients once (on day 0) or twice (on days 0 and 3) after transplantation. The grade of acute rejection was evaluated both macroscopically and microscopically 6 days after transplantation. To elucidate the related mechanism, mRNA levels of inflammatory cytokines and immunomodulatory receptors in the transplanted grafts were measured using quantitative RT-PCR. Results The lung graft tissue from the rats that received MSCs post-surgically was protected from acute rejection significantly better than that from the untreated controls. Notably, the rats administered MSCs twice after surgery exhibited the least signs of rejection, with a markedly upregulated mRNA level of PD-L1 and a downregulated mRNA level of IL-17A. Conclusion This study assessed MSC protection of lung allografts from acute rejection by modulating T cell activity via enforced expression of PD-L1 in transplants and downregulation of IL-17A.