Kidney transplant rejection is a major component in the poor prognosis of organ transplantation. Due to the multiple complicated mechanisms involved, a novel therapy remains under exploration. Endometrial regenerative cells (ERCs) have been ubiquitously applied to various refractory immune-related diseases, but the role of ERC-derived exosomes (ERC-Exos) in alleviating transplant rejection has not been thoroughly studied. Cluster of differentiation 3 (CD3) plays an important role in regulating immune responses. In this study, we have demonstrated for the first time that ERC-Exo carried with siCD3 attenuated allograft rejection by inhibiting T-cell proliferation and differentiation.

C57BL/6 mouse recipients receiving bm12 mouse kidney allografts were randomly divided into four groups. Graft pathological changes were evaluated by H&E staining. Splenic immune cell populations were analyzed using flow cytometry. Serum cytokine profiles of recipients were measured by ELISA. The proliferation capacity of CD8+T cell populations was also assessed in vitro. α-2,6-sialylation levels in CD8+T cells were measured by SNA blot.

In vivo, mice treated with ERC-siCD3 Exos achieved significantly prolonged allograft survival. Serum cytokine profiles of recipients were significantly changed in ERC-siCD3 Exos-treated recipients. In vitro, we found that ERC-siCD3 Exos considerably down-regulated the α-2,6-sialyltransferase (ST6GAL1) expression in CD8+T cells, and significantly reduced α-2,6-sialylation levels. Through desialylation modification, ERC-siCD3 Exo therapy significantly decreased CD8+T cell proliferation and inhibited CD8+T cell differentiation into Th1 and Th17 cells while promoting Treg differentiation.

ERC Exo carrying siCD3 reduces the sialic acid connected to α-2,6 at the end of the N-glycan chain on the CD8+T cell surface, increases the number of therapeutic exosomes endocytosed into CD8+T cells and inhibits activation of T-cell receptor signaling pathways, which prolongs allograft survival. This study confirms the feasibility of ERC-derived exosomes as natural carriers combined with gene therapy, which could be used as a potential therapeutic strategy to alleviate allograft rejection.