Introduction:The immune response occurs against islet graft immediately after islet transplantation has remained a major obstacle. We have shown that both the expression of TNF-related apoptosis-inducing ligand(TRAIL) on liver natural killer(NK) cells and anti-islet cytotoxicity of liver NK cells significantly increased after intraportal islet transplantation in a mouse model, suggesting that liver NK cells play a role in the destruction of islets transplanted into the liver. To resolve this problem, we focused on mesenchymal stem cells(MSCs), which have been shown to possess immune function. We hypothesized that co-transplantation of both MSCs and islets would improve graft function by suppressing the function of liver NK cells through prostaglandin E₂(PGE₂) from MSCs. Methods:We prepared splenocytes and/or liver mononuclear cells(LMNCs) and bone marrow-derived MSCs from C57BL/6 mice. Quantification of PGE₂ was performed using supernatants collected at different condition. To examine the suppressive effect of MSCs on activated splenic or liver NK cells, we cultured splenocytes and/or LMNCs with MSCs(MSCs group) or without MSCs(control group) in the presence of IL-2 for 3 days at various ratio. Then, cells were harvested, and cytotoxic activity against YAC-1(an NK-sensitive cell line) was confirmed by standard 51Cr-release assay. The expression of TRAIL on the NK cells was analyzed by flow cytometry.

Results:Our findings showed that the proliferation of IL-2-stimulated splenocytes and LMNCs was suppressed in a dose-dependent manner, and the proportion of TRAIL-expressing liver NK cells was significantly lesser in the MSC group than in the control group(14.0%±3.1%vs.5.7%±0.5%;p<0.05). Furthermore, the proportion of TRAIL-expressing liver NK cells was correspondingly reduced under co-culture with PGE₂ when compared to the control group(24.5%±4.4%vs.19.7%±3.3%). IL-2-stimulated splenocytes and LMNCs showed potent cytotoxicity against YAC-1 when compared with fresh splenocytes and LMNCs (17.5%±0.4%vs.1.1%±0.0%and54.7%±4.1%vs.8.7%±0.6%,respectively). In contrast, the cytotoxic activity of IL-2-stimulated splenocytes showed a 10-fold reduction when these cells were co-cultured with MSCs(17.5%±0.4%vs.1.4%±1.2%). Conclusion:Our results suggest that PGE₂ secretion from MSCs can suppress both activated splenic and liver NK cells via the TRAIL regulative pathway; thus, MSCs can be used for suppressing liver NK cells to prevent islet destruction in clinical islet transplantation.

« Back to 2013 American Transplant Congress