Stable expression of the human thrombomodulin transgene in pig endothelial cells is associated with a reduction in the inflammatory response

Background: Xenotransplantation is associated with an inflammatory response. The proinflammatory cytokine, TNF-alpha, downregulates the expression of thrombomodulin (TBM), and induces coagulation dysfunction. Although human (h) TBM-transgenic pigs (p) have been developed to reduce coagulation dysfunction, the effect of TNF-alpha on the expression of hTBM and its functional activity has not been fully investigated. The aims of this study were to investigate (i) whether the expression of hTBM on pig (p) cells is down-regulated during TNF-alpha stimulation, and (ii) whether cells from hTBM pigs regulate the inflammatory response. Methods: TNF-alpha-producing T, B, and natural killer cells in blood from baboons with pig heart or kidney xenografts were investigated by flow cytometry. TNF-alpha staining in the grafts was detected by immunohistochemistry. Aortic endothelial cells (AECs) from GTKO/CD46 and GTKO/CD46/hTBM pigs were stimulated by hTNF-alpha, and the expression of the inflammatory/coagulation regulatory protein, TBM, was investigated. Results: After pig organ xenotransplantation, there was a trend to increases in TNF-alpha-producing T and natural killer cells in the blood of baboons. In vitro observations demonstrated that after hTNF-alpha stimulation, there was a significant reduction in the expression of endogenous pTBM on pAECs, and a significant increase in the expression of inflammatory molecules. Blocking of NF-kappa B signaling significantly up-regulated pTBM expression, and suppressed the inflammatory response induced by hTNF-alpha in pAECs. Whereas the expression of pTBM mRNA was significantly reduced by hTNF-alpha stimulation, hTBM expression on the GTKO/CD46/hTBM pAECs was not affected. Furthermore, after hTNF-alpha stimulation, there was significant suppression of expression of inflammatory molecules on GTKO/CD46/hTBM pAECs compared to GTKO/CD46 pAECs. Conclusions: The stable expression of hTBM in pig cells may locally regulate the inflammatory response. This will help suppress the inflammatory response and prevent coagulation dysregulation after xenotransplantation.