Background
Transgenic expression of human complement regulatory proteins (hCRPs) reduces the frequency of hyperacute rejection (HAR) in Gal-positive cardiac xenotransplantation. In this study we examine the impact of human CD55 (hCD55) expression on a Gal knock-out (GTKO) background using pig-to-primate heterotopic cardiac xenotransplantation.
Methods
Cardiac xenotransplantation was performed with GTKO (Group 1; n=6) and GTKO.hCD55 (Group 2; n=5) donor pigs using similar immunosuppression. Cardiac biopsies were obtained 30 minutes after organ reperfusion. Rejection was characterized by histology and immunohistology. Intragraft gene expression, serum non-Gal antibody and antibody recovered from rejected hearts were analyzed.
Results
HAR of a GTKO heart was observed. Remaining grafts developed delayed xenograft rejection. Median survival was 21 and 28 days for Groups 1 and 2 respectively. Vascular antibody deposition was uniformly detected 30 minutes after organ reperfusion and at explant. A higher frequency of vascular C5b deposition was seen in GTKO organs at explant. Serum non-Gal antibody, antibody recovered from the graft and intragraft gene expression were similar between the groups.
Conclusion
HAR of GTKO hearts without hCD55 may occur. Expression of hCD55 appeared to restrict local complement activation, but did not improve graft survival. Chronic vascular antibody deposition with evidence of protracted endothelial cell activation was seen. These observations suggest that non-Gal antibody-induced chronic endothelial cell activation coupled to possible haemostatic incompatibilities may be the primary stimulus for DXR of GTKO hearts. To avoid possible HAR, future clinical studies should employ donors expressing hCRPs in the GTKO background.
Ion channels regulate cell proliferation, differentiation, and migration in normal and neoplastic cells through cell-cell and cell-extracellular matrix (ECM) transmembrane receptors called integrins. K + flux through the human ether-à-gogo-related gene 1 (hERG1) channel shapes action potential firing in excitable cells such as cardiomyocytes. Its abundance is often aberrantly high in tumors, where it modulates integrin-mediated signaling. We found that hERG1 interacted with the b 1 integrin subunit at the plasma membrane of human cancer cells. This interaction was not detected in cardiomyocytes because of the presence of the hERG1 auxiliary subunit KCNE1 (potassium voltage-gated channel subfamily E regulatory subunit 1), which blocked the b 1 integrin-hERG1 interaction. Although open hERG1 channels did not interact as strongly with b 1 integrins as did closed channels, current flow through hERG1 channels was necessary to activate the integrin-dependent phosphorylation of Tyr 397 in focal adhesion kinase (FAK) in both normal and cancer cells. In immunodeficient mice, proliferation was inhibited in breast cancer cells expressing forms of hERG1 with impaired K + flow, whereas metastasis of breast cancer cells was reduced when the hERG1/b 1 integrin interaction was disrupted. We conclude that the interaction of b 1 integrins with hERG1 channels in cancer cells stimulated distinct signaling pathways that depended on the conformational state of hERG1 and affected different aspects of tumor progression.
Significant prolongation in xenograft survival is achieved by improved immunosuppression. These results suggest that ongoing immune responses remain the major stimulus for DXR.
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