GalTKO.hCD46 Transgenic Pig Lungs: 4-Year Experience in a Xenogenic Perfusion Model

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Purpose: Perfusion of wild type pig lungs with human blood leads within minutes to hyperacute rejection that is associated with the immediate sequestration of circulating platelets and neutrophils and the activation of the coagulation and complement cascade. The generation of GalTKO pigs has significantly improved survival, however, the described reactions are still present even though at a lower level only. To further control the activation of the complement cascade, a human complement regulatory protein (hCPRP) gene was inserted on the basis of a GalTKO-pig. Those GalTKO.hCD46 transgenic organs have been use in xenotransplantation for several years now. Here we present the results of our 4-year experience with the use of GalTKO.hCD46 pig lungs in a xenogenic lung perfusion model. Methods: Wildtype (n=17), GalTKO (n=16) and GalTKO.hCD46 transgenic pig lungs (n=31) were perfused with heparinized fresh human blood until failure or elective termination after 4 hours. At prespecified time points, blood and tissue samples were collected. Pulmonary artery (PA) flow and pressure were recorded online. Results: Median survival time (MST) in the wild type group was 10‘, in the GalTKO cohort 120‘. The additional expression of hCD46 showed a trend to higher MST of 180′ (p=0.21). Pulmonary vascular resistance was not improved in the GalTKO.hCD46 group when compared to GalTKO alone. Platelet sequestration was significantly reduced in the early perfusion phase (% initial platelets remaining at 5‘: GalTKO.hCD46 51±34 vs. GalTKO 26±14, p=< 0.05) but not at the later time points. Complement activation measured by C3a level was lower at all time points in the GalTKO.hCD46 group with statistically highly significant lower level after 2h of perfusion (GalTKO.hCD46 237±175 vs. GalTKO 873±1002, p= 0.009). Conclusion: Complement activation is better controlled in GalTKO pig lungs genetically modified to express hCD46, and presumably contributes to the trend toward longer survival of those organs. However, various other rejection mechanisms like activation of the coagulation cascade, platelet sequestration, and/or non-Gal antibody-mediated rejection lead to organ injury. Additional interventions targeted to these mechanisms will very likely be necessary to further advance lung xenotransplantation toward clinical application.