Introduction: Despite significant progress in heart and kidney xenotransplantation, long-term survival after pig-to-NHP lung xenotransplantation has not yet been achieved. The underlying causes of rapid lung failure in most experimental transplantations are not yet fully understood. In contrast, ex vivo organ perfusion of human donor lungs has been established in a few centers worldwide, allowing for constant monitoring of lung function and the possibility to precondition donor lungs using treatments such as cold perfusion and specific gene or cell therapeutics. Here, we used a clinical-grade ex vivo lung perfusion (EVLP) system to simulate xenotransplantation of pig organs and to establish a hypothermic lung perfusion as a conditioning treatment to improve transplantation outcome.
Methods: Eight lungs (four wild-type (wt) and four triple-knockout (GGTA1, CMAH, B4GALNT2)) were surgically explanted and preserved using clinical-grade cold perfusion. After cold ischemia of up to 2 hours, the lungs were connected to an EVLP system (XPS, XVIVO) and perfused at 10°C for 2 hours using cell-free Steen solution. The perfusate was then exchanged for human blood, which was prepared from erythrocyte concentrates, fresh frozen plasma, and a buffy coat obtained from the Hannover Medical School blood bank. Coagulation was inhibited by adding heparin, and calcium was added to maintain functionality. The blood was warmed to 37°C, and porcine lungs were perfused and ventilated for up to 6 hours. In addition to functional parameters, total blood count, D-Dimer, CRP, and IL-6 were measured. Lung edema was quantified at the time of explantation.
Results: Triple-KO porcine lungs could be perfused for 6 hours, whereas the wild-type (wt) lungs could only be perfused for 4-5 hours due to accumulation of pulmonary edema (up to 300% of initial weight). The oxygenation capacity of wt lungs was lower compared to triple-KO lungs, with a high variability observed between individual lungs. IL-6 and CRP levels were barely measurable in both groups, while wt lungs showed a significant higher increase in D-Dimer concentration compared to triple-KO lungs.
Conclusion: The clinical XPS EVLP system was successfully used to simulate pig-to-human xeno- lung transplantation for up to 6 hours, including hypothermic preconditioning. The triple-KO lungs maintained good lung function, but a rise in D-Dimer and weight indicated ongoing processes of rejection and coagulation processes.
Off-note: During the time of experimental xeno- lung perfusions, the team performed the first human EVLP using the XPS system at Hannover Medical School, emphasizing the direct transfer of knowledge between xeno- and allo- lung transplantation.