Xenografts are entering the age of clinical research. Researchers at the University of Maryland School of Medicine performed human heart transplants from pigs at both Massachusetts General Hospital and New York University, and recently performed scientists. Scientists at the University of Pennsylvania used pig liver to treat brain dead people with liver failure12. The current study was conducted to pre-assess the feasibility of pig-to-human liver xenografts. The use of genetic modifications and the environment without the designated pathogen may have prevented excessive rejection and potential PERV, PCMV, or other porcine virus infections in recipients.
An ectopic supplemental liver transplantation was performed as described. To ensure the best match, the donor and recipient major vessel caliber and flow velocity were assessed prior to surgery. This ensured sufficient blood perfusion for recipient xenograft and hemodynamic stability, avoiding graft dysfunction caused by hemodynamic disorders, as reported in the bibliography. 6. Adjuvant liver transplantation is the ideal bridge therapy for individuals with liver failure, as it is not difficult to reconstruct IVCs when the function of the original liver is restored or when an appropriate donor liver is available. The xenografts were removed and the IVC was reconstructed at the end of the study to simulate the above situation. Furthermore, our ectopic co-liver transplant protocol improved the efficiency of interventional thrombolysis directly from deep veins in the lower extremities. In the first case of human heart xenografts from pigs, microtrombi was discovered on terminal stage biopsy. Similarly, the current study found that D-Dimer levels were temporarily increased immediately after surgery (Extended Data Figure 5A). The xenograft was then made functional using timely thrombolysis.
Certainly, the flow of lower IVC is not physiological. Supplementary partially orthodontic liver transplantation must be performed to achieve physiological hemodynamics. However, this can remove part of the original liver and cause potential complications such as patient liver malfunction, bile leakage and bleeding. Our goal is to support patients with acute liver failure throughout a critical period, so there is no need to perform a fully physiologically compatible transplant. As long as xenografts can provide metabolic and coagulation functions at a specific time, this implantation is sufficient. In this study, IVC blood flow was used to supply xenografts, then returned to the heart. Throughout the study, no edema was observed in the lower limbs, indicating that circulation in the lower limbs was guaranteed. More importantly, the xenografts remained functional and hematology remained stable until the study was completed. Therefore, the nonphysiological flow of this study did not cause severe disturbances.
Overactute rejection is one of the most important questions regarding xenografting in preclinical models18. Fortunately, the current study found no evidence of overdose rejection. In addition to editing the glycoprotein α-galactosyltransferase 1 gene, a series of immunosuppressants were used, of which tacrolimus (FK506) played an important role. In this early stage of xenograft, tacrolimus was used at a concentration of 5 mg L -1 (the upper limit of normal) according to previous protocols. However, on the second day after surgery, high blood cell concentrations were observed. This may be due to heterogeneity in drug metabolism. The dose was adjusted within the time limit. In the later stages of this experiment, total bilirubin levels are elevated and may be associated with tacrolimus toxicity.
Whether to use Rituxan (Rituximab) during induced immunosuppression was one of the focuses of preoperative debate. Due to the great benefits of gene editing, humoral immunity has no longer significantly affects graft survival. Therefore, Rituxan is not included in immunosuppressive strategies for work related to liver xenograft19,20. Similarly, rituxan was not used on previous trails of pig-to-monkey xenografts, as B cells were not activated in these studies. Therefore, in this study, Rituxan was not initially used. When B cells began to increase, rituxan, which could theoretically remove the antibodies and plasma cells that were formed, had to be employed, along with plasma exchange and intravenous immunoglobulin therapy. This study shows that B-cell activation can occur in liver xenografts from pigs to humans. Further investigation is needed before incorporating Rituxan into an inducible immunosuppression strategy.
The discrepancies in the amounts of ALT and AST were unexpected and not observed in previous animal studies. Even more interesting, early stage AST spikes were detected in human heart xenografts from pigs performed in previous studies6. It is plausible that AST was released by cardiomyocytes. This is supported by an early increase in the amount of creatine kinase and creatinine kinase fascial zone observed at the same time point (Extended Data Figure 7e). As a result, myocardial damage should be assessed at the initial stages of liver transplantation and pharmacological myocardial protection performed as necessary. In particular, some cholestasis was observed in the original liver tissue of the recipient on day 10. This may explain the rise in bilirubin observed later. However, this was absent in xenografts. Therefore, current treatments may be slightly less toxic to pig liver than human liver.
Coagulation abnormalities are the main cause of xenograft dysfunction and occurred in previous cases of human heart xenograft 7 and monkey liver xenograft from pigs. However, no serious bleeding or coagulation disorder occurred in the current case. PT remained relatively stable after surgery, with APTT temporarily increasing in the early stage and then decreasing, and PLT temporarily decreasing in the early stage and then increasing. Hemorrhage disorders and coagulation disorders are significantly milder in this brain-dead recipient than in previous monkey recipients, indicating that humanized genetic modifications may function better in humans. Due to the advantages of ectopic coexistence liver transplantation, we were able to intervene after early rise of D-dimers to prevent potential PV thrombosis.
Future studies should choose a permanent placement of a ponsive graft or xenograft. Although xenografts were able to secrete bile and produce soy albumin in this study, it is unlikely that bile and soy albumin production would be sufficient to support the human body for a long period of time. As a result, as shown in the references. 17, current liver xenograft modalities may be more suitable as adjuvant bridge therapy for liver failure individuals awaiting the human liver. Nevertheless, it is important to design effective eyeglass-to-human liver xenograft methods for future patients.
We acknowledge the limitations of this study. First, depending on the recipient's family's request, the study was terminated on day 10, resulting in insufficient follow-up periods to analyse changes in xenograft function over a long period. Secondly, we can now measure only basic liver functions, such as albumin synthesis and bile secretion. However, this unique pig-to-human liver xenograft can provide important information that cannot be provided by animal experiments alone.
