Pig Liver Xenotransplant: 171-Day Survival & Future of Hepatology

The field of xenotransplantation took a significant step forward this month, with researchers reporting a patient with hepatocellular carcinoma survived 171 days following a transplant with a genetically modified pig liver. Published in the Journal of Hepatology, the case offers the first evidence of feasibility for this procedure in a living recipient, though experts caution it remains firmly in the proof-of-concept stage. The study, conducted by a team at The First Affiliated Hospital of Anhui Medical University in China, addresses a critical need for increased organ availability for liver transplantation.

Bridging the Gap in Liver Transplantation

Liver transplantation is often hampered by a severe shortage of donor organs. According to the Organ Procurement and Transplantation Network (OPTN), over 40,000 people are currently on the waiting list for liver transplants in the United States alone. OPTN data shows that many die even as waiting. This scarcity drives the search for alternative solutions, and xenotransplantation – transplanting organs from animals, typically pigs – is emerging as a promising avenue. Pigs are considered suitable candidates due to their physiological similarities to humans and their relatively rapid reproductive rates.

The Procedure and Initial Success

The patient in the Chinese study had a large hepatocellular carcinoma (HCC) that rendered their liver ineligible for traditional surgical resection. Researchers incorporated 10 targeted gene edits into the pig liver to minimize the risk of immune rejection and viral transmission. The modified pig liver was transplanted as an auxiliary organ, meaning it was added alongside the patient’s existing liver, rather than replacing it entirely.

In the first month post-transplant, the patient experienced a smooth recovery, with stable liver and kidney function. Notably, the researchers observed no hyperacute or acute rejection, nor any significant complications. “For the first month, everything went smoothly, the patient recovered very well,” explained Beicheng Sun, MD, PhD, lead author of the study. “Liver function was great, everything was good.” The team reported that the pig liver appeared to function effectively, providing essential metabolic support.

Challenges and Complications

However, the initial success was not sustained. After 38 days, the patient developed thrombotic microangiopathy (TMA) – a condition involving the formation of small blood clots – due to complement activation, a part of the immune response. While C5b9 antibody usage was attempted, it did not resolve the TMA. The patient also experienced anemia and renal injury. The xenograft was removed after 38 days, as the remaining portion of the patient’s native liver was deemed capable of functional compensation. The patient unfortunately died on day 171 following repeated upper gastrointestinal hemorrhage.

Despite the patient’s eventual death, researchers emphasize the significance of the 171-day survival as proof of concept. “From this patient People can see that the pig liver can serve as a bridge function to human liver transplantation,” Sun stated. “If we use a pig liver as a bridge, we can have enough time for a liver donor or we can wait for liver regeneration.”

Extracorporeal Liver Cross-Circulation: An Alternative Approach

While the Chinese team focused on in vivo xenotransplantation, other researchers are exploring alternative strategies. A study published in Nature Medicine, led by Abraham Shaked, MD, PhD, at the University of Pennsylvania, investigated extracorporeal liver cross-circulation with genetically modified pig livers in four deceased individuals. The Nature Medicine study assessed early immune responses and the ability of the pig liver to provide physiological support.

This approach involves connecting the patient’s circulatory system to a pig liver outside the body, allowing the pig liver to filter and detoxify the blood. “We are using it as more of a dialysis machine, to provide detoxification, metabolic and synthetic liver in cases of acute or chronic liver failure,” Shaked explained. “The goal is to bridge the patient to recovery or bridge the patient to transplantation.” This method aims to avoid the complexities of long-term immune suppression associated with in vivo transplantation.

Genetic Engineering and Immunosuppression

Both approaches rely heavily on genetic engineering to modify pig organs and minimize the risk of rejection. The pig livers used in Shaked’s study had undergone a “triple glycan knockout” and had been inserted with seven human transgenes, along with inactivation of porcine endogenous retroviruses. Researchers also utilized immunosuppressive agents, such as methylprednisolone, to further suppress the immune response.

Robert S. Brown Jr., MD, MPH, of Weill Cornell Medical College, highlights the ongoing challenges in this area. “The question was whether the patient’s own liver would regenerate, eventually making the graft unnecessary,” he said. “In that paper, when the graft was removed, the patient’s liver does not appear to have recovered enough.” He also noted that auxiliary liver transplants with human livers have shown similar degrees of success, emphasizing the technical difficulties involved.

Ethical Considerations and Future Directions

As xenotransplantation progresses, ethical considerations become increasingly important. Sun emphasized the need for informed consent, particularly given the experimental nature of the procedure. Brown raised concerns about potential coercion, ensuring patients understand the risks and benefits before undergoing xenotransplantation. The ethical treatment of animals used for organ procurement also remains a significant concern.

Looking ahead, researchers are focused on refining genetic engineering techniques to further reduce the risk of rejection and improve organ compatibility. Regulatory hurdles are also being addressed, with agencies like the FDA developing pathways for the clinical evaluation of xenotransplantation products. The involvement of private sector investment is expected to accelerate the pace of research and development.

While widespread clinical application of pig liver xenotransplantation remains some years away, the recent advancements represent a significant milestone in the quest to address the critical shortage of donor organs and offer hope to patients with end-stage liver disease. The field is moving from a theoretical possibility to a tangible reality, with ongoing research paving the way for potentially life-saving therapies.