Xenotransplantation: Pigs and Humans

Ethically and legally sourced organs are always in demand. The high demand and low supply result in an unfortunately high mortality rate, not due to transplantation, but due to waiting for one. In India, the gap between demand and available organs is staggering—roughly 150,000–200,000 patients are waiting for kidney transplants, yet only a few thousand transplants occur.

Here comes the idea of xenotransplantation: where one transplants organs, tissues, or cells from one species into another. In recent years, this idea has shifted from science fiction [Frankenstein] to clinical reality. In 2025–2026 alone, xenotransplants have moved from an idea to the first structured clinical trials, thus offering a potential solution to one of medicine’s most persistent problems.

This article unveils what xenotransplantation actually is, how pig organs are genetically edited, the real-world anecdotes, the challenges that remain, and what the future might look like.

DEFINING XENOTRANSPLANTATION

For practical reasons, the primary animal used is the pig, though some research uses primates or other species. In modern medicine, xenotransplants are being developed for kidneys (for end-stage renal disease), hearts (for severe heart failure), livers (for acute or chronic liver failure), Islet cells (for type 1 diabetes), and skin and corneal tissues (for burns and eye‑disease patients).

BUT WHY PIGS?

• Thanks to their high reproductive capacity, a large number of pigs can be procured in a shorter amount of time.
• This means, in theory, that thousands of “organ-ready” pigs could be bred on demand, unlike the limited supply of human donor organs.
1. Advanced genetic‑editing tools
• CRISPR and other gene‑editing technologies have made it possible to make tailor-made organs fitting an individual.
• In landmark cases, pig kidneys and hearts used in humans carried up to 69 different genetic edits.

Because of this combination—anatomy, scalability, and genetic programmability—pigs have become the workhorse species for modern xenotransplantation.

GENETICALLY ENGINEERED PIGS

In short, we can say there are 3 major goals for genetic engineering:

Prevention of Transplant Rejection

Human immune systems has the ability to detect “self” from “non-self” antigens. Pig antigens like α‑Gal (Galactose‑α‑1,3‑galactose) and other glycan antigens are flagged as “foreign”. This led to hyperacute graft rejections within minutes in early xenotransplant attempts.

The scientists now use CRISPR to overcome this problem. Recent successful pig‑kidney cases involved multiple antigen‑knockout edits plus human‑gene insertions to fine-tune compatibility.

But preventing rejection isn’t just about removing pig markers. The compatibility can also be increased by the addition of human genes.  

• CD46, CD55, CD59: Regulate the complement system
• Thrombomodulin, EPCR (endothelial protein C receptor): Reduce abnormal clotting within the graft [major cause of early failure]
• CD47: Prevents phagocytosis of pig cells
• HO‑1 (heme‑oxygenase‑1): Has anti-inflammatory and protective effects on blood vessels inside the organ

In one landmark pig‑kidney transplant (2024–2025), the donor pig carried 69 different genetic edits—a mix of knockouts, knock-ins, and knockdowns. This genetically engineered organ functioned in a human recipient for over 270 days (nearly nine months).

Tackling Thrombosis

Chances of Zoonotic Infections

Pigs are a host to several different viruses, including porcine endogenous retroviruses (PERVs). These viruses are integrated in the pig’s DNA and can, in theory, infect human cells, raising concerns about long-term safety.

Recent advances include:

• Gene‑editing PERVs out of the pig genome using CRISPR.
• Protocols to check for any viral activation or transmission.

So far, no PERV transmission has been definitively documented in human xenotransplant cases, but the risk remains a key focus of regulatory scrutiny.

REAL-WORLD XENOTRANSPLANT CASES

Now let’s look at the most recent cases of xenotransplants…

Pig Kidney

The first truly durable pig-kidney transplant in a human was a compassionate use case in 2024–2025. A patient with end-stage kidney disease and no hope of a human donor received a kidney from a 69‑gene-edited pig.

Key outcomes:

• Normal filtration function, reducing the need for dialysis.
• The patient reported improved energy, better appetite, and fewer complications tied to chronic dialysis.
• The graft survived for over 270 days, far longer than any previous pig‑kidney xenotransplant.

In 2026, the first FDA‑sanctioned clinical trial for pig‑to‑human kidney xenotransplantation began in the United States at major centers including NYU Langone, Massachusetts General Hospital, and Johns Hopkins.

These trials are small, closely monitored, and follow strict protocols for patient selection, immunosuppression, and follow‑up.

Organizations like the National Kidney Foundation have also highlighted that clinical trials for pig‑to‑human kidney transplantation are now officially underway.

Pig Heart

Pig Liver

In 2025, a world‑first pig‑to‑human liver xenotransplant in a living patient was reported in China. The recipient, a patient with severe liver failure, received a 6‑gene‑edited miniature‑pig liver.

This liver functioned for several weeks, providing metabolic support and buying time for the patient’s condition to stabilize. While the graft did not last years, it demonstrated that pig livers can replace a human’s liver, even for a short duration.

Reports from the European Association for the Study of the Liver (EASL) and other liver‑disease societies now frame pig‑liver xenotransplants as a potential bridge for acute‑liver‑failure patients who would otherwise die within days.

Other Pig Transplants

Researchers are also exploring pig‑derived islet‑cell transplants for type 1 diabetes.

Scientists are also looking at:

• Pig‑skin grafts for burn patients (providing temporary coverage until human‑skin grafts can be prepared).
• Pig‑corneal transplants for patients with corneal scarring or infection.

RESPONSE OF HUMAN IMMUNE SYSTEM

Xenotransplantation is a constant battle against the immune system. The body’s reaction to a pig organ typically follows a sequence:

Chronic Immune Reactions

Even with genetic modifications, the human immune system continues to interact with the pig graft in the long run.

A 2026 immunology paper analyzing the first long‑lasting pig‑kidney xenograft showed that:

• Certain immune‑cell subsets remained active even months after transplant.
• Gene‑expression patterns in the graft revealed subtle changes reflective of ongoing immune stress.

Thrombosis and Coagulation

Thrombotic microangiopathy remains one of the toughest issues. Pig‑human blood‑clotting systems are not perfectly aligned, so:

• Microclots form in small vessels inside the graft.
• Over time, these clots block blood flow and cause organ failure.

Solutions now include:

• Genetic insertion of human-like clot-regulating genes (thrombomodulin, EPCR, CD47).
• Careful use of anticoagulant drugs around the transplant window.

 These interventions have significantly reduced early clotting-related failures in recent xenotransplants.

SIGNIFICANCE IN HUMAN PATIENTS

The primary driver of xenotransplantation is the uneven demand and supply chain. Xenotransplantation offers a possible way to close this gap by:

• Providing on‑demand organs not dependent on sudden accidents or deaths.
• Reducing waiting times and mortality for patients on dialysis, in heart‑failure clinics, or on liver‑support systems.
• Offering time for more options: a pig organ can keep someone alive and stable until a human organ becomes available.

For patients, the benefits are profound, including and not limited to improved quality of life, greater predictability, and potential longevity.

CHALLENGES AND ETHICAL QUESTIONS

Despite the promise, xenotransplantation is still high‑risk, experimental surgery with major open questions.

Long‑Term Survival and Function

Even the best‑case pig‑kidney xenografts have so far lasted months, not decades. Long‑term outcomes—like 10‑ or 20‑year survival—are still unknown.

Immunosuppression and Side Effects

Xenotransplant recipients need strong immunosuppressive drugs to suppress their immune systems enough to accept the pig organ. These drugs:

• Increase susceptibility to infections.
• Raise the risk of cancer.
• Can cause kidney damage, diabetes, and other metabolic problems.

Ethical Considerations

Xenotransplantation raises serious ethical issues:

• Is it acceptable to breed and modify pigs solely for human organ harvesting?
• Patients in end‑stage disease may feel pressured to accept experimental procedures with uncertain outcomes.
• Will xenotransplants become another tool for the wealthy, while the poor remain on dialysis or in heart‑failure clinics?

Cost and Scalability

Right now, xenotransplantation is extremely expensive: gene editing, pathogen‑controlled breeding, surgery, and long‑term monitoring all carry high costs.

Scaling this technology to hundreds of thousands of patients worldwide will require dramatic cost reductions and technological simplification.

REFERENCES

Tao P and Zhou K (2025) Recent progress in pig-to-human kidney xenotransplantation. Front. Immunol. 16:1735113. doi: 10.3389/fimmu.2025.1735113

Shirini, Kasra et al. “Xenotransplantation Literature Update: January-June 2025.” Xenotransplantation vol. 32,4 (2025): e70072. doi:10.1111/xen.70072

Clinical Trials for Pig-to-Human Kidney Transplantation Are Here. National Kidney Foundation. August 05, 2025.

Guilherme T. Ribas et al, Immune profiling in a living human recipient of a gene-edited pig kidney, Nature Medicine (2026). DOI: 10.1038/s41591-025-04053-3

U.S. FDA page summarizing regulatory concerns, infection risks, and oversight of animal‑to‑human transplants. Link. 

International Society for Heart and Lung Transplantation document on rules for patient selection, immunosuppression, and monitoring in pig‑heart xenotransplants. 20 February 2026.

National Kidney Foundation‑style page explaining what xenotransplantation is, how it works, and where trials stand. Link.