January 8th, 2026.
Photo of Tim Andrews, our second xenorecipient, throwing the first pitch at the Red Sox Game. June 2025.
What is xenotransplantation?
Xenotransplantation refers to the transplantation of organs or tissues from a different species into humans. In this case, it involves genetically modified pig kidneys transplanted into human recipients as a potential solution to the severe organ shortage crisis.
How many xenotransplants have been performed at Mass General?
As of January 8th 2026, four xenotransplants have been performed in living recipients at Massachusetts General Hospital (MGH).
- Richard Slayman, 62, received the world’s first genetically edited pig kidney transplant in a living human on March 16, 2024. He passed away nearly two months later due to a cardiac arrhythmia unrelated to the transplant, with the xenograft still functioning at the time of his passing.
- Tim Andrews, 67, received the second transplant on January 25, 2025, as part of the ongoing FDA-approved pilot study. He remained dialysis-free for over 9 months post-transplant, making him the longest-living recipient of a gene-edited pig kidney (video).
- Bill Stewart, 54, received the third xenotransplant on June 14, 2025, and is over 200 days post-transplant, and doing well and off dialysis (video).
- Molly Falco, 56, received the fourth kidney xenotransplant on November 22, 2025.
What is the goal of pig kidney xenotransplantation?
If proven safe and effective, genetically modified pig kidneys could serve as an alternative organ source, potentially ending the kidney organ shortage. The current phase of clinical research aims to evaluate safety, function, and longer-term outcomes in patients with kidney failure.
What is unique about the gene-edited pig kidneys (EGEN-2784)?
The kidneys are from pigs with three classes of genetic modifications to improve compatibility with the human immune system:
- Elimination of glycan antigens to reduce hyperacute rejection.
- Insertion of seven human transgenes to support immune regulation, reduce inflammation, and improve coagulation compatibility.
- Inactivation of porcine endogenous retroviruses (PERVs) for enhanced infectious safety.
Has the FDA approved xenotransplantation in humans?
Yes. In addition to the pilot study under Expanded Access, the FDA has now cleared an Investigational New Drug (IND) application for a Phase 1/2/3 clinical trial of EGEN-2784. This pivotal trial will enroll over 30 patients, assessing safety and function at 24 weeks post-transplant.
Who is a candidate for kidney xenotransplantation?
Candidates are typically patients with end-stage kidney disease (ESKD) who:
- Are between 50 and 70 years old
- Are currently on dialysis
- Have limited access to a human kidney transplant (e.g., long wait time based on blood group, no living donor)
- Are otherwise medically suitable for transplantation (active on a transplant waiting list)
All potential candidates undergo comprehensive multidisciplinary evaluation, including medical, surgical, psychosocial, and infectious disease assessments, and must provide informed consent to participate in the research protocol.
What immunosuppressive drugs are used?
Patients receive a novel combination of immunosuppressive agents, including some used in human transplantation, as well as investigational agents designed to control the unique immune responses to pig organs. Regimens are based on decades of non-human primate (NHP) research.
What are the risks of rejection or complications?
As with all transplants, rejection and infection remain risks. However, the gene edits are designed to reduce rejection, and MGH transplant teams have deep expertise in managing transplant-related complications. One possible difference is that recipients may require erythropoietin to support red blood cell production.
How is patient safety being monitored?
Patients are closely monitored post-transplant with:
- Frequent blood and urine tests
- Imaging and clinical assessments
- Remote monitoring of cardiac rhythm, blood pressure and weight
- Infection surveillance, including novel blood tests (e.g., metagenomic sequencing)
Are infections from pigs a concern?
The pigs are bred in pathogen-free facilities under FDA oversight, and extensive testing is conducted on both organs and recipients. No pig-derived infections have been detected in recipients to date. Overall, we consider the risk of donor infection transmission to the recipient to be low.
What is the follow-up process?
Patients are monitored like other kidney transplant recipients, with:
- Frequent outpatient visits and labs
- Long-term surveillance for immune and infectious events
- Public health reporting through the FDA-mandated monitoring system
How is the xenotransplant program funded?
The pilot study was supported through a collaboration between MGH and eGenesis. The larger upcoming study will be funded by eGenesis.
Which partners are involved?
- eGenesis (Cambridge, MA): Developer of the gene-edited pig kidneys (EGEN-2784)
- Eledon Pharmaceuticals
- Apellis Pharmaceuticals
- Karius
- FDA: Provided rigorous oversight throughout all clinical phases
What is compassionate use or Expanded Access?
This is an FDA-regulated pathway allowing use of investigational treatments in life-threatening conditions when no satisfactory alternatives exist and when rigorous safeguards are in place.
Why is this research important?
There are more than 800,000 Americans living with ESKD. Due to organ shortages, most remain on dialysis, which has a 5-year mortality rate over 50%. Xenotransplantation may offer a lifesaving alternative for those unable to receive a human kidney.
How long do pig kidneys last in humans?
Long-term outcomes are still under investigation. Ongoing follow-up will inform durability and function.
What ethical concerns have been raised?
Some concerns relate to the use of animals and genetic engineering. MGH adheres to the highest standards of animal welfare and scientific rigor, with all procedures governed by ethics boards and federal regulations. Pigs are bred in sterile environments, exclusively for research and clinical use.
Regarding genetic engineering, the donor pigs undergo extensive safety testing, including routine genomic screening to detect any unintended mutations. All gene edits are designed to improve compatibility and safety for human recipients, and every step is conducted under strict regulatory oversight to ensure ethical and responsible application of this technology.
What’s next?
With the FDA-cleared clinical trial now underway, more than 30 patients will be enrolled in a pivotal Phase 1/2/3 study. If successful, this may pave the way for FDA approval and broader access to xenotransplantation for kidney failure. For patients interested in participating in this study, please complete this form: https://www.mghxenotransplant.org