Organs grown in animals for use in humans are beginning to build up a record of clinical success after decades of unfulfilled promise, offering hope for the future of transplants, reports Financial Times.
Five patients at Massachusetts General Hospital in the United States have undergone successful transplants with animal organs – xenotransplantation – since March 2024 after the pig kidneys they received were genetically engineered to avoid rejection, US biotech company eGenesis said.
In three of them, the porcine organs worked for more than eight months without rejection or the need for dialysis.
“The organ shortage is the greatest crisis we have right now in transplantation,” said Leonardo Riella, director of kidney transplantation at Mass General, who led the eGenesis clinical trials.
“It’s amazing to see the progress,” said Mike Curtis, chief executive of eGenesis. “Our goal is to make transplantation available to patients when they need it, without being constrained by the limited supply of human donor organs.”
The animal organs would initially be used “as a bridge to get patients off dialysis while they wait for a human donor kidney”, said Riella, adding that it could eventually be used “as a destination therapy in its own right” if the trials “establish long-term safety and durability”.
The kidneys were grown in Yucatan miniature pigs whose organs are similar in size to their human counterparts. They were genetically engineered to remove three pig proteins that are most likely to lead to immune rejection and add seven human genes to improve compatibility with the patient.
In addition, the porcine DNA was manipulated to inactivate viruses that might infect the recipient.
One patient, Tim Andrews, whose case was described in The Lancet last week, lived with a pig kidney – which he received at 66 – for almost nine months without needing dialysis until the transplanted organ began to fail, though there were no signs of immune rejection.
He then received a kidney from a deceased human donor. Subsequent tests showed that living with the pig kidney had not made it harder for the human transplant to work successfully.
Curtis said the US Food and Drug Administration had authorised an expanded clinical trial of eGenesis pig kidneys in 33 patients with renal failure to start early next year in up to 10 US transplant centres, with the aim of achieving marketing approval by the end of 2029.
The company is also collaborating with a Japanese partner, PorMedTec, to start kidney xenografts in Japan in 2028, he added.
David Crosby, chief research officer at the renal charity Kidney Research UK, said the breakthrough was “an exciting prospect” but warned that further research was needed to determine whether the approach was “safer and better” for patients than spending years on dialysis while they waited for a transplant.
Xenotransplantation has been through cycles of hope and disappointment since serious research on the area started in the 1980s. But recent progress in animal cloning, genetic manipulation and immunology now promises to transform the field.
Public squeamishness and ethical objections to breeding animals for organ transplants had also diminished, said Curtis, who argued that the moral arguments against xenotransplants were “hard to sustain … when you look at the outcomes for our patients”.
For a long time, xeno research focused on heart transplants, but now kidneys are leading the way to clinical approval. “A big advantage of the kidney is that if the transplant fails, we can safely return the patient to dialysis,” said Curtis. “If the transplanted heart fails, there’s not much you can do.”
However, eGenesis and another leading US xenotransplant company, United Therapeutics, are working with hearts as well as kidneys. The FDA has approved a small xenoheart trial led by United Therapeutics.
Study details
Porcine kidney xenotransplantation as a bridge to allotransplantation: a first-in-human study
Leonardo V Riella, Thiago J Borges, Ivy A Rosales et al.
Published in The Lancet on 3 September 2026
Summary
Background
Kidney xenotransplantation offers a potential solution to the organ shortage, but questions remain regarding durability, zoonotic infection risk, and whether the immunological response to the xenograft elicits sensitisation that could complicate subsequent allotransplantation. We report outcomes from a porcine kidney xenograft in a living recipient followed by human allotransplantation.
Methods
A patient with end-stage kidney disease, a prolonged anticipated waiting time for deceased donor transplantation, and with no suitable living donor underwent transplantation at Massachusetts General Hospital (Boston, MA, USA) with a gene-edited porcine kidney (EGEN-2784; eGenesis [Cambridge, MA, USA]) incorporating the deletion of major glycan xenoantigens, inactivation of porcine endogenous retroviruses, and insertion of seven human transgenes. The recipient received costimulation blockade-based immunosuppression with complement inhibition. Monitoring included renal function, flow cytometric crossmatch, anti-HLA antibodies, and porcine microbial surveillance, including metagenomic sequencing. This report describes the first recipient in a planned three-patient study conducted under a US Food and Drug Administration Expanded Access Investigational New Drug application.
Findings
The xenograft functioned immediately after transplantation on Jan 25, 2025, and sustained dialysis independence for 271 days. A biopsy on day 14 showed T-cell-mediated rejection, which resolved with treatment. Graft function remained stable for approximately 6 months until immunosuppression was reduced in the setting of non-zoonotic bacterial infection. Microvascular inflammation with endothelial injury subsequently emerged, progressing to thrombotic microangiopathy despite persistently negative donor-specific crossmatch, leading to graft failure and nephrectomy. Tissue analysis showed a macrophage and natural-killer-cell-predominant infiltrate with minimal T-cell involvement. No porcine pathogen transmission was detected. Anti-HLA antibodies remained unchanged. 82 days after explantation, the patient underwent human kidney allotransplantation with immediate graft function and no evidence of sensitisation during 231 days of follow-up.
Interpretation
This case shows that porcine kidney xenotransplantation can provide prolonged renal support and be discontinued without clinically significant allosensitisation or zoonotic infection. Early cellular rejection resolved with treatment, whereas later graft failure was associated with microvascular injury progressing to thrombotic microangiopathy despite a negative donor-specific crossmatch, supporting the possibility that mechanisms beyond conventional antibody-mediated rejection contributed to late graft injury. Kidney xenotransplantation has the potential to provide prolonged dialysis-free support while also serving as a bridge to subsequent human allotransplantation.
Financial Times article – Pig kidneys successfully transplanted into humans (Restricted access)
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