A decade-long effort, detailed today in Nature Biomedical Engineering, has led to a breakthrough in organ transplantation. Researchers modified a type-A kidney to become universal type O and observed how a living human immune system responded. For two days, the kidney showed no signs of hyperacute rejection the rapid antibody attack that usually destroys mismatched organs within minutes.
The recipient, a 68-year-old type-O patient with high anti-A antibody levels, required no blood-type desensitization a notable departure from current protocols. Typically, incompatible transplants need days of plasmapheresis to remove antibodies, a process that raises bleeding and infection risks and depends on living donors who can coordinate preparation.
Stephen Withers, University of British Columbia professor emeritus and co-developer of the enabling enzymes, explained that his team discovered two molecular “scissors” in 2019. These enzymes remove the sugar molecules defining type-A blood, revealing the underlying type-O structure and making universal transplantation possible.
Molecular “Scissors” Turn Type-A Kidneys into Type-O
The UBC team developed enzymes capable of removing N-acetylgalactosamine, the sugar that distinguishes type-A from type-O blood. These molecular “scissors” work during hypothermic perfusion—the standard method of preserving organs at 4°C. In lab testing, the enzymes eliminated over 96% of A-antigens within two hours, effectively revealing the underlying type-O structure. After perfusion, the kidney was flushed and prepared for transplantation.
This approach flips traditional protocols on their head. Normally, blood-type incompatible transplants require days of plasmapheresis to strip antibodies from recipients, a process that increases bleeding and infection risks. By treating the organ instead of the patient, the team bypassed these challenges entirely.
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Observing Immune Tolerance in Real Time
The kidney’s performance post-transplant revealed the complexity of immune tolerance. Within the first 24 hours, it produced 1,300 milliliters of urine and maintained strong blood flow. No hyperacute rejection occurred, a striking outcome given the recipient’s high anti-A antibody levels.
By day three, some blood-type markers began reappearing on the organ’s surface, triggering a mild immune response. While some antibody-mediated injury occurred, the damage was far less severe than typical mismatches. Researchers also noted early signs of accommodation, a phenomenon where the body gradually tolerates a previously incompatible orga often developing over weeks in standard transplants.
Detailed Tracking of Immune Responses
The research team conducted 40 biopsies over seven days, providing unprecedented insight into antigen regeneration and immune reactions in a living human organ. Single-cell sequencing revealed elevated expression of genes associated with accommodation, including those that inhibit complement activation and prevent cell death.
Antibody-mediated rejection appeared on day four, coinciding with antigen reappearance, but the injury pattern differed dramatically from classical hyperacute rejection cases. For comparison, two traditional mismatched kidney transplants showed extensive microvascular thrombosis, red blood cell congestion, and massive antibody and complement deposition, leading to rapid organ failure.
The Team Behind the Breakthrough
Stephen Withers, UBC professor emeritus and co-developer of the enzymes, first identified two highly efficient molecular scissors in 2019. Jayachandran Kizhakkedathu, UBC pathology professor and co-leader of the enzyme project, described receiving the positive update while traveling overseas in late 2023. The results prompted an immediate call to Withers in British Columbia—a testament to the momentous nature of the findings.
Ethical and Experimental Considerations
The study involved a brain-dead recipient whose medical complications had already excluded them from standard organ donation. This design allowed extended observation without risking a living patient, following strategies similar to recent xenotransplant experiments. The recipient’s family provided informed consent, and the study was approved by ethics committees at West China Hospital of Sichuan University and the Second Affiliated Hospital of Chongqing Medical University.
Despite the success, limitations remain. Only one kidney was tested, and the recipient’s advanced age and poor clinical condition complicated interpretation. Frequent biopsies, while necessary for data collection, caused some tissue damage. Additionally, the observation period of seven days was too short to fully capture accommodation, which usually develops over two to three weeks in blood-type incompatible transplants from living donors.
Nonetheless, the study provides unique insight: direct observation of antigen regeneration kinetics in a functioning human organ. This data will be critical for designing immunosuppressive protocols and planning interventions when antigen levels rise.
Implications for Clinical Translation
Avivo Biomedical, a UBC spin-off, plans to pursue regulatory approval for clinical trials. Future strategies might include enzyme infusion as a post-transplant drug starting around day two, maintaining low antigen levels while accommodation develops. Preclinical studies in baboons and transgenic mice have already shown that similar enzymes can reduce blood-type antigens in kidneys, hearts, and lungs.
The potential extends beyond kidneys. Other solid organs could benefit, making deceased-donor transplants viable for blood-type incompatible recipients a critical advantage when timing is urgent. In 2021, more than 13% of U.S. patients on the kidney waiting list had waited over five years for a compatible organ.
A Donor-Centric Paradigm Shift
Traditional approaches focus on modifying the recipient to accept a mismatched organ. This enzyme-based strategy, in contrast, modifies the donor organ itself, offering several potential advantages:
- Reduced risk of bleeding and infection by avoiding extensive antibody removal in recipients
- Faster allocation of organs, especially life-saving deceased-donor kidneys
- Applicability to multiple organ types
Whether this approach proves safer and more practical than recipient-centric desensitization remains to be determined. However, the enzyme technology has cleared its first human hurdle, demonstrating that chemically modified organs can survive initial contact with the human immune system long enough to matter.
Frequently Asked Questions
What does it mean to convert a kidney’s blood type?
Scientists use specialized enzymes to remove sugar molecules (antigens) that define a donor kidney’s blood type. For example, type-A kidneys can be converted to type-O, making them compatible with a wider range of recipients.
How does this process differ from traditional blood-type incompatible transplants?
Traditional approaches modify the recipient, using plasmapheresis to remove antibodies before transplantation. The enzyme method modifies the donor organ instead, reducing risks such as bleeding, infection, and prolonged preparation times.
How long does the enzyme treatment take?
The UBC team’s method removes over 96% of type-A antigens within two hours during hypothermic perfusion, the standard organ preservation process at 4°C.
Can the immune system still attack the converted kidney?
Some blood-type markers may regenerate, triggering mild immune responses. However, early studies show the damage is far less severe than typical mismatched transplants, and the body may develop accommodation, gradually tolerating the organ.
Has this been tested in humans?
Yes, a recent study involved a single brain-dead recipient, allowing detailed observation of immune responses and antigen regeneration. While promising, clinical trials are needed to confirm safety and effectiveness in living patients.
Could this approach work for other organs?
Potentially. Research suggests similar enzyme treatments could be applied to hearts, lungs, and other solid organs, broadening the pool of compatible deceased-donor transplants.
What are the next steps for this technology?
Avivo Biomedical, a UBC spin-off, aims to pursue regulatory approval for clinical trials. Future strategies may include post-transplant enzyme infusion to maintain low antigen levels while accommodation develops, ultimately making universal organ transplantation more feasible.
Conclusion
The development of enzyme-based blood type conversion represents a major leap in transplant medicine. By chemically redesigning donor kidneys, researchers have shown it’s possible to overcome one of the longest-standing barriers in organ transplantation: blood type compatibility. Early human data demonstrates that converted organs can survive initial immune responses, paving the way for broader access to life-saving transplants.
