This area of research is still in the early stages, but could someday help reduce wait times for patients waiting for kidney transplants

Sarah Kuta - Daily Correspondent

October 10, 2025 10:59 a.m.

Scientists converted a type A kidney to a type O kidney, then transplanted it into a brain-dead patient. Zeng et al. / Natura Biomedical Engineering, 2025

More than 92,000 patients in the United States are on the waiting list for a kidney transplant, and according to the Health Resources & Services Administration, 13 people die each day while waiting their turn for a lifesaving transplant.

Now, scientists say they have completed an experiment that may one day help reduce wait times for transplant patients. They detail the pioneering process in a new paper published October 3 in the journal Nature Biomedical Engineering.

The study is proof of concept that an organ’s blood type can be converted from blood type A to universal blood type O. Though the process is still being refined, medicine is now one step closer to an as-of-yet elusive goal: the ability to transplant organs without triggering a fatal immune response in recipients.

Researchers used enzymes to convert a donor kidney’s blood type, then transplanted the organ into a brain-dead patient, where it functioned well for two days before the body began rejecting it.

Did you know? Organ transplants today

In 2024, there were more than 48,000 transplants performed in the United States, according to the Health Resources & Services Administration. The most common transplants? Kidneys, followed by livers, hearts and kidney/pancreas double transplants.

The successful experiment capitalized on the unique properties of Type O blood, also called the universal blood type. Humans have four major blood groups: A, B, O and AB. Some blood cells also have an antigen related to a protein called the Rhesus factor, while others don’t. As a result, blood types fall into eight categories: A positive, A negative, B positive, B negative, O positive, O negative, AB positive and AB negative.

Each blood type has its own combination of antigens on red blood cells, which can trigger the body’s immune response to transplanted blood. For instance, in a person with group A blood, the body will attack blood cells with B antigens, but not those with A antigens. As a result, blood transfusions can only be performed safely between patients with compatible blood types—otherwise, a recipient may experience severe health problems.

Group O blood is unique, though: It lacks both A and B antigens on its red blood cells, meaning individuals with group O blood can donate to patients with group A, group B and group AB blood, provided that other antigens, including the Rhesus factor, don’t clash.

Usually, surgeons need a donor with the same blood type as the recipient for successful organ transplantation. Doctors have come up with a workaround to this problem: In the days leading up to a transplant, they administer intensive treatments that suppress a recipient’s immune system and deplete their antibodies in the hopes the recipient’s body won’t attack the new organ and the cells it produces.

But this recipient-centric method only works if the patient receives an organ from a living donor, not a deceased donor. Organs from deceased donors must be transplanted right away and there’s not enough time for the recipient to undergo the necessary immune system treatments before surgery, explains Rachel Fieldhouse for Nature News. Deceased-donor transplants are also expensive and can increase the risk of infection and bleeding before, during and after surgery.

So scientists set out to find another possible solution—one that focuses on changing the donor organ itself, rather than the recipient’s immune system. In 2019, researchers discovered two enzymes capable of removing antigens from type A blood. Three years later in 2022, scientists used the newly-discovered enzymes to convert lungs and kidneys from type A to type O, a process known as “enzyme-converted O,” or ECO. But they stopped short of transplanting the ECO organs into human bodies.

In the new study, scientists repeated the process with a type A kidney that had been deemed unsuitable for transplantation. For two hours, they perfused the organ with an enzyme-filled fluid that removed its A antigens—effectively turning it into a type O organ with neither antigen.

“It’s like removing the red paint from a car and uncovering the neutral primer,” says study co-author Stephen Withers, a biochemist at the University of British Columbia, in a statement. “Once that’s done, the immune system no longer sees the organ as foreign.”

The process does not remove the antigens permanently. But scientists were hopeful it would the organ would retain the new blood type long enough to prevent the recipient’s body from immediately rejecting the organ, known as “hyperacute” rejection.

They tested this theory by implanting the ECO kidney into the body of a 68-year-old brain-dead man in Chongqing, China, whose family consented to the experiment. The researchers did not administer antibody therapy—standard protocol for transplants in living patients to help prevent hyperacute rejections—because they wanted to see how the body reacted naturally.

“We needed to understand how things progressed,” Withers writes in an email to LiveScience’s Kristina Killgrove.

The recipient’s body accepted the ECO kidney for two days. On the third day, however, the ECO kidney started producing A antigens again, triggering the body’s immune response.

The scientists were not deterred, as the experiment was meant to help them understand the rate at which an ECO kidney would begin producing A antigens again. Under ordinary circumstances, doctors could use a variety of treatments to minimize the body’s immune response to the organ.

The concept of a universal donor kidney is “potentially game-changing,” Aisling MacMahon, executive director of Kidney Research UK, told the BBC’s Christy Cooney of a similar experiment in August.

It would be an especially helpful development for transplant candidates with type O blood, who wait two to four years longer for organs than individuals with other blood types. These individuals can only accept type-O kidneys. However, because type-O kidneys can be given to type A or type B recipients, they are usually in short supply. And patients from minority groups face further disparities in organ transplantation: In a 2022 report, the National Academies of Science, Engineering, and Medicine found the current system to be “demonstrably inequitable.”

This area of research is still in the early stages, the scientists say. But if the novel, organ-centric approach pans out, it could be a game-changer for transplant medicine. “It will help a lot of people,” says co-author Jayachandran Kizhakkedathu, a pathologist at the University of British Columbia, to CityNews Vancouver’s Jan Schuermann.

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