Pigs have been the most recent research focus to address the organ shortage, but among the hurdles: A sugar in pig cells, foreign to the human body, causes immediate organ rejection. The kidney for this experiment came from a gene-edited animal, engineered to eliminate that sugar and avoid an immune system attack.

Surgeons attached the pig kidney to a pair of large blood vessels outside the body of a deceased recipient so they could observe it for two days. The kidney did what it was supposed to do — filter waste and produce urine — and didn’t trigger rejection.

“It had absolutely normal function,” said Dr. Robert Montgomery, who led the surgical team last month at NYU Langone Health. “It didn’t have this immediate rejection that we have worried about.”

This research is “a significant step,” said Dr. Andrew Adams of the University of Minnesota Medical School, who was not part of the work. It will reassure patients, researchers and regulators “that we’re moving in the right direction.”

The dream of animal-to-human transplants — or xenotransplantation — goes back to the 17th century with stumbling attempts to use animal blood for transfusions. By the 20th century, surgeons were attempting transplants of organs from baboons into humans, notably Baby Fae, a dying infant, who lived 21 days with a baboon heart.

With no lasting success and much public uproar, scientists turned from primates to pigs, tinkering with their genes to bridge the species gap. Pigs have advantages over monkeys and apes. They are produced for food, so using them for organs raises fewer ethical concerns. Pigs have large litters, short gestation periods and organs comparable to humans.

Pig heart valves also have been used successfully for decades in humans. The blood thinner heparin is derived from pig intestines. Pig skin grafts are used on burns and Chinese surgeons have used pig corneas to restore sight.

In the NYU case, researchers kept a deceased woman’s body going on a ventilator after her family agreed to the experiment. The woman had wished to donate her organs, but they weren’t suitable for traditional donation. The family felt “there was a possibility that some good could come from this gift,” Montgomery said.

Montgomery himself received a transplant three years ago, a human heart from a donor with hepatitis C because he was willing to take any organ. “I was one of those people lying in an ICU waiting and not knowing whether an organ was going to come in time,” he said.

Several biotech companies are in the running to develop suitable pig organs for transplant to help ease the human organ shortage. More than 90,000 people in the U.S. are in line for a kidney transplant. Every day, 12 die while waiting.

The advance is a win for Revivicor, a subsidiary of United Therapeutics, the company that engineered the pig and its cousins, a herd of 100 raised in tightly controlled conditions at a facility in Iowa.

The pigs lack a gene that produces alpha-gal, the sugar that provokes an immediate attack from the human immune system.

In December, the Food and Drug Administration approved the gene alteration in the Revivicor pigs as safe for human food consumption and medicine.

But the FDA said developers would need to submit more paperwork before pig organs could be transplanted into living humans.

“This is an important step forward in realizing the promise of xenotransplantation, which will save thousands of lives each year in the not-too-distant future,” said United Therapeutics CEO Martine Rothblatt in a statement. Experts say tests on nonhuman primates and last month’s experiment with a human body pave the way for the first experimental pig kidney or heart transplants in living people in the next several years.

Raising pigs to be organ donors feels wrong to some people, but it may grow more acceptable if concerns about animal welfare can be addressed, said Karen Maschke, a research scholar at the Hastings Center, who will help develop ethics and policy recommendations for the first clinical trials under a grant from the National Institutes of Health.

“The other issue is going to be: Should we be doing this just because we can?” Maschke said.

CARLA K. JOHNSON | AP News

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A small study offers the first hint that an extra dose of COVID-19 vaccines just might give some organ transplant recipients a needed boost in protection.

Even as most vaccinated people celebrate a return to near normalcy, millions who take immune-suppressing medicines because of transplants, cancer or other disorders remain in limbo — uncertain how protected they really are. It’s simply harder for vaccines to rev up a weak immune system.

Monday’s study tracked just 30 transplant patients but it’s an important step toward learning if booster doses could help.

It didn’t help everybody. But of the 24 patients who appeared to have no protection after the routine two vaccinations, eight of them — a third — developed some virus-fighting antibodies after an extra shot, researchers from Johns Hopkins University reported in Annals of Internal Medicine. And six others who’d had only minimal antibodies all got a big boost from the third dose.

“It’s very encouraging,” said Dr. Dorry Segev, a Hopkins transplant surgeon who helped lead the research. “Just because you’re fully negative after two doses doesn’t mean that there’s no hope.”

Next up: Working with the National Institutes of Health, Segev’s team hopes to begin a more rigorous test of a third vaccination in 200 transplant recipients this summer.

For transplant patients, powerful immune-suppressing drugs prevent rejection of their new organs but also leave them extremely vulnerable to the coronavirus. They were excluded from initial testing of the COVID-19 vaccines, but doctors urge that they get vaccinated in hopes of at least some protection.

Some do benefit. The Hopkins team recently tested more than 650 transplant recipients and found about 54% harbored virus-fighting antibodies after two doses of the Pfizer or Moderna vaccines — although generally less than in otherwise healthy vaccinated people.

It’s not just a concern after organ transplants. One study of patients with rheumatoid arthritis, lupus and other autoimmune disorders found 85% developed antibodies, said Dr. Alfred Kim of Washington University in St. Louis. But those who used particular kinds of immune-suppressing drugs produced dramatically lower levels that are a cause for concern.

“We tell our patients to act like the vaccine is not going to work as well as it does for their family and friends,” said Kim, who would like to test a third dose in autoimmune patients, too. “This is very frustrating news to them.”

Doctors sometimes give extra doses of other vaccines, such as the hepatitis B shot, to people with weak immune systems.

And guidelines issued in France recommend a third COVID-19 shot for certain severely immune-suppressed people, including transplant recipients, Segev noted.

The U.S. hasn’t authorized extra COVID-19 vaccinations. But around the country, a growing number of immune-compromised patients are seeking third doses on their own — the people Hopkins sought to test.

In San Francisco, Gillian Ladd agreed to blood tests before and after an extra dose. The recipient of a kidney and pancreas transplant, Ladd, 48, was terrified to leave her house after learning she had no measurable antibodies despite two Pfizer shots.

With the additional dose, “I had gotten what I needed in order to survive,” Ladd said, but she’s still is sticking with masks and other precautions.

“I am being as careful as I possibly can while acknowledging that I’m coming back into the world of the living,” she said.

Further research is needed to tell if a third dose really helps, who’s the best candidate and if there are brand differences — plus whether the extra immune stimulation could increase the risk of organ rejection.

But Segev cautions boosters aren’t the only possibility. In addition to antibodies, vaccinations normally spur other protections such as T cells that can fend off severe illness. He and several other research groups are testing whether immune-compromised patients get that benefit.

For now, “the best way to protect these people is for others to get vaccinated” so they’re less likely to get exposed to the coronavirus, stressed Washington University‘s Kim.

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A new study raised questions about how well COVID-19 vaccines protect organ transplant recipients — and what precautions people with suppressed immune systems should take after the shots.

Vaccines rev up the immune system to recognize the virus, something that’s harder to do if someone’s immune cells aren’t in good working order. Transplant recipients take powerful immune-suppressing drugs to prevent organ rejection, which also increases their risk from the coronavirus — but excluded them from vaccine studies.

Specialists say the shots appear safe for transplant recipients and any protection is better than none. But how much protection do they get?

On Monday, researchers at Johns Hopkins University reported a first attempt to find out. They tested 436 people who had received new organs in recent years and were getting the Pfizer or Moderna vaccines. A few weeks after the first dose, 17% of the transplant recipients had developed antibodies against the coronavirus, said Dr. Dorry Segev, a Hopkins transplant surgeon who co-authored the study.

Segev acknowledged transplant recipients may fare better after the needed second dose — he’ll also check that — but prior studies show the first shot is enough to kickstart antibody production in just about everybody with a well-functioning immune system.

Of most concern, people whose transplant medications include a type called an anti-metabolite were far less likely to respond to the shot than those who don’t require that kind of drug, the team reported in the Journal of the American Medical Association.

The findings come after the U.S. Centers for Disease Control and Prevention said fully vaccinated people can relax some, but not all, of the masking and distancing precautions against the coronavirus.

Segev called on CDC to consider a more nuanced message.

“From what we know, transplant patients cannot assume that they are safe after being vaccinated,” Segev said. They may need post-vaccination blood tests to be sure, he added.

The CDC didn’t immediately comment.

Dr. David Mulligan, Yale University’s chief of transplant surgery and immunology, said Monday’s report is a disappointment but not a surprise, because people with weak immune systems don’t respond as well to other vaccines.

Some transplant groups, including the American Society of Transplantation, already have issued cautions about that.

Yale’s Mulligan urged patients to check in with their transplant center for advice. Those waiting for a life-saving organ transplant might be able to get vaccinated first. He said some people who’ve already had a transplant might be good candidates to temporarily cut back on certain immune-suppressing drugs. And the immune-compromised should be sure to get both vaccine doses for the best chance at protection.

“Our patients are already calling” for advice, Mulligan said. “Until you’ve had your antibodies checked and you know, boy, I’ve got a vigorous immune response — or we’ve got better data,” the immune-compromised shouldn’t let down their guard against the virus.

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