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Illustration of an outline of a pig, showing the internal organ; the outline of a person, showing the internal organs; and a drawing of a kidney between them. Amanda Northrop/Vox

Is it okay to harvest pig kidneys to save human lives?

We’re starting to grow pigs to take their organs and put them in humans. Wait, what?

“David is a great transplant surgeon. Five of his patients need new parts — one needs a heart, the others need, respectively, liver, stomach, spleen, and spinal cord — but all are of the same, relatively rare, blood-type. By chance, David learns of a healthy specimen with that very blood-type. David can take the healthy specimen’s parts, killing him, and install them in his patients, saving them.”

So goes a story, one of the most famous in modern philosophy, told by the late Judith Jarvis Thomson in 1976.

The story raises many important ethical questions, but the core one is simple: Is it okay to sacrifice one life to save five? In this case, only the most hardened utilitarian would say yes. Treating a human being as nothing but a container for organs strikes many as intuitively repugnant, even if so doing would spare five others an early death.

Until recently, the question of trading a life for another through organ donation was largely hypothetical, grist for prize-winning sci-fi novels. But on September 25, Robert Montgomery showed that you could implant a pig kidney in a human, and the question became very concrete, very fast. No, we’re not killing humans to harvest their organs, as Thomson or Kazuo Ishiguro imagined. But we’re killing intelligent animals for their organs, and the moral consequences of that should weigh on us.

Montgomery, a surgeon who runs the Transplant Institute at NYU Langone Medical Center, performed the landmark operation on a dead subject. With the consent of the family, the body of the deceased was maintained using a ventilator for 54 hours, to see how an implanted pig kidney would function.

The kidney functioned about as well as a human kidney transplant, at least during that short window of time. At a press conference announcing the surgery, Montgomery noted that the implanted kidney, attached to a leg, “began functioning and making large amounts of urine within minutes,” a key function of the kidneys. He also said that levels of creatinine (a waste product produced by muscles and filtered out by the kidney) in the donor’s blood were normal, another sign of sound kidney functioning. He predicted that we could be seeing transplants of pig kidneys into living human donors within a year or two.

“If human organs are imagined as the fossil fuel of the organ supply, then pig kidneys are the wind and solar: sustainable and unlimited,” Montgomery concluded.

The NYU Langone Health surgical team examines the porcine kidney for any signs of hyperacute rejection. The organ was implanted outside the body to allow for observation and tissue sampling during the 54-hour study period.
Joe Carrotta for NYU Langone Health

For the 750,000 Americans with end-stage renal disease and the millions of others who care for them, this news is a massive game changer. A recent study found that some 43,000 people die every year in the US for lack of a kidney donation. That’s more people than die annually due to homicide, HIV, or car accidents. Pig kidneys could drop that number to zero.

But here’s the thing that should give us pause: The pig used in Montgomery’s surgery was subsequently euthanized. There are some 63,000 new patients every year who might benefit from a kidney donation. Assuming each donor pig is stripped of both of its kidneys and then euthanized, that’s more than 30,000 pigs killed every year to extend human lives.

Now, in fairness, that 30,000 is a blip next to the 131.6 million pigs slaughtered for their meat in the US in 2020 — a rounding error, given the scale of factory farming.

Nevertheless, Montgomery’s breakthrough forces us to confront two questions: Is it morally justifiable to slaughter thousands of pigs annually to keep humans alive? And is it more morally justifiable than other methods that could also end the kidney shortage?

The ability to transplant pig kidneys into humans would undoubtedly save many human lives, which is, of course, a good thing. But it behooves us to take seriously the moral consequences of such an act, especially if we begin performing it on a wide scale.

The pig kidney breakthrough

Implanting other species’ organs and tissues into humans — or xenotransplantation, to use the technical medical term — is a very old idea.

In the 1920s, the con man John Brinkley became a national celebrity for his surgeries implanting goat testicles into human scrotums, which he claimed could cure impotence (among other ills); he gained such support he almost got elected governor of Kansas in a revenge bid after the state revoked his medical license.

But more reputable figures have attempted xenotransplantations too. Keith Reemtsma at Tulane University performed 13 chimpanzee-to-human transplants in the 1960s, all but one of which failed within a couple of weeks of the procedure due to organ rejection or a resulting infection. One patient lived for another nine months before dying.

In 1984, Leonard Bailey at Loma Linda University implanted a baboon heart into a dying infant with the pseudonym Baby Fae. The baby rejected the organ, dying soon thereafter (and partly inspiring a pretty good Paul Simon song).

A major problem in all these efforts was rejection: the recipient’s immune system interpreting the donated organ as a foreign body and attacking it as if it were a hostile organism. This is also sometimes a problem with human-to-human transplants. But rejection has become less of an issue with humans after the development of better immunosuppressant drugs, which prevent immune attacks on donated organs.

The NYU team went a few steps further than immunosuppressants: They used organs from genetically engineered pigs.

The pig whose kidney was implanted in the NYU surgery was a GalSafe pig, a genetically modified pig variety approved by the Food and Drug Administration this past December. It’s produced by Revivicor, a subsidiary of the biotech firm United Therapeutics; Montgomery specifically thanked Martine Rothblatt, United Therapeutics’ chief executive, in his announcement. The FDA did not evaluate GalSafe pigs for xenotransplantation per se, but Revivicor has been vocal about its ultimate intention being the use of gene-edited pigs as a source for transplants.

The gene modification prevented production of what’s known as the alpha-gal biomolecule. Alpha-gal is present in all mammals besides primates (including humans), and its presence causes primate immune systems to reject organs. By preventing these pigs from producing that molecule, the gene edits enabled them to act as human donors much more effectively.

The ethical quandary posed by pig kidneys

The benefits of pig-to-human kidney transplantation are obvious and profound. A recent study in the American Journal of Nephrology estimated that between 5 million and 10 million people worldwide suffer from kidney failure severe enough to require dialysis, or another kidney-replacement treatment (like transplantation).

Dying for lack of a transplant is awful, but so is being forced to live on dialysis. Dialysis is immensely physically draining, often preventing people from working or traveling; the rate of depression in people on dialysis is more than double that in the general population.

Some kidneys can be recovered from deceased donors, and indeed that serves as the source of most kidneys in the US. In 2020, 17,583 deceased donor kidney transplants were performed. But while there are actions that could be taken to improve recovery of kidneys from deceased donors, the simplest way to solve the kidney shortage would be for living humans to step up and give more. Humans only need one kidney, and only 0.014 percent of people in the US would need to donate a kidney each year to end the waitlist.

Pig kidneys, in that sense, are not strictly medically necessary. Voluntary living human donors could fill the gap.

But in practice, a much lower percentage than that donates a kidney. In 2020, there were only 5,234 living donor transplants — a far smaller number than deceased kidney transplants and a waitlist of more than 106,000.

Indeed, in only one country in the world are there enough human donors to provide kidneys to all who need one: Iran. And there’s one likely reason for that: Kidney donors in Iran are paid for their service. Here in the US and in most of the world, paying a kidney donor is illegal.

Having donated a kidney myself, I can report that while totally manageable, it’s also inconvenient and temporarily painful. And yet we ask people to provide this service, and save a life, for free — or worse, if they have to take unpaid leave for the surgery, we ask them to pay for the privilege of saving a life.

But some bioethicists are vocally opposed to compensating donors for saving a life, for fear that such a system would harm poor people. Such objections make compensation very politically difficult to enact. Polling suggests a strong majority of Americans would support paying for kidney donations if so doing would improve the supply of kidneys (which it would), but it’s hardly a political issue driving many votes.

Until policy on compensation changes, the advancement of pig-organ transplantation could be our best bet for ending the kidney waitlist.

Which forces us to consider the moral quandary of exchanging a pig life for a human one.

Pigs are remarkably intelligent animals. They have good memories, love to play and explore, recognize each other, and have sophisticated social lives. Purdue animal scientist Candace Croney even taught pigs to play video games. (The pigs loved it.)

So imagine an animal like your dog, but perhaps smarter, being killed to save the life of a human. Would you be willing to kill your dog in that case? Does the question disturb you?

Montgomery agreed that the practice raises important animal welfare questions. When I asked him about the euthanizing of the donor pig, he raised the question, “Is it more humane to euthanize the pig and remove both kidneys for two transplants, or to remove one kidney and have the pig sustain the recovery period, where there’s pain and risk of infection?” It’s also not clear who would care for a donor pig that did survive, and who could pay for that care.

The question is even tougher when you get to organs like hearts, lungs, and pancreases, which cannot be given by a living donor. Currently only a few thousand people a year receive heart transplants, mostly because there is such a minimal supply, but the American Heart Association has argued as many as 100,000 people a year could benefit, which is plausible when you consider that heart disease is the single biggest cause of death in the US, killing more than 650,000 people in 2018.

Genetically engineered pig hearts that could work for humans could dramatically extend lifespans for people with heart disease, and the same goes for lungs, liver, and other organs. But in each such surgery, a pig would have to die for a human to live.

A question for philosophers

Peter Singer, the moral philosopher at Princeton who helped launch the modern animal rights movement and is also a vocal advocate for kidney donation, told me in an email that he is cautiously supportive of even lethal pig donations.

“I would not insist on the pig surviving the surgery, because that’s an uncertain benefit and would require twice as many pigs to be used,” Singer wrote. “What I would like to see is that all pigs involved in the procedure — including at the research stage, which obviously will continue for some years, and including the pigs’ parents — are reared in conditions that meet not only their physical needs but their psychological and social needs — so not in a factory farm. That seems a minimum quid pro quo for the benefit the pig is conferring on humans.”

(Revivicor declined to comment when asked about the living conditions of its pigs.)

Singer is a utilitarian. He believes that ethics is about maximizing the welfare of humans and animals, and so is willing to make trade-offs like these that still involve the deaths of sentient animals.

Christine Korsgaard, a professor of philosophy at Harvard, is very much not a utilitarian. She’s perhaps the most eminent Kantian philosopher in the world today. Immanuel Kant, the 18th-century thinker who serves as Korsgaard’s main inspiration, argued human beings must treat each other’s common humanity as an end in itself, not a means to their own ends.

This idea can be hard to grasp, but the important thing to know is it places limits on how much harm you can inflict on someone or some animal in order to produce some greater good. You have to respect the humanity or dignity of all rational beings (including animals).

Korsgaard objects to pig-to-human organ transplants on basically those grounds. “I do not think it is justifiable to kill an animal so that we can use her organs for a person, any more than it would be justifiable to kill one person to use his organs for another person,” Korsgaard wrote me in an email. “I think the pig does have a prior claim on her own life and her own organs. If you kill a pig for her organs, you are treating her as if she is ours, a mere resource for human use, as if she exists for us rather than for herself.”

Genetically modifying the pig compounded this wrong, she wrote, as humans changed the pig’s biology so it could better serve human ends. “Women don’t exist to make homes for men; people of color don’t exist to provide cheap labor for white people; animals don’t exist to provide food, labor, and organs for people,” Korsgaard concluded.

I am more of a consequentialist like Singer than a Kantian like Korsgaard. But Korsgaard’s arguments have incredible force. Just like factory farming, using pigs for organs turns them into a kind of industrial commodity for humans, rather than living creatures who deserve to live full, wonderful lives. There is something distasteful about that, even if the good of increased organ supply outweighs the concern.

Mostly, the development makes me sad that humans have been so unwilling to step up and donate kidneys to each other — or create the policies that would encourage such an act — that they are resorting to taking them from another species. Donating a kidney is a routine, safe procedure, one that humans could and would likely be more willing to provide if compensated.

If the alternative to a world where thousands of pigs are killed for their kidneys every year were one where Medicare carefully screened kidney donors and paid them each $50,000 or however much is necessary to get a full supply of kidneys, then the latter world seems infinitely preferable. No person, and no pigs, would have to die.

But that is not the actual counterfactual at hand. The counterfactual is the current world, where politicians have banned compensation for organ donation and organs are in persistently short supply. Compared to that counterfactual, pig organs seem like a step forward.

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