“The ban was based on the premise that the danger was to make the pigs too human”: why human organs are not grown in pigs in the United States
In a New York operating room, one day in October 2025, doctors wrote the history of medicine in transplant a genetically modified pig kidney in a living patient as part of a clinical trial. THE kidney had been designed to mimic human tissue and was grown in a pig, as an alternative to waiting for a human organ donor who might never come. For decades, this idea lived on the edge of science fiction. NOW it’s on the tableliterally.
The patient is one of six participants in the first clinical trial of pig-to-human kidney transplantation. The goal: to see if genetically modified pig kidneys can safely replace failing human kidneys.
Ten years ago, scientists were looking for a different solution. Instead of modifying pigs’ genes to make their organs suitable for humans, they tried growing human organs – made entirely of human cells – inside pigs. But in 2015, the The National Institutes of Health suspended funding so that this work takes into account its ethical risks. The break remains today.
Inasmuch as bioethicist and philosopher Having spent years studying the ethics of using organs grown from animals — including serving on an NIH-funded national working group examining oversight of human-animal chimera research — I was perplexed by this decision. The ban assumed the danger was making the pigs too humane. Yet regulators now seem comfortable making humans a little naughtier.
Why is it considered ethical to put pig organs into humans but not to grow human organs into pigs?
An urgent need drives xenotransplantation
It’s easy to overlook the desperation that drives these experiences. More than 100,000 Americans are waiting for organ transplants. Demand exceeds supply and thousands of people die each year before a product becomes available.
For decades, scientists have sought help among species – from baboon hearts in the 1960s to today’s genetically modified pigs. The challenge has always been the immune system. The body treats cells that it does not recognize as part of itself as invaders. As a result, it destroys them.
A recent case highlights this fragility. A man from New Hampshire received a genetically modified pig kidney in January 2025. Nine months later, it had to be removed because its function was declining. While this partial success gave scientists hope, it also served as a reminder that rejection remains a central problem for cross-species organ transplantation, also known as xenotransplantation.
Look on it
Researchers are trying to circumvent transplant rejection by creating an organ that the human body could tolerate, inserting a few human genes and removing some porcine genes. However, the recipients of these genetically modified pig organs need strong medications to suppress the immune system both during and long after the transplant procedure, and even this does not prevent rejection. Even human-to-human transplants require lifelong immunosuppressants.
This is why another approach… growing organs from a patient’s own cells – looked promising. This involved turning off the genes that allow pig embryos to form a kidney and injecting human stem cells into the embryo to fill the gap where a kidney would be. As a result, the pig embryo would give rise to a genetically matched kidney for a future patient, theoretically eliminating the risk of rejection.
Although simple in concept, the the execution is technically complex because human and pig cells grow at different rates. Even so, five years before the NIH ban, researchers had already done something similar in growing a mouse pancreas inside a rat.
Organ growth across species was not a fantasy – it was a working proof of concept.
Ethics of creating organs in other species
The concerns that prompted the NIH’s 2015 ban on the insertion of human stem cells into animal embryos stemmed not from worries about scientific failure but rather from moral confusion.
Policymakers feared that human cells could spread through the animal’s body – or even into its brain – and, in doing so, blur the line between human and animal. The NIH has warned of a possible “alterations in the animal’s cognitive state“The Animal Legal Defense Fund, an animal rights organization, argued that if such chimeras acquired human consciousness, they should be treated as human research subjects.
The concern focuses on the possibility that an animal moral status – that is, the extent to which an entity’s interests matter morally and the level of protection it is owed – could change. Higher moral status requires better treatment because it is accompanied by vulnerability to more serious forms of harm.
Think about the harm caused by poking a sensitive animal, versus the harm caused by poking a bothered animal. A sentient animal, that is, one capable of experiencing sensations such as pain or pleasure, would feel pain and try to avoid it. On the other hand, an animal that is self-aware – that is, capable of reflecting on these experiences – would not only feel the pain, but would understand that it itself is the subject of this pain. The latter type of harm is deeper and involves not only sensation but also consciousness.
Thus, the NIH’s concern is that if human cells migrate into an animal’s brain, they could introduce new forms of experience and suffering, thereby elevating its moral status.
The flawed logic of the NIH ban
However, the reasoning behind the NIH ban is flawed. If certain cognitive abilities, such as self-awareness, conferred higher moral status, it follows that regulators would be just as concerned about inserting dolphin or primate cells into pigs as they are about inserting human cells. They are not.
In practice, the moral circle of beings whose interests count is drawn not around self-awareness but around belonging to a species. Regulators protect all humans from harmful research because they are human, not because of their specific cognitive abilities such as the ability to feel pain, use language, or engage in abstract reasoning. In fact, many people do not have these abilities. Moral concern arises from this relationship and not from any particular form of conscience. No research objective can justify the violation of the most fundamental interests human beings.
If a pig embryo infused with human cells actually grew into something close enough to be considered a member of the human species, then current research regulations would dictate that it be owed human-level respect. But the mere presence of human cells does not make pigs human.
Pigs designed for kidney transplants already carry human genes, but they are not called half-human. When someone donates a kidney, the recipient is not part of the donor’s family. Yet current research policies treat a pig with a human kidney as if it could.
There may be good reasons to oppose to the use of animals as living organ factories, including for welfare reasons. But the rationale behind the NIH ban that human cells could make pigs too human rests on a misunderstanding of what gives beings — and human beings in particular — moral standing.
This edited article is republished from The conversation under Creative Commons license. Read the original article.
