Putting pig organs in people is OK in the US, but growing human organs in pigs is not – why is that?

One day in an operating room in New York City in October 2025, doctors took a medical history. genetically modified pig kidney transplant in a living patient as part of a clinical trial. The kidney was 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 who took part in the study. first clinical trial of pig-to-human kidney transplantation. The goal: to see if genetically edited pig kidneys could safely replace failed human kidneys.

Ten years ago, scientists were looking for another solution. Instead of editing the genes of pigs to make their organs suitable for humans, they tried to grow human organs made entirely of human cells inside pigs. But in 2015 National Institutes of Health has suspended funding for this work, consider its ethical risks. The pause continues today.

How bioethicist and philosopher who has spent years studying the ethics of using organs grown from animals, including serving on the NIH-funded national task force overseeing research on human-animal chimeras, I was puzzled by this decision. The ban assumed that danger would make pigs too human. However, regulators now seem comfortable turning people into pigs.

Why is it considered ethical to transplant pig organs into people, but not to grow human organs in pigs?

Urgent need calls for xenotransplantation

It's easy to overlook the desperation driving these experiments. More than 100,000 Americans waiting for an organ transplant. Demand outstrips supply, and thousands of people die every year before any of them become available.

For decades, scientists looked at different species for help – from the hearts of baboons in the 1960s to genetically altered pigs today. The problem has always been the immune system. The body treats cells that it does not recognize as part of itself as invaders. As a result, he destroys them.

A recent case highlights this fragility. Man from New Hampshire received a gene-edited pork kidney in January 2025. Nine months later it had to be removed because its function was deteriorating. While this partial success gave scientists hope, it also served as a reminder that rejection remains a central problem in organ transplantation across species, as well as known as xenotransplantation.

Researchers are trying to get around transplant rejection by creating an organ that can carry a human body by inserting some human genes and removing some pig genes. However, the recipients of these gene-edited pig organs need powerful drugs to suppress the immune system both during and for a long time after the transplant procedure, and even this cannot prevent rejection. Even person-to-person transplantation require lifelong immunosuppressive medications.

Therefore, another approach is growing organs from the 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 the kidney had been. As a result, the pig embryo will grow a kidney that is genetically matched to the future patient, theoretically eliminating the risk of rejection.

Despite the simplicity of the concept, execution is technically complex because human and pig cells develop at different rates. Despite this, five years before the NIH ban, researchers had already done something similar, growing a mouse pancreas inside a rat.

Cross-species organ growth wasn't a fantasy—it was a working proof of concept.

The ethics of creating organs in other species

The concerns that prompted the NIH's 2015 ban on injecting human stem cells into animal embryos stemmed not from concerns about scientific failure, but rather from moral confusion.

Politicians feared that human cells could spread throughout the animal's body – even into its brain – and thereby blur the line between human and animal. NIH warned of possiblechanges in the animal's cognitive state” The Animal Legal Defense Fund, an animal rights organization, argues that if such chimeras acquired human consciousness, they should be considered for human research.

The concern is that the animal moral status – that is, the degree of moral significance of the organization's interests and the level of protection to which it is obliged – may change. Higher moral status requires better treatment because it comes with vulnerability to more serious forms of harm.

Think about the harm caused by poking an intelligent animal compared to the harm caused by poking a shy animal. An animal that is intelligent, that is, capable of experiencing sensations such as pain or pleasure, will feel pain and try to avoid it. In contrast, an animal that is self-conscious—that is, capable of reflecting on an experience—will not only feel pain, but will also understand that it is itself the subject of that pain. The last type of harm is deeper and includes not only sensations, but also awareness.

Thus, the NIH is concerned that if human cells migrate into an animal's brain, they could introduce new forms of experience and suffering, thereby enhancing its moral status.

The Flawed Logic of Banning NCDs

However, the rationale for banning NCDs is flawed. If certain cognitive abilities, such as self-awareness, confer higher moral status, then it follows that regulators would be just as concerned about injecting dolphin or primate cells into pigs as they would about injecting human cells. They don't.

In practice, the moral circle of beings whose interests matter is drawn not around self-awareness, but around belonging to a species. Regulators protect all people from harmful research because they are people, not because of their special cognitive abilities, such as the ability to feel pain, use speech, or engage in abstract reasoning. In fact, many people do not have such abilities. Moral concern arises from these relationships, not from having a particular form of awareness. No research goal can justify violation of the most fundamental interests human beings.

If a pig embryo filled with human cells actually became something close enough to be considered a member of the human species, then current research rules would require it to be treated at the human level. But the mere presence of human cells does not make pigs human.

Pigs created for kidney transplantation already carry human genes, but are not called half-human. When a person donates a kidney, the recipient does not become part of the donor's family. However, current research policy treats a pig with a human kidney as if it were possible.

There might be good reasons to object the use of animals as factories for the production of living organs, including for welfare reasons. But the NIH's rationale for banning human cells from making pigs too human is based on a misunderstanding of what gives creatures—and humans in particular—moral status.

This article has been updated to correct the location and date of the first porcine kidney transplant clinical trial.

This article has been republished from Talka nonprofit, independent news organization bringing you facts and trusted analysis to help you make sense of our complex world. He was written by: Monika Piotrowska, University at Albany, State University of New York

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Monika Piotrowska does not work for, consult for, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations other than her academic position.