Growing human organs inside pigs moved forward in labs, but not in Washington. That divide explains why gene-edited pig kidneys are now transplanted into people, while federally funded efforts to grow fully human organs inside pigs remain blocked.
The distinction traces back to a 2015 decision by the National Institutes of Health, which paused funding for research involving human stem cells placed into animal embryos. The concern, according to NIH statements at the time, was that human cells could migrate into an animal’s brain and alter its cognition. In short, regulators worried about making pigs “too human,” as reported by Live Science.
Fast forward to now. In October 2025, surgeons in New York transplanted a genetically modified pig kidney into a living patient as part of the first clinical trial of its kind. The kidney came from a pig engineered to reduce immune rejection, not from one grown with human cells. Six patients are enrolled in the trial, which aims to test whether gene-edited pig organs can function safely in humans, according to Live Science.
One of Medicine’s Most Ambitious Ideas Ran Into a Wall of Fear About ‘Humanized’ Pigs
This approach, known as xenotransplantation, exists largely because of desperation. More than 100,000 people in the US remain on organ transplant waiting lists. Thousands die each year before a donor organ becomes available. Scientists have chased cross-species solutions for decades, from baboon hearts in the 1960s to today’s pigs modified with CRISPR-like precision.
The immune system remains the major obstacle. Even with extensive gene editing, recipients of pig organs require powerful immunosuppressant drugs, usually for life. A man in New Hampshire who received a pig kidney in January 2025 saw the organ removed nine months later after its function declined, a reminder that rejection still looms.
That’s why earlier research into growing organs from a patient’s own cells inside animals drew so much interest. The idea was elegant. Disable an animal embryo’s ability to grow a specific organ, then introduce human stem cells to fill the gap. In theory, the result would be a patient-matched organ with far less rejection risk. Researchers had already demonstrated proof of concept by growing a mouse pancreas inside a rat years before the NIH pause.
Ethics, not technical limits, brought the research to a halt. Regulators fixated on the idea that human cells might reach an animal’s brain and alter its moral standing. Ethicists cited by Live Science call that distinction arbitrary. Pigs already carry human genes to make organ transplants possible, but no one considers them partly human. In reality, research protections track species, not cellular makeup.
The result is a strange regulatory compromise. Medicine accepts making humans a little more pig through transplanted organs. Growing human organs inside pigs, even to save lives, remains off-limits.
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