Richard Slayman goes to a clinic and sits while a machine takes his blood out, filters it and puts it back. That is what dialysis is: several hours at a sitting, several days a week, indefinitely. He is sixty-two, he lives in Weymouth, Massachusetts, and he had been living with kidney failure for years, with a break in the middle. A human kidney was transplanted into him in 2018. It worked, and about five years later it began to fail, and he went back on the machine.
That is the position from which somebody agrees to be first.
On Saturday 16 March a surgical team at Massachusetts General Hospital spent four hours putting a pig’s kidney into him, the first time a genetically edited pig organ has gone into a living person. The hospital announced it this week.
This is a profile of the organ, because the organ is the engineered object here and the surgery, remarkable as it is, is the part that was already understood.
What the object is
It is a kidney, grown in a pig, from a line whose genome has been altered in sixty-nine places.
Those edits fall into three groups and each group solves a different problem, which is the useful way to hold it.
The first group removes. Pig cells carry sugar molecules on their surfaces that the human immune system recognizes immediately and violently; an unmodified pig organ put into a person is destroyed within minutes by antibodies that were already circulating before the operation. Knocking out the genes that produce those sugars removes the trigger for that immediate rejection.
The second group adds. Human genes are inserted so the organ presents proteins that human immune regulation recognizes and that human clotting machinery can work with. Rejection is not one event; it happens on several timescales, and later rejection is driven by different mechanisms than the first minutes.
The third group deactivates. Pig genomes contain retroviruses embedded in them, inherited and present in every cell. They are not known to have caused disease in a person, and nobody has previously had a pig organ inside them for long enough to find out. Switching them off addresses a risk that is theoretical and that would be extremely serious if it were not.
Why a kidney, and why this patient
The choice of organ is not arbitrary and it is the strongest argument for doing this at all.
Kidney failure is the one form of major organ failure with an established alternative to transplant. Dialysis keeps people alive for years. That means a kidney recipient in whom an experimental organ fails has somewhere to go: back onto the machine, in the condition they were in before.
No equivalent exists for a heart. That asymmetry is why the kidney is the sensible place to test this and why the ethics of consent are tractable here in a way they are not elsewhere.
It also shapes who can be asked. Mr Slayman had already had one transplant fail and was back on dialysis, which for somebody in his position means the wait for another human kidney starts again, and starts from a worse place, because a previous transplant tends to leave a patient harder to match.
What this does and does not demonstrate
Be careful here, because a first is the easiest thing in medicine to overread.
What has been demonstrated is that the organ can be connected and can function in the immediate period after surgery. That is a real result and it retires a specific risk: the immediate, antibody-driven destruction that made this impossible for decades.
What has not been demonstrated is anything about duration, and duration is the entire question. A transplanted organ is not judged at a week. It is judged at a year, at five years, at ten. The mechanisms that end most transplants are slow ones, and none of them has had time to operate.
It is also, precisely, one patient. A single case establishes feasibility and cannot establish rate. Nothing about how often this works, or in whom, or with what complications, can be read from it, and the temptation to treat a first as a result is the standing error in reporting of this kind.
What the object is competing against
The comparison that matters is not a pig kidney against a human one. It is a pig kidney against dialysis, because that is the choice actually in front of the people this is for.
Dialysis is a remarkable technology and it is a poor substitute for an organ. It replaces filtration and not the rest of what a kidney does; it requires a person to organize their life around a machine for twelve hours a week; and survival on it, over years, is substantially worse than survival with a functioning transplant.
Set against that, an organ that works for even a few years is not a marginal improvement. The bar this has to clear is lower than the bar a human transplant clears, and that is the honest framing of why it is worth attempting.
The supply problem underneath all of it
The reason anybody is doing this is arithmetic. The number of people on kidney waiting lists in the United States is far larger than the number of organs that become available, and it has been for decades, and no amount of improvement in donation closes that gap.
An animal source would close it, because the supply would be manufactured rather than discovered. That is the prize the field has been working toward for decades, and it is large enough to justify a program of this difficulty.
What is not resolved
Everything that matters, which is not a criticism of the work but a description of where it stands.
Whether the organ survives a year. Whether the immunosuppression required is tolerable over that period, given that suppressing rejection also suppresses defense against infection, and that this is an organ from another species. Whether the deactivated retroviruses stay deactivated in a human body over time, which is a question no laboratory model can settle because the model is the thing being tested.
And one more, which is not medical. If this works, the organs will be produced on a scale that makes this a supply industry, and nobody has settled what the rules of that are: who grows them, under what welfare standards, at what price, and who is at the front of a queue that will no longer be limited by scarcity but by cost.
None of those questions has an answer this week. What exists this week is one man in Boston with a pig’s kidney inside him that is working, a hospital that has said so, and a schedule of follow-up appointments that runs out past anything the science can currently predict.
