This is good news, to be celebrated with caution. The first patient with a CRISPR-edited pig kidney has left the hospital. A little over two weeks have passed since the surgery at Massachusetts General Hospital, but according to U.S. press reports, Richard Slayman is well enough to have been discharged. Fingers crossed, then, for this 62-year-old man who, thanks to a xeno-rene, no longer needs dialysis.

Before him, two patients had the courage and opportunity to have a pig heart transplanted, both of whom died after a few weeks: David Bennett from a porcine virus infection, Lawrence Faucette from rejection. Specialists believe that the risk of xeno-organs carrying some porcine pathogen can be kept in check with better practices.

To prevent the human immune system from attacking the animal organ, donor pigs are genetically multi-edited, and patients receive anti-rejection therapies, but the risk is always lurking and long-term success stories will be needed before large-scale clinical trials can begin (we reviewed progress and challenges here).

Useful in this pathway are pig-to-monkey transplants and also transplants on brain-dead people who have donated their bodies to science and are kept artificially alive for a while for the purpose of studying the xeno-organ functionality (this approach has already been used for the kidney and, more recently, for the pig liver ).