AP Photo/Matt Dunham

Biologists have announced that, for the first time, they had succeeded in growing human stem cells in pig embryos. It's a huge advance, one that opens the possibility of developing human organs in animals that can later be withdrawn and implanted in humans.

Why this matters: If pigs from such embryos could survive with human organs growing inside them it would open up the possibility of harvesting human organs for transplant that could end the backlog of waiting lists for such organs.

The developments were announced in two separate science journals, by two different sets of research teams experimenting with different aspects of the race to grow human organs in animals such as pigs. It's the first proof of a concept that genomes from species that separated 90 million years ago can be combined. The genetic term is "chimera."

One team of scientists from the Salk Institute proved that human stem cells can be combined in such a way that they actually help form the tissues of a pig. A second team from the University of Tokyo and Stanford, showed how diabetes could be reversed in mice by introducing pancreas glands into them that had been grown in rats. Both studies were published in Cell and Nature.

The two studies, together, clearly show that it is feasible and possible to grow human organs in host animals like pigs, though it will be some time before the research leads to a process for human organs to be grown and harvested for human transplant.

When it is finally developed, it will look something like this for a patient waiting for a transplant: you would take stem cells from the patient's skin, implant it in a pig as it grows and then harvest it once the organ has developed. Because the organ has developed from the patient's own cells, there is less risk of an immune response and rejection.

Our thought bubble: While tens of thousands of people in the United States alone are desperately in need of human organs for transplant, the process is still likely to be controversial when the concept moves from the lab to production. The ability to essentially "humanize" a pig or other large animals is why, in 2015, the National Institutes of Health banned the use of public funds for research that would insert human cells into animal embryos. They tried to lift the ban last August, but got so many responses that it slowed the process down again. It's hard to imagine that the Trump administration will lift the ban on chimera research now, given the potential controversy.

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