Mice Grow Human Kidneys

Dec. 27, 2002 -- Mice have grown new human and pig kidneys. So -- someday -- might you.

It's been possible for some time now to take embryonic stem cells from one kind of animal and transplant them into another. A major problem has been to find stem cells at exactly the right stage of development. Cells that are too young grow into a chaotic jumble of different cell types. Cells that are too old don't adapt to the new species and get rejected by the immune system.

Now scientists report finding just the right time to transplant human and pig stem cells so that they grow into new, working kidneys. Yair Reisner, PhD, of Israel's Weizmann Institute of Science and colleagues report the findings in the Dec. 23 advance online edition of Nature Medicine.

"Our data pinpoint a window of human and pig kidney [organ creation] that may be optimal for human transplantation," the researchers suggest.

Reisner's team transplanted kidney stem cells from human and pig embryos into mice. They found that seven- and eight-week -old human stem cells and four-week-old pig stem cells are best for transplant.

The pig data is perhaps most important, because human fetal tissues are in short supply and pose ethical questions.

Will the human immune system reject newly grown pig kidneys? To get an idea, the researchers grew pig kidneys in mice with no immune systems of their own. They then restored the animals' immunity with human immune cells. The human cells did not attack the newly grown pig kidneys.

No human trials are planned until more studies can be done. But if all goes well, the researchers hope to begin human studies in a few years. Meanwhile, the transplant situation remains critical. In the U.S. there are 50,000 people waiting for new kidneys. This year about 2,000 people died while on the waiting list.