It is possible to create kidneys from pig and human stem cell tissue in mice, opening the prospect of generating organs for human transplant.
Around 50,000 people in the US alone are awaiting a kidney transplant and around 2,000 of them died this year while awaiting a donor organ. These people would be greatly helped if only some other source of donor kidneys could be found.

Researchers at the Weizmann Institute of Science in Israel have opened a new window of opportunity, by creating human and pig kidneys within the body of an experimental mouse. The organs were created from stem cell tissue - that is, cells that were destined to become kidneys in an embryo. It turns out the age of the stem cells is crucial. They must be harvested between seven and eight weeks in a human embryo and four weeks in a pig embryo. Before this, the cells will not be committed to form a kidney - they could form other tissues and organs. After this, rejection of the transplant is more likely.

Further experiments suggested that these new organs were not subject to rejection by the human immune system - even when the organ came from a pig. Further research, if it goes well, may develop these organs for human use within the next few years.