Transplant hope grows with stem cell kidneys

By STEVE CONNOR in London

In a breakthrough that could alleviate the worldwide shortage of kidneys available for transplants, scientists have grown kidneys in laboratory mice using human stem cells, raising the prospect of growing full-sized human organs in pigs.

An Israeli team led by Professor Yair Reisner of the Weizmann Institute of Science in Rehovot grew miniature human kidneys inside the body cavities of mice into which they had transplanted human kidney stem cells. The kidneys were fully functional and produced urine.

The scientists also produced pig kidneys with the same technique.

In both cases the kidneys were the size of the normal mouse organ, but the scientists hope now to grow human kidneys inside pigs, producing organs of a comparable size to those for human transplants.

Alternatively, they might be able to grow functioning pig kidneys inside human patients using pig foetal tissue. However, this risks the possibility of transferring pig viruses to people.

The study, published in the journal Nature Medicine, pinpointed the stage of embryonic development at which the stem cells had the best chance of forming well-functioning kidneys that the patient is least likely to reject.

It appears that seven to eight-week-old human tissue and four-week-old pig tissue is best. If taken earlier, the tissue could include non-kidney structures such as bone, cartilage and muscle. If taken later, the risk it will be rejected by the patient's immune system increases.

The work is part of a series of studies on growing entire organs using stem cells.

Reisner's team also studied how the human immune system might respond to a kidney grown from human stem cells inside an animal.

The scientists injected human lymphocytes - the immune system's "killer cells" - into mice that lacked an immune system of their own.

"The findings were encouraging: as long as the kidney precursors were transplanted within the right time range, the lymphocytes did not attack the new pig or human kidneys - despite the fact that lymphocytes and kidney precursors originated from different donors," a spokesman for the Weizmann Institute said.

This suggests that such organs may not be rejected so readily if they were ever used for transplants.

The team said the research was in a pre-clinical study stage, but that if all went well, a treatment could follow within a few years.

In September American researchers said they had managed to grow teeth in rats, which suggested the existence of dental stem cells, and there was no reason the technique used in rodents would not work in humans.

The shortage of kidneys for transplants is getting worse each year, according to the British Transplant Authority. There are about 1600 kidney transplants in Britain each year, with more than 5000 people on the waiting list.

- INDEPENDENT

Herald feature: Health