Israeli scientists say human, pig kidney cells can develop in m

WASHINGTON -- A team of Israeli researchers transplanted human and pig kidney stem cells into mice, where they developed into small kidneys that appear to work.

Stem cells are parts of a developing embryo that can change into various organs as the baby grows. Harvesting stem cells causes the death of the embryo, which has made the process a focus of controversy.

In this case the cells destined to become human and pig kidneys were transplanted into mice by a team led by Yair Reisner of the Weizmann Institute of Science in Rehovot, Israel.

Their work, reported Monday in the online edition of the journal Nature Medicine, suggests that similar stem cells might also grow into functioning kidneys if transplanted into humans, the researchers said in their paper.

The work is in the preclinical stage only, the researchers noted.

The cells were transplanted into mice with weakened immune systems to prevent rejection. The cells formed a tiny but functional kidney, able to produce dilute urine, according to the paper.

The transplanted kidneys connected to the mouse blood supply, but produced the urine separately from the mouse kidneys.

If taken earlier the cells develop into disorganized non-kidney structures, the team reported, while those taken later increased the risk for immune rejection.

According to the National Kidney Foundation, in February 2002 more than 50,000 patients were on the national waiting list for kidney transplants.