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Human kidney cloned in rats

Researchers in Japan say they've cloned a human kidney by cultivating human stem cells extracted from adult bone marrow into rat embryos.

The development is expected to increase the possibility of expanding regenerative medicine to anatomically complicated organs such as the kidney and the lung as a potential means to treat patients with disorders of those organs.

A report of the study, headed by Takashi Yokoo of the department of internal medicine and gene therapy at Jikei University School of Medicine in Japan, will be published in the online edition of US publication Proceedings of the National Academy of Sciences, dated March 1.

According to Yokoo, the team removed rat embryos from the uterus, implanted human stem cells -- treated with neutrophic factor genes to help the organ development -- into the area in the embryos where the kidneys were being generated and cultured the embryos in vitro.

Two days after the stem cell implantation, the researchers extracted the kidney area from the embryos and, after incubating it for six days, discovered the development of nephrons, or an excretory unit of the kidney, and the surrounding interstitium.

The team members checked the genes and confirmed they were developed from human bone marrow stem cells. They then transplanted the kidney into the stomach of another rat and observed that it grew to about 150 milligrams in two weeks.

The researchers also confirmed that the implanted kidney produced urine, according to Yokoo.

The team was also able to successfully treat a mouse suffering from Fabry's disease, a genetic kidney defect characterised by the deficiency of a metabolism-aiding enzyme, by using the method to replace its nephrons with healthy ones, he said.

Regenerative medicine using stem cells extracted from bone marrow has been put to limited practical use, such as for producing skin and cartilage. But scientists have rarely been able to regenerate human organs using those of different animals.

"Theoretically, there would not be any symptoms of rejection," said Yokoo, referring to the possibility of organ rejections in the event of transplantation.

"I think we can also create the pancreas and liver using the same method."

Kyodo