Liver Cells Replenished by Bone Marrow

The liver has amazing powers of regeneration. Unlike most organs, it can regrow--even after as much as half of its tissue has been surgically removed. Now researchers have found that the credit may not go to the liver itself: New human liver cells come from bone marrow. The finding opens up new possibilities for treating liver disease.

Earlier research suggested that the liver is regenerated thanks to stem cells, but it wasn't clear whether these cellular progenitors were housed within the liver or outside of it. Studies with rats and mice suggested that the liver's new cells come from bone marrow--which hosts stem cells that build red and white blood cells. Two teams transplanted bone marrow from a male rodent into a female. When they examined the female's liver tissue with a stain that homes in on the Y chromosome, which only males carry, they found cells that must have come from the transplant.

The same is true for humans, according to pathologist Neil Theise of New York University and colleagues. They examined stored liver samples from women who had received bone marrow transplants for leukemia from male donors and later died. In one woman, 17% of her liver cells carried a Y chromosome, again pointing to the male bone marrow cells as the source. The researchers also examined livers that had been transplanted from women into men. Here, too, the researchers found liver cells that carried a Y chromosome, suggesting that the men had added new cells to the donated organ--probably from their own bone marrow, the researchers report in the July issue of Hepatology.

The finding has huge clinical implications, says pediatrician Marcus Grompe of Oregon Health Sciences University in Portland, suggesting "liver diseases now treatable only with liver transplants could be treated with bone marrow transplants instead." Bone marrow could be donated by living donors, and it carries less risk of rejection than whole-organ donation.