Raising hopes for a cure for human hemophilia, a new study has shown for the first time that transplanted cells can cure hemophilia A in animals.

Hemophilia A, the most common form of the disease, causes recurrent, spontaneous and uncontrollable bleeding. A hereditary disease, it is best known for its effect on the British and Russian royal families, but there are many less prominent victims.

Scientists at New York's Albert Einstein College of Medicine of Yeshiva University, led by Dr. Sanjeev Gupta, cured hemophilia A by transplanting healthy liver endothelial cells from donor mice into a mouse with the disease. This overturned the conventional idea about which cells produce factor VIII, the crucial clotting protein that is lacking in people with type A hemophilia.

"We've known for three decades that factor VIII is produced in the liver, but precisely where has been controversial," says Dr. Gupta, a professor in the departments of medicine and pathology at Einstein. "It was assumed that factor VIII was made by the hepatocytes — cells that perform many of the liver's functions and comprise most of its bulk. But our research had suggested that the primary sources were special endothelial cells that line the sinusoids, the liver's blood-filled spaces. We did this study to confirm the role of liver endothelial cells in producing factor VIII and to see if transplanting them from a healthy donor liver could correct hemophilia A in an animal model."

Three months after transplantation, when the researchers examined the livers of recipient mice, "We found that the transplanted cells had engrafted and increased in number," says Dr. Antonia Follenzi, an instructor in pathology at Einstein and the lead author of the study. "Even more important, those mice with the most transplanted cells in their livers produced factor VIII in sufficient amounts to completely correct their hemophilia A."

Dr. Gupta cautions that more work is necessary before this technique can be used on people.

The principle established by this study — selectively injuring native endothelial cells and replacing them with healthy donor endothelial cells — might also help in treating hemophilia B (a less common form of the disorder) and might also aid in "tissue engineering" in the many other areas of the body where endothelial cells are found, says Dr. Gupta. For example, he notes that endothelial cells isolated from blood vessels and transplanted into the heart could help in treating cardiovascular disease.

This study appeared in the February 14 online edition of the Journal of Clinical Investigation.