Gene therapy successful in treating hemophilia B, researchers say

March 1, 2000
Web posted at: 10:45 p.m. EST (0345 GMT)

(CNN) -- Researchers at the Children's Hospital of Philadelphia and Stanford University have successfully used gene therapy to treat hemophilia B, according to a study published in this month's Nature Genetics.

The study was small -- only three patients were involved -- but it's promising to researchers who are looking for safer ways to conduct gene therapy.

Hemophilia B is a relatively rare disorder; about 5,000 Americans suffer from it. Their bodies produce insufficient levels of a clotting protein called Factor IX. Because of this, blood leaks into their joints, leaving many sufferers disabled by the time they are 30.

According to researchers, hemophilia B is suitable for gene therapy because the Factor IX gene is small and a healthy copy can be easily substituted.

Gene therapy has come under fire since the death last year of 18-year-old gene study participant Jesse Gelsinger. But the Children's Hospital researchers say they have altered the procedure in a way that makes it much safer.

In gene therapy, doctors give patients with a defective gene a good copy of the same gene. But simply injecting the patient with the good gene usually doesn't work well. So instead, doctors take the good gene and insert it into a vehicle of some kind, usually a virus. The gene, now inside the virus, is then injected into the patient.

But not all viruses are alike. The virus used on Gelsinger actually causes a flu-like illness. Some experts say it's that illness that killed Gelsinger. The search is now on for safer viruses that don't make people sick.

The virus used in the study at the Children's Hospital of Philadelphia is called AAV, and it's found everywhere.

"Most of us are infected with this when we're children, but it doesn't cause disease," said Dr. Kathy High, Children's Hospital of Philadelphia.

Several AAV trials are now being conducted in the United States.

"It has a really impressive safety profile," High said. "You can't really see problems with the vector itself in testing we've done on mice, rats and hemophiliac dogs."

Researchers say if this method of therapy continues to work, it will be one of the few successful genetic treatments of any disease since the approach was first used a decade ago.

Medical Correspondent Elizabeth Cohen and The Associated Press contributed to this report.

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