The past few weeks have brought very good news for hemophilia
suffers after two major advances in understanding and treating the disease
were announced.
First, in late February researchers at the Salk Institute
announced they had used gene therapy to treat hemophilia and dogs. The
treatment continued to work for 10 months in one animal.
Lili Wang and Inder Verma worked with four dogs who naturally
developed hemophilia B. In both dogs and human beings, hemophilia B is
caused by a genetic defect in a single gene for a blood clotting protein,
Factor IX. Because Factor IX production is controlled by only one gene,
it is a logical starting point for understanding and treating genetic
disease.
Researchers modified two genes, one to turn Factor IX production
on, and another to control the production of Factor IX, and then introduced
the genes through a virus they injected directly into the dogsÂ’ livers.
After the infusion of the virus, all the dogs began expressing Factor
IX, and the dog that received the highest dose produced enough Factor
IX to prevent spontaneous bleeding, the most dangerous part of hemophilia.
In the 10 months since the experiment, that dog still has not experienced
any spontaneous bleeding.
Verma said that because of the similar way hemophilia affects
humans and dogs, “[this experiment] suggests strongly that this approach
could work in humans afflicted with the disease.”
Meanwhile, in the first week of March news came of a somewhat
inadvertent success of a genetic treatment for hemophilia in human beings.
Doctors working for California-based Avigen conducted a small Phase I
trail to evaluate the toxicity of a hemophilia treatment that uses a virus
much like the experiment with the dogs that the Salk Institute conducted.
But although the test was only intended to test toxicity, the results
of the small three-patient trial suggest the drug may also be highly efficacious.
According to Dr. Mark Kay of the Stanford University School of Medicine,
“One patient had a 50% reduction in the need to administer factor IX and
the other had an 80% reduction.”
Reference:
Gene therapy used to treat hemophilia
I dogs. Reuters, February 24, 2000.
Gene
therapy successful in treating hemophilia B, researchers say. CNN,
March 1, 2000.
Surprise
gene therapy success. BBC, March 2, 2000.