CHOP treats blood disorder with gene therapy in dogs

Researchers at Children's Hospital of Philadelphia report that they have corrected a rare blood disorder in dogs by administering a single injection of gene therapy.

The condition, called factor VII deficiency, occurs naturally in dogs and also strikes humans, causing spontaneous bleeds in the gastrointestinal and central nervous systems in those with a severe form of the disease.

The researchers, who worked with scientists at the University of North Carolina at Chapel Hill, say the canine findings give them hope that the treatment could be used in human patients.

The results were reported online in the journal Blood.

Humans and dogs with the condition have a mutation that prevents them from making adequate levels of factor VII, one of many proteins needed for proper coagulation.

So the scientists injected four dogs with varying doses of a virus that was programmed to deliver genes with the correct instructions for the clotting factor. The virus also was engineered so that it would not cause disease.

All four dogs started out with levels of the clotting factor below 1 percent of normal, though none had experienced any bleeding -- perhaps because they live in a controlled research setting, said CHOP hematology researcher Paris Margaritis, the study leader.

After the injections, all saw some improvement.

The dog with the lowest dose experienced only a slight increase in the clotting factor, but the three with higher doses all ended up with levels of at least 15 percent of normal -- a level that would be high enough for meaningful therapeutic improvement in humans.

"That would be a huge improvement in their lifestyles," Margaritis said.

In one dog that was followed for nearly three years, the improvement lasted for the entire time, he said. That dog experienced a mild immune response to the treatment but it subsided after two to three weeks, said Margaritis, who works at CHOP's Perelman Center for Cellular and Molecular Therapeutics.

The condition afflicts 1 in 300,000 to 500,000 people, though only a minority of them have a severe enough disease to require treatment.

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