The idea of replacing faulty genes with functional ones is appealing, but it has come under severe criticism from a voluntary patient with a deficit hereditary enzyme died last fall ( science , 17 December 1999, p. 2244). Now a first report from a different research team suggests that, at least for hemophilia, there are reasons for cautious optimism about a new gene therapy.
People with hemophilia have inherited a genetic defect that limits the production of blood clotting factors. This puts them at risk of dying from trauma or internal bleeding. regular and costly transfusions currently allow most hemophiliacs to keep their disease in check. The purpose of this treatment is to maintain a level of coagulation factor which is 1% or more of the level in normal blood.
Hoping to find better treatment of hemophilia, hematologist Katherine High of the Children's Hospital of Philadelphia and colleagues started working on a gene therapy strategy there 6 years. After the success with mice and dogs, they started a preliminary clinical trial with three patients. The team injected the volunteers in the thigh with a virus that has been modified to carry a gene encoding a clotting factor. Muscle tissue near infected, where cells have intensified their production of clotting factor, the team reports in the March Nature Genetics
Although this test preliminary -. To test safety, not efficacy - used very low doses of the virus, patients responded well. Someone required 50% less of clotting factor during the first 100 days after injection, and one needed 80% less. The third patient showed no clear answer. The researchers found no side effects.
High is "cautiously optimistic" that the therapy could provide a new way to treat hemophilia, perhaps by converting severe forms of the disease in a milder condition more manageable. Although early results are "far from being a clear case of successful gene therapy," says molecular biologist Kotoku Kurachi of the University of Michigan, Ann Arbor, he said that the treatment could be very useful - if higher doses are safe and treated tissue continues to produce clotting factor over the long term.
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