Potential permanent genetic cure for hemophilia A

A discovery by Medical College of Wisconsin and BloodCenter of Wisconsin researchers in Milwaukee may be a key to a permanent genetic cure for hemophilia A patients, including a subset who do not respond to conventional blood transfusions.

The study of genetically altered hemophilia mice is published in the July 2006 edition of The Journal of Clinical Investigation.

Hemophilia A affects about one in 5,000 males who lack the hereditary blood clotting protein, Factor VIII (FVIII). Traditional treatment requires infusion of synthetic FVIII two to three times a week to control bleeding episodes. However, about 30 percent of these patients develop antibodies to FVIII, selectively inactivating its clotting properties and negating its therapeutic role. Treatment for adults who have these inhibitory antibodies can cost over $1 million annually if there is a major bleeding episode.

"We developed a Trojan horse approach cloaking FVIII in a platelet so that it is undetected by the antibodies and its clotting properties are preserved until the platelet sticks to a damaged blood vessel and releases its stored protein which now includes FVIII.," explains senior author Robert R. Montgomery, M.D., senior investigator at the BloodCenter of Wisconsin and professor of pediatric hematology at the Medical College. He is also affiliated with the Children's Research Institute.

"This is truly a landmark development for hemophilia A patients," says hematologist, Joan Gill, M.D., professor of pediatric hematology at the Medical College, and director of the Comprehensive Center for Bleeding Disorders at the BloodCenter and Children's Hospital of Wisconsin. "We look forward to the day when basic research is completed and clinical trials can begin in patients."

Normally in an injury, platelets circulating in plasma - the liquid portion of the blood - stick to the site of the blood vessel wound, activating its surface and rapidly stopping bleeding. In hemophilia patients, infusion of FVIII replaces the missing clotting factor and enables normal cessation of bleeding. However, some 30 percent of patients see the FVIII as a foreign protein and mount antibodies to destroy it, rendering the FVIII treatment useless.

Newer FVIII treatment products that bypass this attack can run into $10,000 or $100,000 per treatment episode and costs for a patient may exceed $1 million annually. So far attempts at gene therapy for a permanent cure have not been successful.

According to the lead author, Qizhen Shi, M.D., Ph.D., an American Heart Association supported postdoctoral fellow, "Our team of scientists have developed an approach in mice that not only could make gene therapy successful for patients with hemophilia who don't have antibodies, but more importantly can be used to treat patients with antibodies.

"To get around the antibody attack on FVIII which occurs readily in plasma, we inserted a gene into a blood stem cell so that FVIII is produced and stored in blood platelets, hidden from view and attack, ready to release when a blood vessel is damaged, quickly enabling normal clotting before the antibodies can begin their attack. Our approach was very effective even in mice treated with five to ten thousand times the amount of antibody that would normally prevent treatment of a hemophilia patient with FVIII."

The new method will next be tested in larger animal models before clinical trials can begin in patients. Blood and bone marrow stem cells would be harvested from hemophilia patients in much the same way they are collected from bone marrow donors. A non-replicative virus containing the FVIII gene would be introduced into the stem cells from the patient. The FVIII engineered for production only in platelets would insert itself into the DNA of the stem cells. These same stem cells would then be given back to the donor patient and the stem cells would continue to make blood cells normally, releasing the life saving FVIII only when the platelets stick to a bleeding site of injury.

"This process would last for the rest of the patient's life and will work regardless of whether antibodies are present or absent," says Dr. Montgomery. "There will be many more studies needed to apply this approach in patients but this treatment could normalize bleeding for patients with hemophilia.

"What is most exciting about this first design of gene therapy for hemophilia is that it works not only for routine hemophilia but also for the 30 percent of patients who have developed inhibitory antibodies that make normal replacement treatment impossible," Dr. Montgomery concludes.

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