Thalassemia is a group of inherited blood disorders that affect the production of hemoglobin, the protein in red blood cells that transports oxygen throughout the body.
Hemoglobin is made of two proteins, alpha globin and beta globin. In beta-thalassemia, genetic defects affect the production of the beta globin protein, reducing levels of hemoglobin in the blood.
There are an estimated 288,000 cases of beta-thalassemia across the world, making it one of the most common genetic diseases, according to an editorial accompanying the study. In the United States and the European Union, an estimated 15,000 people have the disorder and approximately 1,500 infants are born each year with it.
Patients with beta-thalassemia typically must begin receiving regular blood transfusions as an infant, so they don't become anemic. Most will remain dependent on blood transfusions for the rest of their life.
In the experimental gene therapy, a person becomes his or her own donor of bone marrow stem cells. Medicines prompt the stem cells that create blood to temporarily circulate in the patient's bloodstream, from which doctors gather and refine the cells, Thompson said.
Those stem cells are then exposed to a virus carrying the normal version of the beta globin gene. The cells adopt the normal gene, allowing them to produce healthy amounts of hemoglobin. In the meantime, patients receive chemotherapy to kill off the defective bone marrow cells in their bodies. Once that's done, the new cells are introduced via an IV drip into their veins.
"Because these are stem cells, they know where they really belong is the bone marrow," Thompson said. "Even putting them into a vein, the cells know to travel to the bone marrow. Once they're in the marrow, they settle in and begin dividing."
Two-thirds of the patients who underwent this one-time treatment wound up with healthy levels of hemoglobin and have not needed transfusions. "Of the ones that did not become independent, there was an almost 70 percent reduction in the volume and frequency of transfusion," Thompson said. "There was clinical benefit in essentially all participants, with the majority of participants becoming transfusion-independent." Even better, the procedure did not cause any side effects.
There had been some concern that the virus would not act as anticipated, and might turn on cancer genes to trigger the development of leukemia in patients, explained Dr. Christopher Walsh, an associate professor of hematology and medical oncology at the Icahn School of Medicine at Mount Sinai in New York City.
The team continues to tweak the protocol to improve the ability of the virus to transfer the normal gene into patients' stem cells, Thompson said. A larger phase 3 clinical trial is already underway. Researchers also have been granted federal approval to test the procedure in children younger than 12, Thompson added.
Courtesy: WebMD
