Gene Therapy Stops Blood Disorder in Patient, Ending Need for Transfusions
A 21-year-old man with a blood disorder who needed monthly transfusions to survive since he was 3 had his condition halted by a gene therapy procedure.
The man suffered from beta thalassemia, a common genetic disease that reduces red blood cell production. He was treated in Paris in 2007 and hasn’t needed a transfusion in two years, according to a study published today in the journal Nature.
The therapy, being developed by closely held Bluebird Bio of Cambridge, Massachusetts, is the latest in a series of successful gene treatments. Bluebird, backed by four venture capital firms and Genzyme Corp., the world’s largest maker of drugs for rare genetic diseases, plans to treat nine more patients who have thalassemia or sickle cell anemia. The company also is developing a gene therapy that has helped patients with a rare vision disorder to see.
“Major journals don’t publish papers very often based on one patient but this is a significant milestone,” said Nick Leschly, chief executive officer of Bluebird, formerly known as Genetix Pharmaceuticals Inc., in a telephone interview yesterday. “Thalassemia doesn’t just go away, so if you get a remission it means the treatment has worked.”
The authors of the study reported one possible side effect. About a year after the therapy, some of the patient’s red blood cell precursors carried high levels of a protein that has been linked in some reports with the development of both benign growths and blood cancer, said Derek Persons, a doctor and scientist at St. Jude’s Children’s Research Hospital in Memphis, in a commentary accompanying the study.
No Cancer Evidence
There was no evidence of a cancerous or precancerous state in the patient, said Philippe Leboulch, a professor at Harvard Medical School and the University of Paris who is leading the trial.
“Long-term follow-up of this and other patients will be needed before its efficacy and safety can be firmly established,” Persons wrote in his commentary.
Still, he said, the experiment “represents a major step forward for the gene therapy” of blood disorders.
Thalassemia and sickle cell anemia, a related disorder, are among the most common genetic diseases in the world, said Leboulch. About 150,000 people a year are born with each condition, he said.
Thalassemia is especially common in Africa, Southeast Asia and the Mediterranean region, where it afflicts as many as 10 percent of people, according to a 1999 study in the New England Journal of Medicine.
Gene therapy is experiencing a revival among scientists and drugmakers in recent years after failed experiments in the early 1990s ended in one death and some children developed leukemia. In November, the journal Science reported that brain damage in two 7-year-olds with an inherited condition called adrenoleukodystrophy was halted or reversed in another gene therapy experiment in Paris.
People with thalassemia are born with a defect in the globin gene that regulates the production of beta globin, a key ingredient of the hemoglobin found in red blood cells. This genetic glitch leaves them unable to provide enough oxygen to the blood.
Those with the most severe form, like the Paris patient, can’t survive without a monthly blood transfusion, Leboulch said. Regular transfusion leads to excess iron in their blood, so they also need regular chelation treatment to remove it.
Some patients with thalassemia can be treated with a bone marrow transplant from a healthy matched donor. The stem cells in the bone marrow rebuild the patient’s blood cell supply and allow them to produce healthy beta globin.
There are drawbacks to this approach, Leboulch said. Many patients don’t have a matching donor and the procedure requires heavy chemotherapy to wipe out the patient’s own bone marrow. There also are risks that cells from the donor will attack those of the transplanted patient, he said.
In the gene therapy procedure, doctors took the patient’s bone marrow and injected into it a harmless virus carrying a corrected copy of the globin gene. The cells were later returned to the patient.
Over time, the new red blood cells became more numerous than the old, uncorrected ones. The patient then made an adequate supply of beta globin and stopped needing transfusions. With the Paris patient, the process took about a year, Leboulch said.
Today, the man is mildly anemic with hemoglobin a bit lower than it would be in a normal person and his condition has been stable for two years, Leboulch said.
“He has not required a drop of blood for two years,” Leboulch said. “He lives a normal life and he has a full-time job and a girlfriend.”
Leboulch expects to treat another patient early next year. It will take at least three years for clinical trials to prove to regulators that the therapy is safe and effective so it can be marketed clinically, Leschly said.
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