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Meanwhile, Mark Kay and Katherine High reported that when they injected their vector into dogs with hemophilia B, the dogs had a therapeutic response. ­Avigen, a biotech company headquartered in ­Alameda, CA, collaborated with High and Kay to plan clinical tests of the treatment’s safety in people.

In November 2002, the French scientists halted their trials. The number of patients was up to 10, but now one of those patients who’d gained a fully normal immune system had come down with a disease similar to leukemia, out-of-control proliferation of the very white blood cells that had been restored.

Then the June 4, 2004, issue of Science reported that Avigen had backed out of the trials of the hemophilia treatment. Two of seven patients had developed slightly elevated levels of liver enzymes.

On September 28, 2005, I went to see Alain Fischer at the Hôpital Necker, a children’s hospital in Paris. He was direct and clear. “I’m not a specialist in gene therapy,” he said at once. “My real field is immunology and, within immunology, genetic diseases of the immune system.” He had been working with these diseases for 25 years. “I am a physician. And here there is a clinical unit where children with immunological diseases are taken care of. So that’s where I’m starting from.” What kinds of diseases? “All kinds,” he said. “From deficiencies in T lymphocytes, B lymphocytes, innate immunity, there are … ” He drew breath. “We don’t know yet exactly. There are at least 140 different immunological diseases.” He added, “They are all very different.”

Fischer went on, “We are not going to become specialists in gene therapy–that is, to try to adapt gene therapy to different diseases. This is not our goal. We are specialists in these immunological diseases, and gene therapy is one strategy to try to treat these patients.” He was drawn to gene therapy in the early 1990s, when a new gene was identified that, mutated, causes a form of SCID. He had encountered patients with the mutation. “We understood very quickly, within one to two years, the pathophysiology of the disease,” Fischer recalled. “And we realized at that time that this disease could be the best candidate to test gene therapy.” The need for some type of effective treatment was certainly dire. Like all forms of SCID, he said, without treatment this one kills within the first year of life. The only treatment was bone-marrow transplants; but their success rate plummets unless close to identical immune-­system matches can be found, and that’s possible only about 20 percent of the time.

The types of cells affected by the disease also made it a good candidate for treatment with gene therapy, Fischer said. First, when the gene in which the mutation occurs is functioning properly, it encodes a protein that is vital if the precursors of T lymphocytes are to survive and proliferate. Second, unlike other types of immune system cells, T ­lymphocytes can survive for decades–sometimes even for an entire lifetime.

These two facts meant that even if the researchers could genetically alter only a few precursor cells, these cells might develop–or, as the scientists say, “differentiate”–into a large number of mature T cells that had a lasting benefit for the patient. “So we had the hope,” Fischer said, “that a very poor technology could–in that context, with that disease–work.”

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Credit: Illustration by Chris Buzelli

Tagged: Biomedicine

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