But when Dr. High, a professor of pediatrics at Children's Hospital of Philadelphia, and her colleagues launched human trials in 2001, the picture darkened. They injected the gene-carrying viruses into the livers of seven patients. Two produced measurable amounts of Factor IX, 3 percent and 12 percent of the normal level. But within a few weeks the levels became undetectable, Dr. High reported last year. The patients' immune systems had apparently killed the cells containing the inserted gene.
Dr. High had some ideas about how to fix that. But in May the biotech company sponsoring her work bailed out.
So it has gone for gene therapy, the great hope of...