A virus derived from HIV can safely fix broken immune systems and correct genetic diseases, suggest two new studies involving children with rare conditions.
For both studies, researchers put healthy genes into the children’s own DNA using lentiviruses, in this case genetically engineered versions of HIV that can no longer cause disease. Earlier gene therapy trials using different viruses had a flaw: When the viruses plunked themselves into the patient’s DNA, they sometimes amped up activity of neighboring cancer-causing genes, leading to leukemia. That side effect, along with the death of a young man participating in another clinical trial, nearly halted gene therapy in the United States in the early 2000s.
Now, researchers led by Luigi Naldini of the San Raffaele Telethon Institute for Gene Therapy in Milan have altered the lentiviruses so that they won’t accidently turn on nearby genes. The researchers then infect bone marrow stem cells with lentiviruses carrying the appropriate gene and transplant the stem cells into patients.
In one study, three boys with Wiskott-Aldrich syndrome, an inherited disease that disables the immune system, received gene therapy. Now, two to three years after the therapy, the former “bubble boys” have healthy immune systems, Naldini and colleagues report July 11 in Science. The boys also show no signs of developing leukemia — which should help allay concerns about the team’s gene therapy approach, says Todd Rosengart, a surgeon and gene therapy researcher at Baylor College of Medicine in Houston.
In the second trial, Naldini and his colleagues treated three children with a metabolic disease called metachromatic leukodystrophy. Children with the disease lack an important enzyme. As a result, they gradually become paralyzed and suffer damage to their ability to think, dying within a couple of years. Up to two years after the therapy, the children in the study are still making enough of the enzyme to keep their brain and spinal cord working normally with no sign of leukemia, the researchers report in the same issue of Science.
The results are encouraging, says Uta Griesenbach, a gene therapist at Imperial College London. “Even after fairly long-term follow up, it appears to be safe and effective.” The boys aren’t out of the woods yet — some of the patients in the original gene therapy trials didn’t develop cancer until four years after treatment. But Griesenbach says that the children in the new studies don’t have warning signs of cancer.
Because the lentiviruses appear safe and work so well, scientists may start doing gene therapy for more common conditions such as Parkinson’s disease, says Senlin Li, a medical researcher at the University of Texas Health Science Center at San Antonio.