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Gene therapy in mice effective but caused serious side effects, study finds.

Gene therapy in mice engineered to have a fatal inherited human disease successfully eliminated nearly all symptoms, but several of the animals developed liver tumors after treatment, according to a report in the September issue of Gene Therapy.

Preliminary evidence indicates that the adeno-associated virus (AAV) used to deliver the gene therapy was not to blame for the tumors, said lead investigator Mark Sands, MD of the Washington University School of Medicine in St. Louis, MO. But exactly what triggered tumor formation remains a mystery.

AAV is not associated with any human disease, and gene therapy using AAV has been considered safe. But after Sands and his colleagues announced the discovery of the tumors earlier this year, the Food and Drug Administration and the National Institutes of Health temporarily halted preliminary human trials. Because no other group reported similar findings, the trials have since resumed. And Sands and his team are repeating their experiments in the designer mice to determine what caused the tumors. They also plan to study other groups of mice to test potential causes aside from AAV, including proteins and other components of gene therapy.

With the exception of the formation of liver tumors in some mice, the results of the gene therapy experiments in mice engineered to mimic a human disease called mucopolysaccharidosis type VII were encouraging. Children with this inherited disorder seem healthy at birth but eventually develop a variety of debilitating symptoms, including mental retardation, blindness, deafness, and severe skeletal malformations. Most youngsters end up in wheelchairs, and few live past their teens. Because children with the disease lack a functional form of an enzyme called beta-glucuronidase (GUSB), Sands and associates tried to prevent the disorder by using AAV as a viral vector to deliver the GUSB to the mice. Up to 1 year after receiving a single injection of gene therapy, the mice showed signs of normal GUSB levels and experienced improvements in growth, eye function, and hearing and lived longer than expected for mice with the disorder.

"The results are extremely promising," Sands said. "In the mouse model, we were able to prevent many of the clinical symptoms."
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Comment:Gene therapy in mice effective but caused serious side effects, study finds.
Publication:Transplant News
Article Type:Brief Article
Geographic Code:1USA
Date:Oct 15, 2001
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