Clearer Day For Gene Therapy: New Vector Carries Big Genes Linked To Inherited Blindness

Some clinicians and researchers hope that individuals with inherited diseases (such as cystic fibrosis and recessive Stargardt disease, which causes progressive loss of sight) might one day be cured by providing them with a corrected version of their disease-causing faulty gene, i.e., by gene therapy.

In gene therapy, the curative gene is packaged in an agent known as a vector, which carries the gene into cells where it is required. One of the most common vectors is derived from a virus, adeno-associated virus (AAV).

However, for some diseases, such as recessive Stargardt disease, one barrier to successful gene therapy is that AAV is not able to accommodate the large size of the curative gene. New data, generated by Alberto Auricchio and colleagues, at the Telethon Institute of Genetics and Medicine, Italy, has revealed that vectors derived from a specific form of AAV known as AAV5 can accommodate large genes, including that missing in a mouse model of recessive Stargardt disease.

In the study, it was found that much larger genes could be packaged into vectors derived from AAV5 than from vectors derived from other forms of AAV. Further, it was shown that AAV5 could be used to induce cells to successfully convert the information in the large genes into protein. When AAV5 containing the mouse gene Abca4, which is the mouse correlate of the gene mutated in individuals with recessive Stargardt disease, was injected into the eye of mice lacking Abca4, improvement in the function of the eye was observed. The authors therefore concluded that vectors derived from AAV5 could be useful for treating individuals with recessive Stargardt disease.

Journal reference: Serotype-dependent packaging of large genes in adeno-associated viral vectors results in effective gene delivery in mice. Journal of Clinical Investigation. April 16, 2008.