Genetic technology applied to medicine — practice question

A number of strategies have been explored for using gene therapy to treat cystic fibrosis. One method relies on viruses to carry normal alleles of the CFTR gene into epithelial cells in the airways. Viral delivery systems have two main drawbacks: • The virus may set off an immune response that destroys the infected cells. • Most non-pathogenic viruses are poor at entering cells, so only a very small number of cells receive the allele. Researchers in the USA produced a new strain, AAV2.5T, of AAV, a non-pathogenic virus. AAV2.5T has a better ability to bind to epithelial cells in the airways. Genes for the CFTR protein and for the enzyme luciferase were inserted into the virus DNA. When luciferin is added, luciferase produces a fluorescent green protein. The standard AAV strain and the AAV2.5T strain were introduced into cultures of epithelial cells from the airways. After luciferin was added, the number of cells that had taken up the viral genes was estimated from the strength of the green fluorescence that developed. The results are shown in Fig. 5.1.