Gene therapy usually seeks to fix a genetic disease at the DNA level. But just like you can sometimes catch a falling vase before it hits the ground, cystic fibrosis researchers have now found they can intervene by correcting a faulty protein as it is being made.
In cystic fibrosis, mutations in a gene called CFTR prevent lung cells from keeping fluids balanced and interfere with the body's ability to fight off bacteria, leading to clogged lungs and chronic infection. Most attempts to correct the problem have tried to deliver extra copies of the "healthy gene" to lung tissue and hope they get expressed. But a team led by cell biologist John Englehardt at the University of Iowa, Iowa City, decided to try to save the protein as it is being made from the faulty gene.
When cells manufacture a protein from the chromosomal blueprint, they first make an intermediate template called messenger RNA (mRNA), which is spliced to a finished form, which is then translated into a protein. Englehardt's group, working with Intronn, a biotechnology company based in Raleigh, North Carolina, hoped to replace the damaged mRNA section in the most common cystic fibrosis mutation, called DF508, by splicing in the normal mRNA fragment. In previous work, the Intronn group showed they could do this in cultured cells.
To follow up, Englehardt created mice that nurtured lung cells from cystic fibrosis patients containing DF508. He infected the human cells with a virus that carried DNA that could produce a normal fragment of mRNA, hoping the cell would replace the defective fragment while splicing the mRNA. After 48 hours, Englehardt looked for repaired mRNA. About 1% of the mRNA molecules had been fixed, the team reports in the January issue of Nature Biotechnology. They then tested how well the cells transported chloride ions, an indication of how well they were functioning. That activity was about 16% of normal. Together, these results are exciting, says Englehardt, because other research suggests that some people are healthy although only 8% of their CFTR mRNA is normal.
Although careful to point out that this technology is a long way from the clinic, molecular biologist Thomas Reynolds at Targeted Genetics Corp. in Seattle, Washington, calls the work a "pretty strong proof of concept." And by correcting the faulty mRNA instead of adding extra copies, there's no risk of overdosing, he says: "This is a next-generation technology that potentially could let us make the right amount of CFTR in the right cells."