Cystic fibrosis flaw reversed in vitro.

Cystic fibrosis flaw reversed in vitro 

In separate laboratory efforts using cultured human cells, two research teams have corrected a cellular defect that causes up to 75 percent of cystic fibrosis cases. They accomplished this feat by inserting a gene that produces a normal protein, known as cystic fibrosis transmembrane conductance regulator (CFTR), into cells bearing a mutant gene that encodes an abnormal version of the protein.

Cystic fibrosis, an inherited disease, strikes one out of every 2,000 white children in North America and kills most of them before age 30. The new studies mark the first time scientists have engineered cells to produce normal CFTR. Last year, researchers isolated the detective protein and identified the mutant gene encoding it (SN: 9/2/89, p.149).

"The research is a milestone," says Robert Beall of the Cystic Fibrosis Foundation in Bethesda, Md. "It means that gene therapy [for this illness] is not a matter of it, but when."

In addition to gene therapy applications, the work suggests other novel ways to help treat cystic fibrosis, says Michael J. Welsh of the Howard Hughes Medical Institute at the University of Iowa in Iowa City, who coauthored one of the new studies. The ability to produce both defective and normal versions of the protein, he says, may enable researchers to identify CFTR's exact function. Scientists know that CFTR helps regulate the transport of chloride ions into and out of cells, and they believe that a flawed version resulting from genetic mutation slows that flow, leading to the thick mucus secretions that clog the airways and leave cystic fibrosis patients vulnerable to lung infections.

Once researchers elucidate the protein's structure, they might succeed in designing drugs to alter the flawed protein so that it no longer causes disease, Welsh suggests. He adds that an antibody test for the abnormal protein could speed disease diagnosis.

Welsh and co-workers from Tufts University School of Medicine in Boston and Genzyme Corp. in Framingham, Mass., used Vaccinia (cowpox) viruses to insert multiple copies of normal CFTR genes into cells cultured from the airways of a cystic fibrosis patient. Before gene insertion, the diseased cells could not activate a messenger chemical, known as cyclic AMP, to open chloride ion channels. After the researchers added copies of the normal gene, biochemical and electrophysiological tests demonstrated that cyclic AMP opened the channels and allowed ion transport, eliminating the cellular defect. Insertion of the mutant version of the gene did not open the chloride channels, the team reports in the Sept. 27 NATURE.

James M. Wilson of the Howard Hughes Medical Institute at the Univesity of Michigan in Ann Arbor, with colleagues from the University in Alabama at Birmingham and the Hospital for Sick Children in Toronto, Ontario, achieved similar results using the same gene but a different virus and cell type.

Wilson says his group chose a retro-virus over the highly efficient Vaccinia because the retrovirus does not kill the cells it infects and thus allows investigators to study cell cultures indefinitely. (Cultured cells infected with Vaccinia survived about 24 hours -- just long enough to show repair, Welsh notes.)

Wilson's group inserted single copies of the gene for CFTR into cultured pancreatic cells with the cystic fibrosis defect. In the Sept. 21 CELL, they report test results showing that the genetic addition repaired the abnormality.