Dr. Kenneth Brigham is studying inherited defects in a gene linked to lung inflammation and pulmonary emphysema. (photo by Dana Johnson)
Gene therapy on horizon for lung disease patients
The first studies to deliver a normal alpha-1 antitrypsin (AAT) gene to human beings were a success, Vanderbilt University Medical Center researchers reported recently in Human Gene Therapy.
The findings are another step towards gene therapy for patients who, because of inherited defects in the AAT gene, have chronic inflammation in the lungs and develop pulmonary emphysema at an early age.
Alpha-1 antitrypsin is an enzyme that limits the activity of inflammatory cells and is important to maintaining healthy lungs. Individuals who produce an abnormal form or none of the enzyme require weekly intravenous infusions of AAT protein purified from pooled human serum to fight lung disease.
"Prolastin (purified AAT protein) is extremely expensive, and as a human serum product, it is sometimes in short supply and carries some risk of serum-born infections. Gene therapy is a desirable alternative to this treatment," said Dr. Kenneth L. Brigham, professor of Medicine, director of the division of Allergy, Pulmonary, and Critical Care Medicine and the Center for Lung Research, and holder of the Ralph and Lulu Owen Chair in Pulmonary Diseases.
Investigators in the Center for Lung Research introduced a liquid containing the normal AAT gene into one nostril of five patients with AAT deficiency. Fat globules called liposomes were used to camouflage the gene and smuggle it into the epithelial cells lining the nose.
Liposomes are less efficient gene delivery vehicles compared to the viruses often used for gene therapy. But they are considered safer, according to Brigham.
The researchers analyzed nasal cells and nasal lavage fluid to determine whether the gene entered the cells and directed production of normal AAT protein.
Their results were encouraging. They found a significant increase in AAT protein in the nostril that was exposed to the gene, but not the other nostril. They were also able to demonstrate the presence of the introduced DNA as well as messenger RNA copied from the gene.
"I think these findings will be recognized as important to the field of gene therapy," Brigham said. "To my knowledge, this is the first study involving gene transfer in humans that shows statistically significant results."
To assess physiologic effects of the gene delivery, the researchers measured levels of interleukin-8, a pro-inflammatory molecule that can serve as an index of inflammation. Studies in animals had suggested that a liposome-gene mixture itself could cause inflammation.
Brigham and colleagues, however, detected reduced levels of interleukin-8 in fluid from the gene-exposed nostril, suggesting an anti-inflammatory effect of the treatment.
In samples collected from the same patients while they were receiving the intravenous infusions of AAT protein — before exposure to the gene — interleukin-8 levels were not reduced.
"The interesting thing was, even though infusion of Prolastin resulted in normal concentrations of AAT protein in the nasal lavage fluid, interleukin-8 was not affected. It's high at baseline when the patients are not on any therapy, and it remains high when they are receiving protein.
But if they express the introduced AAT gene locally in the nose, there is decreased interleukin-8–decreased inflammation," Brigham said.
The researchers hypothesize that local production of the AAT protein in nasal cells gives it special access to places the intravenously introduced protein cannot reach.
"We're very excited about this anti-inflammatory effect," Brigham said. "It could be applicable to a whole range of diseases where there's local inflammation in the lung that isn't due to a deficiency in AAT, but that could be treated by expressing AAT locally in the lungs."
As an initial test of this idea, Brigham and colleagues will introduce the AAT gene-fat globule mix into nostrils of patients with cystic fibrosis and assess whether expression of AAT can suppress nasal inflammation in these patients.
For AAT-deficient patients suffering from pulmonary emphysema, the next step on this march toward gene therapy is a trial of AAT gene delivery to the lungs. The investigators have worked with an aerosol device manufacturer to develop the most efficient instrument for blowing the gene-liposome mix into the lungs. They plan to enroll 12 patients in a trial to begin within the next year.
Brigham's colleagues in the Center for Lung Research are Kirk B. Lane, Barbara Meyrick, Arlene A. Stecenko, Xiang Gao, and Richard Parker. The work was supported by the National Institutes of Health.