When scientists first discovered the faulty gene that causes cystic fibrosis in 1989, many were excited about the possibilities of gene therapy as a treatment for the debilitating disease. There have, however, been many setbacks in the last 26 years, but a new, year-long trial may have just breathed new life into this method of treating sufferers.

Researchers have developed a gene therapy technique whereby patients breathed in molecules of DNA to replace the faulty gene with a normal, working copy of the gene. The study, published in the journal The Lancet Respiratory Medicine, used fatty bubbles called liposomes to deliver the “healthy” gene into the lungs. In the trial, some patients received monthly doses of the therapy and others were given a saline solution as a control. The results showed “encouraging” improvements as those inhaling the new therapy exhibited a 3.7% improvement in lung function.

Cystic fibrosis is a genetic disorder that affects an estimated 30,000 people in the U.S., 10,000 people in the UK and 90,000 worldwide. The disease, which mostly affects patients’ lungs, is caused by a mutation in a gene located on chromosome 7. Sufferers have sticky mucus filling their lungs, making it hard to breathe. There is currently no cure for the life-threatening disease, although there are treatments available to manage symptoms, such as physiotherapy, medication and nutrition.

Lead researcher Eric Alton stressed that the results were “modest and variable” and warned against over-interpreting the findings, Reuters reports. The effects of the gene therapy were inconsistent as some patients responded better than others,

The study is the world’s first demonstration that repeated gene therapy can improve lung function, Alton told The Guardian, but he explained that the technique is not yet ready for clinical use. Researchers plan to carry out further clinical trials to look at the effect of higher, more frequent doses, and look into other, more effective methods for delivering the DNA into the lungs.