US researchers say they are a step closer to developing a gene therapy cure for cystic fibrosis (CF).
In lab tests their altered virus effectively delivered a new gene to replace the faulty one that causes CF and completely rid the lung of disease.
Previous attempts have been hampered by the immune system mopping up the virus before it delivered its cargo.
The University of California work is published in Proceedings of the National Academy of Sciences.
Although the gene therapy is still in its infancy, it has already been used with some success in diseases such as haemophilia.
UK researchers plan to begin the first large scale trial of gene therapy in CF patients this year.
Proof of concept
Around 8,000 people in the UK have CF and one in 25 are carriers for the condition. CF produces thick, sticky mucus that clogs the lungs and the pancreas, leading to life-threatening chest infections and problems with digestion.
Existing treatments only ease symptoms and life expectancy is low - most with CF die before they reach 40.
In the future it is hoped that gene therapy will provide a cure by replacing the defective CF gene which disables or destroys a protein known as CFTR.
In order to get the new, healthy gene into the cells, scientists use a harmless virus.
The University of California team, working with experts from the University of Iowa, found a way to make this virus more effective at entering lung cells.
They mutated the adeno-associated virus to develop two major possessions - the ability to bind to different receptors or bind to a more plentiful receptor on the surface of lung cells and to make it past the cell surface membrane and into the cell.
Lead researcher Professor David Schaffer said: "In human lung tissue, it completely rescued the chloride ion transport properties of the cells after delivering the correct copy of the CFTR gene to replace the mutated copy of the gene that is present in CF patients."
They now plan to test the treatment further and to adapt the virus to gene therapy for other diseases, including Alzheimer's.
A spokeswoman from the UK Cystic Fibrosis Gene Therapy Consortium, which is trialling gene therapy in patients, said: "The techniques used in this research are innovative, but more work is needed before this could be translated into clinical benefit for people with CF.
"Although the results are positive in human lung tissue in a laboratory, it remains to be seen if it would work in the patient."
The UK CF Gene Therapy Consortium, funded by the Cystic Fibrosis Trust, are using a non-viral method to get the gene therapy product into the body and anticipate going to a major multi-dose clinical trial in 2010.