Scottish scientists believe they have found a way to target gene therapy more precisely - avoiding the need for potentially harmful higher doses.
Gene therapy could help treat disease
They have created a virus which stays in the human bloodstream for longer, delivering genes to the right cells.
Viruses are normally removed in large numbers from the blood at the liver, but the virus evades this system.
Researchers at Glasgow University say that even at lower doses, the therapy will work for longer in the body.
Gene therapy was once considered a promising way to treat hundreds of genetic disorders, but there have been relatively few successes in recent years.
Doctors still hope, however, that conditions such as cystic fibrosis, muscular dystrophy and haemophilia could be tackled this way in future.
The biggest problem is getting the replacement genes into sufficient numbers of target cells.
Often, the only way to do this is to introduce huge numbers of copies of the virus created to carry them, which increases the risk of serious side-effects in the patient.
The Glasgow team is one looking for ways to get a bigger effect using fewer copies of the virus.
Dr Andrew Baker, leading the team, wanted to use an "adeno-associated virus" (AAV) - a cold virus - to carry his new genes into the cells that line blood vessels.
In theory, it might be possible to inject the viral "vector" into any vein and let is circulate around naturally, "infecting" these vascular endothelial cells.
However, when circulating blood reaches the liver, a mechanism to filter out foreign particles springs into action, and many of the viral copies are taken out.
Dr Baker's team modified the AAV so that it could avoid being "quarantined" at the liver, and remain in the bloodstream longer, potentially infecting far more cells.
Studies in mice suggested that it stayed in the blood far longer than the unmodified virus.
In addition, the virus carried extra chemicals which helped it bind specifically to the endothelial cells.
Dr Baker said that the finding could lead to gene therapy vectors tailored to individual cell types.
He said: "It may be possible to design and construct genetically engineered 'designer' gene therapy for selectively delivering genes to any part of the body."
Dr Matthew Wood, from the University of Oxford, said that better targeting of gene therapy could lead to lower doses, and improved safety for patients.
He said: "At the moment you would have to give viruses in such numbers that an immune response is far more likely. You simply don't get approval to carry out that kind of trial on human patients.
"Safety is the crucial thing when it comes to gene therapy."
The study was published in the journal Circulation.