What is gene therapy?

Many diseases such as cystic fibrosis, muscular dystrophy, haemophilia and cancer are caused by faulty genes. Gene therapy involves the addition of a healthy, working copy of the faulty gene into the appropriate cells of the body. So instead of treating the symptoms of the disease, like most conventional medicines, gene therapy has the potential to correct the underlying cause.

How does gene therapy work?

The two most common ways used to transfer genes into cells are:

Viruses

Viruses have evolved to enter the cells of the body efficiently. Scientists have harnessed this property for gene therapy by putting a copy of the therapeutic gene into the virus that then carries it into the cell. The adenovirus (one cause of the common cold) is an example of a virus that has been used extensively for gene therapy.

Liposomes

Liposomes are fatty substances that naturally adhere to the surface of cells. Coating the gene with liposomes protects it and encourages it to enter the cell.

Why use gene therapy to treat CF?

Conventional treatments for CF include the use of physiotherapy, antibiotics and pancreatic supplements. Many patients require treatment four times daily, including a considerable time spent on physiotherapy. This combination of treatment has helped increase life expectancy considerably to the current median of approximately 30 years of age. Despite small further improvements, more recently it has become apparent that there is a need for a more effective and convenient therapy. The identification of the gene responsible for CF (the cystic fibrosis transmembrane conductance regulator or CFTR protein) in 1989, was responsible for the advent of potential new treatments for CF. Gene therapy, the transfer of a normal copy of the CFTR gene into the lungs of CF patients, was proposed as an attractive new option.

CF gene therapy - progress to date

Only a year after the gene for CF was identified scientists showed in cells in the laboratory that it was possible to correct the CF defect by adding a healthy copy of the gene. These findings have been consistently repeated by other groups using a variety of models and gene transfer agents. Studies in humans followed quickly. Gene therapy for CF has been tested in humans using both viruses and liposomes. Five of the liposome trials were undertaken by members of the UK CF Gene Therapy Consortium. These early studies were concerned mainly with safety issues. The amount of gene transfer achieved is similar for both systems and is probably still too small to have any real therapeutic benefit - although it is important to note that none of these trials actually measured therapeutic

 benefit. Also at present the effect seen (gene expression) only lasts for a few days.

The future of CF gene therapy

The scientific principle of gene therapy for CF is a sound one and the technology already exists to transfer the CF gene into the airway cells in man but there are still challenges ahead of the field. The two main challenges are getting the gene into the cells more efficiently and to make gene expression last longer. However the field is moving forward rapidly and with the development of better new viruses and liposomes these problems are surmountable. The members of the UK Cystic Fibrosis Gene Therapy Consortium have played a significant role in bringing the field of gene therapy for CF to where it is today. After initial encouraging clinical trials most research for CF gene therapy has returned to the laboratory to solve the problems mentioned above. In the UK there are no trials ongoing at present. It is the goal of the Consortium to work together to meet the challenges and enhance progress to a Phase 3 (large-scale) study by 2009.

More information about: How gene therapy may be improved.

Links to further information on:

CF gene therapy clinical trials

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