Revamped gene therapy for 'bubble boy' immune condition does well in trial

Gene therapy to treat children with 'bubble boy syndrome' seems to be both safe and effective, a study published in the New England Journal of Medicine has found.

Eight out of nine babies treated were alive one to three years after being given the treatment, when they normally would have died before they turned one.

The children lack a gene that produces a protein vital for a functioning immune system; as this gene is found on the X chromosome this condition almost always occurs in boys. Patients with this X-linked severe combined immunodeficiency (SCID-X1) traditionally had to be kept in sterile conditions (or 'bubbles') to prevent infections.

The treatment tested was an altered version of a previous gene therapy that improved immune systems but caused leukaemia in some patients.

Professor Adrian Thrasher, who led the research at Great Ormond Street Hospital, said: 'While the long term effect on the development of cancer across the lifetime in these patients remains unknown, the changes that we have made to this vector appear hugely promising.'

Gene therapy inserts a working copy of the missing gene using a viral vector. The viruses insert their own DNA into the genome of the cell they infect, allowing them to produce the therapeutic protein for as long as that cell lives.

Initial attempts to treat bubble boys with gene therapy proved that it was possible to give these children functioning immune systems; however a quarter of these children went on to develop leukemia. It was later found that the viruses used in these early trials tended to insert themselves in the patients' genome close to certain genes, causing these genes to 'turn on'; the activation of these genes caused these cells to grow and multiply faster, leading to cancer.

This improved version of the therapeutic virus appears to be safer for two reasons: it is less likely to insert next to potentially cancer-related genes, and it is less likely to activate any nearby genes.

While these are only the interim results of the study, they are very encouraging, the scientists say. Of the nine children, seven developed seemingly healthy immune systems, which were able to fight off bacterial and viral infections contracted before treatment. One boy, who received a lower dose of virus, did not seem to rebuild his immune system after the gene therapy, so instead received a successful cord blood stem cell transplant. The last child died from a pre-existing viral infection before the new immune cells had time to properly develop.

None of the children enrolled have developed leukaemia, although they will be monitored throughout childhood to see whether the risk has been entirely removed. If this treatment turns out to be both effective and safe in the long-term, researchers hope that it could be applied to a number of other genetic childhood diseases.