Four patients with haemophilia B have been successfully treated with gene therapy, scientists at University College London and elsewhere reported on 10 December in the New England Journal of Medicine and on 11 December at the American Society of Hematology meeting in San Diego, California.
The trial marks the first unequivocal success in treating haemophilia B using gene therapy; patients no longer require injections of blood clotting factors up to 18 months after the single gene-therapy treatment.
Haemophilia B is caused by recessive mutations in the gene that encodes a protein called factor IX, and the treatment used viruses to deliver a gene that makes this protein to the patients’ liver cells. Two other patients who received the virus started to produce factor IX protein, but levels dwindled over time such that they still require injection of blood clotting factors to control bleeding.
In previous gene-therapy trials, patients produced therapeutic levels of factor IX for only a limited period of time. Scientists suspect that the patients’ immune cells destroyed the gene-modified cells.
In an editorial accompanying the article, Katharine Ponder of the Washington University School of Medicine in St. Louis, Missouri, called the trial a “landmark study.” If the gene-therapy treatment proves safe and effective in larger trials, it could replace the protein therapies conventionally used to treat haemophelia B, which can cost up to US$20 million over the lifetime of a patient.
Gene therapy is beginning to emerge from the dark ages it entered in the late 1990s, after an 18-year-old patient died after receiving an experimental treatment for his liver disease (see: Gene-therapy successes spur hope for embattled field). Gene therapy has been used successfully to treat a rare immune disease and research is underway testing therapies for numerous other conditions.
Image of Queen Victoria, who carried the gene for haemophilia B, via Wikimedia Commons