An international team of scientists completed the first experiment on gene therapy for hemophilia B - a rare disorder of blood clotting due to the recessive mutation of the X chromosome gene encoding the plasma factor IX. In healthy people, the plasma factor IX is produced in the liver and from there goes into the blood, where its concentration is 4-5 ?g per 1 ml of plasma. In hemophilia B, the concentration of factor IX drops to 2% of the norm, which leads to a violation of the first phase of blood coagulation, which means that the slightest mechanical damage leads to the formation of bruising, joint bleeding and late bleeding. Treat hemophilia B symptomatically: when bleeding, external or internal, introduce antihemophilic serum with factor IX and complexes of other blood factors. Without these injections, even a small cut, bruise or spontaneous internal bleeding (and in hemophiliacs they are not uncommon) can lead to serious blood loss and even death, notes naked-science. In an experiment described in an article published in The New England Journal of Medicine, ten hemophilic patients were injected with viral vectors carrying a promoter and a transgene encoding factor IX. Once in the liver, the vectors inserted the promoter and transgene of a particularly active version of factor IX into the liver cells of the patient; this allowed to reduce the dose of viral vectors and avoid an immune response. 18 months after the injection, the liver of the participants in the experiment produced 34% of the normal amount of factor IX; for nine out of ten patients, this was enough to stop bleeding; eight patients no longer need regular injections of factor IX. No side effects were observed in 8 patients out of 10; in two cases, in response to injection of viral factors, the production of certain liver enzymes increased, but it was restored to the norm by steroid preparations.

In previous experiments, injections of viral vectors or transplantation of genetically modified cells with a normal factor IX gene did not yield positive results: in some cases, GM cells elicited a strong immune response, in others, cells did not produce factor IX in sufficient amounts. Hemophilia B suffers about 20% of all patients with coagulation disorders; scientists are looking for a way to cure a more common version of the disease, hemophilia A, associated with a congenital deficiency of the factor of blood coagulation VIII.