Factor VIII or IX is then produced by the invaded cells. If the vector can invade enough cells, and the body does not destroy the vector by creating antibodies to this foreign agent, sufficient Factor VIII or IX can be manufactured in the body to prevent bleeding. Eventually, after a prolonged period of development, gene therapy might deliver a cure for hemophilia. He might even need infusions of factor concentrate for serious bleeds and surgery. The frequency of these infusions is difficult to predict.
Estimates range from once a year to once every several years.
Third, the hemophiliac s genetic mutation will not have been corrected. He will still transmit the hemophilia gene to his daughters. For the present, gene therapy should be seen as a potential dramatic improvement in treatment, and not as a cure for hemophilia. The most obvious benefit of gene therapy is that hemophiliacs would no longer need to have frequent infusions of factor concentrate. Today, hemophiliacs infuse Factor VIII or IX as frequently as three times a week to stop bleeding or to prevent it.