The side effects of factor replacement therapy seen in the past could be avoided. Gene therapy would give peace of mind from such dangers. Safe, effective factor concentrates are far too expensive for the health systems in many countries. Even regular treatment with plasma or cryoprecipitate is difficult to get in countries that do not have a well-organized blood collection network. At the very least, gene therapy provides some hope that hemophilia treatment can eventually be extended to those in the developing world.
Viruses seem to offer the most hope.
This is because viruses are very efficient at getting into cells and entering the cell nucleus. Obviously, it would be of little benefit to the hemophiliac if he were to be infected by a disease-causing virus. Therefore, the virus has to be modified so that the disease-causing parts of the virus are removed. The virus maintains its ability to transfect the cell and deliver the gene. Adenovirus is a common human virus that sometimes results in the symptoms of the common cold.