COMMENTARY Clinical progress in gene therapy : Sustained partial correction of the bleeding disorder in patients suffering from severe hemophilia

The field of gene therapy has gained momentum in recent years thanks largely to the clinical successes for the treatment of monogenetic hereditary diseases. Since the early years of gene therapy, hemophilia had been widely regarded as an important target disease in its own right and a trailblazer for the field at large (Axelrod et al., 1990; Kay & High, 1999). The disease and the underlying genetics are well understood. Moreover, therapeutic efficacy can easily be ascertained based on robust clinical endpoints (i.e. circulating clotting factor levels, bleeding episodes) and there are several wellestablished and validated hemophilic animal models available for pre-clinical testing.