Factors impeding efficient expression of factor VIII complementary DNA minigenes

Haemophilia A is a bleeding disorder that affects approximately 1 in 10,000 males. It is caused by a deficiency of functional blood-clotting factor VIII. Protein-replacement therapy has been effective as treatment, resulting in a vast improvement in the quality of life and dramatically increasing the life expectancy of patients. However, therapy with plasma-derived factor VIII has allowed the transmission of several human viruses, such as hepatitis viruses, human immunodeficiency virus and parvovirus B19. To date, the safety of the therapeutic agent is one of the key issues in haemophilia A treatment. The use of recombinant factor VIII in haemophilia therapy can avoid the dependence on blood-derived products and prevent the occurrence of transfusion-associated infections with blood-borne pathogens. Gene therapy could go further, and offers the prospect of one-time treatment which may, optimally, achieve a total cure of the disease. Therefore, haemophilia is an appealing and challenging target for somatic-cell gene therapy. On the basis of the phenotypic correction that is achieved upon infusion of factor VIII protein, it is expected that an increase in the factor VIII plasma level to 10% of the level found in healthy individuals would suffice to prevent the manifestation of the bleeding tendency. In this paper, we review the progress and the problems of gene therapy for haemophilia, with special focus on the problems specifically associated with the transfer and expression of human factor VIII complementary DNA.