Permanent phenotypic correction of hemophilia B in immunocompetent mice by prenatal gene therapy.

Hemophilia B, also known as Christmas disease, arises from mutations in the factor IX (F9) gene. Its treatment in humans, by recombinant protein substitution, is expensive, thus limiting its application to intermittent treatment in bleeding episodes and prophylaxis during surgery; development of inhibitory antibodies is an associated hazard. This study demonstrates permanent therapeutic correction of his disease without development of immune reactions by introduction of an HIV-based lentiviral vector encoding the human factor IX protein into the fetal circulation of immunocompetent hemophiliac and normal outbred mice. Plasma factor IX antigen remained at around 9%, 13%, and 16% of normal in the 3 hemophilia B mice, respectively, until the last measurement at 14 months. Substantial improvement in blood coagulability as measured by coagulation assay was seen in all 3 mice and they rapidly stopped bleeding after venipuncture. No humoral or cellular immunity against the protein, elevation of serum liver enzymes, or vector spread to the germline or maternal circulation were detected.

Gene therapy for ocular angiogenesis.

Ocular neovascularization is a central feature of diabetic retinopathy and age-related macular degeneration. These conditions are the major causes of blindness in the developed world. Current treatments are of limited efficacy and associated with significant adverse effects. Characterization of the molecular and cellular events involved in angiogenesis has led to the identification of a number of angiostatic molecules with potential therapeutic value. The systemic administration of small molecule angiostatic proteins risks significant systemic adverse effects and the effect of their intraocular injection is short-lived. Local gene transfer, however, offers the possibility of targeted, sustained and regulatable delivery of angiostatic proteins to the retina after a single procedure to introduce a vector to an intraocular site. The effect of intra-ocular delivery of recombinant viruses carrying genes encoding angiostatic proteins has been demonstrated in rodent models of ocular neovascularization. Recombinant adeno-associated virus-mediated local gene transfer of a vascular endothelial growth factor inhibitor controls both retinal and choroidal neovascularization. The clinical application of this approach may require the means to regulate gene expression in order to minimize the potential for adverse effects. Regulation of transgene expression by means of a hypoxia-responsive promoter offers an attractive strategy for the targeted and regulated delivery of angiostatic proteins to the retina in the management of ischaemia-induced ocular neovascularization. Preclinical studies of gene transfer in a large animal model following subretinal delivery of a recombinant adeno-associated virus vector have demonstrated efficient sustained reporter gene expression in cells of the outer retina. Recent progress has enabled the planning of clinical trials of gene therapy for ocular neovascular disorders.