Assessing the Potential of Perinatal Gene Transfer Using Congenital Factor VII Deficiency as a Model System

Abstract 247

Many monogenic disorders are characterised by early onset of pathology that is associated with significant neonatal mortality and irreversible organ damage, thus mandating early therapeutic intervention. This is typified by congenital factor VII (FVII) deficiency (CFVIID), the most common autosomal recessive bleeding disorder, which typically presents with unexpected death during the perinatal period due to spontaneous intracranial haemorrhage. FVII circulates at a low level (0.5 ug/ml) in healthy humans and doses as low as 5% of this are therapeutically useful. This modest therapeutic goal and clinical need for an early intervention make CFVIID ideally suited for these important proof-of-concept studies. Using CFVIID as a model, we therefore explored the efficacy and safety of gene transfer following a single in utero administration of a novel self complementary adeno-associated viral vector (scAAV) encoding human FVII. In our preliminary studies in mice we showed that a single tail-vein injection of 5×10¹² vg/kg of an AAV vector in which infrequently used codons in the hFVII cDNA were replaced with those more commonly found in mammalian genes (codon optimised hFVII=codop-hFVII) resulted in a 37-fold increase in hFVII expression (216%±21.33%, n=3 of normal) over that observed with an equivalent dose of vector encoding the wild-type FVII cDNA (p=0.03). A dose-response study in mice demonstrated that therapeutic levels of hFVII could be achieved following a single tail vein injection of scAAV8-LP1-codop-hFVII at doses as low as 4×10⁸ vg/kg, whilst 1×10¹² vg/kg of scAAV8-LP1-codop-hFVII resulted in supraphysiological levels of expression (174.7%±54.7%) without any toxicity. In nonhuman primates, a single peripheral vein administration of scAAV5-LP1-codop-hFVII at a dose of 2×10¹¹ vg/kg resulted in therapeutic levels of hFVII expression in the plasma of young male (10.7%±3.1%, n=3) and female (12.3%±0.8%, n=3) macaques, suggesting that the gender specific differences in transduction efficiency in mice previously reported by our group is species specific. In utero intraperitoneal delivery of scAAV2/5-LP1-codop-hFVII vector (n=3) under ultrasound guidance at 0.9% gestation conferred therapeutic expression of human FVII at the time of birth (20.4%±3.7%) with expression being maintained above 5% of normal levels for at least 2 months postnatal. Re-administration of scAAV-LP1-codop-hFVII pseudotyped with capsid proteins of an alternative serotype (serotype 8) IV, approximately one year after in utero delivery, resulted in a further increase in plasma hFVII levels to average peak values of 165%±6.2%. In summary, our results demonstrate the safety and efficacy of in utero AAV-mediated FVII gene transfer in non-human primates. This supports the further cautious evaluation of this strategy in the clinic for the treatment of congenital FVII deficiency as well as other disorders with early onset of pathology and neonatal mortality such as Crigler Najjar type I disease, lysosomal storage and urea cycle disorders, where current treatment options are nonexistent or suboptimal.