MICA: An open label dose-escalation study of a novel adeno-associated viral vector for gene transfer in subjects with haemophilia A

Haemophilia A is a bleeding disease in males due to very low levels of coagulation factor VIII (FVIII) in the blood. The major effect on health in severely affected patients is spontaneous (in the absence of trauma or injury) repeated bleeds into joints like the knee, hip, ankles and elbows, cause joint damage and chronic disability. Rarely, the disease causes death due to bleeding into the brain or other important organs. The current treatment is intravenous injection of FVIII clotting factor protein concentrates, in response to bleeding. Regular injection of FVIII clotting factor protein concentrates three times a week prevents spontaneous bleeds and joint damage.

This study plans to use a virus called adeno-associated virus (AAV), which in nature causes no disease, and can be engineered to deliver the human FVIII gene (AAV8-HLP-codop-hFVIII-V3) to the liver, where FVIII is normally made. We have recently used this type of AAV vector for gene therapy of haemophilia B, a related condition with identical clinical manifestation, except that it arises because of low levels of a different protein called factor IX. In this study stable expression of FIX at levels 1-6% of normal were observed in all 10 participants without long lasting toxicity, resulting in significant patient benefit.

Following extensive preclinical studies, a single dose of AAV vector containing a novel more potent human clotting factor VIII variant (AAV8-HLP-codop-hFVIII-V3) will be administered into a peripheral vein of adult patients with severe Haemophilia A. We propose to test three dose levels: 2e11, 6e11 and 2e12 vector genomes per kg body weight, which is the same dose range tested in the Haemophilia B clinical trial.

The main objective will be to establish the safety and to do so we have established a comprehensive monitoring plan which includes an array of clinical and laboratory tests. Enrolment of each subject will proceed only after the previous subject has been observed for at least 28 days for acute toxicity. Enrolment will be suspended if serious adverse toxicity is observed in one subject.

The other objective is to determine the dose of vector that results in expression of FVIII at more than 5% in peripheral blood. This level of expression can significantly reduce the frequency of severe bleeding episodes.

The reason why human studies are critical is because our haemophilia B gene therapy trial, as well as other gene therapy studies in the field, have shown that animal models are poor predictors of outcome in humans. Successful Haemophilia A gene therapy will transform the treatment paradigm for this disease and will also support the development of gene therapy for other diseases affecting the liver including lysosomal storage disorders and hepatocellular carcinoma.

The goal of this proposal is to conduct a Phase I/II gene therapy trial for haemophilia A (HA), the most common inherited bleeding disorder, which results from mutations in the human factor VIII (hFVIII) gene. The same serotype 8 pseudotyped adeno-associated virus vector (AAV8) that mediated stable (>3 years) therapeutic expression of transgenic protein without long-lasting toxicity in subjects with haemophilia B (HB), a related condition, will be used to evaluate a novel FVIII expression cassette: HLP-codop-hFVIII-V3. This expression cassette (5.2kb) has been engineered so that it is efficiently packaged into AAV8 virions, despite being larger than the normal packaging capacity of this vector (4.6kb). Extensive testing in animals showed that in the context of AAV8 this oversized hFVIII cassette was at least 20X more potent than vectors encoding wild-type FVIII. Importantly, AAV8 HLP-codop-hFVIII-V3 had an excellent safety profile even at doses that were 10X higher than planned for use in clinical studies. A first in man, Phase I/II dose escalation study of the oversized hFVIII expression cassette is now proposed in adults with severe HA. The primary objective is to establish the safety and efficacy of systemic administration of AAV8-HLP-codop-hFVIII-V3 vector over three different dosage levels: 2e11, 6e11 and 2e12 vector genomes/kg. This is the same dose range tested in the HB clinical trial. We therefore predict that systemic administration of the oversized hFVIII vector will be safe, with absence of persistent Grade III or greater dose-limiting toxicity (according to modified CTCAE v.4). The key secondary objective is to define the dose of vector that mediates expression of hFVIII at > 5% of normal in peripheral blood; a level that can significantly ameliorate the severe bleeding phenotype. Successful HA gene therapy will transform the treatment paradigm for this disease and impact on a variety of other disorders affecting the liver.

A successful haemophilia A gene therapy trial will have wide ranging impact. The following groups will benefit directly and indirectly from the proposed research:

Scientific community:This study will address a critical research question regarding the safety and efficacy of oversized AAV vector in humans, especially on the question of safety with regards risk of immunogenicity of the AAV8 capsid and the development of neutralising antibodies to transgenic FVIII protein. This is critical information for the scientific community especially as inhibitors occur in over 30% of subjects treated with FVIII concentrates and renders these individuals refractory to further treatment with FVIII protein. In addition, as we will be able to share the outcome data that emerges out of this academic study fully with the wider scientific community, it may guide/inform gene therapy approaches using oversized AAV for other inherited as well as acquired disorders, including hepatocellular carcinoma, Wilson's disease, congenital FVII deficiency, ADA deficiency, Crigler-Najjar, MPS-VI, porphyria, alpha-1 antitrypsin deficiency, and phenylketonuria

Patients: Expression of hFVIII at >1% of normal following gene transfer could have an immediate impact on the participants as illustrated by the haemophilia B clinic trial in which the same vector platform was used. In that study the majority of subjects were able to discontinue prophylaxis and remain free of spontaneous haemorrhage despite leading active lives. Those that could not stop prophylaxis were able to extended the period between prophylactic doses.

Health service: Reduction in treatment cost could result in a substantial financial saving which amounted to ~£1.5M at 3 years. This saving would be available for investment in other worthy treatment approaches.

Industry: The results will provide the core data required for the necessary investment towards the development of AAV8-HLP-codop-hFVIII-V3 as well as two other similar approaches being developed by companies formed by Drs Samulski and High at the University of North Carolina, Chapel Hill and Children's Hospital of Philadelphia respectively.