Development of Recombinant Adeno-Associated Viral Vector (rAAV) for Passive Immunisation Against Ebola.

Tan TK, Rijal P, Townsend AR, Hyde SC, Gill DR

Molecular Therapy, Vol 25 S1, Abstract 393

The American Society of Gene and Cell Therapy Annual Conference, Washington, DC, 2017

The 2014-2016 Ebola outbreak in West Africa was the largest in history leading to 28,639 cases, of which 40% were fatal. Better treatments and effective vaccines against Ebola virus are needed to prevent future recurrence. Multiple, novel, treatment options were assessed during the outbreak, including ZMapp™ monoclonal antibody therapy, which showed promising results in some patients. However, widespread adoption of this approach is hindered by high costs of monoclonal antibody manufacturing and the relatively short half-life of antibody in the blood circulation.

To circumvent such limitations, we propose to utilise recombinant adeno-associated virus (rAAV) delivered to the muscle to express the therapeutic monoclonal antibodies. A single intramuscular dose of rAAV encoding lipoprotein lipase has shown clinical efficacy in patients for at least 6 years demonstrating persistent transgene expression, together with a well-established safety profile. During an initial proof-of-principle study, we showed that a single dose of rAAV2/8 carrying secretory reporter gene (Gaussia luciferase (GLux)) leads to abundant expression of GLux at day 7 post administration, which increases and persisted in the blood circulation for at least 28 days (20,865 RLU/μl, 43,420 RLU/μl and 6220,000 RLU/μl; p<0.01, respectively for 1E9, 1E10 or 1E11 Genome Copies).

We then produced rAAV2/8 encoding KZ52 antibody, the first human anti-Ebola (Zaire strain) neutralising antibody, isolated from a recovered patient during the 1995 Kikwit Ebola outbreak. A single intramuscular dose of rAAV2/8 encoding KZ52 leads to expression of high human IgG (256.36 μg/ml) in the mouse serum at day 28 post administration, which is ~100-fold higher than the EC90 required for in vitro neutralisation of the wild-type Ebola virus (J Virol 73:6024-6030,1999). In terms of functioning titre in the serum, we detected high serum binding and neutralising antibody titre against an Ebola (Zaire) glycoprotein pseudotyped influenza virus (EC50: 1:7000 & 1:4356, respectively) in BALB/c mice following a single dose of 1E10 or 1E11 Genome Copies of rAAV2/8 expressing KZ52. To test its efficacy in preventing Ebola infections, we are currently undertaking a protection study against Ebola in the guinea pig challenge model.

Together, these preliminary data support the generation of rAAV vectors carrying a cocktail of novel antibodies isolated from vaccinated donors for maximum clinical efficacy. In the event of future outbreaks, matched rAAV cocktails which were produced in advance, lyophilised and stockpiled can be used to provide timely prophylaxis among healthcare workers.