Adeno-Associated Virus Vector Development for Monoclonal Antibody Expression to Prevent Ebola Virus Infection

Abstract

Adeno-associated virus (AAV) vectors are a highly efficient method of gene transfer to various cell types in vivo and are recognized for their strong safety profile. In December 2017, the Food and Drug Administration approved Luxturna, an AAV based treatment for blindness, which marks the first gene therapy to become commercially available in North America. This regulatory milestone underscores the potential for AAV therapeutics to expand beyond traditional gene replacement into new applications including AAV-mediated expression of monoclonal antibody (mAb) genes to prevent or treat infectious disease. Since its discovery in 1976, Ebola virus (EBOV) has caused dozens of small outbreaks predominantly in central Africa, however the 2014-2016 West African epidemic infected over 28,000 people and demonstrated the true epidemic potential of this zoonotic virus. Passive immunization through the use of recombinant antibodies has been a successful strategy for preventing EBOV disease in preclinical and clinical settings, albeit a costly and short-term solution. We hypothesized that AAV vectored expression of mAb genes in muscle cells would generate protective and sustained concentrations of mAbs in the serum, thus conferring a survival advantage upon an otherwise lethal EBOV challenge. To facilitate efficient mAb expression, we engineered a triple AAV6 mutant, termed AAV6.2FF, and characterized the in vitro and in vivo vector performance compared to the parental AAV6 as well as other commonly used capsids in the field. Our data demonstrated that AAV6.2FF mediated the most rapid and robust transgene expression following intramuscular injection and was selected as the capsid for all following AAV-mAb vectors. AAV6.2FF-mediated expression of EBOV glycoprotein mAbs 2G4 and 5D2 demonstrated 100% protection in mice against EBOV challenge in as little as seven days and as long as five months post vector administration without impacting the endogenous humoral response. Second generation vectors expressing mAb 100 and MR191 demonstrated serum concentrations as low as 25 g/mL to be protective against Ebola and Marburg virus respectively. Overall, these results demonstrate that AAV6.2FF-mAb expression offers a viable alternative for passive antibody transfer as well as a potential vaccine candidate for the suppression of EBOV outbreaks.