1. ¹Division of Pharmaceutics, The Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, TX
2. ²Special Pathogens Program, National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, MB, Canada
3. ³Department of Medical Microbiology, University of Manitoba, Winnipeg, MB, Canada
4. ⁴Department of Immunology, University of Manitoba, Winnipeg, MB, Canada
5. ⁵Gene Therapy Program, Department of Medicine, University of Pennsylvania Health System, Philadelphia, PA

^|[ast]|James Wilson had equity in Targeted Genetics at the time of the study.

Abstract

The Ebola hemorrhagic fever virus has drawn increasing interest in the past years due to an augmentation in the number of natural outbreaks and its potential use as a bioterror agent. To date, only vaccine based on Vesicular Stomatitis virus and Adenovirus as the vaccine carrier have successfully protected nonhuman primates against a lethal dose of Ebola virus. Adenovirus vector derived from human adenovirus serotype 5 (AdHu5) has the advantage of having a well document track record following in vivo administration to thousand of individuals in different clinical trials. However, natural exposure to Adenovirus may result in the generation of a potent immunity capable of compromising adenovirus-based vaccine efficacy. 30 to 50% of the human population in North America has levels of serum antibodies that can neutralize relatively high doses of AdHu5. The present study evaluated mucosal vaccination of mice with AdHu5 expressing the Ebola glycoprotein (Ad-EboGP) and the impact of pre-existing immunity to the Adenovirus vector on vaccine efficacy. Intramuscular (I.M.), oral or nasal administration of Ad-EboGP fully protected mice against a lethal challenge with mouse-adapted Ebola virus. However, oral or I.M. vaccination of mice pretreated with pooled human antibodies, mimicking the presence of pre-existing immunity as evidenced by neutralizing antibody (NAB) to AdHu5 in mice sera, resulted in 0 to 10% survival after challenge with mouse-adapted Ebola virus. Interestingly, nasalvaccination with Ad-EboGP was protective even in the presence of preexisting immunity and resulted in 100% survival with no weight loss after challenge with Ebola virus. In untreated mice, T (INF-|[gamma]| positive CD8 T cells following peptide re-stimulation) and B cell (NAB) responses were detected in all EboGP vaccinated groups although both responses were lower in mice receiving oral or nasal immunization when compared to mice administered I.M.. The presence of pre-existing immunity severely compromised the T and B cell responses in mice vaccinated orally or I.M. but not in mice receiving nasal immunization. Interestingly, PEGylation of the adenovirus vector partially rescued the B cell response but diminished the T cell response after oral vaccination of mice with pre-existing immunity and failed to improve survival. This study highlights the importance of vaccine delivery routes with regards to efficacy in the presence or absence of pre-existing immunity and provides new evidence for successful vaccination with AdHu5 and possibly readministration.