Adenovirus as a vaccine platform.

Abstract

Adenovirus has been used extensively as a gene therapy vector due to its ability to efficiently infect human cells and achieve high levels of transgene expression. Although adenovirus has proven to be a highly effective gene delivery vehicle, the immune response elicited against components of the virus capsid and foreign transgenes encoded by the vector has limited its therapeutic use. In the present studies two strategies were undertaken that use the immune response elicited by adenovirus in the design of vaccines against anthrax. The first strategy attempted to take advantage of the immune response generated against foreign transgenes encoded by adenovirus vectors. A codon-optimized reading frame encoding domain four of <italic>Bacillus anthracis</italic> protective antigen was incorporated into a first-generation adenovirus vector, Ad.D4, and used for immunization. Vaccination of mice with Ad.D4 produced high levels of anti-protective antigen antibodies two weeks after injection, and these antibodies were able to neutralize anthrax lethal toxin in vitro. In addition, ELISPOT analysis of splenocytes from Ad.D4 immunized mice revealed that high levels of antigen specific interferon-gamma-secreting cells were present after vaccination. Mice vaccinated with Ad.D4 survived challenge with purified anthrax lethal toxin and Sterne 34F₂ strain anthrax spores. The second approach sought to take advantage of the robust antibody response generated against components of the adenovirus capsid. A 30 amino acid peptide from protective antigen was incorporated into hypervariable region five of hexon, the most abundant protein in the adenovirus capsid, to make Ad.HVR5=PA30. Incorporation of this peptide into hexon did not adversely affect virus growth, gene expression, or thermostability. Two immunizations with Ad.HVR5=PA30 elicited anti-protective antigen IgG in mice. However, these antibodies were unable to neutralize lethal toxin in vitro, and did not provide protection upon challenge with purified lethal toxin. These studies outline new approaches for the development of adenovirus-based vaccines against anthrax.