51. Rapid and Long Term Protection to Pseudomonas aeruginosa Using a Platform Vaccine Concept That Mediates Both Passive and Active Immunity

Abstract

We have developed a platform technology against infectious agents that mediates both passive and active immunity, with rapid, passive protection through the genetic delivery of an anti-pathogen monoclonal antibody together with long term protective active immunity evoked through the presentation of a defined pathogen neutralizing epitope. Both strategies are incorporated into an E1 E3 adenovirus (Ad) vector through the coding of an antibody in the transgene and incorporation of a pathogen antigenic sequence into the hexon capsid protein, respectively. As a model to evaluate the vaccine, we have applied this to a public health-important infectious agent, Pseudomonas aeruginosa, a gram-negative ubiquitous pathogen associated with persistent pulmonary infection in hosts with bronchiectasis, such as cystic fibrosis, compromised immune function or who have pulmonary clearance mechanisms disrupted by endotracheal tubes. Although P. aeruginosa is susceptible to antibiotic therapy, chronic colonization of the respiratory tract with frequent exacerbations is typical of high risk populations. Pathogenicity linked to P. aeruginosa infection results from the release of numerous virulence factors that can degrade tissues such as proteases and phospholipase and others that diminish cellular functions via exotoxins. The passive vaccine mediates expression of an antibody to an exotoxin secreting protein, PcrV, a known P. aeruginosa a neutralizing target. Antibody expression is mediated by the nonhuman C7 serotype Ad to avoid the highly prevalent preexisting immunity to serotype 5 Ad. In parallel, the Ad capsid hexon protein has a short epitope, Epi8, derived from the outer membrane protein F of P. aeruginosa, an established neutralizing epitope for long term active immune protection to P. aeruginosa. Western analysis confirmed the expression of the anti-PcrV antibody and ELISA assays of anti-Epi8 antibodies evoked from the hexon modified Ad confirmed the active response. In vivo challenge assays in mice used agar-encapsulated P103 strain of P. aeruginosa titered for lethality. The passive vaccine significantly reduced colonization of the lung of mice intranasally challenged with a lethal dose of P. aeruginosa at 3, 5 and 10 days after vaccination in comparison to mice vaccinated with a control Ad vector, whereas the active vaccine significantly reduced colonization at 5 wk post-vaccination. The combination of the active and passive vaccines therefore provides immediate and long term protection to exposure of P. aeruginosa. The concept of a combined passive and active vaccine to provide immediate protection with long-term immunity could be an important tool for public health, particularly for bioterror-related infectious agents.