975. Immunization with an Adenovirus Vector Expressing a P. aeruginosa OprF Epitope in the Capsid Enables Boosting of Anti-Epitope Immune Responses and Protects Against Pulmonary Infection with P. aeruginosa

Abstract

Top of pageAbstract Pseudomonas aeruginosa causes chronic infections of the respiratory tract, particularly in cystic fibrosis (CF). The outer membrane protein F (OprF) of P. aeruginosa is a promising vaccine candidate and our prior studies have shown that an adenovirus (Ad) vector expressing a secreted form of OprF (AdOprF), evokes protective immunity against P. aeruginosa. The present study is focused on development of a 2nd generation clinical vaccine candidate (AdOprF.RGD.Epi8) by two innovations to AdOprF to enhance the immunogenicity: (1) genetic modification of the Ad hexon to incorporate an epitope (Epi8) from OprF; and (2) genetic modification of the Ad fiber to incorporate an RGD sequence to enhance gene delivery to antigen presenting cells. We first evaluated the immunogenic properties of an Ad vector in which the Ad hexon protein was modified to include the 14-mer OprF epitope Epi8 in the hexon (AdZ.Epi8), with focus on the hypothesis that immune responses against epitopes that are part of the Ad capsid could be augmented with repeat administration. To evaluate the protective effect of immunization with AdZ.Epi8 against pulmonary infection with P. aeruginosa, C57Bl/6 mice, immunized with either AdZ.Epi8 or AdZ were challenged with a lethal dose of agar-encapsulated P. aeruginosa (laboratory strain PAO1 or two isolates of P. aeruginosa derived from patients with CF). Unimmunized mice or mice infected with AdZ died within the first 3 days. In contrast, more than 60% of the mice immunized with AdZ.Epi8 survived more than 2 wk (p 0.1, all comparisons). Similar results were observed in the CD4 Epi8-specific IL-4 as well as CD4 and CD8 Epi8-specific |[gamma]|-interferon cellular responses, suggesting that the addition of an OprF epitope to the Ad capsid enables boosting of the anti-OprF response. Finally, we evaluated the immunogenic properties of the combined AdOprF.RGD.Epi8 vector. Mice received AdOprF.RGD.Epi8, AdOprF, AdNull, (2|[times]|1011pu) or PBS and the anti-OprF antibody titers were determined at 2 and 4 wk. No anti-OprF antibodies were detected in the AdNull or PBS group. The mean titer for AdOprF was 5710 and 8602 at 2 and 4 wk, respectively, vs 11841 and 10632 for the AdOprFRGD.Epi8 injected mice, suggesting a faster and more robust induction of the anti-OprF humoral response with AdOprFRGD.Epi8. We conclude that the capsid modifications in AdOprF.RGD.Epi8 vector make it a more effective candidate vector for vaccination against P. aeruginosa.