Different Adjuvants Significantly Influence the Immunogenicity and Protective Capacity of a Melioidosis Subunit Vaccine

Professor Mary Burtnick, University of Nevada, Reno School of Medicine, USA

Mary N. Burtnick1,2, Sarah B. Weiby1, Sineenart Sengyee1, Sergei S. Biryukov3, Christopher K. Cote3, David DeShazer3 and Paul J. Brett1,2

1Department of Microbiology and Immunology, University of Nevada, Reno School of Medicine, Reno, NV, United States

2Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand

3Bacteriology Division, United States Army Medical Research Institute of Infectious Diseases, Frederick, MD, United States

Burkholderia pseudomallei, the etiologic agent of melioidosis, is a bacterial pathogen that causes severe disease in humans and animals. Diagnosis and treatment of melioidosis can be challenging and no licensed vaccines currently exist. Several studies have shown that this Centers for Disease Control Tier 1 select agent expresses a variety of structurally conserved protective antigens that include cell-surface polysaccharides, cell-associated and secreted proteins. Based on this, such antigens have become important components of the subunit vaccine candidates that we are currently developing in our laboratory. In the present study, the 6-deoxyheptan capsular polysaccharide (CPS) was purified from Burkholderia thailandensis E555, chemically activated and covalently linked to recombinant CRM197 diphtheria toxin mutant (CRM197) to produce CPS-CRM197. Additionally, affinity chromatography techniques were used to prepare highly purified, recombinant, tag-less B. pseudomallei hemolysin co-regulated protein 1 (Hcp1) from E. coli. Immunization of C57BL/6 mice with CPS-CRM197 plus Hcp1 formulated with Alhydrogel and ODN 2006 resulted high-titer IgG responses against the CPS component of the glycoconjugate as well as high-titer IgG and robust IFN-g secreting T cell responses against Hcp1. When the same vaccine antigens were formulated with Adju-Phos and ODN 2006, however, only high-titer IgG responses against CPS were detected. Furthermore, studies demonstrated that immunization of mice with the antigens formulated with ODN 2006 alone resulted in IgG responses against CPS but no IgG or IFN-g secreting T cell responses against Hcp1. In contrast, immunization with the vaccine antigens formulated with Alhydrogel alone resulted high-titer IgG responses against both CPS and Hcp1 but no IFN-g secreting T cell responses against Hcp1. Interestingly, this loss of T cell responses correlated with a lack of protection of immunized mice when challenged with a lethal inhalational dose of B. pseudomallei K96243. Collectively, these studies highlight the influence of different adjuvant systems on our vaccine antigens and provide valuable insights towards the development of a safe, affordable and effective melioidosis vaccine to combat disease caused by B. pseudomallei.