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Development of Subunit Vaccines That Provide High-Level Protection and Sterilizing Immunity against Acute
Mary N Burtnick1,2, Teresa L Shaffer3,2, Brittany N Ross4
1Department of Microbiology and Immunology, University of South Alabama, Mobile, Alabama, USA mburtnick@med.unr.edu pbrett@med.unr.edu.
Abstract:
Burkholderia pseudomallei, the etiologic agent of melioidosis, 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 pathogen expresses a variety of structurally conserved protective antigens that include cell surface polysaccharides and cell-associated and cell-secreted proteins. Based on those findings, such antigens have become important components of the subunit vaccine candidates that we are currently developing. In the present study, the 6-deoxyheptan capsular polysaccharide (CPS) from B. pseudomallei was purified, chemically activated, and covalently linked to recombinant CRM197 diphtheria toxin mutant (CRM197) to produce CPS-CRM197. Additionally, tandem nickel-cobalt affinity chromatography was used to prepare highly purified recombinant B. pseudomallei Hcp1 and TssM proteins. Immunization of C57BL/6 mice with CPS-CRM197 produced high-titer IgG and opsonizing antibody responses against the CPS component of the glycoconjugate, while immunization with Hcp1 and TssM produced high-titer IgG and robust gamma interferon-secreting T cell responses against the proteins. Extending upon these studies, we found that when mice were vaccinated with a combination of CPS-CRM197 and Hcp1, 100% of the mice survived a lethal inhalational challenge with B. pseudomallei Remarkably, 70% of the survivors had no culturable bacteria in their lungs, livers, or spleens, indicating that the vaccine formulation had generated sterilizing immune responses. Collectively, these studies help to better establish surrogates of antigen-induced immunity against B. pseudomallei as well as provide valuable insights toward the development of a safe, affordable, and effective melioidosis vaccine.
Insights
A novel vaccine combining a capsular polysaccharide (CPS) with bacterial proteins protected mice against lethal melioidosis. This combination induced sterilizing immunity, clearing bacteria and preventing death, offering hope for a new melioidosis vaccine.
Area of Science:
- Bacteriology and Immunology
- Vaccine Development
- Infectious Disease Research
Background:
- Melioidosis, caused by *Burkholderia pseudomallei*, is a severe disease with no licensed vaccines.
- Protective antigens, including polysaccharides and proteins, have been identified on *B. pseudomallei*.
- Subunit vaccine candidates are being developed using these identified antigens.
Purpose of the Study:
- To develop and evaluate a novel subunit vaccine against *Burkholderia pseudomallei*.
- To assess the immunogenicity and protective efficacy of a combined vaccine formulation.
- To investigate the potential for sterilizing immunity induced by the vaccine.
Main Methods:
- Purification and chemical activation of *B. pseudomallei* 6-deoxyheptan capsular polysaccharide (CPS).
- Covalent linkage of CPS to recombinant CRM197 diphtheria toxin mutant to create CPS-CRM197.
- Purification of recombinant *B. pseudomallei* Hcp1 and TssM proteins using affinity chromatography.
- Immunization of C57BL/6 mice with CPS-CRM197, Hcp1, TssM, or a combination thereof.
- Assessment of antibody responses, T cell responses, and survival following a lethal *B. pseudomallei* inhalational challenge.
Main Results:
- CPS-CRM197 vaccination induced high-titer IgG and opsonizing antibodies against the CPS.
- Hcp1 and TssM vaccination induced high-titer IgG and robust gamma interferon-secreting T cell responses.
- Combined vaccination with CPS-CRM197 and Hcp1 resulted in 100% survival in mice challenged with lethal *B. pseudomallei*.
- Remarkably, 70% of surviving mice showed no culturable bacteria in key organs, indicating sterilizing immunity.
Conclusions:
- The combined vaccine formulation demonstrated significant protective efficacy against lethal melioidosis.
- The vaccine elicited both humoral and cellular immune responses, leading to sterilizing immunity.
- These findings provide valuable insights for developing a safe, affordable, and effective melioidosis vaccine.
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