Analysis of the immunogenicity of peptide mimotopes of Burkholderia pseudomallei exopolysaccharide

Burkholderia pseudomallei is the causative agent of the disease melioidosis, which is endemic in the tropics and a concern elsewhere as a biological warfare agent. Currently no human vaccine exists either in clinical trials or in a licensed form. Recently passively transferred monoclonal antibodies directed toward the expolysaccharide of B. pseudomallei have been shown to impart survival when administered prior to lethal challenge and active immunization using purified exopolysaccharide extends the mean time to death. Short peptides, termed mimotopes, mimicking native carbohydrate have been developed and used to induce protective responses against extracellular bacteria. Here the ability of mimotopes to generate a protective response against a pathogen that can invade host cells was investigated. Mimotopes immunoreactive to the passive protective monoclonals were developed and used to generate an antibody response against B. pseudomallei. Preliminary evaluation of the mimotopes in a murine challenge model of acute melioidosis identified one mimotope which may have utility by extending the mean time to death.; Previous work with the Protective Antigen (PA) and first domain of Lethal Factor (LFn) has focused on delivering cytotoxic T cell antigens to the host cell. Here the antibody response to a B cell antigen fused to LFn as modeled by Yersinia pestis LcrV was examined. When LcrV was fused to the N terminal of LFn and codelivered with PA, the anti-LcrV titer was significantly increased. This increased titer for a B cell antigen fused to LFn was further examined as a B cell epitope modeled by the mimotopes of B. pseudomallei exopolysaccharide. Antibody titer against B. pseudomallei raised by LFn-mimotope fusions was not increased over peptide conjugates of the mimotope. Fusion to LFn did increase the avidity of immune sera for B. pseudomallei to levels matching that of the parent monoclonal antibodies for B. pseudomallei. Taken together, LFn can be used to deliver B cell antigens to the immune system and should be considered as a means to present peptide mimotopes of carbohydrates to the immune system.