Burkholderia pseudomallei (Bp) is a major public health concern in the endemic regions of southeast Asia and northern Australia, yet the organism has a worldwide distribution and cases are likely under-reported. In northeast Thailand the mortality rate associated with Bp infection is over 40%. The inherent resistance of Bp to multiple antibiotics impairs treatment, and relapse is seen in more than 25% of survivors. Beyond its public health significance, Bp is considered a potential biological warfare agent by the U.S. DHHS and was recently listed as a Tier 1 select agent. Despite enhanced research and vaccine efforts, traditional vaccine strategies employing attenuated bacterial strains, recombinant proteins, or purified polysaccharides have failed to elicit complete protection against aerosol challenge with Bp. We have previously shown that immunization with outer membrane vesicles (OMVs) derived from Bp can protect mice from lethal melioidosis. In this work we characterize the interactions of OMVs with antigen presenting cells in order to elucidate innate immune responses to the OMV vaccine. Vaccine-mediated antibody responses and protective efficacy were characterized in BALB/c mice. We also tested the safety and immunogenicity of the OMV vaccine in non-human primates (NHP). We show that Bp OMVs interact with dendritic cells and macrophages and are internalized by these antigen presenting cells (APCs).Internalization is dependent on actin polymerization and cholesterol present in APC membranes. OMVs also upregulate MHC class I and II on APCs, as well as promote the production of pro-inflammatory cytokines in a TLR2/4 dependent manner. Immunization of mice with Bp OMVs by the s.c. and i.m. routes induced the production of OMV-specific IgM and IgG and significantly protected mice against aerosol challenge. Addition of alum and MPL did not significantly change the antibody profiles of immunized mice and did not significantly enhance vaccine mediated protection. OMVs were well tolerated in a large animal NHP model. There were no adverse clinical reactions, and NHPs mounted significantly increased levels of OMV-specific IgG and OMV specific CD4+ T cell responses. These results suggest that Bp OMVs can stimulate innate and adaptive immune responses and may represent a safe and efficacious vaccine against melioidosis
