Abstract
ABSTRACT Melioidosis is a severe infectious disease with a high mortality that is endemic in South-East Asia and Northern Australia. The causative pathogen, Burkholderia pseudomallei, is listed as potential bioterror weapon due to its high virulence and potential for easy dissemination. Currently, there is no licensed vaccine for prevention of melioidosis. Here, we explore the use of rapid plasmid DNA vaccination against B. pseudomallei flagellin for protection against respiratory challenge. We tested three flagellin DNA vaccines with different subcellular targeting designs. C57BL/6 mice were vaccinated via skin tattoo on day 0, 3 and 6 before intranasal challenge with B. pseudomallei on day 21. Next, the most effective construct was used as single vaccination on day 0 by tattoo or intranasal formulation. Mice were sacrificed 72 hours post-challenge to assess bacterial loads, cytokine responses, inflammation and microscopic lesions. A construct encoding a cellular secretion signal resulted in the most effective protection against melioidosis via tattooing, with a 10-fold reduction in bacterial loads in lungs and distant organs compared to the empty vector. Strikingly, a single intranasal administration of the same vaccine resulted in >1000-fold lower bacterial loads and increased survival. Pro-inflammatory cytokine responses were significantly diminished and strong reductions in markers for distant organ damage were observed. A rapid vaccination scheme using flagellin DNA tattoo provides significant protection against intranasal challenge with B. pseudomallei, markedly improved by a single administration via airway mucosa. Hence intranasal vaccination with flagellin-encoding DNA may be applicable when acute mass vaccination is indicated and warrants further testing.
Highlights
Burkholderia pseudomallei is a facultative intracellular Gram negative bacterium that causes melioidosis and is endemic in Southeast Asia and Northern Australia.[1,2] Infection usually occurs through dermal lesions via rice paddies and infected soil
All vaccines were codon-optimized for mouse tRNA and contained a Kozak sequence to optimize translation efficiency and ribosomal binding (Fig. 1A). “pVAX-hTPA-FliC” contained an N-terminal signal peptide from human tissue plasminogen activator, enabling protein secretion and augmenting MHC-II presentation by antigen presenting cells. “pVAX-FliC-KDEL” had a four-amino acid C-terminal KDEL sequence leading to FliC accumulation in the endoplasmatic reticulum (ER) of transfected cells, which via ER stress and improved MHC-I presentation may increase T-cell priming effectiveness of the vaccine
Mice were immunized by tattoo vaccination with 20 mg of plasmid DNA on day 0, 3 and 6, with a control group receiving an equal amount of empty pVAX vector via tattoo
Summary
Burkholderia pseudomallei is a facultative intracellular Gram negative bacterium that causes melioidosis and is endemic in Southeast Asia and Northern Australia.[1,2] Infection usually occurs through dermal lesions via rice paddies and infected soil. During severe weather events, when the soil is disturbed and B. pseudomallei becomes aerosolized, inhalation is thought to cause infection. B. pseudomallei was recently upgraded to a Tier 1 select agent by the National Select Agent Registry due to its high associated morbidity and mortality, intrinsic resistance to standard antimicrobial agents and lack of a vaccine. Even when treated with adequate antibiotics, mortality remains high and varies between 14 to 40% depending on geographic regions.[1,2] Deliberate release in an aerosol form may infect large populations and poses a potential bioterrorist threat
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