Proteomics-driven Antigen Discovery for Development of Vaccines Against Gonorrhea

Abstract

Expanding efforts to develop preventive gonorrhea vaccines is critical because of the dire possibility of untreatable gonococcal infections. Reverse vaccinology, which includes genome and proteome mining, has proven very successful in the discovery of vaccine candidates against many pathogenic bacteria. However, progress with this approach for a gonorrhea vaccine remains in its infancy. Accordingly, we applied a comprehensive proteomic platform-isobaric tagging for absolute quantification coupled with two-dimensional liquid chromatography and mass spectrometry-to identify potential gonococcal vaccine antigens. Our previous analyses focused on cell envelopes and naturally released membrane vesicles derived from four different Neisseria gonorrhoeae strains. Here, we extended these studies to identify cell envelope proteins of N. gonorrhoeae that are ubiquitously expressed and specifically induced by physiologically relevant environmental stimuli: oxygen availability, iron deprivation, and the presence of human serum. Together, these studies enabled the identification of numerous potential gonorrhea vaccine targets. Initial characterization of five novel vaccine candidate antigens that were ubiquitously expressed under these different growth conditions demonstrated that homologs of BamA (NGO1801), LptD (NGO1715), and TamA (NGO1956), and two uncharacterized proteins, NGO2054 and NGO2139, were surface exposed, secreted via naturally released membrane vesicles, and elicited bactericidal antibodies that cross-reacted with a panel of temporally and geographically diverse isolates. In addition, analysis of polymorphisms at the nucleotide and amino acid levels showed that these vaccine candidates are highly conserved among N. gonorrhoeae strains. Finally, depletion of BamA caused a loss of N. gonorrhoeae viability, suggesting it may be an essential target. Together, our data strongly support the use of proteomics-driven discovery of potential vaccine targets as a sound approach for identifying promising gonococcal antigens. Molecular & Cellular

Deciphering the Function of New Gonococcal Vaccine Antigens Using Phenotypic Microarrays

“…1D). In our proteomic profiling, we found that this protein was upregulated during growth under iron-limited conditions (5). The meningococcal homolog, NMB1971, has been described as a paralog of the surface lipoprotein assembly modulator Slam and was designated Slam2.…”

“…1C). We have recently determined that NGO2054 is surface exposed, induces bactericidal antibodies, and is continuously expressed at the same level throughout all stages of gonococcal growth and under tested host-relevant conditions (5).…”

“…Little is known about the functions of most lipoproteins (1), but those for which information is available have been shown to be involved in nutrient acquisition, cell wall structure and metabolism, cell signaling, antibiotic resistance, attachment to host cells, and ligands for Toll-like receptor 2, which triggers an innate immune response and helps establish adaptive immunity (4). Because of this potential interaction between host and pathogen, we are currently pursuing 20 novel outer membrane-localized proteins, including lipoproteins, as vaccine candidates against Neisseria gonorrhoeae, the gonococcus (GC) (5,6).…”

“…Using proteomics-based reverse vaccinology (16), we have investigated the composition of N. gonorrhoeae cell envelopes and naturally released membrane vesicles across common laboratory strains, including FA1090, MS11, and FA19 (6), as well as FA1090 cell envelopes under four different host-relevant growth conditions (5) to identify vaccine candidate targets. Among the ubiquitously expressed proteins in four examined isolates were novel vaccine candidates NGO2121, NGO1985, NGO2054, NGO2111, NGO1205, and NGO1344 (5,6), with predicted functions associated with cell envelope homeostasis. Herein, we utilized Biolog Phenotype MicroArrays (PMs) to identify the phenotypes of gene knockout mutants in our six vaccine candidates.…”

Could Vaccination Against Neisseria Gonorrhoeae be on the Horizon?

“…The estradiol-treated female mouse model [16] has now been applied to this effort [17], and further refinements of the model using transgenic mice that express various human factors involved in gonococcal pathogenesis afford scope for more detailed analysis of the mechanisms whereby immune protection can be attained [10]. Third, efforts are now underway to apply proteomics technology to the discovery of novel, conserved surface antigens shared by different strains of N. gonorrhoeae [18]. Already some initial candidate antigens have been identified, although these have not yet been evaluated in animal models of protection.…”