PNNL

Abstract

In the last decade, an increasingly severe trend of antibiotic-resistant Neisseria gonorrhoeae strains has been reported worldwide, emphasizing the need for new therapeutic strategies to treat this sexually-transmitted infection. There is an urgent need to develop a vaccine to prevent gonococcal infections. Unfortunately, this has been delayed by the scarcity of suitable vaccine antigens, along with the elusiveness of the correlates of protective immunity in humans and insufficient animal models of gonococcal reproductive tract infection for testing protection. Our previous “omic”-based studies demonstrated that N. gonorrhoeae expresses a distinct set of genes during natural human mucosal infection as compared during in vitro growth. Significantly, a major subset of genes regulated during mucosal infection were encoding for hypothetical proteins. In the current study, these hypothetical proteins were mined using a “reverse vaccinology”-like approach together with bioinformatic tools for the discovery of new candidate vaccine antigens. A Candidate Antigen Selection Strategy (CASS) was designed, divided into Discovery Phases DP-1 and DP-2. This strategy allowed us to identify 36 gonococcal hypothetical proteins predicted to be immunogenic and membrane-associated, conserved in N. gonorrhoeae strains and with structural features suitable for recombinant expression and manufacturing. Six antigens were selected for immune characterization in mice, showing induction of cross-reactive immune responses across N. gonorrhoeae laboratory strains and clinically-relevant strains. Antisera to three hypothetical proteins exhibited bactericidal activity against all gonococcal strains tested, and one additional antiserum showed strain-dependent bacterial killing. Our results support the CASS as a tool for discovery of new antigens among gonococcal hypothetical proteins expressed during human natural infection and their inclusion in the pool of vaccine candidates for an improved gonococcal vaccine.