Functional Selection of Vaccine Candidate Peptides from Staphylococcus aureus Whole-Genome Expression Libraries In Vitro

Abstract

An in vitro protein selection method, ribosome display, has been applied to comprehensively identify and map the immunologically relevant proteins of the human pathogen Staphylococcus aureus. A library built up from genomic fragments of the virulent S. aureus COL strain (methicillin-resistant S. aureus) allowed us to screen all possible encoded peptides for immunoreactivity. As selective agents, human sera exhibiting a high antibody titer and opsonic activity against S. aureus were used, since these antibodies indicate the in vivo expression and immunoreactivity of the corresponding proteins. Identified clones cluster in distinct regions of 75 genes, most of them classifiable as secreted or surface-localized proteins, including previously identified virulence factors. In addition, 14 putative novel short open reading frames were identified and their immunoreactivity and in vivo mRNA expression were confirmed, underscoring the annotation-independent, true genomic nature of our approach. Evidence is provided that a large fraction of the identified peptides cannot be expressed in an in vivo-based surface display system. Thus, in vitro protein selection, not biased by the context of living entities, allows screening of genomic expression libraries with a large number of different ligands simultaneously. It is a powerful approach for fingerprinting the repertoire of immune reactive proteins serving as target candidates for active and passive vaccination against pathogens.

Biofilm Matrix Exoproteins Induce a Protective Immune Response against Staphylococcus aureus Biofilm Infection

“…Success of S. aureus as a pathogen is the result of different abilities, such as the capacity to invade a wide variety of cell types, to secrete a diversity of proteins and toxins, and to persist in the host, remaining resistant to clearance by the immune system or antibiotics through a biofilm mode of growth. Numerous approaches have been adopted in order to identify staphylococcal surface-and cell wall-associated proteins as antigenic candidates for a vaccine against S. aureus infections (34,49,51,53,(56)(57)(58)(59)(60). However, few works have been focused on the selection of antigens that could also protect against biofilm-associated bacteria (14,(24)(25)(26).…”

Successful Selection of Cross-Protective Vaccine Candidates for Ornithobacterium rhinotracheale Infection

“…So far, several approaches have been reported that allowed in vitro identification of antigens out of proteomic samples or expression libraries by using specific antiserum raised upon encountering a given pathogenic microorganism, for example, the detection of enteropathogenic Escherichia coli antigens using secretory immunoglobulin A antibodies isolated from human breast milk (18); the application of in vitro protein selection methods, such as ribosome display, to identify and map immunologically relevant proteins of Staphylococcus aureus (36); and the characterization of Vibrio vulnificus antigens preferentially expressed during infection by using in vivo-induced antigen technology (14). The application of an immunoscreening approach has also been described previously (3,12,37,38).…”

Proteomics-Based Identification of Anchorless Cell Wall Proteins as Vaccine Candidates againstStaphylococcus aureus

“…Therefore, identification of novel targets for an effective S. aureus vaccine has repeatedly been recognized as a high priority by experts in this field (20,28,34,40,43,48). Indeed, numerous staphylococcal surface proteins predicted to be promising antigenic targets have been identified so far using recently adopted technologies, like proteomics (19,36,57) or protein selection methods based on expression libraries (10,13,58,59). Unfortunately, most studies have not provided functional proof that identified proteins are vaccine candidates.…”