Birgit Noiges

Novel conserved group A streptococcal proteins identified by the antigenome technology as vaccine candidates for a non-M protein-based vaccine.

ABSTRACT Group A streptococci (GAS) can cause a wide variety of human infections ranging from asymptomatic colonization to life-threatening invasive diseases. Although antibiotic treatment is very effective, when left untreated, Streptococcus pyogenes infections can lead to poststreptococcal sequelae and severe disease causing significant morbidity and mortality worldwide. To aid the development of a non-M protein-based prophylactic vaccine for the prevention of group A streptococcal infections, we identified novel immunogenic proteins using genomic surface display libraries and human serum antibodies from donors exposed to or infected by S. pyogenes. Vaccine candidate antigens were further selected based on animal protection in murine lethal-sepsis models with intranasal or intravenous challenge with two different M serotype strains. The nine protective antigens identified are highly conserved; eight of them show more than 97% sequence identity in 13 published genomes as well as in approximately 50 clinical isolates tested. Since the functions of the selected vaccine candidates are largely unknown, we generated deletion mutants for three of the protective antigens and observed that deletion of the gene encoding Spy1536 drastically reduced binding of GAS cells to host extracellular matrix proteins, due to reduced surface expression of GAS proteins such as Spy0269 and M protein. The protective, highly conserved antigens identified in this study are promising candidates for the development of an M-type-independent, protein-based vaccine to prevent infection by S. pyogenes.

Immunological fingerprinting of group B streptococci: from circulating human antibodies to protective antigens.

Group B streptococcus is one of the most important pathogens in neonates, and causes invasive infections in non-pregnant adults with underlying diseases. Applying a genomic approach that relies on human antibodies we identified antigenic GBS proteins, among them most of the previously published protective antigens. In vitro analyses allowed the selection of conserved candidate antigens that were further evaluated in murine lethal sepsis models using several GBS strains. In active and passive immunization models, we identified four protective GBS antigens, FbsA and BibA, as well as two hypothetical proteins, all shown to contribute to virulence based on gene deletion mutants. These protective antigens have the potential to be components of novel vaccines or targets for passive immune prophylaxis against GBS disease.

Composition of the ANTIGENome of Helicobacter pylori defined by human serum antibodies

Helicobacter pylori is the most prevalent human pathogen and although, it remains silent in most individuals for lifetime, colonization may develop into severe gastric and duodenal conditions. Rapidly developing resistance to antibiotic treatment urgently calls for the development of effective vaccines. We determined the ANTIGENome of two clinical isolates of H. pylori, KTH-Ca1 and KTH-Du, derived from patients with gastric cancer and duodenal ulcer, respectively. Using disease-relevant human sera from well-characterized donors we identified 124 annotated ORFs and 54 non-annotated peptides as antigens. Through in vitro validation assays we selected the 20 most promising vaccine candidates. Importantly, two candidates represent proteins that were previously shown to provide protection in models of H. pylori infection. One of the most frequently selected and conserved protein, the siderophore-dependent transporter HP1341, was confirmed to show high reactivity with human serum IgGs. These analyses provide the means to identify novel antigens for the selection of vaccine candidates, as well as disease associated biomarkers.

Chemokine degradation by the Group A streptococcal serine proteinase ScpC can be reconstituted in vitro and requires two separate domains

Streptococcus pyogenes is one of the most common human pathogens and possesses diverse mechanisms to evade the human immune defence. One example of its immune evasion is the degradation of the chemokine IL (interleukin)-8 by ScpC, a serine proteinase that prevents the recruitment of neutrophils to an infection site. By applying the ANTIGENome technology and using human serum antibodies, we identified Spy0416, annotated as ScpC, as a prominent antigen that induces protective immune responses in animals. We demonstrate here for the first time that the recombinant form of Spy0416 is capable of IL-8 degradation in vitro in a concentration- and time-dependent manner. Mutations in the conserved amino acid residues of the catalytic triad of Spy0416 completely abolished in vitro activity. However, the isolated predicted proteinase domain does not exhibit IL-8-degrading activity, but is dependent on the presence of the C-terminal region of Spy0416. Binding to IL-8 is mainly mediated by the catalytic domain. However, the C-terminal region modulates substrate binding, indicating that the proteolytic activity is amenable to regulation via the non-catalytic regions. The specificity for human substrates is not restricted to IL-8, since we also detected in vitro protease activity for another CXC chemokine GRO-alpha (growth-related oncogene alpha), but not for NAP-2 (neutrophil-activating protein 2), SDF (stromal-cell-derived factor)-1alpha, PF-4 (platelet factor 4), I-TAC (interferon-gamma-inducible T-cell alpha-chemoattractant), IP-10 (interferon-gamma-inducible protein 10) and MCP-1 (monocyte chemoattractant protein 1). The degradation of two human CXC chemokines in vitro, the high sequence conservation, the immunogenicity of the protein in humans and the shown protection in animal studies suggest that Spy0416 is a promising vaccine candidate for the prevention of infections by S. pyogenes.