Protective and Nonprotective Epitopes from Amino Termini of M Proteins from Australian Aboriginal Isolates and Reference Strains of Group A Streptococci

Abstract

The M protein is the primary vaccine candidate to prevent group A streptococcal (GAS) infection and the subsequent development of rheumatic fever (RF). However, the large number of serotypes have made it difficult to design a vaccine against all strains. We have taken an approach of identifying amino-terminal M protein epitopes from GAS isolates that are highly prevalent in GAS-endemic populations within the Northern Territory (NT) of Australia. Australian Aboriginals in the NT experience the highest incidence of RF worldwide. To develop a vaccine for this population, 39 peptides were synthesized, representing the amino-terminal region of the M protein from endemic GAS. Mice immunized with these peptides covalently linked to tetanus toxoid and emulsified in complete Freund's adjuvant raised high-titer antibodies. Over half of these sera reduced bacterial colony counts by >80% against the homologous isolate of GAS. Seven of the peptide antisera also cross-reacted with at least three other heterologous peptides by enzyme-linked immunosorbent assay. Antiserum to one peptide, BSA10 1-28 , could recognize six other peptides, and five of these peptides could inhibit opsonization mediated by BSA10 1-28 antiserum. Cross-opsonization studies showed that six of these sera could opsonize at least one heterologous isolate of GAS. These data reveal vaccine candidates specific to a GASendemic area and show the potential of some to cross-opsonize multiple isolates of GAS. This information will be critical when considering which epitopes may be useful in a multiepitope vaccine to prevent GAS infection.

Serum Opacity Factor (SOF) ofStreptococcus pyogenesEvokes Antibodies That Opsonize Homologous and Heterologous SOF-Positive Serotypes of Group A Streptococci

“…The major strength of a vaccine based on the conserved domains of M proteins is that protection against both homologous and heterologous serotypes is provided (1,4,6,7,(36)(37)(38). The major concern is that these conserved domains may stimulate T-and B-cell responses that target human tissues (12,14,15).…”

An efficient, chemically-defined semisynthetic lipid-adjuvanted nanoparticulate vaccine development system

“…Confocal microscopy was used to assess the capacity of murine antibodies elicited against 1 (primed with CFA) or 6 (administered in PBS) to bind cell surface M proteins from GAS serotypes represented by N-terminal M protein peptides included in our polytope constructs (88/30 (emm97), PL1 (emm54), NS1 (emm100), Y504S (emm11), BSA10 (emm2.3), NS27 (emm91), NS5 (emm101)) 16 , or against pM1 (emm1), 17 which contains the conserved M protein J14i 18 epitope found in J14. The confocal microscope was calibrated for positive and negative samples using pM1 GAS and murine antisera raised against recombinant M1 protein (primed with CFA) 19 as a positive control, or antisera from sham (PBS) immunized mice as a negative control.…”

“…As over 200 strains have been identified, the development of a broadly protective vaccine requires the incorporation of multiple protective antigens, 16 favoring a recombinant approach. Further, many well--defined protective GAS antigens have been reported, 17--20 providing valuable knowledge for antigen selection.…”

“…Group A Streptococcus (GAS; Streptococcus pyogenes), which is associated with diseases including pharyngitis (sore throat) and RHD, 16 was selected as a model organism for developing this platform. As over 200 strains have been identified, the development of a broadly protective vaccine requires the incorporation of multiple protective antigens, 16 favoring a recombinant approach.…”

“…Further, many well--defined protective GAS antigens have been reported, 17--20 providing valuable knowledge for antigen selection. For this work, peptide antigens from the GAS cell--surface M protein, which are amongst the most promising GAS vaccine targets, 16 were selected. A 'string--of--beads' (polytope) approach was used (1, Figure 2, A) to link seven strain--specific N--terminal M protein antigens, from GAS isolates prevalent in the Australian Aboriginal population of the Northern Territory, 18 to a conserved M protein conformational B cell epitope (J14i; bold sequence in J14), which is flanked by peptides designed to promote its native α--helical structure (J14: KQAEDKVKASREAKKQVEKALEQLEDKVK).…”