Immunogenic and protective potential of mutans streptococcal glucosyltransferase peptide constructs selected by MHC class II allele binding

ABSTRACT Mutans streptococcal glucosyltransferases (GTF) have been demonstrated to be effective components of dental caries vaccines. We had previously selected peptide subunits of GTF for vaccine development based on putative functional significance and conservation of GTF primary structure among enzyme isoforms. In this study, twenty 20-mer linear GTF peptides were synthesized, seventeen identified on the basis of the highest potential MHC class II-binding activity using computer-generated algorithms (Epimatrix, ProPred) and three with previously demonstrated functional significance. The immunoreactivity of these peptides was explored in rodent systems. Sera from GTF-immunized rats, assessed for binding to linear peptides by ELISA, demonstrated IgG antibody reactivity with peptides 6 and 11 and T cell proliferation to peptides 6, 9, 11 and 16. Multiple antigenic peptide (MAP) constructs were synthesized from promising linear sequences. Rats that were immunized with MAPs 7, 11 or 16, respectively responded well to the immunizing MAP. Most importantly, robust immune response (antibody and T cell proliferation) was observed to native GTF following MAP 11 (AA 847-866; VVINNDKFVSWGITDFEM) immunization. This response inhibited GTF enzyme function. Two dental caries pathogenesis experiments were performed wherein rats were immunized with MAP constructs 11, 16 and/or 11 + 16, followed by infection with cariogenic S. sobrinus. In both experiments cariogenic bacterial recoveries were reduced relative to total streptococci in MAP 11 and in MAP 11+16 immunized groups and the extent of dental caries was also significantly reduced in these groups. Thus, we have identified a peptide with projected avid MHC-binding activity that elicited immunoreactivity with native GTF and demonstrated protection against dental caries infection after immunization, implying that this peptide may be important in a subunit dental caries vaccine.