IMMUNOGENICITY OF A SYNTHETIC OLIGOPEPTIDE CORRESPONDING TO ANTIGENICALLY COMMON T-HELPER AND B-CELL NEUTRALIZING EPITOPES OF THE MAJOR OUTER-MEMBRANE PROTEIN OF CHLAMYDIA-TRACHOMATIS

Sexually transmitted diseases (STDs) caused by Chlamydia trachomatis are an important public health problem and a vaccine to prevent or control these diseases is badly needed. The major outer membrane protein (MOMP) is the principal candidate antigen for the development of subunit vaccine against chlamydial STDs. The immunogenicity of a synthetic oligopeptide, termed A8-VDIV, corresponding to MOMP sequences containing both C. trachomatis species common T-helper (A8) and B-cell (VDIV) epitopes was studied in mice and non-human primates. Six of eight H-2 congenic mouse strains immunized with peptide A8-VDIV produced high-litre IgG antibodies against the VDIV B-cell portion of the oligopeptide. Fine mapping of the anti-peptide antibodies by pepscan ELISA showed that each of the responding mouse strains made antibodies reactive with a species-common septmeric neutralizing epitope 298LNPTIAG304 contained in the VDIV sequence. The mouse anti-peptide.antibodies reacted with intact C. trachomatis elementary bodies (EBs) by ELISA and neutralized chlamydial infectivity for cultured eukaryotic celLs with sub-species specificity. Three cynomolgus monkeys were immunized with peptide A8-VDIV and their IgG antibody responses were similarly studied. All three monkeys produced IgG antibodies which reacted with the VDIV peptide and which recognized the species-common LNPTIAG neutralizing site within the VDIV sequence. Monkey anti-peptide antibodies bound to intact C. trachomatis EBs and were neutralizing in vitro. The immunogeniciity of peptide A8-VDIV in different strains of mice disparate at H-2, its immunogenicity in non-human primates, and its ability to target cross-reactive neutralizing antibody responses against multiple C. trachomatis serovars are encouraging findings in terms of the potential utility of the oligopeptide as an experimental vaccine against chlamydial STDs.