Identification of multiple protective epitopes (protectopes) in the central conserved domain of a prototype human respiratory syncytial virus G protein

A recombinant fusion protein (BBG2Na) comprising the central conserved doma in of the respiratory syncytial virus subgroup A (RSV-A) (Long) G protein ( residues 130 to 230) and an albumin binding domain of streptococcal protein G was shown previously to protect mouse upper (URT) and lower (LRT) respir atory tracts against intranasal RSV challenge (U. F. Power, H. Plotnicky-Gi lquin, T. Huss, A. Robert, M. Trudel, S. Stahl, M. Uhlen, T. N. Nguyen, and B. Binz, Virology 230:155-166, 1997). Panels of monoclonal antibodies (MAb s) and synthetic peptides were generated to facilitate dissection of the st ructural elements of this domain implicated in protective efficacy. All MAb s recognized native RSV-A antigens, and five linear B-cell epitopes were id entified; these mapped to residues 152 to 163, 165 to 172, 171 to 187 (two overlapping epitopes), and 196 to 204, thereby covering the highly conserve d cysteine noose domain. Antibody passive-transfer and peptide immunization studies revealed that all epitopes were implicated in protection of the LR T, but not likely the URT, against RSV-A challenge. Pepscan analyses of ant i-RSV-A and anti-BBG2Na murine polyclonal sera revealed lower-level epitope usage within the central conserved region in the former, suggesting dimini shed immunogenicity of the implicated epitopes in the context of the whole virus. However, Pepscan analyses of RSV-seropositive human sera revealed th at all of the murine B-cell protective epitopes (protectopes) that mapped t o the central conserved domain were recognized in man. Should these murine protectopes also be implicated in human LRT protection, their clustering ar ound the highly conserved cysteine noose region will have important implica tions for the development of RSV vaccines.