Influence of live respiratory syncytial virus priming on the immune response generated by a recombinant vaccine candidate, BBG2Na

Respiratory syncytial virus is one of the major respiratory pathogens for i nfants and immunocompromized children. With the exception of young children , all the population has encountered RSV and is seropositive. Recent report s have demonstrated however that the virus also affects the elderly and rep resents a major cause of illness associated with an excess of morbidity and mortality. We have generated a recombinant RSV vaccine, BBG2Na, which is h ighly protective in rodents against RSV infection. The aim of this study wa s to evaluate the ability of the vaccine to increase anti-RSV protection in RSV-primed mice and to characterize the induced immune responses. Immunization with BBG2Na increased the anti-RSV-A serum antibody titers of RSV-primed mice with induction of both IgG1 and IgG2a antibodies attesting for a mixed Th response. Moreover, the level of the induced anti-G2Na antib odies was greater in seropositive mice. Finally, sera from RSV-primed mice displayed a higher protective efficacy after transfer into naive mice follo wing subsequent immunization with BBG2Na than sera of mice immunized with R SV-A only. Our results demonstrate that BBC2Na is immunogenic and increases the protec tive efficacy of serum antibodies in RSV-primed mice; they support the poss ibility of performing clinical trials in the seropositive human population. (C) 2000 Elsevier Science Ltd. AU rights reserved.