Protective effect of a RSV subunit vaccine candidate G1F/M2 was enhanced by a HSP70-Like protein in mice

Respiratory syncytial virus (RSV) is a major respiratory pathogen in newborns. Neonate vaccine should induce strong protective immunity. We have engineered a subunit vaccine candidate G1F/M2. A major problem in developing subunit vaccines is their limited immunogenicity. Aluminium adjuvants with a long history of use with routine childhood vaccines have some limitations, especially inability to elicit CTL response. There is a need for alternative adjuvants. Heat shock proteins (HSPs) are characterized as potent immunoadjuvants. In this study, HSP70-like protein 1 (HSP70L1) gene was cloned. The recombinant protein HSP70L1 was expressed in E. coli, purified and renaturated. We evaluated the potential of HSP70L1 used as the adjuvant of G1F/M2. G1F/M2 was chemically cross-linked with HSP70L1 (HSP-G1F/M2). HSP70L1 enhanced significantly the immunogenicity and protective effect of G1F/M2. HSP-G1F/M2 induced significant higher levels of antibodies, neutralizing antibodies and CTL activity than unadjuvanted G1F/M2. The antibody titers induced by HSP-G1F/M2 were similar to that by G1F/M2 + Alum. RSV-specific CTL activity induced by HSP-G1F/M2 was stronger than that by G1F/M2 + Alum. Interestingly, the protective effect of HSP-G1F/M2 against RSV was significantly stronger than that of G1F/M2 + Alum. The results suggest that HSP70L1 is a potent adjuvant of G1F/M2.