MOUSE HEPATITIS-VIRUS SPIKE AND NUCLEOCAPSID PROTEINS EXPRESSED BY ADENOVIRUS VECTORS PROTECT MICE AGAINST A LETHAL INFECTION

Infection with the mouse hepatitis coronavirus (MHV) provides an excel lent model for the study of viral diseases of the central nervous syst em and the gastrointestinal tract. With the ultimate aim of studying m ucosal immunity to MHV we have cloned the genes encoding the structura l proteins of MHV strain A59 (MHV-A59) into the E3 region of a human a denovirus type 5 vector. Infection of HeLa cells with the resulting re combinant adenoviruses AdMHVS, AdMHVN and AdMHVM revealed the cot-rect expression of the spike (S), nucleocapsid (N) and membrane (M) protei ns, respectively. Intraperitoneal inoculation of BALB/c mice with the recombinant viruses elicited serum antibodies which specifically recog nized the respective MHV proteins in an immunoprecipitation assay. Onl y antibodies to the S protein neutralized MHV-A59 in vitro but titres were low. When analysed by ELISA or by immunofluorescence only the ant ibody response to the N protein was significant; weak responses or no detectable response at all were found for S and M, respectively. Upon intracerebral challenge with a lethal dose of MHV-A59 we found that a significant fraction of animals vaccinated with adenovirus vectors exp ressing either the S protein or N protein were protected. This protect ive effect was significantly stronger when the animals were given a bo oster immunization with the same vector prior to challenge. No protect ion was induced by AdMHVM. Interestingly, enhanced protection resulted when AdMHVS and AdMHVN were applied in combination as compared to sur vival after single immunizations. The results indicate that both the N and S proteins generate a protective immune response and suggest that this response is enhanced by combined expression of the two proteins.