DNA immunization of mice against the VP1 capsid protein of coxsackievirus B4

The protective activity of a DNA plasmid encoding the immunodominant capsid protein VP1 of coxsackievirus B4 (CBV-4) was studied in BALB/c mice. The plasmid pCI-B4-1-c - which gave the highest expression level of VP1 in cultured monkey and human cells - was chosen for immunization. Two injections of pCI-B4-1-c (1 month apart) into the regenerating mouse muscle tissue induced a specific antibody response to CBV-4, as shown by immunoenzyme and neutralization assays. Upon challenge with live CBV-4, the mortality rate of mice vaccinated with the recombinant plasmid was significantly reduced (21% versus >58%) as compared with that of mice that had been either nontreated or injected with a control plasmid devoid of the insert. The VP1-based vaccine, however, did not provide complete protection as - after virus challenge - moderate viraemia occurred together with modest plasma elevations of pathogenesis-related enzymes (amylase and creatine kinase). Yet, immunofluorescence of the small intestine and heart did confirm the protective effect of the VP1-encoding vaccine. In order to obtain a more complete protection against CBV-4, it may be beneficial to immunize mice with combinations of separate DNA plasmids encoding not only VP1 but also the VP2 and VP3 capsid proteins.