Enhancement of the immunity to foot-and-mouth disease virus by DNA primingand protein boosting immunization

Subunit vaccination is effective in eliciting humoral responses to a variet y of viral antigens, however, it has not generated persistent protective im munity to foot-and-mouth disease virus (FMDV). In this study, we observed t hat priming mice with a DNA plasmid encoding VP1 of the FMDV O/Taiwan/97 ca psid protein followed by boosting with a VP1 peptide conjugate (P29-KLH) re sulted in production of not only high titers of antibodies but also antibod ies with FMDV neutralizing activities. Moreover, the mice immunized in this manner cleared the virus from their sera in FMDV challenge experiments. Mi ce subjected to DNA plasmid priming and P29-KLH protein boosting had relati vely higher ratio of IgG2a/IgG1 than those primed and boosted with P29-KLH conjugate. Addition of an oligodeoxynucleotide (ODN) containing immunostimu latory cytosine-phosphate-guanosine (CpG) motifs to P29-KLH conjugate also induced a higher ratio of IgG2a/IgG1 and significantly higher titer of neut ralizing antibodies. These results indicate that treating animals with DNA plasmids priming and FMDV antigen(s) boosting may elicit immunity to FMD an d this immune response may be augmented by CpG ODN. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.