ANTIBODY-RESPONSE IN MICE INOCULATED WITH DNA EXPRESSING FOOT-AND-MOUTH-DISEASE VIRUS CAPSID PROTEINS

Candidate foot and-mouth disease (FMD) DNA vaccines designed to produc e viral capsids lacking infectious viral nucleic acid were evaluated. Plasmid DNAs containing a portion of the FMDV genome coding for the ca psid precursor protein (P1-2A) and wild-type or mutant viral proteinas e 3C (plasmids P12X3C or P12X3C-mut, respectively) were constructed, C ell-free translation reactions programmed with pP12X3C (wild-type 3C) and pP12X3C-mut produced a capsid precursor, but only the reactions pr ogrammed with the plasmid encoding the functional proteinase resulted in P1-2A processing and capsid formation. Baby hamster kidney (BHK) ce lls also produced viral capsid proteins when transfected with these pl asmids. Plasmid P12X3C was administered to mice by intramuscular, intr adermal, and epithelial (gene gun) inoculations. Anti-FMD virus (FMDV) antibodies were detected by radioimmunoprecipitation (RIP) and plaque reduction neutralization assays only in sera of mice inoculated by us ing a gene gun. When pP12X3C and pP12X3C-mut were inoculated into mice by using a gene gun, both plasmids elicited an antibody response dete ctable by RIP but only pP12X3C elicited a neutralizing antibody respon se, These results suggest that capsid formation in situ is required fo r effective immunization. Expression and stimulation of an immune resp onse was enhanced by addition of an intron sequence upstream of the co ding region, while addition of the FMDV internal ribosome entry site o r leader proteinase (L) coding region either had no effect or reduced the immune response.