PLASMID DNA ENCODING REPLICATING FOOT-AND-MOUTH-DISEASE VIRUS GENOMESINDUCES ANTIVIRAL IMMUNE-RESPONSES IN SWINE

DNA vaccine candidates for foot and-mouth disease (FMD) were engineere d to produce FMD virus (FMDV particles that were noninfectious in cell culture or animals, The prototype plasmid, pWRM, contains a cytomegal ovirus immediate-early promoter-driven genome-length type All cDNA fol lowed by the bovine growth hormone polyadenylation site, BHK cells tra nsfected with this plasmid produced virus, but the specific infectivit y of pWRM was much lon-er than that achieved with in vitro-generated R NA genomes, To improve the infectivity of the plasmid, a cDNA encoding the hepatitis delta virus ribozyme was added to the 3' end of the FMD V cDNA. The resulting plasmid. pWRMH, exhibited slightly increased inf ectivity in in cell culture and produced virus when inoculated into su ckling mice. A third plasmid, pWRMHX, was created by removal of the se quences encoding the cell binding site found in capsid protein VP1 of pWRMH. Although cells transfected with pWRMHX produced viral capsids. this plasmid was not lethal in suckling mice, indicating that particle s lacking the cell binding site were not able to initiate secondary in fectious cycles. Swine inoculated with pWRMHX did not show any signs o f disease and produced neutralizing antibodies to FMDV and 20% of the vaccinated animals Here protected from challenge. A derivative of pWRM HX, pWRMHX-pol(-), harboring a mutation designed to inactivate the vir al polymerase was much less immunogenic, indicating that immunogenicit y of pWRMHX resulted, in part, from amplification of the viral genome in the animal.