IMMUNOGENICITY OF AN APHTHOVIRUS CHIMERA OF THE GLYCOPROTEIN OF VESICULAR STOMATITIS-VIRUS

An oligodeoxynucleotide coding for amino acids 139 through 149 of anti genic site A (ASA) of the VP, capsid protein of the foot-and-mouth dis ease virus C3 serotype (FMDV C3) was inserted into three different in- frame sites of the vesicular stomatitis virus New Jersey serotype (VSV -NJ) glycoprotein (G) gene cDNA present in plasmid pBG97 under control of the bacteriophage T7 polymerase promoter, Transfection of these pl asmids into CV1 cells coinfected with the T7 polymerase-expressing vac cinia virus recombinant vTF1-6,2 resulted in expression of chimeric pr oteins efficiently reactive with both anti-FMDV and anti-VSV G antibod ies. However, in vitro translation of transcripts of these VSV-G/FMDV- ASA chimeric plasmids resulted in proteins that were recognized by ant i-G serum but not by anti-FMDV serum, indicating a requirement for in vivo conformation to expose the ASA antigenic determinant, insertion o f DNA coding for a dimer of the ASA unidecapeptide between the VSV-NJ G gene region coding for amino acids 160 and 161 gave rise to a chimer ic ASA-dimer protein designated GF2d, which reacted twice as strongly with anti-FMDV antibody as did chimeric proteins in which the ASA mono mer was inserted in the same position or two other G-gene positions, F or even greater expression of chimeric VSV-G/FMDV-ASA proteins, plasmi d pGF2d and a deletion mutant p Delta GF2d (G protein deleted of 324 C -terminal amino acids) were inserted into baculovirus vectors expressi ng chimeric proteins GF2d-bac and Delta GF2d-bac produced in Sf9 insec t cells, Mice vaccinated with three booster injections of 30 mu g each of partially purified GF2d-bac protein responded by enzyme-linked imm unosorbent assay with FMDV antibody titers of 1,000 units, and those i njected with equivalent amounts of Delta GF2d-bac protein showed serum titers of up to 10,000 units. Particularly impressive were FMDV neutr alizing antibody titers In serum of mice vaccinated with Delta GF2d-ba c protein, which approached those in the sera or mice vaccinated with three 1-mu g doses of native FMDV virions. Despite excellent reactivit y with native FMDV, the anti-Delta GF2d-bac antibody present in vaccin ated mouse serum showed no capacity to bind to sodium dodecyl sulfate (SDS)-denatured FMDV virions and only minimal reactivity with Vp(1) pr otein by Western blotting (immunoblotting) after SDS-polyacrylamide ge l electrophoresis. It was also shown in a competitive binding assay th at a synthetic ASA unidecapeptide, up to concentrations of 200 mu g/ml , was quite limited in its ability to inhibit binding of anti-Delta GF Z-bac antibody to native FMDV virions. These results suggest that the chimeric VSV-G/FMDV-ASA proteins mimic the capacity of FMDV to raise a nd react with neutralizing antibodies to a restricted number of ASA co nformations present on the surface of native FMDV particles.