IMMUNIZATION WITH RECOMBINANT VACCINIA VIRUSES EXPRESSING STRUCTURAL AND PART OF THE NONSTRUCTURAL REGION OF TICK-BORNE ENCEPHALITIS-VIRUS CDNA PROTECT MICE AGAINST LETHAL ENCEPHALITIS

Three recombinant vaccinia viruses containing different fragments of t ick-borne encephalitis virus (TBEV) cDNA representing the 5'-noncoding region (5'NCR), all structural and part of the nonstructural regions were constructed, Western blot analysis showed that E and NS1 proteins were expressed and processed correctly in cells infected with recombi nant viruses vC-NS1 (coding for C-prM-E-NS1 region) and vC-NS3 (coding for C-prM-E-NS1-NS2A-NS2B-NS3 region). In contrast, in cells infected with recombinant virus v5'C-NS2A (coding for 5'NCR and C-prM-E-NS1-NS 2A regions) expression of NS1 protein was greatly reduced and no E pro tein was detected, Immunization of mice with vC-NS3 induced high level s of TBEV-specific antibodies and protected them against intraperitone al challenge with 10(7) LD(50) of TBEV. The level of protection was ve ry similar to the level of protection achieved by immunization with co mmercially available inactivated TBEV vaccine, Although the immunizati on of mice with recombinants vC-NS1 and v5'C-NS2A induced much lower l evels of TBEV-specific antibodies, they were still protected against i ntraperitoneal challenge with 10(4) and 10(3.6) LD(50) of TBEV, respec tively. The high level of protection against TBEV infection achieved b y the immunization of mice with the recombinant vaccinia virus vC-NS3 makes this virus a very attractive candidate for development of a live recombinant vaccine against TBEV.