Immunogenicity of a recombinant vaccinia virus expressing envelope a glycoprotein of bovine leukaemia virus.

We constructed a recombinant vaccinia virus (RVV) expressing envelope (env) glycoprotein (gp51) of bovine leukaemia virus (BLV): the expression of gp51 was detected by Western blot of the lysates of rabbit kidney cells infected with the RVV. The rabbits inoculated intradermally with the RVV alone failed to induce detectable anti-gp51 antibodies even 10 weeks after immunization. However, when these animals were boosted with inactivated BLV virion in saline, significant levels of anti-gp51 antibodies were induced as shown both in Western blot and immunodiffusion analyses. In these animals, antibodies against gag product (p24) were not detected. On the other hand, the rabbits inoculated with wild-type vaccinia virus and boosted similarly three times with the BLV virion in saline did not induce detectable anti-gp51 antibodies at all. The present experiment revealed that the RVV possessed the capability to endow immunological memory without inducing apparent anti-gp51 antibody responses, meaning that the RVV activated helper T cells far more strongly than B cells. The applicability of the RVV to vaccine development is discussed.