Earlier studies have shown that the B haplotype has a significant influence on the protective efficacy of
vaccines against
Marek's disease (MD) and that the level of protection varies dependent on the serotype of MD virus (MDV) used in the
vaccine. To determine if the protective
glycoprotein gene gB is a basis for this association, we compared recombinant fowlpox virus (rFPV) containing a single gB gene from three serotypes of MDV. The rFPV were used to vaccinate 15.B congenic lines. Nonvaccinated chickens from all three haplotypes had 84%-97% MD after challenge. The rFPV containing gB1 provides better protection than rFPV containing gB2 or gB3 in all three B genotypes. Moreover, the gB
proteins were critical, since the B*21/*21 chickens had better protection than chickens with B*13/*13 or B*5/*5 using rFPV with gB1, gB2, or gB3. A newly described combined rFPV/gB1gEgIUL32 + HVT
vaccine was analyzed in chickens of lines 15 x 7 (
B*2/*15) and N (B*21/*21) challenged with two vv+ strains of MDV. There were line differences in protection by the
vaccines and line N had better protection with the rFPV/gB1gEgIUL32 + HVT
vaccines (92%-100%) following either MDV challenge, but protection was significantly lower in 15 X 7 chickens (35%) when compared with the
vaccine CVI988/Rispens (94%) and 301B1 + HVT (65%). Another experiment used four lines of chickens receiving the new rFPV + HVT
vaccine or CVI988/Rispens and challenge with 648A MDV. The CVI 988/Rispens generally provided better protection in lines P and 15 X 7 and in one replicate with line TK. The combined rFPV/gB1gEgIUL32 + HVT
vaccines protected line N chickens (90%) better than did CVI988/Rispens (73%). These data indicate that rFPV + HVT
vaccines may provide protection against MD that is equivalent to or superior to CVI988/ Rispens in some chicken strains. It is not clear whether the rFPV/gB1gEgIUL32 + HVT
vaccine will offer high levels of protection to commercial strains, but this
vaccine, when used in line N chickens, may be a useful model to study interactions between
vaccines and chicken genotypes and may thereby improve future MD
vaccines.