Secondary vaccination with vaccinia virus recombinants: role of residual virulence of recombinants and immunogenicity of extrinsic antigens

Effect of virulence on immunogenicity of single and double vaccinia virus recombinants expressing differently immunogenic antigens: antibody-response inhibition induced by immunization with a mixture of recombinants differing in virulence

It has been shown recently that the residual virulence of vaccinia virus (VV) is an important factor that influences the outcome of immunization with VV recombinants. This study focused on the correlation of the residual virulence of several VV recombinants with antibody responses against the strongly immunogenic extrinsic glycoprotein E of varicella-zoster virus and the weakly immunogenic extrinsic protein preS2-S of hepatitis B virus and against VV proteins, with mice used as a model organism. Furthermore, the effects of mixing different recombinants on the antibody response were studied. The results obtained indicated that: (i) the antibody response depended on the residual virulence of the recombinants, more so in the case of the weakly immunogenic protein; (ii) the residual virulence, the growth rate of the VV recombinants in extraneural tissues and the immunogenicity were associated features; (iii) immunization with mixtures of two differently virulent recombinants or with unequal amounts of two similarly virulent recombinants sometimes led to the suppression of antibody response. The appearance of this suppression was dependent on three factors: the residual virulence of the recombinants, the immunogenicity of the extrinsic proteins and the ratio of the recombinants in the mixtures. Thus, the data obtained demonstrate that there are various limitations to the use of replicating VV recombinants for immunization purposes.