Role of genes that modulate host immune responses in the immunogenicity and pathogenicity of vaccinia virus

Abstract

Poxvirus vaccine vectors, although capable of eliciting potent immune responses, pose serious health risks in immunosuppressed individuals. We therefore constructed five novel recombinant vaccinia virus vectors which contained overlapping deletions of coding regions for the B5R, B8R, B12R, B13R, B14R, B16R, B18R, and B19R immunomodulatory gene products and assessed them for both immunogenicity and pathogenicity. All five of these novel vectors elicited both cellular and humoral immunity to the inserted HIV-BH10 env comparable to that induced by the parental Wyeth strain vaccinia virus. However, deletion of these immunomodulatory genes did not increase the immunogenicity of these vectors compared with the parental vaccinia virus. Furthermore, four of these vectors were slightly less virulent and one was slightly more virulent than the Wyeth strain virus in neonatal mice. Attenuated poxviruses have potential use as safer alternatives to current replication-competent vaccinia virus. Improved vaccinia virus vectors can be generated by deleting additional genes to achieve a more significant viral attenuation.

FIG. 1.

Serum anti-vaccinia virus (A) and anti-gp120 (B) antibody titers in mice following immunization with gene-deleted recombinant vaccinia virus constructs. Serum samples were obtained at 0 weeks, 4 weeks after prime (pi), and at 2 and 15 weeks postboost (pb) immunization with 50 × 10⁶ PFU vaccinia by the intraperitoneal route. All anti-gp120 and antivector antibody responses in naïve (week 0) animals are not shown, as all absorbances from these serum samples fell below the cutoff used for the determination of antibody titer values in immunized animals. Antibody titers are expressed as the geometric mean (± standard error) of 4 mice per group. Symbols are as defined in the figure key.

FIG. 2.

Immunogenicity of novel recombinant vaccinia virus constructs after prime (day 0) and boost (day 56) vaccinations with 50 × 10⁶ PFU by the intraperitoneal route. Peripheral blood samples were stained with H-2D^d/p18 tetramer and anti-CD8 antibody and analyzed by flow cytometry. Levels of p18/Env-specific CD8⁺ cells are expressed as the median (± standard error) of 4 mice per group. Symbols: Δ, vT134; *, vT273; ▴, vT287; •, vT285; ▪, vT290; ♦, vT281; —, vT284.