Human T-Cell Responses to Vaccinia Virus Envelope Proteins

Abstract

One approach for a safer smallpox vaccine is to utilize recombinant subunits rather than live vaccinia virus (VACV). The products of the VACV envelope genes A27L, L1R, B5R, and A33R induce protective antibodies in animal models. We propose that proteins that elicit T-cell responses, as well as neutralizing antibodies, will be important to include in a molecular vaccine. To evaluate VACV-specific memory T-cell responses, peripheral blood mononuclear cells (PBMC) from four VACV vaccinees were tested against whole VACV and the individual envelope proteins A27, B5, L1, and A33, using gamma interferon enzyme-linked immunospot and cytokine flow cytometry assays. PBMC were stimulated with autologous dendritic cells infected with VACV or electroporated with individual VACV protein mRNAs. T-cell lines from all donors, vaccinated from 1 month to over 20 years ago, recognized all four VACV envelope proteins. Both CD4؉ and CD8 ؉ T-cell responses to each protein were detected. Further analysis focused on representative proteins B5 and A27. PBMC from a recent vaccinee exhibited high frequencies of CD4 ؉ and CD8 ؉ T-cell precursors to both B5 (19.8 and 20%, respectively) and A27 (6.8 and 3.7%). In comparison, B5-and A27-specific T-cell frequencies ranged from 0.4 to 1.3% in a donor vaccinated 3 years ago. Multiple CD4؉ and CD8 ؉ T-cell epitopes were identified from both A27 and B5, using overlapping 15-mer peptides. These data suggest that all four VACV envelope proteins may contribute to protective immunity, not only by inducing antibody responses, but also by eliciting T-cell responses.

Vaccination of BALB/c Mice withEscherichia coli-Expressed Vaccinia Virus Proteins A27L, B5R, and D8L Protects Mice from Lethal Vaccinia Virus Challenge

“…Most importantly, we have detected strong reactivity to the E. coliexpressed A27L, D8L, and B5R proteins in human sera from several individuals who received Dryvax vaccination (data not shown). This observation, combined with the detection of CD4 ϩ and CD8 ϩ T-cell responses to A27L and B5R from the peripheral blood mononuclear cells of vaccinees, as reported by Tang et al (48), suggests that the triple-protein vaccination may also induce protective immunity in humans. Future studies with nonhuman primates, assessing the safety, immunogenicity, and efficacy of vaccination with E. coli-expressed A27L, D8L, and B5R proteins, will be important in determining the potential of this protein combination as a safe and effective subunit vaccine.…”

Dominance and Diversity in the Primary Human CD4 T Cell Response to Replication-Competent Vaccinia Virus

“…Recently, CD4 reactivity was documented with vaccinia ORFs A27L, L1R, B5R, and A33R, which are each targets of neutralizing Abs (58). Three epitopes were identified in A27L.…”

“…We compared CD4 Ags to those that drive human or murine HLA-transgenic CD8 ϩ responses (26,53,58,62,(73)(74)(75)(76)(77). Overall 16 ORFs (A3L, A10L, A33R, A34R, A48R, A50R, B19R, C3L, C10L, D5R, E3L, G7L, H3L, I3L, J6R, and O1L) are both CD4 and CD8 Ags.…”

Human Cytotoxic CD4+ T Cells Recognize HLA-DR1-Restricted Epitopes on Vaccinia Virus Proteins A24R and D1R Conserved among Poxviruses

“…ϩ T cell responses were demonstrated against four envelope proteins on VV, A27L, B5R, L1R, and A33R (32). The study analyzed three class IIrestricted epitopes on A27L defined using overlapping 15-mer peptides, but did not define MHC restrictions of the epitopes, nor are the minimal epitopes outlined.…”

“…Xu et al (25) have shown that, in acute infection, the CD4 ϩ T cell-dependent Ab response is more important for clearing VV using Ab-depleted and gene knockout mice. Recently, Tang et al (32) identified CD8 ϩ and CD4 ϩ responses to VV envelope proteins A27L, B5R, L1R, and A33R. They studied four VV envelope proteins expressed from mRNA in autologous dendritic cells and reported CD4 ϩ T cell responses.…”