Identification of vaccinia virus epitope-specific HLA-A*0201-restricted T cells and comparative analysis of smallpox vaccines

Abstract

Despite worldwide eradication of naturally occurring variola virus, smallpox remains a potential threat to both civilian and military populations. New, safe smallpox vaccines are being developed, and there is an urgent need for methods to evaluate vaccine efficacy after immunization. Here we report the identification of an immunodominant HLA-A*0201-restricted epitope that is recognized by cytotoxic CD8 ؉ T cells and conserved among Orthopoxvirus species including variola virus. This finding has permitted analysis and monitoring of epitope-specific T cell responses after immunization and demonstration of the identified T cell specificity in an A*0201-positive human donor. Vaccination of transgenic mice allowed us to compare the immunogenicity of several vaccinia viruses including highly attenuated, replication-deficient modified vaccinia virus Ankara (MVA). MVA vaccines elicited levels of CD8 ؉ T cell responses that were comparable to those induced by the replication-competent vaccinia virus strains. Finally, we demonstrate that MVA vaccination is fully protective against a lethal respiratory challenge with virulent vaccinia virus strain Western Reserve. Our data provide a basis to rationally estimate immunogenicity of safe, second-generation poxvirus vaccines and suggest that MVA may be a suitable candidate.

HLA class I-restricted responses to vaccinia recognize a broad array of proteins mainly involved in virulence and viral gene regulation

“…We report 48 previously uncharacterized epitopes restricted by various HLA molecules, thus greatly increasing the number of epitopes available for further study (10,11). Importantly, because several epitopes restricted by molecules other than A2 were identified, our results effectively enable the study of human poxvirus cellular immunity in the general population in a non-ethnically biased fashion.…”

“…Some of these antigens (B5R and L1R) have been considered for the development of subunit recombinant vaccines. Recent studies have defined five T cell epitopes restricted by murine MHC molecules (9), and three epitopes restricted by the human class I MHC molecule, HLA A*0201 (10)(11)(12)(13). A more extensive definition of the antigens and the epitopes contained within VACV is necessary to (i) enable adequate immunogenicity testing of new vaccine candidates, (ii) help elucidate the correlates of protection offered by the current vaccine, and (iii) understand human cellular immune responses to complex viruses.…”

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

“…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.…”

Genetically stable and fully effective smallpox vaccine strain constructed from highly attenuated vaccinia LC16m8

“…Recently, several groups have reevaluated the available vaccinia strains, including the replication-defective MVA, in a search for safer smallpox vaccines (37)(38)(39)(40). Although 10 9 pfu of MVA was shown to be safe in monkeys (41), a large quantity of virus, 10 8 pfu, an amount that is 1,000-fold more than a conventional vaccination dosage, was necessary to induce protective immunity (40).…”