title: Hierarchy among multiple H-2b-restricted cytotoxic T-lymphocyte epitopes within simian virus 40 T antigen.
abstract: Simian virus 40 large tumor (T) antigen contains three H-2Db-restricted (I, II/III, and V) and one H-2Kb-restricted (IV) cytotoxic T lymphocyte (CTL) epitopes. We demonstrate that a hierarchy exists among these CTL epitopes, since vigorous CTL responses against epitopes I, II/III, and IV are detected following immunization of H-2b mice with syngeneic, T-antigen-expressing cells. By contrast, a weak CTL response against the H-2Db-restricted epitope V was detected only following immunization of H-2b mice with epitope loss variant B6/K-3,1,4 cells, which have lost expression of CTL epitopes I, II/III, and IV. Limiting-dilution analysis confirmed that the lack of epitope V-specific CTL activity in bulk culture splenocytes correlated with inefficient expansion and priming of epitope V-specific CTL precursors in vivo. We examined whether defined genetic alterations of T antigen might improve processing and presentation of epitope V to the epitope V-specific CTL clone Y-5 in vitro and/or overcome the recessive nature of epitope V in vivo. Deletion of the H-2Db-restricted epitopes I and II/III from T antigen did not increase target cell lysis by epitope V-specific CTL clones in vitro. The amino acid sequence SMIKNLEYM, which species an optimized H-2Db binding motif and was found to induce CTL in H-2b mice, did not further reduce epitope V presentation in vitro when inserted within T antigen. Epitope V-containing T-antigen derivatives which retained epitopes I and II/III or epitope IV did not induce epitope V-specific CTL in vivo: T-antigen derivatives in which epitope V replaced epitope I failed to induce epitope V-specific CTL. Recognition of epitope V-H-2Db complexes by multiple independently derived epitope V-specific CTL clones was rapidly and dramatically reduced by incubation of target cells in the presence of brefeldin A compared with the recognition of the other T-antigen CTL epitopes by epitope specific CTL, suggesting that the epitope V-H-2Db complexes either are labile or are present at the cell surface at reduced levels. Our results suggest that processing and presentation of epitope V is not dramatically altered (reduced) by the presence of immunodominant CTL epitopes in T antigen and that the immunorecessive nature of epitope V is not determined by amino acids which flank its native location within simian virus 40 T antigen.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics / Q000276:immunology*; D001665:Binding Sites; D002460:Cell Line; D003602:Cytotoxicity, Immunologic; D000939:Epitopes / Q000276:immunology; D014644:Genetic Variation; D006183:H-2 Antigens / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016297:Mutagenesis, Site-Directed; D011994:Recombinant Proteins / Q000276:immunology; D017384:Sequence Deletion; D013539:Simian virus 40 / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
chemical_list: D000952:Antigens, Polyomavirus Transforming; D000939:Epitopes; D006183:H-2 Antigens; D011994:Recombinant Proteins