Quantitation of CD8+ T-Lymphocyte Responses to Multiple Epitopes From Simian Virus 40 (SV40) Large T Antigen in C57Bl/6 Mice Immunized With SV40, SV40 T-Antigen-Transformed Cells, or Vaccinia Virus Recombinants Expressing Full-Length T Antigen or Epitope Minigenes

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The cytotoxic T-lymphocyte response to wild-type simian virus 40 large tumor antigen (Tag) in C57BL/6 (H2b) mice is directed against three H2-Db- restricted epitopes, I, II/III, and V, and one H2-Kb-restricted epitope, IV. Epitopes I, II/III, and IV are immunodominant, while epitope V is immunorecessive. We investigated whether this hierarchical response was established in vivo or was due to differential expansion in vitro by using direct enumeration of CD8+ T lymphocytes with Tag epitope/major histocompatibility complex class I tetramers and intracellular gamma interferon staining. The results demonstrate that epitope IV-specific CD8+ cells dominated the Tag-specific response in vivo following immunization with full-length Tag while CD8+ T cells specific for epitopes I and II/III were detected at less than one-third of this level. The immunorecessive nature of epitope V was apparent in vivo, since epitope V-specific CD8+ T cells were undetectable following immunization with full-length Tag. In contrast, high levels of epitope V-specific CD8+ T lymphocytes were recruited in vivo following immunization and boosting with a Tag variant in which epitopes I, II/III, and IV had been inactivated. In addition, analysis of the T-cell receptor β (TCRβ) repertoire of Tag epitope-specific CD8+ cells revealed that multiple TCRβ variable regions were utilized for each epitope except Tag epitope II/III, which was limited to TCRβ10 usage. These results indicate that the hierarchy of Tag epitope-specific CD8+ T-cell responses is established in vivo.