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-2D b -restricted (I, II/III, and V) and one H-2K brestricted (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-2 b mice with syngeneic, T-antigen-expressing cells. By contrast, a weak CTL response against the H-2D b -restricted epitope V was detected only following immunization of H-2 b 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-2D b -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 specifies an optimized H-2D b binding motif and was found to induce CTL in H-2 b 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-2D b 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-2D b 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.

Adoptive immunotherapy prevents prostate cancer in a transgenic animal model

“…Per experiment, three TRAMP mice and three Tag-negative littermates were injected i. p. with 5 × 10 6 syngeneic B6 fibroblasts transformed by Tag (B6-Tag). After 11 to 14 days, splenocytes from the injected animals were restimulated in vitro with B6-Tag cells and with three immunodominant peptides known to be recognized by Tag-specific CTL [17]. While Tag-negative animals showed a very strong response to B6-Tag cells ( Fig.…”

MHC class I-restricted epitope spreading in the context of tumor rejection following vaccination with a single immunodominant CTL epitope

“…These observations describe the potential existence of hierarchies of tumor antigen-specific CTL responses, a phenomenon that was observed following infection with many different pathogenic organisms [19][20][21][22][23]. Determinant spreading has been associated in the past several years with autoreactivity to self antigens.…”

CD8+ T‐cell cross‐competition is governed by peptide–MHC class I stability

“…However, it is not known whether pMHC stability contributes to CD8 + T‐cell competition, and if this property can be exploited to broaden responses to polyepitope vaccines. To this end we employed a model system based in part on analyses by Mylin et al 20, who characterized the B6 (H‐2 b ) response hierarchy to SV40 large T antigen (Tag). They identified three IDEs (designated T1, T2/3, and T4), and one SDE (designated T5) that elicits a CD8 + T‐cell response in the absence of the IDEs.…”