Identification of a ras oncogene peptide that contains both CD4(+) and CD8(+) T cell epitopes in a nested configuration and elicits both T cell subset responses by peptide or DNA immunization.
Mutations in ras proto-oncogenes are commonly found in a diversity of malignancies and may encode unique, non-self epitopes for T cell-mediated antitumor activity. In a BALB/c (H-2(d)) murine model, we have identified a single peptide sequence derived from the ras oncogenes that contained both CD8(+) and CD4(+) T cell epitopes in a nested configuration. This peptide reflected ras sequence 4-16, and contained the substitution of Gly to Val at position 12 ¿i.e., 4-16(Val12)¿. Mice immunized with this 13-mer peptide induced a strong antigen (Ag)-specific CD4(+) proliferative response in vitro. In contrast, mice inoculated with the wild-type ras sequence failed to generate a peptide-specific T cell response. Additionally, mice immunized with the ras 4-16(Val12) peptide concomitantly displayed an Ag-specific CD8(+) cytotoxic T lymphocyte (CTL) response, as determined by lysis of syngeneic tumor target cells incubated with the nominal 9-mer nested epitope peptide ¿i.e., 4-12(Val12)¿, as well as lysis of tumor target cells expressing the corresponding ras codon 12 mutation. Analysis of the Valpha- and Vbeta-chains of the T cell receptor (TCR) expressed by these CTL revealed usage of the Valpha1 and Vbeta9 subunits, consistent with the TCR phenotype of anti-ras Val12 CTL lines produced by in vivo immunization with the nominal peptide epitope alone. Moreover, immunization with the nested epitope peptide, as compared to immunization with either the 9-mer CTL peptide alone or an admixture of the 9-mer CTL peptide with an overlapping 13-mer CD4(+) T cell helper peptide ¿i.e., 5-17(Val12)¿ lacking the class I N-terminus anchor site, enhanced the production of the CD8(+) T cell response. Finally, immunization with plasmid DNA encoding the ras 4-16(Val12) sequence led to the induction of both Ag-specific proliferative and cytotoxic responses. Overall, these results suggested that a single peptide immunogen containing nested mutant ras-specific CD4(+) and CD8(+) T cell epitopes: (1) can be processed in vivo to induce both subset-specific T lymphocyte responses; and (2) leads to the generation of a quantitatively enhanced CD8(+) CTL response, likely due to the intimate coexistence of CD4(+) help, which may have implications in peptide- or DNA-based immunotherapies.
Bristol
J A
JA
Laboratory of Tumor Immunology and Biology, National Cancer Institute, Bethesda, Maryland 20892, USA.
Orsini
C
C
Lindinger
P
P
Thalhamer
J
J
Abrams
S I
SI
D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D019496:Cancer Vaccines / Q000276:immunology*; D002478:Cells, Cultured; D018984:Epitopes, T-Lymphocyte / Q000235:genetics / Q000276:immunology*; D005260:Female; D051379:Mice; D008807:Mice, Inbred BALB C; D016296:Mutagenesis; D010455:Peptides / Q000235:genetics / Q000276:immunology; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics / Q000276:immunology*; D014611:Vaccination; D019444:Vaccines, DNA / Q000276:immunology*
D019496:Cancer Vaccines; D018984:Epitopes, T-Lymphocyte; D010455:Peptides; D019444:Vaccines, DNA; D016283:Proto-Oncogene Proteins p21(ras)