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Identification of new epitopes from four different tumor-associated antigens: recognition of naturally processed
E Keogh1, J Fikes, S Southwood
1Epimmune, 5820 Nancy Ridge Drive, San Diego, CA 92121, USA.
Abstract:
Forty-two wild-type and analogue peptides derived from p53, carcinoembryonic Ag, Her2/neu, and MAGE2/3 were screened for their capacity to induce CTLs, in vitro, capable of recognizing tumor target lines. All the peptides bound HLA-A*0201 and two or more additional A2 supertype alleles with an IC(50) of 500 nM or less. A total of 20 of 22 wild-type and 9 of 12 single amino acid substitution analogues were found to be immunogenic in primary in vitro CTL induction assays, using normal PBMCs and GM-CSF/IL-4-induced dendritic cells. These results suggest that peripheral T cell tolerance does not prevent, in this system, induction of CTL responses against tumor-associated Ag peptides, and confirm that an HLA class I affinity of 500 nM or less is associated with CTL epitope immunogenicity. CTLs generated by 13 of 20 of the wild-type epitopes, 6 of 9 of the single, and 2 of 5 of the double substitution analogues tested recognized epitopes generated by endogenous processing of tumor-associated Ags and expressed by HLA-matched cancer cell lines. Further analysis revealed that recognition of naturally processed Ag was correlated with high HLA-A2.1-binding affinity (IC(50) = 200 nM or less; p = 0.008), suggesting that high binding affinity epitopes are frequently generated and can be recognized as a result of natural Ag processing. These results have implications for the development of cancer vaccines, in particular, and for the process of epitope selection in general.
Insights
This study shows that tumor-associated antigen peptides with high HLA class I binding affinity can induce effective cytotoxic T lymphocyte (CTL) responses, crucial for cancer vaccine development.
Area of Science:
- Immunology
- Oncology
- Vaccinology
Background:
- Tumor-associated antigens (TAAs) are targets for cancer immunotherapy.
- Cytotoxic T lymphocytes (CTLs) play a key role in tumor surveillance and rejection.
- Peptide epitopes derived from TAAs can be used to elicit anti-tumor CTL responses.
Purpose of the Study:
- To screen wild-type and analogue peptides for their ability to induce CTLs recognizing tumor cell lines.
- To determine the correlation between HLA class I binding affinity and CTL epitope immunogenicity.
- To assess the recognition of naturally processed TAAs by induced CTLs.
Main Methods:
- Screening of 42 peptides (wild-type and analogues) derived from p53, carcinoembryonic antigen, Her2/neu, and MAGE2/3.
- In vitro CTL induction assays using peripheral blood mononuclear cells (PBMCs) and dendritic cells.
- Assessment of peptide binding to HLA-A*0201 and other A2 supertype alleles (IC(50) ≤ 500 nM).
- Evaluation of CTL recognition of tumor cell lines and naturally processed antigens.
Main Results:
- 20 of 22 wild-type and 9 of 12 analogue peptides were immunogenic in vitro.
- Peripheral T cell tolerance did not prevent CTL induction against TAA peptides.
- CTLs recognized naturally processed antigens expressed by cancer cell lines, particularly those with high HLA-A2.1 binding affinity (IC(50) ≤ 200 nM).
Conclusions:
- An HLA class I affinity of 500 nM or less is associated with CTL epitope immunogenicity.
- High binding affinity epitopes are frequently generated and recognized via natural antigen processing.
- These findings support the development of cancer vaccines and refine strategies for epitope selection.
