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Apoptosis-dependent subversion of the T-lymphocyte epitope hierarchy in lymphoma cells
Paola Castiglioni1, Alfonso Martin-Fontecha, Gabriella Milan
1Cancer Immunotherapy and Gene Therapy Program, Istituto Scientifico H San Raffaele, Milan Italy, 20132.
Abstract:
Tumor cells undergoing programmed death are an attractive source of tumor-associated antigens, and evidences are available for their therapeutic efficacy in vivo when used either alone or in association with dendritic cells. However, little is known about the specificity of the immune response induced by such antigen formulation. Indeed, activation of specific proteases during apoptosis may influence the cytoplasmic degradation of proteins and the generation of CTL epitopes. We show here that on injection of C57BL/6 mice either with RMA lymphoma cells induced to apoptosis or bone marrow-derived dendritic cells pulsed with apoptotic RMA cells, a specific and protective CTL response is induced, which, however, is not directed against the immunodominant CTL epitope gag(85-93). Lack of in vivo expansion of gag(85-93)-specific CTL in vaccinated mice is attributable to the apoptosis-dependent loss of gag(85-93) in dying tumor cells. Indeed, we found loss of gag(85-93) in RMA, MBL-2, and EL-4G+ lymphoma cells, which share gag(85-93) as an immunodominant CTL epitope, induced to apoptosis by UV irradiation, mitomycin C, doxorubicin, or daunorubicin. This phenomenon appears to be caspase-dependent, because caspase inhibition by N-benzyloxycarbonyl-Val-Ala-asp-fluoromethylketone prevents apoptosis of lymphoma cells and loss of gag(85-93). Therefore, subversion of the epitope hierarchy in apoptotic tumor cells might be relevant in the induction of tumor-specific T-lymphocyte responses.
Insights
Apoptotic tumor cells can induce a tumor-specific immune response, but a key antigen (gag(85-93)) is lost during programmed cell death. This loss, dependent on caspases, impacts the effectiveness of cancer vaccines by altering the T-cell response.
Area of Science:
- Immunology
- Cancer Biology
- Molecular Biology
Background:
- Apoptotic tumor cells are a source of tumor-associated antigens for cancer immunotherapy.
- The specificity of the immune response to these antigens is not well understood.
- Protease activation during apoptosis may affect the generation of cytotoxic T-lymphocyte (CTL) epitopes.
Purpose of the Study:
- To investigate the specificity of the CTL response induced by apoptotic tumor cells.
- To determine the fate of the immunodominant CTL epitope gag(85-93) during apoptosis.
- To explore the role of caspases in antigen processing during tumor cell apoptosis.
Main Methods:
- Induction of apoptosis in lymphoma cells (RMA, MBL-2, EL-4G+) using various agents (UV, mitomycin C, doxorubicin, daunorubicin).
- Vaccination of C57BL/6 mice with apoptotic RMA cells or dendritic cells pulsed with apoptotic RMA cells.
- Analysis of CTL response specificity and quantification of gag(85-93) epitope in apoptotic cells.
- Inhibition of caspases using N-benzyloxycarbonyl-Val-Ala-asp-fluoromethylketone.
Main Results:
- Apoptotic tumor cells induced a specific and protective CTL response in mice.
- This response was not directed against the gag(85-93) epitope.
- The gag(85-93) epitope was lost in dying tumor cells, a phenomenon dependent on caspases.
- Caspase inhibition prevented both apoptosis and epitope loss.
Conclusions:
- Apoptosis-induced loss of the gag(85-93) epitope in tumor cells subverts the expected T-cell epitope hierarchy.
- This altered epitope presentation during apoptosis may influence the induction of tumor-specific T-lymphocyte responses.
- Understanding these mechanisms is crucial for developing effective cancer immunotherapies.