RESUMO
It is becoming increasingly apparent that the majority of tumours display defects in the MHC class I antigen processing pathway, particularly low levels of the transporters-associated with antigen processing (TAP) and tapasin. Thus, immunotherapy approaches targeting such tumours with CD8+ cytotoxic T lymphocytes (CTL) requires strategies to overcome these defects. Previously we had identified an antigen processing pathway by which cytosolically derived hydrophobic peptides could be presented in the absence of TAP. Here we show in the tapasin-negative cell line 721.220 that a number of these hydrophobic TAP-independent peptides can also be presented in a tapasin-independent manner. Yet when these experiments were extended to tumour cell lines derived from small cell lung cancer (SCLC), which we show to be tapasin deficient in addition to TAP-negative, the TAP-, tapasin-independent peptides were not presented. This lack of presentation could be rectified by pre-treatment of SCLC cells with IFNgamma. Alternatively, by directing the TAP-, tapasin-independent peptides into the endoplasmic reticulum (ER) via an ER signal sequence, these peptides were presented efficiently by SCLC cells. We infer from this data that the TAP-independent pathway for presentation of hydrophobic peptides generates a low concentration of peptide in the ER and, for tumour cells which also lack tapasin, this concentration of antigenic peptide is insufficient to load onto MHC class I molecules. Thus, for immunotherapeutic approaches to target SCLC and other tumours with defects in the MHC class I antigen processing pathway it will be important to consider strategies that address tapasin-defects.
Assuntos
Transportadores de Cassetes de Ligação de ATP/fisiologia , Apresentação de Antígeno , Antígenos Virais/imunologia , Linfócitos T CD8-Positivos/imunologia , Retículo Endoplasmático/metabolismo , Antígenos de Histocompatibilidade Classe I/imunologia , Proteínas de Membrana Transportadoras/fisiologia , Fragmentos de Peptídeos/imunologia , Membro 2 da Subfamília B de Transportadores de Cassetes de Ligação de ATP , Membro 3 da Subfamília B de Transportadores de Cassetes de Ligação de ATP , Transportadores de Cassetes de Ligação de ATP/genética , Antígenos Virais/metabolismo , Carcinoma de Células Pequenas/patologia , Linhagem Celular Transformada , Linhagem Celular Tumoral , Citosol/metabolismo , Antígenos HLA-A/imunologia , Antígeno HLA-A2/imunologia , Antígeno HLA-A24 , Herpesvirus Humano 4/imunologia , Humanos , Interações Hidrofóbicas e Hidrofílicas , Proteínas Imediatamente Precoces/imunologia , Proteínas Imediatamente Precoces/metabolismo , Membranas Intracelulares/metabolismo , Neoplasias Pulmonares/patologia , Proteínas de Membrana Transportadoras/deficiência , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Fosfoproteínas/imunologia , Fosfoproteínas/metabolismo , Sinais Direcionadores de Proteínas/fisiologia , Transporte Proteico , Especificidade do Receptor de Antígeno de Linfócitos T , Transativadores/imunologia , Transativadores/metabolismo , Transfecção , Proteínas da Matriz Viral/imunologia , Proteínas da Matriz Viral/metabolismo , Proteínas Virais/imunologia , Proteínas Virais/metabolismoRESUMO
For recognition by CD8(+) lymphocytes, peptides derived from cytosolically processed antigen need to access MHC class I molecules en route to the target cell surface. This normally requires peptide transport into the endoplasmic reticulum via the transporter associated with antigen presentation (TAP) complex. However, as recent work with Epstein-Barr virus illustrates, TAP-independent presentation pathways also exist and are growing in number.
Assuntos
Apresentação de Antígeno , Antígenos Virais/imunologia , Herpesvirus Humano 4/imunologia , Antígenos de Histocompatibilidade Classe I/metabolismo , Membro 2 da Subfamília B de Transportadores de Cassetes de Ligação de ATP , Transportadores de Cassetes de Ligação de ATP/fisiologia , Cisteína Endopeptidases/metabolismo , Epitopos/imunologia , Antígenos Nucleares do Vírus Epstein-Barr/metabolismo , Humanos , Interações Hidrofóbicas e Hidrofílicas , Interleucina-10/metabolismo , Modelos Biológicos , Complexos Multienzimáticos/metabolismo , Complexo de Endopeptidases do Proteassoma , Proteínas da Matriz Viral/metabolismo , Proteínas Virais/metabolismoRESUMO
We have identified an HLA-A2-restricted CD8(+) T-cell epitope, FLYALALLL, in the Epstein-Barr virus (EBV) latent membrane protein 2 (LMP2), an important target antigen in the context of EBV-associated malignancies. This epitope is TAP independent, like other hydrophobic LMP2-derived epitopes, but uniquely is dependent upon the immunoproteasome for its generation.