RESUMEN
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.
Asunto(s)
Presentación de Antígeno , Antígenos Virales/inmunología , Herpesvirus Humano 4/inmunología , Antígenos de Histocompatibilidad Clase I/metabolismo , Transportador de Casetes de Unión a ATP, Subfamilia B, Miembro 2 , Transportadoras de Casetes de Unión a ATP/fisiología , Cisteína Endopeptidasas/metabolismo , Epítopos/inmunología , Antígenos Nucleares del Virus de Epstein-Barr/metabolismo , Humanos , Interacciones Hidrofóbicas e Hidrofílicas , Interleucina-10/metabolismo , Modelos Biológicos , Complejos Multienzimáticos/metabolismo , Complejo de la Endopetidasa Proteasomal , Proteínas de la Matriz Viral/metabolismo , Proteínas Virales/metabolismoRESUMEN
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.
Asunto(s)
Transportadoras de Casetes de Unión a ATP/fisiología , Presentación de Antígeno , Antígenos Virales/inmunología , Linfocitos T CD8-positivos/inmunología , Retículo Endoplásmico/metabolismo , Antígenos de Histocompatibilidad Clase I/inmunología , Proteínas de Transporte de Membrana/fisiología , Fragmentos de Péptidos/inmunología , Transportador de Casetes de Unión a ATP, Subfamilia B, Miembro 2 , Miembro 3 de la Subfamilia B de Transportadores de Casetes de Unión a ATP , Transportadoras de Casetes de Unión a ATP/genética , Antígenos Virales/metabolismo , Carcinoma de Células Pequeñas/patología , Línea Celular Transformada , Línea Celular Tumoral , Citosol/metabolismo , Antígenos HLA-A/inmunología , Antígeno HLA-A2/inmunología , Antígeno HLA-A24 , Herpesvirus Humano 4/inmunología , Humanos , Interacciones Hidrofóbicas e Hidrofílicas , Proteínas Inmediatas-Precoces/inmunología , Proteínas Inmediatas-Precoces/metabolismo , Membranas Intracelulares/metabolismo , Neoplasias Pulmonares/patología , Proteínas de Transporte de Membrana/deficiencia , Fragmentos de Péptidos/química , Fragmentos de Péptidos/metabolismo , Fosfoproteínas/inmunología , Fosfoproteínas/metabolismo , Señales de Clasificación de Proteína/fisiología , Transporte de Proteínas , Especificidad del Receptor de Antígeno de Linfocitos T , Transactivadores/inmunología , Transactivadores/metabolismo , Transfección , Proteínas de la Matriz Viral/inmunología , Proteínas de la Matriz Viral/metabolismo , Proteínas Virales/inmunología , Proteínas Virales/metabolismoRESUMEN
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.