Major histocompatibility complex (MHC) class I molecules associate with a variety of peptide ligands during biosynthesis and present these ligands on the cell surface for recognition by cytotoxic T cells. We have designed conditional MHC ligands that form stable complexes with MHC molecules but degrade on command, by exposure to a defined photostimulus. 'Empty MHC molecules' generated in this manner can be loaded with arrays of peptide ligands to determine MHC binding properties and to monitor antigen-specific T-cell responses in a high-throughput manner. We document the value of this approach by identifying cytotoxic T-cell epitopes within the H5N1 influenza A/Vietnam/1194/04 genome.

Epstein-Barr virus (EBV) persists lifelong in infected hosts

Epstein-Barr virus (EBV) resides as a persistent infection in human leukocyte antigen (HLA) class II؉ B lymphocytes and is associated with a number of malignancies. The EBV lytic-phase protein gp42 serves at least two functions: gp42 acts as the coreceptor for viral entry into B cells and hampers T-cell recognition via HLA class II molecules through steric hindrance of T-cell receptor-class II-peptide interactions. Here, we show that gp42 associates with class II molecules at their various stages of maturation, including immature ␣␤Ii heterotrimers and mature ␣␤-peptide complexes. When analyzing the biosynthesis and maturation of gp42 in cells stably expressing the viral protein, we found that gp42 occurs in two forms: a full-length type II membrane protein and a truncated soluble form. Soluble gp42 is generated by proteolytic cleavage in the endoplasmic reticulum and is secreted. Soluble gp42 is sufficient to inhibit HLA class II-restricted antigen presentation to T cells. In an almost pure population of Burkitt's lymphoma cells in the EBV lytic cycle, both transmembrane and soluble forms of gp42 are detected. These results imply that soluble gp42 is generated during EBV lytic infection and could contribute to undetected virus production by mediating evasion from T-cell immunity. Epstein-Barr virus (EBV)is a large DNA virus belonging to the family Herpesviridae, subfamily Gammaherpesviriniae, genus Lymphocryptovirus. Like other herpesviruses, EBV persists for life, establishing a latent infection in B lymphocytes with occasional viral reactivation (29). Approximately 90% of the adult population carries EBV DNA. EBV is the causative agent of infectious mononucleosis and is associated with malignancies that originate from lymphoid cells (e.g., Burkitt's lymphoma and Hodgkin's lymphoma) and epithelial cells (e.g., nasopharyngeal carcinoma). In immunosuppressed or immunocompromised individuals, EBV can cause (fatal) lymphoproliferative disease. In contrast, in healthy individuals, EBV is well controlled by the immune system. The widespread and mostly asymptomatic persistent EBV infections in adults reflect the balance between viral replication and host immune control.EBV dedicates part of its genome to immune evasion functions (15). Modulation of T-cell recognition is an important target for EBV, as the virus resides intracellularly for most of its life cycle. Fragments of viral proteins can be displayed at the cell surface by human leukocyte antigen (HLA) class I and class II molecules for the activation of T cells carrying receptors of the appropriate specificity. Activated T cells may then lead to elimination of the pathogen, among other ways through destruction of the infeced cell. To escape from antiviral immunity, EBV should interfere with both CD8 ϩ and CD4 ϩ T-cell responses, particularly as the virus infects B lymphocytes expressing both classes of HLA molecules. The EBV nuclear protein EBNA1 contains a glycine-alanine repeat domain that renders the protein resistant to proteasomal degradation and inhibits...

These data suggest that the presence of TAA-specific TILs forms a prognostic factor, predicting improved survival in advanced-stage melanoma patients. The absence of TAA-specific T cells in the circulation suggests that homing of the tumor-specific T cell population to the tumor site contributes to the effectiveness of antitumor immunity.