Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.10.3.1 (tyrosinase)
 9,065 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Specific CD8(+) CTL recognition of melanoma requires expression of MHC class I molecules as well as melanoma-associated peptide epitopes. Human melanoma cells may escape immune recognition by a variety of means, including global or allelic down-regulation of MHC class I molecules. Stable MHC class I cell surface expression requires delivery of cytosolic peptides into the endoplasmic reticulum by the peptide transporter molecules TAP1 and TAP2, with peptides subsequently transported to the cell surface in complexes containing MHC class I heavy chain and beta2-microglobulin. We have evaluated a series of mechanisms resulting in MHC class I down-regulation in a human melanoma cell line, Mz18, typed as HLA-A2(+), A3(+), B7(+), B57(+), Cw1(+), and Cw6(+) by genomic PCR analysis. The melanoma cell line Mz18 exhibits a global down-regulation of MHC class I heavy chain transcripts; beta2-microglobulin; the proteasome subunits LMP2/7, involved in generating cytosolic peptide fragments; and the peptide transporter molecules TAP1 and TAP2, involved in peptide transport from the cytosol into the endoplasmic reticulum. IFN-gamma treatment of Mz18 melanoma cells leads to up-regulation of LMP2/7 and TAP1/2, as well as to up-regulation of HLA-B and HLA-C MHC loci alleles, but not HLA-A2 or HLA-A3. Karyotypic analysis and fluorescence in situ hybridization with chromosome 6 and MHC class I-specific probes showed complex rearrangement of one chromosome 6 involving the MHC class I locus on 6p and translocation of 6q to the long arm of chromosome 19. To evaluate the capability of melanoma Mz18 to present tumor-specific peptides to HLA-A2-restricted, melanoma-specific CTLs, we restored HLA-A2 surface expression by retroviral-mediated transfer of functional HLA-A2 cDNA. Melanoma peptides could only be presented and recognized by CTLs if the HLA-A2-transfected Mz18 cell line was first treated with IFN-gamma, thereby restoring LMP2/7 and TAP1/2 expression and function. Because several melanoma antigens recognized by T cells have been reported to be presented by HLA-A2 (MART-1/Melan-A, tyrosinase, gp100, and MAGE-3), the loss of HLA-A2 molecules may represent an important mechanism by which many melanomas evade immune recognition. These findings suggest that patients entering clinical trials for immunotherapy with melanoma vaccines should be carefully examined for tumor cell allelic MHC class I loss and whether such MHC class I antigen down-regulation can be restored by cytokines.
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PMID:Tumor escape from immune recognition: loss of HLA-A2 melanoma cell surface expression is associated with a complex rearrangement of the short arm of chromosome 6. 981 14

We previously described different cytotoxic T lymphocyte (CTL) clones isolated from the blood lymphocytes of a melanoma patient after in vitro stimulation with autologous tumor cells. These CTL clones recognized at least 2 distinct antigens on the melanoma cells. Here, we show that one of them consists of a peptide derived from tyrosinase and presented by HLA-B35. The peptide is 9 amino acids long and has the sequence LPSSADVEF. It can be presented by the 2 major B35 allelic subtypes, B*3501 and B*3503. As HLA-B35 is one of the most frequent HLA-B specificities, being present in about 20% of Caucasian individuals, it may be a useful target for peptide-based immunotherapy of melanoma.
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PMID:A tyrosinase peptide presented by HLA-B35 is recognized on a human melanoma by autologous cytotoxic T lymphocytes. 1059 91

The authors describe a patient who experienced recurrence of metastatic melanoma after an initial dramatic response to immunotherapy using peptides derived from gp100, MART-1, and tyrosinase emulsified in incomplete Freund's adjuvant, and present data to support the hypothesis that the progression of disease in this patient was due to in vivo immunoselection for immunoresistant tumor variants. The authors previously demonstrated the existence of T-cell clones in this patient's peripheral blood and tumor-infiltrating lymphocytes (TILs) reactive against multiple antigens, including gp100, the tyrosinase-related protein (TRP)-2, a novel TRP-2 isoform-TRP-2-6b, SOX10, and the melanoma antigen NY-ESO-1. In addition to the multiple HLA-A2 restricted T-cell clones, the authors have now identified additional HLA-B/C-restricted as well as class II (HLA-DP)-restricted anti-melanoma antigen T-cell clones from this patient's TIL. One recurrent tumor showed loss of expression of multiple tumor antigens but retention of HLA class I expression. The other recurrent lesion showed total loss of HLA class I expression even though the tumor cells still expressed many melanoma antigens. This paper thus provides evidence for both the effectiveness of the immune destruction of cancer as well as problems associated with antigen-loss tumor escape mechanisms.
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PMID:Identification of multiple antigens recognized by tumor-infiltrating lymphocytes from a single patient: tumor escape by antigen loss and loss of MHC expression. 1507 35

Our understanding of pathways leading to antitumor immunity may depend on an undistorted knowledge of the primary antigenic targets of patients' autologous T cell responses. In the melanoma model derived from patient DT, we applied cryopreserved short-term autologous mixed lymphocyte-tumor cell cultures (MLTCs) in combination with an IFN-gamma enzyme-linked immunospot (ELISPOT) assay to cDNA expression screening. We identified three previously unknown peptides processed from melanosomal proteins tyrosinase (presented by HLA-A(*)2601 and -B(*)3801) and gp100 (presented by HLA-B(*)07021) and five neoantigens generated by somatic point mutations in the patient's melanoma. The mutations were found in the genes SIRT2, GPNMB, SNRP116, SNRPD1, and RBAF600. Peptides containing the mutated residues were presented by HLA-A(*)03011, -B(*)07021, and -B(*)3801. Mutation-induced functional impairment was so far demonstrated for SIRT2. Within MLTC responder populations that were independently expanded from the patient's peripheral blood lymphocytes of different years, T cells against mutated epitopes clearly predominated. These results document a high degree of individuality for the cellular antitumor response and support the need for individualizing the monitoring and therapeutic approaches to the primary targets of the autologous T cell response, which may finally lead to a more effective cancer immunotherapy.
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PMID:The response of autologous T cells to a human melanoma is dominated by mutated neoantigens. 1624 14

This review is focused on research within three different areas of tumor immunology: discovery of new T-cell epitopes and a new immunological antigen (reported in Paper I and II), elucidation of the immunological effects of treatment with a hypomethylating drug (reported in Paper III) and discovery of new conditional ligands (reported in Paper IV). Many melanoma-associated T-cell epitopes have been described, but 45% of these are restricted to human leukocyte antigen (HLA)-A2, leaving the remaining 36 different HLA molecules with only a few described T-cell epitopes each. Therefore we wanted to expand the number of T-cell epitopes restricted to HLA-A1, -A3, -A11 and -B7, all HLA molecules frequently expressed in Caucasians in Western Europe and Northern America. In Paper I we focused on the proteins gp100, Mart1, MAGE-A3, NY-ESO-1, tyrosinase and TRP-2, all melanoma-associated antigens frequently recognized by T cells from HLA-A2 patients. On contrary, in Paper II we wanted to investigate the protein Nodal as a novel immunological target. We took advantage of a T-cell epitope mapping platform in which HLA ligands are predicted by computer-based algorithms, further tested in the laboratory by an ELISA-based method and used for flow cytometry-based detection of specific T-cell responses by use of combinatorial encoded major histocompatibility (MHC) class I multimers. This procedure resulted in 127 (Paper I) and 32 (Paper II) confirmed HLA ligands, respectively, which we used for screening of the T-cell recognition within peripheral blood mononuclear cell samples from melanoma patients. As spontaneous tumor-specific T-cell responses tend to be of very low frequency and probably below the detection threshold of the method, we incorporated a T-cell enrichment step prior to the detection of these responses. Our screening of 39 melanoma patients resulted in 26 (17 different) T-cell responses against the common melanoma-associated antigens and 10 (8 different) T-cell responses against Nodal. We were further able to show processing and presentation on the cell-surface in K562 and melanoma cells expressing relevant protein and HLA molecules of four of these peptide sequences from tyrosinase, gp100 (2 peptides) and Nodal, respectively. However, one of the gp100 peptides has previously been described as a T-cell epitope. In addition to identifying new melanoma-associated T-cell epitopes we could thus describe Nodal as a new immunological antigen found of relevance in melanoma patients. In Paper III we wanted to investigate if the hypomethylating drug 5-azactytidine (Vidaza, Celgene Inc.) modulates the immune system in patients with myeloproliferative diseases. It has previ-ously been shown that 5-azacytidine-mediated demethylation of gene promoter regions results in enhanced transcription and expression of tumor suppressor genes and cancer-testis antigens. Cancer-testis antigens have frequently been recognized by T-cells in many cancers, and we hypothesized that 5-azacytidine treat-ment in the clinic would increase their frequency with resulting enhanced anti-tumor reactivity. We investigated separately the effect on T cells and tumor cells, and found that tumor cells af-fected by the treatment were better recognized, resulting in higher numbers of activated T cells, than tumor cells not exposed to 5-azacytidine. No effects were observed on the T-cell population. A screen of the T-cell recognition of 43 cancer-testis antigens in blood from our patients revealed increased T-cell recognition upon start of therapy which, though, stabilized or declined at later time points. We further investigated the general immune effector and inhibitory cell populations and found only minor effects of drug exposure, suggesting that 5-azacytidine primarily affects the tumor cells. From these results we are currently initiating a phase I clinical trial of cancer-testis antigen-peptide vaccination in combination with 5-azacytidine therapy for patients with myeloproliferative diseases. In Paper IV we wanted to expand the library of conditional ligands for use with the UV light-mediated peptide-exchange method. This method enables high-throughput generation of MHC class I molecules with different peptide-specificities. These MHC monomers can be multimerized and used for detection of specific T cell populations by flow or mass cytometry. The HLA molecules are highly genetically variable and this necessitates unique design of conditional ligands for each HLA molecule. Thus, to screen for the T-cell recognition in a given setting within all patients or healthy donors present in a cohort, a broad library of conditional ligands is needed. We designed and evaluated conditional ligands for HLA-B*08:01, HLA-B*35:01 and HLA-B*44:02/03/05, all HLA-B molecules present in high frequency among Caucasians. In addition, we provided proof for the use of a conditional ligand first designed for HLA-B*15:02 in complex with HLA-B*15:01. We compared the staining patterns of HLA-B*15:01 and HLA-B*15:02 MHC multimers and found remarkable dissimilarities, although the two heavy chains in these MHC molecules only differ in a few amino acid positions.
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PMID:Elucidating the immunological effects of 5-azacytidine treatment in patients with myelodysplastic syndrome and identifying new conditional ligands and T-cell epitopes of relevance in melanoma. 2623 96