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T Boon

Publications and source records attributed to T Boon.

At least 73 records · Page 4Linked to original sources
PubMed1997

Two members of the human MAGEB gene family located in Xp21.3 are expressed in tumors of various histological origins.

Genes of the MAGE family direct the expression of tumor antigens recognized on a human melanoma by autologous cytolytic T lymphocytes. Twelve closely related MAGE genes are located in the Xq28 region. These genes share 60-98% nucleotide identity in their coding region. The presence of homologous genes in a region of Xp21.3 has been reported previously. We obtained the complete sequence of a 42-kb stretch of this region. It contains four MAGE-related genes, which we propose to name MAGE-B1, B2, B3, and B4 (HGMW-approved symbols MAGEB1, MAGEB2, MAGEB3, and MAGEB4). The coding regions of these genes share 66-81% nucleotide identity and show 45-63% identity with those of the MAGE genes located in Xq28. Like the MAGE genes located in Xq28, the MAGE-B genes are silent in normal tissues with the exception of testis. Like MAGE-1, 2, 3, 4, 6 and 12 (HGMW-approved symbols MAGEA1, 2, 3, 4, 6, and 12), genes MAGE-B1 and MAGE-B2 are expressed in a significant fraction of tumors of various histological types. The transcription of MAGE-B1 and MAGE-B2 can be induced by 5-aza-2'-deoxycytidine, suggesting that the activation of these genes in tumors results from a demethylation process.

Alternative Splicing↗
PubMed1997

Identification of HLA-A*0201-restricted CTL epitopes encoded by the tumor-specific MAGE-2 gene product.

MAGE-2 is expressed in many tumors, including melanoma, laryngeal tumors, lung tumors and sarcomas, but not in healthy tissue, with the exception of testis. Thus, MAGE-2-derived peptides that bind to HLA class I molecules and elicit cytotoxic T lymphocyte (CTL) responses could be of significant therapeutic importance. In this study, we show that several MAGE-2-derived peptides bind with high affinity to HLA-A*0201. Three of them form complexes with HLA-A*0201 that are stable at 37 degrees C and are immunogenic in HLA-A*0201Kb transgenic mice. Moreover, CTLs against 2 of them (M2 112-120, and M2 157-166) specifically recognize cells that express both the MAGE-2 protein and HLA-A*0201Kb. These 2 peptides are processed and presented in the context of HLA-A*0201. Therefore, these peptides are candidate components in peptide-based vaccines for the treatment and prevention of several types of MAGE-2-expressing cancers.

Animals↗
PubMed1997

A CASP-8 mutation recognized by cytolytic T lymphocytes on a human head and neck carcinoma.

Of the antigens recognized on human tumors by autologous cytolytic T lymphocytes, all those defined thus far have been identified on melanoma or renal cell carcinoma. We report here the identification of an antigen recognized by autologous cytolytic T lymphocytes on a human squamous cell carcinoma of the oral cavity. The antigen is encoded by a mutated form of the CASP-8 gene. This gene, also named FLICE or MACH, codes for protease caspase-8, which is required for induction of apoptosis through the Fas receptor and tumor necrosis factor receptor-1. The mutation, which was found in the tumor cells but not in the normal cells of the patient, modifies the stop codon and adds an Alu repeat to the coding region, thereby lengthening the protein by 88 amino acids. The ability of the altered protein to trigger apoptosis appears to be reduced relative to the normal caspase-8. The antigenic peptide is a nonamer presented by HLA-B*3503. The five last amino acids are encoded by the extension of the reading frame caused by the mutation. This, together with previous observations of CDK4 and beta-catenin mutations, suggests that a significant fraction of the point mutations generating a tumor antigen also play a role in the tumoral transformation or progression.

Aged↗
PubMed1997

Alternative promoters of gene MAGE4a.

Gene MAGE-4 (HGMW-approved symbol MAGE4) is expressed in several types of tumors, but not in normal tissues, except testis and placenta. The 5' end of this gene contains eight homologous exons spread over a 5.8-kb region. These exons are alternatively spliced to a unique second exon and a unique third exon, which encodes a protein of 317 amino acids. The analysis of transcripts found in testis, placenta, and a sarcoma cell line showed that each of the alternative first exons is used in at least one of these tissues. Various regions of the promoter of the fifth alternative exon (1.5) were cloned in a luciferase reporter plasmid, and the constructs were transfected in a sarcoma cell line that expresses MAGE-4. Two Ets motifs located between positions -70 and -29 relative to the transcription start site were found to drive 55% of the promoter activity. A region containing a Sp1 consensus binding site located upstream of the two Ets motifs was found to be responsible for 44% of the transcriptional activity. MAGE-4a promoters 1.4 and 1.6, which also contain the Sp1 and the two Ets binding motifs, supported a level of transcription comparable to that of promoter 1.5, whereas promoter 1.1, which contains only one Ets binding site, was sixfold less active. In line with observations made with gene MAGE-1 (HGMW-approved symbol MAGE1), we found that promoter 1.5 stimulated a high level of transcription in a melanoma cell line that does not express MAGE-4. This suggests that the tumor-specific expression of MAGE genes is not determined by the presence of specific transcription factors.

Alternative Splicing↗
PubMed1997

The expression of mouse gene P1A in testis does not prevent safe induction of cytolytic T cells against a P1A-encoded tumor antigen.

Tumor antigen P815AB is recognized by cytolytic T lymphocytes (CTL) on mouse mastocytoma P815. This antigen is encoded by P1A, a gene activated in several tumors but silent in normal tissues except for testis and placenta. Notwithstanding the expression of P1A in testis, we found that male mice mounted P815AB-specific CTL responses as efficiently as females. The responding males remained fertile and no autoimmune lesions were observed in their testes. By immunohistochemistry with a rabbit antiserum directed against the P1A protein, we identified spermatogonia as the testicular cells expressing P1A. The absence of MHC class-I molecules on spermatogonia could be one of the mechanisms of protection against testicular autoimmunity, as the antigenic peptide should not be displayed at the cell surface. Human genes MAGE, BAGE and GAGE, which also code for tumor antigens recognized by autologous CTL, are not expressed in normal tissues other than testis. The results obtained in mice with antigen P815AB suggest that immunization of human males with such antigens will not generate autoimmune side-effects. Although P1A is strongly expressed in placenta, we also found that gestation did not prevent generation of CTL responses against antigen P815AB, and that such CTL responses did not affect gestation outcome. We identified labyrinthine trophoblasts as the placental cells expressing P1A. Again, the absence of MHC class-I molecules on these cells provides a plausible explanation for placental protection, although other mechanisms may also play a role.

Animals↗
PubMed1997

Control of B cell lymphoma recognition via natural killer inhibitory receptors implies a role for human Vgamma9/Vdelta2 T cells in tumor immunity.

The Vgamma9/Vdelta2 T cell receptor (TCR) is expressed by most human gammadelta T cells. We show here that cytotoxic T lymphocytes of the Vgamma9/Vdelta2 subset, but not of the Vdelta1 subset of human gammadelta T cells, express natural killer inhibitory receptors (KIR) with specificity for different HLA class I alleles that down-regulate TCR-mediated signaling in response to HLA class I-expressing B cell lymphomas. Vgamma9/Vdelta2 T cell clones with a T helper cell phenotype lack KIR and produce lymphokines in response to most human B cell lymphomas, just as they do upon recognition of the HLA class I-deficient human Burkitt's lymphoma Daudi. Thus, human Vgamma9/Vdelta2 T cells have an innate specificity for nonpolymorphic cell surface structures expressed by many lymphoma cells and their cytotoxic activity is controlled by KIR. These results imply a general role of human Vgamma9/Vdelta2 T cells in the defense against hematopoietic tumors that is distinct from NK cells.

Cells, Cultured↗
PubMed1997

Identification of genes coding for tumor antigens recognized by cytolytic T lymphocytes.

Strategies have been developed to characterize tumor antigens recognized by cytolytic T lymphocytes (CTL). We use a genetic approach based on the transfection of HLA genes and cDNA libraries in COS cells to isolate the gene producing the antigenic peptide. The tumor-specific expression of this gene can be evaluated by cDNA synthesis and quantitative PCR amplification. Transfection of fragments of the isolated gene allows the identification of the region encoding the antigenic peptide. Peptides are synthesized and tested for their ability to sensitize target cells to lysis by the CTL.

Amino Acid Sequence↗
PubMed1997

Tumor antigens recognized by T lymphocytes.

In the last five years, knowledge of human tumor antigens recognized by autologous cytolytic T lymphocytes (CTL) has increased considerably. So far, genetic and biochemical approaches have led to the molecular identification of three classes of antigens. Most of these antigens consist of peptides that are presented to T cells by HLA molecules. The first class comprises antigens encoded by genes such as MAGE, BAGE, and GAGE, which are expressed in various tumors of different histological origins, but not in normal tissues other than testis. The second class represents differentiation antigens encoded by genes that are only expressed in melanoma and normal melanocytes like tyrosinase, Melan-A/MART-1, gp100 and gp75. The third class includes antigens produced by unique point mutations in genes that are ubiquitously expressed. In most cases, the antigenic peptide is encoded by the mutated region of the gene. A number of these antigens provide promising targets for new protocols of specific cancer immunotherapy.

Amino Acid Sequence↗
PubMed1997

Characterization of an antigen that is recognized on a melanoma showing partial HLA loss by CTL expressing an NK inhibitory receptor.

Melanoma lines MEL.A and MEL.B were derived from metastases removed from patient LB33 in 1988 and 1993, respectively. The MEL.A cells express several antigens recognized by autologous cytolytic T lymphocytes (CTL) on HLA class I molecules. The MEL.B cells have lost expression of all class I molecules except for HLA-A24. By stimulating autologous lymphocytes with MEL.B, we obtained an HLA-A24-restricted CTL clone that lysed these cells. A novel gene, PRAME, encodes the antigen. It is expressed in a large proportion of tumors and also in some normal tissues, albeit at a lower level. Surprisingly, the CTL failed to lyse MEL.A, even though these cells expressed the gene PRAME. The CTL expresses an NK inhibitory receptor that inhibits its lytic activity upon interaction with HLA-Cw7 molecules, which are present on MEL.A cells and not on MEL.B. Such CTL, active against tumor cells showing partial HLA loss, may constitute an intermediate line of anti-tumor defense between the CTL, which recognize highly specific tumor antigens, and the NK cells, which recognize HLA loss variants.

Amino Acid Sequence↗
PubMed1997

Genes coding for melanoma antigens recognised by cytolytic T lymphocytes.

It is now well established that human melanoma cells express antigens that are recognised by cytolytic T lymphocytes derived from the tumour-bearing patient. The molecular definition of these antigens is progressing at an accelerated pace. The currently characterised melanoma antigens can be classified into three categories: differentiation antigens, antigens encoded by genes that are specifically expressed in tumours, and antigens encoded by mutated genes. Several of these antigens are sufficiently tumour-specific to qualify them as candidate anti-cancer vaccines in melanoma patients.

Antigens↗
PubMed1997

Antigen-specific regression of established tumors induced by active immunization with irradiated IL-12- but not B7-1-transfected tumor cells.

Transfection of modestly immunogenic tumors to express B7 family co-stimulator molecules results in their rejection by syngeneic mice, suggesting a possible clinical application in cancer patients. Immunization of naive mice with irradiated B7-1-transfected P1.HTR cells is sufficient to induce specific cytolytic T lymphocytes (CTL) and to protect against tumor challenge. However, patients to be treated will have an existing tumor burden; thus, preclinical models should examine therapeutic efficacy in an established tumor setting. Contrary to expectations, immunization of mice with irradiated B7-1-transfected P1.HTR cells had no impact on the growth of pre-established control-transfected tumors. Mice bearing control-transfected P1.HTR tumors successfully rejected living B7-1 transfectants on the contralateral flank, demonstrating the ability of tumor-bearing mice to respond to B7 co-stimulation. Inasmuch as IL-12 is another important factor for CTL maturation, P1.HTR transfectants expressing B7-1 and/or IL-12 were then constructed. Remarkably, regression of pre-established tumors was achieved following immunization with irradiated IL-12 transfectants, even without co-expression of B7-1. Rejection required a shared antigen with the tumor used for immunization, could not be reproduced with rIL-12 alone, depended on host T lymphocytes and correlated with a high IFN-gamma-producing T cell phenotype. In addition, IL-12-facilitated tumor rejection required co-operation with a CTLA-4 ligand provided by the host, and correlated with up-regulation of B7-1 and B7-2 on host antigen-presenting cells. Thus, active immunization in the established tumor setting is benefitted greatly by the provision of IL-12, which may recruit participation of sufficient B7 co-stimulation from the host that it need not be provided exogenously.

Abatacept↗
PubMed1997

MAGE-1 expression threshold for the lysis of melanoma cell lines by a specific cytotoxic T lymphocyte.

Human gene MAGE-1 codes for an antigen that is recognized on a melanoma by an autologous cytotoxic T lymphocyte (CTL). Because MAGE-1 is expressed on a significant proportion of tumours of various histological types and not on normal tissues, the encoded antigen may serve as a target for cancer immunotherapy. Evaluation of the expression of the gene by reverse transcription polymerase chain reaction (RT-PCR) in various tumour samples and tumour cell lines has suggested great variability in the level of expression. It was therefore important to evaluate the minimal level of expression required for lysis by CTL. We tested a number of melanoma cell lines by a quantitative RT-PCR assay to correlate their level of MAGE-1 expression and recognition by the relevant CTL clone. We found that only cell lines expressing more than 10% of the MAGE-1 messenger RNA (mRNA) level of reference cell line MZ2-MEL.3.0 (i.e. more than three mRNA molecules per cell) were lysed by the CTL or induced significant tumour necrosis factor release.

Antigens, Neoplasm↗
PubMed1996

Isolation of tyrosinase-specific CD8+ and CD4+ T cell clones from the peripheral blood of melanoma patients following in vitro stimulation with recombinant vaccinia virus.

The identification of Ags expressed by tumor cells and recognized by autologous T cells has led to the prospect of treating cancer by adoptive transfer of tumor-reactive T cells selected for Ag specificity. Tyrosinase is an Ag expressed by normal melanocytes as well as melanoma cells for which responses by autologous T cells have been detected. To evaluate the frequency with which tyrosinase-specific T cells can be isolated from melanoma patients for potential use in therapy, a recombinant vaccinia virus expressing tyrosinase was constructed for infection of autologous APCs that could be used to stimulate T cells reactive with this protein. Eight patients were studied, with peripheral blood serving as the source of both responder T cells and autologous APCs. Tyrosinase-specific CD8+ CTL clones were isolated from five of the eight patients with melanoma. The tyrosinase-specific CTL generated in this manner recognized autologous tumor cells as well as targets expressing the recombinant virus vector. CTL clones from three of the individuals were restricted to HLA-A28, -B8, and -B60, which have not previously been identified as alleles that can present immunogenic tyrosinase peptides. Tyrosinase-specific CD4+ T cell clones were isolated from six of the eight patients by stimulation with autologous APCs infected with recombinant vaccinia virus, and all these CD4+ clones were capable of recognizing autologous tumor cells. These studies demonstrate a high prevalence of CD4+ and CD8+ tyrosinase-specific responses in peripheral blood and support the feasibility of using peripheral blood to generate T cells for tumor therapy without the requirement for isolating T cells that have infiltrated tumor sites.

Animals↗
PubMed1996

Induction of a cytolytic T-cell response in mice with a recombinant adenovirus coding for tumor antigen P815A.

We investigated the efficacy of a recombinant adenovirus in inducing a cytolytic T-lymphocyte (CTL) response in mice against tumor antigen P815A, which is present on mouse mastocytoma P815. The recombinant adenoviral vector (Adeno.PIA) contained the sequence coding for the antigenic nonapeptide which binds to the H-2.Ld molecule to form antigen P815A. We verified that murine cells infected in vitro with Adeno. PIA were lysed by an anti-P815A CTL clone. Mice then received a single intradermal injection of Adeno. PIA, and after a few weeks their spleen cells were stimulated in vitro with tumor cells expressing antigen P815A. An anti-P815A CTL response was observed with the spleen lymphocytes of nearly all the mice, providing the lymphocytes were re-stimulated in vitro with cells expressing both P815A and co-stimulatory molecule B7.1. When the stimulatory cells did not express B7.1, a specific CTL response was observed in only 45% of the mice, and it was less intense. The Adeno. P1A viral vector was unable to raise an anti-P815A response in mice that had been previously infected with a recombinant adenovirus carrying the beta-galactosidase gene or with a defective adenovirus. We conclude that adenoviral vectors may be very useful for the priming of cytolytic T-cell responses directed against human tumor antigens. Other modes of immunization may be necessary to boost the responses induced with adenoviral vectors.

Adenoviridae↗
PubMed1996

The activation of human gene MAGE-1 in tumor cells is correlated with genome-wide demethylation.

Human gene MAGE-1 encodes tumor-specific antigens that are recognized on melanoma cells by autologous cytolytic T lymphocytes. This gene is expressed in a significant proportion of tumors of various histological types, but not in normal tissues except male germ-line cells. We reported previously that reporter genes driven by the MAGE-1 promoter are active not only in the tumor cell lines that express MAGE-1 but also in those that do not. This suggests that the critical factor causing the activation of MAGE-1 in certain tumors is not the presence of the appropriate transcription factors. The two major MAGE-1 promoter elements have an Ets binding site, which contains a CpG dinucleotide. We report here that these CpG are demethylated in the tumor cell lines that express MAGE-1, and are methylated in those that do not express the gene. Methylation of these CpG inhibits the binding of transcription factors, as seen by mobility shift assay. Treatment with the demethylating agent 5-aza-2'-deoxycytidine activated gene MAGE-1 not only in tumor cell lines but also in primary fibroblasts. Finally, the overall level of CpG methylation was evaluated in 20 different tumor cell lines. It was inversely correlated with the expression of MAGE-1. We conclude that the activation of MAGE-1 in cancer cells is due to the demethylation of the promoter. This appears to be a consequence of a genome-wide demethylation process that occurs in many cancers and is correlated with tumor progression.

Antigens, Neoplasm↗