MAGE-1 gene is expressed in T-cell leukemia

Selective inhibition of TGF-β1 produced by GARP-expressing Tregs overcomes resistance to PD-1/PD-L1 blockade in cancer

TGF-β1, β2 and β3 bind a common receptor to exert vastly diverse effects in cancer, supporting either tumor progression by favoring metastases and inhibiting anti-tumor immunity, or tumor suppression by inhibiting malignant cell proliferation. Global TGF-β inhibition thus bears the risk of undesired tumor-promoting effects. We show that selective blockade of TGF-β1 production by Tregs with antibodies against GARP:TGF-β1 complexes induces regressions of mouse tumors otherwise resistant to anti-PD-1 immunotherapy. Effects of combined GARP:TGF-β1/PD-1 blockade are immune-mediated, do not require FcγR-dependent functions and increase effector functions of anti-tumor CD8⁺ T cells without augmenting immune cell infiltration or depleting Tregs within tumors. We find GARP-expressing Tregs and evidence that they produce TGF-β1 in one third of human melanoma metastases. Our results suggest that anti-GARP:TGF-β1 mAbs, by selectively blocking a single TGF-β isoform emanating from a restricted cellular source exerting tumor-promoting activity, may overcome resistance to PD-1/PD-L1 blockade in patients with cancer.

Inhibiting TGF-β1 to increase immune responses against tumors bears the risk of tumor-promoting toxicity. Here the authors show that selectively blocking TGF-β1 produced by immunosuppressive cells is feasible with anti-GARP:TGF-β1 antibodies and improves the efficacy of PD-1 blockade immunotherapy.

mRNA expression of MAGE-A3 gene in leukemia cells

Leukemia-associated antigens such as proteins encoded by MAGE genes might provide tools for immunotherapy of leukemia. Positive and negative results of MAGE-A gene expression in hematological malignancies have been reported. This led us to study MAGE-A gene expression in human leukemias using RT-PCR. Among 115 leukemias from various subtypes, 14/34 (41.17%) AML were positive for one of the three genes analyzed (MAGE-A1 1/32; MAGE-A3 10/32; MAGE-B2 3/12). Expression was also detected in 23/76 (30.26%) B-cell ALL patients (MAGE-A1 2/53; MAGE-A3 20/53; MAGE-B2 1/32). One of these patients expressed both MAGE-A1 (weak signal) and -A3 (strong signal) genes. Other patient with CML were positive for MAGE-B2 (1/5, 20%). MAGE-A3 expression data were corroborated by real time RT-PCR through determination of MAGE-A3 transcript levels. We concluded that the MAGE-A3 gene is expressed at the mRNA level in a proportion of human leukemias.

Epigenetic Treatment of Hematopoietic Malignancies: In Vivo Targets of Demethylating Agents

Although the first studies using DNA demethylating agents at low doses in hematologic neoplasia and hemoglobinopathies were initiated more than 20 years ago, development of this type of nonintensive treatment has only been spurred in the last 6 to 8 years by the discovery of many genes that are specifically hypermethylated in cancer. These provide a powerful rationale for using azanucleosides (and other small molecules being developed for DNA demethylation) as a novel means of pharmacologic targeting of cancer cells that is distinct from low-dose chemotherapy. Encouraging response rates of about 50% in myelodysplasia with 5-azacytidine and 5-aza-2'-deoxycytidine (decitabine or DAC) have resulted in a number of phase III studies being initiated in this disorder. The development of such drugs for the treatment of acute myeloid leukemia (AML) is ongoing. While the specificity of DNA demethylation has been delineated by studying distinct genes or sets of genes, and proof-of-principle studies of in vivo methylation report demethylation and reactivation of genes like p15/INK4b and gamma-globin, responses to demethylating agents may be more complex. Specifically, so-called cancer testis antigens (CTAs) are intriguing targets for demethylation, since they are silenced in many hematopoietic disorders and may be reactivated by epigenetic therapy. Thus, demethylating agents and histone deacetylase inhibitors may also induce a T-cell-mediated antileukemic or antitumor effect.

A gene expressed exclusively in acute B lymphoblastic leukemias

Representational difference analysis, a cDNA subtraction approach, was used to identify genes that are expressed in acute leukemia but not in normal hematological tissues. We isolated a cDNA fragment from a cell line derived from a B cell acute lymphoblastic leukemia bearing two Philadelphia chromosomes. The cDNA derives from an orphan gene that was named BLACE. BLACE is located in region 7q36 and encodes a major 5.3-kb transcript and several alternatively spliced minor transcripts. Significant expression of BLACE was detected by RT-PCR and quantitative RT-PCR in bone marrow samples from B cell acute lymphoblastic leukemia patients. BLACE was not or was scarcely expressed in other types of hematological malignancies, in normal tissues, and in solid tumors.

Expression of serologically identified tumor antigens in acute leukemias

Cancer/testis antigens (CTA) are an expanding family of immunogenic proteins selectively expressed in human neoplasms. As little is known about the expression of serologically identified CTA in leukemias so far, we investigated the expression of 5 CT genes (SSX-1, HOM-MEL-40/SSX-2, HOM-TES-14/SCP-1, SCP-3 and NY-ESO-1) in leukemic blood samples obtained from patients with either acute lymphatic leukemias (ALL) or myelocytic leukemia (AML). RT-PCR-analyses showed no expression of any of the CT-genes in the leukemia samples of 19 patients with AML, whereas frequent expression was found in ALL. In the 17 ALL cases studied, SCP3a, SSX-1, HOM-MEL-40/SXX-2 and HOM-TES-14/SCP-1 were expressed in 47, 29, 29 and 12%, respectively, whereas no case was positive for NY-ESO-1. 65% of patients with ALL showed expression of at least one, 41% of two or more of the five CT-genes investigated. We conclude that a majority of the ALLs might be amenable for specific immunotherapeutic interventions. However, the identification of additional antigens with a frequent expression in leukemias is warranted to allow the development of widely applicable polyvalent leukemia vaccines.

The MAGE-A1 gene expression is not determined solely by methylation status of the promoter region in hematological malignancies

Tumor antigens such as MAGE-A1 are aberrantly expressed in many human tumors and could be recognized by CTL. Thus, they could be targets for cancer immunotherapy. It is presently considered that the expression of the MAGE-A1 gene is regulated by methylation of its promoter region. To estimate the possibility of activating the MAGE-A1 gene with demethylating agents with a view toward clinical use, we assessed the methylation status of its CpG-rich promoter by sodium bisulfite mapping both of samples that express the gene and those that do not. Cell lines and samples from patients with hematological malignancies were examined. Surprisingly, the methylation status of the MAGE-A1 gene did not clearly correlate with the expression of the gene. Our results indicate that the MAGE-A1 gene expression is not determined solely by the methylation status of the promoter region in hematological malignancies.

Minor H antigens: genes and peptides

In this review, we describe the evidence from which the existence of non-MHC histocompatibility (H) antigens was deduced, the clinical setting of bone marrow transplantation in which they are important targets for T cell responses, and the current understanding of their molecular identity. We list the peptide epitopes, their MHC restriction molecules and the genes encoding them, of the human and murine minor H antigens now identified at the molecular level. Identification of the peptide epitopes allows T cell responses to these antigens following transplantation of MHC-matched, minor H-mismatched tissues to be enumerated using tetramers and elispot assays. This will facilitate analysis of correlations with HVG, GVH and GVL reactions in vivo. The potential to use minor H peptides to modulate in vivo responses to minor H antigens is discussed. Factors controlling immunodominance of T cell responses to one or a few of many potential minor H antigens remain to be elucidated but are important for making predictions of in vivo HVG, GVH and GVL responses and tailoring therapy after HLA-matched BMT and DLI.

MAGE-A genes are not expressed in human leukemias

Immunotherapy is promising to improve the prognosis of human leukemias, at least as adjuvant treatment. Tumor-associated antigens such as antigens encoded by MAGE-A1, -A2, -A3, -A4, -A6 and -A12 genes might provide tools in this field. We demonstrated recently that the presentation peptides encoded by MAGE-A genes might make leukemic blasts suitable targets to cytolytic T lymphocytes. We reported previously negative data of MAGE-A1 gene expression in hematological malignancies, but in further studies positive results of MAGE-A gene expression were published in some subtypes of hematological malignancies such as T leukemia, myeloma and Hodgkin's disease. This led us to enlarge the screening of MAGE-A gene expression in human leukemias. In the RT-PCR screening of a large panel including 154 patients, only weak signal were detected in a few samples. We conclude that MAGE-A genes are not expressed in human leukemias.

Minor H antigens: genes and peptides

In this review, we describe the evidence from which the existence of non-MHC histocompatibility (H) antigens was deduced, the clinical setting of bone marrow transplantation in which they are important targets for T-cell responses, and the current understanding of their molecular identity. We list the peptide epitopes of the human and murine minor H antigens now identified at the molecular level, their MHC restriction molecules and the genes encoding them. Identification of the peptide epitopes allows T-cell responses to these antigens following transplantation of MHC-matched, minor H-mismatched tissues to be enumerated using tetramers and elispot assays. This will facilitate analysis of correlations with host-versus-graft (HVG), graft-versus-host (GVH) and graft-versus-leukaemia (GVL) reactions in vivo. The potential to use minor H peptides to modulate in vivo responses to minor H antigens is discussed. Factors controlling immunodominance of T-cell responses to one or a few of many potential minor H antigens remain to be elucidated but are important for making predictions of in vivo HVG, GVH and GVL responses and tailoring therapy after HLA-matched bone marrow transplantation and donor lymphocyte infusion.

Antitumor immunity at work in a melanoma patient

This review covers the results obtained so far with a chronological analysis of the antitumor cytolytic T lymphocyte (CTL) cell response of a melanoma patient who enjoys an unusually favorable evolution. Two melanoma cell lines, MEL.A and MEL.B, were derived from metastases removed from the patient in 1988 and 1993, respectively. The patient developed a very strong CTL response against the MEL.A cells. Several antigens on these cells, presented by various HLA class I molecules, result from point mutations present in the genome of the tumor. The MEL.B cells, on the other hand, resist lysis by these CTLs because they have lost expression of most HLA class I molecules, suggesting that they were selected in vivo by the anti-MEL.A CTLs. New CTLs recognize MEL.B cells specifically, however. Analysis of their specificity indicates that they carry inhibitory receptors similar to those present on natural killer (NK) cells. These results illustrate the relationship between a tumor and the immune system in vivo over a period of several years. They are discussed in the context of the recent identification of many human tumor antigens recognized by CTLs, and the perspectives of specific immunotherapy opened up by these discoveries.

PRAME, a gene encoding an antigen recognized on a human melanoma by cytolytic T cells, is expressed in acute leukaemia cells

Gene PRAME was found to encode an antigen recognized on a human melanoma cell line by an autologous cytolytic T-lymphocyte clone. This gene is expressed at a high level in a very large fraction of tumours, such as melanomas, non-small-cell lung carcinomas, sarcomas, head and neck tumours and renal carcinomas. It is therefore a candidate for tumour immunotherapy even though some low expression is found in certain normal tissues. We tested by RT-PCR the expression of PRAME on more than 250 bone marrow or blood samples from patients with a haematological malignancy. Approximately 25% of the acute leukaemia samples were positive. Remarkably, all acute myeloblastic leukaemias that carried the chromosomal translocation t(8;21), which fuses the genes AML1 and ETO, expressed PRAME at a high level.

T cell defined tumor antigens

T cell defined antigens have now been characterized in a large variety of tumor types, in both mice and humans. An increasing number of these antigens appear to result from tumor-specific mutations, and some of these mutations may be implicated in oncogenesis. The priority is now to demonstrate that immunization against some of these antigens is clinically valuable for antitumor therapy, and the first results of clinical pilot studies are now emerging.

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.

Expression of MAGE genes in osteosarcoma

Expression of MAGE genes that encode tumor-rejection antigens recognized by cytotoxic T lymphocytes with major histocompatibility complex class-I antigens was investigated in human osteosarcomas (20 cell lines and eight fresh tumor tissues). MAGE-1, 2, 3, 4, and 6 genes were expressed at the mRNA level in 11 (52.4%), 10 (47.6%), 10 (47.6%) one (4.8%), and 10 (47.6%) of 21 tumor cell lines, respectively, and in five (62.5%), six (75%), five (62.5%), one (12.5%), and five (62.5%) of eight fresh tumor tissues as determined by the reverse transcription-polymerase chain reaction method. MAGE-1 or 4 protein was detected by immunoblot analysis in eight of 11 or one of one tumor cell lines, respectively, where it was expressed at the mRNA level. Major histocompatibility complex class-I antigens were expressed in 19 of 21 tumor cell lines. These results suggest that MAGE tumor-rejection antigens are expressed in substantial numbers of osteosarcomas in a major histocompatibility class-I-restricted manner.