Lack of HLA class I antigen expression by melanoma cells SK-MEL-33 caused by a reading frameshift in beta 2-microglobulin messenger RNA

The immune-related role of beta-2-microglobulin in melanoma

Despite the remarkable success of immunotherapy in the treatment of melanoma, resistance to these agents still affects patient prognosis and response to therapies. Beta-2-microglobulin (β2M), an important subunit of major histocompatibility complex (MHC) class I, has important biological functions and roles in tumor immunity. In recent years, increasing studies have shown that B2M gene deficiency can inhibit MHC class I antigen presentation and lead to cancer immune evasion by affecting β2M expression. Based on this, B2M gene defect and T cell-based immunotherapy can interact to affect the efficacy of melanoma treatment. Taking into account the many recent advances in B2M-related melanoma immunity, here we discuss the immune function of the B2M gene in tumors, its common genetic alteration in melanoma, and its impact on and related improvements in melanoma immunotherapy. Our comprehensive review of β2M biology and its role in tumor immunotherapy contributes to understanding the potential of B2M gene as a promising melanoma therapeutic target.

Cancer stem cells and macrophages: molecular connections and future perspectives against cancer

Cancer stem cells (CSCs) have been considered the key drivers of cancer initiation and progression due to their unlimited self-renewal capacity and their ability to induce tumor formation. Macrophages, particularly tumor-associated macrophages (TAMs), establish a tumor microenvironment to protect and induce CSCs development and dissemination. Many studies in the past decade have been performed to understand the molecular mediators of CSCs and TAMs, and several studies have elucidated the complex crosstalk that occurs between these two cell types. The aim of this review is to define the complex crosstalk between these two cell types and to highlight potential future anti-cancer strategies.

MHC/HLA Class I Loss in Cancer Cells

In this chapter I describe Tumour Immune Escape mechanisms associated with MHC/HLA class I loss in human and experimental tumours. Different altered HLA class-I phenotypes can be observed that are produced by different molecular mechanisms. Experimental and histological evidences are summarized indicating that at the early stages of tumour development there is an enormous variety of tumour clones with different MHC class I expression patterns. This phase is followed by a strong T cell mediated immune-selection of MHC/HLA class-I negative tumour cells in the primary tumour lesion. This transition period results in a formation of a tumour composed only of HLA-class I negative cells. An updated description of this process observed in a large variety of human tumors is included. In the second section I focus on MHC/HLA class I alterations observed in mouse and human metastases, and describe the generation of different tumor cell clones with altered MHC class I phenotypes, which could be similar or different from the original tumor clone. The biological and immunological relevance of these observations is discussed. Finally, the interesting phenomenon of metastatic dormancy is analyzed in association with a particular MHC class I negative tumor phenotype.

Prostate cancer health disparities: An immuno-biological perspective

Prostate cancer (PCa) is the most commonly diagnosed malignancy in males, and, in the United States, is the second leading cause of cancer-related death for men older than 40 years. There is a higher incidence of PCa for African Americans (AAs) than for European-Americans (EAs). Investigations related to the incidence of PCa-related health disparities for AAs suggest that there are differences in the genetic makeup of these populations. Other differences are environmentally induced (e.g., diet and lifestyle), and the exposures are different. Men who immigrate from Eastern to Western countries have a higher risk of PCa than men in their native countries. However, the number of immigrants developing PCa is still lower than that of men in Western countries, suggesting that genetic factors are involved in the development of PCa. Altered genetic polymorphisms are associated with PCa progression. Androgens and the androgen receptor (AR) are involved in the development and progression of PCa. For populations with diverse racial/ethnic backgrounds, differences in lifestyle, diet, and biology, including genetic mutations/polymorphisms and levels of androgens and AR, are risk factors for PCa. Here, we provide an immuno-biological perspective on PCa in relation to racial/ethnic disparities and identify factors associated with the disproportionate incidence of PCa and its clinical outcomes.

The human application of gene therapy to re-program T-cell specificity using chimeric antigen receptors

The adoptive transfer of T cells is a promising approach to treat cancers. Primary human T cells can be modified using viral and non-viral vectors to promote the specific targeting of cancer cells via the introduction of exogenous T-cell receptors (TCRs) or chimeric antigen receptors (CARs). This gene transfer displays the potential to increase the specificity and potency of the anticancer response while decreasing the systemic adverse effects that arise from conventional treatments that target both cancerous and healthy cells. This review highlights the generation of clinical-grade T cells expressing CARs for immunotherapy, the use of these cells to target B-cell malignancies and, particularly, the first clinical trials deploying the Sleeping Beauty gene transfer system, which engineers T cells to target CD19⁺ leukemia and non-Hodgkin's lymphoma.

β2-Microglobulin-free HLA-G activates natural killer cells by increasing cytotoxicity and proinflammatory cytokine production

Human leukocyte antigen-G (HLA-G) is a nonclassical HLA class-I molecule and plays a role in tissue specific immunoregulation. Many studies have addressed functional aspects of β2-microglobulin (β2m)-associated HLA-G1. β2m-free HLA-G has been found in human placental cytotrophoblasts and pancreatic β cells although its function remains unclear. In the present study, we investigated the function of β2m-free HLA-G by transfecting HLA-G1 and -G3 into human β2m deficient rat pancreatic β cell carcinoma (BRIN-BD11) cells. RT-PCR and western blots studies confirmed high expression of HLA-G1 and -G3 in -G1 and -G3 transfectants, respectively. HLA-G1 and -G3 were detected mainly in intracellular compartments of BRIN-BD11 transductants by confocal fluorescent microscopy and flow cytometry. Functional analysis revealed that β2m-free HLA-G promoted xenogeneic cytotoxic lysis of BRIN-BD11 cells by natural killer (NK) cells and increased production of IL-1β, TNF-α, and IFN-γ. Stimulation of cytotoxic lysis was impaired by blocking the MAPK and DNA-PKcs pathways in NK cells. Importantly, treatment with 33mAb, a KLR2DL4 receptor agonist, induced NK-mediated cytotoxic lysis of BRIN-BD11 cells transfected with a mock vector. Our data suggest that β2m-free HLA-G activates NK cells via engagement of KLR2DL4 receptors.

Mechanisms of action underlying the immunotherapeutic activity of Allovectin in advanced melanoma

Allovectin (velimogene aliplasmid) is a cancer immunotherapeutic currently completing a pivotal phase 3 study for metastatic melanoma. Consisting of a bicistronic plasmid encoding both major histocompatibility complex (MHC) class I heavy and light chains (HLA-B7 and β2-microglobulin, respectively) formulated with a cationic lipid-based system, it is designed for direct intratumoral administration. Following injection into a single lesion, the product is intended to induce anti-tumor immune responses against both treated and distal lesions. Both the plasmid and lipid components of Allovectin contribute to the biological activity of the drug product, and its therapeutic activity is hypothesized to derive from multiple mechanisms of actions (MOAs). These include the induction of both cytotoxic T-cell and innate immune responses directed against allogeneic as well as tumor-derived targets, consequences of both an increased MHC class I expression on tumor cells and the induction of a localized immune/inflammatory response. In this paper, we review Allovectin's proposed MOAs, placing their contributions in the context of anti-tumor immunity and highlighting both preclinical and clinical supporting data.

Implication of the β2-microglobulin gene in the generation of tumor escape phenotypes

Classical MHC molecules present processed peptides from endogenous protein antigens on the cell surface, which allows CD8(+) cytotoxic T lymphocytes (CTLs) to recognize and respond to the abnormal antigen repertoire of hazardous cells, including tumor cells. The light chain, β2-microglobulin (β2m), is an essential constant component of all trimeric MHC class I molecules. There is convincing evidence that β2m deficiency generates immune escape phenotypes in different tumor entities, with an exceptionally high frequency in colorectal carcinoma (CRC) and melanoma. Damage of a single β2m gene by LOH on chromosome 15 may be sufficient to generate a tumor cell precommitted to escape. In addition, this genetic lesion is followed in some tumors by a mutation of the second gene (point mutation or insertion/deletion), which produces a tumor cell unable to express any HLA class I molecule. The pattern of mutations found in microsatellite unstable colorectal carcinoma (MSI-H CRC) and melanoma showed a striking similarity, namely the predominance of frameshift mutations in repetitive CT elements. This review emphasizes common but also distinct molecular mechanisms of β2m loss in both tumor types. It also summarizes recent studies that point to an acquired β2m deficiency in response to cancer immunotherapy, a barrier to successful vaccination or adoptive cellular therapy.

Immune evasion of microsatellite unstable colorectal cancers

Colorectal cancers (CRC) develop through 2 major pathways of genetic instability. In contrast to the majority of CRCs, which are characterized by chromosomal instability, high-level microsatellite unstable (MSI-H) CRCs arise as a consequence of the loss of DNA mismatch repair (MMR) functions and show accumulation of insertion and deletion mutations particularly in microsatellite sequences. MSI-H occurs in about 15% of CRCs, and virtually all CRCs occurring in the context of the hereditary cancer-predisposing Lynch syndrome. These tumors are characterized by a comparably good prognosis and a low frequency of distant metastases. Because of the expression of a defined set of tumor-specific antigens, MSI-H CRCs elicit a strong local and systemic antitumoral immune response of the host and therefore use different strategies to evade the control of the immune system. In this review, we will summarize novel molecular mechanisms that at the same time drive pathogenesis, immunogenicity and immune evasion during the development and progression of MSI-H CRCs. We will focus on the current knowledge about alterations in human leukocyte antigen (HLA) antigen presentation and discuss how immune evasion-while offering protection against local antitumoral immune responses-paradoxically might interfere with the ability of the tumor to form distant organ metastases.

"Hard" and "soft" lesions underlying the HLA class I alterations in cancer cells: implications for immunotherapy

The ability of cancer cells to escape from the natural or immunotherapy-induced antitumor immune response is often associated with alterations in the tumor cell surface expression of Major Histocompatibility Complex (MHC) Class I antigens. Considerable knowledge has been gained on the prevalence of various patterns of MHC Class I defects and the underlying molecular mechanisms in different types of cancer. In contrast, few data are available on the changes in MHC Class I expression happening during the course of cancer immunotherapy. We have recently proposed that the progression or regression of a tumor lesion in cancer patients undergoing immunotherapy could be predetermined by the molecular mechanism responsible for the MHC Class I alteration and not by the type of immunotherapy used, i.e., interleukin-2 (IL-2), Bacillus Calmette-Guèrin (BCG), interferon-alpha (IFN-alpha), peptides alone, dendritic cells loaded with peptides, protein-bound polysaccharide etc. If the molecular alteration responsible for the changes in MHC Class I expression is reversible by cytokines ("soft" lesion), the MHC Class I expression will be upregulated, the specific T cell-mediated response will increase and the lesion will regress. However, if the molecular defect is structural ("hard" lesion), the MHC Class I expression will remain low, the escape mechanism will prevail and the primary tumor or the metastatic lesion will progress. According to this idea, the nature of the preexisting MHC Class I lesion in the cancer cell has a crucial impact determining the final outcome of cancer immunotherapy. In this article, we discuss the importance of these two types of molecular mechanisms of MHC Class I-altered expression.

Altered molecular pathways in melanocytic lesions

To identify gene expression changes in melanocytic lesions, biopsies from 18 common nevi (CMN), 11 dysplastic nevi (DN), 8 radial and 15 vertical growth phase melanomas (RGPM, VGPM), and 5 melanoma metastases (MTS) were analyzed using whole genome microarrays. The comparison between CMN and RGPM showed an enrichment of Gene Ontology terms related to inter and intracellular junctions, whereas the transition from RGPM to VGPM underlined the alteration of apoptosis. Upregulation of genes involved in dsDNA break repair and downregulation of cellular adhesion genes were observed in MTS with respect to VGPM. DN exhibited rather heterogeneous molecular profiles, with some proliferation genes expressed at higher levels than in CMN, altered regulation of transcription compared to RGPM and a subset of processes, such as mismatch repair, equally expressed as in VGPM. Furthermore, the expression profile of genes involved into cellular detoxification and antigen presentation split them into two classes, with different proliferation potential. Finally, molecular profiling of individual lesions identified altered biological processes, such as regulation of apoptosis, regulation of transcription and T-cell activation, not associated with specific histological classes but rather with subgroups of samples without apparent relationship. This holds true for dysplastic nevi in particular. Our data indicate that generally the intersection between stage specific and sample specific molecular alterations may lead to a more precise determination of the individual progression risk of melanocytic lesions.

Class I HLA folding and antigen presentation in beta 2-microglobulin-defective Daudi cells

To present virus and tumor Ags, HLA class I molecules undergo a complex multistep assembly involving discrete but transient folding intermediates. The most extensive folding abnormalities occur in cells lacking the class I L chain subunit, called beta(2)-microglobulin (beta(2)m). Herein, this issue was investigated taking advantage of eight conformational murine mAbs (including the prototypic W6/32 mAb) to mapped H chain epitopes of class I molecules, four human mAbs to class I alloantigens, as well as radioimmunoprecipitation, in vitro assembly, pulse-chase, flow cytometry, and peptide-pulse/ELISPOT experiments. We show that endogenous (HLA-A1, -A66, and -B58) as well as transfected (HLA-A2) heavy chains in beta(2)m-defective Burkitt lymphoma Daudi cells are capable of being expressed on the cell surface, although at low levels, and exclusively as immature glycoforms. In addition, HLA-A2 is: 1) partially folded at crucial interfaces with beta(2)m, peptide Ag, and CD8; 2) receptive to exogenous peptide; and 3) capable of presenting exogenous peptide epitopes (from virus and tumor Ags) to cytotoxic T lymphocytes (bulk populations as well as clones) educated in a beta(2)m-positive environment. These experiments demonstrate a precursor-product relationship between novel HLA class I folding intermediates, and define a stepwise mechanism whereby distinct interfaces of the class I H chain undergo successive, ligand-induced folding adjustments in vitro as well as in vivo. Due to this unprecedented class I plasticity, Daudi is the first human cell line in which folding and function of class I HLA molecules are observed in the absence of beta(2)m. These findings bear potential implications for tumor immunotherapy.

Induction of maturation and activation of human dendritic cells: a mechanism underlying the beneficial effect of Viscum album as complimentary therapy in cancer

BACKGROUND

Viscum album (VA) preparations have been used as a complimentary therapy in cancer. In addition to their cytotoxic properties, they have also been shown to have immunostimulatory properties. In the present study, we examine the hypothesis that the VA preparations induce activation of human DC that facilitates effective tumor regression.

METHODS

Four day old monocyte-derived immature DCs were treated with VA Qu Spez at 5, 10 and 15 microg/ml for 48 hrs. The expression of surface molecules was analyzed by flow cytometry. The ability of Qu Spez-educated DC to stimulate T cells was analyzed by allogeneic mixed lymphocyte reaction and activation of Melan-A/MART-1-specific M77-80 CD8+T cells. Cytokines in cell free culture supernatant was analyzed by cytokine bead array assay.

RESULTS

VA Qu Spez stimulated DCs presented with increased expression of antigen presenting molecule HLA-DR and of co-stimulatory molecules CD40, CD80 and CD86. The VA Qu Spez also induced the secretion of inflammatory cytokines IL-6 and IL-8. Further, Qu Spez-educated DC stimulated CD4+T cells in a allogeneic mixed lymphocyte reaction and activated melanoma antigen Melan-A/MART-1-specific M77-80 CD8+T cells as evidenced by increased secretion of TNF-alpha and IFNgamma.

CONCLUSION

The VA preparations stimulate the maturation and activation of human DCs, which may facilitate anti-tumoral immune responses. These results should assist in understanding the immunostimulatory properties of VA preparations and improving the therapeutic strategies.

Lack and restoration of sensitivity of lung cancer cells to cellular attack with special reference to expression of human leukocyte antigen class I and/or major histocompatibility complex class I chain related molecules A/B

Both cytotoxic T lymphocytes (CTL) and natural killer (NK) cells may play major roles in the host defense against cancer. However, their relationship against the same tumor remains to be elucidated. Among 26 human lung cancer cell lines established in our laboratory, 10 (38%) exhibited human leukocyte antigen (HLA)-class I haplotype loss and three (12%) lost HLA-class I expression totally by flow cytometry analysis. The two cell lines (E522L and C831L) that lost their expression of HLA-class I in vitro and in vivo were applied for further evaluations. Genetic abnormalities of beta2-microglobulin gene were observed in both E522L (loss of mRNA) and C831L (point mutation). Transduction of the wild-type beta2-microglobulin gene rendered them positive for HLA-class I expression. The CTL were induced from autologous peripheral blood mononuclear cells or regional lymph node lymphocytes by stimulation with wild-type beta2-microglobulin transduced-E522L or -C831L, and they showed tumor-specific cytotoxicity against wild-type beta2-microglobulin-transductant, but not parental cells. In NK cell cytotoxicity, E522L showed high sensitivity to NK cells; however, C831L showed resistance despite loss of HLA-class I expression. E522L expressed MHC class I chain related molecules A/B, but C831L did not. The transduction of the MHC class I chain related molecule A gene from E522L rendered C831L positive for expression and sensitive to NK cell cytotoxicity. Reconstruction of HLA-class I and MHC class I chain related molecules A expression could abrogate evasion from cellular attack by CTL and NK cells, and it may lead to a breakthrough in the development of cancer immunotherapy.

Synthesis of beta(2)-microglobulin-free, disulphide-linked HLA-G5 homodimers in human placental villous cytotrophoblast cells

Human leucocyte antigen-G (HLA-G) is a natural immunosuppressant produced in human placentas that binds differently to the inhibitory leucocyte immunoglobulin-like receptors LILRB1 (ILT2) and LILRB2 (ILT4) according to its biochemical structure. To predict the binding functions of the HLA-G5 soluble isoform synthesized in placental villous cytotrophoblast (vCTB) cells, we investigated structural features of this protein. Biochemical and immunological studies showed that vCTB cell HLA-G5 heavy (H)-chain proteins are disulphide-bonded homodimers unassociated with beta(2)-microglobulin (beta2m) light-chain proteins. Although comparatively low levels of beta2m messenger RNA (mRNA) were identified by real-time reverse transcription-polymerase chain reaction, immunoprecipitation studies failed to detect beta2m protein even when specific mRNA was doubled by transduction of a lentivirus-beta2m complementary DNA into vCTB cells. No abnormalities were identified in the translational start codon of vCTB cell beta2m mRNA and differentiation into syncytium did not promote beta2m synthesis. The failure of vCTB cells to exhibit beta2m in vitro was paralleled by a lack of detectable beta2m in vCTB cells in vivo. Lack of the beta2m protein could be the result of low levels of beta2m transcripts or of as yet unidentified translational defects. Experiments with recombinant ectodomains of LILRB indicate that beta2m-free HLA-G binds strongly to LILRB2, a receptor that is expressed by macrophages. This potentially immunosuppressive cell type is abundant in the pregnant uterus. Thus, our findings are consistent with the postulate that the natural beta2m-free homodimeric form of HLA-G5 synthesized in primary vCTB cells could comprise a particularly effective tolerogenic molecule at the maternal-fetal interface.

Low-molecular-weight protein (LMP)2/LMP7 abnormality underlies the downregulation of human leukocyte antigen class I antigen in a hepatocellular carcinoma cell line

BACKGROUND

Tumor cells may alter the expression of numerous components involved in antigen-processing machinery to decrease human leukocyte antigen (HLA) class I expression, allowing the tumor cells to escape immune surveillance. The purpose of the present study was to investigate the involvement of these components in the downregulation of HLA class I expression in human hepatocellular carcinoma cell line BEL7,404.

METHODS

Expression of HLA-I and antigen presentation-related genes were analyzed by flow cytometry and polymerase chain reaction. The HLA class I-deficient BEL7,404 cell was transfected with the low-molecular-weight protein (LMP) 2 and LMP7 gene and were analyzed by flow cytometry for restoration of surface HLA class I expression.

RESULTS

The BEL7,404 cells downregulated the expression of HLA class I antigen and lacked expression of LMP2 and LMP7. Interferon (IFN)-gamma treatment increased the expression of LMP2 but not LMP7. The LMP2-transfected BEL7,404 cells or LMP2 and LMP7-cotransfected cells restored surface HLA class I expression while LMP7-transfected cells did not. However, in IFN-gamma-treated BEL7,404 cells, transfection with the LMP7 gene induced more HLA class I expression than mock transfection.

CONCLUSIONS

The LMP2 gene was required for the expression of HLA class I molecules in BEL7,404. The LMP7 was not the major reason for loss of HLA class I in BEL7,404 cells, although the supply of exogenous LMP7 could increase surface expression of HLA class I antigen.

Immunosuppressive strategies that are mediated by tumor cells

Despite major advances in understanding the mechanisms leading to tumor immunity, a number of obstacles hinder the successful translation of mechanistic insights into effective tumor immunotherapy. Such obstacles include the ability of tumors to foster a tolerant microenvironment and the activation of a plethora of immunosuppressive mechanisms, which may act in concert to counteract effective immune responses. Here we discuss different strategies employed by tumors to thwart immune responses, including tumor-induced impairment of antigen presentation, the activation of negative costimulatory signals, and the elaboration of immunosuppressive factors. In addition, we underscore the influence of regulatory cell populations that may contribute to this immunosuppressive network; these include regulatory T cells, natural killer T cells, and distinct subsets of immature and mature dendritic cells. The current wealth of preclinical information promises a future scenario in which the synchronized blockade of immunosuppressive mechanisms may be effective in combination with other conventional strategies to overcome immunological tolerance and promote tumor regression.

Concordant loss of melanoma differentiation antigens in synchronous and asynchronous melanoma metastases: implications for immunotherapy

Because of its known heterogeneity, the analysis of antigen expression is crucial prior to the initiation of antigen-specific immunotherapy for melanoma. The melanoma differentiation antigens gp100, MART-1 and tyrosinase are involved in a common pathway of melanin synthesis. Peptides derived from these melanoma differentiation antigens are used in the immunotherapy of melanoma and antibodies recognizing these antigens are commonly applied to detect melanocytic lesions. One hundred and ninety-one paraffin-embedded melanoma metastases from 28 patients with 2-19 lesions (mean, 6.8) developing synchronously (n = 67) or asynchronously (n = 124) were analysed by immunohistochemistry for the expression of the melanoma differentiation antigens, as well as cancer/testis antigens of the melanoma antigen-A (MAGE-A) family (monoclonal antibodies 77B and 57B), anti-S100 and SM5-1. The overall reactivities were 81.6% (gp100), 79.5% (MART-1), 59.6% (tyrosinase), 59.1% (77B), 60.7% (57B), 93.2% (S100) and 91.6% (SM5-1). Twenty-seven lesions (14.1%) were positive for all tumour-associated antigens, 75 lesions (39.2%) were negative for one antigen and 87 lesions (45.5%) were negative for several tumour-associated antigens. Co-ordinated loss was found for lesions negative for gp100 and MART-1 (9.4%, P < 0.0005), gp100 and tyrosinase (11.0%, P = 0.009), MART-1 and tyrosinase (15.2%, P < 0.0005) and gp100, MART-1 and tyrosinase (8.9%, P < 0.0005), which is up to six times higher than the expected calculated loss. This co-ordinated loss of melanoma differentiation antigens in melanoma did not include cancer testis antigens and S100 or SM5-1. On average, the melanoma differentiation antigens stained 50-65% of cells within a lesion, and 10-39% of synchronous clusters were heterogeneous for melanoma differentiation antigen expression. In conclusion, broader polypeptide vaccines should be used for melanoma immunotherapy.

Mechanisms of immune evasion by tumors

In the past decade, basic studies in animal models have begun to elucidate the physiological barriers which impede a successful antitumor immune response. These barriers operate at a number of levels, and involve the tumor, the tumor microenvironment and various components of the innate and adaptive immune systems. In this review, we discuss the multiple mechanisms by which tumors evade an immune response, with an emphasis on clinically relevant strategies to overcome these inhibitory checkpoints.

Classical and nonclassical HLA class I antigen and NK Cell-activating ligand changes in malignant cells: current challenges and future directions

Changes in classical and nonclassical HLA class I antigen and NK cell-activating ligand expression have been identified in malignant lesions. These changes, which are described in this chapter, are believed to play a major role in the clinical course of the disease since both HLA class I antigens and NK cell-activating ligands are critical to the interaction between tumor cells and components of both innate and adaptive immune systems. Nevertheless, there is still debate in the literature about the biologic and functional significance of HLA class I antigen and NK cell-activating ligand abnormalities in malignant lesions. The reasons for this debate are reviewed. They include (i) the incomplete association between classical HLA class I antigen changes and the clinical course of the disease; (ii) the relatively limited number of malignant lesions that have been analyzed for nonclassical HLA class I antigen and NK cell-activating ligand expression; and (iii) the conflicting data regarding the role of immunoselection in the generation of malignant cells with HLA antigen and NK cell-activating ligand abnormalities. The technical limitations associated with the assessment of HLA antigen and NK cell-activating ligand expression in malignant lesions as well as the immunological and nonimmunological variables that may confound the impact of HLA antigen and NK cell-activating ligand changes on the clinical course of the disease are also discussed. Future studies aimed at overcoming these limitations and characterizing these variables are expected to provide a solution to the current debate regarding the significance of HLA class I antigen and NK cell-activating ligand abnormalities in malignant lesions.

Immune selection of hot-spot beta 2-microglobulin gene mutations, HLA-A2 allospecificity loss, and antigen-processing machinery component down-regulation in melanoma cells derived from recurrent metastases following immunotherapy

Scanty information is available about the mechanisms underlying HLA class I Ag abnormalities in malignant cells exposed to strong T cell-mediated selective pressure. In this study, we have characterized the molecular defects underlying HLA class I Ag loss in five melanoma cell lines derived from recurrent metastases following initial clinical responses to T cell-based immunotherapy. Point mutations in the translation initiation codon (ATG-->ATA) and in codon 31 (TCA-->TGA) of the beta(2)-microglobulin (beta(2)m) gene were identified in the melanoma cell lines 1074MEL and 1174MEL, respectively. A hot-spot CT dinucleotide deletion within codon 13-15 was found in the melanoma cell lines 1106MEL, 1180MEL, and 1259MEL. Reconstitution of beta(2)m expression restored HLA class I Ag expression in the five melanoma cell lines; however, the HLA-A and HLA-B,-C gene products were differentially expressed by 1074MEL, 1106MEL, and 1259MEL cells. In addition, in 1259MEL cells, the Ag-processing machinery components calnexin, calreticulin, and low m.w. polypeptide 10 are down-regulated, and HLA-A2 Ags are selectively lost because of a single cytosine deletion in the HLA-A2 gene exon 4. Our results in conjunction with those in the literature suggest the emergence of a preferential beta(2)m gene mutation in melanoma cells following strong T cell-mediated immune selection. Furthermore, the presence of multiple HLA class I Ag defects within a tumor cell population may reflect the accumulation of multiple escape mechanisms developed by melanoma cells to avoid distinct sequential T cell-mediated selective events.

Immunotherapy for melanoma

The immunogenicity of melanoma and the identification of melanoma-associated antigens is the basis for immunotherapy. This review will discuss the current status of melanoma immunotherapy with a focus on non-specific cytokines and highly specific vaccines, including peptides, viruses, dendritic cells, and whole cell vaccines. The passive transfer of melanoma-specific monoclonal antibodies and T-cells will also be reviewed. The problem of tumor escape and the association of immunotherapy to autoimmunity will be discussed. The use of immunotherapy in combination with other therapeutic agents and genetic profiling to predict responses suggests that immunotherapy will continue to play a role in the treatment of melanoma.

Tumor antigens for cancer immunotherapy: therapeutic potential of xenogeneic DNA vaccines

Preclinical animal studies have convincingly demonstrated that tumor immunity to self antigens can be actively induced and can translate into an effective anti-tumor response. Several of these observations are being tested in clinical trials. Immunization with xenogeneic DNA is an attractive approach to treat cancer since it generates T cell and antibody responses. When working in concert, these mechanisms may improve the efficacy of vaccines. The use of xenogeneic DNA in overcoming immune tolerance has been promising not only in inbred mice with transplanted tumors but also in outbred canines, which present with spontaneous tumors, as in the case of human. Use of this strategy also overcomes limitations seen in other types of cancer vaccines. Immunization against defined tumor antigens using a xenogeneic DNA vaccine is currently being tested in early phase clinical trials for the treatment of melanoma and prostate cancers, with proposed trials for breast cancer and Non-Hodgkin's Lymphoma.

Endoplasmic reticulum chaperone-specific monoclonal antibodies for flow cytometry and immunohistochemical staining

Endoplasmic reticulum (ER) chaperones of the antigen processing machinery play a crucial role in HLA class I antigen complex assembly and antigen presentation. The characterization of the expression of these chaperones in normal tissues and malignant lesions has been hampered by the lack or limited availability of ER chaperone-specific monoclonal antibodies (mAb) that are suitable for immunohistochemical staining. To overcome this limitation, we have generated human calnexin, ERp57, calreticulin and tapasin-specific mAb-secreting hybridomas from BALB/c mice immunized with peptides and recombinant proteins. The mAb TO-5, TO-2, TO-11 and TO-3 were shown to be specific for calnexin, ERp57, calreticulin and tapasin, respectively, as they react specifically with the corresponding immunizing peptides in ELISA and with the corresponding proteins when tested with human lymphoid cell lysates in Western blotting. Furthermore, the reactivity of the four mAb with the corresponding intracellular antigens yielded intracellular staining when the mAb were tested with formalin-fixed, microwave-treated and saponin-permeabilized cells in indirect immunofluorescence and with formalin-fixed, paraffin-embedded tissue sections in the immunoperoxidase reaction. These results suggest that the ER chaperone-specific mAb we have developed are useful probes for characterizing the expression of ER chaperones of the antigen processing machinery in normal and pathological cells. This information will contribute to defining the effects of abnormalities in their expression on HLA class I antigen expression and function and on the interactions of target cells with the host's immune system.

Does the immune system see tumors as foreign or self?

Given the vast number of genetic and epigenetic changes associated with carcinogenesis, it is clear that tumors express many neoantigens. A central question in cancer immunology is whether recognition of tumor antigens by the immune system leads to activation (i.e., surveillance) or tolerance. Paradoxically, while strong evidence exists that specific immune surveillance systems operate at early stages of tumorigenesis, established tumors primarily induce immune tolerance. A unifying hypothesis posits that the fundamental processes of cancer progression, namely tissue invasion and metastasis, are inherently proinflammatory and thus activating for innate and adaptive antitumor immunity. To elude immune surveillance, tumors must develop mechanisms that block the elaboration and sensing of proinflammatory danger signals, thereby shifting the balance from activation to tolerance induction. Elucidation of these mechanisms provides new strategies for cancer immunotherapy.

HLA class I antigen loss, tumor immune escape and immune selection

Poor clinical response rates have been observed in the majority of the T cell-based immunotherapy clinical trials conducted to date. One reason might be the presence of abnormalities in HLA class I antigen presentation in malignant lesions. An increased frequency of HLA class I abnormalities has been observed in malignant lesions from patients treated with T cell-based immunotherapy and in lesions which have recurred in patients who had experienced clinical responses following T cell-based immunotherapy. These observations are compatible with the possibility that the outgrowth of a patient's tumor reflects immune selection of tumor cells which have acquired escape mechanisms from immune recognition.

The heavy chain of neonatal Fc receptor for IgG is sequestered in endoplasmic reticulum by forming oligomers in the absence of beta2-microglobulin association

The heavy chain (HC) of the neonatal Fc receptor (FcRn) for IgG is non-convalently associated with beta(2)-microglobulin (beta(2)m). In beta(2)m(-/-) mice, FcRn functions are greatly impaired. We sought to determine how FcRn HC, particularly its structure and biogenesis, is affected by the absence of beta(2)m. Human FcRn HC, expressed from the beta(2)m-null cell line FO-1(FcRn), was present as a monomeric 45-kDa protein under reducing conditions but primarily as a 92-kDa oligomeric protein under non-reducing conditions. Two-dimensional electrophoresis and MS analysis showed that the 92-kDa protein was a dimer of the 45-kDa HC. Immunostaining showed that FcRn HC in FO-1(FcRn) was co-localized with the endoplasmic reticulum (ER) protein Bip/GRP78 but not with an endosome protein, EEA1. In contrast, FcRn HC in FO-1(FcRn+beta2m) was detected in both the ER and endosome. The dimeric HC in FcRn oligomers was free of beta(2)m association in FO-1(FcRn+beta2m). Mutation of non-paired cysteine residues at positions 48 and 251 within the human FcRn cDNA failed to eliminate the oligomers. The FcRn HC oligomers could be reduced by reconstitution of FO-1(FcRn) with beta(2)m or by balanced expression of FcRn HC with beta(2)m, or beta(2)m fused with a KDEL retention sequence. Similarly, the majority of FcRn HC isolated from neonatal beta(2)m(-/-) mice was in a dimeric form under non-reducing conditions. The amount of FcRn HC was significantly decreased in beta(2)m(-/-) mice and FO-1(FcRn). Furthermore, beta(2)m-free FcRn HC was sensitive to endoglycosidase digestion. These results indicate that FcRn HC alone can form disulphide-bonded oligomers in the ER, which may represent a misfolded protein. The beta(2)m association with FcRn HC is critical for correct folding of FcRn and exiting the ER for routing to endosomes and the cell surface.

Downregulation of the proteasome subunits, transporter, and antigen presentation in hepatocellular carcinoma, and their restoration by interferon-gamma

BACKGROUND

In our previous study, expressions of human histocompatibility leukocyte antigens class I molecules (HLA-I) and the transporter associated with antigen processing (TAP) 1/2 genes were investigated in seven hepatocellular carcinoma (HCC) cell lines. Two cell lines, Hep-3B and HuH-7, showed a reduced level of TAP, which might cause the low surface expression of HLA-I. In order to understand the downregulation mechanism of antigen presentation in tumors, the two cell lines were further investigated.

METHODS

Expressions of HLA-I and antigen presentation-related genes were analyzed by flow cytometry and polymerase chain reaction, respectively. Antigen presentation was tested in 51Cr-release assays.

RESULTS

Flow cytometric analyses revealed low surface expression of HLA-I on Hep-3B and HuH-7 cells. Introduction of HLA-A2 gene did not result in a high surface expression of HLA-A2. This suggested the downregulation of HLA-I expression might be related to defects in the antigen presentation machinery. We then examined expression levels of various antigen presentation-related genes. Hep-3B and HuH-7 demonstrated low expression of the low-molecular-weight protein (LMP) 2, LMP7, TAP1, and HLA-I heavy-chain transcripts. The downregulation of these genes was dissolved by treatment with gamma-interferon. Furthermore, allo-specific cytotoxic T lymphocyte (CTL) lines failed to recognize Hep-3B and HuH-7 cells, while they killed IFN-gamma-treated Hep-3B and HuH-7 cells.

CONCLUSIONS

Our results suggest that defects in the antigen presentation-related molecules might cause downregulation of HLA-I expression, antigen presentation, and subsequently, escape from specific CTL killing. The downregulation could be restored by IFN-gamma treatment, suggesting the potential use of IFN-gamma for therapeutic purposes.

Loss of single HLA class I allospecificities in melanoma cells due to selective genomic abbreviations

Expression of human leucocyte antigen (HLA) Class I molecules is essential for the recognition of malignant melanoma (MM) cells by CD8(+) T lymphocytes. A complete or partial loss of HLA Class I molecules is a potent strategy for MM cells to escape from immunosurveillance. In 2 out of 55 melanoma cell cultures we identified a complete phenotypic loss of HLA allospecificities. Both patients have been treated unsuccessfully with HLA-A2 peptides. To identify the reasons underlying the loss of single HLA-A allospecificities, we searched for genomic alterations at the locus for HLA Class I alpha-chain on chromosome 6 in melanoma cell cultures established from 2 selected patients with MM in advanced stage. This deficiency was associated with alterations of HLA-A2 gene sequences as determined by polymerase chain reaction-sequence specific primers (PCR-SSP). Karyotyping revealed a chromosomal loss in Patient 1, whereas melanoma cell cultures established from Patient 2 displayed 2 copies of chromosome 6. Loss of heterozygosity (LOH) using markers located around position 6p21 was detected in both cases. By applying group-specific primer-mixes spanning the 5'-flanking region of the HLA-A2 gene locus the relevant region was amplified by PCR and subsequent sequencing allowed alignment with the known HLA Class I reference sequences. Functional assays using HLA-A2-restricted cytotoxic T-cell clones were performed in HLA-A2 deficient MM cultures and revealed a drastically reduced susceptibility to CTL lysis in HLA-A2 negative cells. We could document the occurrence of selective HLA-A2 deficiencies in cultured advanced-stage melanoma metastases and identify their molecular causes as genomic alterations within the HLA-A gene locus.

Impaired surface antigen presentation in tumors: implications for T cell-based immunotherapy

The identification of tumor-associated antigens has suggested new possibilities for cancer therapy. However, multiple mechanisms may contribute to the ability of tumor to escape antitumor immune responses. Tumor antigen heterogeneity, modulation of HLA expression and immune suppressive mechanisms may occur at any time during tumor cell progression, and can affect the outcome of therapeutic immune intervention. In particular, the appearance of altered HLA class I phenotypes during tumor development may have important biological and medical implications due to the role of these molecules in T and NK cell functions. Exhaustive tumor tissue studies are necessary before deciding whether a particular patient is suitable for inclusion in T cell-based immunotherapy protocols.

Introduction of tapasin gene restores surface expression of HLA class I molecules, but not antigen presentation of an HIV envelope peptide in a hepatoma cell line

A hepatoma cell line, Hep G2, reveals the diminished HLA class I surface expression and the reduced expression of LMP2, LMP7, and tapasin transcripts, suggesting that the reduced expression of these transcripts may be associated with the low expression of HLA class I molecules. Introduction of tapasin gene dramatically up-regulates the surface expression of HLA class I molecules on Hep G2 cells, and unexpectedly, enhances the expression of LMP2 and LMP7 transcripts as well. Unlike Hep G2, these tapasin-transfected Hep G2 cells are recognized by allo-specific CTL. However, the transfectant is unable to endogenously present an HIV envelope peptide to an HIV-specific CTL clone, suggesting that a proteasome-independent antigen processing pathway exists and still remains defective in the transfectant. These data may provide significant evidence that the nonproteasomal antigen processing pathway as well as the proteasomal pathway may be impaired in tumor cells to escape immune surveillance performed by CTL.

T-cell-directed cancer vaccines: mechanisms of immune escape and immune tolerance

Recent clinical trials using vaccines directed toward tumour-associated antigens (TA) have shown the increasing capacity of vaccines to cause immunologic responses. In fact, strongly reactive TA-specific cytolytic T-lymphocytes and tumour-infiltrating lymphocytes (TIL) can be identified and expanded ex vivo from patients with metastatic melanoma vaccinated with melanoma-associated antigens. Paradoxically, this strong immunological response does not correlate with clinical tumour regression. Proposed mechanisms responsible for this glaring inconsistency are numerous and varied; systemic immunosuppressive as well as local mechanistic factors are implicated. In this review we will critically evaluate the possible mechanisms that allow tumours to escape immune destruction and be tolerated by the immune system. In addition, strategies that may allow further insight into the biology of tumour rejection are discussed, in the hope of deepening the understanding of this phenomenon and enhancing its therapeutic potential.

Beta2-microglobulin gene mutation is not a common mechanism of HLA class I total loss in human tumors

One hundred and sixty-two tumor samples were analyzed for HLA class I expression using immunohistological techniques. HLA class I total loss (phenotype no. I) was detected in 31 cases (19%), comprising 20 colorectal, 3 laryngeal, and 2 bladder carcinomas and 6 melanomas. Twenty-one cases were selected for molecular analysis due to a higher proportion of tumor cells versus stroma cells (75%). We investigated whether beta2-microglobulin mutation was responsible for HLA downregulation. Single-strand conformation polymorphism and sequencing analysis of DNA samples was performed. Alterations were detected only in melanomas M78 (a point mutation in the initiation ATG sequence), M79 (a mutation in codon 31 producing a stop codon), and M34 (a TTCT deletion introducing a termination codon signal). We found no beta2-microglobulin gene mutation in the other 18 samples. Loss of heterozygosity in 15q close to the beta2-microglobulin gene was found in 5 cases. We conclude that HLA class I total loss can frequently occur without beta2-microglobulin gene mutations.

High expression of HLA-A2 on an oral squamous cell carcinoma with down-regulated transporter for antigen presentation

Using the reverse transcription PCR, we evaluated expression levels of various antigen presentation-related genes, including LMP2, LMP7, MECL-1, PA28alpha, PA28beta, TAP1, TAP2, and tapasin, in two oral squamous cell carcinoma cell lines, HSC5 and HSC7. Expression levels of LMP2, MECL-1, TAP1, and TAP2 transcripts are reduced in both cell lines in comparison with a normal epithelial cell line. Further, HSC5 and HSC7 show diminished expression of LMP7/tapasin, and PA28alpha/beta, respectively. Surface expression of HLA-B alleles is down-regulated in both lines presumably due to low expression of TAP1/2. However, HLA-A2 surface expression is not significantly down-regulated in HSC5 cells, suggesting an involvement of signal-sequence derived peptides in the TAP-independent pathway. The current study would contribute to our understanding of significance of abnormalities in the antigen presentation machinery of oral squamous cell carcinoma, and provide meaningful information in the design of CTL-based tumor vaccines by intra-cellular delivery system.

Changes in cell surface molecules associated with in vitro culture of prostatic stromal cells

BACKGROUND

Prostate stromal cells can be readily cultured in vitro. Are these proliferating cells representative of stromal cells in situ? Since the expression of cell surface molecules, like the cluster of differentiation (CD) antigens, can be affected by changes in physiological conditions cultured stromal cells may differ from uncultured stromal cells in their complement of CD molecules.

METHODS

Prostate stromal cells were prepared from tissue specimens and cultured. Flow cytometry was used to analyze the expression of 107 CD molecules in the resultant cells. Expression of the CD molecules by prostate cells in situ was done by immunohistochemistry.

RESULTS

The expression of a number of cell surface molecules such as CD10, CD13, CD26, and CD44 is elevated in prostatic stromal cells cultured in vitro. These are markers of epithelial cells in tissue. Other molecules expressed by the cultured stromal cells include CD29, CD49a, CD49b, CD49d, CD49f, CD51/61, CD54, CD55, CD56, CD58, CD59, CD61, CD71, CD79b, CD81, CD82, CD90, CD95, CD107a, CD130, and CD147. Among these are stromal, epithelial, and nonstromal/nonepithelial markers as defined by tissue immunohistochemistry.

CONCLUSION

Cultured stromal cells express a number of CD molecules normally found in other cell types of the prostate. Cells can express different CD molecules under different conditions.

Selective histocompatibility leukocyte antigen (HLA)-A2 loss caused by aberrant pre-mRNA splicing in 624MEL28 melanoma cells

Histocompatibility leukocyte antigen (HLA)-A2 is used as a restricting element to present several melanoma-associated antigen (MAA)-derived peptides to cytotoxic T lymphocytes (CTLs). HLA-A2 antigen is selectively lost in primary melanoma lesions and more frequently in metastases. Only scanty information is available about the molecular mechanisms underlying this abnormality, in spite of its potentially negative impact on the clinical course of the disease and on the outcome of T cell-based immunotherapy. Therefore, in this study we have shown that the selective HLA-A2 antigen loss in melanoma cells 624MEL28 is caused by a splicing defect of HLA-A2 pre-mRNA because of a base substitution at the 5' splice donor site of intron 2 of the HLA-A2 gene. As a result, HLA-A2 transcripts are spliced to two aberrant forms, one with exon 2 skipping and the other with intron 2 retention. The latter is not translated because of an early premature stop codon in the retained intron. In contrast, the transcript with exon 2 skipping is translated to a truncated HLA-A2 heavy chain without the alpha(1) domain. Such a polypeptide is synthesized in vitro but is not detectable in cells, probably because of the low steady state level of the corresponding mRNA and the low translation efficiency. These results indicate that a single mutational event in an HLA class I gene is sufficient for loss of the corresponding allele. This may account, at least in part, for the high frequency of selective HLA class I allele loss in melanoma cells. Our conclusion emphasizes the need to implement active specific immunotherapy with a combination of peptides presented by various HLA class I alleles. This strategy may counteract the ability of melanoma cells with selective HLA class I allele loss to escape from immune recognition.

Biosynthesis of HLA-C heavy chains in melanoma cells with multiple defects in the expression of HLA-A, -B, -C molecules

Recent investigations have shown that malignant transformation may down-regulate the expression of class I HLA molecules, beta2-microglobulin (beta2m) and members of the antigen-processing machinery. In the present study, we HLA-genotyped and identified at a biochemical level the three (HLA-A25, -B8, -Cw7) class I alleles expressed by the previously described [D'Urso CM et al (1992) J Clin Invest 87: 284-292] beta2m-defective human melanoma FO-1 cell line and tested their ability to interact with calnexin, calreticulin and the TAP (transporter associated with antigen processing) complex. All these alleles were found to bind calnexin, but not calreticulin or the poorly expressed TAP complex, both in parental and beta2m-transfected FO-1 cells, demonstrating a complex defect of class I expression in FO-1 cells. In these conditions, Cw7 heavy chains interacted with calnexin more strongly than A25 and B8, and preferentially accumulated in the endoplasmic reticulum, in both a calnexin-associated and a calnexin-free form. In addition, they could be transported to the cell surface at low levels even in the absence of beta2m, without undergoing terminal glycosylation. These results establish a parallel between HLA-C and the murine Db and Ld molecules which have been found to be surface expressed and functional in beta2m-defective cells. They also demonstrate distinctive features of HLA-C molecules. We propose that the accumulation of several assembly intermediates of HLA-C might favour the binding of peptide antigens not readily bound by HLA-A and -B molecules in neoplastic cells with suboptimal class I expression.

Induction and functional characterization of beta2-microglobulin (beta2-mu)-free HLA class I heavy chains expressed by beta2-mu-deficient human FO-1 melanoma cells

The frequent loss of beta2-microglobulin (beta2-mu) in malignant cells has stimulated interest in the functional characteristics of beta2-mu-free HLA class I heavy chains, since this information contributes to assess the impact of beta2-mu abnormalities on the interaction of malignant cells with immune cells. Therefore, the present study has investigated the ability of beta2-mu-free HLA class I heavy chains to modulate NK cell-mediated lysis of melanoma cells and to present melanoma-associated antigen (MAA)-derived peptides to HLA class I-restricted, MAA-specific cytotoxic T lymphocytes (CTL). Beta2-mu-free HLA class I heavy chains were induced on beta2m null FO-1 cells by sequential incubation with IFN-alpha for 48 h at 37 degrees C and for 24 h at 26 degrees C. Transfection of cells with a wild-type H-2Ld gene (FO-1Ld) enhanced the induction of beta2-mu-free HLA class I heavy chains under such experimental conditions. Beta2-mu-free HLA class I heavy chains expressed on the cell membrane did not protect the B2m null FO-1 cells from NK cell-mediated lysis. Furthermore, FO-1 cells which express beta2-mu-free HLA-A2 heavy chains following transfection with a wild-type HLA-A2 gene were not lysed by HLA-A2-restricted, MAA-specific CTL lines and clones. These results indicate that association with beta2-mu is required for interaction of HLA class I molecules with NK inhibitory receptors and for peptide presentation to CTL.

beta2-Microglobulin mutations, HLA class I antigen loss, and tumor progression in melanoma

The potential negative impact of HLA class I antigen abnormalities on the outcome of T cell-based immunotherapy of melanoma has prompted us to investigate the mechanisms underlying lack of HLA class I antigen expression by melanoma cell lines Me18105, Me9923, and Me1386. Distinct mutations in the beta2-microglobulin (beta2m) gene were identified in each cell line which result in loss of functional beta2m. In Me18105 cells, an aberrant splicing mechanism caused by an A--> G point mutation in the splice acceptor site of intron 1 of the beta2m gene, deletes 11 bp from the beta2m mRNA creating a shift in the reading frame. In Me9923 cells a 14-bp deletion in exon 2 and in Me1386 cells a CT deletion in exon 1 of the beta2m gene produce a frameshift mutation. The beta2m gene mutations identified in Me18105, Me9923, and Me1386 cells were also detected in the surgically removed melanoma lesions from which the cell lines originated. Transfection of each melanoma cell line with a wild-type beta2m gene restored HLA class I antigen expression and, in Me18105 cells, recognition by Melan-A/MART-1-specific, HLA-A2-restricted cytotoxic T lymphocytes. Interestingly, the beta2m mutation present in Me9923 cells that were derived from a metastatic lesion was also found in the Me9923P cell line that originated from the autologous primary lesion. These data suggest that beta2m mutations in melanoma cells may be an early event in progression to the malignant phenotype.

Review: analogies between trophoblastic and malignant cells

PROBLEM

The question of how trophoblastic and malignant cells evade immunologic recognition and rejection by their host was studied.

METHOD OF STUDY

A literature review was conducted.

RESULTS

Trophoblastic and malignant cells share a number of similarities. These include a lack of major histocompatibility complex antigen expression, resistance to lysis by natural killer cells, T-helper cell-2 (TH2)-biased response, prostaglandin E production, and response to transforming growth factor beta. In addition, the analogies between trophoblastic and malignant cells extend into immunotherapy in which anti-idiotype therapy has a viable role in the prevention of pregnancy loss and the treatment of cancer.

CONCLUSIONS

Trophoblastic and malignant cells use a number of similar mechanisms to resist rejection by their host. By using similar strategies these cells are able to successfully co-exist in an immunologically hostile environment.

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.

Immunoselection in vivo: independent loss of MHC class I and melanocyte differentiation antigen expression in metastatic melanoma

Peptides derived from melanocyte differentiation antigens have been identified as targets for MHC class I-restricted cytolytic T lymphocytes (CTLs) in human melanoma Regression of antigen-expressing tumors as well as selection of antigen-loss variants in the presence of antigen-specific CTLs have previously been reported. In the present study, we determined the expression of the melanocyte differentiation antigens Melan A/MART-1 and tyrosinase by mRNA analysis and by immunohistochemical staining with the monoclonal antibodies (MAbs) A103 and T311. Co-expression of Melan A/MART-1 and tyrosinase was detected by both methods in 18/20 melanomas tested. However, immunohistochemistry provided additional information on intensity and microheterogeneity of antigen expression that cannot be detected by mRNA analysis as a molecular basis for the escape from CTL recognition of antigen-negative tumor cells. Comparative analysis of repeated biopsies of metastatic lesions in 5 HLA-A2+ patients showed a gradual loss of Melan A/MART-1 expression in 4/5 and of tyrosinase in 2/5 samples in association with tumor progression. However, 3 of these patients had growing antigen-positive tumors in the presence of antigen-specific CTLs. This led us to assess the expression of MHC class I, the essential restriction element for CTL recognition, and of HLA-A2. We found an unexpectedly high frequency of MHC class I-negative tumors (9/20). Loss of MHC class I expression was detected in 3/5 progressive tumors and isolated loss of HLA-A2 in 1/5 tumors. Our results suggest that strategies enhancing the expression of MHC class I and tumor-associated antigens need to be considered in attempts at making vaccination more effective.

Structural and functional analysis of beta2 microglobulin abnormalities in human lung and breast cancer

The escape of tumor cells from immune recognition is a central problem in tumor immunology. Here, we examined the functional role of somatic beta 2-microglobulin (beta2m) gene mutations in human lung and breast cancers. Using single-strand conformational polymorphism (SSCP) analysis and DNA sequencing, we found mutations in the beta2m gene in 2 of 110 tested lung, colon and breast tumors and tumor cell lines. No mutations were identified in 63 breast cancer tumors, in B-lymphoblastoid cell lines or normal tissues from these or other patients. In these cell lines, beta2m protein was undetectable by Western blot analysis and there was no MHC class I on their cell surface even after treatment with interferon-gamma. Transfection of these tumor cell lines with the beta2m gene, but not addition of purified beta2m protein restored MHC expression without addition of exogenous pepticles, indicating that endogenous beta2m expression is necessary for proper intracellular MHC assembly and stabilization by endogeneous pepticles. Mutation in beta2m caused cell line H2009 to be resistant to specific lysis by influenza virus-specific CTL from HLA matched donors, and transfection of the beta2m gene restored this killing. A small cell lung cancer cell line with low class I expression and with a normal beta2m genomic sequence nonetheless also demonstrated increased class I expression after transfection of the beta2m expression vector alone, indicating that the availability of beta2m may be rate limiting for MHC assembly in this line. Our results indicate that somatic mutations or selective loss of expression of the beta2m gene in human lung cancer is rare, but can cause defective MHC class I expression and function allowing these cells to escape recognition by cytotoxic T cells.

Immunologic dysfunction in cancer

The interactions between the tumor and its host are complex, and many aspects of the immune system appear to be adversely affected directly or indirectly by the presence of the tumor. Virtually all of the processes involved in immune induction and action have been implicated in the observed deficient response in tumor-bearing patients. Improved understanding and molecular analysis of the mechanisms underlying the escape of tumors from immune surveillance may lead to the development of novel strategies for the prevention of T-cell immunosuppression in cancer patients, the development of novel immunotherapeutic strategies, and potentially prevention of tumor progression or development.

Metastatic potential of human melanoma cells in nude mice--characterisation of phenotype, cytokine secretion and tumour-associated antigens

Incidence and mortality of human malignant melanoma has risen rapidly over recent decades. Although the notorious resistance to treatment is characteristic for metastatic malignant melanoma, only a few experimental models have been established to study the metastatic cascade or to test new alternative treatment modalities. Thus, new human models are wanted. Here, we describe the metastatic behaviour of seven human melanoma cell lines derived from two primary cutaneous melanomas (WM 98-1, WM 1341) and five metastases established from liver (UKRV-Mel-4), skin (M7, M13), pleural effusion (UKRV-Mel-2) and lymph node (MV3). All cell lines were analysed for their capacity to grow in nude mice after s.c. and i.v. administration. M13 cells developed liver metastases spontaneously after s.c. injection, and subsequent passages of M13 and M7 melanoma cells caused liver metastases after i.v. injection, whereas MV3 and WM98-1 gave rise to lung metastases, using the same inoculation route. In contrast, WM 1341, UKRV-Mel-2 and UKRV-Mel-4 grew only very slowly in nude mice after s.c. injection and did not cause any metastases after i.v. or s.c. administration. The pattern of metastases or growth kinetics did not correlate with the interleukin 8 or tumour necrosis factor secretion of cell lines. Adhesion molecules and growth factor receptor expression on the cell lines differed widely, as determined by flow cytometry, with the low metastatic cell lines (UKRV-Mel-2, UKRV-Mel-4 and WM 1341) demonstrating a marked reduction in VLA-1 and VLA-5 expression compared with the metastatic lines (M7, M13, MV3 and WM 98-1). Expression of pigment-related proteins such as tyrosinase, TRP-1, TRP-2, Melan-A/MART-1, gp100, MAGE1 or MAGE-3 was not associated with growth and metastatic characteristics of the melanoma cell lines analysed. In conclusion, the established human melanoma cell lines exhibited diverse growth behaviour in nude mice in congruence with some early established prognostic markers such as VLA-1 and VLA-5. The xenografts provide good models for further study of metastatic processes as well as for evaluation of alternative treatment modalities including new pharmaceutical drugs and gene therapeutic targeting using tissue-specific gene regulatory elements for gene targeting.