HLA class I antigen abnormalities and immune escape by malignant cells

Expression and prognostic significance of prothymosin-alpha and ERp57 in human gastric cancer

PURPOSE

Prothymosin-alpha and ERp57 were previously identified as markers for gastric metaplasia in a mouse model of Helicobacter-induced gastric metaplasia and neoplasia. In this paper we assess whether the expression of these putative biomarkers in humans is correlated with gastric metaplasia and adenocarcinoma and clinical outcomes.

METHODS

Eight tissue microarrays, containing 749 paraffin-embedded tissue cores from 164 gastric cancer patients, were stained for prothymosin-alpha and ERp57 by horseradish peroxidase immunohistochemical techniques. The proportion of stained cells per core was quantitated using the Ariol SL-50 automated image analysis system.

RESULTS

Prothymosin-alpha stained a significantly higher percentage of nuclei in cancer and metastases compared with normal gastric mucosa. ERp57 staining was significantly decreased in cancer and metastases compared with both normal gastric mucosa and metaplasias. ERp57 expression also correlated with greater depth of tumor invasion and advanced stage of disease. Kaplan-Meier survival analysis determined that tumors with the highest quartile of ERp57 expression were statistically associated with longer postoperative survival. A Cox proportional hazard analysis showed that maintenance of ERp57 expression was associated with longer postoperative survival.

CONCLUSIONS

These results suggest that although prothymosin-alpha is overexpressed in gastric adenocarcinoma, it is not associated with alterations in survival. In contrast, loss of ERp57 expression correlated with more aggressive disease and could provide useful prognostic information for gastric cancer patients.

Frequent Loss of HLA-A2 Expression in Metastasizing Ovarian Carcinomas Associated with Genomic Haplotype Loss and HLA-A2-Restricted HER-2/neu-Specific Immunity

Defective expression of HLA class I molecules is common in tumor cells and may allow escape from CTL-mediated immunity. We here investigate alterations in expression of HLA class I and their underlying molecular mechanisms in ovarian cancer patients. The HLA class I and HLA-A2 expression levels on noncultured tumor cells of 12 patients diagnosed with ovarian carcinoma were investigated by flow cytometry. Molecular analyses of antigen-processing machinery (APM) components were done in metastatic cancer cells, and the HLA genotype was determined in both these and the primary tumor. HER-2/neu-specific immunity was evaluated by enzyme-linked immunospot assays. The metastatic tumor cells from all patients expressed low levels of HLA class I surface antigens. In six of nine HLA-A2+ patients, HLA-A2 expression was heterogeneous with a subpopulation of tumor cells exhibiting decreased or absent HLA-A2 expression. One patient-derived tumor cell line completely lacked HLA-A2 but exhibited constitutive expression of APM components and high HLA class I expression that was further inducible by IFN-gamma treatment. Genotyping showed a haplotype loss in the metastatic tumor cells, whereas tumor tissue microdissected from the primary tumor exhibited an intact HLA gene complex. Interestingly, HLA-A2-restricted HER-2/neu-specific T-cell responses were evident among the lymphocytes of this patient. Abnormalities in HLA class I antigen expression are common features during the progression of ovarian cancer, and haplotype loss was, for the first time, described as an underlying mechanism.

Expression and antigenicity of survivin, an inhibitor of apoptosis family member, in bladder cancer: Implications for specific immunotherapy

OBJECTIVES

To assess the expression of survivin in transitional cell carcinoma of the bladder and to study whether survivin is a transitional cell carcinoma-specific antigen that could be a target for immunotherapy. Survivin, an inhibitor of apoptosis family member, has been reported to be expressed in various cancers but not in normal adult tissues.

METHODS

Immunohistochemical staining for survivin and human leukocyte antigen (HLA) class I was performed on specimens from 88 patients who underwent transurethral resection and radical cystectomy. To determine whether survivin was recognized as a tumor antigen by the host immune system, we assessed anti-survivin antibodies in the sera of 52 patients and 18 healthy volunteers with an enzyme-linked immunosorbent assay using recombinant survivin.

RESULTS

Survivin and HLA class I were expressed in 77 (87.5%) and 59 (67.0%) of the 88 bladder cancer specimens, respectively, and 56 (63.6%) expressed both survivin and HLA class I. The absorbance values of anti-survivin antibodies in patients with bladder cancer were significantly greater than those in the healthy volunteers. A relationship was found between the level of serum anti-survivin antibodies and the staining intensity of survivin in the specimen.

CONCLUSIONS

Survivin is expressed in carcinoma of the bladder with high sensitivity. It is suggested that survivin is presented on HLA class I molecules of antigen-presenting cells in 64% of patients with bladder cancer. Therapeutic targeting of survivin in bladder cancer is a future possibility.

Escape strategies and reasons for failure in the interaction between tumour cells and the immune system: how can we tilt the balance towards immune-mediated cancer control?

The last decade has witnessed an exponential increase in the attempts to demonstrate that adaptive immunity can effectively detect cancer cells and impair their growth in vivo in cancer patients. However, clinical trials of immunotherapy with a broad array of immunisation strategies have depicted a rather disappointing scenario, suggesting that successful control of tumour growth by immunotherapeutic treatments may not be an easy task to achieve. The attention of tumour immunologists has thus been switched to the potential reasons of failure, and extensive efforts are being made in defining the cellular and molecular pathways interfering with the capacity of the immune system to develop powerful immunological reactions against tumour cells. Although many of these pathways have been well characterised in murine models, little and controversial information about their role in determining neoplastic progression in cancer patients is available. This discrepancy at the moment represents one of the major limitations in understanding the obstacles to the in vivo development of protective T cell-mediated immune responses against tumours, and how pharmacological or biological interventions aimed at bypassing tumour escape mechanisms would indeed result in a clinical benefit. The study of the reasons for the failure of the immune system to control tumour growth, which have to be ascribed to highly interconnected phenomena occurring at both tumour and immune levels, could in the near future provide adequate tools to fight cancer by finely tuning the host environment through biological therapies.

Identification of melanoma-specific peptide epitopes by HLA-A2.1-restricted cytotoxic T lymphocytes

HLA-A2.1-associated peptides, extracted from human melanoma cells, were used to study epitopes for melanoma-specific HLA-A2.1-restricted cytotoxic T lymphocytes (CTLs) by epitope reconstitution, active peptide sequence characterization and synthetic peptide verification. CTL were generated from tumor-involved nodes by in vitro stimulation, initially with autologous melanoma cells and subsequently with allogeneic HLA-A2.1 positive melanoma cells. The CTLs could lyse autologous and allogeneic HLA-A2.1 positive melanomas, but not HLA-A2.1 negative melanomas or HLA-A2.1 positive non-melanomas. The lysis of melanomas could be inhibited by anti-CD3, anti-HLA class I and anti-HLA-A2.1 monoclonal antibodies. HLA-A2.1 molecules were purified from detergent-solubilized human melanoma cells by immunoaffinity column chromatography and further fractionated by reversed phase high performance liquid chromatography. The fractions were assessed for their ability to reconstitute melanoma-specific epitopes with HLA-A2.1 positive antigen-processing mutant T2 cells. Three reconstitution peaks were observed in lactate dehydrogenase release assay. Mass spectrometry and ion-exchange high performance liquid chromatography analysis were used to identify peptide epitopes. Peptides with a mass-to-charge ratio of 948 usually consist of nine amino acid residues. The data from reconstitution experiments confirmed that the synthetic peptides contained epitopes and that the peptides associated with HLA-A2.1 and recognized by melanoma-specific CTL were present in these different melanoma cells. These peptides could be potentially exploited in novel peptide-based antitumor vaccines in immunotherapy for CTL.

Culture of melanoma cells in 3-dimensional architectures results in impaired immunorecognition by cytotoxic T lymphocytes specific for Melan-A/MART-1 tumor-associated antigen

OBJECTIVE

To assess the effects of the culture of melanoma cells in 3-dimensional (3D) architectures on their immunorecognition by cytotoxic T lymphocytes (CTLs) specific for tumor-associated antigens.

SUMMARY BACKGROUND DATA

Growth in 3D architectures has been shown to promote the resistance of cancers to treatment with drugs, cytokines, or irradiation, thereby potentially playing an important role in tumor expansion. We investigated the effects of 3D culture on the recognition of melanoma cells by antigen-specific HLA class I-restricted CTLs.

METHODS

Culture of HBL melanoma cells expressing Melan-A/Mart-1 tumor-associated antigen and HLA-A0201 on poly-2-hydroxyethyl methacrylate (polyHEMA)-coated plates resulted in the generation of aggregates of 400- to 500-microm diameters containing on average 30,000 cells and characterized by slower proliferation, as compared with monolayer (2-dimensional) cultures. HLA-A0201 restricted Melan-A/Mart-127-35-specific CTL clones were used to evaluate tumor cell immunorecognition measured as specific IFN-gamma production. Comparative gene and protein expression in 2D and 3D cultures was studied by real-time PCR and flow cytometry, respectively. Overall differences in gene expression profiles between 2D and 3D cultures were evaluated by high-density oligonucleotide array hybridization.

RESULTS

HLA-A0201 restricted Melan-A/Mart-127-35 specific CTL clones produced high amounts of IFN-gamma upon short-term (4-24 hours) coincubation with HBL cells cultured in 2D but not in 3D, thus suggesting altered antigen recognition. Indeed, Melan-A/Mart-1 expression, at both gene and protein levels, was significantly decreased in 3D as compared with 2D cultures. Concomitantly, a parallel decrease of HLA class I molecule expression was also observed. Differential gene profiling studies on HBL cells showed an increased expression of genes encoding molecules involved in intercellular adhesion, such as junctional adhesion molecule 2 and cadherin-like 1 (>20- and 8-fold up-regulated, respectively) in 3D as compared with 2D cultures.

CONCLUSIONS

Taken together, our data suggest that mere growth of melanoma cells in 3D architectures, in the absence of immunoselective pressure, may result in defective recognition by tumor-associated antigen-specific CTL.

Molecular mechanisms of HLA class I antigen abnormalities following viral infection and transformation

In humans as in other animal species, CD8+ cytotoxic T lymphocytes (CTLs) play an important if not the major role in controlling virus-infected and malignant cell growth. The interactions between CD8+ T cells and target cells are mediated by human leukocyte antigen (HLA) class I antigens loaded with viral and tumor antigen-derived peptides along with costimulatory receptor/ligand stimuli. Thus, to escape from CD8+ T-cell recognition and destruction, viruses and tumor cells have developed strategies to inhibit the expression and/or function of HLA class I antigens. In contrast, cells with downregulated MHC class I surface expression can be recognized by NK cells, although NK cell-mediated lysis could be abrogated by the expression of inhibiting NK cell receptors. This review discusses the molecular mechanisms utilized by viruses to inhibit the formation, transport and/or expression of HLA class I antigen/peptide complexes on the cell surface. The knowledge about viral interference with MHC class I antigen presentation is not only crucial to understand the pathogenesis of viral diseases, but contributes also to the design of novel strategies to counteract the escape mechanisms utilized by viruses. These investigations may eventually lead to the development of effective immunotherapies to control viral infections and virus-associated malignant diseases.

Mechanisms of tumor evasion

The results from in vitro immunological experiments, murine tumor models and patients with cancer clearly demonstrate that tumors have multiple mechanisms to evade the immune response. During the early stages of tumor development malignant cells can be poor stimulators, present poor targets or become resistant to the innate immune response, while at later stages, progressively growing tumors impair the adaptive immune response by blocking the maturation and function of antigen presenting cells and causing alterations in T cell signal transduction and function. Preliminary results also suggest a correlation between some of these changes and an increased metastatic potential of the tumor cells, a diminished response to immunotherapy, and poor prognosis. Carefully coordinated basic research studies and clinical immunotherapy trials will be required to fully determine the impact on the outcome of the disease and the response to treatment. However, understanding the mechanisms used by tumor cells to evade the immune system could result in new therapeutic approaches for preventing and/or reversing these immune alterations and have the potential of improving the current results of immunotherapy trials.

Mechanisms of immune evasion of human neuroblastoma

Neuroblastoma (NB) is a common neuroectodermal tumor of childhood with low response to conventional therapy in patients with advanced stage disease. Among novel strategies, immumotherapy has attracted much interest. However, scanty information is available about the immunogenicity of human NB. Here, we review our data showing that human NB may evade the control mediated by T cytotoxic lymphocytes and natural killer (NK) cells through multiple mechanisms: (i) downregulation of HLA class I molecules and antigen processing machinery components (ii) downregulation of activating ligands for the activating immunoreceptor NKG2D expressed by cytotoxic T lymphocytes and NK cells. Additional mechanisms of immune evasion used by human NB cells are discussed.

Epigenetic Modulation of Solid Tumors as a Novel Approach for Cancer Immunotherapy

Emerging evidence demonstrates that epigenetic events associated with tumor development and progression may impair immunogenicity and immune recognition of cancer cells, possibly favoring their escape also from vaccination-induced antitumor immune responses. In fact, DNA hypermethylation and/or histone deacetylation plays a critical role in the downregulation and/or silencing of several genes involved in the recognition of neoplastic cells by the immune system, including human leukocyte antigens (HLAs), tumor-associated antigens, and accessory/costimulatory molecules. However, as opposed to genetic alterations, epigenetic events can be successfully handled through pharmacologic agents that induce DNA hypomethylation or inhibit histone deacetylation, resulting in a functionally "more efficient" immune profile of cancer cells. In light of the encouraging immunomodulatory results obtained with these "epigenetic drugs," they certainly will be used for the development of combined chemo-immunotherapeutic strategies for the treatment of patients with solid malignancies of different histology.

Immunoselective pressure and human leukocyte antigen class I antigen machinery defects in microsatellite unstable colorectal cancers

In colorectal cancer, the immune response is particularly pronounced against tumors displaying the high microsatellite instability (MSI-H) phenotype. MSI-H tumors accumulate mutations affecting microsatellites located within protein encoding regions (coding microsatellites, cMS), which lead to translational shifts of the respective reading frames. Consequently, novel tumor-specific frameshift-derived neopeptides (FSP) are generated and presented by MSI-H tumor cells, thus eliciting effective cytotoxic immune responses. To analyze whether the immunoselective pressure was reflected by the phenotype of MSI-H colorectal cancer cells, we compared here the expression of antigen processing machinery (APM) components and human leukocyte antigen (HLA) class I antigen subunits in 20 MSI-H and 20 microsatellite-stable (MSS) colorectal cancer using a panel of newly developed APM component-specific monoclonal antibodies. In addition, we did a systematic analysis of mutations at cMS located within APM genes and beta2-microglobulin (beta2m). Total HLA class I antigen loss was observed in 12 (60.0%) of the 20 MSI-H lesions compared with only 6 (30.0%) of the 20 MSS colorectal cancer lesions. Moreover, total loss of membraneous HLA-A staining was significantly more frequent in MSI-H colorectal cancer (P = 0.0024). Mutations at cMS of beta2m and genes encoding APM components (TAP1 and TAP2) were detected in at least 7 (35.0%) of 20 MSI-H colorectal cancers but in none of the MSS colorectal cancers (P = 0.0002). These data show that defects of HLA class I antigen processing and presentation seem to be significantly more frequent in MSI-H than in MSS colorectal cancer, suggesting that in MSI-H colorectal cancer the immunoselective pressure leads to the outgrowth of cells with defects of antigen presentation.

Multiple defects of the antigen-processing machinery components in human neuroblastoma: immunotherapeutic implications

Low expression of human leukocyte antigen (HLA) class I in human tumors may be related to defects of the antigen-processing machinery (APM) components. Neuroblastoma cells are virtually HLA class I negative, but (i) the underlying mechanisms are unknown, and (ii) expression of the APM components has never been investigated. Here we have used a panel of novel monoclonal antibodies to proteasomal and immunoproteasomal components, chaperons and transporter associated with antigen processing (TAP) to characterize 24 stroma-poor neuroblastoma tumors and six neuroblastoma cell lines. Primary tumors showed defects in the expression of zeta, tapasin, TAP1 or TAP2, HLA class I heavy chain and beta2 microglobulin, LMP2 and LMP7, as compared to normal adrenal medulla. Neuroblastoma cell lines displayed roughly similar patterns of APM expression in comparison to primary tumors. Incubation of neuroblastoma cell lines with interferon-gamma caused upregulation of HLA class I molecules and reduced lysis by killer inhibitory receptor HLA ligand-matched NK cells. Defects in APM components explain reduced peptide loading on HLA class I molecules, their instability and failure to be expressed on the cell surface. HLA class I upregulation by interferon-gamma, although enhancing neuroblastoma cell recognition by cytotoxic T cells, dampens their susceptibility to NK cells.

Detection of Spontaneous CD4+ T-Cell Responses in Melanoma Patients against a Tyrosinase-Related Protein-2–Derived Epitope Identified in HLA-DRB1*0301 Transgenic Mice

PURPOSE

The frequently expressed differentiation antigen tyrosinase-related protein-2 (TRP-2) has repeatedly been described as a target of spontaneous cytotoxic T-cell responses in melanoma patients, suggesting that it might be an ideal candidate antigen for T cell-based immunotherapy. As a prerequisite for immunization, T-cell epitopes have to be identified. Whereas a number of HLA class I-presented TRP-2-derived epitopes are known, information about HLA class II-presented antigenic ligands recognized by CD4+ T helper (Th) cells is limited.

EXPERIMENTAL DESIGN

The search for TRP-2-derived Th epitopes was carried out by competitive in vitro peptide binding studies with predicted HLA-DRB1*0301 ligands in combination with peptide and protein immunizations of HLA-DRB1*0301 transgenic mice. In vivo selected candidate epitopes were subsequently verified for their immunogenicity in human T-cell cultures.

RESULTS

This strategy led to the characterization of TRP-2(60-74) as an HLA-DRB1*0301-restricted Th epitope. Importantly, TRP-2(60-74)-reactive human CD4+ Th cell lines, specifically recognizing target cells loaded with recombinant TRP-2 protein, could be established by repeated peptide stimulation of peripheral blood lymphocytes from several HLA-DRB1*03+ melanoma patients. Even short-term peptide stimulation of patients' peripheral blood lymphocytes showed the presence of TRP-2(60-74)-reactive T cells, suggesting that these T cells were already activated in vivo.

CONCLUSION

Peptide TRP-2(60-74) might be a useful tool for the improvement of immunotherapy and immune monitoring of melanoma patients.

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.

Analysis of human lymphocyte antigen class I expression in gastric cancer by reverse transcriptase-polymerase chain reaction

Malignant cells have been reported to escape immune surveillance by modulation of human lymphocyte antigen (HLA) class Ia molecule and/or other accessory molecules like TAP (transporter associated with antigen processing) and beta2-M expression. Most of these reports, however, are based on immunohistochemistry techniques with polymorphic- or isotype-specific antibodies. In the present study, we have instead used a locus-specific reverse transcriptase-polymerase chain reaction-based approach to detect the transcriptional expression of HLA class Ia as well as accessory molecules in gastric cancer. Our results indicate that HLA class Ia transcript is totally absent in only approximately 9% of cancer cases. Locus-specific expression of HLA-A and -B could, however, be detected in approximately 54% cases, whereas HLA-C was expressed in most of the cancer tissues. Interestingly, in some cases where HLA class Ia expression was observed, TAP1 expression could not be detected. Furthermore, we also investigated the frequency of nonclassical or HLA class Ib expression for molecules such as HLA-E and -G. HLA-G transcript was absent in gastric tissues both in cancerous and autologous normal region, whereas HLA-E was observed in a number of gastric cancers. Altogether these selective locus-specific losses of HLA class I along with impaired expression of accessory molecules may explain the complex phenomena by which gastric tumors escape both cytotoxic T-lymphocyte- as well as natural killer cell-mediated immune defense.

Involvement of the chaperone tapasin in HLA-B44 allelic losses in colorectal tumors

Tumors can exhibit selective allelic losses of HLA class I antigens as part of altered HLA phenotypes. In colorectal tumors, the HLA class I allele most frequently lost is HLA-B44, although the precise mechanism responsible for this loss has not been described to date. From a total of 95 colorectal cryopreserved tumor samples, we selected (by immunohistochemical staining) 13 tumors with HLA-B44-negative expression. Loss of heterozygosity at 6p21.3 was demonstrated to be the cause of the negative expression in 4 cases. In the remaining 9 cases, structural analyses of microdissected tissue samples of the 3 subtypes of HLA-B44 loss in these tumors (B*4402, B*4403 and B*4405) did not reveal any mutations. However, all 3 subtypes of HLA-B44 presented in this study shared a common characteristic: the presence of an aspartic amino acid residue at position 114 in the HLA class I heavy chain. This residue has been described as determining tapasin dependence for the surface expression of these alleles and therefore for antigen presentation. We studied tapasin transcription by RT-PCR in these tumors and found tapasin downregulation in all 9 tumors samples with the HLA-B44-negative phenotype. In contrast, tapasin was normally transcribed in HLA-B44-positive colorectal tumors samples, as well as in 3 HLA-B44-negative laryngeal carcinomas and 1 bladder tumor. Defective tapasin transcription seems to be an alteration responsible for the absence of HLA-B44 expression in colorectal tumors, thus contributing to the generation of tumor immune escape phenotypes.

Real-time RT-PCR detection of CK19, CK7 and MUC1 mRNA for diagnosis of lymph node micrometastases in non small cell lung carcinoma

Metastatic lymph nodes (LNs) are the major prognostic factor in resected non small cell lung carcinoma (NSCLC). However, almost 50% of pN0 patients relapse, suggesting metastatic cells undetected by current staging procedures. A combination of markers [cytokeratins 19 and 7 (CK19, CK7) and mucin type 1 (MUC1) mRNAs] was therefore evaluated by real-time RT-PCR in order to detect occult cancer cells. Forty-three NSCLC tumor samples, 4 micrometastatic, 6 metastatic and 84 histologically negative mediastinal LNs from 19 patients with NSCLC were evaluated as well as blood mononuclear cells from 29 healthy volunteers and 17 benign LNs. When tested on cell lines, RT-PCR was particularly efficient for evaluation of CK19, CK7 and MUC1 mRNA expression. All tumor samples were positive for at least 1 marker and 74% of samples were positive for all 3 markers. CK7 and CK19 mRNA were not detected in benign LN and blood cells from healthy donors in contrast with MUC1 mRNA. Only CK7 and CK19 mRNA were therefore used for evaluation of mediastinal LNs: the 6 histologically metastatic and the 4 micrometastatic LNs were positive for at least one marker. Among the 84 histologically negative LNs, 6 (7%) were positive for at least one marker, potentially changing the stage of 2 out of 19 patients. In conclusion, in our feasibility study, parallel molecular detection of CK19 and CK7 mRNA can be considered a specific diagnostic tool for the assessment of microscopic lymphatic spread. Its prognostic impact remains to be evaluated in a prospective study.

Reciprocal changes in tumor antigenicity and antigen-specific T cell function during tumor progression

Two seemingly incompatible models exist to explain the progression of cancers in immunocompetent hosts. The cancer immunosurveillance hypothesis posits that recognition of transformed cells by the immune system results in the generation of an effector response that may impede tumor growth. Clinically detectable cancer results from the emergence of tumor variants that escape this selective pressure. Alternatively, induction of immune tolerance to tumor antigens may enable cancer progression. We established a model where changes in the function of tumor-specific T cells and in tumor antigen expression could be followed during cancer progression. Early recognition of antigen led to activation, expansion, and effector function in tumor-specific CD4⁺ T cells resulting in the outgrowth of tumors expressing substantially reduced levels of antigen. Antigen loss was not complete, however, and levels remained above the threshold required for tumor-specific T cell recognition in vivo. In the face of persisting antigen, T cell tolerance ensued, leading to an impaired ability to mediate further antigen loss. Together, these studies establish that the processes of immunosurveillance and tumor editing coexist with a process in which the functional tumor-specific T cell repertoire is also “edited,” reconciling two hypotheses historically central to our attempts to understand host antitumor immunity.

Targeting the immune system: novel therapeutic approaches in squamous cell carcinoma of the head and neck

Despite advances in surgery, radiotherapy, and chemotherapy, the overall survival rates for patients with squamous cell carcinoma of the head and neck (SCCHN) have not changed over the last decades. Clearly, novel therapeutic strategies are needed for this cancer, which is highly immunosuppressive. Therefore, biologic therapies able to induce and/or up-regulate antitumor immune responses could represent a complementary approach to conventional treatments. Because patients with SCCHN are frequently immunocompromised due to the elimination or dysfunction of critical effector cells of the immune system, it might be necessary to restore these immune functions to allow for the generation of more effective antitumor host responses. Simultaneously, to prevent tumor escape, it might be necessary to alter attributes of the malignant cells. The present review summarizes recent advances in the field of immunotherapy of SCCHN, including techniques of nonspecific immune stimulation, the use of monoclonal antibodies, advances in adoptive immunotherapy and genetic engineering, as well as anticancer vaccines. These biologic therapies, alone or in combination with conventional treatment, are likely to develop into useful future treatment options for patients with SCCHN.

Immunological Prevention of a Multigene Cancer Syndrome

Vaccines effectively prevent the onset of tumors in transgenic mice carrying activated oncogenes; however, human tumors are caused by combined alterations in oncogenes and oncosuppressor genes. We evaluated the impact of prophylactic vaccines in HER-2/neu transgenic, p53 wild-type/null mice that succumb to an aggressive cancer syndrome comprising mammary and salivary gland carcinomas and rhabdomyosarcoma. A vaccine made of allogeneic mammary carcinoma cells expressing HER-2/neu and interleukin 12 afforded long-term protection from tumor onset. Tumor prevention was mediated by T cell-derived cytokines, in particular gamma-interferon, and by anti-HER-2/neu antibodies. HER-2/neu expression was inhibited in target tissues of vaccinated mice, and somatic loss of the wild-type p53 allele did not occur. A highly effective vaccine against a single oncoprotein induced a powerful immune response that arrested multistep carcinogenesis in distinct target tissues.

Autocrine secretion of Fas ligand shields tumor cells from Fas-mediated killing by cytotoxic lymphocytes

Mechanisms responsible for resistance of tumors to death receptor-mediated damage by cytotoxic lymphocytes are not well understood. Uveal melanoma cells expressed Fas but were insensitive to Fas triggering induced by bystander cytotoxic T lymphocytes or a Fas-specific agonistic antibody; this could not be ascribed to tumor counterattack against T cells or general resistance of the tumors to apoptosis. Treatment with inhibitors of metalloproteases rendered uveal melanomas sensitive to Fas-mediated cytotoxicity. Metalloprotease inhibitors did not affect the expression of Fas but increased the surface expression of Fas ligand (FasL), which correlated with the disappearance of soluble FasL from culture supernatants of tumor cells. FasL eluted from the surface of uveal melanomas specifically inhibited cytotoxic T lymphocyte lysis of tumor cells pretreated with an inhibitor of metalloproteases. In addition to uveal melanomas, a number of other tumor cell lines of various cellular origins were sensitized to Fas-mediated cytotoxicity by metalloprotease inhibitors. Our results show that autocrine secretion of FasL shields tumor cells from Fas-mediated killing by cytotoxic lymphocytes. This defines a novel mechanism of tumor escape from immune surveillance.

Mechanisms of tumor evasion from the immune response

The results from in vitro immunological experiments, murine tumor models and patients with cancer clearly demonstrate that tumors have multiple mechanisms to evade the immune response. During the early stages of tumor development malignant cells can be poor stimulators, present poor targets or become resistant to the innate immune response, while at later stages, progressively growing tumors impair the adaptive immune response by blocking the maturation and function of APCs and causing alterations in T-cell signal transduction and function. Preliminary results also suggest a correlation between some of these changes and an increased metastatic potential of the tumor cells, a diminished response to immunotherapy, and poor prognosis. Carefully coordinated basic research studies and clinical immunotherapy trials will be required to fully determine the impact of these mechanisms of tumor evasion on the outcome of the disease and the response to treatment. However, understanding the mechanisms used by tumor cells to evade the immune system could result in new therapeutic approaches for preventing and/or reversing these immune alterations and could have the potential of improving the current results of immunotherapy trials.

The beta 2-microglobulin locus of rainbow trout (Oncorhynchus mykiss) contains three polymorphic genes

Beta2-microglobulin (beta2m) associates with MHC and related class I H chains to form cell surface glycoproteins that mediate a variety of functions in defense. In humans, monomorphism of a single beta2m gene contrasts with the diversity and polymorphism of the class I H chain genes, and a similar picture was seen in almost all other species examined. In this regard, rainbow trout (Oncorhynchus mykiss) appeared unusual: trout beta2m genes gave a complicated and polymorphic pattern in Southern blots, and a minimum of 10 different mRNA encoding two distinct types of beta2m were expressed by a single fish. Characterization of genomic clones from the same fish now shows that the rainbow trout beta2m locus consists of two expressed genes and one partial gene that are closely linked. Four copies of the locus were identified and allelic variants of each gene defined, largely through comparison of the noncoding regions. A dramatic variation in the lengths of introns is caused by variable repetitive elements and accounts for the complex pattern seen in Southern blots. By comparison to noncoding sequences, the coding regions are conserved but the three loci differ within a cluster of codons that encode residues of beta2m that do not interact with class I H chains. Additional diversity in the trout beta2m genes appears to be due to somatic mutation that might be facilitated by the abundance of repetitive DNA elements within the 12 beta2m genes of an individual rainbow trout.

Stable expression of chimeric anti-CD3 receptors on mammalian cells for stimulation of antitumor immunity

Expression of CD80 or CD86 costimulatory molecules on tumor cells can produce rejection of immunogenic but not poorly immunogenic tumors. We have previously shown that anti-CD3 single-chain antibodies expressed on the surface of cells can directly activate T cells. We therefore investigated whether anti-CD3 "receptors" could enhance CD86-mediated rejection of poorly immunogenic tumors. Expression of anti-CD3 receptors on cells was increased by introduction of membrane-proximal "spacer" domains containing glycosylation sites between the single-chain antibody and the transmembrane domain of the chimeric receptors. Removal of glycosylation sites in the spacer reduced surface expression due to increased shedding of chimeric receptors from the cell surface. Induction of T-cell proliferation by anti-CD3 receptors did not correlate with the expression level of chimeric protein, but rather depended on the physical properties of the spacer. Anti-CD3 receptors effectively induced T-cell cytotoxicity, whereas coexpression with CD80 or CD86 was required for generating T-cell proliferation and IL-2 secretion. Although expression of CD86 did not significantly delay the growth of poorly immunogenic B16-F1 tumors, expression of anti-CD3 receptors with CD86 produced complete tumor rejections in 50% of mice and induced significant protection against wild-type B16-F1 tumor cells. Our results show that spacer domains can dramatically influence the surface expression and the biological activity of chimeric antibody receptors. The strong antitumor activity produced by anti-CD3 receptors and CD86 on tumor cells indicates that this strategy may be beneficial for the gene-mediated therapy of poorly immunogenic tumors.

Low frequency of HLA haplotype loss associated with loss of heterozygocity in chromosome region 6p21 in clear renal cell carcinomas

HLA class I loss or downregulation is a widespread mechanism used by tumor cells to avoid tumor recognition by cytotoxic T lymphocytes favoring tumor immune escape. Multiple molecular mechanisms are responsible for these altered HLA class I tumor phenotypes. It has been described in different epithelial tumors that loss of heterozygosity (LOH) at chromosome region 6p21.3 is a frequent mechanism that leads to HLA haplotype loss, ranging between 40 and 50%, depending on the tumor entity analyzed. Here we have tested the frequency of LOH at 6p21 chromosome region in Renal Cell Carcinomas (RCC) of the clear cell and chromophobe subtype. A low frequency of HLA haplotype loss (6.6%) was found in clear cell RCC. These data significantly differ from those reported in other epithelial tumors. In contrast, in RCC of chromophobe subtype this frequency was 10 times higher (3 out of 5 cases analyzed). These results indicate that LOH at 6p21.3 is not a frequent mechanism that leads to HLA class I abnormalities in clear cell RCC. In addition, the chromophobe RCC subtypes differ not only in histopathological criteria but also in the frequency of LOH-mediating HLA class I alterations. These results might help to understand the significantly different biological behavior of both RCC subtypes.

Surgical removal of primary tumor reverses tumor-induced immunosuppression despite the presence of metastatic disease

Immunotherapy is a promising approach for the management of malignancies. It may be particularly useful for tumors that do not respond to conventional therapies, such as many metastatic cancers. The efficacy of immunotherapy will depend on many factors, one of which is the immunocompetence of the host. Patients with large primary tumors frequently are immunosuppressed, making them poor candidates for immunotherapy. Although a few studies have reported that surgical removal of primary tumor reverses immunosuppression, it is not known whether metastatic disease in postsurgery patients inhibits this recovery. To determine the role of metastatic disease, we examined tumor-free mice versus mice with primary tumor and metastatic disease versus mice whose primary tumors were removed surgically but who had metastatic disease. We have used the mouse 4T1 mammary carcinoma, a BALB/c-derived transplantable tumor that shares many characteristics with human breast cancer and is an established model for spontaneous, metastatic cancer. Cell-mediated and humoral adaptive immunity, as measured by rejection of allogeneic tumor, antigen-specific T-cell proliferation, and antigen-specific antibody responses, was suppressed in 4T1-bearing nonsurgery mice relative to tumor-free mice. Surgical removal of primary tumor resulted in rebounding of antibody and cell-mediated responses, even in mice with metastatic disease. Macrophage activity, as measured by lipopolysaccharide responsiveness, and dendritic cell function, as measured by nominal and alloantigen presentation, were not suppressed in tumor-bearing mice. Therefore, the presence of primary tumor suppresses T-cell and antibody responses; however, surgical removal of primary tumor restores immunocompetence even when disseminated metastatic disease is present.

Identification of a shared epitope recognized by melanoma-specific, HLA-A3-restricted cytotoxic T lymphocytes

We previously established a melanoma-reactive cytotoxic T lymphocyte (CTL) line that recognizes multiple epitopes in the context of HLA-A3. To increase the number of peptides available for use in a vaccine for the treatment of melanoma, we identified one of these epitopes, SQNFPGSQK, through a combination of epitope reconstitution experiments and mass spectrometry. The SQNFPGSQK peptide was also found to be associated with HLA-A3 on an additional melanoma tumor line, thus indicating that the peptide is not unique to the melanoma tumor line from which it was isolated and thus, unlikely to arise through a mutational event. Although the protein origin of SQNFPGSQK has yet to be established, the shared nature of this epitope and the fact that it elicits a natural immune response indicates that it warrants further study to determine its usefulness as a vaccine component for the treatment of melanoma. The peptide may also be useful as a research tool for evaluating spontaneous anti-tumor immune responses in patients with melanoma.

MHC class I antigen processing pathway defects, ras mutations and disease stage in colorectal carcinoma

Colorectal tumorigenesis has been associated with the progressive acquisition of a variety of genetic alterations. These include mutations of the Ki-ras proto-oncogene in codons 12 and 13, which account for 85% of genetic changes in colorectal cancer. In murine in vitro models of oncogenic transformation, an association between ras-mediated transformation and downregulation of different components of the MHC class I antigen processing machinery (APM) has been described. In order to investigate whether this association also exists in human tumors, 10 cases of high-grade intraepithelial neoplasia (HIN), as well as primary tumors and autologous lymph node metastases from 42 patients with colorectal carcinoma, were monitored by allele-specific restriction analysis for Ki-ras mutations. In parallel, APM component expression and tumor cell proliferation were analyzed by immunohistochemistry. In comparison to autologous colorectal mucosa, TAP1, LMP2 and tapasin loss was found in 68%, 67% and 80% of HIN, respectively. In contrast, impaired TAP1, LMP2 and tapasin expression was found in 42%, 42% and 63% of primary adenocarcinomas of stage III disease and in 63%, 47% and 79% of the matched lymph node metastases, respectively. More than 60% of colorectal tumor lesions with TAP1, LMP2 and/or tapasin defects displayed Ki-ras mutations. The frequency of TAP1, LMP2 and tapasin loss varied between 33% of primary adenocarcinomas, 40% of HIN to approximately 67% of metastases. These data suggest that i) APM component deficiencies occur more frequently in Ki-ras-mutated colorectal carcinoma lesions and ii) APM abnormalities in conjunction with Ki-ras mutations appear to be associated with disease stage. These findings support the hypothesis that Ki-ras mutations may contribute to immune escape mechanisms of tumors by downregulating the MHC class I APM component expression.

Identification of Novel and Widely Expressed Cancer/Testis Gene Isoforms That Elicit Spontaneous Cytotoxic T-Lymphocyte Reactivity to Melanoma

Multiple isoforms (TAG-1, TAG-2a, TAG-2b, and TAG-2c) of a novel cancer/testis antigen gene have been identified and are expressed in 84-88% of melanoma cell lines tested. The tumor antigen (TAG) genes are also expressed in K562, a myelogenous leukemia cell line, and they have homology to two chronic myelogenous leukemia-derived clones and a hepatocellular carcinoma clone in the human expressed sequence tags (EST) database, thus indicating that their expression is not restricted to melanomas. In contrast to the fact that many cancer/testis antigens are poorly immunogenic, the TAG-derived peptide, RLSNRLLLR, is recognized by HLA-A3-restricted, melanoma-specific CTLs that were obtained from a melanoma patient with spontaneous reactivity to the peptide. Unlike most cancer/testis antigen genes which are located on the X chromosome, the TAG genes are located on chromosome 5. The genes have the additional unusual features of being coded for in an open reading frame that is initiated by one of three nonstandard initiation codons, and the sequence coding the RLSNRLLLR peptide crosses an exon-exon boundary. The properties of the TAG antigens indicate that they are excellent vaccine candidates for the treatment of melanoma and perhaps other cancers.

Down-Regulation of HLA Class I Antigen Processing Molecules: An Immune Escape Mechanism of Renal Cell Carcinoma?

PURPOSE

Proper HLA class I antigen processing and presentation is a prerequisite for the recognition of tumor cells by cytotoxic T lymphocytes. To date there exist only limited information on the expression of components of the HLA class I associated antigen processing machinery (APM) in surgically removed benign renal cell adenoma, and primary and metastatic renal cell carcinoma (RCC).

MATERIALS AND METHODS

A total of 133 primary RCCs of different subtypes, 10 renal cell adenoma biopsies, 32 matched metastases of different localization and autologous normal kidney epithelium were immunohistochemically analyzed for the expression of HLA class I antigens, low molecular weight protein (LMP)2 and LMP7, the transporter associated with antigen processing subunit (TAP1) and beta 2-microglobulin (beta 2-m).

RESULTS

Normal kidney tissue showed strong cytoplasmic staining intensity for LMP2, LMP7 and TAP1, whereas beta 2-m and HLA class I heavy chains were detected on the cell surface. A low frequency of HLA class I HC and beta 2-m down-regulation was found in RCC. In contrast, primary RCC and metastases showed a high frequency of a total lack of heterogeneous TAP1, LMP2 and LMP7 expression, which was often coordinately regulated. APM component deficiencies were associated with RCC subtypes but not with tumor grading and staging.

CONCLUSIONS

HLA class I APM component abnormalities appear to represent an immune escape mechanism of RCC. This finding emphasizes the need to evaluate the integrity and expression of these molecules in patients with RCC, especially in those selected for treatment with T-cell based immunotherapy.

HLA-DRB alleles are differentially expressed by tumor cells in breast carcinoma

The biologic and prognostic significance of HLA-DR expression and T-cell infiltration in breast carcinoma are presently controversial. To test the hypothesis that these factors are influenced by particular HLA-DRB alleles, 52 breast tumor samples, composed of 26 DRB1*04 and 26 non-DRB1*04 tumors, were assessed using immunohistochemistry for expression of DR and its associated invariant chain (Ii) and for infiltrating CD3+ T cells. While DR expression by tumor cells was significantly associated with T-cell infiltration, DRB1*04 tumors were more frequently DR+ Ii+ and contained smaller CD3+ infiltrates than non-DRB1*04 tumors. This difference was largely attributable to DRB1*07 tumors, which were typically DR- Ii-, although they contained similar numbers of T cells to DR+ Ii+ tumors. Further analysis of DR+ tumors using allotype discriminating antibodies revealed that DRB1*04 alleles were always expressed, while non-DRB1*04 alleles were inconsistently expressed. The results of this study provide the first reported evidence that DRB alleles influence DR expression and T-cell infiltration in breast carcinoma and suggest that multiple factors contribute to DR expression. Ongoing studies aimed at elucidating the molecular and immunologic mechanisms controlling differential DR expression and implications for prognosis and outcome should further our understanding of the antitumor immune response and evasion strategies employed by tumor cells.

DNA methylation and expression of major histocompatibility complex class I and class II transactivator genes in human developmental tumor cells and in T cell malignancies

Major histocompatibility complex (MHC) class I and class II molecules play essential roles in the immune response by virtue of their ability to present peptides to T lymphocytes. Given their central role in adaptive immunity, the genes encoding these peptide-presenting molecules are regulated in a tight fashion to meet with local requirements for an adequate immune response. In contrast to MHC class I gene products, which are expressed on almost all nucleated cells, constitutive expression of MHC class II molecules is found in specialized antigen presenting cells of the immune system only. Transcription of both MHC class I and class II genes can be induced by immune regulators and upon cell activation. Transcription of MHC class I genes is mediated by a set of conserved cis acting regulatory elements in their promoters. Of these regulatory elements, MHC class II promoters share the SXY-module. Essential for activation of MHC class II promoters is the class II transactivator (CIITA), which acts through protein/protein interactions with regulatory factors bound to the SXY module. In this review, we discuss the role of DNA methylation in relation to altered expression of MHC class I and CIITA genes as observed in malignancies and in development.

Epigenetic targets for immune intervention in human malignancies

Emerging evidences suggest that epigenetic events associated with tumor development and progression, such as deregulated methylation of CpG dinucleotides and aberrant histone acetylation, may impair the immunogenic potential of cancer cells. In fact, DNA hypermethylation and/or histone deacetylation contribute to the absent or downregulated expression of different components of the 'tumor recognition complex' (i.e., HLA class I antigens, cancer/testis antigens and accessory/costimulatory molecules) in solid and hemopoietic human malignancies. However, pharmacologic agents that induce DNA hypomethylation or inhibit histone deacetylation can modify these epigenetic phenomena, restoring the defective expression of selected components of the 'tumor recognition complex' in cancer cells. These antigenic modifications positively modulate the immunogenicity and the immune recognition of cancer cells, making epigenetic drugs attractive agents to design new combined chemoimmunotherapeutic strategies for the treatment of cancer patients.

Altered expression of nonclassical HLA class Ib antigens in human renal cell carcinoma and its association with impaired immune response

An optimal antitumoral immune response requires the activation of both CD8(+) and CD4(+) T lymphocytes by the peptide antigen presentation via the human leukocyte antigen (HLA) class I and class II molecules, respectively. Downregulation or loss of HLA molecules has been found in human renal cell carcinoma (RCC) and provides a strategy of these tumors to evade T-cell mediated immunosurveillance. In addition, a tumor-specific upregulation of HLA-G has been recently described in RCC, which also leads to an impaired immune response. We here summarize the frequency of the constitutive and/or interferon-gamma (IFN-gamma) inducible expression of nonclassical HLA class Ib antigens in RCC cell lines, surgically removed RCC lesions and normal kidney epithelium, the molecular characteristics of HLA-G expression, and its role in immune recognition.

HLA-G and IL-10 expression in human cancer—different stories with the same message

Immune evasion in cancer may result from structural and functional alterations of human leukocyte antigen (HLA) class I molecules and/or local release of immunosuppressive cytokines, such as interleukin (IL)-10. In lung cancer, both of these mechanisms seem to often take place, resulting in the impaired tumor recognition and the progression of the disease. In primary cutaneous lymphomas on the other side, the shift towards immunosuppressive T helper (Th)2 cytokine profile and the secretion of IL-10 appears to occur more frequently than the loss of HLA class I molecules. In addition to down-regulation of HLA class I expression, IL-IO appears to be one of the factors responsible for the up-regulation of HLA-G, another molecule involved in the immunescape. It is possible that the expression of HLA-G itself may account for induction of Th2-skewing state and the production of IL-10, thence establishing a vicious circle of immune abrogation in cancer. This article reviews the current literature on this topic and provides new insights into the role of HLA-G and IL-10 in cancer.

HLA-G in cancer: a way to turn off the immune system

The expression of HLA-G in cancer represents a strategy employed by tumors to avoid immune destruction. Indeed, this non-classical HLA class I molecule suppresses various immune cell functions through binding to inhibitory receptors. We here review the studies done by our group that described for the first time (i) HLA-G expression in malignancies such as melanomas, renal and breast carcinomas. (ii) the up-regulation of HLA-G gene transcription by tumor environmental factors such as cytokines and stress and by agents used in chemotherapy such as demethylating molecules, and (iii) the biological relevance of such HLA-G expression in the evasion of malignant cells from antitumor immune response.

Cloning and functional analyses of the mouse tapasin promoter

The expression of tapasin is critical for an optimized MHC class I assembly and stable MHC class I surface expression. Thus, impaired MHC class I antigen expression of tumors can be attributable to tapasin downregulation. In order to understand the molecular mechanisms of deficient tapasin expression, the mouse tapasin promoter region and its 5'-flanking sequences were characterized. The mouse tapasin promoter lacks the TATA box and its transcription is initiated at multiple sites within a 51-nucleotide stretch. Sequence analyses revealed transcription factor binding motifs for NF-kappaB, GATA, E2F, p300, AP1, SP1 and IRF-1/2. Detailed analysis of deletion mutants and elimination of transcription factor binding motifs demonstrated an important role of NF-kappaB at position -468 for its basal activity, whereas E2F at position -229 represses constitutive promoter activity. Furthermore, the IRF-1/2 binding site is required for gamma interferon inducibility of the tapasin promoter in vitro, but also negatively interferes with its constitutive activity. Thus, characterization of the tapasin promoter represents the molecular basis for the understanding of the heterogeneous expression levels of tapasin under physiological and pathophysiological conditions.

Immunization in tumor prevention

Recent experimental data suggest that immunity can be activated to prevent tumors. The rationale for prevention is strong because the setting is one endowed with an immune system that is neither impaired by tumor and treatment-induced suppression, nor tolerant to tumor-associated antigens. Oncogenic growth factor receptors are tumor antigens and rational targets for specific immunoprevention. Successful prevention of mammary carcinomas in Her-2/neu transgenic mice is cited as an evidence of the validity of this approach. The specific properties of the Her-2/neu gene product as an antigen and the nature of the immune responses induced by effective preventive treatments are summarized.

MHC class I antigens, immune surveillance, and tumor immune escape

Oncogenic transformation in human and experimental animals is not necessarily followed by the appearance of a tumor mass. The immune system of the host can recognize tumor antigens by the presentation of small antigenic peptides to the receptor of cytotoxic T-lymphocytes (CTLs) and reject the nascent tumor. However, cancer cells can sometimes escape these specific T-cell immune responses in the course of somatic (genetic and phenotypic) clonal evolution. Among the tumor immune escape mechanisms described to date, the alterations in the expression of major histocompatibility complex (MHC) molecules play a crucial step in tumor development due to the role of MHC antigens in antigen presentation to T-lymphocytes and the regulation of natural killer cell (NK) cell function. In this work, we have (1) updated information on the mechanisms that allow CTLs to recognize tumor antigens after antigen processing by transformed cells, (2) described the altered MHC class I phenotypes that are commonly found in human tumors, (3) summarized the molecular mechanisms responsible for MHC class I alteration in human tumors, (4) provided evidence that these altered human leukocyte antigens (HLA) class I phenotypes are detectable as result of a T-cell immunoselection of HLA class I-deficient variants by an immunecompetent host, and (5) presented data indicating the MHC class I phenotype and the immunogenicity of experimental metastatic tumors change drastically when tumors develop in immunodeficient mice.

Complete loss of HLA class I antigen expression on melanoma cells: a result of successive mutational events

Alterations in the surface expression of HLA class I molecules have been described as a strategy of tumors to evade recognition by cytotoxic T cells. We detected complete loss of HLA class I antigen presentation for 2 tumor cell lines from 1 melanoma patient, the first originated from a regional lymph node lesion diagnosed simultaneously with the primary tumor and the second established 8 months later from a metastatic pleural effusion sample. Antigen presentation was not inducible with IFN-gamma but could be restored after transfection of tumor cells with b2m cDNA, indicating a defect in b2m expression. Analysis of the nature of this defect revealed that it originated from at least 2 mutational events affecting both copies of the b2m gene: a microdeletion of 498 bp in one b2m gene, including its entire exon 1, and a macrodeletion involving the entire copy of the second b2m gene. Microsatellite analysis pointed to the macrodeletion by demonstrating LOH for several specific markers on the long arm (q) of chromosome 15. Structural imbalance of 15q was verified by FISH. FISH studies also indicated the coexistence of a structurally abnormal variant of chromosome 15q with 2 apparently entire chromosomes 15q harboring the homozygous b2m microdeletion. Block of b2m expression in tumor cells builds a barrier to immunotherapy of cancer patients, and its early incidence should be of major consideration in the development and design of immunotherapeutic strategies.

22. Immune responses to malignancies

Immune responses to tumor-associated antigens exist in tumor-bearing hosts but are usually not successful in eliminating malignant cells or preventing the development of metastases. Patients with cancer generate robust immune responses to infectious agents (bacteria and viruses) perceived as a "danger signal" but only ineffective, weak responses to tumor-associated antigens, which are considered as "self." This fundamental difference in responses to self versus non-self is further magnified by the ability of tumors to subvert the host immune system. Tumors induce dysfunction, as well as apoptosis in CD8(+) antitumor effector cells. The escape of tumors from immune cells is mediated by several distinct molecular mechanisms. Insights into these mechanisms and more effective control of tumor-orchestrated immune dysfunction are needed. Novel strategies for immunotherapy of cancer must address protection and survival of antitumor effector cells in the tumor microenvironment.

Analysis of HLA-E expression in human tumors

Downregulation of MHC class Ia molecule expression is a widespread mechanism used by tumor cells to escape antitumor T-cell-mediated immune responses. However, it is not known why NK cells cannot lyse these MHC class-Ia-deficient tumor targets. Tumors must select additional routes of escape from NK cells. An attractive hypothesis is that the aberrant expression of nonclassical HLA class Ia molecules in tumors provides the required inhibitory signal to NK cells, rendering tumor cells resistant to NK lysis. To analyze the possible role of HLA-E molecules in providing tumor cells with an NK escape mechanism, we studied the cell surface expression of this HLA class Ib molecule in a variety of tumor cell lines with well-defined HLA class Ia alterations. Tests were done with the monoclonal antibody 3D12 recognizing cell surface HLA-E molecules. Our results indicate that HLA-E was mainly detected in leukemia-derived cell lines. In addition, HLA-E was detected in tumor cell lines of different origin. This expression was related with the availability of free beta(2)-microglobulin (beta(2)m) in the cytoplasm of tumor cells. Expression was detected in tumor cell lines showing an imbalance in heavy chain/beta(2)m expression, particularly in tumor cell lines with alterations in the expression of heavy-chain genes. Several lines of evidence favor these conclusions: (1) In the FM55 and NW145 melanoma tumor systems, the reduction in HLA class Ia expression paralleled the increased cell surface detection of HLA-E. (2) A cervical tumor (808) and a melanoma cell line (R22.2) expressing a single HLA-A1 allele also expressed HLA-E. (3) The addition of human beta(2)m to tumor cell lines that expressed the HLA-E(G) allele increased HLA-E cell surface expression. (4) There was no HLA-E cell surface expression in tumor cell lines with total loss of HLA class Ia expression, including cell lines with low transcription of HLA class I heavy chains or with beta(2)m mutations. Our findings suggest that the biological consequences of these cumulative genetic and molecular changes in tumor cells lead to the appearance of HLA-E in a limited number of tumor cell lines with peculiar phenotypic and genotypic characteristics, namely: HLA-class Ia downregulation, free beta(2)m and HLA-E(G) genotype. The aberrant HLA-E expression might be of particular biological relevance in those HLA tumor phenotypes that express a single HLA-A allele when NK inhibition is markedly reduced due to the downregulation of HLA-B and -C alleles.

Induction of heat shock protein gp96 by immune cytokines

Cytokines play a major role in regulating both humoral and cell-mediated immune responses. Recent advances in our understanding of cell-mediated immune responses have focused on the antigen presentation machinery and the proteins in the endoplasmic reticulum (ER). These proteins help the formation and stabilization of the major histocompatibility complex (MHC)-peptide interaction. A 96-kDa, ER-resident glycoprotein (gp96) is being evaluated as a therapeutic agent in cancer because of its ability to associate with a vast number of cellular peptides irrespective of size or sequence. Because the antigen presentation complex is assembled in the ER and a number of ER-resident proteins are modulated by cytokines, it is important to examine the regulation of gp96 in response to immune cytokines interferon gamma (IFN-gamma), and interleukin 2 (IL-2). Defects in signaling pathway in either of the cytokines can result in suboptimal immune response. We examined the effect of the cytokines IFN-gamma and IL-2 on the induction of gp96 in different cancer cell lines and examined the induction of DNA-binding proteins that recognize gamma interferon-activating sequence (GAS), present in the promoter region of gp96. The induction of GAS binding protein correlated with the induction of STAT 1 protein, a transcriptional regulator and mediator of IFN-gamma-mediated gene expression. The use of cytokines in inducing gp96 levels may have significance in maintaining high levels of gp96 for a sustained immune response.

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.

Soluble HLA class I induces NK cell apoptosis upon the engagement of killer-activating HLA class I receptors through FasL-Fas interaction

The engagement of the activating isoforms of C-type lectin inhibitory receptor (CLIR) or killer Ig-like receptor (KIR) by their natural ligands, represented by soluble HLA-I (sHLA-I) molecules, induced programmed cell death of natural killer (NK) cells. Indeed, NK cell apoptosis elicited by either putative HLA-E and HLA-F (sHLA-I non-A, -B, -C, and -G) or sHLA-I-Cw4 or -Cw3 from untransfected or -Cw4 or -Cw3 alleles transfected HLA-A(-), B(-), C(-), G(-), E(+), F(+) 721.221 lymphoblastoid cell line, respectively, was blocked by covering the corresponding activating receptor with either anti-CLIR- or anti-KIR-specific monoclonal antibodies (mAbs). After sHLA-I-activating receptor interaction, NK cells produced and released Fas ligand (FasL), which in turn led to NK cell apoptosis by interacting with Fas at the NK cell surface. Blocking anti-Fas mAb, or anti-FasL mAb, inhibited sHLA-I-mediated apoptosis via activating receptor in NK cell clones. This apoptosis was inhibited by NK cell treatment with cyclosporin A, whereas this drug had no effect on activating receptor-mediated activation of cytolysis. Conversely, concanamycin A, an inhibitor of vacuolar type H(+)-adenosine triphosphatase (H(+)-ATPase) of granules, inhibited activating receptor-induced NK cell cytolysis, suggesting that activating receptor-mediated apoptosis and cytolysis can use different intracellular pathways. Furthermore, a large amount of interferon-gamma (IFN-gamma) was detectable in culture supernatant of activating receptor(+) NK cells incubated with the appropriate sHLA-I ligand. Again, cyclosporin A, but not concanamycin A, strongly reduced activating receptor-mediated IFN-gamma production. This suggests that activating receptor-induced apoptosis of NK cells could play a role in eliminating potentially harmful NK cell clones and, at the same time, it leads to production of IFN-gamma, an antiviral cytokine able to amplify immune responses.