MHC antigens and tumor escape from immune surveillance

Defective MHC class I antigen surface expression promotes cellular survival through elevated ER stress and modulation of p53 function

Defects in Major Histocompatibility class I cell surface expression is thought to allow escape of tumor cells from immune surveillance. Hitherto, it is unclear whether this deficiency confers immune-independent survival advantage. We show here that class I cell surface expression deficiency due to defects in beta2 microglobulin or the transporter-associated with antigen processing (TAP) results in resistance to apoptosis in response to various cytotoxic signals. Reduced apoptosis correlated with altered p53 activation, which was due to compromised nuclear translocation of p53. Binding of p53 to glycogen synthase kinase-3beta (GSK3beta), which is known to phosphorylate and lead to cytoplasmic sequestration of p53, was enhanced in these cells. Consistently, endoplasmic reticulum (ER) stress, which promotes binding of p53 to GSK3beta was constitutively elevated in the absence of class I cell surface expression. Taken together, the results suggest a non-immunological causal role for defective class I cell surface expression in regulating cellular survival in a p53-dependent manner, through the upregulation of ER stress, which could be another mechanism leading to carcinogenesis.

Characterization of HLA class I altered phenotypes in a panel of human melanoma cell lines

BACKGROUND

Altered HLA class I cell surface expression is one of the major mechanisms by which tumor cells escape from T lymphocytes. Immunohistochemistry-defined phenotypes of lost HLA class I expression have been described in human solid tumors, nut less information is available on melanoma cell lines.

OBJECTIVES

To describe the frequency and distribution of different types of HLA class I antigen alterations in 91 melanoma cell lines from the European Searchable Tumour Cell and Databank (ESTDAB).

METHODS

The HLA class I expression was assessed by flow cytometry and HLA genotyping.

RESULTS

We found various types of HLA class I cell surface alterations in about 67% of the melanoma cell lines. These alterations range from total to selective HLA class I loss due to loss of heterozygosity (LOH), haplotype loss, beta2-microglobulin gene mutation, and/or total or selective down-regulation of HLA class I molecules. The most frequently observed phenotype is down-regulation of HLA-B locus that was reversible after treatment with IFN -gamma.

CONCLUSIONS

In general, HLA class I alterations in the majority of the cells analyzed were of regulatory nature and could be restored by IFN-gamma. Analysis of the frequency of distinct HLA class I altered phenotypes in these melanoma cell lines revealed specific differences compared to other types of tumors.

From T-cell activation signals to signaling control of anti-cancer immunity

The activation of resting T cells is crucial to most immune processes. Recognition of foreign antigen by T-cell receptors has to be correctly translated into signal transduction events necessary for the induction of an effective immune response. In this review, we discuss the essential signals, molecules, and processes necessary to achieve full T-cell activation. In addition to describing these key biological events, we also discuss how T-cell receptor signaling may be harnessed to yield new therapeutic targets for a next generation of anti-cancer drugs.

Induction of protective CTL immunity against peptide transporter TAP-deficient tumors through dendritic cell vaccination

A large proportion of human cancers show deficiencies in the MHC class I antigen-processing machinery. Such defects render tumors resistant to immune eradication by tumoricidal CTLs. We recently identified a unique population of CTL that selectively targets tumor immune-escape variants through recognition of MHC-presented peptides, termed TEIPP (T cell epitopes associated with impaired peptide processing), expressed on cells lacking functional TAP-peptide transporters. Previously, we showed that vaccination with TEIPP peptides mediates protection against TAP-deficient tumors. Here, we further explored the concept of TEIPP-targeted therapy using a dendritic cell (DC)-based cellular vaccine. Impairment of TAP function in DC induced the presentation of endogenous TEIPP antigens by MHC class I molecules, and immunization with these DCs protected mice against the outgrowth of TAP-deficient lymphomas and fibrosarcomas. Immune analysis of vaccinated mice revealed strong TEIPP-specific CTL responses, and a crucial role for CD8(+) cells in tumor resistance. Finally, we show that TEIPP antigens could be successfully induced in wild-type DC by introducing the viral TAP inhibitor UL49.5. Our results imply that immune intervention strategies with TAP-inhibited DC could be developed for the treatment of antigen processing-deficient cancers in humans.

Long-term follow-up of patients treated by adoptive transfer of melanoma tumor-infiltrating lymphocytes as adjuvant therapy for stage III melanoma

The first analysis of our clinical trial on interest of using tumor-infiltrating lymphocytes (TIL) as adjuvant therapy for stage III (regional lymph nodes) melanoma was published in 2002 [5]. The aim of this paper is to update clinical results of 7 years of follow-up after the last treated patient. In the trial conducted between December 1993 and January 1999, patients without any detectable metastases after lymph node excision were randomly assigned to receive either TIL plus interleukin-2 (IL-2) for 2 months, or IL-2 only. The duration of the relapse-free interval was the primary objective. Eighty-eight patients were enrolled in the study. Currently, the last analysis performed in June 2006, after a median follow-up of 114.8 months, did not show change of non-significant extension of the relapse-free interval or overall survival. However, this second analysis strengthens our first hypothesis about the relationship between number of invaded lymph nodes and TIL treatment effectiveness. In the group with only one invaded lymph node, the estimated relapse rate was significantly lower (P (adjusted) = 0.0219) and the overall survival was increased (P (adjusted) = 0.0125) in the TIL+IL-2 arm compared with the IL-2 only arm. No differences between the two arms, either with regard to the duration of disease-free survival (P (adjusted) = 0.38) or overall survival (P (adjusted) = 0.43), were noted in the group with more than one invaded lymph node, whatever the number of invaded lymph nodes. Treatment was compatible with normal daily activity. This study, with a very long follow up (median of almost 10 years), postulates for the first time relationship between TIL efficiency in stage III melanoma (AJCC) and number of invaded lymph nodes, indicating that tumor burden might be a crucial factor in the production of an effective in vitro expansion of T cells specific for autologous tumor antigen, a finding which could be of value in future vaccine development for the treatment of melanoma.

Role of altered expression of HLA class I molecules in cancer progression

HLA class I antigens play a key role in immune recognition of transformed and virally infected cells via binding to the peptides of "non-self" or aberrantly expressed proteins and subsequent presentation of the newly formed "HLA-I-peptide" complex to T lymphocytes. Consequently, a chain of immune reactions is initiated leading to tumor cell elimination by cytotoxic T cells. Altered tumor expression of HLA class I is frequently observed in various types of malignancies. It represents one of the main mechanisms used by cancer cells to evade immunosurveillance. Because of immune selection, HLA class I-negative variants escape and lead to tumor growth and metastatic colonization. Loss or downregulation of HLA class I antigens on tumor cell surface is a factor that limits clinical outcome of peptide-based cancer vaccines aimed to increasing specific anti-tumor activity of cytotoxic T lymphocytes. Thus, gaining more knowledge regarding frequency of HLA class I defect, its tissue specificity, and underlying molecular mechanisms may help designing appropriate therapeutic strategies in cancer treatment. Here, we describe various types of HLA class I alterations found in different malignancies and molecular mechanisms that underlie these defects. We also discuss a correlation between HLA class I defects cancer progression in melanoma patients with poor clinical response to autologous vaccination.

Immune suppression in renal cell carcinoma

The clear evidence that tumor-infiltrating lymphocytes with anti-tumor activity exist in situ raises the question why renal cell carcinomas (RCCs) progress in vivo. A complex array of factors and pathways has been identified that impinges on innate and adaptive effector cells thereby inhibiting their activity against RCCs. The current picture of suppressive mechanisms that contribute to the failure of the immune system to control RCCs is reviewed here. Understanding these complex host-tumor interactions has broad implications for successful application of cytokine therapy and other forms of immunotherapy for RCC.

Spontaneous regression of colorectal cancer: a review of cases from 1900 to 2005

INTRODUCTION

Spontaneous regression of cancer is an exceptional but well-documented biological event. Further understanding of this phenomenon and harnessing of the mechanisms involved will have significant preventative and therapeutic implications.

DISCUSSION

In this review, the literature of spontaneous regression of colon or rectal cancer is reviewed from 1965 to 2005 to update reviews by Everson et al., Boyd and Challis et al. By adding to these, the author reports the entire series of colorectal cancer, which underwent documented spontaneous regression from 1900 to 2005. The demographic and pathologic characteristics, the details of regression and the outcome of reported cases are presented and discussed. Special emphasis is placed on identifying possible causes hypothesized by authors for occurrence of regression. Possible mechanisms operating to affect these regressions are also discussed.

Analysis of HLA class I alterations in tumors: choosing a strategy based on known patterns of underlying molecular mechanisms

The application of peptide-based immunotherapy in the treatment of cancer has known limitations in patients with loss or downregulation of human leukocyte antigen (HLA) class I expression on tumor cells. These alterations diminish the ability of cancer cells to present tumor peptides to T cells and therefore lead to failure of peptide-based cancer vaccination. Abnormal expression of HLA class I molecules in malignant cells is a frequent event that ranges from total loss of class I molecules to partial loss of HLA-specific haplotypes or alleles. Different mechanisms underlie these alterations and might require different therapeutic approaches. A complete characterization of molecular defects may suggest strategies for the selection and follow-up of patients undergoing T-cell based immunotherapy. Moreover, a precise identification of the mechanism leading to HLA class I defects in patients with cancer will help develop new, personalized patient-tailored treatment protocols. Here, we describe several examples showing the necessity and feasibility of making detailed individual analysis of HLA alteration mechanisms based on previously described molecular patterns in different types of malignancy. We recommend using this approach, at least in some patients, to enhance the therapeutic benefit of cancer immunotherapy.

Different mechanisms can lead to the same altered HLA class I phenotype in tumors

Human leukocyte antigen (HLA) class I plays an important role in tumor recognition and rejection. Total or selective losses of HLA class I antigens (classified into seven HLA class I altered phenotypes) represent one of the main routes of tumor escape from immune surveillance. Abnormal expression of HLA class I has been reported in different human tumor samples with distinct underlying mechanisms. Notably, different molecular mechanisms can generate the same altered HLA class I phenotype. Here, we describe various molecular mechanisms that can lead to HLA total loss or downregulation (phenotype I) in melanoma, colorectal carcinoma and bladder cancer.

TNF-alpha induction of GM2 expression on renal cell carcinomas promotes T cell dysfunction

Previous studies from our laboratory demonstrated the role of tumor-derived gangliosides as important mediators of T cell apoptosis, and hence, as one mechanism by which tumors evade immune destruction. In this study, we report that TNF-alpha secreted by infiltrating inflammatory cells and/or genetically modified tumors augments tumor-associated GM2 levels, which leads to T cell death and immune dysfunction. The conversion of weakly apoptogenic renal cell carcinoma (RCC) clones to lines that can induce T cell death requires 3-5 days of TNF-alpha pretreatment, a time frame paralleling that needed for TNF-alpha to stimulate GM2 accumulation by SK-RC-45, SK-RC-54, and SK-RC-13. RCC tumor cell lines permanently transfected with the TNF-alpha transgene are similarly toxic for T lymphocytes, which correlates with their constitutively elevated levels of GM2. TNF-alpha increases GM2 ganglioside expression by enhancing the mRNA levels encoding its synthetic enzyme, GM2 synthase, as demonstrated by both RT-PCR and Southern analysis. The contribution of GM2 gangliosides to tumor-induced T cell death was supported by the finding that anti-GM2 Abs significantly blocked T cell apoptosis mediated by TNF-alpha-treated tumor cells, and by the observation that small interfering RNA directed against TNF-alpha abrogated GM2 synthase expression by TNF-transfected SK-RC-45, diminished its GM2 accumulation, and inhibited its apoptogenicity for T lymphocytes. Our results indicate that TNF-alpha signaling promotes RCC-induced killing of T cells by stimulating the acquisition of a distinct ganglioside assembly in RCC tumor cells.

The varicellovirus-encoded TAP inhibitor UL49.5 regulates the presentation of CTL epitopes by Qa-1b1

Impairment of MHC class I Ag processing is a commonly observed mechanism that allows viruses and tumors to escape immune destruction by CTL. The peptide transporter TAP that is responsible for the delivery of MHC class I-binding peptides into the endoplasmic reticulum is a pivotal target of viral-immune evasion molecules, and expression of this transporter is frequently lost in advanced cancers. We recently described a novel population of CTL that intriguingly exhibits reactivity against such tumor-immune escape variants and that recognizes self-peptides emerging at the cell surface due to defects in the processing machinery. Investigations of this new type of CTL epitopes are hampered by the lack of an efficient inhibitor for peptide transport in mouse cells. In this article, we demonstrate that the varicellovirus protein UL49.5, in contrast to ICP47 and US6, strongly impairs the activity of the mouse transporter and mediates degradation of mouse TAP1 and TAP2. Inhibition of TAP was witnessed by a strong reduction of surface MHC class I display and a decrease in recognition of conventional tumor-specific CTL. Analysis of CTL reactivity through the nonclassical molecule Qa-1(b) revealed that the presentation of the predominant leader peptide was inhibited. Interestingly, expression of UL49.5 in processing competent tumor cells induced the presentation of the new category of peptides. Our data show that the varicellovirus UL49.5 protein is a universal TAP inhibitor that can be exploited for preclinical studies on CTL-based immune intervention.

CD4+ CD25high regulatory T cells reduce T cell transendothelial migration in cancer patients

Cell-mediated immunity is thought to be the main mechanism of anti-tumour responses of the host, but it is not known if cancer disease affects T cell recruitment from blood to tissues. Therefore, we compared Heliobacter pylori-induced T cell transendothelial migration (TEM) in H. pylori-infected gastric carcinoma patients, colon and lung carcinoma patients and healthy volunteers. H. pylori induced significant T cell migration from all groups. However, there was a dramatic reduction of T cell TEM in gastric carcinoma patients (80%) compared to healthy individuals. A similarly reduced transmigration was also seen in colon and lung carcinoma patients. We found significantly increased frequencies of T(reg) cells in the blood of gastric carcinoma patients compared to healthy individuals, and depletion of T(reg) cells from the blood of these patients prior to TEM restored T cell migration. The effect of T(reg) cells was largely dependent on cell-cell contact, but not on IL-10 or TGF-beta. In addition, the presence of T(reg) cells led to reduced T cell attachment to endothelium and decreased production of T cell-recruiting chemokines during TEM. In conclusion, T(reg) cell-mediated reduction of T cell TEM may reduce T cell recruitment in patients with epithelial malignancies, thereby hampering anti-tumour responses.

MHC Class I Antigens and Immune Surveillance in Transformed Cells

MHC class I antigens play a crucial role in the interaction of tumor cells with the host immune system, in particular, in the presentation of peptides as tumor-associated antigens to cytotoxic lymphocytes (CTLs) and in the regulation of cytolytic activity of natural killer (NK) cells. In this review we discuss the role of MHC class I antigens in the recognition and elimination of transformed cells and in the generation of tumor immune escape routes when MHC class I losses occur in tumors. The different altered MHC class I phenotypes and their distribution in different human tumors are the main topic of this review. In addition, molecular defects that underlie MHC alterations in transformed cells are also described in detail. Future research directions in this field are also discussed, including the laboratory analysis of tumor MHC class I-negative variants and the possible restoration of MHC class I expression.

Identification of different tumor escape mechanisms in several metastases from a melanoma patient undergoing immunotherapy

The cytotoxic activity of T cells selects the outgrowth of tumor cells that escape from immune surveillance by different strategies. The different mechanisms that interfere with immune recognition and limit vaccination efficiency are still poorly understood. We analysed six cell lines established from different metastases of melanoma patient UKRV-Mel-20 for specific characteristics known to have an impact on the tumor-T cell interaction: (1) alterations in the HLA class I phenotype, (2) expression of Fas/CD95, and (3) expression of specific cytokines and chemokines. One of the cell lines, UKRV-Mel-20f, exhibited an HLA class I haplotype loss and just this cell line was also characterised by the expression of Fas/CD95 and of relatively high levels of proinflammatory chemokines suggesting that the cytotoxic activity of tumor-infiltrating T cells might have selected the outgrowth of this tumor cell variant. All other cell lines analysed showed no alterations in HLA class I expression, but, in contrast to UKRV-Mel-20f, expressed much lower levels of Fas/CD95 and of proinflammatory chemokines and some of them produced high levels of immunosuppressive TGF-beta1. These results suggest that in patient UKRV-Mel-20, tumor cells interfere with T cell recognition by different strategies which might partially explain why this patient did not have a clinical response to an autologous tumor cell vaccine.

Review article: immune suppression and colorectal cancer

BACKGROUND

Advances in immunology and molecular biology have shown that colorectal cancer is potentially immunogenic and that host immune responses influence survival. However, immune surveillance and activation is frequently ineffective in preventing and/or controlling tumour growth.

AIM

To discuss potential ways in which colorectal cancer induces immune suppression, its effect upon prognosis and avenues for therapeutic development.

METHOD

A literature review was undertaken for evidence of colorectal cancer-induced immune suppression using PubMed and Medline searches. Further studies were identified from the reference lists of identified papers.

RESULTS

Immune suppression occurs at a molecular and cellular level and can result in a shift from cellular to humoral immunity. Several mechanisms for immune suppression have been described affecting innate and adaptive immunity with suppression linked to poorer clinical outcome.

CONCLUSIONS

Colorectal cancer causes direct inhibition of the host's immune response with a detrimental effect upon prognosis. Immunotherapy offers a therapeutic strategy to counteract these effects with promising results seen particularly in precancerous conditions and early tumours. This review strongly suggests that immunotherapy should be incorporated into adjuvant therapeutic trials for stage 2 tumours and be considered as adjuvant treatment in conjunction with standard chemotherapy regimes for advanced disease.

Interleukin-10-secreting type 1 regulatory T cells in rodents and humans

Interleukin-10 (IL-10)-secreting T regulatory type 1 (Tr1) cells are defined by their specific cytokine production profile, which includes the secretion of high levels of IL-10 and transforming growth factor-beta(TGF-beta), and by their ability to suppress antigen-specific effector T-cell responses via a cytokine-dependent mechanism. In contrast to the naturally occurring CD4+ CD25+ T regulatory cells (Tregs) that emerge directly from the thymus, Tr1 cells are induced by antigen stimulation via an IL-10-dependent process in vitro and in vivo. Specialized IL-10-producing dendritic cells, such as those in an immature state or those modulated by tolerogenic stimuli, play a key role in this process. We propose to use the term Tr1 cells for all IL-10-producing T-cell populations that are induced by IL-10 and have regulatory activity. The full biological characterization of Tr1 cells has been hampered by the difficulty in generating these cells in vitro and by the lack of specific marker molecules. However, it is clear that Tr1 cells play a key role in regulating adaptive immune responses both in mice and in humans. Further work to delineate the specific molecular signature of Tr1 cells, to determine their relationship with CD4+ CD25+ Tregs, and to elucidate their respective role in maintaining peripheral tolerance is crucial to advance our knowledge on this Treg subset. Furthermore, results from clinical protocols using Tr1 cells to modulate immune responses in vivo in autoimmunity, transplantation, and chronic inflammatory diseases will undoubtedly prove the biological relevance of these cells in immunotolerance.

Antitumor activity of chimeric immunoreceptor gene-modified Tc1 and Th1 cells against autologous carcinoembryonic antigen-expressing colon cancer cells

To generate tumor-specific and interferon (IFN)-gamma-producing Tc1 and Th1 cells applicable for many cancer patients, we previously developed a protocol for generating carcinoembryonic antigen (CEA)-specific Tc1 and Th1 cells from healthy human T cells by transduction with a lentivirus containing a chimeric immunoglobulin T-cell receptor (cIgTCR) gene composed of single-chain variable fragments from an anti-CEA-specific monoclonal antibody fused to an intracellular signaling domain of CD28 and CD3zeta. These cells, designated Tc1-T and Th1-T bodies, respectively, showed strong antitumor activity against CEA-expressing tumor cells in RAG2-/- mice when both of them were transferred. However, it remains unclear whether it is possible to generate Tc1-T and Th1-T bodies from cancer patients with defective T-cell function because of significant immunosuppression. Here, we prepared Tc1-T and Th1-T bodies from T cells of a colon cancer patient, and asked whether these T bodies can exert effective T-cell function against autologous tumor cells. These T bodies showed high cytotoxicity and produced IFN-gamma in response to CEA-expressing autologous tumor cells, even in the presence of soluble CEA. It was also demonstrated that Th1-T bodies supported the survival of Tc1-T bodies through cell-to-cell interactions. Furthermore, our protocol utilized retrovirus for cIgTCR transduction to achieve better induction efficiency compared to lentivirus-mediated transduction. Taken together, our findings here indicate that retrovirally transduced Tc1-T and Th1-T bodies will become a promising strategy for adoptive immunotherapy of human cancer.

The correlation between colorectal cancer rates of proliferation and apoptosis and systemic cytokine levels; plus their influence upon survival

Colorectal cancer development is associated with a shift in host immunity with suppression of the cell-mediated immune system (CMI) and a predominance of humoral immunity (HI). Tumour progression is also associated with increased rates of cell proliferation and apoptosis. The aim of this study was to investigate whether these factors correlate and have an influence upon prognosis. Long-term follow-up was performed on 40 patients with colorectal cancer who had levels of tumour necrosis factor (TNF)-alpha, interferon (IFN)-gamma and interleukin (IL)-10 measured from stimulated blood cultures before surgery. Their archived tumour specimens were analysed to determine a Ki-67-derived proliferation index (PI) and a M30-derived apoptosis index (AI). Tumour necrosis factor-alpha levels negatively correlated to tumour proliferation (rho=-0.697, P=0.01). Interleukin-10 levels had a positive correlation with tumour proliferation (rho=0.452, P=0.05) and apoptosis (rho=0.587, P=0.01). Patient survival correlates to tumour pathological stage (P=0.0038) and vascular invasion (P=0.0014). An AI< or =0.6% and TNF-alpha levels > or =8148 pg ml(-1) correlate to improved survival (P=0.032, P=0.021). Tumour proliferation and apoptosis correlate to progressive suppression of the CMI-associated cytokine TNF-alpha and to and higher levels of IL-10. Survival is dependent upon the histological stage of the tumour, vascular invasion, rates of apoptosis and proliferation and systemic immunity which are all interconnected.

LOH at 6p21.3 region and HLA class I altered phenotypes in bladder carcinomas

Alterations in HLA class I antigen expression have been frequently described in different epithelial tumors and are thought to favor tumor immune escape from T lymphocyte recognition. Multiple molecular mechanisms are responsible for these altered HLA class I tumor phenotypes. Some are structural defects that produce unresponsiveness to treatment with interferons. Others include alterations in regulatory mechanisms that can be switched on by treatment of tumor cells with different cytokines. One important mechanism belonging to the first group is loss of heterozygosity (LOH) at chromosome region 6p21.3, which can lead to HLA haplotype loss. In this investigation, the frequency of LOH at 6p21 chromosome region was studied in 69 bladder carcinomas. Short tandem repeat analysis showed that 35% of cases had LOH in this chromosome region. By considering these results together with immunohistological findings previously published by our group, we identified a distribution pattern of HLA class I altered phenotypes in bladder cancer. The most frequently altered phenotype in bladder carcinomas was total loss of HLA class I expression (17 cases, 25%), followed by phenotype II associated with HLA haplotype loss (12 cases, 17.5%), and HLA allelic loss (ten cases, 14.5%). Nine cases (13%) were classified as having a compound phenotype, five cases (7%) as having HLA locus loss, and in 16 cases (23%) no alteration in HLA expression was detected. An important conclusion of this report is that a combination of different molecular and immunohistological techniques is required to precisely define which HLA alleles are lost during tumor progression and to characterize the underlying mechanisms of these losses. These studies should be performed when a cancer patient is to be included in an immunotherapy protocol that aims to stimulate different immune effector mechanisms.

Vaccines for tumour prevention

Despite tremendous progress in basic and epidemiological research, effective prevention of most types of cancer is still lacking. Vaccine use in cancer therapy remains a promising but difficult prospect. However, new mouse models that recapitulate significant features of human cancer progression show that vaccines can keep precancerous lesions under control and might eventually be the spearhead of effective and reliable ways to prevent cancer.

Immunodominance and Immunodomination: Critical Factors in Developing Effective CD8+ T‐Cell–Based Cancer Vaccines

The focusing of cellular immunity toward one, or just a few, antigenic determinant, even during immune responses to complex microorganisms or antigens, is known as immunodominance. Although described in many systems, the mechanisms of determinant immunodominance are only just beginning to be appreciated, especially in relation to the interplay between T cells of differing specificities and the interactions between T cells and the antigen-presenting cells (APCs). The outcome of these cellular interactions can lead to a form of immune suppression of one specificity by another-described as "immunodomination". The specific and detailed mechanisms involved in this process are now partly defined. A full understanding of all the factors that control immunodominance and influence immunodomination will help us to develop better viral and cancer vaccines.

Selective antibody-mediated targeting of class I MHC to EGFR-expressing tumor cells induces potent antitumor CTL activityin vitro andin vivo

Epidermal growth factor receptor (EGFR) is highly overexpressed in many tumor types. We present a new fusion molecule that can target solid tumors that express EGFR. The fusion molecule combines the advantage(s) of the well-established tumor targeting capabilities of high affinity recombinant fragments of antibodies with the known efficient, specific and potent killing ability of CD8 T lymphocytes directed against highly antigenic MHC/peptide complexes. A recombinant chimeric molecule was created by the genetic fusion of the scFv antibody fragment derived from the anti-EGFR monoclonal antibody C225, to monomeric single-chain HLA-A2 complexes containing immunodominant tumor or viral-specific peptides. The fusion protein can induce very efficiently CTL-dependent lysis of EGFR-expressing tumor cells regardless of the expression of self peptide-MHC complexes. Moreover, the molecule exhibited very potent antitumor activity in vivo in nude mice bearing preestablished human tumor xenografts. These in vitro and in vivo results indicate that recombinant scFv-MHC-peptide fusion molecules might represent a novel and powerful approach to immunotherapy of solid tumors, bridging antibody and T lymphocyte attack on cancer cells.

Immunosurveillance is active in colorectal cancer as downregulation but not complete loss of MHC class I expression correlates with a poor prognosis

Many colorectal tumors lose or downregulate cell surface expression of MHC class I molecules conferring resistance to T-cell-mediated attack. It has been suggested that this phenomenon is due to in vivo immune-tumor interactions. However, evidence of the impact of MHC class I loss on outcomes from colorectal cancer is scarce. In our study of more than 450 colorectal cancers in tissue microarray format, we have shown that both high levels of MHC class I expression and absent MHC class I expression are associated with similar disease-specific survival times, possibly due to natural killer cell-mediated clearance of MHC class I-negative tumor cells. However, tumors with low level expression of MHC class I were found to confer a significantly poorer prognosis, retaining independent significance on multivariate analysis. The existence of these poor prognosis tumors, which may avoid both NK- and T-cell-mediated immune surveillance, has important implications for the design of immunotherapeutic strategies in colorectal cancer.

Tumor immunotherapy targeting fibroblast activation protein, a product expressed in tumor-associated fibroblasts

Murine studies have shown that immunologic targeting of the tumor vasculature, a key element of the tumor stroma, can lead to protective immunity in the absence of significant pathology. In the current study, we expand the scope of stroma-targeted immunotherapy to antigens expressed in tumor-associated fibroblasts, the predominant component of the stroma in most types of cancer. Mice were immunized against fibroblast activation protein (FAP), a product up-regulated in tumor-associated fibroblasts, using dendritic cells transfected with FAP mRNA. Using melanoma, carcinoma, and lymphoma models, we show that tumor growth was inhibited in tumor-bearing mice vaccinated against FAP and that the magnitude of the antitumor response was comparable to that of vaccination against tumor cell-expressed antigens. Both s.c. implanted tumors and lung metastases were susceptible to anti-FAP immunotherapy. The antitumor response could be further enhanced by augmenting the CD4+ T-cell arm of the anti-FAP immune response, achieved by using a lysosomal targeting sequence to redirect the translated FAP product into the class II presentation pathway, or by covaccination against FAP and a tumor cell-expressed antigen, tyrosinase-related protein 2. No morbidity or mortality was associated with anti-FAP vaccination except for a small delay in wound healing. The study suggests that FAP, a product which is preferentially expressed in tumor-associated fibroblasts, could function as a tumor rejection antigen in a broad range of cancers.

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.

Differential mechanisms for T lymphocyte recruitment in normal and neoplastic human gastric mucosa

Worldwide, gastric adenocarcinoma (GC) is the second most common cause of death from malignant disease. The reason why immune responses are unable to clear the tumour is not fully understood, although aberrant lymphocyte recruitment to the tumour site might be one factor. Therefore, we investigated the homing phenotype of mucosal T lymphocytes in GC, compared to tumour-free mucosa. We could detect significantly decreased frequencies of mucosal homing alpha4beta7+ T cells in the tumour tissues and increased frequencies of L-selectin+ T cells. This was probably due to the correlated decrease in MAdCAM-1 positive and increase in PNAd positive blood vessels in the tumour mucosa. There were also fewer CXCR3+ T lymphocytes in the tumour tissue. These findings provide evidence that endothelial cells within tumours arising at mucosal sites do not support extravasation of typical mucosa-infiltrating T cells. This may be of major relevance for future immunotherapeutic strategies for treatment of GC.

Antibody-mediated targeting of human single-chain class I MHC with covalently linked peptides induces efficient killing of tumor cells by tumor or viral-specific cytotoxic T lymphocytes

Soluble forms of human MHC class I HLA-A2 were produced in which the peptide binding groove was uniformly occupied by a single tumor or viral-derived peptides attached via a covalent flexible peptide linker to the N terminus of a single-chain beta-2-microglobulin-HLA-A2 heavy chain fusion protein. A tetravalent version of this molecule with various peptides was found to be functional. It could stimulate T cells specifically as well as bind them with high avidity. The covalently linked single chain peptide-HLA-A2 construct was next fused at its C-terminal end to a scFv antibody fragment derived from the variable domains of an anti-IL-2R alpha subunit-specific humanized antibody, anti-Tac. The scFv-MHC fusion was thus encoded by a single gene and produced in E. coli as a single polypeptide chain. Binding studies revealed its ability to decorate Ag-positive human tumor cells with covalent peptide single-chain HLA-A2 (scHLA-A2) molecules in a manner that was entirely dependent upon the specificity of the targeting Antibody fragment. Most importantly, the covalent scHLA-A2 molecule, when bound to the target tumor cells, could induce efficient and specific HLA-A2-restricted, peptide-specific CTL-mediated lysis. These results demonstrate the ability to generate soluble, stable, and functional single-chain HLA-A2 molecules with covalently linked peptides, which when fused to targeting antibodies, potentiate CTL killing. This new approach may open the way for the development of new immunotherapeutic strategies based on antibody targeting of natural cognate MHC ligands and CTL-based cytotoxic mechanisms.

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.

Human leucocyte antigen determinants of susceptibility to Barrett's oesophagus in Asians--a preliminary study

BACKGROUND

Characteristic immune profiles have been demonstrated in gastro-oesophageal reflux disease. However, the genetic basis of gastro-oesophageal reflux disease remains unclear.

AIM

To investigate whether certain human leucocyte antigen genes are associated with Barrett's oesophagus.

METHODS

Asian patients of Malay, Chinese and Indian descent with Barrett's oesophagus (n = 59) and those without reflux symptoms and a normal oesophagus (n =60) were recruited prospectively using endoscopic and histopathological criteria. Human leucocyte antigen class I and II typing was performed using a polymerase chain reaction sequence-specific primers method.

RESULTS

The HLA-B7 allele was present in 17% (10 of 59) of patients with Barrett's oesophagus when compared with 0% (zero of 60) of controls [P = 0.0006, corrected P = 0.0171, OR = 25.67]. Subgroup analysis revealed that the HLA-B7 allele was confined almost exclusively to Indians with Barrett's oesophagus, 43% (nine of 21) vs. 0% (zero of 19) Indian controls (P = 0.0014, corrected P = 0.0406, OR = 29.64). No class II associations, protective human leucocyte antigens or extended haplotypes for disease susceptibility were identified.

CONCLUSIONS

Barrett's oesophagus in Asians, particularly Indians, is strongly positively associated with HLA-B7; reinforcing a genetic component to gastro-oesophageal reflux disease. A larger sample size and different ethnic populations should be genotyped to further confirm this association and identify possible additional risk factors in the human leucocyte antigen locus.

Natural killer cells: can they be useful as adoptive immunotherapy for cancer?

As part of the innate immune system, natural killer (NK) cells form the first line of defence against pathogens or transformed/cancerous host cells. Recent experimental and clinical data show the possibility of exploiting NK activity as a cell-based immunotherapy to treat cancer. This review discusses the recent knowledge on NK cell biology that has impacted on its development as a treatment for cancer.

Expression of MHC class I, MHC class II, and cancer germline antigens in neuroblastoma

BACKGROUND

Neuroblastoma is the most common solid extracranial tumor in childhood, still with poor survival rates for metastatic disease. Neuroblastoma cells are of neuroectodermal origin and express a number of cancer germline (CG) antigens. These CG antigens may represent a potential target for immunotherapy such as peptide-based vaccination strategies.

OBJECTIVE

The purpose of this study was to analyze the presence of MAGE-A1, MAGE-A3/A6, and NY-ESO-1 on an mRNA and protein level and to determine the expression of MHC class I and MHC class II antigens within the same tumor specimens.

METHODS

A total of 68 tumors were available for RT-PCR, and 19/68 tumors were available for immunohistochemical (IHC) analysis of MAGE-A1, MAGE-A3/A6, and NY-ESO-1. In parallel, the same tumors were stained with a panel of antibodies for MHC class I and MHC class II molecules.

RESULTS

Screening of 68 tumor specimens by RT-PCR revealed expression of MAGE-A1 in 44%, MAGE-A3/A6 in 21%, and NY-ESO-1 in 28% of cases. Immunohistochemistry for CG antigens of selected tumors showed good agreement between protein and gene expression. However, staining revealed a heterogeneous expression of CG antigens. None of the selected tumors showed MHC class I or MHC class II expression.

CONCLUSIONS

mRNA expression of MAGE-A1, MAGE-A3/A6, and NY-ESO-1 is congruent with the protein expression as determined by immunohistochemistry. The heterogeneous CG-antigen expression and the lack of MHC class I and II molecules may have implications for T-cell-mediated immunotherapy in neuroblastoma.

Altered phenotype of dextran sulfate sodium colitis in interferon regulatory factor-1 knock-out mice

BACKGROUND AND AIMS

Interferon regulatory factor-1 (IRF-1) is a transcription factor with antiviral, proinflammatory and tumor suppressor properties. We examined the role of IRF-1 in dextran sulfate sodium colitis, a murine model of inflammatory bowel disease, to determine if absence of the gene would protect against colitis.

METHODS

C57BL/6J mice with a targeted disruption of IRF-1 and wild-type C57BL/6J controls received five 7-day cycles of 2% dextran sulfate sodium alternating with five 7-day cycles of water. Colonic tissue was formalin fixed for histological analysis and total RNA extracted for gene chip and SYBR green real-time polymerase chain reaction (PCR) analysis.

RESULTS

Histological analysis revealed increased distortion of crypt architecture in the dextran sulfate sodium-treated, IRF-1 -/- animals as compared to dextran sulfate sodium-treated wild-type animals. Five of 15 dextran sulfate sodium-treated IRF-1 -/- mice, but only one of 14 dextran sulfate sodium-treated wild-type mice, developed colonic dysplasia. Microarray analysis comparing colonic gene expression in IRF-1 -/- and wild-type animals revealed decreased expression of caspases, genes involved in antigen presentation, and tumor suppressor genes in the IRF-1 -/- animals. Increased expression of genes involved in carcinogenesis and immunoglobulin and complement genes was also noted in the knock-out animals.

CONCLUSIONS

Absence of IRF-1 is not protective in dextran sulfate sodium colitis.

Cancer immunoprevention

Immunoprevention is a fresh approach to cancer prevention based on the stimulation of the immune system before tumor onset. Immunoprevention was effective in various models of carcinogen-induced or autochthonous tumor progression. Vaccines made of cells or DNA plasmids combined with appropriate adjuvants completely blocked mammary carcinogenesis in HER-2/neu transgenic mice. At variance with cancer immunotherapy, the mediators of immunoprevention are antibodies and T-cell-derived cytokines, rather than cytotoxic T-cells. Immunopreventive approaches and chemoprevention with tamoxifen or cyclooxygenase-2 inhibitors can be combined advantageously. The success obtained in preclinical studies suggests that cancer immunoprevention should progress to clinical testing.

Immunological aspects of head and neck cancer: biology, pathophysiology and therapeutic mechanisms

Advanced cancer and head and neck cancer, in particular, remains a major clinical challenge with its associated morbidity and inevitable mortality. Local control of early disease is achievable in many solid tumours with current surgical and radiotherapeutic techniques but metastatic disease is associated with poor outcome and prognosis. It is known that, by the time of presentation, many patients will already have occult microscopic metastatic disease, and surgery and radiotherapy will not result in long-term survival. What little effect modern chemotherapeutic agents have on microscopic disease is, however, limited by systemic toxicity and multi-drug resistance. Immune surveillance is postulated to be operative in man. There is evidence, however, that patients with progressive tumour growth have failure of host defences both locally and systemically. Various possible defects and tumour escape mechanisms are discussed in the review. Immunotherapy and, in particular adoptive T cell therapy and DC therapy, show promise as putative tumour-specific therapy with clinical benefits. These techniques are undergoing development and evaluation in phase 1 clinical trials. Preliminary data suggest that the treatments are well tolerated. Unfortunately, there is limited evidence of significant and prolonged improvements in clinical outcome. Further developments of beneficial protocols (adjuvants, mode and frequency of vaccination etc) and multicentre studies of the use of immunotherapy in cancer are now required.

Coordinated downregulation of the antigen presentation machinery and HLA class I/beta2-microglobulin complex is responsible for HLA-ABC loss in bladder cancer

Downregulation of MHC class I expression is a widespread phenomenon used by tumor cells to escape antitumor T-cell-mediated immune responses. These alterations may play a role in the clinical course of the disease. The aim of our study was to investigate the molecular mechanism underlying the absence of HLA-class I molecule expression in bladder cancer cells. Microdissected tumor tissues were characterized by real-time quantitative PCR for the expression of HLA-ABC, beta2-microglobulin and the members of the antigen processing machinery (APM) of HLA class I molecules (LMP2, LMP7, TAP1, TAP2 and tapasin). Our results showed that irreversible HLA loss by mutations in the beta2-microglobulin gene was not the cause of low HLA class I expression in bladder cancers. In contrast, we observed a coordinated transcription downregulation of HLA-ABC and beta2-microglobulin and APM genes in microdissected tumor tissue derived from bladder carcinomas. This mechanism may represent a major factor for the downregulation of HLA class I expression and in the subsequent direct recognition of cancer cells by cytolytic T lymphocytes. Because this regulatory mechanism is frequently reversible by IFN-gamma treatment, we conclude that HLA class I expression should be a major consideration for immunotherapeutic purposes in patients with bladder cancer.

Epigenetic inactivation of class II transactivator (CIITA) is associated with the absence of interferon-gamma-induced HLA-DR expression in colorectal and gastric cancer cells

Tightly regulated at the level of transcription, expression of MHC class II molecules varies significantly among gastrointestinal cancers. High levels of MHC class II expression are often associated with a better prognosis, which is indicative of the involvement of CD4+ lymphocytes in tumor suppression, but the molecular mechanism by which MHC class II expression is regulated remains unclear. In the present study, we investigated the expression of one inducible MHC class II molecule, HLA-DR, and its coactivators in a panel of colorectal and gastric cancer cell lines. Interferon-gamma induced expression of HLA-DR in 14 of 20 cell lines tested; the remaining six cell lines did not express HLA-DR. Analysis of the expression of transcription factors and coactivators associated with HLA-DR revealed that the loss of CIITA expression was closely associated with the absence of HLA-DR induction. Moreover, DNA methylation of the 5' CpG island of CIITA-PIV was detected in all cancer cells that lacked CIITA. The methylation and resultant silencing of CIITA-PIV depended on the activities of two DNA methyltransferases, DNMT1 and DNMT3B, and their genetic inactivation restored CIITA-PIV expression. It thus appears that CIITA methylation is a key mechanism that enables some gastrointestinal cancer cells to escape immune surveillance.

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.

Systematic Comparison of Dendritic Cell-based Immunotherapeutic Strategies for Malignant Gliomas: In Vitro Induction of Cytolytic and Natural Killer-like T Cells

OBJECTIVE

To compare the efficacy of various immunotherapeutic strategies of loading dendritic cells (DCs) with whole-glioma cell antigens and characterize the effector responses induced.

METHODS

DCs were either fused with major histocompatibility complex (MHC)-matched glioma cells (Fusion) or pulsed with apoptotic tumor cells (DC/Apo), total tumor ribonucleic acid (RNA) (DC/RNA), or tumor lysate (DC/Lys). These tumor-DC preparations were then assessed for their phenotype, cytokine profile, and capacity to stimulate autologous peripheral blood mononuclear cells (PBMCs) in vitro. Phenotype and tumor-specific cytolytic activities of various effector cell populations were characterized and compared.

RESULTS

The various tumor-DC preparations exhibited similar phenotype and cytokine profiles irrespective of the method of loading tumor-cell antigens. However, the fusion, DC/Apo, and DC/RNA induced superior tumor cytolytic activities in PBMCs compared with DC/Lys or DC and tumor controls. DC/Apo induced the greatest expansion of tumor-specific lymphocytes, as detected by trypan blue exclusion and thymidine incorporation assays. Flow cytometric analyses also revealed the highest relative percentages of T helper cells (CD3+CD4+), cytotoxic T lymphocytes (CTLs) (CD3+CD8+), and natural killer (NK)-like T cells (CD3+CD56+) in the DC/Apo group among all the groups studied, indicating that DC/Apo induced expansion of PBMCs bearing multiple T and NK cell markers. Interestingly, isolated NK-like T cells demonstrated significantly higher tumor cytotoxicity compared with CTLs isolated from the same groups and was also non-MHC-restricted.

CONCLUSION

Apoptotic tumor cells may be an optimal source of whole-tumor-cell antigen for immunotherapy of gliomas. The study also demonstrates for the first time that both CTLs and NK-like T cells are expanded and stimulated by mature, tumor-pulsed DCs.

Enhanced antilymphoma efficacy of CD19-redirected influenza MP1-specific CTLs by cotransfer of T cells modified to present influenza MP1

To enhance the in vivo antitumor activity of adoptively transferred, CD19-specific chimeric antigen receptor (CAR)-redirected cytotoxic T lymphocytes (CTLs), we studied the effect of restimulating CAR(+) CTLs through their endogenous virus-specific T-cell antigen receptor (TcR) by the cotransfer of engineered T-cell antigen-presenting cells (T-APCs). Using influenza A matrix protein 1 (MP1) as a model antigen, we show that ex vivo-expanded CD4(+) and CD8(+) T-APCs expressing a hygromycin phosphotransferase-MP1 fusion protein (HyMP1) process and present MP1 to autologous human leukocyte antigen (HLA)-restricted, MP1-specific CD4(+) and CD8(+) CTL precursors. The MP1-specific CTLs are amenable to subsequent genetic modification to express a CD19-specific CAR, designated CD19R, and acquire HLA-unrestricted reactivity toward CD19(+) leukemia and lymphoma tumor targets while maintaining HLA-restricted MP1 specificity. The restimulation of MP1xCD19 dual-specific CTLs in vivo by the adoptive transfer of irradiated HyMP1(+) T-APCs resulted in the enhanced antilymphoma potency of bispecific effector cells, as measured by elimination of the biophotonic signal of established firefly luciferase-expressing Burkitt lymphoma xenografts in nonobese diabetic/severe combined immunodeficiency (NOD/scid) animals compared with control groups restimulated by Hy(+)MP1(neg) T-APCs. Engineered T-APCs are a novel and versatile antigen-delivery system for generating antigen-specific T cells in vitro and enhancing the in vivo effector functioning of CAR-redirected antitumor effector cells.

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.

Dendritic Cell-Based Immunotherapy of Malignant Gliomas

The failure of conventional treatment modalities for gliomas, in spite of tremendous progress in research in the past two decades, has led to increasing interest in alternative treatment strategies, including immunotherapy. It has become evident that vaccination with dendritic cells (DC), designed to express tumor antigens, is a potent strategy to elicit anti-tumor immune response in both pre-clinical and clinical settings. Various methods have been applied in order to induce DC to express tumor antigens including: pulsing with isolated tumor peptides or whole tumor lysate; fusion with tumor cells; and pulsing with apoptotic tumor cells. Herein, we review the recent progress in DC biology with regard to tumor immunity and discuss current DC-based strategies and future prospects in immunotherapy for malignant gliomas.

Walker 256 tumor MHC class I expression during the shift from A variant to the immunogenic AR variant

Novel tumor cell variants can be obtained by serially passaging tumor cells in different media and/or environments. Serial intraperitoneal (ip) passages of the Walker 256 tumor A variant was followed for studying the generation of its regressive AR variant. MHC class I molecule expression was assessed since variations in this molecule would explain changes in tumor cell immunogenicity and therefore, the shift from progressive A variant to the regressive AR variant. Within 25 ip passages all serial repetitions shifted from A to AR variant, which was characterized by a significant increase in red blood cell (RBC) osmotic fragility with marked spleen hypertrophy in the host. In one serial repetition AR tumor cells were rejected (ip passage number 36) and immunity against the AR and A variants was conferred. Flow cytometry analysis showed a significant increase in the number MHC class I positive cells in AR variant (n = 15, 14.21 +/- 1.32) compared with A variant (n = 10, 9.10 +/- 1.22). These data provide evidence that the generation of the AR variant could result from factors present in the ip environment leading to an increase in the number of Walker 256 MHC class I positive tumor cells, probably due to immune selection of MHC class I negative tumor cells.

Distribution of HLA class I altered phenotypes in colorectal carcinomas: high frequency of HLA haplotype loss associated with loss of heterozygosity in chromosome region 6p21

HLA class I loss or down-regulation is a widespread mechanism used by tumor cells to avoid tumor recognition by cytotoxic T lymphocytes, and thus favor tumor immune escape. Multiple mechanisms are responsible for these HLA class I alterations. In different epithelial tumors, loss of heterozygosity (LOH) at chromosome region 6p21.3, leading to HLA haplotype loss, occurs in 6-50% of all cases depending on the tumor entity. In this paper we report the frequency of LOH at 6p21 in 95 colorectal carcinomas (CRC) previously analyzed for altered HLA class I expression with immunohistological techniques. We used PCR microsatellite amplification of selected STR markers located on Chromosome 6 to identify LOH with DNA from microdissected tumor tissues and the surrounding stroma. Sequence-specific oligonucleotide analysis was performed in microdissected stroma and tumor cells for HLA typing, and to detect HLA haplotype loss. A high frequency (40%) of HLA haplotype loss was found in CRC. Eight tumors showed microsatellite instability. We sometimes observed two or more mechanisms responsible for HLA alteration within the same HLA-altered phenotype, such as LOH and HLA class I total loss. In 25 tumors (26%) no HLA class I alteration could be identified. These data are potentially relevant for CRC patients undergoing T-cell-based immunotherapy.

Anaplastic lymphoma kinase proteins in growth control and cancer

The normal functions of full-length anaplastic lymphoma kinase (ALK) remain to be completely elucidated. Although considered to be important in neural development, recent studies in Drosophila also highlight a role for ALK in gut muscle differentiation. Indeed, the Drosophila model offers a future arena for the study of ALK, its ligands and signalling cascades. The discovery of activated fusion forms of the ALK tyrosine kinase in anaplastic large cell lymphoma (ALCL) has dramatically improved our understanding of the pathogenesis of these lymphomas and enhanced the pathological diagnosis of this subtype of non-Hodgkin's lymphoma (NHL). Likewise, the realisation that a high percentage of inflammatory myofibroblastic tumours express activated-ALK fusion proteins has clarified the causation of these mesenchymal neoplasms and provided for their easier discrimination from other mesenchymal-derived inflammatory myofibroblastic tumour (IMT) mimics. Recent reports of ALK expression in a range of carcinoma-derived cell lines together with its apparent role as a receptor for PTN and MK, both of which have been implicated in tumourigenesis, raise the possibility that ALK-mediated signalling could play a role in the development and/or progression of a number of common solid tumours. The therapeutic targeting of ALK may prove to have efficacy in the treatment of many of these neoplasms.

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.

Dynamic response of cancer under the influence of immunological activity and therapy

The dynamical basis of tumoral growth has been controversial. Many models have been proposed to explain cancer development. The descriptions employ exponential, potential, logistic or Gompertzian growth laws. Some of these models are concerned with the interaction between cancer and the immunological system. Among other properties, these models are concerned with the microscopic behavior of tumors and the emergence of cancer. We propose a modification of a previous model by Stepanova, which describes the specific immunological response against cancer. The modification consists of the substitution of a Gompertian law for the exponential rate used for tumoral growth. This modification is motivated by the numerous works confirming that Gompertz's equation correctly describes solid tumor growth. The modified model predicts that near zero, tumors always tend to grow. Immunological contraposition never suffices to induce a complete regression of the tumor. Instead, a stable microscopic equilibrium between cancer and immunological activity can be attained. In other words, our model predicts that the theory of immune surveillance is plausible. A macroscopic equilibrium in which the system develops cancer is also possible. In this case, immunological activity is depleted. This is consistent with the phenomena of cancer tolerance. Both equilibrium points can coexist or can exist without the other. In all cases the fixed point at zero tumor size is unstable. Since immunity cannot induce a complete tumor regression, a therapy is required. We include constant-dose therapies and show that they are insufficient. Final levels of immunocompetent cells and tumoral cells are finite, thus post-treatment regrowth of the tumor is certain. We also evaluate late-intensification therapies which are successful. They induce an asymptotic regression to zero tumor size. Immune response is also suppressed by the therapy, and thus plays a negligible role in the remission. We conclude that treatment evaluation should be successful without taking into account immunological effects.