The immune system--is it relevant to cancer development, progression and treatment?

The ability of the immune system to effectively respond to human tumours is a matter of long-term controversy. There is an increasing body of recent evidence to support a role for the immune system in eliminating pre-clinical cancers, an old concept termed 'immunosurveillance'. 'Immunoediting' is an updated hypothesis, in which selection pressures applied by the immune response to tumours modulate tumour immunogenicity and growth. Tumour infiltration by immune cells has been shown to have powerful prognostic significance in a host of cancer types. Paradoxically, in some circumstances the immune system can promote tumour development. Cytotoxic therapies, including radiotherapy and chemotherapy, induce potentially immunogenic cell death, releasing tumour-associated antigens in the context of a 'danger' signal to the immune system. An understanding of the interaction between immune cells, tumour cells and treatment modalities will therefore guide the future combination of immunotherapy with conventional therapy to achieve optimal anti-tumour effects.     

Tumour-mediated TRAIL-Receptor expression indicates effective apoptotic depletion of infiltrating CD8+ immune cells in clinical colorectal cancer

Expression of apoptosis-related proteins on tumour cells has been shown in several experimental models to be an efficient mechanism for a counterattack against host anti-tumour immune responses in solid tumours. Here we provide a clinical evidence for such a tumour immune escape mechanism by demonstrating tumour to T cell-directed death receptor signalling (TRAIL/TRAIL-Receptor (TRAIL-R)) in colorectal cancer (CRC). In a series of patients with CRC and completed 5-year follow up, we investigated apoptosis and expression levels of apoptosis-related proteins. Gene and protein profiles in the tumours demonstrated intratumoural upregulated gene expression for Fas, Fas-L, TRAIL, TRAIL-R and TNF-α (RT-qPCR). Levels of terminaldeoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick-end labelling (TUNEL)-positive events were positively correlated with TRAIL-R1-expression on tumour infiltrating immune cells. Among the immune cells, preferentially CD8+ T cells were found to express TRAIL-R1 while serial immunostaining in the same patient tumours showed abundant apoptotic (TUNEL-positive) immune cells. In conclusion, our results in tumour samples from CRC patients suggest TRAIL-R1-mediated apoptotic depletion of infiltrating immune cells (CD8+) in response to TRAIL expression by the tumour itself. This supports the notion of an efficient escape from tumour immune response and thus evasion from the attack of activated CD8+ T cells. These findings may enhance our understanding of tumour progression in CRC and might be helpful for the development of TRAIL and its death receptor-based therapy.     

Radiostrontium-induced oncogenesis and the role of immunosuppression. II. Influence of 90Sr dose, adult thymectomy and antilymphocyteglobulin treatment on the development of lympho-reticular and extraskeletal, neoplastic lesions in CBA mice

The significance of depressed immune function for the development and progression of tumours induced by 90Sr (mainly osteosarcomas and malignant lymphomas) was investigated in a series of experiments by comparing the tumour responses in normal mice with those in immunocompromised mice. The present paper (part II) reports on lympho-reticular (LR) and extraskeletal neoplastic lesions in male CBA/SU mice after exposure to different single doses of 90Sr with or without additional immunosuppression by adult thymectomy (ATx) and/or prolonged antilymphocyteglobulin (ALG) treatment. Neoplastic lesions in bone were reported in part I. The status of the animal's immune system and responsive ability were examined in parallel experiments. The tumour yields were analysed in relation to the dosage of 90Sr and the immunosuppressive treatments employed. Although the incidences and latency times of induced tumours were clearly dose-dependent, they were never significantly influenced by ATx/ALG treatments. Thus, no substantial support was gained for the theory that the immune system plays a controlling or modifying role in 90Sr carcinogenesis. The results, which are in agreement with the bone tumour responses, suggest that 90Sr induced tumours either do not express the antigens necessary for immune rejection or that the decline in immune responsiveness induced by ATx/ALG was of little consequence for tumour development and spread. The pathogenesis of 90Sr induced malignant lymphomas (MLs) and their immunophenotypes are discussed.     

Cell subpopulations dispersed from solid tumours and separated by centrifugal elutriation.

The degree of non-neoplastic host-cell infiltration was assessed in 3 in vivo-in vitro tumour models commonly used in radiobiological studies: EMT6/Ro mammary carcinoma, 9L/Ro tumour and KHT sarcoma. While the 2 former tumour models have been shown to be moderately to highly immunogenic when grown s.c., the KHT sarcoma is apparently non-immunogenic. Using differential staining on single-cell suspensions from enzymatically dissociated solid tumours, all 3 tumour types were found to contain large proportions (30-60%) of non-neoplastic host cells. The actual host-cell component found in the cell suspensions differed both in type and percentage for the 3 tumours studied. These host and neoplastic cells in the cell suspensions prepared from the solid tumours could be readily separated by centrifugal elutriation. After separation the clonogenic potential of the neoplastic cells was assessed, and was found to be higher than the clonogenic capacity of the unseparated cell suspension by a factor directly related to the host/neoplastic cell ratio. Even after the removal of the host cells, the clonogenic capacities of the neoplastic EMT6 and 9L tumour cells were lower than that of the corresponding in vitro sublines (approximately 30 vs 75%). However, in the KHT sarcoma the removal of the host cell component raised the plating efficiency to approximately 60%, which was similar to the value for the in vitro cell subline of this tumour.     

Galectins as modulators of tumour progression

Galectins are a family of animal lectins with diverse biological activities. They function both extracellularly, by interacting with cell-surface and extracellular matrix glycoproteins and glycolipids, and intracellularly, by interacting with cytoplasmic and nuclear proteins to modulate signalling pathways. Current research indicates that galectins have important roles in cancer; they contribute to neoplastic transformation, tumour cell survival, angiogenesis and tumour metastasis. They can modulate the immune and inflammatory responses and might have a key role helping tumours to escape immune surveillance. How do the different members of the Galectin family contribute to these diverse aspects of tumour biology?     

Engineering T cells for cancer therapy

It is generally accepted that the immune system plays an important role in controlling tumour development. However, the interplay between tumour and immune system is complex, as demonstrated by the fact that tumours can successfully establish and develop despite the presence of T cells in tumour. An improved understanding of how tumours evade T-cell surveillance, coupled with technical developments allowing the culture and manipulation of T cells, has driven the exploration of therapeutic strategies based on the adoptive transfer of tumour-specific T cells. The isolation, expansion and re-infusion of large numbers of tumour-specific T cells generated from tumour biopsies has been shown to be feasible. Indeed, impressive clinical responses have been documented in melanoma patients treated with these T cells. These studies and others demonstrate the potential of T cells for the adoptive therapy of cancer. However, the significant technical issues relating to the production of natural tumour-specific T cells suggest that the application of this approach is likely to be limited at the moment. With the advent of retroviral gene transfer technology, it has become possible to efficiently endow T cells with antigen-specific receptors. Using this strategy, it is potentially possible to generate large numbers of tumour reactive T cells rapidly. This review summarises the current gene therapy approaches in relation to the development of adoptive T-cell-based cancer treatments, as these methods now head towards testing in the clinical trial setting.     

Positive and negative influences of regulatory T cells on tumour immunity

Clinicians and scientists have long questioned whether the immune system has a role in destroying cancerous tissue. Studies performed in animal models have, however, recently revealed that the immune system can, at least in principle, effectively control tumours. In parallel with these findings, a large body of evidence indicates that although the immune system has the capacity to control tumours, there are also regulatory mechanisms that subdue these responses. A major challenge of tumour immunotherapy, therefore, is to find ways of disabling these regulatory functions while restoring or priming any immune responses that are protective.     

Oncolytic Viruses and Hematological Malignancies: A New Class of Immunotherapy Drugs

The use of viruses for tumour treatment has been imagined more than one hundred years ago, when it was reported that viral diseases were occasionally leading to a decrease in neoplastic lesions. Oncolytic viruses (OVs) seem to have a specific tropism for tumour cells. Previously, it was hypothesised that OVs’ antineoplastic actions were mainly due to their ability to contaminate, proliferate and destroy tumour cells and the immediate destructive effect on cells was believed to be the single mechanism of action of OVs’ action. Instead, it has been established that oncolytic viruses operate via a multiplicity of systems, including mutation of tumour milieu and a composite change of the activity of immune effectors. Oncolytic viruses redesign the tumour environment towards an antitumour milieu. The aim of our work is to evaluate the findings present in the literature about the use of OVs in the cure of haematological neoplastic pathologies such as multiple myeloma, acute and chronic myeloid leukaemia, and lymphoproliferative diseases. Further experimentations are essential to recognize the most efficient virus or treatment combinations for specific haematological diseases, and the combinations able to induce the strongest immune response.     

Gut microbiota and immune system in liver cancer: Promising therapeutic implication from development to treatment

Liver cancer is a leading cause of death worldwide, and hepatocellular carcinoma (HCC) is the most frequent primary liver tumour, followed by cholangiocarcinoma. Notably, secondary tumours represent up to 90% of liver tumours. Chronic liver disease is a recognised risk factor for liver cancer development. Up to 90% of the patients with HCC and about 20% of those with cholangiocarcinoma have an underlying liver alteration. The gut microbiota-liver axis represents the bidirectional relationship between gut microbiota, its metabolites and the liver through the portal flow. The interplay between the immune system and gut microbiota is also well-known. Although primarily resulting from experiments in animal models and on HCC, growing evidence suggests a causal role for the gut microbiota in the development and progression of chronic liver pathologies and liver tumours. Despite the curative intent of “traditional” treatments, tumour recurrence remains high. Therefore, microbiota modulation is an appealing therapeutic target for liver cancer prevention and treatment. Furthermore, microbiota could represent a non-invasive biomarker for early liver cancer diagnosis. This review summarises the potential role of the microbiota and immune system in primary and secondary liver cancer development, focusing on the potential therapeutic implications.     

Forty years of cancer modelling in the mouse

Mouse models of human cancer have played an important role in formulating modern concepts of multistage carcinogenesis, and are providing us with a new armoury of tools for the testing of novel therapeutic approaches to cancer treatment. The development of inducible and conditional technologies provide us with greater opportunity to generate mouse models which faithfully recapitulate human tumorigenesis, in terms of both the biology and the genetics of this disease. It is now feasible to control, in time and space, the development of tumours in almost any mouse tissue, such that we now have available mouse models of all major human cancers. Moreover, novel non-invasive approaches to tumour imaging will enable us to follow tumour development and metastasis in vivo, as well as the effects of candidate therapeutic drugs. Such new generation tumour models, which accurately emulate the disease state in situ, should provide a useful platform with which to experimentally test drugs targeted to specific gene products, or combinations of genes that control rate-limiting steps of tumour development.     

Thermal regulation of lymphocyte trafficking: Hot spots of the immune response

Lymphocytes use extensive vascular networks to traffic to various destinations in the body, including lymphoid organs and extra-lymphoid tissues. This discussion will focus on the emerging evidence that thermal stress regulates the traffic signals that direct the exit of lymphocytes from the vascular freeway. This issue is particularly relevant to T cell-based cancer immunotherapy where delivery of immune effector lymphocytes to neoplastic lesions depends on their extravasation across tumour micro-vessels. Although tumours are frequently highly vascularized by vessels that are competent to support blood flow, the tumour micro-environment has been characterized as non-permissive to lymphocyte extravasation. This may lead to a scenario where limited leukocyte infiltration at tumour sites correlates with a poor prognosis. These observations support the thesis that adjuvant strategies that promote trafficking of tumour-reactive cytolytic leukocytes to tumour sites have the potential to improve the efficacy of immune-based cancer therapy.     

Adult human mesenchymal stem cell as a target for neoplastic transformation

The neoplastic process may involve a cancer stem cell. This concept has emerged largely from the careful analysis of tumour biopsy systems from haematological, breast and brain tumours. However, the experimental systems necessary to provide the cellular and molecular evidence to support this important concept have been lacking. We have used adult mesenchymal stem cells (hMSC) transduced with the telomerase hTERT gene to investigate the neoplastic potential of adult stem cells. The hTERT-transduced line, hMSC-TERT20 at population doubling level (PDL) 256 showed loss of contact inhibition, anchorage independence and formed tumours in 10/10 mice. hMSC-TERT4 showed loss of contact inhibition at PDL 95, but did not exhibit anchorage independence and did not form tumours in mice. Both lines had a normal karyotype but showed deletion of the Ink4a/ARF locus. At later passage, hMSC-TERT4 also acquired an activating mutation in KRAS. In hMSC-TERT20, expression of the cell cycle-associated gene, DBCCR1 was lost due to promoter hypermethylation. This epigenetic event correlated with acquisition of tumorigenicity. These data suggest that the adult hMSCs can be targets for neoplastic transformation and have implications for the development of novel anticancer therapeutics and for the use of hMSC in tissue engineering and transplantation protocols.     

Thermal regulation of lymphocyte trafficking: hot spots of the immune response.

Lymphocytes use extensive vascular networks to traffic to various destinations in the body, including lymphoid organs and extra-lymphoid tissues. This discussion will focus on the emerging evidence that thermal stress regulates the traffic signals that direct the exit of lymphocytes from the vascular freeway. This issue is particularly relevant to T cell-based cancer immunotherapy where delivery of immune effector lymphocytes to neoplastic lesions depends on their extravasation across tumour micro-vessels. Although tumours are frequently highly vascularized by vessels that are competent to support blood flow, the tumour micro-environment has been characterized as non-permissive to lymphocyte extravasation. This may lead to a scenario where limited leukocyte infiltration at tumour sites correlates with a poor prognosis. These observations support the thesis that adjuvant strategies that promote trafficking of tumour-reactive cytolytic leukocytes to tumour sites have the potential to improve the efficacy of immune-based cancer therapy.     

Genetic and molecular aspects of human multigenerational carcinogenesis

The notion that cancer is a genetic disease has gained increasing credence from the now numerous studies in which specific alterations of chromosome and of gene structure and activity in a variety of cancers have been identified, and, in particular, with the increasing awareness of the heritability of factors that predispose to the development of early, specific cancers in the offspring of parents carrying these predisposing genes. That the inheritance of a single allele is a major causal factor in certain childhood cancers, e.g., retinoblastoma and Wilms' tumour, has long been known, and the locations of the genes predisposing to these tumours have been mapped and at least one has been isolated. Over the past year, using genetic analysis, a further five different loci have been mapped that are involved in five other inherited cancer predispositions. Moreover, in most of these cases the evidence again suggests that one of the pair of alleles at the locus linked to the predisposition undergoes somatic mutation (loss) within the cells that give rise to each of these tumours. A major factor in the origin of these tumours therefore is a loss of a tumour suppressing role of the loci in question. At the present time, seven such suppressor loci on six different chromosomes have been identified, and in a number of cases evidence has been presented for the occurrence of other specific genetic changes that may be necessary for the emergence of a neoplasm. Specific gene or chromosome loss is, however, not confined to cancers associated with the inheritance of a single gene but is increasingly being observed in various more common sporadic cancers, and these data are reviewed and some new data presented. Studies on sporadic cancers have revealed a wide range of different oncogenes in which mutation or abnormal regulation is a cardinal factor leading to a neoplastic state. The products of many of these oncogenes have homologies to growth factors, growth factor receptors or are signal or DNA binding proteins, and specific mutations have been characterized in a number of e-oncogenes in neoplastic human cells. In contrast to genes which may suppress neoplasia, the c-oncogenes act as positive factors, although the presence of a single mutated oncogene is not sufficient on its own to result in neoplastic transformation.(ABSTRACT TRUNCATED AT 400 WORDS)     

An integrative hypothesis about the origin and development of sporadic and familial breast cancer subtypes

Do breast cancer tumours have a common cell origin? Do different breast cancer molecular phenotypes arise from distinct cell types? The studies we have performed during the last few years in familial breast tumours (BRCA1, BRCA2 and non-BRCA1/2) widen questions about the development of sporadic breast cancer to hereditary breast cancer. Array-comparative genomic hybridisation (CGH) studies show universal genomic aberrations in both familial and sporadic breast cancer subtypes that may be selected in the breast tumour development. The inactivation of BRCA1 seems to play a critical role in oestrogen receptor (ER)-negative cancer stem cells (CSCs), driving the tumour development mostly towards a basal-like or, in some cases, to a luminal B phenotype, but other carcinogenetic events are proposed to explain the remaining tumour subtypes. The existence of common genomic alterations in basal-like, ERBB2 and luminal B breast tumours may suggest a common cell origin or clonal selection of these tumour subtypes, arising from an ER-negative CSC or from a progenitor cell (PC). Finally, specific genomic aberrations in ER-positive tumours could provide cellular proliferation advantages when the cells are exposed to oestrogen. We propose a combination of the CSC hypothesis (for the carcinogenesis processes) and the clonal selection model (in terms of tumour development). We uphold that the basal-like-, ERBB2- and luminal B-sporadic and familial tumour subtypes have an ER-negative breast stem/PC origin, whereas luminal A tumours arise from an ER-positive PC, supporting a hierarchical breast carcinogenesis model, whereas crucial genomic imbalances are clonally selected during the tumour development.     

How tumours escape mass destruction

It is now well established that the immune system can control neoplastic development and growth in a process termed immunosurveillance. A link between host immunosurveillance and neoplastic progression is revealed in cases where the immune response becomes compromised due to genetic or other pathological conditions, resulting in a substantially increased incidence and rate of spontaneous tumour formation in both preclinical animal models and patients. It has also been demonstrated in tumour-bearing hosts that the tumorigenic process itself can promote a state of immunosuppression that, in turn, facilitates neoplastic progression. The ability of neoplastic populations to induce a hostile microenvironment through both cell contact-dependent and -independent immunosuppressive networks is a significant barrier to effective cell-mediated immunity and immunotherapy. Thus, a competent immune system is integral for the control of neoplastic disease, and dissecting the plethora of tumour escape mechanisms that disrupt this essential host defense capability is integral for the development of effective immunotherapeutic paradigms.     

Monoclonal antibodies in oncology

Monoclonal antibodies (MCAs) can be used to differentiate between normal and neoplastic cells and thus exploited for diagnostic and, ultimately, therapeutic gain. The evidence for the existence of human tumour antigens is reviewed. Several areas of diagnosis are already benefiting from the application of the monoclonal technology. Immunohistology can help the pathologist with difficult diagnostic problems. New classifications of lymphoma and leukaemia can be based on specific surface molecules. Similarly, the detection of shed tumour antigens is already established as part of the routine assessment of many patients with common solid tumours. Isotopically labelled monoclonal antibodies have been used to localise primary and metastatic tumours. The use of antibodies in this way is not only a promising diagnostic tool but also the first step in studying the possibility of arming antibodies to provide therapeutic agents. Such trials are currently in progress.     

Immune-refractory cancers and their little helpers—An extended role for immunetolerogenic MHC molecules HLA-G and HLA-E?

There is strong evidence to support a role for non-classical MHC class I (class Ib) molecules, most notably HLA-E and HLA-G in tumour immune escape. In this article, we summarize the current knowledge on their expression, regulation and functional relevance in various malignancies, particularly brain tumours. Special emphasis is devoted to the phenomenon that these tolerogenic molecules are expressed by non-transformed cells that are found in close neighborhood to tumour cells representing either parenchymal cells or immune cells attracted to the tumour microenvironment. Here they may act as “natural” or “inducible” suppressors of anti-tumoural immune responses. We thus speculate about the role of HLA-G expressing T cells, a novel population of natural regulatory cells that was identified recently. It is suggested that various cell types within a tumour cooperate in order to inhibit anti-tumour immunity—and that immunetolerogenic HLA-G may play a major role in this context.     

IL2 treatment for cancer: from biology to gene therapy.

In this review we shall discuss the biological rationale and the clinical findings obtained using Interleukin 2 (IL2)-based immunotherapy in the management of cancer patients. Objective and long-lived clinical responses have been documented in a proportion of cases, particularly renal cell carcinoma, melanoma and acute myeloid leukaemia. Though encouraging, the clinical use of IL2 has so far been limited by toxicity, as well as by the heterogeneous and unpredictable responses and by the lack of specific anti-tumour effect. These considerations have led to the belief that more sophisticated technologies aimed at introducing the IL2 gene into the neoplastic cells may potentially overcome some of the limitations coupled to the in vivo infusion of high doses of IL2. The data accumulated in animal models and, more recently, also with human tumour cells indicate that the IL2 gene may be successfully inserted into neoplastic cells. The constitutive secretion of IL2 by the tumour cells leads to a reduced or abrogated tumorigenicity in several different tumour models. The evidence that in some experimental tumours the transduction of the IL2 gene into the neoplastic cells may elicit a specific cytotoxic response and confer anti-tumour memory, suggests that vaccination protocols based on this innovative strategy may represent a potential new tool in the management of cancer patients.     

Cell types expressing the Wilms' tumour gene (WT1) in Wilms' tumours: implications for tumour histogenesis.

Wilms' tumour (nephroblastoma), a childhood embryonal kidney tumour, is believed to arise from malignant transformation of abnormally persistent metanephric blastemal cells. At a histological level, tumours show a remarkable mimicry of the normal nephrogenic pathway. There is histological and epidemiological evidence for at least two pathogenetic groupings within Wilms' tumour which may reflect different timings of the tumorigenic insult in this pathway and/or involvement of different genes. Tumorigenesis is thought to result from loss of function of a so-called tumour-suppressor gene which has an essential role in control of normal genitourinary development. Such a candidate, Wilms' tumour gene (WT1) mapping to chromosome 11p13, has been isolated and is known to be mutated in some tumours. We have examined the cell types expressing this gene in 32 Wilms' tumours and in nephroblastomatosis by in situ mRNA hybridization. Our results show that WT1 is expressed only in neoplastic structures whose normal counterparts also express the gene and that abnormally persistent high levels of expression are common in both these lesions. Thus, WT1 expression is a good marker for tumour differentiation and reveals how the normal pattern of differentiation is disrupted in Wilms' tumours. We postulate that mutation of the WT1 gene at the 11p13 locus results in Wilms' tumours associated with intralobar nephrogenic rests, which frequently show stromal-predominant histology. We have used our results and ideas to reinterpret current theories on tumour histogenesis and propose a model which explains how patterns of epithelial differentiation are disrupted in Wilms' tumour and how malignant stroma can result from mutation in WT1.