A critical analysis of the tumour immunosurveillance controversy for 3-MCA-induced sarcomas

The Naked Mole-Rat as a Model for Healthy Aging

Naked mole-rats (NMRs, Heterocephalus glaber) are the longest-lived rodents with a maximum life span exceeding 37 years. They exhibit a delayed aging phenotype and resistance to age-related functional decline/diseases. Specifically, they do not display increased mortality with age, maintain several physiological functions until nearly the end of their lifetime, and rarely develop cancer and Alzheimer's disease. NMRs live in a hypoxic environment in underground colonies in East Africa and are highly tolerant of hypoxia. These unique characteristics of NMRs have attracted considerable interest from zoological and biomedical researchers. This review summarizes previous studies of the ecology, hypoxia tolerance, longevity/delayed aging, and cancer resistance of NMRs and discusses possible mechanisms contributing to their healthy aging. In addition, we discuss current issues and future perspectives to fully elucidate the mechanisms underlying delayed aging and resistance to age-related diseases in NMRs.

Immunology of Canine Melanoma

Malignant melanoma is one of the most important tumors in dogs and is highly metastatic and aggressive disease. In recent years, molecular knowledge regarding canine melanoma has increased, and some chromosomal imbalances and tyrosine kinase pathways have been identified to be dysregulated. Mxoreover, canine melanoma is an immunogenic tumor that provides opportunities to administer immunotherapy to the patient. Podoplanin and chondroitin sulfate proteoglycan-4 (CSPG4) are markers against which monoclonal antibodies have been developed and tested in dogs in vivo with promising results. Owing to the importance of canine melanoma in the veterinary oncology field, this chapter reviews the most important aspects related to immunological involvement in the prognosis and treatment of canine melanoma.

Novel Mouse Models for Cancer Immunology

Mouse models for the study of cancer immunology provide excellent systems in which to test biological mechanisms of the immune response against cancer. Historically, these models have been designed to have different strengths based on the current major research questions at the time. As such, many mouse models of immunology used today were not originally developed to study questions currently plaguing the relatively new field of cancer immunology, but instead have been adapted for such purposes. In this review, we discuss various mouse model of cancer immunology in a historical context as a means to provide a fuller perspective of each model's strengths. From this outlook, we discuss the current state of the art and strategies for tackling future modeling challenges.

A mathematical model for treatment using chemo-immunotherapy

In this study, we investigated a mathematical model for chemoimmunotherapy (a combination of chemotherapy and immunotherapy) for brain cancer. In most cases, the standard protocol for cancer treatment is fixed in terms of treatment time intervals and dosages. We offer a wide range of non-fixed protocols, which essentially vary in terms of time intervals and dosages (i.e., personalised medicine). The functions that describe this treatment are explicit and analytical. Hence, the parameters of the function can be easily changed and a new protocol can be obtained. We compared different protocols and obtained an optimal solution. In addition, we applied the singular perturbed vector field (SPVF) method to determine the hierarchy of the system of equations, which enabled us to identify the equilibrium points of the mathematical model and investigate their stability.

Resistance to chemical carcinogenesis induction via a dampened inflammatory response in naked mole-rats

Naked mole-rats (NMRs) have a very low spontaneous carcinogenesis rate, which has prompted studies on the responsible mechanisms to provide clues for human cancer prevention. However, it remains unknown whether and how NMR tissues respond to experimental carcinogenesis induction. Here, we show that NMRs exhibit extraordinary resistance against potent chemical carcinogenesis induction through a dampened inflammatory response. Although carcinogenic insults damaged skin cells of both NMRs and mice, NMR skin showed markedly lower immune cell infiltration. NMRs harbour loss-of-function mutations in RIPK3 and MLKL genes, which are essential for necroptosis, a type of necrotic cell death that activates strong inflammation. In mice, disruption of Ripk3 reduced immune cell infiltration and delayed carcinogenesis. Therefore, necroptosis deficiency may serve as a cancer resistance mechanism via attenuating the inflammatory response in NMRs. Our study sheds light on the importance of a dampened inflammatory response as a non-cell-autonomous cancer resistance mechanism in NMRs.

Naked mole rats are found to be resistant to cancer development through dampened inflammatory response due to genetically determined impaired necroptosis, with essential necroptosis genes RIPK3 and MLKL containing mutations causing premature stop codons.

Type 1 Innate Lymphoid Cells Limit the Antitumoral Immune Response

Natural killer (NK) cells are known to be able to kill established tumor cell lines, but important caveats remain regarding their roles in the detection and elimination of developing primary tumors. Using a genetic model of selective ILC1 and NK cell deficiency, we showed that these cells were dispensable for tumor immunosurveillance and immunoediting in the MCA-induced carcinogenesis model. However, we were able to generate primary cell lines derived from MCA-induced tumors with graded sensitivity to NK1.1⁺ cells (including NK cells and ILC1). This differential sensitivity was associated neither with a modulation of intratumoral NK cell frequency, nor the capacity of tumor cells to activate NK cells. Instead, ILC1 infiltration into the tumor was found to be a critical determinant of NK1.1⁺ cell-dependent tumor growth. Finally, bulk tumor RNAseq analysis identified a gene expression signature associated with tumor sensitivity to NK1.1⁺ cells. ILC1 therefore appear to play an active role in inhibiting the antitumoral immune response, prompting to evaluate the differential tumor infiltration of ILC1 and NK cells in patients to optimize the harnessing of immunity in cancer therapies.

Decoupling tumor cell metastasis from growth by cellular pilot protein TNFAIP8

Cancer metastasis accounts for nearly 90% of all cancer deaths. Metastatic cancer progression requires both cancer cell migration to the site of the metastasis and subsequent proliferation after colonization. However, it has long been recognized that cancer cell migration and proliferation can be uncoupled; but the mechanism underlying this paradox is not well understood. Here we report that TNFAIP8 (tumor necrosis factor-α-induced protein 8), a "professional" transfer protein of phosphoinositide second messengers, promotes cancer cell migration or metastasis but inhibits its proliferation or cancer growth. TNFAIP8-deficient mice developed larger tumors, but TNFAIP8-deficient tumor cells completely lost their ability to migrate toward chemoattractants and were defective in colonizing lung tissues as compared to wild-type counterparts. Mechanistically, TNFAIP8 served as a cellular "pilot" of tumor cell migration by locally amplifying PI3K-AKT and Rac signals on the cell membrane facing chemoattractant; at the same time, TNFAIP8 also acted as a global inhibitor of tumor cell growth and proliferation by regulating Hippo signaling pathway. These findings help explain the migration-proliferation paradox of cancer cells that characterizes many cancers.

Using methylcholanthrene-induced fibrosarcomas to study tumor immunology

Mouse models of cancer are essential in furthering our understanding both of the mechanisms that drive tumor development and the immune response that develops in parallel, and also in providing a platform for testing novel anti-cancer therapies. The majority of solid tumor models available rely on the injection of existing cancer cell lines into naïve hosts which, while providing quick and reproducible model systems, typically lack the development of a tumor microenvironment that recapitulates those seen in human cancers. Administration of the carcinogen 3-methylcholanthrene (MCA), allows tumors to develop in situ, forming a tumor microenvironment with an established stroma and vasculature. This article provides a detailed set of protocols for the administration of MCA into mice and the subsequent monitoring of tumors. Protocols are also provided for some of the routinely used downstream applications that can be used for MCA tumors.

Tumor-Derived Retinoic Acid Regulates Intratumoral Monocyte Differentiation to Promote Immune Suppression

The immunosuppressive tumor microenvironment (TME) is a major barrier to immunotherapy. Within solid tumors, why monocytes preferentially differentiate into immunosuppressive tumor-associated macrophages (TAMs) rather than immunostimulatory dendritic cells (DCs) remains unclear. Using multiple murine sarcoma models, we find that the TME induces tumor cells to produce retinoic acid (RA), which polarizes intratumoral monocyte differentiation toward TAMs and away from DCs via suppression of DC-promoting transcription factor Irf4. Genetic inhibition of RA production in tumor cells or pharmacologic inhibition of RA signaling within TME increases stimulatory monocyte-derived cells, enhances T cell-dependent anti-tumor immunity, and synergizes with immune checkpoint blockade. Furthermore, an RA-responsive gene signature in human monocytes correlates with an immunosuppressive TME in multiple human tumors. RA has been considered as an anti-cancer agent, whereas our work demonstrates its tumorigenic capability via myeloid-mediated immune suppression and provides proof of concept for targeting this pathway for tumor immunotherapy.

Loss of HIF-1α in macrophages attenuates AhR/ARNT-mediated tumorigenesis in a PAH-driven tumor model

Activation of hypoxia-inducible factor (HIF) and macrophage infiltration of solid tumors independently promote tumor progression. As little is known how myeloid HIF affects tumor development, we injected the polycyclic aromatic hydrocarbon (PAH) and procarcinogen 3-methylcholanthrene (MCA; 100 μg/100 μl) subcutaneously into myeloid-specific Hif-1α and Hif-2α knockout mice (C57BL/6J) to induce fibrosarcomas (n = 16). Deletion of Hif-1α but not Hif-2α in macrophages diminished tumor outgrowth in the MCA-model. While analysis of the tumor initiation phase showed comparable inflammation after MCA-injection, metabolism of MCA was impaired in the absence of Hif-1α. An ex vivo macrophage/fibroblast coculture recapitulated reduced DNA damage after MCA-stimulation in fibroblasts of cocultures with Hif-1α^LysM−/− macrophages compared to wild type macrophages. A loss of myeloid Hif-1α decreased RNA levels of arylhydrocarbon receptor (AhR)/arylhydrocarbon receptor nuclear translocator (ARNT) targets such as Cyp1a1 because of reduced Arnt but unchanged Ahr expression. Cocultures using Hif-1α^LysM−/− macrophages stimulated with the carcinogen 7,12-dimethylbenz[a]anthracene (DMBA; 2 μg/ml) also attenuated a DNA damage response in fibroblasts, while the DNA damage-inducing metabolite DMBA-trans-3,4-dihydrodiol remained effective in the absence of Hif-1α. In chemical-induced carcinogenesis, HIF-1α in macrophages maintains ARNT expression to facilitate PAH-biotransformation. This implies a metabolic activation of PAHs in stromal cells, i.e. myeloid-derived cells, to be crucial for tumor initiation.

Mice null for the deubiquitinase USP18 spontaneously develop leiomyosarcomas

Background

USP18 (ubiquitin-specific protease 18) removes ubiquitin-like modifier interferon stimulated gene 15 (ISG15) from conjugated proteins. USP18 null mice in a FVB/N background develop tumors as early as 2 months of age. These tumors are leiomyosarcomas and thus represent a new murine model for this disease.

Methods

Heterozygous USP18 +/− FVB/N mice were bred to generate wild-type, heterozygous and homozygous cohorts. Tumors were characterized immunohistochemically and two cell lines were derived from independent tumors. Cell lines were karyotyped and their responses to restoration of USP18 activity assessed. Drug testing and tumorigenic assays were also performed. USP18 immunohistochemical staining in a large series of human leiomyosacomas was examined.

Results

USP18 −/− FVB/N mice spontaneously develop tumors predominantly on the back of the neck with most tumors evident between 6–12 months (80 % penetrance). Immunohistochemical characterization of the tumors confirmed they were leiomyosarcomas, which originate from smooth muscle. Restoration of USP18 activity in sarcoma-derived cell lines did not reduce anchorage dependent or independent growth or xenograft tumor formation demonstrating that these cells no longer require USP18 suppression for tumorigenesis. Karyotyping revealed that both tumor-derived cell lines were aneuploid with extra copies of chromosomes 3 and 15. Chromosome 15 contains the Myc locus and MYC is also amplified in human leiomyosarcomas. MYC protein levels were elevated in both murine leiomyosarcoma cell lines. Stabilized P53 protein was detected in a subset of these murine tumors, another feature of human leiomyosarcomas. Immunohistochemical analyses of USP18 in human leiomyosarcomas revealed a range of staining intensities with the highest USP18 expression in normal vascular smooth muscle. USP18 tissue array analysis of primary leiomyosarcomas from 89 patients with a clinical database revealed cases with reduced USP18 levels had a significantly decreased time to metastasis (P = 0.0441).

Conclusions

USP18 null mice develop leiomyosarcoma recapitulating key features of clinical leiomyosarcomas and patients with reduced-USP18 tumor levels have an unfavorable outcome. USP18 null mice and the derived cell lines represent clinically-relevant models of leiomyosarcoma and can provide insights into both leiomyosarcoma biology and therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1883-8) contains supplementary material, which is available to authorized users.

Perforin: a key pore-forming protein for immune control of viruses and cancer

Perforin (PFN) is the key pore-forming molecule in the cytotoxic granules of immune killer cells. Expressed only in killer cells, PFN is the rate-limiting molecule for cytotoxic function, delivering the death-inducing granule serine proteases (granzymes) into target cells marked for immune elimination. In this chapter we describe our current understanding of how PFN accomplishes this task. We discuss where PFN is expressed and how its expression is regulated, the biogenesis and storage of PFN in killer cells and how they are protected from potential damage, how it is released, how it delivers Granzymes into target cells and the consequences of PFN deficiency.

Interleukin-27 signaling promotes immunity against endogenously arising murine tumors

Interleukin-27 (IL-27) is a pleiotropic cytokine but its immunosuppressive effects predominate during many in vivo immunological challenges. Despite this, evidence from tumor cell line transfer models suggested that IL-27 could promote immune responses in the tumor context. However, the role of IL-27 in immunity against tumors that develop in situ and in tumor immunosurveillance remain undefined. In this study, we demonstrate that tumor development and growth are accelerated in IL-27 receptor α (Il27ra)-deficient mice. Enhanced tumor growth in both carcinogen-induced fibrosarcoma and oncogene-driven mammary carcinoma was associated with decreased interferon-γ production by CD4 and CD8 T cells and increased numbers of regulatory T-cells (T_reg). This is the first study to show that IL-27 promotes protective immune responses against endogenous tumors, which is critical as the basis for future development of an IL-27 based therapeutic agent.

Suppression, subversion and escape: the role of regulatory T cells in cancer progression

Regulatory T cells (T(regs) ) are crucial in mediating immune homeostasis and promoting the establishment and maintenance of peripheral tolerance. However, in the context of cancer their role is more complex, and they are thought to contribute to the progress of many tumours. As cancer cells express both self- and tumour-associated antigens, T(regs) are key to dampening effector cell responses, and therefore represent one of the main obstacles to effective anti-tumour responses. Suppression mechanisms employed by T(regs) are thought to contribute significantly to the failure of current therapies that rely on induction or potentiation of anti-tumour responses. This review will focus on the current evidence supporting the central role of T(regs) in establishing tumour-specific tolerance and promoting cancer escape. We outline the mechanisms underlying their suppressive function and discuss the potential routes of T(regs) accumulation within the tumour, including enhanced recruitment, in-situ or local proliferation, and de-novo differentiation. In addition, we review some of the cancer treatment strategies that act, at least in part, to eliminate or interfere with the function of T(regs) . The role of T(regs) is being recognized increasingly in cancer, and controlling the function of these suppressive cells in the tumour microenvironment without compromising peripheral tolerance represents a significant challenge for cancer therapies.

The pharmacologic inhibition of the xc- antioxidant system improves the antitumor efficacy of COX inhibitors in the in vivo model of 3-MCA tumorigenesis

The chemopreventive and therapeutic efficacy of the cyclooxygenase (COX) inhibitor ibuprofen (IB) and of sulfasalazine (SASP), a drug that targets the antioxidant xc- system, were exploited in the experimental model of 3-methylcholantrene (3-MCA)-induced mouse sarcoma. The chemopreventive treatments gave unsatisfactory results because administration of IB one day after the 3-MCA injection only slightly delayed the tumor development, whereas SASP dispensed under the same conditions resulted in accelerated tumorigenesis. Similarly, the therapeutic treatment with either drug, administrated daily from the tumor detection, decreased the proliferation rate of tumor cells and increased the survival of treated mice only at a low extent. Remarkably, the combined chemopreventive treatment with IB and therapeutic treatment with SASP displayed a better efficacy, with strong delay of sarcoma growth, reduced tumor size and increased survival of treated mice. The two drugs target not only tumor cells but also tumor-associated macrophages that were dramatically decreased in the tumor infiltrate of mice subjected to the combined treatment. The synergistic effects of the association between a broad anti-inflammatory compound, such as IB, and a redox-directed drug, such as SASP, shed new light in the role of inflammation and of the redox response in chemical tumorigenesis and point to the combined chemopreventive plus therapeutic treatment with IB and SASP as a promising novel approach for antitumor therapy.

Differences in serum cytokine levels between wild type mice and mice with a targeted mutation suggests necessity of using control littermates

To enhance protection from pathogens, housing conditions have been improved constantly. We wanted to test whether various environmental conditions and caging systems affect serum cytokine levels of immunodeficient mice differently than they affect immunocompetent control animals. We compared serum cytokine levels of immunodeficient and immunocompetent mice kept in three different environments: a specific pathogen free (SPF) breeding barrier with open cages. An SPF experimental unit with individually ventilated cages. An experimental semi-barrier with open cages. Serum from Rag1(-/-), μMT(-/-), IFN-γR(-/-), IFN-γ(-/-), IL-4(-/-), the heterozygous controls and wild type C57BL/6 or BALB/c mice was analyzed for the presence of 10 cytokines (IL-1α, IL-2, IL-4, IL-5, IL-6, IL-10, IL-17, IFN-γ, TNF-α and GM-CSF). No major changes in cytokine levels were detected in mice exposed to different housing conditions. However, irrespective of immunodeficiency at 4 weeks of age a number of mice from the breeding colonies with a targeted mutation (TM), both -/- and +/- mice, showed a statistically significant elevation of some cytokines (primarily IL-1α, IL-5) when compared to wild type BALB/c and C57BL/6 mice. We conclude that under SPF conditions, immunodeficient mice can be kept either in open caging or IVC systems without affecting serum cytokine levels. The more important conclusion, however, stems from the observation that there is a significant difference in serum cytokine levels between wild type and mice carrying either one or two alleles of a targeted mutation (either -/- and +/- mice). This suggests an altered base-line inflammatory responsiveness in the TM-breeding colonies.

The immune response to melanoma is limited by thymic selection of self-antigens

The expression of melanoma-associated antigens (MAA) being limited to normal melanocytes and melanomas, MAAs are ideal targets for immunotherapy and melanoma vaccines. As MAAs are derived from self, immune responses to these may be limited by thymic tolerance. The extent to which self-tolerance prevents efficient immune responses to MAAs remains unknown. The autoimmune regulator (AIRE) controls the expression of tissue-specific self-antigens in thymic epithelial cells (TECs). The level of antigens expressed in the TECs determines the fate of auto-reactive thymocytes. Deficiency in AIRE leads in both humans (APECED patients) and mice to enlarged autoreactive immune repertoires. Here we show increased IgG levels to melanoma cells in APECED patients correlating with autoimmune skin features. Similarly, the enlarged T cell repertoire in AIRE^−/− mice enables them to mount anti-MAA and anti-melanoma responses as shown by increased anti-melanoma antibodies, and enhanced CD4⁺ and MAA-specific CD8⁺ T cell responses after melanoma challenge. We show that thymic expression of gp100 is under the control of AIRE, leading to increased gp100-specific CD8⁺ T cell frequencies in AIRE^−/− mice. TRP-2 (tyrosinase-related protein), on the other hand, is absent from TECs and consequently TRP-2 specific CD8⁺ T cells were found in both AIRE^−/− and AIRE^+/+ mice. This study emphasizes the importance of investigating thymic expression of self-antigens prior to their inclusion in vaccination and immunotherapy strategies.

B-cells and IL-4 promote methylcholanthrene-induced carcinogenesis but there is no evidence for a role of T/NKT-cells and their effector molecules (Fas-ligand, TNF-α, perforin)

Mice deficient either in subtypes of immune cells, cytokines or lytic pathways have been subjected to chemical carcinogenesis by methylcholanthrene to evaluate whether these components of the immune system affect tumor development. Inbred mice of the same genotype but from different sources differed in tumor development in magnitude comparable to that previously attributed to differences in immunocompetence. This suggested that genetic drift between separate inbred colonies of mice and/or environmental factors (e.g., transport of the animals) influenced carcinogenesis. Therefore, littermates were used as control in subsequent experiments. Although deficiency of T-cells, NKT-cells, perforin, Fas-ligand, TNF-α-receptor failed to reveal significant differences in tumor development, the presence of B-cells and IL-4 enhanced tumor development under similar experimental conditions.

Assessment of the humoral immune response to cancer

One of the deadly hallmarks of cancer is its ability to prosper within the constraints of the host immune system. Recent advances in immunoproteomics and high-throughput technologies have lead to profiling of the antibody repertoire in cancer patients. This in turn has lead to the identification of tumour associated antigens/autoantibodies. Autoantibodies are extremely attractive and promising biomarker entities, however there has been relatively little discussion on how to interpret the humoral immune response. It may be that autoantibody profiles hold the key to ultimately uncovering neoplastic associated pathways and through the process of immunosculpting the tumour may have yielded an immune response in the early stages of malignant tumour development. The aim of this review is to discuss the utility of the autoantibody response that is elicited as a result of malignancy and discuss the advantages and limitations of autoantibody profiling. This article is part of a Special Issue entitled: Translational Proteomics.

Defining the critical hurdles in cancer immunotherapy

Scientific discoveries that provide strong evidence of antitumor effects in preclinical models often encounter significant delays before being tested in patients with cancer. While some of these delays have a scientific basis, others do not. We need to do better. Innovative strategies need to move into early stage clinical trials as quickly as it is safe, and if successful, these therapies should efficiently obtain regulatory approval and widespread clinical application. In late 2009 and 2010 the Society for Immunotherapy of Cancer (SITC), convened an "Immunotherapy Summit" with representatives from immunotherapy organizations representing Europe, Japan, China and North America to discuss collaborations to improve development and delivery of cancer immunotherapy. One of the concepts raised by SITC and defined as critical by all parties was the need to identify hurdles that impede effective translation of cancer immunotherapy. With consensus on these hurdles, international working groups could be developed to make recommendations vetted by the participating organizations. These recommendations could then be considered by regulatory bodies, governmental and private funding agencies, pharmaceutical companies and academic institutions to facilitate changes necessary to accelerate clinical translation of novel immune-based cancer therapies. The critical hurdles identified by representatives of the collaborating organizations, now organized as the World Immunotherapy Council, are presented and discussed in this report. Some of the identified hurdles impede all investigators; others hinder investigators only in certain regions or institutions or are more relevant to specific types of immunotherapy or first-in-humans studies. Each of these hurdles can significantly delay clinical translation of promising advances in immunotherapy yet if overcome, have the potential to improve outcomes of patients with cancer.

Dual biological effects of the cytokines interleukin-10 and interferon-γ

It is generally thought that each cytokine exerts either immune stimulatory (inflammatory) or immune inhibitory (antiinflammatory or regulatory) biological activities. However, multiple cytokines can enact both inhibitory and stimulatory effects on the immune system. Two of these cytokines are interleukin (IL)-10 and interferon-gamma (IFNγ). IL-10 has demonstrated antitumor immunity even though it has been known for years as an immunoregulatory protein. Generally perceived as an immune stimulatory cytokine, IFNγ can also induce inhibitory molecule expression including B7-H1 (PD-L1), indoleamine 2,3-dioxygenase (IDO), and arginase on multiple cell populations (dendritic cells, tumor cells, and vascular endothelial cells). In this review, we will summarize current knowledge of the dual roles of both of these cytokines and stress the previously underappreciated stimulatory role of IL-10 and inhibitory role of IFNγ in the context of malignancy. Our progressive understanding of the dual effects of these cytokines is important for dissecting cytokine-associated pathology and provides new avenues for developing effective immune therapy against human diseases, including cancer.

[Prostate carcinoma: vaccination as a new option for treatment]

Immune therapy and tumor cell vaccination is a challenging option in prostate cancer therapy, especially as side effects rarely occur. This review highlights recent developments in vaccination therapy of prostate cancer. The FDA approved antigen presenting cell vaccine Sipuleucel-T is described and new strategies of immune therapy like RNA and peptide vaccination are discussed in detail. Currently the effect of prostate cancer vaccination has still limitations, at least partially due to the immune suppressive effects of the tumor microenvironment and regulatory T cells, which suppress the immune effector function. To overcome these hurdles the concept of immune checkpoint modulation, which has the aim to break tolerance mechanisms, is discussed. Potential clinical therapies of checkpoint modulation are outlined.

The aging immune system and its relationship with cancer

The incidence of most common cancers increases with age. This occurs in association with, and is possibly caused by a decline in immune function, termed immune senescence. Although the size of the T-cell compartment is quantitatively maintained into older age, several deleterious changes (including significant changes to T-cell subsets) occur over time that significantly impair immunity. This article highlights some of the recent findings regarding the aging immune system, with an emphasis on the T-cell compartment and its role in cancer.

The tissue organization field theory of cancer: a testable replacement for the somatic mutation theory

The somatic mutation theory (SMT) of cancer has been and remains the prevalent theory attempting to explain how neoplasms arise and progress. This theory proposes that cancer is a clonal, cell-based disease, and implicitly assumes that quiescence is the default state of cells in multicellular organisms. The SMT has not been rigorously tested, and several lines of evidence raise questions that are not addressed by this theory. Herein, we propose experimental strategies that may validate the SMT. We also call attention to an alternative theory of carcinogenesis, the tissue organization field theory (TOFT), which posits that cancer is a tissue-based disease and that proliferation is the default state of all cells. Based on epistemological and experimental evidence, we argue that the TOFT compellingly explains carcinogenesis, while placing it within an evolutionarily relevant context.

Harnessing the effect of adoptively transferred tumor-reactive T cells on endogenous (host-derived) antitumor immunity

Adoptive T cell transfer therapy, the ex vivo activation, expansion, and subsequent administration of tumor-reactive T cells, is already the most effective therapy against certain types of cancer. However, recent evidence in animal models and clinical trials suggests that host conditioning interventions tailored for some of the most aggressive and frequent epithelial cancers will be needed to maximize the benefit of this approach. Similarly, the subsets, stage of differentiation, and ex vivo expansion procedure of tumor-reactive T cells to be adoptively transferred influence their in vivo effectiveness and may need to be adapted for different types of cancer and host conditioning interventions. The effects of adoptively transferred tumor-reactive T cells on the mechanisms of endogenous (host-derived) antitumor immunity, and how to maximize their combined effects, are further discussed.

The initial immune reaction to a new tumor antigen is always stimulatory and probably necessary for the tumor's growth

All nascent neoplasms probably elicit at least a weak immune reaction. However, the initial effect of the weak immune reaction on a nascent tumor is always stimulatory rather than inhibitory to tumor growth, assuming only that exposure to the tumor antigens did not antedate the initiation of the neoplasm (as may occur in some virally induced tumors). This conclusion derives from the observation that the relationship between the magnitude of an adaptive immune reaction and tumor growth is not linear but varies such that while large quantities of antitumor immune reactants tend to inhibit tumor growth, smaller quantities of the same reactants are, for unknown reasons, stimulatory. Any immune reaction must presumably be small before it can become large; hence the initial reaction to the first presentation of a tumor antigen must always be small and in the stimulatory portion of this nonlinear relationship. In mouse-skin carcinogenesis experiments it was found that premalignant papillomas were variously immunogenic, but that the carcinomas that arose in them were, presumably because of induced immune tolerance, nonimmunogenic in the animal of origin.

Perforin: structure, function, and role in human immunopathology

The secretory granule-mediated cell death pathway is the key mechanism for elimination of virus-infected and transformed target cells by cytotoxic lymphocytes. The formation of the immunological synapse between an effector and a target cell leads to exocytic trafficking of the secretory granules and the release of their contents, which include pro-apoptotic serine proteases, granzymes, and pore-forming perforin into the synapse. There, perforin polymerizes and forms a transmembrane pore that allows the delivery of granzymes into the cytosol, where they initiate various apoptotic death pathways. Unlike relatively redundant individual granzymes, functional perforin is absolutely essential for cytotoxic lymphocyte function and immune regulation in the host. Nevertheless, perforin is still the least studied and understood cytotoxic molecule in the immune system. In this review, we discuss the current state of affairs in the perforin field: the protein's structure and function as well as its role in immune-mediated diseases.

Immunologic mechanisms in RCC and allogeneic renal transplant rejection

The tolerance state that exists between renal cell carcinoma (RCC) and the host's immune system would be an ideal situation in the setting of human kidney transplantation, in which graft tolerance is the ultimate goal of immunosuppressive therapy. On the other hand, acute rejection, as it appears in renal allografts, would be the optimal immunologic situation in patients with RCC. Analysis of the underlying mechanisms of acute allograft rejection and local pro-tumor immunosuppression could help to identify potential therapeutic targets for inducing immune tolerance in allograft recipients and immune rejection in RCC patients. Experimental kidney transplantation might be a suitable model in which to analyze these processes. Macrophages are a prominent and vital cell type in the cellular infiltrate seen in both RCC and renal allografts. Depending on their polarization, they can initiate and promote either proinflammatory or pro-tumor responses, which lead to tissue rejection or acceptance, respectively. Improved understanding of macrophage biology could lead to therapeutic modification of their function in order to promote a desirable immunologic response in either RCC or transplant tissue.

Tumor immunogenicity and responsiveness to cancer vaccine therapy: the state of the art

Despite enormous effort, promising pre-clinical data in animal studies and over 900 clinical trials in the United States, no cancer vaccine has ever been approved for clinical use. Over the past decade a great deal of progress has been in both laboratory and clinical studies defining the interactions between developing tumors and the immune system. The results of these studies provide a rationale that may help explain the failure of recent therapeutic cancer vaccines in terms of vaccine principles, in selecting which tumors are the most appropriate to target and instruct the design and implementation of state-of-the-art cancer vaccines.