T lymphocytes restrain spontaneous metastases in permanent dormancy

Metastasis Models: Thermodynamics and Complexity

The thermodynamic formalism of nonequilibrium systems together with the theory of complex systems and systems biology offer an appropriate theoretical framework to explain the complexity observed at the macroscopic level in physiological phenomena. In turn, they allow the establishment of an appropriate conceptual and operational framework to address the study of phenomena such as the emergence and evolution of cancer.This chapter is organized as follows: In Subheading 1, an integrated vision of these disciplines is offered for the characterization of the emergence and evolution of cancer, seen as a nonlinear dynamic system, temporally and spatially self-organized out of thermodynamic equilibrium. The development of the various mathematical models and different techniques and approaches used in the characterization of cancer metastasis is presented in Subheading 2. Subheading 3 is devoted to the time course of cancer metastasis, with particular emphasis on the epithelial-mesenchymal transition (EMT henceforth) as well as chronotherapeutic treatments. In Subheading 4, models of the spatial evolution of cancer metastasis are presented. Finally, in Subheading 5, some conclusions and remarks are presented.

SARS-CoV-2 Vaccination and the Multi-Hit Hypothesis of Oncogenesis

Cancer is a complex and dynamic disease. The "hallmarks of cancer" were proposed by Hanahan and Weinberg (2000) as a group of biological competencies that human cells attain as they progress from normalcy to neoplastic transformation. These competencies include self-sufficiency in proliferative signaling, insensitivity to growth-suppressive signals and immune surveillance, the ability to evade cell death, enabling replicative immortality, reprogramming energy metabolism, inducing angiogenesis, and activating tissue invasion and metastasis. Underlying these competencies are genome instability, which expedites their acquisition, and inflammation, which fosters their function(s). Additionally, cancer exhibits another dimension of complexity: a heterogeneous repertoire of infiltrating and resident host cells, secreted factors, and extracellular matrix, known as the tumor microenvironment, that through a dynamic and reciprocal relationship with cancer cells supports immortality, local invasion, and metastatic dissemination. This staggering intricacy calls for caution when advising all people with cancer (or a previous history of cancer) to receive the COVID-19 primary vaccine series plus additional booster doses. Moreover, because these patients were not included in the pivotal clinical trials, considerable uncertainty remains regarding vaccine efficacy, safety, and the risk of interactions with anticancer therapies, which could reduce the value and innocuity of either medical treatment. After reviewing the available literature, we are particularly concerned that certain COVID-19 vaccines may generate a pro-tumorigenic milieu (i.e., a specific environment that could lead to neoplastic transformation) that predisposes some (stable) oncologic patients and survivors to cancer progression, recurrence, and/or metastasis. This hypothesis is based on biological plausibility and fulfillment of the multi-hit hypothesis of oncogenesis (i.e., induction of lymphopenia and inflammation, downregulation of angiotensin-converting enzyme 2 (ACE2) expression, activation of oncogenic cascades, sequestration of tumor suppressor proteins, dysregulation of the RNA-G quadruplex-protein binding system, alteration of type I interferon responses, unsilencing of retrotransposable elements, etc.) together with growing evidence and safety reports filed to Vaccine Adverse Effects Report System (VAERS) suggesting that some cancer patients experienced disease exacerbation or recurrence following COVID-19 vaccination. In light of the above and because some of these concerns (i.e., alteration of oncogenic pathways, promotion of inflammatory cascades, and dysregulation of the renin-angiotensin system) also apply to cancer patients infected with SARS-CoV-2, we encourage the scientific and medical community to urgently evaluate the impact of both COVID-19 and COVID-19 vaccination on cancer biology and tumor registries, adjusting public health recommendations accordingly.

Dormant tumors circumvent tumor-specific adaptive immunity by establishing a Treg-dominated niche via DKK3

Approximately 30% of breast cancer survivors deemed free of disease will experience locoregional or metastatic recurrence even up to 30 years after initial diagnosis, yet how residual/dormant tumor cells escape immunity elicited by the primary tumor remains unclear. We demonstrate that intrinsically dormant tumor cells are indeed recognized and lysed by antigen-specific T cells in vitro and elicit robust immune responses in vivo. However, despite close proximity to CD8+ killer T cells, dormant tumor cells themselves support early accumulation of protective FoxP3+ T regulatory cells (Tregs), which can be targeted to reduce tumor burden. These intrinsically dormant tumor cells maintain a hybrid epithelial/mesenchymal state that is associated with immune dysfunction, and we find that the tumor-derived, stem cell/basal cell protein Dickkopf WNT signaling pathway inhibitor 3 (DKK3) is critical for Treg inhibition of CD8+ T cells. We also demonstrate that DKK3 promotes immune-mediated progression of proliferative tumors and is significantly associated with poor survival and immunosuppression in human breast cancers. Together, these findings reveal that latent tumors can use fundamental mechanisms of tolerance to alter the T cell microenvironment and subvert immune detection. Thus, targeting these pathways, such as DKK3, may help render dormant tumors susceptible to immunotherapies.

Metastasis prevention: How to catch metastatic seeds

Despite considerable advances in the evolution of anticancer therapies, metastasis still remains the main cause of cancer mortality. Therefore, current strategies for cancer cure should be redirected towards prevention of metastasis. Targeting metastatic pathways represents a promising therapeutic opportunity aimed at obstructing tumor cell dissemination and metastatic colonization. In this review, we focus on preclinical studies and clinical trials over the last five years that showed high efficacy in suppressing metastasis through targeting lymph node dissemination, tumor cell extravasation, reactive oxygen species, pre-metastatic niche, exosome machinery, and dormancy.

Locally sourced: site-specific immune barriers to metastasis

Tumour cells migrate very early from primary sites to distant sites, and yet metastases often take years to manifest themselves clinically or never even surface within a patient's lifetime. This pause in cancer progression emphasizes the existence of barriers that constrain the growth of disseminated tumour cells (DTCs) at distant sites. Although the nature of these barriers to metastasis might include DTC-intrinsic traits, recent studies have established that the local microenvironment also controls the formation of metastases. In this Perspective, I discuss how site-specific differences of the immune system might be a major selective growth restraint on DTCs, and argue that harnessing tissue immunity will be essential for the next stage in immunotherapy development that reliably prevents the establishment of metastases.

The Challenges of HLA Class I Loss in Cancer Immunotherapy: Facts and Hopes

HLA class I molecules are key in tumor recognition and T cell-mediated elimination. Loss of tumor HLA class I expression with different underlying molecular defects results in reduced antigen presentation and facilitates cancer immune evasion. It is also linked to significant changes in tumor microenvironment and tissue architecture. In this review, we summarize the current advances and future perspectives in the understanding of the mechanisms of MHC/HLA class I alterations during the natural history of tumor progression from a primary lesion to distant metastases. We also focus on recent clinical and experimental data demonstrating that lack of response to cancer immunotherapy frequently depends on the molecular nature of tumor HLA class I aberrations. Finally, we highlight the relevance of detecting and correcting the absence of tumor HLA expression to improve immunotherapy protocols.

Thorny ground, rocky soil: Tissue-specific mechanisms of tumor dormancy and relapse

Disseminated tumor cells (DTCs) spread systemically yet distinct patterns of metastasis indicate a range of tissue susceptibility to metastatic colonization. Distinctions between permissive and suppressive tissues are still being elucidated at cellular and molecular levels. Although there is a growing appreciation for the role of the microenvironment in regulating metastatic success, we have a limited understanding of how diverse tissues regulate DTC dormancy, the state of reversible quiescence and subsequent awakening thought to contribute to delayed relapse. Several themes of microenvironmental regulation of dormancy are beginning to emerge, including vascular association, co-option of pre-existing niches, metabolic adaptation, and immune evasion, with tissue-specific nuances. Conversely, DTC awakening is often associated with injury or inflammation-induced activation of the stroma, promoting a proliferative environment with DTCs following suit. We review what is known about tissue-specific regulation of tumor dormancy on a tissue-by-tissue basis, profiling major metastatic organs including the bone, lung, brain, liver, and lymph node. An aerial view of the barriers to metastatic growth may reveal common targets and dependencies to inform the therapeutic prevention of relapse.

Multifaceted functions of chronic inflammation in regulating tumor dormancy and relapse

Inflammation is a double-edged sword exhibiting multifaceted functions. On one hand, it either induces tumor cell apoptosis, or establishes tumor dormancy by inhibiting tumor cell proliferation; on the other hand, it either facilitates the tumorigenesis process or reawakens dormant tumor cells, resulting in disease recurrences. Each outcome would depend on the balance between type I and type II inflammation as well as the duration of inflammation being acute or chronic. In this essay, we provide a critical review of the empirical evidence suggesting that chronic inflammation, dominated by type I inflammatory cells and cytokines as a result of trauma and microbiome dysbiosis, could facilitate the carcinogenesis process in normal cells and retain nascent transformed cells in a dormant state. On the other hand, an elevated type II inflammation along with inefficient resolution of type I inflammation following trauma or major surgeries could delay the wound healing process and promote the growth and reawakening of dormant tumor cells, resulting in disease recurrences. Finally, cytokines exhibiting type I and II inflammatory functions, simultaneously, tend to promote tumor recurrence when become chronic. Therefore, the risk of reawakening dormant tumor cells should be considered in cancer survivors who experience major surgeries and trauma, or suffer from chronic inflammatory diseases.

Antimetastatic defense by CD8+ T cells

Metastasis is an intricate process whereby tumor cells migrate from the primary tumor, survive in the circulation, seed distal organs, and proliferate to create metastatic foci. CD8⁺ T cells can detect and eliminate tumor cells. Research on CD8⁺ T cell-dependent antitumor immunity has classically focused on its role in the primary tumor. There is increasing evidence, however, that CD8⁺ T cells have unique antimetastatic functions in various steps of the metastatic cascade. Here, we review the mechanisms whereby CD8⁺ T cells control metastatic lesions. We discuss their role in each step of metastasis, metastatic dormancy, and metastatic clonal evolution as well as the consequent clinical repercussions.

Mechanisms of Immunosuppressive Tumor Evasion: Focus on Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is a malignancy with high heterogeneity in its biological features and treatments. Although the overall survival (OS) of patients with ALL has recently improved considerably, owing to the application of conventional chemo-therapeutic agents, approximately 20% of the pediatric cases and 40-50% of the adult patients relapse during and after the treatment period. The potential mechanisms that cause relapse involve clonal evolution, innate and acquired chemoresistance, and the ability of ALL cells to escape the immune-suppressive tumor response. Currently, immunotherapy in combination with conventional treatment is used to enhance the immune response against tumor cells, thereby significantly improving the OS in patients with ALL. Therefore, understanding the mechanisms of immune evasion by leukemia cells could be useful for developing novel therapeutic strategies.

The metabolic flexibility of quiescent CSC: implications for chemotherapy resistance

Quiescence has been observed in stem cells (SCs), including adult SCs and cancer SCs (CSCs). Conventional chemotherapies mostly target proliferating cancer cells, while the quiescent state favors CSCs escape to chemotherapeutic drugs, leaving risks for tumor recurrence or metastasis. The tumor microenvironment (TME) provides various signals that maintain resident quiescent CSCs, protect them from immune surveillance, and facilitates their recurrence potential. Since the TME has the potential to support and initiate stem cell-like programs in cancer cells, targeting the TME components may prove to be a powerful modality for the treatment of chemotherapy resistance. In addition, an increasing number of studies have discovered that CSCs exhibit the potential of metabolic flexibility when metabolic substrates are limited, and display increased robustness in response to stress. Accompanied by chemotherapy that targets proliferative cancer cells, treatments that modulate CSC quiescence through the regulation of metabolic pathways also show promise. In this review, we focus on the roles of metabolic flexibility and the TME on CSCs quiescence and further discuss potential treatments of targeting CSCs and the TME to limit chemotherapy resistance.

Neutrophil Extracellular Traps in Tumor Metastasis: Pathological Functions and Clinical Applications

Simple Summary

Tumor-associated neutrophils constitute an important portion of the infiltrating immune cells in the tumor microenvironment. One of the abilities of neutrophils is forming neutrophil extracellular traps. Recent studies on tumor-associated neutrophils have drawn increasing attention to the role of neutrophil extracellular traps in the tumor microenvironment. There were also some reviews summarize the pro-tumorigenic activity of NETs in tumors. The specific novelty of this article is the specific summarization on the pivotal roles of NETs in tumor invasion-metastasis cascade and the recapitulation on the potential of NETs in clinical applications.

Abstract

Neutrophil extracellular trap (NET) formation is an ability of neutrophils to capture and kill pathogens by releasing chromatin scaffolds, along with associated cytotoxic enzymes and proteases, into the extracellular space. NETs are usually stimulated by pathogenic microorganisms and their products, surgical pressure or hypoxia. Interestingly, a number of recent studies suggest that tumor cells can induce NET formation, which in turn confers tumor cell malignancy. Notably, emerging studies indicate that NETs are involved in enhancing local invasion, increasing vascular permeability and facilitating immune escape and colonization, thus promoting tumor metastasis. In this article, we review the pivotal roles of NETs in the tumor metastasis cascade. We also recapitulate the potential of NETs as a cancer prognostic biomarker and therapeutic target.

Emerging Next-Generation Target for Cancer Immunotherapy Research: The Orphan Nuclear Receptor NR2F6

Simple Summary

The most successful strategies for solid cancer immunotherapy have centered on targeting the co-stimulatory and co-inhibitory T cell molecules that regulate T cell activation. Although immunotherapy that targets surface receptors such as CTLA-4 and/or PD-1 with recombinant antibodies has been a game changer for cancer treatment, a sizeable subset of patients still fail to respond to, and even fewer patients are cured by, these therapy regimens. Here, we discuss the unique potential of NR2F6 as an emerging target for cancer immunotherapy to significantly increase response rates of cancer patients and/or to extend treatment to a broader range of cancer types.

Abstract

Additional therapeutic targets suitable for boosting anti-tumor effector responses have been found inside effector CD4⁺ and CD8⁺ T cells. It is likely that future treatment options will combine surface receptor and intracellular protein targets. Utilizing germline gene ablation as well as CRISPR/Cas9-mediated acute gene mutagenesis, the nuclear receptor NR2F6 (nuclear receptor subfamily 2 group F member 6, also called Ear-2) has been firmly characterized as such an intracellular immune checkpoint in effector T cells. Targeting this receptor appears to be a strategy for improving anti-tumor immunotherapy responses, especially in combination with CTLA-4 and PD-1. Current preclinical experimental knowledge firmly validates the immune checkpoint function of NR2F6 in murine tumor models, which provides a promising perspective for immunotherapy regimens in humans in the near future. While the clinical focus remains on the B7/CD28 family members, protein candidate targets such as NR2F6 are now being investigated in laboratories around the world and in R&D companies. Such an alternative therapeutic approach, if demonstrated to be successful, could supplement the existing therapeutic models and significantly increase response rates of cancer patients and/or expand the reach of immune therapy regimens to include a wider range of cancer entities. In this perspective review, the role of NR2F6 as an emerging and druggable target in immuno-oncology research will be discussed, with special emphasis on the unique potential of NR2F6 and its critical and non-redundant role in both immune and tumor cells.

Immune Responses against Disseminated Tumor Cells

Most cancer-related deaths are a consequence of metastases, a series of linear events, notably the invasion-metastasis cascade. The current understanding of cancer immune surveillance derives from studies in primary tumors, but disseminated cancer cells acquire mutations and, in some cases, appear to progress independently after spreading from primary sites. An early step in this process is micrometastatic dissemination. As such, the equilibrium between the immune system and disseminated cancer cells controls the fate of the cancer. Immune checkpoint inhibitors (ICIs) exhibit significant clinical activity in patients, but the efficacy of ICIs depends on both the tumor and its microenvironment. Data often suggest that disseminated cancer cells are not adequately targeted by the immune system. In this review, we summarize the main basic findings of immune responses against disseminated tumor cells and their organ-specific characteristics. Such studies may provide new directions for cancer immune therapy.

MHC heterogeneity and response of metastases to immunotherapy

In recent years, immunotherapy has proven to be an effective treatment against cancer. Cytotoxic T lymphocytes perform an important role in this anti-tumor immune response, recognizing cancer cells as foreign, through the presentation of tumor antigens by MHC class I molecules. However, tumors and metastases develop escape mechanisms for evading this immunosurveillance and may lose the expression of these polymorphic molecules to become invisible to cytotoxic T lymphocytes. In other situations, they may maintain MHC class I expression and promote immunosuppression of cytotoxic T lymphocytes. Therefore, the analysis of the expression of MHC class I molecules in tumors and metastases is important to elucidate these escape mechanisms. Moreover, it is necessary to determine the molecular mechanisms involved in these alterations to reverse them and recover the expression of MHC class I molecules on tumor cells. This review discusses the role and regulation of MHC class I expression in tumor progression. We focus on altered MHC class I phenotypes present in tumors and metastases, as well as the molecular mechanisms responsible for MHC-I alterations, emphasizing the mechanisms of recovery of the MHC class I molecules expression on cancer cells. The individualized study of the HLA class I phenotype of the tumor and the metastases of each patient will allow choosing the most appropriate immunotherapy treatment based on a personalized medicine.

Could Extracellular Vesicles Contribute to Generation or Awakening of "Sleepy" Metastatic Niches?

Pre-metastatic niches provide favorable conditions for tumor cells to disseminate, home to and grow in otherwise unfamiliar and distal microenvironments. Tumor-derived extracellular vesicles are now recognized as carriers of key messengers secreted by primary tumors, signals that induce the formation of pre-metastatic niches. Recent evidence suggests that tumor cells can disseminate from the very earliest stages of primary tumor development. However, once they reach distal sites, tumor cells can persist in a dormant state for long periods of time until their growth is reactivated and they produce metastatic lesions. In this new scenario, the question arises as to whether extracellular vesicles could influence the formation of these metastatic niches with dormant tumor cells? (here defined as "sleepy niches"). If so, what are the molecular mechanisms involved? In this perspective-review article, we discuss the possible influence of extracellular vesicles in early metastatic dissemination and whether they might play a role in tumor cell dormancy. In addition, we comment whether extracellular vesicle-mediated signals may be involved in tumor cell awakening, considering the possibility that extracellular vesicles might serve as biomarkers to detect early metastasis and/or minimal residual disease (MRD) monitoring.

Local and distant tumor dormancy during early stage breast cancer are associated with the predominance of infiltrating T effector subsets

Background

Although breast cancer mortality is a result of distant recurrences associated with the establishment of tumor dormancy, current clinical practice guidelines recommend a wait and watch approach for tumor recurrences. This is because of our limited understanding of tumor dormancy and insufficient evidence in support of immunological control of tumor dormancy.

Methods

We used FVBN202 transgenic mice expressing rat neu oncogene in the mammary glands, and their parental FVB strain lacking neu expression. These models allowed the detection of tumor dormancy at distant sites using the rat neu protein as a tumor marker. We also used Ki67 for the detection of the indolent and quiescent types of tumor dormancy. Multicolor flow cytometry was used to detect dormant tumor cells and T cell subsets. Co-culture studies were performed to determine the role of T cells in preventing regrowth of dormant cells.

Results

We demonstrated that dormant tumor cells were present at the site of primary breast cancer and at distant sites in the lungs and in the liver very early in the course of early stage breast cancer when no distant metastasis was evident. Dormant tumor cells were characterized as neu expressing Ki67⁻ and Ki67^low fractions associated with the induction of local immune responses predominated by CD4+ and CD8+ T effector cell subsets. The presence of neu-autoreactive T cells from FVBN202 mice only prevented regrowth of dormant cells. On the other hand, presence of neu-alloreactive anti-tumor T cells in FVB mice prior to tumor challenge resulted in the protection of mice from the dissemination of dormant tumor cells to distant organs.

Conclusion

Our results suggest that immunotherapeutic targeting of semi-allogeneic mutant neoantigens during tumor dormancy might prevent distant recurrence of the disease.

COVID-19-Induced Modifications in the Tumor Microenvironment: Do They Affect Cancer Reawakening and Metastatic Relapse?

Severe coronavirus disease 2019 (COVID-19) causes an uncontrolled activation of the innate immune response, resulting in acute respiratory distress syndrome and systemic inflammation. The effects of COVID-19–induced inflammation on cancer cells and their microenvironment are yet to be elucidated. Here, we formulate the hypothesis that COVID-19–associated inflammation may generate a microenvironment favorable to tumor cell proliferation and particularly to the reawakening of dormant cancer cells (DCCs). DCCs often survive treatment of primary tumors and populate premetastatic niches in the lungs and other organs, retaining the potential for metastatic outgrowth. DCCs reawakening may be promoted by several events associated to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, including activation of neutrophils and monocytes/macrophages, lymphopenia and an uncontrolled production of pro-inflammatory cytokines. Among pro-inflammatory factors produced during COVID-19, neutrophil extracellular traps (NETs) released by activated neutrophils have been specifically shown to activate premetastatic cancer cells disseminated in the lungs, suggesting they may be involved in DCCs reawakening in COVID-19 patients. If confirmed by further studies, the links between COVID-19, DCCs reactivation and tumor relapse may support the use of specific anti-inflammatory and anti-metastatic therapies in patients with COVID-19 and an active or previous cancer.

Reductive Stress, Bioactive Compounds, Redox-Active Metals, and Dormant Tumor Cell Biology to Develop Redox-Based Tools for the Treatment of Cancer

Significance: Cancer is related to redox biology from many points of view, such as initiation and promotion, metabolism and growth, invasion and metastasis, vascularization, or through the interaction with the immune system. In addition, this extremely complex relationship depends on the redox homeostasis of each cellular compartment, which might be used to fight cancer. Recent Advances: New ways of modulating specific and little explored aspects of redox biology have been revealed, as well as new delivery methods or uses of previously known treatments against cancer. Here, we review the latest experimental evidence regarding redox biology in cancer treatment and analyze its potential impact in the development of improved and more effective antineoplastic therapies. Critical Issues: A critical issue that deserves particular attention is the understanding that both extremes of redox biology (i.e., oxidative stress [OS] and reductive stress) might be useful or harmful in relation to cancer prevention and treatment. Future Directions: Additional research is needed to understand how to selectively induce reductive or OS adequately to avoid cancer proliferation or to induce cancer cell death.

Restoration of MHC-I on Tumor Cells by Fhit Transfection Promotes Immune Rejection and Acts as an Individualized Immunotherapeutic Vaccine

The capacity of cytotoxic-T lymphocytes to recognize and destroy tumor cells depends on the surface expression by tumor cells of MHC class I molecules loaded with tumor antigen peptides. Loss of MHC-I expression is the most frequent mechanism by which tumor cells evade the immune response. The restoration of MHC-I expression in cancer cells is crucial to enhance their immune destruction, especially in response to cancer immunotherapy. Using mouse models, we recovered MHC-I expression in the MHC-I negative tumor cell lines and analyzed their oncological and immunological profile. Fhit gene transfection induces the restoration of MHC-I expression in highly oncogenic MHC-I-negative murine tumor cell lines and genes of the IFN-γ transduction signal pathway are involved. Fhit-transfected tumor cells proved highly immunogenic, being rejected by a T lymphocyte-mediated immune response. Strikingly, this immune rejection was more frequent in females than in males. The immune response generated protected hosts against the tumor growth of non-transfected cells and against other tumor cells in our murine tumor model. Finally, we also observed a direct correlation between FHIT expression and HLA-I surface expression in human breast tumors. Recovery of Fhit expression on MHC class I negative tumor cells may be a useful immunotherapeutic strategy and may even act as an individualized immunotherapeutic vaccine.

Thymic Function Associated With Cancer Development, Relapse, and Antitumor Immunity - A Mini-Review

The thymus is the central lymphoid organ for T cell development, a cradle of T cells, and for central tolerance establishment, an educator of T cells, maintaining homeostatic cellular immunity. T cell immunity is critical to control cancer occurrence, relapse, and antitumor immunity. Evidence on how aberrant thymic function influences cancer remains largely insufficient, however, there has been recent progress. For example, the involuted thymus results in reduced output of naïve T cells and a restricted T cell receptor (TCR) repertoire, inducing immunosenescence and potentially dampening immune surveillance of neoplasia. In addition, the involuted thymus relatively enhances regulatory T (Treg) cell generation. This coupled with age-related accumulation of Treg cells in the periphery, potentially provides a supportive microenvironment for tumors to escape T cell-mediated antitumor responses. Furthermore, acute thymic involution from chemotherapy can create a tumor reservoir, resulting from an inflammatory microenvironment in the thymus, which is suitable for disseminated tumor cells to hide, survive chemotherapy, and become dormant. This may eventually result in cancer metastatic relapse. On the other hand, if thymic involution is wisely taken advantage of, it may be potentially beneficial to antitumor immunity, since the involuted thymus increases output of self-reactive T cells, which may recognize certain tumor-associated self-antigens and enhance antitumor immunity, as demonstrated through depletion of autoimmune regulator (AIRE) gene in the thymus. Herein, we briefly review recent research progression regarding how altered thymic function modifies T cell immunity against tumors.

Mutational landscape of immune surveillance genes in diffuse large B-cell lymphoma

INTRODUCTION

Immune surveillance is the dynamic process whereby the immune system identifies and kills tumor cells based on their aberrant expression of stress-related surface molecules or presentation of tumor neoantigens. It plays a crucial role in controlling the initiation and progression of hematologic cancers such as leukemia and lymphoma, and it has been reported that diffuse large B-cell lymphoma (DLBCL) fails to express specific cell-surface molecules that are necessary for the recognition and elimination of tumor cells.

AREAS COVERED

This review is based on a systematic search strategy to identify relevant literature in the PubMed and Embase databases. Ten candidate genes are identified based on mutational frequency, and functions with detailed mapping performed for hotspot alterations that may have a functional impact on malignant transformation and decreased immune surveillance efficacy.

EXPERT OPINION

Ongoing development of technology and bioinformatics tools combined with data from large clinical cohorts have the potential to define the mutational landscape associated with immune surveillance in DLBCL. Specific functional studies are required to make an unambiguous link between genetic aberrations and biological impact on impaired immune surveillance.

The Immune Microenvironment and Cancer Metastasis

The dynamic interplay between neoplastic cells and the immune microenvironment regulates every step of the metastatic process. Immune cells contribute to invasion by secreting a cornucopia of inflammatory factors that promote epithelial-to-mesenchymal transition and remodeling of the stroma. Cancer cells then intravasate to the circulatory system assisted by macrophages and use several pathways to avoid recognition by cytotoxtic lymphocytes and phagocytes. Circulating tumor cells that manage to adhere to the vasculature and encounter premetastic niches are able to use the associated myeloid cells to extravasate into ectopic organs and establish a dormant microscopic colony. If successful at avoiding repetitive immune attack, dormant cells can subsequently grow into overt, clinically detectable metastatic lesions, which ultimately account to most cancer-related deaths. Understanding how disseminated tumor cells evade and corrupt the immune system during the final stages of metastasis will be pivotal in developing new therapeutic modalities that combat metastasis.

Tumor Immunology and Tumor Evolution: Intertwined Histories

Cancer is a complex disease whose outcome depends largely on the cross-talk between the tumor and its microenvironment. Here, we review the evolution of the field of tumor immunology and the advances, in lockstep, of our understanding of cancer as a disease. We discuss the involvement of different immune cells at distinct stages of tumor progression and how immune contexture determinants shaping tumor development are being exploited therapeutically. Current clinical stratification schemes focus on the tumor histopathology and the molecular characteristics of the tumor cell. We argue for the importance of revising these stratification systems to include immune parameters so as to address the immediate need for improved prognostic and/or predictive information to guide clinical decisions.

Tumor Cell Dormancy: Threat or Opportunity in the Fight against Cancer

Tumor dormancy, a clinically undetectable state of cancer, makes a major contribution to the development of multidrug resistance (MDR), minimum residual disease (MRD), tumor outgrowth, cancer relapse, and metastasis. Despite its high incidence, the whole picture of dormancy-regulated molecular programs is far from clear. That is, it is unknown when and which dormant cells will resume proliferation causing late relapse, and which will remain asymptomatic and harmless to their hosts. Thus, identification of dormancy-related culprits and understanding their roles can help predict cancer prognosis and may increase the probability of timely therapeutic intervention for the desired outcome. Here, we provide a comprehensive review of the dormancy-dictated molecular mechanisms, including angiogenic switch, immune escape, cancer stem cells, extracellular matrix (ECM) remodeling, metabolic reprogramming, miRNAs, epigenetic modifications, and stress-induced p38 signaling pathways. Further, we analyze the possibility of leveraging these dormancy-related molecular cues to outmaneuver cancer and discuss the implications of such approaches in cancer treatment.

Cell-intrinsic survival signals. The role of autophagy in metastatic dissemination and tumor cell dormancy

Metastasis is the main cause of cancer-related deaths. Disseminated tumor cells (DTCs), which seed metastasis, can remain undetected in a dormant state for decades after treatment of the primary tumor and their persistence is the main cause of late relapse and death in a substantial proportion of cancer patients. Understanding the mechanisms underlying the survival of dormant DTCs is of utmost importance to develop new therapies that effectively kill DTCs while in a quiescent state, therefore preventing metastatic disease and minimizing the chance of future relapses. Besides key interactions with the local microenvironment, dormant DTCs must integrate survival mechanisms to remain viable for long periods of time. Here, the pro-survival role of autophagy in tumor cell dissemination and dormant DTC maintenance are discussed, as well as the implications of the current knowledge for future research efforts.

Metastatic Latency, a Veiled Threat

Metastatic relapse is observed in cancer patients with no clinical evidence of disease for months to decades after initial diagnosis and treatment. Disseminated cancer cells that are capable of entering reversible cell cycle arrest are believed to be responsible for these late metastatic relapses. Dynamic interactions between the latent disseminated tumor cells and their surrounding microenvironment aid cancer cell survival and facilitate escape from immune surveillance. Here, we highlight findings from preclinical models that provide a conceptual framework to define and target the latent metastatic phase of tumor progression. The hope is by identifying patients harboring latent metastatic cells and providing therapeutic options to eliminate metastatic seeds prior to their emergence will result in long lasting cures.

Targeting Immune-Mediated Dormancy: A Promising Treatment of Cancer

Immune-mediated dormancy is when the immune system keeps proliferating tumor cells unchanged, mostly via cytotoxic activity of immune cells. Cancer dormancy, especially immune-mediated dormancy, may be the explanation for tumor refractory and may be responsible for resistance to conventional chemo- and radiotherapies. Here, we will describe different scenarios as to how the immune cells and cytokines involved in cancer progression are connected with the initiation of dormancy and cancer treatment. Two distinct treatment methods, such as maintaining metastatic tumor cells dormant and awakening them, are also discussed. A better understanding of immune-mediated dormancy will help to design novel and effective immunotherapies and will likely increase the efficiency of tumor treatment inhibiting metastasis.

MHC/HLA Class I Loss in Cancer Cells

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

Enrichment and detection of bone disseminated tumor cells in models of low tumor burden

Breast cancer cells frequently home to the bone, but the mechanisms controlling tumor colonization of the bone marrow remain unclear. We report significant enrichment of bone-disseminated estrogen receptor positive human MCF7 cells by 17 β-estradiol (E2) following intracardiac inoculation. Using flow cytometric and quantitative PCR approaches, tumor cells were detected in >80% of MCF7 tumor-inoculated mice, regardless of E2, suggesting that E2 is not required for MCF7 dissemination to the bone marrow. Furthermore, we propose two additional models in which to study prolonged latency periods by bone-disseminated tumor cells: murine D2.0R and human SUM159 breast carcinoma cells. Tumor cells were detected in bone marrow of up to 100% of D2.0R and SUM159-inoculated mice depending on the detection method. These findings establish novel models of bone colonization in which to study mechanisms underlying tumor cell seeding to the marrow and prolonged latency, and provide highly sensitive methods to detect these rare events.

Uncovering the underlying physical mechanism for cancer-immunity of MHC class I diversity

The cancer cells are heterogeneous populated, which can be classified as MHC class I positive and MHC I class negative. They influence the immune system differently. In this work, we build a core cancer-immune circuit of MHC class I diversity including MHC class I positive cancer type, MHC I class I negative cancer type and 4 immune cell types to uncover the underlying mechanism of the cancer immunity based on the underlying landscape topography. We quantify four steady state attractors, normal state, two low cancer states and a high cancer state. The landscape topography changes upon changes in cancer self-activation and the related killing rate of the killer cells are illustrated. It demonstrates that the competition between the two cancer cell types. We simulate the tumorigenesis and development of cancer according to its biological process and classify these into 7 stages. This landscape framework provides a quantitative way to understand characteristics of these two cancer cell types under immune microenvironment and the underlying physical mechanisms of cancer cell evolution along cancer development.

Abiraterone acetate/androgen deprivation therapy combination versus docetaxel/androgen deprivation therapy combination in advanced hormone-sensitive prostate cancer: a network meta-analysis on safety and efficacy

BACKGROUND

A major, yet precisely studied, shift has occurred in the treatment of advanced hormone-sensitive prostate cancer (HSPC) by the addition of docetaxel to androgen deprivation therapy (ADT) in the first line. Recently, two landmark trials showed that abiraterone acetate (AA) can be an effective alternative along with ADT in the same setting. We implemented a network meta-analysis to compare the safety and efficacy of the two combinations.

METHODS

PubMed database, ASCO and ESMO meeting library databases of all results published until June 2017 were searched using the keywords: "prostate cancer" AND "docetaxel" OR "abiraterone acetate". Efficacy endpoints including progression-free survival (PFS) and overall survival (OS), and safety endpoints (including treatment related deaths and selected adverse events) were assessed.

RESULTS

Twenty relevant studies were retrieved and assessed for eligibility. Of those trials, eight were found potentially eligible. Inconsistent reporting of efficacy outcomes limited our analysis to M1 HSPC. The pooled hazard ratios (HRs) of OS and PFS of the direct comparison of abiraterone acetate plus ADT versus ADT were 0.63 (95% CI: 0.545-0.717) and 0.38 (95% CI: 0.34-0.43), respectively. Meanwhile, in the trials of docetaxel plus ADT the pooled HRs of OS and PFS were 0.75 (95% CI: 0.65-0.86) and 0.634 (95% CI: 0.57-0.70), respectively. The indirect comparison showed that the HRs of OS and PFS in DOC + ADT in comparison to AA + ADT were 1.2 (95% CI: 0.98-1.46) and 1.65 (1.40-1.94), respectively. The pooled RR of treatment-related mortality in docetaxel + ADT versus AA + ADT was 1.438 (95% CI: 0.508-4.075).

CONCLUSION

Patients with metastatic HSPC (mHSPC) who received abiraterone acetate with ADT had better PFS and less toxicity compared to those receiving docetaxel with ADT. A trend towards superior OS and fewer treatment-related deaths was also observed, but was statistically non-significant. In view of lacking clear OS advantage, the choice between docetaxel and AA should include a discussion with the patient about the potential toxicities and impact on quality of life of each regimen.

The possibility of cancer immune editing in gliomas. A critical review

The relationship between anti-tumoral immunity and cancer progression is complex. Recently, immune editing has emerged as a model to explain the interplay between the immune system and the selection of genetic alterations in cancer. In this model, the immune system selects cancer cells that grow as these are fit to escape immune surveillance during tumor development. Gliomas and glioblastoma, the most aggressive and most common of all primary malignant brain tumors are genetically heterogeneous, are relatively less antigenic, and are less responsive to immunotherapy than other cancers. In this review, we provide an overview of the relationship between glioma´s immune suppressive features, anti-tumoral immunity and cancer genomics. In this context, we provide a critical discussion of evidence suggestive of immune editing in this disease and discuss possible alternative explanations for these findings.

MHC Intratumoral Heterogeneity May Predict Cancer Progression and Response to Immunotherapy

An individual tumor can present intratumoral phenotypic heterogeneity, containing tumor cells with different phenotypes that do not present irreversible genetic alterations. We have developed a mouse cancer model, named GR9, derived from a methylcholanthrene-induced fibrosarcoma that was adapted to tissue culture and cloned into different tumor cell lines. The clones showed diverse MHC-I phenotypes, ranging from highly positive to weakly positive MHC-I expression. These MHC-I alterations are due to reversible molecular mechanisms, because surface MHC-I could be recovered by IFN-γ treatment. Cell clones with high MHC-I expression demonstrated low local oncogenicity and high spontaneous metastatic capacity, whereas MHC-I-low clones showed high local oncogenicity and no spontaneous metastatic capacity. Although MHC-I-low clones did not metastasize, they produced MHC-I-positive dormant micrometastases controlled by the host immune system, i.e., in a state of immunodormancy. The metastatic capacity of each clone was directly correlated with the host T-cell subpopulations; thus, a strong decrease in cytotoxic and helper T lymphocytes was observed in mice with numerous metastases derived from MHC-I positive tumor clones but a strong increase was observed in those with dormant micrometastases. Immunotherapy was administered to the hosts after excision of the primary tumor, producing a recovery in their immune status and leading to the complete eradication of overt spontaneous metastases or their decrease. According to these findings, the combination of MHC-I surface expression in primary tumor and metastases with host T-cell subsets may be a decisive indicator of the clinical outcome and response to immunotherapy in metastatic disease, allowing the identification of responders to this approach.

Innate and acquired immune surveillance in the postdissemination phase of metastasis

Metastasis is responsible for the majority of death in cancer patients. Of the different steps in the metastasis cascade, the postdissemination phase is perhaps one of the least understood. Many factors, both from the disseminated tumor cells and the microenvironment, impact the success of the metastatic outgrowth. In this article, we discuss the interactions between colonizing cancer cells and immune cells in the period between vascular arrest in a secondary organ and metastatic outgrowth. We address the ambiguity in the findings of current research regarding the role of immune cells in regulating the metastatic microenvironment, and their hand in determining cancer cell fate.

Characterization and functional analysis of a slow-cycling subpopulation in colorectal cancer enriched by cell cycle inducer combined chemotherapy

The concept of cancer stem cells has been proposed in various malignancies including colorectal cancer. Recent studies show direct evidence for quiescence slow-cycling cells playing a role in cancer stem cells. There exists an urgent need to isolate and better characterize these slow-cycling cells. In this study, we developed a new model to enrich slow-cycling tumor cells using cell-cycle inducer combined with cell cycle-dependent chemotherapy in vitro and in vivo. Our results show that Short-term exposure of colorectal cancer cells to chemotherapy combined with cell-cycle inducer enriches for a cell-cycle quiescent tumor cell population. Specifically, these slow-cycling tumor cells exhibit increased chemotherapy resistance in vitro and tumorigenicity in vivo. Notably, these cells are stem-cell like and participate in metastatic dormancy. Further exploration indicates that slow-cycling colorectal cancer cells in our model are less sensitive to cytokine-induced-killer cell mediated cytotoxic killing in vivo and in vitro. Collectively, our cell cycle inducer combined chemotherapy exposure model enriches for a slow-cycling, dormant, chemo-resistant tumor cell sub-population that are resistant to cytokine induced killer cell based immunotherapy. Studying unique signaling pathways in dormant tumor cells enriched by cell cycle inducer combined chemotherapy treatment is expected to identify novel therapeutic targets for preventing tumor recurrence.

Tumor Dormancy and Relapse: From a Natural Byproduct of Evolution to a Disease State

Species evolve by mutations and epigenetic changes acting on individuals in a population; tumors evolve by similar mechanisms at a cellular level in a tissue. This article reviews growing evidence about tumor dormancy and suggests that (i) cellular malignancy is a natural byproduct of evolutionary mechanisms, such as gene mutations and epigenetic modifications, which is manifested in the form of tumor dormancy in healthy individuals as well as in cancer survivors; (ii) cancer metastasis could be an early dissemination event that could occur during malignant dormancy even before primary cancer is clinically detectable; and (iii) chronic inflammation is a key factor in awakening dormant malignant cells at the primary site, leading to primary cancer development, and at distant sites, leading to advanced stage diseases. On the basis of this evidence, it is reasonable to propose that we are all cancer survivors rather than cancer-free individuals because of harboring dormant malignant cells in our organs. A better understanding of local and metastatic tumor dormancy could lead to novel cancer therapeutics for the prevention of cancer. Cancer Res; 77(10); 2564-9. ©2017 AACR.

The Escape of Cancer from T Cell-Mediated Immune Surveillance: HLA Class I Loss and Tumor Tissue Architecture

Tumor immune escape is associated with the loss of tumor HLA class I (HLA-I) expression commonly found in malignant cells. Accumulating evidence suggests that the efficacy of immunotherapy depends on the expression levels of HLA class I molecules on tumors cells. It also depends on the molecular mechanism underlying the loss of HLA expression, which could be reversible/“soft” or irreversible/“hard” due to genetic alterations in HLA, β2-microglobulin or IFN genes. Immune selection of HLA-I negative tumor cells harboring structural/irreversible alterations has been demonstrated after immunotherapy in cancer patients and in experimental cancer models. Here, we summarize recent findings indicating that tumor HLA-I loss also correlates with a reduced intra-tumor T cell infiltration and with a specific reorganization of tumor tissue. T cell immune selection of HLA-I negative tumors results in a clear separation between the stroma and the tumor parenchyma with leucocytes, macrophages and other mononuclear cells restrained outside the tumor mass. Better understanding of the structural and functional changes taking place in the tumor microenvironment may help to overcome cancer immune escape and improve the efficacy of different immunotherapeutic strategies. We also underline the urgent need for designing strategies to enhance tumor HLA class I expression that could improve tumor rejection by cytotoxic T-lymphocytes (CTL).

Immune Regulation of the Metastatic Process: Implications for Therapy

Metastatic disease is the major cause of fatalities in cancer patients, but few therapies are designed to target the metastatic process. Cancer cells must perform a number of steps to successfully establish metastatic foci, including local invasion, intravasation, survival, extravasation, and growth in ectopic tissue. Due to the nonrandom distribution of metastasis, it has long been recognized that the tissue microenvironment must be an important determinant of colonization. More recently it has been established in animal models that immune cells regulate the metastatic process, including a dominant role for monocytes and macrophages, and emerging roles for neutrophils and various lymphocyte populations. While most research has focused on the early dissemination process, patients usually present clinically with disseminated, if not macroscopic, disease. Identifying pathways by which immune cells regulate growth and therapeutic resistance within metastatic sites is therefore key to the development of pharmacological agents that will significantly extend patient survival.

The urgent need to recover MHC class I in cancers for effective immunotherapy

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Tumor immune escape compromises the efficacy of cancer immunotherapy.

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Loss of MHC class I expression is a frequent event in cancer cells.

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Three tumor phenotypes determine cancer fate: escape, rejection and dormancy.

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Recovery of MHC class I expression is required to improve cancer immunotherapy.

Immune escape strategies aimed to avoid T-cell recognition, including the loss of tumor MHC class I expression, are commonly found in malignant cells. Tumor immune escape has proven to have a negative effect on the clinical outcome of cancer immunotherapy, including treatment with antibodies blocking immune checkpoint molecules. Hence, there is an urgent need to develop novel approaches to overcome tumor immune evasion. MHC class I antigen presentation is often affected in human cancers and the capacity to induce upregulation of MHC class I cell surface expression is a critical step in the induction of tumor rejection. This review focuses on characterization of rejection, escape, and dormant profiles of tumors and its microenvironment with a special emphasis on the tumor MHC class I expression. We also discuss possible approaches to recover MHC class I expression on tumor cells harboring reversible/‘soft’ or irreversible/‘hard’ genetic lesions. Such MHC class I recovery approaches might well synergize with complementary forms of immunotherapy.

Cancer Dormancy: A Regulatory Role for Endogenous Immunity in Establishing and Maintaining the Tumor Dormant State

The significant contribution of host immunity in early tumorigenesis has been recently recognized as a result of our better understanding of the molecular pathways regulating tumor cell biology and tumor-lymphocyte interactions. Emerging evidence suggests that disseminated dormant tumor cells derived from primary tumors before or after immune surveillance, are responsible for subsequent metastases. Recent trends from the field of onco-immunology suggest that efficiently stimulating endogenous anticancer immunity is a prerequisite for the successful outcome of conventional cancer therapies. Harnessing the immune system to achieve clinical efficacy is realistic in the context of conventional therapies resulting in immunogenic cell death and/or immunostimulatory side effects. Targeted therapies designed to target oncogenic pathways in tumor cells can also positively regulate the endogenous immune response and tumor microenvironment. Identification of T cell inhibitory signals has prompted the development of immune checkpoint inhibitors, which specifically hinder immune effector inhibition, reinvigorating and potentially expanding the preexisting anticancer immune response. This anticancer immunity can be amplified in the setting of immunotherapies, mostly in the form of vaccines, which boost naturally occurring T cell clones specifically recognizing tumor antigens. Thus, a promising anticancer therapy will aim to activate patients' naturally occurring anticancer immunity either to eliminate residual tumor cells or to prolong dormancy in disseminated tumor cells. Such an endogenous anticancer immunity plays a significant role for controlling the balance between dormant tumor cells and tumor escape, and restraining metastases. In this review, we mean to suggest that anticancer therapies aiming to stimulate the endogenous antitumor responses provide the concept of the therapeutic management of cancer.

Generation of MHC class I diversity in primary tumors and selection of the malignant phenotype

Intratumor heterogeneity among cancer cells is promoted by reversible or irreversible genetic alterations and by different microenvironmental factors. There is considerable experimental evidence of the presence of a variety of malignant cell clones with a wide diversity of major histocompatibility class I (MHC-I) expression during early stages of tumor development. This variety of MHC-I phenotypes may define the evolution of a particular tumor. Loss of MHC-I molecules frequently results in immune escape of MHC-negative or -deficient tumor cells from the host T cell-mediated immune response. We review here the results obtained by our group and other researchers in animal models and humans, showing how MHC-I intratumor heterogeneity may affect local oncogenicity and metastatic progression. In particular, we summarize the data obtained in an experimental mouse cancer model of a methylcholanthrene-induced fibrosarcoma (GR9), in which isolated clones with different MHC-I expression patterns demonstrated distinct local tumor growth rates and metastatic capacities. The observed "explosion of diversity" of MHC-I phenotypes in primary tumor clones and the molecular mechanism ("hard"/irreversible or "soft"/reversible) responsible for a given MHC-I alteration might determine not only the metastatic capacity of the cells but also their response to immunotherapy. We also illustrate the generation of further MHC heterogeneity during metastatic colonization and discuss different strategies to favor tumor rejection by counteracting MHC-I loss. Finally, we highlight the role of MHC-I genes in tumor dormancy and cell cycle control.

Metastases in immune-mediated dormancy: a new opportunity for targeting cancer

The aim of any anticancer treatment is to avoid, control, or eliminate disseminated tumor cells. Clinical and experimental evidence has revealed that metastases can remain in a latency state, that is, metastasis dormancy. Three mechanisms are thought to be involved in cancer dormancy: cellular dormancy, angiogenic dormancy, and immune-mediated dormancy. Here, we review the mechanisms and cells involved in immune-mediated cancer dormancy and discuss current and future immunotherapeutic strategies. Recent results indicate that the immune system can restrain disseminated cancer cells, promoting their permanent dormancy. CD8(+) T lymphocytes play a relevant role in maintaining immune equilibrium with metastatic dormant cells, and MHC class I surface expression on tumor cells may also be involved. Natural killer (NK) cells have an activator function that triggers a cytotoxic T lymphocyte (CTL) response. Furthermore, immune dormancy promotes cancer cell growth arrest and angiogenic control. Immunotherapeutic interventions in metastatic dormancy may help to control or eradicate cancer disease. Treatments that activate or increase the CTL immune response or reverse cancer cell-induced CTL immunosuppression might be useful to restrain or destroy metastatic cells. These objectives may be achieved by recovering or increasing MHC class I surface expression on cancer cells or even by activating NK cells. Immune-mediated metastasis dormancy provides an opportunity for targeting cancer in novel immune treatments.

A novel preclinical murine model of immune-mediated metastatic dormancy

The mechanisms underlying cancer dormancy are poorly understood. We have developed a preclinical murine model in which immunosurveillance restrains spontaneous metastases in permanent dormancy. The model faithfully recapitulates human metastatic dormancy and may be useful to decipher the immune mechanisms constraining disease progression, thereby facilitating the development of novel immunotherapeutic approaches to control metastatic disease.