Tumor microvasculature as a barrier to antitumor immunity

Interrelationships between the extracellular matrix and the immune microenvironment that govern epithelial tumour progression

Solid tumours are composed of cancer cells characterised by genetic mutations that underpin the disease, but also contain a suite of genetically normal cells and the extracellular matrix (ECM). These two latter components are constituents of the tumour microenvironment (TME), and are key determinants of tumour biology and thereby the outcomes for patients. The tumour ECM has been the subject of intense research over the past two decades, revealing key biochemical and mechanobiological principles that underpin its role in tumour cell proliferation and survival. However, the ECM also strongly influences the genetically normal immune cells within the microenvironment, regulating not only their proliferation and survival, but also their differentiation and access to tumour cells. Here we review recent advances in our knowledge of how the ECM regulates the tumour immune microenvironment and vice versa, comparing normal skin wound healing to the pathological condition of tumour progression.

Leveraging microenvironmental synthetic lethalities to treat cancer

Treatment resistance leads to cancer patient mortality. Therapeutic approaches that employ synthetic lethality to target mutational vulnerabilities in key tumor cell signaling pathways have proven effective in overcoming therapeutic resistance in some cancers. Yet, tumors are organs composed of malignant cells residing within a cellular and noncellular stroma. Tumor evolution and resistance to anticancer treatment are mediated through a dynamic and reciprocal dialogue with the tumor microenvironment (TME). Accordingly, expanding tumor cell synthetic lethality to encompass contextual synthetic lethality has the potential to eradicate tumors by targeting critical TME circuits that promote tumor progression and therapeutic resistance. In this Review, we summarize current knowledge about the TME and discuss its role in treatment. We outline the concept of tumor cell-specific synthetic lethality and describe therapeutic approaches to expand this paradigm to leverage TME synthetic lethality to improve cancer therapy.

High endothelial venules (HEVs) in human melanoma lesions: Major gateways for tumor-infiltrating lymphocytes

The presence of tumor-infiltrating lymphocytes (TILs) is a strong prognostic parameter for local dissemination and overall survival in melanoma. Lymphocyte migration from blood into peripheral tissues is mainly regulated by vascular endothelium. However, the blood vessels and mechanisms governing the recruitment of TILs in melanoma tumors remain poorly understood. Here, we show that high endothelial venules (HEVs), specialized blood vessels for lymphocyte extravasation into lymphoid tissues, are frequently found in melanoma tumors and are associated with high levels of lymphocyte infiltration. The analysis of 225 primary melanomas revealed that lymphocytes specifically infiltrated HEV-rich areas of melanoma tumors and that the density of MECA-79+ HEVs was variable among patients and strongly correlated with CD3+, CD8+ and CD20+ TIL densities. Inflammatory (CCL5, CXCL9, CXCL10 and CXCL11) and lymphoid (CCL21, CCL19 and CXCL13) chemokines as well as TH1 and naïve T-cell genes were overexpressed in melanoma samples with high densities of tumor HEVs. Mature dendritic cells (mDCs) were frequently found around tumor HEVs and densities of HEVs and DC-LAMP+ mDCs within tumor stroma were strongly correlated. DCs which maintain HEVs in lymph nodes, may thus also contribute to the regulation of HEVs in melanomas. Finally, we found significantly higher densities of tumor HEVs in melanomas with tumor regression, low Clark level of invasion and thin Breslow thickness (all p < 0.001). The strong association between tumor HEVs, TILs, mDCs and clinical parameters of melanoma, supports a critical role for HEVs in limiting malignant melanoma development through both naïve and effector T-lymphocyte recruitment and activation.

Mutually Supportive Mechanisms of Inflammation and Vascular Remodeling

Chronic inflammation is often accompanied by angiogenesis, the development of new blood vessels from existing ones. This vascular response is a response to chronic hypoxia and/or ischemia, but is also contributory to the progression of disorders including atherosclerosis, arthritis, and tumor growth. Proinflammatory and proangiogenic mediators and signaling pathways form a complex and interrelated network in these conditions, and many factors exert multiple effects. Inflammation drives angiogenesis by direct and indirect mechanisms, promoting endothelial proliferation, migration, and vessel sprouting, but also by mediating extracellular matrix remodeling and release of sequestered growth factors, and recruitment of proangiogenic leukocyte subsets. The role of inflammation in promoting angiogenesis is well documented, but by facilitating greater infiltration of leukocytes and plasma proteins into inflamed tissues, angiogenesis can also propagate chronic inflammation. This review examines the mutually supportive relationship between angiogenesis and inflammation, and considers how these interactions might be exploited to promote resolution of chronic inflammatory or angiogenic disorders.

Radiation for Awakening the Dormant Immune System, a Promising Challenge to be Explored

Recent advances that have been made in our understanding of cancer biology and immunology show that infiltrated immune cells and cytokines in the tumor microenvironment may play different functions that appear tightly related to clinical outcomes. Strategies aimed at interfering with the cross-talk between microenvironment tumor cells and their cellular partners have been considered for the development of new immunotherapies. These novel therapies target different cell components of the tumor microenvironment and importantly, they may be coupled and boosted with classical treatments, such as radiotherapy. In this work, we try to summarize recent data on the microenvironment impact of radiation therapy, from pre-clinical research to the clinic, while taking into account that this new knowledge will probably translate into indication and objective of radiation therapy changes in the next future.

Radiation for Awakening the Dormant Immune System, a Promising Challenge to be Explored

Recent advances that have been made in our understanding of cancer biology and immunology show that infiltrated immune cells and cytokines in the tumor microenvironment may play different functions that appear tightly related to clinical outcomes. Strategies aimed at interfering with the cross-talk between microenvironment tumor cells and their cellular partners have been considered for the development of new immunotherapies. These novel therapies target different cell components of the tumor microenvironment and importantly, they may be coupled and boosted with classical treatments, such as radiotherapy. In this work, we try to summarize recent data on the microenvironment impact of radiation therapy, from pre-clinical research to the clinic, while taking into account that this new knowledge will probably translate into indication and objective of radiation therapy changes in the next future.

Characteristics of tertiary lymphoid structures in primary cancers

Tumors are sustained by complex networks of interactions between malignant cells, stromal cells and tumor-infiltrating immune cells. These networks differ from patient to patient in terms of nature, composition and organization as well as with regard to the precise localization of tumor-infiltrating cells. Of note, the heterogeneity of the immunological component of the tumor microenvironment, as opposed to its mere abundance, has been shown to influence disease outcome. However, a key question remains: where does the activation of tumor-specific T cells take place? The recently described, tumor-associated lymph node-like entities termed “tertiary lymphoid structures” exhibit a structural organization that is reminiscent of secondary lymphoid organs, and thus may imprint the local immune contexture. Here, we discuss how cancer-associated tertiary lymphoid structures impact on the tumor micro-architecture, immune microenvironment, and ultimately, patient survival.

Preconditioning thermal therapy: flipping the switch on IL-6 for anti-tumour immunity

Cancer immunotherapy aims to generate long-lived, tumour-specific adaptive immunity to limit dysregulated tumour progression and metastasis. Tumour vasculature has emerged as a critical checkpoint controlling the efficacy of immunotherapy since it is the main access point for cytotoxic T cells to reach tumour cell targets. Therapeutic success has been particularly challenging to achieve because of the local, cytokine-rich inflammatory milieu that drives a pro-tumourigenic programme supporting the growth and survival of malignant cells. Here, we focus on recent evidence that systemic thermal therapy can switch the activities of the inflammatory cytokine, interleukin-6 (IL-6), to a predominantly anti-tumourigenic function that promotes anti-tumour immunity by mobilising T cell trafficking in the recalcitrant tumour microenvironment.

Role of T lymphocytes in tumor response to radiotherapy

Over thirty years ago, Helen Stone and colleagues compared the effects of local tumor irradiation in immunocompetent and T cell deficient mice, providing the first evidence that tumor response to radiotherapy is impaired in the absence of a normal T cell repertoire. In the following three decades there has been an exponential growth in understanding T cells and the complex molecular mechanisms that regulate their activation, migration to tumors and effector functions. We now also know that tumor progression is intrinsically linked to the development of multiple immunosuppressive mechanisms that allow cancer cells to escape immune control. Recent evidence about the role of T cells in determining the prognosis and outcome of patients at any clinical stages of cancer has been instrumental in re-directing the concept of immunosurveillance and immunoediting from the realm of preclinical models to the reality of clinical observations. Importantly, cell death induced by standard anti-cancer therapies like chemotherapy and radiation has been demonstrated to involve the immune system and, in certain specific settings, enable a specific immune response. It is, therefore, not surprising that the last few years have seen an increase in investigations exploring how to harness the ability of radiation to induce anti-tumor immune responses. We will review here the experimental evidence that anti-tumor T cells are key players in tumor control achieved by radiotherapy. The effects of radiation on the tumor that have been shown to enhance the priming and effector phases of anti-tumor immunity will be discussed. Finally, we will highlight promising combinations of immune response modifiers that enhance T cell function with radiotherapy which are being tested in the clinic.

Matrix architecture defines the preferential localization and migration of T cells into the stroma of human lung tumors

Appropriate localization and migration of T cells is a prerequisite for antitumor immune surveillance. Studies using fixed tumor samples from human patients have shown that T cells accumulate more efficiently in the stroma than in tumor islets, but the mechanisms by which this occurs are unknown. By combining immunostaining and real-time imaging in viable slices of human lung tumors, we revealed that the density and the orientation of the stromal extracellular matrix likely play key roles in controlling the migration of T cells. Active T cell motility, dependent on chemokines but not on β1 or β2 integrins, was observed in loose fibronectin and collagen regions, whereas T cells migrated poorly in dense matrix areas. Aligned fibers in perivascular regions and around tumor epithelial cell regions dictated the migratory trajectory of T cells and restricted them from entering tumor islets. Consistently, matrix reduction with collagenase increased the ability of T cells to contact cancer cells. Thus, the stromal extracellular matrix influences antitumor immunity by controlling the positioning and migration of T cells. Understanding the mechanisms by which this collagen network is generated has the potential to aid in the development of new therapeutics.

Thiodigalactoside inhibits murine cancers by concurrently blocking effects of galectin-1 on immune dysregulation, angiogenesis and protection against oxidative stress

Cancer cells produce galectin-1 as a tumor promoting protein. Thiodigalactoside (TDG) as a non-metabolised small drug, is shown to suppress tumor growth by inhibiting multiple cancer enhancing activities of galectin-1, including immune cell dysregulation, angiogenesis and protection against oxidative stress. Thus, using B16F10 melanoma and 4T1 orthotopic breast cancer models, intratumoral injection of TDG significantly raised the levels of tumor-infiltrating CD8⁺ lymphocytes and reduced CD31⁺ endothelial cell content, reducing tumor growth. TDG treatment of tumors in Balb/c nude mice (defective in T cell immunity) reduced angiogenesis and slowed tumor growth by a third less than in immunocompetent mice. Knocking down galectin-1 expression (G1KD) in both cancer cell types significantly impeded tumor growth and the sensitivity of the G1KD tumors to TDG was severely reduced, highlighting a specific role for galectin-1. Endothelial cells were protected by galectin-1 from oxidative stress-induced apoptosis induced by H₂O₂, but TDG inhibited this antioxidant protective effect of galectin-1 and reduced tube forming activity in angiogenic assays. We show for the first time that the single agent, TDG, concurrently prevents many tumor promoting effects of galectin-1 on angiogenesis, immune dysregulation and protection against oxidative stress, providing a potent and novel small molecule as an anti-cancer drug.

Loci controlling lymphocyte production of interferon c after alloantigen stimulation in vitro and their co-localization with genes controlling lymphocyte infiltration of tumors and tumor susceptibility

Low infiltration of lymphocytes into cancers is associated with poor prognosis, but the reasons why some patients exhibit a low and others a high infiltration of tumors are unknown. Previously we mapped four loci (Lynf1–Lynf4) controlling lymphocyte infiltration of mouse lung tumors. These loci do not encode any of the molecules that are involved in traffic of lymphocytes. Here we report a genetic relationship between these loci and the control of production of IFNγ in allogeneic mixed lymphocyte cultures (MLC). We found that IFNγ production by lymphocytes of O20/A mice is lower than by lymphocytes of OcB-9/Dem mice (both H2^pz) stimulated in MLC by irradiated splenocytes of C57BL/10SnPh (H2^b) or BALB/cHeA (H2^d) mice, or by ConA. IFNγ production in MLCs of individual (O20 × OcB-9)F₂ mice stimulated by irradiated C57BL/10 splenocytes and genotyped for microsatellite markers revealed four IFNγ-controlling loci (Cypr4-Cypr7), each of which is closely linked with one of the four Lynf loci and with a cluster of susceptibility genes for different tumors. This suggests that inherited differences in certain lymphocyte responses may modify their propensity to infiltrate tumors and their capacity to affect tumor growth.

Three-dimensional characterization of the vascular bed in bone metastasis of the rat by microcomputed tomography (MicroCT)

Background

Angiogenesis contributes to proliferation and metastatic dissemination of cancer cells. Anatomy of blood vessels in tumors has been characterized with 2D techniques (histology or angiography). They are not fully representative of the trajectories of vessels throughout the tissues and are not adapted to analyze changes occurring inside the bone marrow cavities.

Methodology/Principal Findings

We have characterized the vasculature of bone metastases in 3D at different times of evolution of the disease. Metastases were induced in the femur of Wistar rats by a local injection of Walker 256/B cells. Microfil®, (a silicone-based polymer) was injected at euthanasia in the aorta 12, 19 and 26 days after injection of tumor cells. Undecalcified bones (containing the radio opaque vascular casts) were analyzed by microCT, and a first 3D model was reconstructed. Bones were then decalcified and reanalyzed by microCT; a second model (comprising only the vessels) was obtained and overimposed on the former, thus providing a clear visualization of vessel trajectories in the invaded metaphysic allowing quantitative evaluation of the vascular volume and vessel diameter. Histological analysis of the marrow was possible on the decalcified specimens. Walker 256/B cells induced a marked osteolysis with cortical perforations. The metaphysis of invaded bones became progressively hypervascular. New vessels replaced the major central medullar artery coming from the diaphyseal shaft. They sprouted from the periosteum and extended into the metastatic area. The newly formed vessels were irregular in diameter, tortuous with a disorganized architecture. A quantitative analysis of vascular volume indicated that neoangiogenesis increased with the development of the tumor with the appearance of vessels with a larger diameter.

Conclusion

This new method evidenced the tumor angiogenesis in 3D at different development times of the metastasis growth. Bone and the vascular bed can be identified by a double reconstruction and allowed a quantitative evaluation of angiogenesis upon time.

AACR centennial series: the biology of cancer metastasis: historical perspective

Metastasis resistant to therapy is the major cause of death from cancer. Despite almost 200 years of study, the process of tumor metastasis remains controversial. Stephen Paget initially identified the role of host-tumor interactions on the basis of a review of autopsy records. His "seed and soil" hypothesis was substantiated a century later with experimental studies, and numerous reports have confirmed these seminal observations. An improved understanding of the metastatic process and the attributes of the cells selected by this process is critical for the treatment of patients with systemic disease. In many patients, metastasis has occurred by the time of diagnosis, so metastasis prevention may not be relevant. Treating systemic disease and identifying patients with early disease should be our goal. Revitalized research in the past three decades has focused on new discoveries in the biology of metastasis. Even though our understanding of molecular events that regulate metastasis has improved, the contributions and timing of molecular lesion(s) involved in metastasis pathogenesis remain unclear. Review of the history of pioneering observations and discussion of current controversies should increase understanding of the complex and multifactorial interactions between the host and selected tumor cells that contribute to fatal metastasis and should lead to the design of successful therapy.

AACR centennial series: the biology of cancer metastasis: historical perspective

Metastasis resistant to therapy is the major cause of death from cancer. Despite almost 200 years of study, the process of tumor metastasis remains controversial. Stephen Paget initially identified the role of host-tumor interactions on the basis of a review of autopsy records. His "seed and soil" hypothesis was substantiated a century later with experimental studies, and numerous reports have confirmed these seminal observations. An improved understanding of the metastatic process and the attributes of the cells selected by this process is critical for the treatment of patients with systemic disease. In many patients, metastasis has occurred by the time of diagnosis, so metastasis prevention may not be relevant. Treating systemic disease and identifying patients with early disease should be our goal. Revitalized research in the past three decades has focused on new discoveries in the biology of metastasis. Even though our understanding of molecular events that regulate metastasis has improved, the contributions and timing of molecular lesion(s) involved in metastasis pathogenesis remain unclear. Review of the history of pioneering observations and discussion of current controversies should increase understanding of the complex and multifactorial interactions between the host and selected tumor cells that contribute to fatal metastasis and should lead to the design of successful therapy.

Cancer immunotherapy: will expanding knowledge lead to success in pediatric oncology?

The past 25 years have seen an increase in our understanding of immunology and further expansion in the clinical use of immunotherapeutic modalities. How immunotherapy will be integrated with chemotherapy, radiation, and surgery remains to be established. Although there have been successes in the field of immunotherapy, they have been inconsistent, and it is hoped that increased understanding of the basic principles of immunology will improve the consistency of beneficial effects. In this article, we briefly provide a general overview of our current understanding of the immune system, with a focus on concepts in tumor immunology, followed by a discussion of how these concepts are being used in the clinic.

The Potential of the Tumor Microenvironment to Influence Apo2L/TRAIL Induced Apoptosis

Apo2L/TRAIL ligation of specific cell surface receptors (DR4 and DR5) induces apoptosis of many malignant cells with little effect on normal cells. This anti-tumor capability has been demonstrated using cell lines of many tumor types, both in vitro and in vivo when the cells are grown as xenografts. We have extended these studies to investigate the efficacy of Apo2L/TRAIL against patient tumor xenografts in SCID mice and found that the growth of many tumors, both of primary and metastatic origin, can be inhibited by Apo2L/TRAIL. The basis of resistance to Apo2L/TRAIL induced apoptosis in malignant cells and normal cells is not completely understood, but it is known that a variety of factors including hypoxia, MMPs and cytokines present in the tumor microenvironment can influence the response of malignant cells to Apo2L/TRAIL. Currently, the clinical potential of several molecules targeting the Apo2L/TRAIL receptors DR4 and DR5 is being investigated. Our goal in this review is to provide a brief overview of a number of factors that have potential to influence the response of patient tumors to Apo2L/TRAIL.

Multiphoton imaging of cytotoxic T lymphocyte-mediated antitumor immune responses

The actual contribution of T lymphocytes to protection against tumors is still unclear. In vitro imaging experiments show that tumor specific cytotoxic T lymphocytes (CTLs) are competent to kill target cells by conventional cytotoxic pathways. The emergence of multiphoton imaging in the past decade now allows real time in vivo imaging of CTLs. New insights are available on the behavior of antitumor T cells during the priming phase, during their traffic within the tumor tissue, and on their interactions with tumor cells during the effector phase. Recent reports suggest that direct killing of tumor cells by CTLs is a slow process, suggesting that the ratio of effector to target cells is determinant, or that additional cytotoxic contribution by other cell types is required to induce efficient tumor rejection. This review will focus on the publications that have imaged antitumor immune responses dynamically and discuss how this new information contributes to understand the implication of CTLs in tumor rejection.

Interleukin-15/interleukin-15R alpha complexes promote destruction of established tumors by reviving tumor-resident CD8+ T cells

Tumors often escape immune-mediated destruction by suppressing lymphocyte infiltration or effector function. New approaches are needed that overcome this suppression and thereby augment the tumoricidal capacity of tumor-reactive lymphocytes. The cytokine interleukin-15 (IL-15) promotes proliferation and effector capacity of CD8(+) T cells, natural killer (NK) cells, and NKT cells; however, it has a short half-life and high doses are needed to achieve functional responses in vivo. The biological activity of IL-15 can be dramatically increased by complexing this cytokine to its soluble receptor, IL-15R alpha. Here, we report that in vivo delivery of IL-15/IL-15R alpha complexes triggers rapid and significant regression of established solid tumors in two murine models. Despite a marked expansion of IL-2/IL-15R beta(+) cells in lymphoid organs and peripheral blood following treatment with IL-15/IL-15R alpha complexes, the destruction of solid tumors was orchestrated by tumor-resident rather than newly infiltrating CD8(+) T cells. Our data provide novel insights into the use of IL-15/IL-15R alpha complexes to relieve tumor-resident T cells from functional suppression by the tumor microenvironment and have significant implications for cancer immunotherapy and treatment of chronic infections.

Synergistic antitumor effects of CpG oligodeoxynucleotide and STAT3 inhibitory agent JSI-124 in a mouse melanoma tumor model

One of the major limitations for cancer immunotherapy is related to the frequent existence of an intra-tumoral immunosuppressive environment, to which STAT3 (Signal transducer and activator of transcription-3) activation in tumor and dendritic cells (DCs) are believed to contribute. In this study, we tested the hypothesis that the combination of CpG (a DC activator) and JSI-124 (a STAT3 inhibitor) may generate synergistic antitumor effects compared to CpG or JSI-124 alone. B16-F10, a mouse melanoma cell line that has constitutively active STAT3, was grafted in C57BL/6 mice and then tumor-bearing mice treated intra-tumorally with (a) phosphate buffered saline, (b) 10 microg CpG, (c) 1 mg kg(-1) JSI-124 or (d) 10 microg CpG+1 mg kg(-1) JSI-124. The effects of treatments on tumor growth, survival and antitumor immune responses were evaluated. Although significant antitumor effects were detected with the single-agent treatments, the CpG+JSI-124 treatment resulted in synergistic antitumor effects compared to CpG or JSI-124 alone. Correlating with these findings, the combination therapy resulted in significantly higher intra-tumoral levels of several proinflammatory, TH1-related cytokines (including IL-12, IFN-gamma, TNF-alpha and IL-2), increases in intra-tumoral CD8+ and CD4+ T cells expressing activation/memory markers and NK cells and increases in activated DCs in the tumors and regional lymph nodes (LNs). Concomitantly, the combination therapy led to a significantly decreased level of immunosuppression, as evidenced by lower intra-tumoral level of VEGF and TGF-beta, and decreased number of CD4+CD25+Foxp3+ regulatory T cells in the regional LNs. This study has provided the proof-of-principle for combining CpG and JSI-124 to enhance antitumor immune responses.

Sensors of ionizing radiation effects on the immunological microenvironment of cancer

PURPOSE

When cancer develops in an immunocompetent host it represents the result of a successful deception of the immune system as to the nature of the danger and the type of response needed to reject the neoplastic tissue. We will briefly review some of the recently emerged evidence that irradiation of the tumor and its microenvironment can induce essential molecular signals required for an effective response of the immune system to the tumor.

CONCLUSIONS

The subversion of a highly organized tissue architecture is a hallmark of cancer, and results in uneven distribution of oxygen and nutrients, interstitial pressure gradients and areas of patchy necrosis and inflammation. In this microenvironment, cancer cells that carry mutations favoring survival rather than cell death in response to stress find a selection advantage. Importantly, the signals derived from the disruption of orderly physiology within tissues are also what the immune system has evolved to respond to. The type of response is tuned to be adequate to the cause of the disruption. An infectious organism will carry or elicit from the involved tissue a number of 'danger signals' leading to development of cell mediated and humoral responses to both eliminating the invader and preventing future infections. In contrast, a simple wound will call for a repair response. The sensors of the type of damage are complex molecular interactions between the damaged organ and cells of the innate and adaptive immune system. Progress in the identification of these interactions elucidates which pathways are specifically altered in cancer. It also provides a novel understanding of the radiation-induced effects on tumor immunogenicity. We propose that specific radiation-induced effects could be successfully exploited to improve the effectiveness of immunotherapy.

Cancer immunotherapy: will expanding knowledge lead to success in pediatric oncology?

The past 25 years have seen an increase in our understanding of immunology and further expansion in the clinical use of immunotherapeutic modalities. How immunotherapy will be integrated with chemotherapy, radiation, and surgery remains to be established. Although there have been successes in the field of immunotherapy, they have been inconsistent, and it is hoped that increased understanding of the basic principles of immunology will improve the consistency of beneficial effects. In this article, we briefly provide a general overview of our current understanding of the immune system, with a focus on concepts in tumor immunology, followed by a discussion of how these concepts are being used in the clinic.

Control of lymphocyte infiltration of lung tumors in mice by host's genes: mapping of four Lynf (lymphocyte infiltration) loci

Tumor infiltration by lymphocytes is essential for cell-mediated immune elimination of tumors in experimental systems and in immunotherapy of cancer. Presence of lymphocytes in several human cancers has been associated with a better prognosis. We present evidence that individual propensity to tumor infiltration is genetically controlled. Infiltrating lymphocytes are present in 50% of lung tumors in O20/A mice, but in only 10% of lung tumors in OcB-9/Dem mice. This difference has been consistent in experiments conducted over 8 years in two different animal facilities. To test whether this strain difference is controlled genetically, we analyzed the presence of infiltrating lymphocytes in N-ethyl-N-nitroso-urea (ENU) induced lung tumors in (O20 x OcB-9) F(2) hybrids. We mapped four genetic loci, Lynf1 (Lymphocyte infiltration 1), Lynf2, Lynf3, and Lynf4 that significantly modify the presence and intensity of intra-tumoral infiltrates containing CD4(+) and CD8(+) T lymphocytes. These loci appear to be distinct from the genes encoding the molecules that are presently implicated in lymphocyte infiltration. Our findings open a novel approach for the assessment of individual propensity for tumor infiltration by genotyping the genes of the host that influence this process using DNA from any normal tissue. Such prediction of probability of tumor infiltration in individual cancer patients could help considerably to assess their prognosis and to decide about the application and the type of immunotherapy.

Inflammatory cell infiltration of tumors: Jekyll or Hyde

Inflammatory cell infiltration of tumors contributes either positively or negatively to tumor invasion, growth, metastasis, and patient outcomes, creating a Dr. Jekyll or Mr. Hyde conundrum when examining mechanisms of action. This is due to tumor heterogeneity and the diversity of the inflammatory cell phenotypes that infiltrate primary and metastatic lesions. Tumor infiltration by macrophages is generally associated with neoangiogenesis and negative outcomes, whereas dendritic cell (DC) infiltration is typically associated with a positive clinical outcome in association with their ability to present tumor antigens (Ags) and induce Ag-specific T cell responses. Myeloid-derived suppressor cells (MDSCs) also infiltrate tumors, inhibiting immune responses and facilitating tumor growth and metastasis. In contrast, T cell infiltration of tumors provides a positive prognostic surrogate, although subset analyses suggest that not all infiltrating T cells predict a positive outcome. In general, infiltration by CD8(+) T cells predicts a positive outcome, while CD4(+) cells predict a negative outcome. Therefore, the analysis of cellular phenotypes and potentially spatial distribution of infiltrating cells are critical for an accurate assessment of outcome. Similarly, cellular infiltration of metastatic foci is also a critical parameter for inducing therapeutic responses, as well as establishing tumor dormancy. Current strategies for cellular, gene, and molecular therapies are focused on the manipulation of infiltrating cellular populations. Within this review, we discuss the role of tumor infiltrating, myeloid-monocytic cells, and T lymphocytes, as well as their potential for tumor control, immunosuppression, and facilitation of metastasis.

Leukocyte infiltration and tumor cell plasticity are parameters of aggressiveness in primary cutaneous melanoma

Various clinical and experimental observations detected an immunological host defense in cutaneous melanoma. In order to investigate the prognostic value of leukocyte effector mechanisms, we examined the presence of different subsets of leukocytes in tumor samples of 58 patients diagnosed with primary cutaneous melanoma. The presence of T lymphocytes, cytotoxic T lymphocytes, B lymphocytes, CD16+ cells and macrophages was correlated to Breslow depth. A significantly higher amount of several subsets of leukocytes was found in samples with a more progressed tumor stage and survival analysis demonstrated that a higher amount of T lymphocytes and CD16+ cells was associated with a short survival. The amount of FOXP3+ regulatory T lymphocytes did not correlate with survival, nevertheless, it correlated with the amount of total infiltrate. In contrast, analysis of the expression of CD69, a marker for activated lymphocytes, demonstrated that patients with a higher amount of CD69+ lymphocytes had a better survival. In addition, a new parameter for aggressiveness of melanoma, tumor cell plasticity [i.e., the presence of periodic acid Schiff's (PAS) reagent positive loops], also predicted short survival and a trend of a higher amount of tumor infiltrating leukocytes in tumors with PAS positive loops was observed. These findings demonstrate that leukocyte infiltration and the presence of PAS loops is a sign of tumor aggressiveness and may have prognostic value.

Primary immune surveillance: some like it hot

The thermal element of fever has been found to be beneficial in models of infectious disease. The contributions of fever-range temperatures to the efficacy of the adaptive immune response have only begun to be delineated. There is accumulating evidence that fever-range thermal stress bolsters primary immune surveillance of lymph nodes and Peyer patches by augmenting lymphocyte extravasation across specialized vessels termed high endothelial venules. Molecular mechanisms have recently come to light by which the thermal component of fever alone may promote lymphocyte trafficking, and thereby the probability of mounting a defense against microbial infection. Acquired knowledge of the molecular changes associated with thermal stress may allow for the development of novel therapies for a variety of disease processes.

Spontaneous mammary tumors differ widely in their inherent sensitivity to adoptively transferred T cells

Immunotherapy of cancer can lead to the selection of antigen loss variants, which provides strong rationale to target oncogenes that are essential for tumor growth or viability. To investigate this concept, we tagged the HER2/neu oncogene with epitopes from ovalbumin to confer recognition by T-cell receptor transgenic CD8(+) (OT-I) and CD4(+) (OT-II) T cells. Transgenic mice expressing neu(OT-I/OT-II) developed mammary adenocarcinomas at 6 to 10 months of age. Adoptively transferred naive OT-I cells (with or without OT-II cells) proliferated vigorously on encountering neu(OT-I/OT-II)-expressing tumors. This was followed by the complete regression of 37% of tumors, whereas others showed partial/stable responses (40%) or progressive disease (23%). Those tumors undergoing complete regression never recurred. In mice with multiple primary tumors, simultaneous regressions and nonregressions were often seen, indicating that immune evasion occurred at a local rather than systemic level. The majority of nonregressing tumors expressed Neu(OT-I/OT-II) and MHC class I, and many avoided rejection through a profound block to T-cell infiltration. Thus, T cells directed against an essential oncogene can permanently eradicate a subset of spontaneous, established mammary tumors. However, in other tumors, local barriers severely limit the therapeutic response. To maximize the efficacy of immunotherapy against spontaneous cancers, predictive strategies that take into account the heterogeneity of the tumor microenvironment will be required.

Impact of fever-range thermal stress on lymphocyte-endothelial adhesion and lymphocyte trafficking

The evolutionarily conserved febrile response has been associated with improved survival during infection in endothermic and ectothermic species although its protective mechanism of action is not fully understood. Temperatures within the range of physiologic fever influence multiple parameters of the immune response including lymphocyte proliferation and cytotoxic activity, neutrophil and dendritic cell migration, and production or bioactivity of proinflammatory cytokines. This review focuses on the emerging role of fever-range thermal stress in promoting lymphocyte trafficking to secondary lymphoid organs that are major sites for launching effective immune responses during infection or inflammation. Specific emphasis will be on the molecular basis of thermal control of lymphocyte-endothelial adhesion, a critical checkpoint controlling lymphocyte extravasation, as well as the contribution of interleukin-6 (IL-6) trans-signaling to thermal activities. New results are presented indicating that thermal stimulation of lymphocyte homing potential is evident in evolutionarily distant endothermic vertebrate species. These observations support the view that the evolutionarily conserved febrile response contributes to immune protection and host survival by amplifying lymphocyte access to peripheral lymphoid organs.

Immune cell migration as a means to control immune privilege: lessons from the CNS and tumors

Certain organs, such as the brain, eye, and gonads, are particularly sensitive to damage by inflammation. Therefore, these tissues have developed unique immunological properties that curtail inflammatory responses, a phenomenon termed immune privilege. In addition, by co-opting some of the regulatory cues operant in immune privilege in normal organs, tumors can evade immunosurveillance. While many different mechanisms contribute to immune privilege, there is evidence that leukocyte migration is an important checkpoint in its control. This hypothesis is based on the fact that leukocyte entry into these organs is restricted by physical barriers and that the collapse of these obstacles marks a critical step in the development of inflammatory/autoimmune disease at these sites. Numerous studies in a variety of experimental systems have characterized the molecular and cellular mechanisms involved in leukocyte homing to immune-privileged organs. Recently, two-photon microscopy has revealed critical insights into the events occurring in the extravascular space of immune-privileged organs, including locomotion patterns and interactive behavior of leukocytes in the interstitial space. Here, we review our current understanding of immune cell migration to and within immune-privileged organs and highlight how this knowledge may be exploited for immunotherapeutic purposes.

Hurdles to lymphocyte trafficking in the tumor microenvironment: implications for effective immunotherapy

An important consideration in the development of T cell-based cancer immunotherapy is that effector T cells must efficiently traffic to the tumor microenvironment in order to control malignant progression. T cell trafficking to target tissues is orchestrated by dynamic interactions between circulating lymphocytes and endothelial cells lining blood vessels. It is informative, in this regard, to compare and contrast the molecular mechanisms governing lymphocyte extravasation at distinct vascular sites: (1) high endothelial venules (HEV) of secondary lymphoid organs, which are portals for efficient trafficking of naive and central memory T lymphocytes; (2) non-activated endothelium of normal tissues that mediate relatively low basal levels of trafficking but are rapidly transformed into HEV-like vessels in response to local inflammatory stimuli; and (3) vessels within the intratumoral region and the surrounding peritumoral areas. These vessels can be distinguished by differential expression of hallmark trafficking molecules that function as molecular beacons directing lymphocyte migration across vascular barriers. This article reviews evidence that recruitment of effector T cells to the intratumoral microenvironment is impeded by sub-threshold expression of trafficking molecules on tumor microvessels. Emerging data support the thesis that when considered from the perspective of extravasation, vessels embedded within the intratumoral microenvironment of established tumors do not exhibit stereotypical characteristics of a chronic inflammatory state. A major challenge will be to develop therapeutic approaches to improve trafficking of effector T lymphocytes to tumor sites without skewing the balance in favor of a chronic inflammatory milieu that facilitates tumor maintenance and progression.

Monocyte/macrophage infiltration in tumors: modulators of angiogenesis

The role of a tumor immune infiltrate in cancer progression and metastasis has been debated frequently. Although often considered to be associated with improved prognosis and leading to the enhanced survival of cancer patients, inflammatory cells have also been described to assist the tumor's capabilities to progress, proliferate, and metastasize. Tumor-associated macrophages (TAMs), for example, have been shown to be symbiotically related to tumor cells: Tumor cells recruit TAMs and provide them with survival factors, and TAMs in turn produce a variety of angiogenic factors in response to the tumor microenvironment. This review will describe the composition of an immune infiltrate in tumors and the angiogenic and angiostatic properties of the cells present. Special emphasis will be on the angiogenesis-associated activities of TAMs. The development of immunotherapy and gene therapy using TAMs to mediate tumor cytotoxicity or to deliver gene constructs will be discussed as well. As immunotherapy has so far not been as effective as anticipated, a combination therapy in which angiostatic agents are used as well is put forward as a novel strategy to treat cancer.

Dynamic control of lymphocyte trafficking by fever-range thermal stress

Migration of blood-borne lymphocytes into tissues involves a tightly orchestrated sequence of adhesion events. Adhesion molecules and chemokine receptors on the surface of circulating lymphocytes initiate contact with specialized endothelial cells under hemodynamic shear prior to extravasation across the vascular barrier into tissues. Lymphocyte-endothelial adhesion occurs preferentially in high endothelial venules (HEV) of peripheral lymphoid organs. The continuous recirculation of naïve and central memory lymphocytes across lymph node and Peyer's patch HEV underlies immune surveillance and immune homeostasis. Lymphocyte-endothelial interactions are markedly enhanced in HEV-like vessels of extralymphoid organs during physiological responses associated with acute and chronic inflammation. Similar adhesive mechanisms must be invoked for efficient trafficking of immune effector cells to tumor sites in order for the immune system to have an impact on tumor progression. Here we discuss recent evidence for the role of fever-range thermal stress in promoting lymphocyte-endothelial adhesion and trafficking across HEV in peripheral lymphoid organs. Findings are also presented that support the hypothesis that lymphocyte-endothelial interactions are limited within tumor microenvironments. Further understanding of the molecular mechanisms that dynamically promote lymphocyte trafficking in HEV may provide the basis for novel approaches to improve recruitment of immune effector cells to tumor sites.

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

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

Lung tumor location and lymphocyte infiltration in mice are genetically determined

Lung cancer is a heterogeneous disease with individual differences in histological type, rate of progression, and response to therapy. Definition of the molecular and genetic basis of specific tumor characteristics would provide a better assessment of prognosis and a basis for a more individualized therapy. Here the authors compare the quantitative and qualitative phenotypes of lung tumors in mice of O20/A and OcB-9/Dem strains subjected to 2 regimens of N-ethyl-N-nitrosourea (ENU) treatment: (1) prenatal tumor induction by a single intraperitoneal (IP) injection of 40 mg/kg body weight into pregnant females and (2) after the same prenatal induction, the progeny received on weeks 9 and 11 additional IP ENU injections. The numbers, size, and histological characteristics of tumors were determined microscopically in semiserial lung sections. Unexpectedly, the authors observed very highly significant strain differences in a novel polymorphic phenotype-peribronchial versus nonperibronchial location of lung tumors, as well as in frequency of lymphocyte infiltration. To assess the reproducibility of these genetic differences, the authors classified both tumor location and lymphocyte infiltration also in an independent set of lung tumors that were induced in these strains in experiments performed more than 10 years ago in a different mouse facility and found the same strain differences. These results indicate that these qualitative phenotypes are very robust (P(c) 5.52 x 10(-6) and 2.27 x 10(-8), respectively) and relatively independent of environmental influences. They likely reflect different stages of lung differentiation at the time of tumor induction and differences in molecules involved in intercellular signaling, respectively. The definition of genes controlling these traits will provide novel insights into the determination of tumor phenotype.