Interleukin-10 expressed at early tumour sites induces subsequent generation of CD4(+) T-regulatory cells and systemic collapse of antitumour immunity

Deciphering and reversing tumor immune suppression

Generating an anti-tumor immune response is a multi-step process that is executed by effector T cells that can recognize and kill tumor targets. However, tumors employ multiple strategies to attenuate the effectiveness of T-cell-mediated attack. They achieve this by interfering with nearly every step required for effective immunity, from deregulation of antigen-presenting cells to establishment of a physical barrier at the vasculature that prevents homing of effector tumor-rejecting cells and the suppression of effector lymphocytes through the recruitment and activation of immunosuppressive cells such as myeloid-derived suppressor cells, tolerogenic monocytes, and T regulatory cells. Here, we review the ways in which tumors exert immune suppression and highlight the new therapies that seek to reverse this phenomenon and promote anti-tumor immunity. Understanding anti-tumor immunity, and how it becomes disabled by tumors, will ultimately lead to improved immune therapies and prolonged survival of patients.

Natural and induced T regulatory cells in cancer

CD4+Foxp3+ T regulatory (Treg) cells control many facets of immune responses ranging from autoimmune diseases, to inflammatory conditions, and cancer in an attempt to maintain immune homeostasis. Natural Treg (nTreg) cells develop in the thymus and constitute a critical arm of active mechanisms of peripheral tolerance particularly to self antigens. A growing body of knowledge now supports the existence of induced Treg (iTreg) cells which may derive from a population of conventional CD4+ T cells. The fork-head transcription factor (Foxp3) typically is expressed by natural CD4+ Treg cells, and thus serves as a marker to definitively identify these cells. On the contrary, there is less consensus on what constitutes iTreg cells as their precise definition has been somewhat elusive. This is in part due to their distinct phenotypes which are shaped by exposure to certain inflammatory or "assault" signals stemming from the underlying immune disorder. The "policing" activity of Treg cells tends to be uni-directional in several pathological conditions. On one end of the spectrum, Treg cell suppressive activity is beneficial by curtailing T cell response against self-antigens and allergens thus preventing autoimmune diseases and allergies. On the other end however, their inhibitory roles in limiting immune response against pseudo-self antigens as in tumors often culminates into negative outcomes. In this review, we focus on this latter aspect of Treg cell immunobiology by highlighting the involvement of nTreg cells in various animal models and human tumors. We further discuss iTreg cells, relationship with their natural counterpart, and potential co-operation between the two in modulating immune response against tumors. Lastly, we discuss studies focusing on these cells as targets for improving anti-tumor immunity.

Natural and induced T regulatory cells in cancer

CD4+Foxp3+ T regulatory (Treg) cells control many facets of immune responses ranging from autoimmune diseases, to inflammatory conditions, and cancer in an attempt to maintain immune homeostasis. Natural Treg (nTreg) cells develop in the thymus and constitute a critical arm of active mechanisms of peripheral tolerance particularly to self antigens. A growing body of knowledge now supports the existence of induced Treg (iTreg) cells which may derive from a population of conventional CD4+ T cells. The fork-head transcription factor (Foxp3) typically is expressed by natural CD4+ Treg cells, and thus serves as a marker to definitively identify these cells. On the contrary, there is less consensus on what constitutes iTreg cells as their precise definition has been somewhat elusive. This is in part due to their distinct phenotypes which are shaped by exposure to certain inflammatory or “assault” signals stemming from the underlying immune disorder. The “policing” activity of Treg cells tends to be uni-directional in several pathological conditions. On one end of the spectrum, Treg cell suppressive activity is beneficial by curtailing T cell response against self-antigens and allergens thus preventing autoimmune diseases and allergies. On the other end however, their inhibitory roles in limiting immune response against pseudo-self antigens as in tumors often culminates into negative outcomes. In this review, we focus on this latter aspect of Treg cell immunobiology by highlighting the involvement of nTreg cells in various animal models and human tumors. We further discuss iTreg cells, relationship with their natural counterpart, and potential co-operation between the two in modulating immune response against tumors. Lastly, we discuss studies focusing on these cells as targets for improving anti-tumor immunity.

Comparative analysis of cancer vaccine settings for the selection of an effective protocol in mice

Background

Cancer vaccines are considered a promising therapeutic approach. However, their clinical results are not yet satisfactory. This may be due to the the difficulty of selection of an efficient tumor associated antigen (TAA) and immunization protocol. Indeed, the weak antigenicity of many TAA impairs the design of robust procedures, therefore a systematic analysis to identify the most efficient TAA is mandatory. Here, we performed a study to compare different gp100 vaccination strategies to identify the best strategy to provide a 100% protection against experimental melanoma in a reproducible manner.

Methods

C57BL/6J mice were challenged subcutaneously with B16F10 melanoma cells, after vaccination with: a) mouse or human gp100_25-33 peptide plus CpG adjuvant; b) mouse or human gp100 gene; c) mouse or human gp100_25-33 peptide-pulsed dendritic cells (DC). Alternatively, a neutralizing anti-IL-10 monoclonal antibody (mAb) was subcutaneously administered at the site of tumor challenge to counteract regulatory cells. Finally, combinatorial treatment was performed associating human gp100_25-33 peptide-pulsed DC vaccination with administration of the anti-IL-10 mAb.

Results

Vaccination with human gp100_25-33 peptide-pulsed DC was the most effective immunization protocol, although not achieving a full protection. Administration of the anti-IL-10 mAb showed also a remarkable protective effect, replicated in mice challenged with a different tumor, Anaplastic Large Cell Lymphoma. When immunization with gp100_25-33 peptide-pulsed DC was associated with IL-10 counteraction, a 100% protective effect was consistently achieved. The analysis on the T-cell tumor infiltrates showed an increase of CD4+granzyme+ T-cells and a decreased number of CD4+CD25+Foxp3+ Treg elements from mice treated with either gp100_25-33 peptide-pulsed DC vaccination or anti-IL-10 mAb administration. These data suggest that processes of intratumoral re-balance between effector and regulatory T cell subpopulations may play a critical protective role in immunotherapy protocols.

Conclusions

Here we demonstrate that, in the setting of a cancer vaccine strategy, a comparative analysis of different personalized approaches may favour the unveiling of the most effective protocol. Moreover, our findings suggest that counteraction of IL-10 activity may be critical to revert the intratumoral environment promoting Treg polarization, thus increasing the effects of a vaccination against selected TAA.

Functional macrophage heterogeneity in a mouse model of autoimmune central nervous system pathology

Functional macrophage heterogeneity is well appreciated outside the CNS in wound healing and cancer, and was recently also demonstrated in several CNS compartments after "sterile" insults. Yet, such heterogeneity was largely overlooked in the context of inflammatory autoimmune pathology, in which macrophages were mainly associated with disease induction and propagation. In this article, we show the diversity of monocyte-derived macrophages along the course of experimental autoimmune uveitis, an inflammatory condition affecting the ocular system, serving as a model for CNS autoimmune pathology. Disease induction resulted in the appearance of a distinct myeloid population in the retina, and in the infiltration of monocyte-derived macrophages that were absent from control eyes. During the disease course, the frequency of CX3CR1(high) infiltrating macrophages that express markers associated with inflammation-resolving activity was increased, along with a decrease in the frequency of inflammation-associated Ly6C(+) macrophages. Inhibition of monocyte infiltration at the induction phase of experimental autoimmune uveitis prevented disease onset, whereas monocyte depletion at the resolution phase resulted in a decrease in Foxp3(+) regulatory T cells and in exacerbated disease. Thus, monocyte-derived macrophages display distinct phenotypes throughout the disease course, even in an immune-induced pathology, reflecting their differential roles in disease induction and resolution.

Presence of tumour-infiltrating FOXP3+ lymphocytes correlates with immature tumour angiogenesis in renal cell carcinomas

BACKGROUND

FOXP3+ regulatory T cells (Tregs) inhibit effector T cell functions and are implicated in tumour progression. However, together with microvessel density (MVD) they remain controversial prognostic predictors for renal cell carcinoma (RCC), and potential associations have yet to be determined. The objective of this study was to determine the prognostic significance of Tregs and MVD and their potential relationship in RCCs.

DESIGN

Paraffin-embedded tissues from 62 RCC patients were analysed using immunohistochemistry to detect FOXP3+ lymphocytes, and double immunohistochemistry to detect different microvessel types in the tumour interior, rim and normal kidney tissue, and their correlation with clinicopathological characteristics. Survival analysis was also performed.

RESULTS

The presence of FOXP3+ cells in the tumour interior or the rim showed no correlation with death from RCC and other pathological characteristics. Negative correlations were noted between the immature MVD in the tumour interior or the rim and tumour size, tumour stage and overall survival; however, there was no correlation with the nuclear grade or pathological type. A positive correlation between FOXP3+ Tregs and immature MVD (r=0.363, P=0.014) and mature MVD (r=0.383, P=0.009) was confirmed in the tumour interior. However, there was no correlation between FOXP3+ Tregs and mature MVD (r=0.281, P=0.076) or immature MVD (r=0.064, P=0.692) in the tumour rim.

CONCLUSIONS

In this study, a positive correlation between the presence of FOXP3+ Tregs and immature and mature MVD in RCC was confirmed, which suggests a link between suppression of immunity, tumour angiogenesis and poor prognosis.

T-regulatory cells: key players in tumor immune escape and angiogenesis

T-regulatory cells (Tregs) are found infiltrating tumors in a vast array of tumor types, and tumor-infiltrating Tregs are often associated with a poor clinical outcome. Tregs are potent immunosuppressive cells of the immune system that promote progression of cancer through their ability to limit antitumor immunity and promote angiogenesis. Here, we discuss the ways in which Tregs suppress the antitumor immune response and elaborate on our recent discovery that Tregs make significant direct contributions to tumor angiogenesis. Further, we highlight several current therapies aimed at eliminating Tregs in cancer patients. Given the multifaceted role of Tregs in cancer, a greater understanding of their functions will ultimately strengthen future therapies.

Cellular and cytokine-dependent immunosuppressive mechanisms of grm1-transgenic murine melanoma

Grm1-transgenic mice spontaneously develop cutaneous melanoma. This model allowed us to scrutinize the generic immune responses over the course of melanoma development. To this end, lymphocytes obtained from spleens, unrelated lymph nodes and tumor-draining lymph nodes of mice with no evidence of disease, and low or high tumor burden were analyzed ex vivo and in vitro. Thereby, we could demonstrate an increase in the number of activated CD4⁺ and CD8⁺ lymphocytes in the respective organs with increasing tumor burden. However, mainly CD4⁺ T cells, which could constitute both T helper as well as immunosuppressive regulatory T cells, but not CD8⁺ T cells, expressed activation markers upon in vitro stimulation when obtained from tumor-bearing mice. Interestingly, these cells from tumor-burdened animals were also functionally hampered in their proliferative response even when subjected to strong in vitro stimulation. Further analyses revealed that the increased frequency of regulatory T cells in tumor-bearing mice is an early event present in all lymphoid organs. Additionally, expression of the immunosuppressive cytokines TGF-β1 and IL-10 became more evident with increased tumor burden. Notably, TGF-β1 is strongly expressed in both the tumor and the tumor-draining lymph node, whereas IL-10 expression is more pronounced in the lymph node, suggesting a more complex regulation of IL-10. Thus, similar to the situation in melanoma patients, both cytokines as well as cellular immune escape mechanisms seem to contribute to the observed immunosuppressed state of tumor-bearing grm1-transgenic mice, suggesting that this model is suitable for preclinical testing of immunomodulatory therapeutics.

Adoptive transfer with in vitro expanded human regulatory T cells protects against porcine islet xenograft rejection via interleukin-10 in humanized mice

T cell-mediated rejection remains a barrier to the clinical application of islet xenotransplantation. Regulatory T cells (Treg) regulate immune responses by suppressing effector T cells. This study aimed to determine the ability of human Treg to prevent islet xenograft rejection and the mechanism(s) involved. Neonatal porcine islet transplanted NOD-SCID IL2rγ(-/-) mice received human peripheral blood mononuclear cells (PBMC) with in vitro expanded autologous Treg in the absence or presence of anti-human interleukin-10 (IL-10) monoclonal antibody. In addition, human PBMC-reconstituted recipient mice received recombinant human IL-10 (rhIL-10). Adoptive transfer with expanded autologous Treg prevented islet xenograft rejection in human PBMC-reconstituted mice by inhibiting graft infiltration of effector cells and their function. Neutralization of human IL-10 shortened xenograft survival in mice receiving human PBMC and Treg. In addition, rhIL-10 treatment led to prolonged xenograft survival in human PBMC-reconstituted mice. This study demonstrates the ability of human Treg to prevent T-cell effector function and the importance of IL-10 in this response. In vitro Treg expansion was a simple and effective strategy for generating autologous Treg and highlighted a potential adoptive Treg cell therapy to suppress antigraft T-cell responses and reduce the requirement for immunosuppression in islet xenotransplantation.

Dermal mast cells affect the development of sunlight-induced skin tumours

Ultraviolet (UV) radiation contained in sunlight is considered a major risk in the induction of skin cancer. While mast cells are best known for their role in allergic responses, they have also been shown to play a crucial role in suppressing the anti-tumour immune response following UV exposure. Evidence is now emerging that UV may also trigger mast cell release of cutaneous tissue remodelling and pro-angiogenic factors. In this review, we will focus on the cellular and molecular mechanisms by which UV recruits and then activates mast cells to initiate and promote skin cancer development.

Tumour-derived IL-10 within tumour microenvironment represses the antitumour immunity of Socs1-silenced and sustained antigen expressing DCs

It has been shown that silencing of suppressor of cytokine signalling 1 (Socs1) or stably expressing transgenic protein Ags in antigen-presenting dentritic cells (DCs) strongly enhances antigen-specific anti-tumour immunity. However, whether the strong and long-lasting T cell responses induced by the modified DCs could modulate the immunosuppressive tumour microenvironment has not been clarified. In this study, we explored the anti-tumour immunity of DCs modified by Socs1-shRNA lentiviral transduction combined with sustained expression of TRP2 in different tumour models. We showed that transfer Socs1-silenced or tumour antigen TRP2 persistent expressed DCs, or DCs modified by combination of Socs1-silencing and sustaining TRP2 expression prior to inoculation of tumour cells delayed B16 tumour cell growth, prolonged mouse survival and increased the ratio of CD8+ T/Treg as well as the CTL activity in tumours. However, there was no significant effect on tumour growth and mouse survival rate upon tumour established. Further, we showed that tumour cell secreted IL-10 counteracted the immunity of modified DCs in established tumour model, injection of Socs1-shRNA and TRP2 antigen modified significantly inhibited growth of the established B16-IL-10(-/-) tumours. These data indicated that the high level of IL-10 within tumour microenvironment is one of factors that compromise DC vaccine functions.

Targeting the tumor microenvironment by immunotherapy: part 2

Cancer therapy was traditionally centered on the neoplastic cells. This included mainly surgery, radiation, and chemotherapy, in some cases hormone therapy and to a lesser extent immunotherapy – all traditionally targeted to the highly proliferating mutated tumor cells. In view of our present understanding of the powerfull influence of the tumor microenvironment (TME) on cancer behavior and response – and lack of response – to treatment, this previously ignored constituent of cancer now has to be considered as an important, even indispensable target for therapy. The TME may be targeted both to its immune and to its nonimmune components. The various immune evasion elements of the TME should be targeted as well.

Mycobacteria activate γδ T-cell anti-tumour responses via cytokines from type 1 myeloid dendritic cells: a mechanism of action for cancer immunotherapy

Attenuated and heat-killed mycobacteria display demonstrable activity against cancer in the clinic; however, the induced immune response is poorly characterised and potential biomarkers of response ill-defined. We investigated whether three mycobacterial preparations currently used in the clinic (BCG and heat-killed Mycobacterium vaccae and Mycobacterium obuense) can stimulate anti-tumour effector responses in human γδ T-cells. γδ T-cell responses were characterised by measuring cytokine production, expression of granzyme B and cytotoxicity against tumour target cells. Results show that γδ T-cells are activated by these mycobacterial preparations, as indicated by upregulation of activation marker expression and proliferation. Activated γδ T-cells display enhanced effector responses, as shown by upregulated granzyme B expression, production of the T_H1 cytokines IFN-γ and TNF-α, and enhanced degranulation in response to susceptible and zoledronic acid-treated resistant tumour cells. Moreover, γδ T-cell activation is induced by IL-12, IL-1β and TNF-α from circulating type 1 myeloid dendritic cells (DCs), but not from type 2 myeloid DCs or plasmacytoid DCs. Taken together, we show that BCG, M. vaccae and M. obuense induce γδ T-cell anti-tumour effector responses indirectly via a specific subset of circulating DCs and suggest a mechanism for the potential immunotherapeutic effects of BCG, M. vaccae and M. obuense in cancer.

Novel highly sensitive IL-10-beta-lactamase reporter mouse reveals cells of the innate immune system as a substantial source of IL-10 in vivo

In this study, we report on a novel, highly sensitive IL-10 reporter mouse based on the reporter enzyme β-lactamase and the fluorescence resonance energy transfer substrate coumarin-cephalosporin-fluorescein (4). In contrast to an IL-10 reporter mouse model that we generated by using enhanced GFP as reporter and allowed tracking IL-10 expression only in T cells, the IL-10-β-lactamase reporter (ITIB) mouse enables us to easily analyze and quantify IL-10 production at the single-cell level in all myeloid and lymphoid cell types. Furthermore, the ITIB mouse allows studying of the kinetics of IL-10 expression on a single-cell basis and provides a valuable tool for in vivo screening of cell type-specific IL-10-modulating drugs. Remarkably, the ITIB mouse revealed that, although a significant portion of each myeloid and lymphoid cell type produces IL-10, macrophages represent the major IL-10 producer population in several organs of naive mice. Moreover, using the examples of bacterial infection and transplantable skin melanoma models, we demonstrate the exceptional applicability of the ITIB mouse for the identification of IL-10-producing cells during immune responses in vivo. In this study, we identified tumor-infiltrating F4/80(+) macrophages as the major source for IL-10 in B16-F10 melanoma in vivo. During systemic infection with Yersinia enterocolitica, although the proportion of IL-10(+) cells increased in each myeloid and lymphoid cell type population, infiltrating CD11b(+)Ly6G(+) neutrophils represent a majority among IL-10-producing cells at the site of infection. We conclude that cells of the innate immune system that are involved in immune homeostasis or immune responses are substantial sources of IL-10.

Effect of tiotropium bromide on expression of CD(8) (+)CD (25) (+)FoxP (3) (+) regulatory T cells in patients with stable chronic obstructive pulmonary disease

The expression of CD(8) (+)CD(25) (+)FoxP(3) (+) regulatory T cells (CD(8) (+)Tregs) in the peripheral blood of patients with stable chronic obstructive pulmonary disease (COPD), and the effect of muscarinic cholinergic receptor antagonist tiotropium bromide on the expression of CD(8) (+)Tregs were investigated. Twenty-three patients with moderate to severe stable COPD were enrolled in this study. All patients inhaled tiotropium bromide (18 μg daily) for 3 months. Before and after inhalation of tiotropium bromide, peripheral blood samples were collected from the patients, and T cells were labeled by three-color labeled monoclonal antibodies. Flow cytometry was used to detect the quantity and percentage of CD(8) (+)T cells, CD(8) (+)CD(25) (+)T cells, CD(8) (+)Tregs, CD(4) (+)T cells, CD(4) (+)CD(25) (+)T cells and CD(4) (+)CD(25) (+)FoxP(3) (+) regulatory T cells (CD(4) (+)Tregs) respectively. The percentage of CD(4) (+)T cells was increased from (27.82±2.18)% to (35.53±1.3)% (t=3.20, P=0.004) in the peripheral blood of patients with stable COPD after inhalation of tiotropium bromide for 3 months, that of CD(4) (+)CD(25) (+)T cells was decreased from (10.03 ±1.42)% to (4.21 ±0.65)% (t=3.78, P=0.001), and that of CD(8) (+)Tregs was increased from (8.41 ±1.68)% to (21.34 ±4.20)% (t=2.72, P=0.013). At baseline, CD(8) (+)T cells, CD(8) (+)CD(25) (+)T cells and CD(4) (+)Tregs were detectable in the peripheral blood, but no significant changes were observed after treatment. Linear correlation analysis revealed that the difference before and after treatment in CD(4) (+)T cells and CD(4) (+)CD(25) (+)T cells was negatively correlated with the ratio of change in CD(8) (+)Tregs before and after treatment (r=-0.61, P=0.013; r=-0.72, P=0.001 respectively). In the peripheral blood of patients with stable COPD, there was the expression of CD(8) (+)Tregs and CD(4) (+)Tregs. Muscarinic receptor antagonist, tiotropium bromide, can promote the amplification of CD(4) (+)T cells, inhibit the expression of CD(25) (+)T cells, and enhance the expression of CD(8) (+)Tregs. CD(8) (+)Tregs and CD(4) (+)Tregs can be used as new indicators to understand the immune status of patients. They are helpful in judging the treatment efficacy and disease immunophenotype.

The variation of CD4+CD25+ regulatory T cells in the periphery blood and tumor microenvironment of non-small cell lung cancer patients and the downregulation effects induced by CpG ODN

The aim of the study was to observe the variation of CD4(+)CD25(+) regulatory T cells in periphery blood and tumor microenvironment of non-small cell lung cancer (NSCLC) patients and the effects of CpG ODN. The proportion of CD4(+)CD25(+) regulatory T cells, Foxp3 gene expression, levels of tumor growth factor-β (TGF-β) and immunoreactive fibronectin-γ (IFN-γ) in the periphery blood of 30 NSCLC patients and 30 healthy volunteers were compared. These indicators were compared before and after CpG ODN treatment. Foxp3 gene expression in the tumor microenvironment of NSCLC patients was also observed. The results showed CD4(+)CD25(+) regulatory T cell proportion, Foxp3 expression and TGF-β levels in the periphery blood of NSCLC patients were higher than those of healthy volunteers (p < 0.05), and these indicators of patients were significantly decreased after CpG ODN 2006 treatment (p < 0.05). Foxp3 expression in the metastatic lymph nodes was higher than that in the non-metastatic ones of NSCLC patients (p = 0.000). In conclusion, a rise in the proportion of CD4(+)CD25(+)Foxp3(+) regulatory T cells was demonstrated in the periphery blood and tumor microenvironments of NSCLC patients. CpG ODN 2006 downregulated the CD4(+)CD25(+)Foxp3(+) regulatory T cells proportion and TGF-β levels in the periphery blood of these patients.

Blocking the immunosuppressive axis with small interfering RNA targeting interleukin (IL)-10 receptor enhances dendritic cell-based vaccine potency

Improving dendritic cell (DC) functions is highly promising for therapeutic intervention of diverse diseases, including cancer. Immunosuppressive cytokines such as interleukin (IL)-10 produced by DCs themselves (autocrine) and other regulatory immune cells (paracrine) down-regulate functional profiles of DCs through specific cell surface receptors such as IL-10R. Here, we tried to improve DC functions using small interfering RNA (siRNA) technology to block an IL-10R-mediated immunosuppressive axis. DCs modified with siRNA targeting against IL-10R or IL-10 (DC/siIL-10R or DC/siIL-10) led to up-regulation of major histocompatibility complex (MHC) class II, CD40 co-stimulatory molecule, and IL-12 proinflammatory cytokine after lipopolysacharide (LPS) stimulation compared to DC/siGFP. Notably, the LPS-induced functional profiles of DC/siIL-10R were strongly resistant to the addition of recombinant IL-10, which mimicked paracrine IL-10. In contrast, those of DC/siIL-10 were reversed by adding exogenous IL-10. Consistently, DC/siIL-10R generated more human papilloma virus (HPV) E7-specific CD8(+) T cells and stronger anti-tumour effects against E7-expressing TC-1 tumour cells in vaccinated mice than DC/siGFP, as well as DC/siIL-10. Taken together, these results provide the groundwork for future clinical translation of siRNA-mediated strategy targeting IL-10R to enhance DC-based vaccine potency.

Cross-talk between tumor and myeloid cells: how to tip the balance in favor of antitumor immunity

Myeloid differentiation is often disturbed in cancer, leading to reduced frequencies of immunostimulatory dendritic cells and an over-representation of immunosuppressive immature myeloid cells, granulocytes and macrophages. As a result of this skewed myeloid differentiation, a highly immunosuppressive myeloid subset becomes prevalent during cancer development; these myeloid-derived suppressor cells are also recruited as a collateral to certain protumorigenic inflammatory processes, resulting in an effective downregulation of T-cell-mediated immune surveillance and antitumor immunity. In this article, some of the important myeloid cell subsets and mediators involved in cancer-related immune suppression are reviewed. Furthermore, cross-talk between tumors and the myeloid compartment, and ways in which it can suppress effective cell-mediated immunity, are discussed, as well as possible therapeutic approaches to tip the balance in favor of antitumor immunity.

Anti-tumor immunity and mechanism of immunosuppression mediated by tumor cells: role of tumor-derived soluble factors and cytokines

The immune system plays a crucial role in the protection against tumor growth and progression. However, the activation of the immune system against the neoplastic cells does not always occur and, therefore, tumor cells are able to grow and progress continually in the host. It has now been realized that tumor cells themselves produce many of the important factors that are responsible for dismounting of effective immune response. These tumor-derived soluble factors invariably subdue the functions of almost every immune cell population. Therefore, we attempted to underline the mechanism of anti-tumor immune response and immunosuppression induced by tumor cells.

ATP confers tumorigenic properties to dendritic cells by inducing amphiregulin secretion

ATP, which has an important proinflammatory action as danger signal, induces the semimaturation of dendritic cells (DCs) that can be associated with immune tolerance. We identified epidermal growth factor receptor ligands as target genes of ATPγS, a slowly hydrolyzed ATP derivative, by a gene profiling approach in DCs. Amphiregulin was the most highly up-regulated gene in response to ATPγS. Human monocyte-derived DCs and mouse bone marrow-derived DCs released amphiregulin (AREG) after purinergic receptor activation, with a contribution of P2Y(11) and A(2B) receptor, respectively. Supernatants of LPS+ATPγS-stimulated DCs induced smooth muscle cell and Lewis Lung Carcinoma (LLC) cell growth in vitro. The coinjection of LPS+ATPγS-stimulated DCs or their supernatants with LLC cells increased tumor weight in mice compared with LPS-treated DCs. The preincubation of LPS+ATPγS-treated DC supernatants with an anti-AREG blocking antibody inhibited their positive effect on smooth muscle cell density and tumor growth. The present study demonstrates for the first time that DCs can be a source of AREG. ATP released from tumor cells might exert a tumorigenic action by stimulating the secretion of AREG from DCs. Antagonists of purinergic receptors expressed on DCs and anti-AREG blocking antibodies could have a therapeutic potential as antitumor agents.

Regulatory T cells in cancer

At the present time, regulatory T cells (Tregs) are an integral part of immunology but the route from discovery of "suppressive" lymphocytes in the 1980s to the current established concept of Tregs almost 20 years later has been a rollercoaster ride. Tregs are essential for maintaining self-tolerance as defects in their compartment lead to severe autoimmune diseases. This vitally important function exists alongside the detrimental effects on tumor immunosurveillance and antitumor immunity. Beginning with the identification of CD4(+)CD25(+) Tregs in 1995, the list of Treg subsets, suppressive mechanisms, and knowledge about their various origins is steadily growing. Increase in Tregs within tumors and circulation of cancer patients, observed in early studies, implied their involvement in pathogenesis and disease progression. Several mechanisms, ranging from proliferation to specific trafficking networks, have been identified to account for their systemic and/or local accumulation. Since various immunotherapeutic approaches are being utilized for cancer therapy, various strategies to overcome the antagonistic effects exerted by Tregs are being currently explored. An overview on the biology of Tregs present in cancer patients, their clinical impact, and methods for modulating them is given in this review. Despite the extensive studies on Tregs in cancer many questions still remain unanswered. Even the paradigm that Tregs generally are disadvantageous for the control of malignancies is now under scrutiny. Insight into the specific role of Tregs in different types of neoplasias is the key for targeting them in a way that is beneficial for the clinical outcome.

miR-17-92 expression in differentiated T cells - implications for cancer immunotherapy

Background

Type-1 T cells are critical for effective anti-tumor immune responses. The recently discovered microRNAs (miRs) are a large family of small regulatory RNAs that control diverse aspects of cell function, including immune regulation. We identified miRs differentially regulated between type-1 and type-2 T cells, and determined how the expression of such miRs is regulated.

Methods

We performed miR microarray analyses on in vitro differentiated murine T helper type-1 (Th1) and T helper type-2 (Th2) cells to identify differentially expressed miRs. We used quantitative RT-PCR to confirm the differential expression levels. We also used WST-1, ELISA, and flow cytometry to evaluate the survival, function and phenotype of cells, respectively. We employed mice transgenic for the identified miRs to determine the biological impact of miR-17-92 expression in T cells.

Results

Our initial miR microarray analyses revealed that the miR-17-92 cluster is one of the most significantly over-expressed miR in murine Th1 cells when compared with Th2 cells. RT-PCR confirmed that the miR-17-92 cluster expression was consistently higher in Th1 cells than Th2 cells. Disruption of the IL-4 signaling through either IL-4 neutralizing antibody or knockout of signal transducer and activator of transcription (STAT)6 reversed the miR-17-92 cluster suppression in Th2 cells. Furthermore, T cells from tumor bearing mice and glioma patients had decreased levels of miR-17-92 when compared with cells from non-tumor bearing counterparts. CD4⁺ T cells derived from miR-17-92 transgenic mice demonstrated superior type-1 phenotype with increased IFN-γ production and very late antigen (VLA)-4 expression when compared with counterparts derived from wild type mice. Human Jurkat T cells ectopically expressing increased levels of miR-17-92 cluster members demonstrated increased IL-2 production and resistance to activation-induced cell death (AICD).

Conclusion

The type-2-skewing tumor microenvironment induces the down-regulation of miR-17-92 expression in T cells, thereby diminishing the persistence of tumor-specific T cells and tumor control. Genetic engineering of T cells to express miR-17-92 may represent a promising approach for cancer immunotherapy.

Immunology of the Testis and Male Reproductive Tract

A large body of evidence points to the existence of a close, dynamic relationship between the immune system and the male reproductive tract, which has important implications for our understanding of both systems. The testis and the male reproductive tract provide an environment that protects the otherwise highly immunogenic spermatogenic cells and sperm from immunological attack. At the same time, secretions of the testis, including androgens, influence the development and mature functions of the immune system. Activation of the immune system has negative effects on both androgen and sperm production, so that systemic or local infection and inflammation compromise male fertility. The mechanisms underlying these interactions have begun to receive the attention from reproductive biologists and immunologists that they deserve, but many crucial details remain to be uncovered. A complete picture of male reproductive tract function and its response to toxic agents is contingent upon continued exploration of these interactions and the mechanisms involved.

Intratumoral expression of mature human neutrophil peptide-1 mediates antitumor immunity in mice

PURPOSE

Human neutrophil peptides (HNP1-3), small molecular antimicrobial peptides, are expressed within tumors and associated with tumor necrosis and inhibition of angiogenesis. Recent investigations have suggested that HNP1-3 are likely to be involved in the host immune responses to tumors.

EXPERIMENTAL DESIGN

We used recombinant pSec-HNP1, which expresses a secretable form of HNP1, to obtain expression of HNP1 in the tumor milieu in immunocompetent mice to explore the possible roles of HNP1 in tumor immunity. The antitumor effects were investigated in established CT26 colon cancer and 4T1 breast cancer models.

RESULTS

HNP1-mediated chemotactic and activating effects on immature dendritic cells were detected both in vitro and in vivo. Intratumoral expression of HNP1 resulted in not only significant tumor growth inhibition but also increased CTL infiltration within tumors. Adoptive transfer of splenocytes and a (51)Cr release assay revealed specific cellular immune responses. Furthermore, increased antibodies were also found in sera from pSec-HNP1-treated mice supporting specific humoral immune responses. Increased apoptosis and decreased angiogenesis were also shown in treated tumors.

CONCLUSIONS

These findings indicate that HNP1 can exert multiple antitumor effects through different mechanisms; more importantly, HNP1 mediates host immune responses to tumors in situ through the recruitment and subsequent activation of immature dendritic cells and thus shows promising potential in cancer therapy.

Promises and Limitations of Murine Models in the Development of Anticancer T-Cell Vaccines

Murine models have been instrumental in defining the basic mechanisms of antitumor immunity. Most of these mechanisms have since been shown to operate in humans as well. Based on these similarities, active vaccination strategies aimed at eliciting antitumor T-cell responses have been elaborated and successfully implemented in various mouse models. However, the results of human antitumor vaccination trials have been rather disappointing thus far. This review summarizes the different experimental approaches used in mice to induce antitumor T-cell responses and identifies some critical parameters that should be considered when evaluating results from murine models.

Tumor emergence is sensed by self-specific CD44hi memory Tregs that create a dominant tolerogenic environment for tumors in mice

Early responses of Tregs and effector T cells (Teffs) to their first encounter with tumor cells have been poorly characterized. Here we have shown, in both implanted and in situ-induced mouse tumor models, that the appearance of tumor cells is immediately sensed by CD44hi memory Tregs that are specific for self antigens. The rapid response of these Tregs preceded and prevented activation of naive antitumor Teffs. The relative speed of the Treg versus the Teff response within the first 2-4 days determined the outcome of the antitumor immune response: tolerance or rejection. If antitumor memory Teffs were present at the time of tumor emergence, both Tregs and Teffs were recruited and activated with memory kinetics; however, the Tregs were unable to control the Teffs, which eradicated the tumor cells. This balance between effector and regulatory responses did not depend on the number of Tregs and Teffs, but rather on their memory status. Thus, in the natural setting, dominant tolerogenic immunosurveillance by self-specific memory Tregs protects tumors, just as it protects normal tissues. More generally, our results reveal that the timing of Treg and Teff engagement, determined by their memory status, is an important mode of regulation of immune responses.

Immune therapy for cancer

Over the past decade, immune therapy has become a standard treatment for a variety of cancers. Monoclonal antibodies, immune adjuvants, and vaccines against oncogenic viruses are now well-established cancer therapies. Immune modulation is a principal element of supportive care for many high-dose chemotherapy regimens. In addition, immune activation is now appreciated as central to the therapeutic mechanism of bone marrow transplantation for hematologic malignancies. Advances in our understanding of the molecular interactions between tumors and the immune system have led to many novel investigational therapies and continue to inform efforts for devising more potent therapeutics. Novel approaches to immune-based cancer treatment strive to augment antitumor immune responses by expanding tumor-reactive T cells, providing exogenous immune-activating stimuli, and antagonizing regulatory pathways that induce immune tolerance. The future of immune therapy for cancer is likely to combine many of these approaches to generate more effective treatments.

Sunitinib reverses type-1 immune suppression and decreases T-regulatory cells in renal cell carcinoma patients

PURPOSE

Immune dysfunction is well documented in renal cell carcinoma (RCC) patients and likely contributes to tumor evasion. This dysfunction includes a shift from a type-1 to a type-2 T-cell cytokine response and enhanced T-regulatory (Treg) cell expression. Given the antitumor activity of select tyrosine kinase inhibitors such as sunitinib in metastatic RCC (mRCC) patients, it is relevant to assess their effect on the immune system.

EXPERIMENTAL DESIGN

Type-1 (IFNgamma) and type-2 (interleukin-4) responses were assessed in T cells at baseline and day 28 of treatment with sunitinib (50 mg/d) by measuring intracellular cytokines after in vitro stimulation with anti-CD3/anti-CD28 antibodies.

RESULTS

After one cycle of treatment, there was a significant increase in the percentage of IFNgamma-producing T cells (CD3(+), P < 0.001; CD3(+)CD4(+), P = 0.001), a reduction in interleukin-4 production (CD3(+) cells, P = 0.05), and a diminished type-2 bias (P = 0.005). The increase in type-1 response may be partly related to modulation of Treg cells. The increased percentage of Treg cells noted in mRCC patients over healthy donors (P = 0.001) was reduced after treatment, although not reaching statistical significance. There was, however, an inverse correlation between the increase in type-1 response after two cycles of treatment and a decrease in the percentage of Treg cells (r = -0.64, P = 0.01). In vitro studies suggest that the effects of sunitinib on Treg cells are indirect.

CONCLUSIONS

The demonstration that sunitinib improved type-1 T-cell cytokine response in mRCC patients while reducing Treg function provides a basis for the rational combination of sunitinib and immunotherapy in mRCC.

CpG methylation of the IFNG gene as a mechanism to induce immunosuppression [correction of immunosupression] in tumor-infiltrating lymphocytes

The execution of appropriate gene expression patterns during immune responses is of eminent importance where CpG methylation has emerged as an essential mechanism for gene silencing. We have charted the methylation status of regulatory elements in the human IFNG gene encoding the signature cytokine of the Th1 response. Surprisingly, human naive CD4(+) T lymphocytes displayed hypermethylation at the IFNG promoter region, which is in sharp contrast to the completely demethylated status of this region in mice. Th1 differentiation induced demethylation of the IFNG promoter and the upstream conserved nucleotide sequence 1 enhancer region, whereas Th2-differentiated lymphocytes remained hypermethylated. Furthermore, CD19(+) B lymphocytes displayed hypomethylation at the IFNG promoter region with a similar pattern to Th1 effector cells. When investigating the methylation status among tumor-infiltrating CD4(+) T lymphocytes from patients with colon cancer, we found that tumor-infiltrating lymphocytes cells are inappropriately hypermethylated, and thus not confined to the Th1 lineage. In contrast, CD4(+) T cells from the tumor draining lymph node were significantly more demethylated than tumor-infiltrating lymphocytes. We conclude that there are obvious interspecies differences in the methylation status of the IFNG gene in naive CD4(+) T lymphocytes, where Th1 commitment in human lymphocytes involves demethylation before IFNG expression. Finally, investigations of tumor-infiltrating lymphocytes and CD4(+) cells from tumor draining lymph node demonstrate methylation of regulatory regions within key effector genes as an epigenetic mechanism of tumor-induced immunosuppression.

Stat6 signaling suppresses VLA-4 expression by CD8+ T cells and limits their ability to infiltrate tumor lesions in vivo

VLA-4 plays a critical role in T cell trafficking into inflammatory sites. Our recent studies have suggested that VLA-4 expression on CD8+ T cells is negatively controlled by IL-4 and serves as a functionally distinguishing variable for why Type-1, but not Type-2, CD8+ T cells are able to traffic into tumors. In this study, using in vitro culture of murine CD8+ T cells under Type-1 and Type-2 cytokine conditions, we show that IL-4-mediated down-regulation of VLA-4 expression is completely abrogated in Stat6-deficient CD8+ T cells. Conversely, CD8+ T cells expressing a constitutively active mutant form Stat6 (Stat6VT) failed to express VLA-4 even in the absence of IL-4-stimulation. Notably, Type-2 CD8+ T cells developed from Stat6-/- but not wild-type mice were competent to migrate into tumor lesions in vivo. These results suggest that Stat6-signaling is necessary and sufficient to restrict CD8+ T cell expression of VLA-4 (by IL-4), thereby serving as a regulator for CD8+ T cell infiltration into tumors.

Role of secreted conjunctival mucosal cytokine and chemokine proteins in different stages of trachomatous disease

Background

Chlamydia trachomatis is responsible for trachoma, the primary cause of preventable blindness worldwide. Plans to eradicate trachoma using the World Health Organization's SAFE program (Surgery, Antibiotics, Facial Cleanliness and Environment Improvement) have resulted in recurrence of infection and disease following cessation of treatment in many endemic countries, suggesting the need for a vaccine to control infection and trachomatous disease. Vaccine development requires, in part, knowledge of the mucosal host immune responses in both healthy and trachomatous conjuctivae—an area of research that remains insufficiently studied.

Methodology/Principal Findings

We characterized 25 secreted cytokines and chemokines from the conjunctival mucosa of individuals residing in a trachoma endemic region of Nepal using Luminex X100 multiplexing technology. Immunomodulating effects of concurrent C. trachomatis infection were also examined. We found that proinflammatory cytokines IL-1β (r = 0.259, P = 0.001) and TNFα (r = 0.168, P<0.05) were significantly associated with trachomatous disease and concurrent C. trachomatis infection compared with age and sex matched controls from the same region who did not have trachoma. In support of these findings, anti-inflammatory cytokine IL-1 receptor antagonist (IL-1Ra) was negatively associated with chronic scarring trachoma (r = −0.249, P = 0.001). Additional cytokines (Th1, IL-12p40 [r = −0.212, P<0.01], and Th2, IL-4 and IL-13 [r = −0.165 and −0.189, respectively, P<0.05 for both]) were negatively associated with chronic scarring trachoma, suggesting a protective role. Conversely, a pathogenic role for the Th3/Tr1 cytokine IL-10 (r = 0.180, P<0.05) was evident with increased levels for all trachoma grades. New risk factors for chronic scarring trachoma included IL-6 and IL-15 (r = 0.259 and 0.292, respectively, P<0.005 for both) with increased levels for concurrent C. trachomatis infections (r = 0.206, P<0.05, and r = 0.304, P<0.005, respectively). Chemokine protein levels for CCL11 (Eotaxin), CXCL8 (IL-8), CXCL9 (MIG), and CCL2 (MCP-1) were elevated in chronic scarring trachoma compared with age and sex matched controls (P<0.05, for all).

Conclusions/Significance

Our quantitative detection of previously uncharacterized and partially characterized cytokines, a soluble cytokine receptor, and chemokines for each trachoma grade and associations with C. trachomatis infections provide, to date, the most comprehensive immunologic evaluation of trachoma. These findings highlight novel pathologic and protective factors involved in trachomatous disease, which will aid in designing immunomodulating therapeutics and a vaccine.

Trachoma, a disease of antiquity dating back to the 16th century B.C.E., predominates among developing countries, where it remains the primary cause of preventable blindness worldwide. In trachoma, recurrent Chlamydia trachomatis bacterial infections during childhood are thought to result in inflammation and subsequent conjunctival scarring that can progress to trichiasis (TT; chronic trachoma; inversion of ≥1 eyelash that touches the globe of the eye). The trachomatous follicular grade (TF; active disease) is a self-limiting disease, suggesting the coexistence of protective inflammatory proteins. The trachomatous inflammatory grade (TI; active disease) is more likely to progress to trachomatous scarring (TS; chronic trachoma). To date, there are only a handful of studies that have examined the immune response in trachoma, and these were primarily based on gene expression. Characterizing quantified conjunctival mucosal immune differences for secreted proteins among individuals with no, active, and chronic trachoma may identify protein biomarkers associated with protection versus disease, which would greatly aid our understanding of the immunopathogenesis of trachoma. In this study, we characterized 25 cytokine and chemokine proteins for all trachoma grades. We identified eight cytokines and chemokines as risk factors for chronic trachoma and four as protective. Together, these findings further characterize the immunopathologic responses involved during trachoma, which will likely aid in the design of a vaccine and immunomodulating therapeutics for trachoma.

Regulatory T cells: what role do they play in antitumor immunity in patients with head and neck cancer?

Advances in the treatment modalities for head and neck squamous cell carcinoma (HNSCC) over the last 20 years involving surgery, radiotherapy, chemotherapy, and immunotherapy are not fully reflected in increases in the 5-year survival rates, mainly due to locoregional recurrences and to a lesser extent, distant metastasis. This can, in part, be attributed to the fact that HNSCC induces severe depression of a patient's immune system. Recent advances in understanding the complex host-tumor interactions have led to the identification of a distinct suppressor cell population known as regulatory T cells that play a crucial role in maintaining T-cell tolerance to self-antigens. Here, we present a critical review of our understanding of the involvement of regulatory T cells in controlling the T-cell immune response in tumor occurrence and progression in HNSCC with an emphasis on current and future immunotherapeutic approaches involving regulatory T cells.

Apoptosis resistance in epithelial tumors is mediated by tumor-cell-derived interleukin-4

We investigated the mechanisms involved in the resistance to cell death observed in epithelial cancers. Here, we identify that primary epithelial cancer cells from colon, breast and lung carcinomas express high levels of the antiapoptotic proteins PED, cFLIP, Bcl-xL and Bcl-2. These cancer cells produced interleukin-4 (IL-4), which amplified the expression levels of these antiapoptotic proteins and prevented cell death induced upon exposure to TRAIL or other drug agents. IL-4 blockade resulted in a significant decrease in the growth rate of epithelial cancer cells and sensitized them, both in vitro and in vivo, to apoptosis induction by TRAIL and chemotherapy via downregulation of the antiapoptotic factors PED, cFLIP, Bcl-xL and Bcl-2. Furthermore, we provide evidence that exogenous IL-4 was able to upregulate the expression levels of these antiapoptotic proteins and potently stabilized the growth of normal epithelial cells rendering them apoptosis resistant. In conclusion, IL-4 acts as an autocrine survival factor in epithelial cells. Our results indicate that inhibition of IL-4/IL-4R signaling may serve as a novel treatment for epithelial cancers.

The current status and future direction of percutaneous peptide immunization against melanoma

Dendritic cell (DC)-based tumor immunotherapy is widely known to elicit protective anti-tumor immune responses, although the safety and effectiveness have yet to be thoroughly explored. We reported that a disruption in the stratum corneum barrier resulted in enhanced permeability and alterations in the skin immune system in such a way that epidermal Langerhans cells (LCs) functioned as vigorous antigen presenters for T helper (Th) cells and cytotoxic T lymphocytes (CTLs). In both human and murine models, topical application of melanoma-associated antigen peptides onto stratum corneum barrier-disrupted skin, specifically induced tumoricidal immune responses in vivo and in vitro accompanying an increased expression of MHC and co-stimulatory molecules on LCs. In addition, for reasons of simplicity, safety and effectiveness, percutaneous peptide application has demonstrated a certain degree of feasibility in clinical approach in patients with melanoma. In the future, resolution of some of the outstanding issues concerning the selection of the most effective adjuvants in combination with barrier disruption and depletion of regulatory T (Treg) cell-mediated immune suppression would appear as essential to improve percutaneous melanoma immunotherapy.

A unique subset of CD4+CD25highFoxp3+ T cells secreting interleukin-10 and transforming growth factor-beta1 mediates suppression in the tumor microenvironment

PURPOSE

Immunosuppression, including that mediated by CD4(+)CD25(high)Foxp3(+) regulatory T cells (Treg), is a characteristic feature of head and neck squamous cell carcinoma (HNSCC). Tregs with a distinct phenotype in tumor-infiltrating lymphocytes (TIL) contribute to local immune suppression.

EXPERIMENTAL DESIGN

The frequency and phenotype of Treg in TIL and/or peripheral blood mononuclear cells (PBMC) in 15 HNSCC patients and PBMC in 15 normal controls were compared. Single-cell sorted CD4(+)CD25(high) T cells were tested for regulatory function by coculture with carboxyfluorescein diacetate succinimidyl ester-labeled and activated autologous CD4(+)CD25(-) responder T cells. Transwell inserts separating Treg from responders and neutralizing interleukin-10 (IL-10) or transforming growth factor-beta1 (TGF-beta1) antibodies were used to evaluate the mechanisms used by Treg to suppress responder cell proliferation.

RESULTS

In TIL, CD25(+) cells were enriched in the CD3(+)CD4(+) subset (13 +/- 3%) relative to circulating CD3(+)CD4(+) T cells (3 +/- 0.7%) in HNSCC patients (P < or = 0.01) or normal controls (2 +/- 1.5%; P < or = 0.001). Among the CD3(+)CD4(+) subset, CD25(high) Treg represented 3 +/- 0.5% in TIL, 1 +/- 0.3% in PBMC, and 0.4 +/- 0.2% in normal controls. Tregs in TIL were GITR(+), IL-10(+), and TGF-beta1(+), although circulating Treg up-regulated CD62L and CCR7 but not GITR, IL-10, or TGF-beta1. Treg in TIL mediated stronger suppression (P < or = 0.001) than Treg in PBMC of HNSCC patients. The addition of neutralizing IL-10 and TGF-beta antibodies almost completely abrogated suppression (5 +/- 2.51%). Transwell inserts partly prevented suppression (60 +/- 5% versus 95 +/- 5%).

CONCLUSIONS

Suppression in the tumor microenvironment is mediated by a unique subset of Treg, which produce IL-10 and TGF-beta1 and do not require cell-to-cell contact between Treg and responder cells for inhibition.

Exploiting Regulatory T-cell Populations for the Immunotherapy of Cancer

Tumor escape from the immune system hampers effective immunotherapy for cancer. Recent evidence indicates that in cancer patients the altered activities of 2 innatelike ("natural") immunoregulatory T-cell populations could prevent the establishment of effective antitumor immune responses. These are CD4+ CD25+ (natural) regulatory T cells and invariant natural killer T cells, which normally play critical roles in orchestrating immune responses to self and nonself. Therapeutic modulation of these regulatory T-cell populations is clinically feasible and will potentially allow the induction of effective antitumor immune responses when combined with currently available immunotherapeutic strategies.

Overexpression of interleukin-10 in sentinel lymph node with breast cancer

BACKGROUND

In breast carcinoma, identification of tumor cells in the sentinel lymph nodes is a predictor of the tumor's metastatic potential. Sentinel lymph node may be targeted not only by tumor cell metastasis but also by cytokines from the emergence of antitumor immune responses.

METHODS

Between February 2003 and February 2004, the investigator evaluated 38 cases that underwent sentinel lymph node biopsy at the Samsung Medical Center. Eighty paraffin-embedded sections, 49 sentinel, and 31 nonsentinel lymph node, from breast carcinoma without lymphatic metastases were analyzed by real-time polymerase chain reaction to evaluate the cytokine profile (interferon-gamma, interleukin-2, interleukin-10 and interleukin-12) for the T cell response.

RESULTS

A higher expression of interleukin-10 was observed in sentinel lymph node than in nonsentinel lymph node (P = 0.03). The expressions of interferon-gamma, interleukin-2, and interleukin-12 were similar between sentinel and nonsentinel lymph node.

CONCLUSIONS

Theses results indicate that T cell response was downregulated by interleukin-10 overexpression in sentinel lymph node with breast cancer.

TAP expression reduces IL-10 expressing tumor infiltrating lymphocytes and restores immunosurveillance against melanoma

Many immune therapeutic strategies are under development for melanoma to treat metastatic disease and prevent disease reoccurrence. However, human melanoma cells are often deficient in antigen processing and this appears to play a role in their expansion and escape from immunosurveillance. For example, expression of the transporters associated with antigen processing (TAP1 and TAP2) is down‐regulated in the mouse melanoma cell line B16F10. This results in a lack of tumor‐associated antigen processing, low surface expression of MHC Class I molecules and low immunogenicity. We observe that restoration of TAP1 expression by transfection resurrects the processing and presentation of viral antigens, and the melanoma‐associated antigen, TRP‐2. Immunization with irradiated B16F10/rTAP1 transfected cells generates CTLs that are capable of killing B16F10/rTAP1 transfected targets and B16F10 targets deficient in TAP1. Furthermore, B16F10/rTAP1 transfectants grow at a significantly slower rate in mice than B16F10 cells. In an experimental model that closely recapitulates the clinical situation, treatment of B16F10 tumors in mice with a vaccinia virus vector expressing TAP1 also significantly decreases tumor growth in vivo. Furthermore, tumors treated with vaccinia TAP1 had significantly reduced numbers of immunosuppressive, CD3⁺/IL‐10 positive, tumor infiltrating lymphocytes. Therefore, TAP1 expression restores both antigen presentation and immunogenicity in B16F10 melanoma cells and concomitantly reduces immunosuppressive IL‐10 production at the local tumor site, thereby increasing immunosurveillance mechanisms against tumors. © 2007 Wiley‐Liss, Inc.

Effect of tumor-derived cytokines and growth factors on differentiation and immune suppressive features of myeloid cells in cancer

It is well established that cancers affect differentiation of dendritic cells and promote systemic expansion of immune suppressive immature myeloid cells. This phenomenon may represent a mechanism of tumor escape from immune attack and could have significant impact on tumor progression. In this review we discuss the role of different tumor-derived factors, which were implicated in abnormal myeloid cell differentiation. The role of reactive oxygen species as well as JAK/STAT signaling in mechanisms of the effects of tumor-derived factors on myeloid cells is also discussed.

Inhibitory effect of tumor cell-derived lactic acid on human T cells

A characteristic feature of tumors is high production of lactic acid due to enhanced glycolysis. Here, we show a positive correlation between lactate serum levels and tumor burden in cancer patients and examine the influence of lactic acid on immune functions in vitro. Lactic acid suppressed the proliferation and cytokine production of human cytotoxic T lymphocytes (CTLs) up to 95% and led to a 50% decrease in cytotoxic activity. A 24-hour recovery period in lactic acid-free medium restored CTL function. CTLs infiltrating lactic acid-producing multicellular tumor spheroids showed a reduced cytokine production. Pretreatment of tumor spheroids with an inhibitor of lactic acid production prevented this effect. Activated T cells themselves use glycolysis and rely on the efficient secretion of lactic acid, as its intracellular accumulation disturbs their metabolism. Export by monocarboxylate transporter-1 (MCT-1) depends on a gradient between cytoplasmic and extracellular lactic acid concentrations and consequently, blockade of MCT-1 resulted in impaired CTL function. We conclude that high lactic acid concentrations in the tumor environment block lactic acid export in T cells, thereby disturbing their metabolism and function. These findings suggest that targeting this metabolic pathway in tumors is a promising strategy to enhance tumor immunogenicity.

The tumor-draining lymph node as an immune-privileged site

Lymph nodes that lie immediately downstream of tumors [tumor-draining lymph nodes (TDLNs)] undergo profound alterations due to the presence of the upstream tumor. The antigen-presenting cell population in TDLNs becomes modified such that tumor-derived antigens are cross-presented by host cells in a tolerizing fashion. In addition, the number and suppressor activity of regulatory T cells (Tregs) are increased in the TDLN. Emerging evidence suggests that some of these Tregs may be generated de novo against specific tumor-derived antigens, and thus they arise as a direct consequence of antigen presentation in the TDLN. Others may represent Tregs against self-antigens, which undergo preferential activation in the tolerogenic milieu of the TDLN. The TDLN thus becomes an anatomic context in which presentation of new antigens not only fails to elicit a protective immune response but also actively creates systemic tolerance. In this regard, the TDLN displays features analogous to classical immune privilege. Accumulating evidence thus suggests that the TDLNs, although small in size, may exert a profound tolerizing influence on the rest of the immune system. These mechanisms will need to be interrupted in order for clinical anti-tumor immunotherapy to be successful.

Improving antitumor immune responses by circumventing immunoregulatory cells and mechanisms

Although numerous immunotherapeutic strategies have been studied in patients with cancer, consistent induction of clinical responses remains a formidable challenge. Cancer vaccines are often successful at generating elevated numbers of tumor-specific T lymphocytes in peripheral blood, however, despite this, tumors usually continue to grow unabated. Recent evidence suggests that endogenous regulatory cells, known to play a major role in the induction of immune tolerance to self and prevention of autoimmunity, as well as suppressive myeloid cells invoked in the tumor-bearing state, may be largely responsible for preventing effective antitumor immune responses. This review will focus on the major regulatory cell subtypes, including CD4(+)CD25(+) T-regulatory cells, type 1 regulatory T cells, natural killer T cells, and immature myeloid cells. Studies in humans and in animal models have shown a role for all of these cells in tumor progression, although the mechanisms by which they act to suppress immunity remain largely undefined. Elucidation of the dominant molecular mechanisms mediating immune suppression in vivo will allow more precise targeting of the relevant regulatory cell populations, as well as the development of novel strategies and clinical reagents that will directly block molecules that induce the suppression of antitumor immunity.

Dendritic cells and tumor microenvironment: a dangerous liaison

The fact that the immune response to cancer is compromised has been convincingly demonstrated in murine tumor models as well as in cancer patients. The unresponsiveness of the host immune system is one of the major mechanisms of tumor escape as well as an important factor that limits the success of cancer immunotherapy. Inadequate function of professional antigen presenting cells dendritic cells (DC) in cancer is one of the major elements of compromised anti-tumor immune response. Despite substantial progress in recent years, the mechanism of inadequate DC function in cancer still remains unclear. The tumor microenvironment has emerged as an important component contributing to DC malfunction. In this review we will discuss the potential role of tumor microenvironment in DC dysfunction.