Interleukin-10–Treated Human Dendritic Cells Induce a Melanoma-Antigen–Specific Anergy in CD8+ T Cells Resulting in a Failure to Lyse Tumor Cells

Targeting of tolerogenic dendritic cells towards heat-shock proteins: a novel therapeutic strategy for autoimmune diseases?

Tolerogenic dendritic cells (tolDCs) are a promising therapeutic tool to restore immune tolerance in autoimmune diseases. The rationale of using tolDCs is that they can specifically target the pathogenic T-cell response while leaving other, protective, T-cell responses intact. Several ways of generating therapeutic tolDCs have been described, but whether these tolDCs should be loaded with autoantigen(s), and if so, with which autoantigen(s), remains unclear. Autoimmune diseases, such as rheumatoid arthritis, are not commonly defined by a single, universal, autoantigen. A possible solution is to use surrogate autoantigens for loading of tolDCs. We propose that heat-shock proteins may be a relevant surrogate antigen, as they are evolutionarily conserved between species, ubiquitously expressed in inflamed tissues and have been shown to induce regulatory T cells, ameliorating disease in various arthritis mouse models. In this review, we provide an overview on how immune tolerance may be restored by tolDCs, the problem of selecting relevant autoantigens for loading of tolDCs, and why heat-shock proteins could be used as surrogate autoantigens.

Immune surveillance in melanoma: From immune attack to melanoma escape and even counterattack

Pharmacologic inhibition of the cytotoxic T lymphocyte antigen 4 (CTLA4) and the programmed death receptor-1 (PD1) has resulted in unprecedented durable responses in metastatic melanoma. However, resistance to immunotherapy remains a major challenge. Effective immune surveillance against melanoma requires 4 essential steps: activation of the T lymphocytes, homing of the activated T lymphocytes to the melanoma microenvironment, identification and episode of melanoma cells by activated T lymphocytes, and the sensitivity of melanoma cells to apoptosis. At each of these steps, there are multiple factors that may interfere with the immune surveillance machinery, thus allowing melanoma cells to escape immune attack and develop resistance to immunotherapy. We provide a comprehensive review of the complex immune surveillance mechanisms at play in melanoma, and a detailed discussion of how these mechanisms may allow for the development of intrinsic or acquired resistance to immunotherapeutic modalities, and potential avenues for overcoming this resistance.

Molecular mechanisms involved in dendritic cell dysfunction in cancer

Dendritic cells (DC) play a pivotal role in the tumor microenvironment (TME). As the primary antigen-presenting cells in the tumor, DCs modulate anti-tumor responses by regulating the magnitude and duration of infiltrating cytotoxic T lymphocyte responses. Unfortunately, due to the immunosuppressive nature of the TME, as well as the inherent plasticity of DCs, tumor DCs are often dysfunctional, a phenomenon that contributes to immune evasion. Recent progresses in our understanding of tumor DC biology have revealed potential molecular targets that allow us to improve tumor DC immunogenicity and cancer immunotherapy. Here, we review the molecular mechanisms that drive tumor DC dysfunction. We discuss recent advances in our understanding of tumor DC ontogeny, tumor DC subset heterogeneity, and factors in the tumor microenvironment that affect DC recruitment, differentiation, and function. Finally, we describe potential strategies to optimize tumor DC function in the context of cancer therapy.

Tolerogenic dendritic cells

Deficits in immunological tolerance against self-antigens and antigens provided by the diet and commensal microbiota can result in the development of inflammatory and autoimmune disorders. Dendritic cells (DCs) are pivotal regulators of the immune response, specialized in antigen presentation to drive T cell priming and differentiation. DCs also have a tolerogenic function, participating in the enforcement of central and peripheral tolerance and the resolution of ongoing immune responses. Thus, DCs control effector and regulatory mechanisms relevant to the pathology of autoimmune disorders. In this review, we discuss recent findings regarding the control of the adaptive immune response by tolerogenic DCs. A thorough understanding of the mechanisms that control the tolerogenic DC phenotype will guide the development of novel strategies for the treatment of autoimmunity.

Dendritic cells as gatekeepers of tolerance

Dendritic cells (DC) are unique hematopoietic cells, linking innate and adaptive immune responses. In particular, they are considered as the most potent antigen presenting cells, governing both T cell immunity and tolerance. In view of their exceptional ability to present antigen and to interact with T cells, DC play distinct roles in shaping T cell development, differentiation and function. The outcome of the DC-T cell interaction is determined by the state of DC maturation, the type of DC subset, the cytokine microenvironment and the tissue location. Both regulatory T cells (Tregs) and DC are indispensable for maintaining central and peripheral tolerance. Over the past decade, accumulating data indicate that DC critically contribute to Treg differentiation and homeostasis.

Inflammation by Breast Implants and Adenocarcinoma: Not Always a Bad Company

BACKGROUND

Inflammation and tumor are now an inseparable binomial. Inflammation may also derive by the use of breast implants followed by the formation of a periprosthetic capsule. It is known that tumor cells, in an inflamed microenvironment, can profit by the paracrine effect exerted also by mesenchymal stem cells (MSCs). Here we evaluated the role of inflammation on the immunobiology of MSCs before and after cocultures with cells derived from breast adenocarcinoma.

METHODS

MSCs derived from both inflamed (I-MSCs) and control (C-MSCs) tissues were isolated and cocultured with MCF7 cells derived from breast adenocarcinoma. Before and after cocultures, the proliferation rate of MCF7 cells and the expression/secretion of cytokines related to inflammation were tested.

RESULTS

Before cocultures, higher levels of cytokine related to chronic inflammation were detected in I-MSCs than in C-MSCs. After cocultures with MCF7, C- and I-MSCs show a variation in cytokine production. In detail, IL-2, IL-4, IL-5, IL-10, IL-13, TGF-β and G-CSF were decreased, whereas IL-6, IL-12, IFN-γ, and IL-17 were oversecreted. Proliferation of MCF7 was significantly increased after cocultures with I-MSCs.

CONCLUSIONS

Inflammation at the site of origin of MSCs affects their immunobiology. Even if tumor cells increased their proliferation rate after cocultures with I-MSCs, the analysis of the cytokines, known to play a role in the interference of tumor cells with the host immune system, absolves completely the breast implants from the insult to enforce the risk of adenocarcinoma.

Tumor-associated immune factors are associated with recurrence and metastasis in non-small cell lung cancer

Dynamic interaction between tumor cells and the microenvironment is critical for tumorigenesis, and cancer immunosurveillance plays an important role in the tumor evolution. In some tumors (such as esophageal cancer, pancreatic cancer and colorectal cancer), studies have shown that the number of tumor-infiltrating lymphocytes (TILs) has a significant relationship with the prognosis, but there is little research on the prognosis of TILs and non-small cell lung cancer (NSCLC) has been performed. Therefore, it is necessary to discover the relationship between the TILs and cytokines with NSCLC prognosis and metastasis in patients. Tumor samples were carefully examined for tissue preservation and complete follow-up. A total of 107 tumor samples from NSCLC patients with radical surgical resection were enrolled for the analysis. All samples were subjected to immunohistochemistry for detection of CD3, CD4, CD8, CD28, forkhead box protein P3 (Foxp3), cytotoxic T lymphocyte-associated protein-4, cyclooxygenase2 (COX-2), transforming growth factor β 1, interleukin-2 (IL-2), interleukin-6, interleukin-10, interleukin-12 receptor and hypoxia inducible factor 1a (HIF-1a). The number, function and location of the targets were analyzed to determine their correlation with disease-free survival (DFS) and overall survival (OS). Immunhistochemical results from 107 samples indicated that the FoxP3+ regulatory TIL (HR=1.336, P=0.031), IL-2 (HR=0.595, P=0.007) and HIF-1a (HR=1.510, P=0.002) levels in tumor cells closely correlated with DFS in a COX analysis model. FoxP3+ regulatory TILs (HR=1.566, P=0.002) significantly correlated with OS and tumor node metastasis staging. The patients were divided into two groups due to the coexpression pattern of the IL-2, FoxP3+ and HIF-1a. The high-risk group had an overall worse survival than those at low risk. We confirmed that Foxp3 expression in lymphocyte and IL-2 expression in tumor cells were associated with recurrence or transfer. Furthermore, we also observed that HIF-1a expression significantly correlated with DFS and OS.

IL-10-Modulated Human Dendritic Cells for Clinical Use: Identification of a Stable and Migratory Subset with Improved Tolerogenic Activity

Dendritic cells (DCs) are key regulators of protective immune responses and tolerance to (self-)Ags. Therefore, the scientific rationale for the use of tolerogenic DC therapy in the fields of allergies, autoimmunity, and transplantation medicine is strong. In this study, we analyzed the tolerogenic capacity of IL-10-modulated DC (IL-10DC) subpopulations to identify a DC subset that combines potent immunosuppressive activities with valuable immune properties for clinical implementation. IL-10DCs consist of two phenotypically distinct subpopulations: CD83highCCR7+ IL-10DCs and CD83lowCCR7- IL-10DCs. Suppressor assays with activated effector T cells revealed that CD4+ regulatory T cells generated by CD83high IL-10DCs (iTreg+) exhibited a significantly higher suppressive capacity compared with CD4+ regulatory T cells generated by CD83low IL-10DCs (iTreg-). In this context, iTreg+ displayed a more activated phenotype (proliferation, cytokine production) compared with iTreg- In contrast to CD83low IL-10DCs, CD83high IL-10DCs exerted a strong migratory capacity toward the secondary lymphoid organ chemokine CCL21 and retained a functionally stable phenotype under inflammatory conditions. In addition, CD83high IL-10DCs expressed significantly higher levels of surface and soluble CD25. Functional analysis demonstrated that IL-10DC-related soluble CD25 efficiently inhibited the proliferation of activated T cells and that blockade of CD25 function abolished the induction of regulatory T cells by IL-10DCs, indicating a critical role for IL-10DC-related CD25 in shifting the immune response toward an iTreg- controlled tolerance reaction. In conclusion, the selective use of the CD83high IL-10DC subset may result in a higher efficacy of tolerance induction in vivo and may support the development of novel DC vaccination strategies for transplantations, as well as for allergic and autoimmune diseases.

Myeloid cells as orchestrators of the tumor microenvironment: novel targets for nanoparticular cancer therapy

Macrophages, myeloid-derived suppressor cells and tolerogenic dendritic cells are central players of a heterogeneous myeloid cell population, with the ability to suppress innate and adaptive immune responses and thus to promote tumor growth. Their influx and local proliferation are mainly induced by the cancers themselves, and their numbers in the tumor microenvironment and the peripheral blood correlate with decreased survival. Therapeutic targeting these innate immune cells, either aiming at their elimination or polarization toward tumor suppressive cells is an attractive novel approach to control tumor progression and block metastasis. We review the current understanding of cancer immunology including immune surveillance and immune editing in the context of these prominent innate suppressor cells, and their targetability by nanoparticular immunotherapy with small molecules or siRNA.

microRNA-155 deficiency impairs dendritic cell function in breast cancer

In antitumor immunity, dendritic cells (DCs) capture, process, and present tumor antigens to T cells, initiating a tumoricidal response. However, DCs are often dysfunctional due to their exposure to the tumor microenvironment (TME), leading to tumor escape from immune surveillance. Here, a vital role of microRNA-155 (miR-155) in regulating the function of DCs in breast cancer is reported. Host miR-155 deficiency enhanced breast cancer growth in mice, accompanied by reduced DCs in the tumors and draining lymph nodes. miR-155 deficiency in DCs impaired their maturation, migration ability, cytokine production, and the ability to activate T cells. We demonstrate that miR-155 regulates DC migration through epigenetic modulation of CCR7 expression. Moreover, IL-6 and IL-10, two cytokines abundant in the TME, are found to impair DC maturation by suppressing miR-155 expression. Furthermore, animal studies show that a lack of miR-155 diminishes the effectiveness of DC-based immunotherapy for breast cancer. In conclusion, these findings suggest that miR-155 is a master regulator of DC function in breast cancer, including maturation, cytokine secretion, migration toward lymph nodes, and activation of T-cells. These results suggest that boosting the expression of a single microRNA, miR-155, may significantly improve the efficacy of DC-based immunotherapies for breast cancer.

Downregulation of the Syk Signaling Pathway in Intestinal Dendritic Cells Is Sufficient To Induce Dendritic Cells That Inhibit Colitis

Helminthic infections modulate host immunity and may protect people in less-developed countries from developing immunological diseases. In a murine colitis model, the helminth Heligmosomoides polygyrus bakeri prevents colitis via induction of regulatory dendritic cells (DCs). The mechanism driving the development of these regulatory DCs is unexplored. There is decreased expression of the intracellular signaling pathway spleen tyrosine kinase (Syk) in intestinal DCs from H. polygyrus bakeri-infected mice. To explore the importance of this observation, it was shown that intestinal DCs from DC-specific Syk(-/-) mice were powerful inhibitors of murine colitis, suggesting that loss of Syk was sufficient to convert these cells into their regulatory phenotype. DCs sense gut flora and damaged epithelium via expression of C-type lectin receptors, many of which signal through the Syk signaling pathway. It was observed that gut DCs express mRNA encoding for C-type lectin (CLEC) 7A, CLEC9A, CLEC12A, and CLEC4N. H. polygyrus bakeri infection downmodulated CLEC mRNA expression in these cells. Focusing on CLEC7A, which encodes for the dectin-1 receptor, flow analysis showed that H. polygyrus bakeri decreases dectin-1 expression on the intestinal DC subsets that drive Th1/Th17 development. DCs become unresponsive to the dectin-1 agonist curdlan and fail to phosphorylate Syk after agonist stimulation. Soluble worm products can block CLEC7A and Syk mRNA expression in gut DCs from uninfected mice after a brief in vitro exposure. Thus, downmodulation of Syk expression and phosphorylation in intestinal DCs could be important mechanisms through which helminths induce regulatory DCs that limit colitis.

INFα-2b inhibitory effects on CD4(+)CD25(+)FOXP3(+) regulatory T cells in the tumor microenvironment of C57BL/6 J mice with melanoma xenografts

Background

Regulatory T cells (Treg_s), particularly the CD4⁺CD25⁺Foxp3⁺ Treg_s, down regulate immunity and promote tumor cell growth by directly suppressing CD8⁺ and CD4⁺ T cells. Alternatively they can promote tumor growth by generating interleukin-10 (IL-10) and transforming growth factor β (TGFβ) in situ, which help tumor cells to evade the immune system.

Methods

In vivo tumor models were prepared via subcutaneous injection with a suspension of B16 melanoma cells into the left upper flank of C57BL/6 J mice. The mice were randomized into five groups: radiotherapy (RT), chemotherapy (CT), radiochemotherapy (RCT), Inteferon α (INFα) groups, and a control group. Flow cytometry was used to determine the Treg_s levels in the spleen and peripheral blood, and immunohistochemistry was performed to determine the expression levels of TGFβ and IL-10 in the tumor microenvironment.

Results

Tumor weight was significantly reduced in the CT or RCT groups (40.91 % and 41.83 %, respectively), while the reduction in tumor weight was relatively lower for the RT and IFNα groups (15.10 % and 13.15 %, respectively). The flow cytometry results showed that the ratios of CD4⁺CD25⁺Foxp3⁺ Treg_s to lymphocytes and CD4⁺ cells in the spleen and in peripheral blood were significantly decreased after treatment with IFNα (P < 0.05). Expression of TGFβ and IL-10 in the tumor microenvironment in the CT and RT groups was higher compared with the control group (P < 0.01), while the expression of TGFβ and IL-10 in the INFα group was not significantly different (P > 0.05).

Conclusions

The results show that INFα-2b inhibits cancer cell immune evasion by decreasing the levels of CD4⁺CD25⁺Foxp3⁺ Treg_s and suppressing the expression of TGFβ and IL-10 in the tumor microenvironment.

Protective role of adenovirus vector-mediated interleukin-10 gene therapy on endogenous islet β-cells in recent-onset type 1 diabetes in NOD mice

The aim of the present study was to provide an animal experimental basis for the protective effect of the adenoviral vector-mediated interleukin-10 (Ad-mIL-10) gene on islet β-cells during the early stages of type 1 diabetes (T1D) in non-obese diabetic (NOD) mice. A total of 24 female NOD mice at the onset of diabetes were allocated at random into three groups (n=8 per group): Group 1, intraperitoneally injected with 0.1 ml Ad-mIL-10; group 2, intraperitoneally injected with 0.1 ml adenovirus vector; and group 3, was a diabetic control. In addition to groups 1, 2 and 3, 8 age- and gender-matched NOD mice were intraperitoneally injected with 0.1 ml PBS and assigned to group 4 as a normal control. All mice were examined weekly for body weight, urine glucose and blood glucose values prior to onset of diabetes, and at 1, 2 and 3 weeks after that, and all mice were sacrificed 3 weeks after injection. Serum levels of interleukin (IL)-10, interferon (IFN)-γ, IL-4, insulin and C-peptide were evaluated, and in addition the degree of insulitis and the local expression of IL-10 gene in the pancreas were detected. The apoptosis rate of pancreatic β-cells was determined using a TUNEL assay. Compared with groups 2 and 3, IL-10 levels in the serum and pancreas were elevated in group 1. Serum IFN-γ levels were decreased while serum IL-4 levels and IFN-γ/IL-4 ratio were significantly increased in group 1 (P<0.01). C-peptide and insulin levels were higher in group 1 compared with groups 2 and 3, (P<0.01). Furthermore, compared with groups 2 and 3, the degree of insulitis, islet β-cell apoptosis rate and blood glucose values did not change significantly (P>0.05). The administration of the Ad-mIL-10 gene induced limited immune regulatory and protective effects on islet β-cell function in NOD mice with early T1D, while no significant reduction in insulitis, islet β-cell apoptosis rate and blood glucose was observed.

MSCs and inflammation: new insights into the potential association between ALCL and breast implants

Possible association between anaplastic large cell lymphoma (ALCL) and breast implants has been suggested. In this context, formation of the periprosthetic capsule has been reported as a cause of inflammation, which plays a key role in tumor onset. Tumors take advantage of inflammation to influence and interfere with the host immune response by secreting multiple factors, and their onset and survival is in turn affected by the paracrine effects from mesenchymal stem cells (MSCs). In this study, we tried to clarify how inflammation can modify the immunobiology and the exerted paracrine effect of MSCs. MSCs derived from both inflamed (I-MSCs) and control (C-MSCs) tissues were isolated and co-cultured with an ALCL cell line. Proliferation rate and the expression of selected cytokines were tested. I-MSCs secrete higher levels of cytokine related to chronic inflammation than C-MSCs. After co-cultures with KI-JK cells, C- and I-MSCs show the same variation in the cytokine expression, with an increase of IL2, IL4, IL5, IL10, IL13, TNF-α, TGF-β, and G-CSF. Proliferation of ALCL cells was not influenced by co-cultures. Our results state that (i) inflamed microenvironment affects the immunobiology of MSCs modifying the profile of the expressed cytokines, and (ii) the paracrine effects exerted by MSCs on ALCL cells are not influenced by inflammation. Moreover, it seems that ALCL cells are able to manipulate MSCs' immunoregulatory properties to evade the host immune control. Nevertheless, this ability is not associated with inflammation and the question about BIA-ALCL is not proved by our experiments.

Antibody Targeting of "Steady-State" Dendritic Cells Induces Tolerance Mediated by Regulatory T Cells

Dendritic cells (DCs) are often defined as pivotal inducers of immunity, but these proinflammatory properties only develop after stimulation or ex vivo manipulation of DCs. Under non-inflammatory conditions in vivo, DCs are embedded into a tissue environment and encounter a plethora of self-antigens derived from apoptotic material. This material is transported to secondary lymphoid organs. As DCs maintain their non-activated phenotype in a sterile tissue environment, interaction with T cells will induce rather regulatory T cells than effector T cells. Thus, DCs are not only inducers of immunity but are also critical for maintenance of peripheral tolerance. Therapeutically, intervention for the induction of long-lasting tolerance in several autoimmune conditions may therefore be possible by manipulating DC activation and/or targeting of DCs in their “natural” tissue environment.

Type 1 diabetes genetic susceptibility and dendritic cell function: potential targets for treatment

Type 1 diabetes is an autoimmune disease that results from the defective induction or maintenance of T cell tolerance against islet β cell self-antigens. Under steady-state conditions, dendritic cells with tolerogenic properties are critical for peripheral immune tolerance. Tolerogenic dendritic cells can induce T cell anergy and deletion and, in some contexts, induce or expand regulatory T cells. Dendritic cells contribute to both immunomodulatory effects and triggering of pathogenesis in type 1 diabetes. This immune equilibrium is affected by both genetic and environmental factors that contribute to the development of type 1 diabetes. Genome-wide association studies and disease association studies have identified >50 polymorphic loci that lend susceptibility or resistance to insulin-dependent diabetes mellitus. In parallel, diabetes susceptibility regions known as insulin-dependent diabetes loci have been identified in the nonobese diabetic mouse, a model for human type 1 diabetes, providing a better understanding of potential immunomodulatory factors in type 1 diabetes risk. Most genetic candidates have annotated immune cell functions, but the focus has been on changes to T and B cells. However, it is likely that some of the genomic susceptibility in type 1 diabetes directly interrupts the tolerogenic potential of dendritic cells in the pathogenic context of ongoing autoimmunity. Here, we will review how gene polymorphisms associated with autoimmune diabetes may influence dendritic cell development and maturation processes that could lead to alterations in the tolerogenic function of dendritic cells. These insights into potential tolerogenic and pathogenic roles for dendritic cells have practical implications for the clinical manipulation of dendritic cells toward tolerance to prevent and treat type 1 diabetes.

Nonspreading Rift Valley Fever Virus Infection of Human Dendritic Cells Results in Downregulation of CD83 and Full Maturation of Bystander Cells

Vaccines based on nonspreading Rift Valley fever virus (NSR) induce strong humoral and robust cellular immune responses with pronounced Th1 polarisation. The present work was aimed to gain insight into the molecular basis of NSR-mediated immunity. Recent studies have demonstrated that wild-type Rift Valley fever virus efficiently targets and replicates in dendritic cells (DCs). We found that NSR infection of cultured human DCs results in maturation of DCs, characterized by surface upregulation of CD40, CD80, CD86, MHC-I and MHC-II and secretion of the proinflammatory cytokines IFN-β, IL-6 and TNF. Interestingly, expression of the most prominent marker of DC maturation, CD83, was consistently downregulated at 24 hours post infection. Remarkably, NSR infection also completely abrogated CD83 upregulation by LPS. Downregulation of CD83 was not associated with reduced mRNA levels or impaired CD83 mRNA transport from the nucleus and could not be prevented by inhibition of the proteasome or endocytic degradation pathways, suggesting that suppression occurs at the translational level. In contrast to infected cells, bystander DCs displayed full maturation as evidenced by upregulation of CD83. Our results indicate that bystander DCs play an important role in NSR-mediated immunity.

Tolerogenic Dendritic Cells for Regulatory T Cell Induction in Man

Dendritic cells (DCs) are highly specialized professional antigen-presenting cells that regulate immune responses, maintaining the balance between tolerance and immunity. Mechanisms via which they can promote central and peripheral tolerance include clonal deletion, the inhibition of memory T cell responses, T cell anergy, and induction of regulatory T cells (Tregs). These properties have led to the analysis of human tolerogenic DCs as a therapeutic strategy for the induction or re-establishment of tolerance. In recent years, numerous protocols for the generation of human tolerogenic DCs have been developed and their tolerogenic mechanisms, including induction of Tregs, are relatively well understood. Phase I trials have been conducted in autoimmune disease, with results that emphasize the feasibility and safety of treatments with tolerogenic DCs. Therefore, the scientific rationale for the use of tolerogenic DCs therapy in the fields of transplantation medicine and allergic and autoimmune diseases is strong. This review will give an overview on efforts and protocols to generate human tolerogenic DCs with focus on IL-10-modulated DCs as inducers of Tregs and discuss their clinical applications and challenges faced in further developing this form of immunotherapy.

Is sentinel node susceptibility to metastases related to nodal immune modulation?

Sentinel lymph nodes (SLNs), the initial site of regional metastases, directly receive lymph containing immune-modulatory cytokines and tumor cells from primary melanomas. Immune-suppressed SLNs are ideal for studies of tissue susceptibility to metastases. They show reduced antigen-presenting dendritic cells, activated T cells, high endothelial venules, and transvenular immigration of T cells. Tumor-induced immune suppression contributes to establishment of nodal metastases. SLNs may serve as an effective model to study reversal of tumor-induced immune suppression. We reviewed this topic in Nature Reviews of Immunology in 2006. We here summarize the Nature paper and provide additional results from ongoing studies and the recent literature.

T-cell Expression of IL10 Is Essential for Tumor Immune Surveillance in the Small Intestine

IL10 is attributed with immune-suppressive and anti-inflammatory properties, which could promote or suppress cancer in the gastrointestinal tract. Loss of IL10 exacerbates colonic inflammation, leading to colitis and cancer. Consistent with this, transfer of IL10-competent regulatory T cells (Treg) into mice with colitis or hereditary polyposis protects against disease, while IL10-deficient mice are predisposed to polyposis with increased colon polyp load. Little is known about the protective or pathogenic function of IL10 in cancers of the small intestine. We found CD4(+) T cells and CD4(+) Foxp3(+) Tregs to be the major sources of IL10 in the small intestine and responsible for the increase in IL10 during polyposis in the APC(Δ468) mouse model of hereditary polyposis. Targeted ablation of IL10 in T cells caused severe IL10 deficiency and delayed polyp growth. However, these polyps progressively lost cytotoxic activity and eventually progressed to cancer. Several observations suggested that the effect was due to the loss of IFNγ-dependent immune surveillance. IL10-incompetent CD4(+) T cells failed to secrete IFNγ when stimulated with polyp antigens and were inefficient in T-helper-1 (TH1) commitment. By contrast, the TH17 commitment was unaffected. These findings were validated using mice whose T cells overexpress IL10. In these mice, we observed high intra-polyp cytotoxic activity and attenuation of polyposis. Thus, expression of IL10 by T cells is protective and required for immune surveillance in the small intestine.

Acquired and intrinsic resistance in cancer immunotherapy

A number of immunotherapies, in particular immune checkpoint targeting antibodies and adoptive T-cell therapies, are starting to transform the treatment of advanced cancers. The likelihood to respond to these immunotherapies differs strongly across tumor types, with response rates for checkpoint targeting being the highest in advanced melanoma, renal cell cancer and non-small cell lung cancer. However, also non-responsiveness is observed, indicating the presence of intrinsic resistance or naturally acquired resistance. In addition, a subgroup of patients that do initially respond to immunotherapy will later recur, thereby also pointing towards a role of therapy-induced acquired resistance. Here, we review our current understanding of both intrinsic and acquired resistance mechanisms in cancer immunotherapy, and discuss potential strategies to overcome them.

Up-regulation of PD-L1, IDO, and T(regs) in the melanoma tumor microenvironment is driven by CD8(+) T cells

Tumor escape from immune-mediated destruction has been associated with immunosuppressive mechanisms that inhibit T cell activation. Although evidence for an active immune response, including infiltration with CD8(+) T cells, can be found in a subset of patients, those tumors are nonetheless not immunologically rejected. In the current report, we show that it is the subset of T cell-inflamed tumors that showed high expression of three defined immunosuppressive mechanisms: indoleamine-2,3-dioxygenase (IDO), PD-L1/B7-H1, and FoxP3(+) regulatory T cells (T(regs)), suggesting that these inhibitory pathways might serve as negative feedback mechanisms that followed, rather than preceded, CD8(+) T cell infiltration. Mechanistic studies in mice revealed that up-regulated expression of IDO and PD-L1, as well as recruitment of T(regs), in the tumor microenvironment depended on the presence of CD8(+) T cells. The former was driven by interferon-γ and the latter by a production of CCR4-binding chemokines along with a component of induced proliferation. Our results argue that these major immunosuppressive pathways are intrinsically driven by the immune system rather than being orchestrated by cancer cells, and imply that cancer immunotherapy approaches targeting negative regulatory immune checkpoints might be preferentially beneficial for patients with a preexisting T cell-inflamed tumor microenvironment.

Current status of interleukin-10 and regulatory T-cells in cancer

PURPOSE OF REVIEW

Tumor growth elicits antigen-specific cytotoxic as well as immune suppressive responses. Interleukin-10 (IL-10) is a key immune-suppressive cytokine produced by regulatory T-cells and by helper T-cells. Here, we review pleiotropic functions of IL-10 that impact the immune pathology of cancer.

RECENT FINDINGS

The role of IL-10 in cancer has become less certain with the knowledge of its immune stimulatory functions. IL-10 is needed for T-helper cell functions, T-cell immune surveillance, and suppression of cancer-associated inflammation. By promoting tumor-specific immune surveillance and hindering pathogenic inflammation, IL-10 is emerging as a key cytokine in the battle of the host against cancer.

SUMMARY

IL-10 functions at the cross-roads of immune stimulation and immune suppression in cancer. Immunological mechanisms of action of IL-10 can be ultimately exploited to develop novel and effective cancer therapies.

Cluster of differentiation 45 activation is crucial in interleukin-10-dependent tumor-associated dendritic cell differentiation

Tumor-associated dendritic cells (TADCs) are important in tumor immune surveillance, and it has been reported that the secretion of interleukin (IL)-10 by cancer cells is a major factor involved in the induction of TADCs in the tumor microenvironment. In the present study, IL-10 was found to activate cluster of differentiation (CD)45 protein tyrosine phosphatase (PTPase), inducing a TADC-like phenomenon. The PTPase inhibitor, phenylarsine oxide, and a CD45 inhibitor reversed the IL-10-induced impaired differentiation of the DCs, and also reversed the induction of the TADCs by A549, MDA-MB-231 and SW480 conditioned media, which thus represents a novel therapy to reduce immune surveillance in the tumor microenvironment. The present study is the first to identify that CD45 is involved in IL-10-activated signaling in myeloid lineage cells.

CD40-activated B cells as antigen-presenting cells: the final sprint toward clinical application

Efficient antigen presentation is a prerequisite for the development of a T-cell-mediated immune response in vitro and in vivo. CD40-activated B cells (CD40B cells) are a promising alternative to dendritic cells as professional APCs for immunotherapy. CD40 activation dramatically improves antigen presentation by normal and malignant B cells, efficiently inducing naive and memory CD4(+) and CD8(+) T-cell responses. Moreover, CD40B cells do not only attract T cells by release of chemokines, but also home to secondary lymphoid organs. Furthermore, CD40B cells can be expanded exponentially over several weeks at high purity without a loss of antigen-presenting function, providing an almost unlimited source of cellular adjuvant. Vaccination with CD40B cells was shown in mice and dogs to induce a specific immune response. This article summarizes the achievements of intense research on CD40B cells over the last decade, as well as novel developments critical for a rapid translation into clinical application.

Inflammation-induced cancer: crosstalk between tumours, immune cells and microorganisms

Inflammation is a fundamental innate immune response to perturbed tissue homeostasis. Chronic inflammatory processes affect all stages of tumour development as well as therapy. In this Review, we outline the principal cellular and molecular pathways that coordinate the tumour-promoting and tumour-antagonizing effects of inflammation and we discuss the crosstalk between cancer development and inflammatory processes. In addition, we discuss the recently suggested role of commensal microorganisms in inflammation-induced cancer and we propose that understanding this microbial influence will be crucial for targeted therapy in modern cancer treatment.

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.

Dendritic cell-based approaches for therapeutic immune regulation in solid-organ transplantation

To avoid immune rejection, allograft recipients require drug-based immunosuppression, which has significant toxicity. An emerging approach is adoptive transfer of immunoregulatory cells. While mature dendritic cells (DCs) present donor antigen to the immune system, triggering rejection, regulatory DCs interact with regulatory T cells to promote immune tolerance. Intravenous injection of immature DCs of either donor or host origin at the time of transplantation have prolonged allograft survival in solid-organ transplant models. DCs can be treated with pharmacological agents before injection, which may attenuate their maturation in vivo. Recent data suggest that injected immunosuppressive DCs may inhibit allograft rejection, not by themselves, but through conventional DCs of the host. Genetically engineered DCs have also been tested. Two clinical trials in type-1 diabetes and rheumatoid arthritis have been carried out, and other trials, including one trial in kidney transplantation, are in progress or are imminent.

Human dendritic cells subsets as targets and vectors for therapy

The skin immune system includes a complex network of dendritic cells (DCs). In addition to generating cellular and humoral immunity against pathogens, skin DCs are involved in tolerogenic mechanisms that maintain immune homeostasis and in pathogenic chronic inflammation in which immune responses are unrestrained. Harnessing DC function by directly targeting DC-derived molecules or by selectively modulating DC subsets is a novel strategy for ameliorating inflammatory diseases. In this short review, we discuss recent advances in understanding the functional specialization of skin DCs and the potential implication for future DC-based therapeutic strategies.

Local secretion of IL-12 augments the therapeutic impact of dendritic cell-tumor cell fusion vaccination

BACKGROUND

The development of dendritic cell (DC)-tumor fusion vaccines is a promising approach in cancer immunotherapy. Using fusion vaccines allows a broad spectrum of known and unidentified tumor-associated antigens to be presented in the context of MHC class I and class II molecules, with potent co-stimulation provided by the DCs. Although DC-tumor fusion cells are immunogenic, murine studies have shown that effective immunotherapy requires a third signal, which can be provided by exogenous interleukin 12 (IL-12). Unfortunately, systemic administration of IL-12 induces severe toxicity in cancer patients, potentially precluding clinical use of this cytokine to augment fusion vaccine efficacy. To overcome this limitation, we developed a novel approach in which DC-tumor fusion cells locally secrete IL-12, then evaluated the effectiveness of this approach in a murine B16 melanoma model.

MATERIALS AND METHODS

Tumor cells were stably transduced to secrete murine IL-12p70. These tumor cells were then electrofused to DC to form DC-tumor heterokaryons. These cells were used to treat established B16 pulmonary metastases. Enumeration of these metastases was performed and compared between experimental groups using Wilcoxon rank sum test. Interferon γ enzyme-linked immunosorbent spot assay was performed on splenocytes from treated mice.

RESULTS

We show that vaccination with DCs fused to syngeneic melanoma cells that stably express murine IL-12p70 significantly reduces counts of established lung metastases in treated animals when compared with DC-tumor alone (P = 0.029). Interferon γ enzyme-linked immunosorbent spot assays suggest that this antitumor response is mediated by CD4(+) T cells, in the absence of a tumor-specific CD8(+) T cell response, and that the concomitant induction of antitumor CD4(+) and CD8(+) T cell responses required exogenous IL-12.

CONCLUSIONS

This study is, to the best of our knowledge, the first report that investigates the impact of local secretion of IL-12 on antitumor immunity induced by a DC-tumor fusion cell vaccine in a melanoma model and may aid the rational design of future clinical trials.

Dendritic cell-based vaccination for renal cell carcinoma: challenges in clinical trials

After decades of research, dendritic cell (DC)-based vaccines for renal cell carcinoma have progressed from preclinical rodent models and safety assessments to Phase I/II clinical trials. DC vaccines represent a promising therapy that has produced measurable immunological responses and prolonged survival rates. However, there is still much room to improve in terms of therapeutic efficacy. The key issues that affect the efficiency and reliability of DC therapy include the selection of patients who will respond best to treatment, the proper preparation and administration of DC vaccines, and a combination of DC vaccination with other immune-enhancing therapies (e.g., removal of Tregs, CTLA-4 blockade and lymphodepletion). Additional antiangiogenic agents will hopefully lead to greater survival benefits for patients in early disease stages. This review focuses on the different approaches of DC-based vaccination against renal cell carcinoma and potential strategies to enhance the efficacy of DC vaccination.

Newer developments in the immunotherapy of malignant melanoma

Individuals with malignant melanoma present a variety of immune abnormalities including but not limited to cellular immune dysfunction, antigen presentation deficits, and cytokine production defects. Therefore, enhancing the immune system potential represents an appealing avenue for melanoma therapy. The authors review the immune therapies currently in clinical use as well as the most promising immunotherapy candidates. Ipilimumab, a monoclonal antibody against the CTLA-4, was approved for the therapy of advanced melanoma in 2011. In addition, sizeable anti-melanoma activity has recently been shown with the use of other agents including anti-PD-1/anti-PD-1 ligand antibodies. Consequently, these experimental immunotherapy agents may soon become important items in the anti-melanoma armamentarium.

Mast cell interleukin-10 drives localized tolerance in chronic bladder infection

The lower urinary tract's virtually inevitable exposure to external microbial pathogens warrants efficient tissue-specialized defenses to maintain sterility. The observation that the bladder can become chronically infected in combination with clinical observations that antibody responses after bladder infections are not detectable suggest defects in the formation of adaptive immunity and immunological memory. We have identified a broadly immunosuppressive transcriptional program specific to the bladder, but not the kidney, during infection of the urinary tract that is dependent on tissue-resident mast cells (MCs). This involves localized production of interleukin-10 and results in suppressed humoral and cell-mediated responses and bacterial persistence. Therefore, in addition to the previously described role of MCs orchestrating the early innate immunity during bladder infection, they subsequently play a tissue-specific immunosuppressive role. These findings may explain the prevalent recurrence of bladder infections and suggest the bladder as a site exhibiting an intrinsic degree of MC-maintained immune privilege.

RNA pulsed dendritic cells: an approach for cancer immunotherapy

The immunotherapy of cancer is aimed at evoking both branches of immune system to elicite specific immune responses directed against tumor antigens to deal with residual tumor cells upon interaction, and thereby decreases mortality as well as morbidity of cancer patients. As dendritic cells (DCs) are specialized for antigen presentation, and their immunogenicity leads to the induction of antigen specific immune responses, various immunotherapeutic approaches have been designed for using DCs to present tumor-associated antigens to T-lymphocytes. As a part of proposed strategy ex vivo generated DCs might be loaded with antigens and re-infused to the patients and/or they can be used for the ex vivo expansion of anti-tumor lymphocytes. The DCs loaded ex vivo with RNA can be safely administered which proves to be an asset for producing antigen specific immune responses. Furthermore, already conducted studies have prompted clinical trials to be designed to investigate immunological and clinical effects of RNA pulsed DCs administered as an engineered therapeutic vaccine in cancer patients. However, selection of the antigens of interest, methods for introducing TAAgs into MHC class I and II processing pathways, methods for isolation and activation of DCs, and route of administration are the parameters to be considered for designing and conducting clinical trials with engineered DCs. The enhanced RNA transfection efficiency would further improve antigen processing and presentation and T-cell co-stimulation, resulting in the induction of heightened anti-tumor immune responses. Therefore, RNA transfected dendritic cells continue to hold promise for cellular immunotherapy and opens new avenues to devising further strategies for cancer therapeutic interventions.

Cell therapy using tolerogenic dendritic cells in transplantation

Organ transplantation is the main alternative to the loss of vital organ function from various diseases. However, to avoid graft rejection, transplant patients are treated with immunosuppressive drugs that have adverse side effects. A new emerging approach to reduce the administration of immunosuppressive drugs is to co-treat patients with cell therapy using regulatory cells. In our laboratory, as part of a European project, we plan to test the safety of tolerogenic dendritic cell (TolDC) therapy in kidney transplant patients. In this mini-review, we provide a brief summary of the major protocols used to derive human TolDC, and then focus on the granulocyte macrophage-TolDC generated by our own team. Proof of safety of TolDC therapy in the clinic has already been demonstrated in patients with diabetes. However, in transplantation, DC therapy will be associated with the administration of immunosuppressive drugs, and interactions between drugs and DC are possible. Finally, we will discuss the issue of DC origin, as we believe that administration of autologous TolDC is more appropriate, as demonstrated by our experiments in animal models.

Regional lymphatic immunity in melanoma

Melanoma is an immunogenic tumor that has developed methods to successfully evade immune recognition, while paradoxically spreading through the lymphatic system. Increasing evidence supports that melanoma-derived factors suppress regional immunity within the host. At a very early stage, melanoma communicates with the tumor-draining lymph nodes, and prepares them for seeding of metastatic disease by stimulating lymphangiogenesis and downregulation of the sentinel lymph node immunity well before the malignant cells arrive. Investigations have demonstrated that the induction of suppressor cells, peripheral tolerance, and a less tumor-responsive Th2 cytokine environment may provide a hospitable environment for subsequent lymphatic metastasis. Patients with early-stage disease may benefit from the restoration of the regional immune function to a level that controls the progression of residual occult metastases and ensures a durable clinical response. Herein we provide a succinct summary of the current progress in this field in order to guide future investigations.

Impact of HDAC inhibitors on dendritic cell functions

Histone deacetylase inhibitors are presently used in the routine clinic treatment against cancers. Recent data have established that some of these treatments have potent anti-inflammatory or immunomodulatory effects at noncytotoxic doses that might be of benefit in immuno-inflammatory disorders or post-transplantation. At least some of these effects result from the ability of histone deacetylase inhibitors to modulate the immune system. Dendritic cells are professional antigen presenting cells that play a major role in this immune system. Data summarized in this review brings some novel information on the impact of histone deacetylase inhibitors on dendritic cell functions, which may have broader implications for immunotherapeutic strategies.

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.

Induction of prolonged asthma tolerance by IL-10-differentiated dendritic cells: differential impact on airway hyperresponsiveness and the Th2 immunoinflammatory response

IL-10-differentiated dendritic cells (DC10s) can prevent allergen sensitization and reverse the asthma phenotype in mice with established disease. However, little is known about the time-frames over which this tolerance is effective. We report that at 2 wk after i.p. or transtracheal delivery of 1 × 10(6) OVA-, but not house dust mite- presenting, DC10s to OVA-asthmatic mice, significant diminution of airway hyperresponsiveness (AHR) was first apparent, whereas AHR was abrogated between 3 and 10 wk posttreatment. At 13 wk, AHR returned to pretreatment levels but could again be reversed by DC10 retreatment. The impact of a single DC10 treatment on airway eosinophil and Th2 cytokine responses to recall OVA challenge, and on OVA-specific IgE/IgG1 responses, was substantial at 3 wk posttreatment, but progressively increased thereafter, such that at 8 mo, airway eosinophil and Th2 responses to recall allergen challenge remained ∼85-95% suppressed relative to saline-treated asthmatic mice. Four biweekly DC10 treatments, whether transtracheal or i.p., reduced all asthma parameters to near background by 8 wk, whereas s.c. DC10 treatments did not affect AHR but did reduce the airway Th2 responses (i.v. DC10 had no discernible effects). Repeated challenge of the DC10-treated mice with aerosolized OVA (100 μg/ml) did not reverse tolerance, but treatment with the indoleamine-2,3-dioxygenase antagonist 1-methyltryptophan or neutralizing anti-IL-10R from days 12 to 21 after DC10 therapy partially reversed tolerance (Th2 cytokine responses, but not AHR). These findings indicate that DC10-induced Th2 tolerance in asthmatic animals is long lived, but that DC10s employ distinct mechanisms to affect AHR versus Th2 immunoinflammatory parameters.

The immunosuppressive factors IL-10, TGF-β, and VEGF do not affect the antigen-presenting function of CD40-activated B cells

Background

Progress in recent years strengthened the concept of cellular tumor vaccinations. However, a crucial barrier to successful cancer immunotherapy is tumor-mediated immunosuppression. Tumor-derived soluble factors such as IL-10, TGF-β, and VEGF suppress effector cells either directly or indirectly by disruption of dendritic cell (DC) differentiation, migration and antigen presentation. Human B cells acquire potent immunostimulatory properties when activated via CD40 and have been shown to be an alternative source of antigen-presenting cells (APCs) for cellular cancer vaccines. Nevertheless, in contrast to DCs little knowledge exists about their susceptibility to tumor derived immunosuppressive factors. Thus, we assessed whether IL-10, TGF-β, or VEGF do affect key aspects of the immunostimulatory function of human CD40-activated B cells.

Methods

Cell surface expression of adhesion and costimulatory molecules and the proliferation capacity of CD40-activated B cells were compared to untreated controls by flow cytometry. Migration towards important chemokines of secondary lymph organs was measured with or without exposure to the immunosuppressive cytokines. Finally, an influence on T cell stimulation was investigated by allogeneic mixed lymphocyte reactions. For statistical analysis Student’s t test or two-way analysis of variance followed by Bonferroni's post-hoc test was used to compare groups. P values of <0.05 were considered statistically significant.

Results

Neither cell adhesion nor the expression of MHC class II and costimulatory molecules CD80 and CD86 was inhibited by addition of IL-10, TGF-β, or VEGF. Likewise, the proliferation of CD40-activated B cells was not impaired. Despite being exposed to IL-10, TGF-β, or VEGF the B cells migrated equally well as untreated controls to the chemokines SLC and SDF-1α. Most importantly, the capacity of CD40-activated B cells to stimulate CD4⁺ and CD8⁺ T cells remained unaffected.

Conclusion

Our findings suggest that key immunostimulatory functions of CD40-activated B cells are resistant to inhibition by the immunosuppressive factors IL-10, TGF-β, and VEGF. This supports considerations to use ex vivo generated CD40-activated B cells as a promising alternative or additional APC for cellular immunotherapy, especially in settings where these immunosuppressive cytokines are present in tumor environment.

Effects of Gekko sulfated polysaccharide-protein complex on the defective biorheological characters of dendritic cells under tumor microenvironment

We previously isolated a sulfated polysaccharide-protein complex from Gekko swinhonis Guenther, a traditional Chinese medicine, and have demonstrated its direct anti-cancer effect on human hepatocellular carcinoma cell line SMMC-7721. Here we investigated the effects of Gekko sulfated polysaccharide-protein complex (GSPP) on the defective biorheological characters of dendritic cells (DCs) under SMMC-7721 microenvironment. Our findings have shown that the biorheological properties of DCs were severely impaired by SMMC-7721 microenvironment, including decreased cell deformability, migration, and electrophoresis mobility, increased osmotic fragilities, and changed organizations of cytoskeletal proteins. We also found decreased secretion of interleukin (IL)-12 and increased secretion of IL-10 in DCs. However, supernatant collected from nonmalignant liver cells had no effect on these parameters. SMMC-7721 cells were treated with GSPP and the supernatant was used to culture DCs. We found that the defective biorheological parameters of DCs, except for osmotic fragility, were partially or completely improved. The secretion of IL-12 did not change as compared with that of DCs in SMMC-7721 microenvironment, but the secretion of IL-10 was resumed to the control level. Our results indicate that GSPP could partially restore the defective biorheological characteristics of DCs via modifying the tumor microenvironment and decreasing the secretion of IL-10 of DCs.

The differential production of cytokines by human Langerhans cells and dermal CD14(+) DCs controls CTL priming

We recently reported that human epidermal Langerhans cells (LCs) are more efficient than dermal CD14(+) DCs at priming naive CD8(+) T cells into potent CTLs. We hypothesized that distinctive dendritic cell (DC) cytokine expression profiles (ie, IL-15 produced by LCs and IL-10 expressed by dermal CD14(+) DCs) might explain the observed functional difference. Blocking IL-15 during CD8(+) T-cell priming reduced T-cell proliferation by ∼ 50%. These IL-15-deprived CD8(+) T cells did not acquire the phenotype of effector memory cells. They secreted less IL-2 and IFN-γ and expressed only low amounts of CD107a, granzymes and perforin, and reduced levels of the antiapoptotic protein Bcl-2. Confocal microscopy analysis showed that IL-15 is localized at the immunologic synapse of LCs and naive CD8(+) T cells. Conversely, blocking IL-10 during cocultures of dermal CD14(+) DCs and naive CD8(+) T cells enhanced the generation of effector CTLs, whereas addition of IL-10 to cultures of LCs and naive CD8(+) T cells inhibited their induction. TGF-β1 that is transcribed by dermal CD14(+) DCs further enhanced the inhibitory effect of IL-10. Thus, the respective production of IL-15 and IL-10 explains the contrasting effects of LCs and dermal CD14(+) DCs on CD8(+) T-cell priming.