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

Induction of antigen-specific regulatory T cells in the liver-draining celiac lymph node following oral antigen administration

Regulatory T cells are induced by oral administration of an antigen, but the physiological requirements and localization of the inductive sites are largely unknown. Using an adoptive transfer system of cells transgenic for ovalbumin T-cell receptor (OVA TCR tg), we found that antigen-specific CD4+ T cells were activated in the liver-draining celiac lymph node (CLN) shortly after ovalbumin feeding, and that a significantly higher proportion of the T cells in the CLN developed into the putative regulatory phenotype [co-expressing CD25 with the glucocortico-induced tumour necrosis factor (TNF) receptor family related gene (GITR), cytotoxic T-lymphocyte antigen (CTLA)-4 and CD103] than in Peyer's patches, the mesenteric and peripheral lymph nodes and the spleen. In addition, a particularly high level of expression of CD103 on the OVA-specific T cells in the CLN may favour homing to the epithelium of the intestine. While equally suppressive, OVA tg T cells isolated from the CLN of OVA-fed DO11.10 mice were less dependent on transforming growth factor (TGF)-beta for suppression than cells isolated from the peripheral and mesenteric lymph nodes, which indicates the involvement of an additional suppressive mechanism. The expression of FoxP3 was not up-regulated in any of the lymph node compartments studied. Our phenotypic and functional findings suggest that the induction of regulatory T cells in the CLN may be relevant in the control of the immune response to dietary antigens.

Regulatory balance between the immune response of tumor antigen-specific T-cell receptor gene-transduced CD8 T cells and the suppressive effects of tolerogenic dendritic cells

Tumor immune responses, including some immunotherapy strategies, can fail because of a number of reasons, such as poor tumor cell immunogenicity or local suppressive cytokine release by dendritic cells (DC) at tumor sites. The retroviral transfer of T-cell receptor (TCR) genes encoding tumor-specific receptors into T cells is a fascinating approach to bypass antigen-presenting cells and allow T cells to directly recognize antigen. It also allows the generation and expansion of potent antitumor cytotoxic T lymphocytes with defined cancer antigen specificities more readily than naive T cells. However, interleukin-10 (IL-10)-exposed dendritic cells (IL-10-DC) have been labeled tolerogenic because of the suppressive effects they have on T cell responses. Whether TCR gene-transduced effector CD8(+) T cells can break through suppressive functions mediated by IL-10-DC is not known. In the current study, we demonstrate the role of IL-10 in modifying the function of DC that otherwise would activate potent TCR gene-transduced T cells against tumor antigens. TCR gene-transduced T cells maintained their cytolytic activity in the presence of DC exposed to low doses of IL-10 during maturation; however, they lost this activity in an antigen-specific manner when exposed to DC matured with high doses of IL-10.

CD8 alpha+, but not CD8 alpha-, dendritic cells tolerize Th2 responses via contact-dependent and -independent mechanisms, and reverse airway hyperresponsiveness, Th2, and eosinophil responses in a mouse model of asthma

Splenic CD8alpha+ dendritic cells reportedly tolerize T cell responses by inducing Fas ligand-mediated apoptosis, suppressing IL-2 expression, or catabolizing T cell tryptophan reserves through expression of IDO. We report in this study that CD8alpha+, but not CD8alpha-, dendritic cells purified from the spleens of normal mice can tolerize the Th2 responses of cells from asthma phenotype mice through more than one mechanism. This tolerance could largely be reversed in vitro by anti-IL-10 or anti-TGFbeta Ab treatment. However, loss of direct dendritic cell-T cell contact also reduced tolerance, although to a lesser extent, as did adding the IDO inhibitor 1-methyltryptophan or an excess of free tryptophan to the cultures. Within 3 wk of reconstituting asthma phenotype mice with 1 x 10(5) OVA-pulsed CD8alpha+, but not CD8alpha-, dendritic cells, the mice experienced a reversal of airway hyperresponsiveness, eosinophilic airway responses, and pulmonary Th2 cytokine expression. This data indicates that CD8alpha+ dendritic cells can simultaneously use multiple mechanisms for tolerization of T cells and that, in vivo, they are capable of tolerizing a well-established disease complex such as allergic lung disease/asthma.

Interleukin-10 and the immune response against cancer: a counterpoint

Although interleukin-10 (IL-10) is commonly regarded as an anti-inflammatory, immunosuppressive cytokine that favors tumor escape from immune surveillance, a wealth of evidence is accumulating that IL-10 also possesses some immunostimulating properties. In fact, IL-10 has the pleiotropic ability of influencing positively and negatively the function of innate and adaptive immunity in different experimental models, which makes it questionable to merely categorize this cytokine as a target of anti-immune escape therapeutic strategies or rather, as an immunological adjuvant in the fight against cancer. Here, we review available data about the immunostimulating anticancer properties of IL-10, and in particular, we focus on the hypothesis that in contrast to what occurs in secondary lymphoid organs, IL-10 overexpression within the tumor microenvironment may catalyze cancer immune rejection.

Apoptotic cells at the crossroads of tolerance and immunity

Clearance of apoptotic cells by phagocytes can result in either anti-inflammatory and immunosuppressive effects or prostimulatory consequences through presentation of cell-associated antigens to T cells. The differences in outcome are due to the conditions under which apoptosis is induced, the type of phagocytic cell, the nature of the receptors involved in apoptotic cell capture, and the milieu in which phagocytosis of apoptotic cells takes place. Preferential ligation of specific receptors on professional antigen-presenting cells (dendritic cells) has been proposed to induce potentially tolerogenic signals. On the other hand, dendritic cells can efficiently process and present antigens from pathogen-infected apoptotic cells to T cells. In this review, we discuss how apoptotic cells manipulate immunity through interactions with dendritic cells.

Immunomodulatory dendritic cells require autologous serum to circumvent nonspecific immunosuppressive activity in vivo

In immunotherapy, dendritic cells (DCs) can be used as powerful antigen-presenting cells to enhance or suppress antigen-specific immunity upon in vivo transfer in mice or humans. However, to generate sufficient numbers of DCs, most protocols include an ex vivo culture step, wherein the cells are exposed to heterologous serum and/or antigenic stimuli. In mouse models of virus infection and virus-induced autoimmunity, we tested how heterologous serum affects the immunomodulatory capacity of immature DCs generated in the presence of IL-10 by comparing fetal bovine serum (FBS)- or normal mouse serum (NMS)-supplemented DC cultures. We show that FBS-exposed DCs induce a systemic immune deviation characterized by reduction of virus-specific T cells, delayed viral clearance, and enhanced systemic production of interleukin 4 (IL-4), IL-5, and IL-10 to FBS-derived antigens, including bovine serum albumin (BSA). By contrast, DCs generated in NMS-supplemented cultures modulated immunity and autoimmunity in an antigen-specific fashion. These cells did not induce systemic IL-4, IL-5, or IL-10 production and inhibited generation of virus-specific T cells or autoimmunity only if pulsed with a viral antigen. These data underscore the importance of using autologous serum-derived immature DCs in preclinical animal studies to accurately assess their immunomodulatory potential in future human therapeutic settings, where application of FBS is not feasible.

Increased expression of CD86 and reduced production of IL-12 and IL-10 by monocyte-derived dendritic cells from allergic asthmatics and their effects on Th1- and Th2-type cytokine balance

BACKGROUND

In allergic asthma, allergen-specific T cells have a Th2-biased phenotype, and it is thought that dendritic cells (DCs) contribute to the induction of allergic immune responses. Therefore, we hypothesized that DCs from allergic asthmatics and healthy donors differ with regard to their preference to induce Th1 or Th2 immune responses.

OBJECTIVES

To investigate differences in DC-expressed costimulatory molecules and DC-secreted cytokines between allergic asthmatics and healthy donors, and their influence on the Th1- and Th2-type cytokine balance.

METHODS

Circulating monocytes from patients with allergic asthma and healthy donors were cultured with GM-CSF and IL-4, respectively, for 5 days and subsequently with lipopolysaccharide for 2 days to create mature DCs (mDCs). CD1a, CD83, CD40 and CD86 expression on mDCs was examined using a fluorescence-activated cell sorter. IL-12 and IL-10 secreted by mDCs were measured by ELISA. Naïve cord blood T cells were primed by mDCs from two groups, and IL-4 and IFN-gamma production by polarized T-helper cells (Th) was measured by ELISA.

RESULTS

(1) CD86 expression on mDCs from allergic asthmatics was higher than that from healthy donors. (2) IL-12, IL-12p40 and IL-10 production by mDCs from allergic asthmatics was significantly lower than that from healthy donors, respectively. (3) IL-4 production by Th cells primed by mDCs from allergic asthmatics was increased compared with that from healthy donors.

CONCLUSIONS

mDCs from allergic asthmatics preferentially priming naïve T cells towards Th2-cell development might be due to increased expression of CD86 and reduced production of IL-12 and IL-10.

Tolerogenic semimature dendritic cells suppress experimental autoimmune thyroiditis by activation of thyroglobulin-specific CD4+CD25+ T cells

Ex vivo treatment of bone marrow-derived dendritic cells (DCs) with TNF-alpha has been previously shown to induce partial maturation of DCs that are able to suppress autoimmunity. In this study, we demonstrate that i.v. administration of TNF-alpha-treated, semimature DCs pulsed with thyrogloblin (Tg), but not with OVA Ag, inhibits the subsequent development of Tg-induced experimental autoimmune thyroiditis (EAT) in CBA/J mice. This protocol activates CD4(+)CD25(+) T cells in vivo, which secrete IL-10 upon specific recognition of Tg in vitro and express regulatory T cell (Treg)-associated markers such as glucocorticoid-induced TNFR, CTLA-4, and Foxp3. These CD4(+)CD25(+) Treg cells suppressed the proliferation and cytokine release of Tg-specific, CD4(+)CD25(-) effector cells in vitro, in an IL-10-independent, cell contact-dependent manner. Prior adoptive transfer of the same CD4(+)CD25(+) Treg cells into CBA/J hosts suppressed Tg-induced EAT. These results demonstrate that the tolerogenic potential of Tg-pulsed, semimature DCs in EAT is likely to be mediated through the selective activation of Tg-specific CD4(+)CD25(+) Treg cells and provide new insights for the study of Ag-specific immunoregulation of autoimmune diseases.

Effect of Tinospora cordifolia on the antitumor activity of tumor-associated macrophages-derived dendritic cells

We and others previously have reported that extract prepared from medicinal plant Tinospora cordifolia shows a wide spectrum of immunoaugmentary effects. Tinospora cordifolia was shown to upregulate antitumor activity of tumor-associated macrophages (TAM). In this article we present evidence to show that an alcoholic extract of Tinospora cordifolia (ALTC) enhances the differentiation of TAM to dendritic cells (DC) in response to granulocyte/macrophage-colony-stimulating factor, interleukin-4, and tumor necrosis factor. DC differentiated in vitro from TAM that were harvested from tumor-bearing mice after i.p. administration of ALTC (200 mg/kg body weight) 2 days posttumor transplantation shows an enhanced tumor cytotoxicity and production of tumoricidal soluble molecules like TNF, IL-1, and NO. Adoptive transfer of these TAM-derived DC to Dalton's lymphoma-bearing mice resulted in prolongation of survival of tumor-bearing mice. This is the first report regarding the differentiation and antitumor functions of TAM-derived DC obtained from tumor-bearing host administered with ALTC. The possible mechanisms involved also are discussed.

An anti-CD45RO/RB monoclonal antibody modulates T cell responses via induction of apoptosis and generation of regulatory T cells

The effects of a chimeric monoclonal antibody (chA6 mAb) that recognizes both the RO and RB isoforms of the transmembrane protein tyrosine phosphatase CD45 on human T cells were investigated. Chimeric A6 (chA6) mAb potently inhibited antigen-specific and polyclonal T cell responses. ChA6 mAb induced activation-independent apoptosis in CD4⁺CD45RO/RB^high T cells but not in CD8⁺ T cells. In addition, CD4⁺ T cell lines specific for tetanus toxoid (TT) generated in the presence of chA6 mAb were anergic and suppressed the proliferation and interferon (IFN)-γ production by TT-specific effector T cells by an interleukin-10–dependent mechanism, indicating that these cells were equivalent to type 1 regulatory T cells. Similarly, CD8⁺ T cell lines specific for the influenza A matrix protein-derived peptide (MP.58-66) generated in the presence of chA6 mAb were anergic and suppressed IFN-γ production by MP.58-66–specific effector CD8⁺ T cells. Furthermore, chA6 mAb significantly prolonged human pancreatic islet allograft survival in nonobese diabetic/severe combined immunodeficiency mice injected with human peripheral blood lymphocytes (hu-PBL-NOD/SCID). Together, these results demonstrate that the chA6 mAb is a new immunomodulatory agent with multiple modes of action, including deletion of preexisting memory and recently activated T cells and induction of anergic CD4⁺ and CD8⁺ regulatory T cells.

Dendritic cells: sentinels of immunity and tolerance

The induction of effective antigen-specific T-cell immunity to pathogens without the initiation of autoimmunity has evolved as a sophisticated and highly balanced immunoregulatory mechanism. This mechanism assures the generation of antigen-specific effector cells as well as the induction and maintenance of antigen-specific tolerance to self-structures of the body. As professional antigen-presenting cells of the immune system, dendritic cells (DC) are ideally positioned throughout the entire body and equipped with a unique capability to transport antigens from the periphery to lymphoid tissues. There is growing evidence that DC, besides their well-known immunostimulatory properties, also induce and regulate T-cell tolerance in the periphery. This regulatory function of DC is strictly dependent on their different stages of maturation and activation. Additionally, immunosuppressive agents and cytokines further influence the functions of maturing DC. The regulatory properties of DC include induction of T-cell anergy, apoptosis, and the generation of T-cells with regulatory capacities. This brief review summarizes the current knowledge about the immunoregulatory role of DC as guardians for the induction of T-cell immunity and tolerance.

A GM-CSF/CD40L Producing Cell Augments Anti-tumor T Cell Responses

BACKGROUND

Tumors evade T cell-mediated rejection despite the presence of tumor associated antigens (TAAs) and T cells specific for these TAAs in cancer patients. Therapeutic tumor vaccines are being developed to prevent this evasion. Previous reports revealed that anti-tumor T cell responses could be activated in mice when granulocyte macrophage-colony stimulating factor (GM-CSF) or CD40L are produced at tumor vaccine sites. We sought to test the hypothesis that production of GM-CSF and CD40L by a bystander cell line could induce an anti-tumor T cell response in an in vitro human model.

MATERIALS AND METHODS

The K562 cell line was stably transfected with the human GM-CSF and CD40L genes. The effect of this cell line on T cell responses was tested in a human autologous mixed tumor cell/lymph node cell model using tissue from a series of cancer patients.

RESULTS

There was no significant anti-tumor T cell response when human lymphocytes derived from tumor-draining lymph nodes were stimulated with autologous tumor cells in vitro. However, significant anti-tumor T cell responses were observed when bystander cells transfected with CD40L and GM-CSF were added to the cultures.

CONCLUSIONS

A fully autologous human model consisting of tumor cells as stimulator cells and tumor-draining lymph nodes as responder cells can be used to test immunotherapeutic strategies. T cells in these lymph nodes are unresponsive to autologous tumor cells, but this lack of responsiveness can be reversed in the presence of GM-CSF and CD40L. These data provide a rationale for testing tumor cell vaccines incorporating GM-CSF- and CD40L-expressing bystanders in clinical trials.

Engagement of human monocyte-derived dendritic cells into interleukin (IL)-12 producers by IL-1beta + interferon (IFN)-gamma

Dendritic cells (DCs) are potent antigen-presenting cells and can induce tumour- or pathogen-specific T cell responses. For adoptive immunotherapy purposes, immature DCs can be generated from adherent monocytes using granulocyte macrophage colony stimulating factor (GM-CSF) and interleukin (IL)-4, and further maturation is usually achieved by incubation with tumour necrosis factor (TNF)-alpha. However, TNF-alpha-stimulated DCs produce low levels of IL-12. In this study, we compared the effects of TNF-alpha, interferon (IFN)-gamma, IL-1beta or IFN-gamma + IL-1beta on the phenotypic and functional maturation of DCs. Our results show that IFN-gamma, but not IL-1beta, augmented the surface expression of CD80, CD83 and CD86 molecules without inducing IL-12 production from DCs. However, IL-1beta, but not IFN-gamma, induced IL-12 p40 production by DCs without enhancing phenotypic maturation. When combined, IFN-gamma + IL-1beta treatment profoundly up-regulated the expression of CD80, CD83, CD86 and major histocompatibility complex (MHC) class II antigens. Furthermore, IFN-gamma + IL-1beta-treated DCs produced larger amounts of IL-12 and induced stronger T cell proliferation and IFN-gamma secretion in primary allogeneic mixed lymphocyte reaction (MLR) than did TNF-alpha-treated DCs. Our results show that IFN-gamma + IL-1beta induced human monocyte-derived DCs to differentiate into Th1-prone mature DCs.

Highly efficient antigen targeting to M-DC8+ dendritic cells via FcgammaRIII/CD16-specific antibody conjugates

Conjugates of peptide antigens with antibodies specifically recognizing surface molecules on dendritic cells (DC) represent an attractive approach to target antigens to antigen-presenting cells (APC) for the induction of specific T cell responses. The present study evaluates the potential of M-DC8(+) DC, a sub-population of professional APC in the blood, for an antibody-based vaccination strategy. We prepared, by chemical cross-linking, conjugates of peptide model antigens with antibodies directed against different cell surface molecules of DC. Antigen-peptide conjugates using an anti-CD16 (FcgammaRIII) antibody were most potent in inducing in vitro activation of a specific CD4(+) T cell response. They were at least 300 times more efficient than two other antibody-antigen conjugates and approximately 500 times more efficient than unconjugated antigen peptides. Our data demonstrate that specific antigen targeting via CD16 on M-DC8(+) DC is a promising vaccination approach for the efficient induction of specific CD4(+) T cell responses ex vivo, and perhaps in vivo.

CD4+CD25+ T Regulatory Cells, Immunotherapy of Cancer, and Interleukin-2

CD4+CD25+ T regulatory (Treg) cells control immunologic tolerance to self-antigens and play a role in suppressing antitumor immune responses, but the mechanism of suppression in vivo remains uncertain. Recently, signaling through the high-affinity interleukin-2 (IL-2) receptor has been shown to be critical for Treg cell differentiation and survival in vivo. Mice deficient in IL-2 or its receptor (CD25 or CD122) or deficient in downstream signaling molecules, including JAK-3 and STAT-5, do not develop a stable population of Treg cells and subsequently acquire lymphoproliferative disease and autoimmunity. in vitro, IL-2 is required to expand Treg cells and to induce their suppressive characteristics. Conversely, IL-2-based regimens can activate cellular antitumor immunity and are the mainstay of immunotherapies directed against melanoma and kidney cancers. Given the seemingly disparate effects of IL-2, the authors discuss the possibility that IL-2 may not be the optimal T-cell growth factor in vivo, but rather an inducer of self-tolerance. The authors propose that other gamma c-signaling cytokines, including IL-15, may be alternative choices for the immunotherapy of cancer.

IL-6 produced by type I IFN DC controls IFN-gamma production by regulating the suppressive effect of CD4+ CD25+ regulatory T cells

The dendritic cell family is composed of different subsets differentially governing the immune response. Type I interferon (IFN) dendritic cells (DC) are endowed with the ability to trigger both Th1 and Th2 type responses. In view of the pivotal role of regulatory T cells in limiting the effectiveness of effector cells, we analyzed the interactions between these cells and type I IFN DC. DC were generated from monocytes in the presence of IFN-beta and interleukin (IL)-3 (DCI3) or granulocyte macrophage-colony-stimulating factor and IL-4 (DCG4) and activated by poly(I:C). Despite the release of lower amounts of IL-12 after maturation, DCI3 were able to induce a higher IFN-gamma production by T lymphocytes during the mixed leucocyte reaction (MLR) as compared with DCG4. mRNA analysis disclosed that DCI3 overtranscribed the IL-6 gene and secreted high amounts of the protein. Neutralization of IL-6 revealed that this cytokine specifically contributed to the IFN-gamma release induced by DCI3. Finally, depletion of CD25+ T cells before the MLR identified these cells as a target for IL-6. We conclude that DCI3 are endowed with the property of regulating the suppressive effect of regulatory T cells through high IL-6 production. This novel mechanism of T cell control is relevant for the use of DCI3 in vaccination strategies.

Novel monoclonal antibodies detect elevated levels of the chemokine CCL18/DC-CK1 in serum and body fluids in pathological conditions

CC chemokine ligand 18/dendritic cell-chemokine 1 (CCL18/DC-CK1) is a CC chemokine, preferentially expressed by DC, which acts as a chemoattractant for naive T cells and mantle zone B cells. Applying a newly developed CCL18/DC-CK1 sandwich enzyme-linked immunosorbent assay, we demonstrate that DC secrete high amounts of CCL18/DC-CK1 and that this expression can be increased by interleukin-10. High levels of CCL18/DC-CK1 were also detected in human serum (average of 88 ng/ml). Moreover, elevated CCL18/DC-CK1 levels were detected in synovial fluid from rheumatoid arthritis patients and in drain fluid (average of 254 ng/ml and 122 ng/ml, respectively). Immunoprecipitation experiment using anti-CCL18/DC-CK1 monoclonal antibodies revealed a protein of 6-7 kDa in serum and drain fluid that was indistinguishable from recombinant CCL18/DC-CK1 on Western blot and in re-aggregation assays. The concentration of CCL18/DC-CK1 found in human serum is in the same order of magnitude as was previously reported to completely inhibit CCL11/eotaxin-induced CC chemokine receptor 3 (CCR3) activation and consequent migration of eosinophils. CCL18/DC-CK1 may therefore function as an agonist (for naive T and B cells) and as an antagonist for CCR3-expressing leukocytes such as eosinophils.

CD4+CD25+ regulatory T cells that secrete TGFbeta and IL-10 are preferentially induced by a vaccine vector

CD4CD25 T cells generated in a vaccine scenario can play a critical role in limiting antitumor therapy, thus having widespread implications for the immunotherapy-based treatment of cancer. The authors previously used Listeria monocytogenes to develop two vaccine constructs that express HPV-16 E7 protein and induce strong cellular immunity to HPV-E7-expressing tumors. Immunization of mice bearing established E7-expressing tumors with Lm-LLO-E7 induced regression of the tumors, whereas Lm-E7 showed little or no tumor regression. To investigate the possibility that regulatory CD4CD25 T-cell populations may be responsible for the differences in tumor regression, the authors characterized the role of these cells generated by the two vaccine systems. The authors compared the prevalence of CD4CD25 T cells in tumor-bearing vaccinated mice and demonstrate that Lm-E7-vaccinated mice have significantly increased numbers of CD4CD25 T cells in both the spleen and tumor-infiltrating lymphocytes compared with Lm-LLO-E7-vaccinated mice. The authors confirm that these increased numbers of CD4CD25 T cells are indeed suppressor in function by in vitro suppression assays and that the mechanism of action of the tumor-infiltrating cells involves the production of suppressor cytokines interleukin-10 and transforming growth factor beta. These results show that it is possible for a tumor vaccine system to generate tumor-infiltrating CD4CD25 regulatory T cells that critically affect tumor regression and the overall success of vaccine therapy.

Antigen presentation by MART-1 adenovirus-transduced interleukin-10-polarized human monocyte-derived dendritic cells

Dendritic cells (DC) play critical roles in generating an immune response and in inducing tolerance. Diverse microenvironmental factors can 'polarize' DC toward an immunogenic or non-immunogenic phenotype. Among the various microenvironmental factors, interleukin-10 (IL-10) exhibits a potent immunosuppressive effect on antigen-presenting cells (APC). Here, we show that monocyte-derived DC generated in the presence of IL-10 exhibit a profound down-regulation of many genes that are associated with immune activation and show that the IL-10-grown DC are poor stimulators of CD8(+) T cells in a strictly autologous and major histocompatibility complex (MHC) class I-restricted melanoma antigen recognized by T cells (MART-1) epitope presentation system. However, these IL-10-grown DC can efficiently activate the epitope-specific CD8(+) T cells when they are made to present the epitope following transduction with an adenoviral vector expressing the MART-1 antigen. In addition, we show that the MART-1 protein colocalizes with the MHC class I protein, equally well, in the iDC and in the DC cultured in presence of IL-10 when both DC types are infected with the viral vector. We also show that the vector transduced DC present the MART-1(27-35) epitope for a sustained period compared to the peptide pulsed DC. These data suggest that although DCs generated in the presence of IL-10 tend to be non-immunogenic, they are capable of processing and presenting an antigen when the antigen is synthesized within the DC.

Metastatic melanoma secreted IL-10 down-regulates CD1 molecules on dendritic cells in metastatic tumor lesions

CD1 molecules are expressed by antigen-presenting cells such as dendritic cells and mediate primary immune responses to lipids and glycolipids which have been shown to be expressed by various tumors. Glycolipids are expressed by melanoma cells but, despite their immunogenicity, no efficient spontaneous immune responses are elicited. As IL-10 has previously been shown to down-regulate CD1a on dendritic cells and is known to be expressed by various melanoma cell lines, we investigated if melanoma-derived IL-10 could down-regulate CD1 molecule expression on dendritic cells as a possible way to circumvent immune recognition. We found that CD1a, CD1b, CD1c, and CD1d were significantly down-regulated on dendritic cells in metastatic (n = 10) but not in primary melanoma lesions (n = 10). We further detected significantly higher IL-10 protein levels in metastatic than in primary melanomas. Moreover, supernatants from metastatic melanomas were significantly more effective in down-regulating CD1 molecules on dendritic cells than supernatants from primary melanoma cultures. This effect was blocked using a neutralizing IL-10 antibody in a dose dependent manner. Our findings suggest that metastatic but not primary melanomas can down-regulate CD1 molecules on infiltrating dendritic cells by secreting IL-10 which may represent a novel way to escape the immune response directed against the tumor.

Immunosuppression in Renal Cancer: Differential Expression of Signal Transduction Molecules in Tumor-Infiltrating, Near-Tumor Tissue, and Peripheral Blood Lymphocytes

Alterations in the expression of signal activation molecules, such as the T-cell receptor (TCR) zeta and epsilon chains and p56lck tyrosine kinase, are described in tumor-infiltrating lymphocytes (TIL). The aim of this study was to ascertain if such molecules were present in near-tumor-tissue lymphocytes (NTTL) and peripheral blood lymphocytes (PBL), as well as TIL, of renal cell carcinoma patients, to verify whether this tumor induces immunosuppression only locally or affects distant lymphocytes as well. Tissue from the tumor and from healthy nearby sites, as well as blood samples, were obtained from 27 consecutive patients who had undergone radical nephrectomy for renal cell carcinoma. Phenotype analysis and immunohistochemical staining of the TCR zeta and epsilon chains and p56lck were performed with standard techniques on TIL, NTTL, and PBL, and values were compared for each patient. Low expression of the TCR zeta chain and an almost complete absence of TCR epsilon chain and p56lck expression was observed in TIL (median values: 10% for zeta chain and 0% for epsilon and p56lck). In NTTL, these signal transduction molecules were expressed by a higher percentage of cells (60%, 50%, and 60%, respectively; p=0.000 vs. TIL), whereas PBL showed an almost normal expression of zeta and epsilon chains (80% and 90%, respectively; p=0.000 vs. TIL). Conversely, p56lck was detected in a greater proportion of NTTL than PBL (50% vs. 10%; p=0.001). The absence or the very low expression of signaling activation molecules in TIL compared with NTTL and PBL in renal cancer patients suggest that tumor-induced immunosuppression generally occurs or starts locally.

Challenges facing adjuvants for cancer immunotherapy

An adjuvant is defined as a product that increases or modulates the immune response against an antigen (Ag). Based on this general definition many authors have postulated that the ideal adjuvant should increase the potency of the immune response, while being non-toxic and safe. Although dozens of different adjuvants have been shown to be effective in preclinical and clinical studies, only aluminium-based salts (Alum) and squalene-oil-water emulsion (MF59) have been approved for human use. However, for the development of therapeutic vaccines to treat cancer patients, the prerequisites for an ideal cancer adjuvant differ from conventional adjuvants for many reasons. First, the patients that will receive the vaccines are immuno-compromised because of, for example, impaired mechanisms of antigen presentation, non-responsiveness of activated T cells and enhanced inhibition of self-reactivity by regulatory T cells. Second, the tumour Ag are usually self-derived and are, therefore, poorly immunogenic. Third, tumours develop escape mechanisms to avoid the immune system, such as tumour editing, low or non-expression of MHC class I molecules or secretion of suppressive cytokines. Thus, adjuvants for cancer vaccines need to be more potent than for prophylactic vaccines and consequently may be more toxic and may even induce autoimmune reactions. In summary, the ideal cancer adjuvant should rescue and increase the immune response against tumours in immuno-compromised patients, with acceptable profiles of toxicity and safety. The present review discusses the role of cancer adjuvants at the different phases of the generation of antitumour immunity following vaccination.

Phosphatidylserine regulates the maturation of human dendritic cells

Phosphatidylserine (PS), which is exposed on the surface of apoptotic cells, has been implicated in immune regulation. However, the effects of PS on the maturation and function of dendritic cells (DCs), which play a central role in both immune activation and regulation, have not been described. Large unilamellar liposomes containing PS or phosphatidylcholine were used to model the plasma membrane phospholipid composition of apoptotic and live cells, respectively. PS liposomes inhibited the up-regulation of HLA-ABC, HLA-DR, CD80, CD86, CD40, and CD83, as well as the production of IL-12p70 by human DCs in response to LPS. PS did not affect DC viability directly but predisposed DCs to apoptosis in response to LPS. DCs exposed to PS had diminished capacity to stimulate allogeneic T cell proliferation and to activate IFN-gamma-producing CD4(+) T cells. Exogenous IL-12 restored IFN-gamma production by CD4(+) T cells. Furthermore, activated CTLs proliferated poorly to cognate Ag presented by DCs exposed to PS. Our findings suggest that PS exposure provides a sufficient signal to inhibit DC maturation and to modulate adaptive immune responses.

Shaping phenotype, function, and survival of dendritic cells by cytomegalovirus-encoded IL-10

Human dendritic cells (DCs) are essential for the antiviral immune response and represent a strategically important target for immune evasion of viruses, including human CMV (HCMV). Recently, HCMV has been discovered to encode a unique IL-10 homologue (cmvIL-10). In this study we investigated the capacity of cmvIL-10 to shape phenotype, function, and survival of DCs. For comparison we included human IL-10 and another IL-10 homologue encoded by EBV, which does not directly target DCs. Interestingly, cmvIL-10 strongly activated STAT3 in immature DCs despite its low sequence identity with human IL-10. For most molecules cmvIL-10 blocked LPS-induced surface up-regulation, confirming its role as an inhibitor of maturation. However, a small number of molecules on LPS-treated DCs including IDO, a proposed tolerogenic molecule, showed a different behavior and were up-regulated in response to cmvIL-10. Intriguingly, the expression of C-type lectin DC-specific ICAM-grabbing nonintegrin, a receptor for HCMV infection found exclusively on DCs, was also enhanced by cmvIL-10. This phenotypic change was mirrored by the efficiency of HCMV infection. Moreover, DCs stimulated with LPS and simultaneously treated with cmvIL-10 retained the function of immature DCs. Finally, cmvIL-10 increased apoptosis associated with DC maturation by blocking up-regulation of the antiapoptotic long form cellular FLIP. Taken together, these findings show potential mechanisms by which cmvIL-10 could assist HCMV to infect DCs and to impair DC function and survival.

Protective potential of experimental autoimmune myasthenia gravis in Lewis rats by IL-10-modified dendritic cells

Dendritic cells (DC) are usually regarded as antigen-presenting cells (APC) involved in T cell activation, but DC also directly or indirectly affect B cell function, antibody synthesis and isotype switch. In this study, we explore potential of DC-based immunotherapy in ongoing experimental autoimmune myasthenia gravis (EAMG) in Lewis rats, which is mediated by anti-acetylcholine receptor (AChR) antibodies. Spleen DC were isolated from onset of Lewis rat EAMG on day 39 post immunization (p.i.), exposed in vitro to IL-10 and then injected intraperitoneally into ongoing EAMG Lewis rats at dose of 1 x 10(6) cells/rat on day 5 p.i. with AChR + complete Freund's adjuvant. IL-10-modified DC resulted in lower clinical scores, less body weight loss, lower numbers of anti-AChR IgG antibody-secreting cells and lower affinity of anti-AChR antibodies in rats receiving IL-10-modified DC, accompanied with lower expression of CD80 and CD86 and lower lymphocyte proliferation among lymph node mononuclear cells compared with control EAMG rats. Lower levels of IL-10 and IFN-gamma were also found in the supernatants of AChR-stimulated lymph node MNC culture in rats receiving IL-10-modified DC. These results demonstrate that IL-10-modified DC induced hypo-responsiveness by down-regulating co-stimulatory molecules, and reduced production of anti-AChR antibodies possibly by inhibiting IL-10 production. Importantly, this procedure that autologous DC from EAMG were adopted to treat ongoing EAMG is more close to clinical trial in human, encouraging future evaluation in human myasthenia gravis.

Bacterial probiotic modulation of dendritic cells

Intestinal dendritic cells are continually exposed to ingested microorganisms and high concentrations of endogenous bacterial flora. These cells can be activated by infectious agents and other stimuli to induce T-cell responses and to produce chemokines which recruit other cells to the local environment. Bacterial probiotics are of increasing use against intestinal disorders such as inflammatory bowel disease. They act as nonpathogenic stimuli within the gut to regain immunologic quiescence. This study was designed to determine the ability of a bacterial probiotic cocktail VSL#3 to alter cell surface antigen expression and cytokine production in bone marrow-derived dendritic cell-enriched populations. Cell surface phenotype was monitored by monoclonal fluorescent antibody staining, and cytokine levels were quantitated by enzyme-linked immunosorbent assay. High-dose probiotic upregulated the expression of C80, CD86, CD40, and major histocompatibility complex class II I-Ad. Neither B7-DC or B7RP-1 was augmented after low-dose probiotic or Lactobacillus casei treatment, but B7RP-1 showed increased expression on dendritic cells stimulated with the gram-negative bacterium Escherichia coli. Functional studies showed that probiotic did not enhance the ability of dendritic cells to induce allogeneic T-cell proliferation, as was observed for E. coli. Substantial enhancement of interleukin-10 release was observed in dendritic cell-enriched culture supernatants after 3 days of probiotic stimulation. These results demonstrate that probiotics possess the ability to modulate dendritic cell surface phenotype and cytokine release in granulocyte-macrophage colony-stimulating factor-stimulated bone marrow-derived dendritic cells. Regulation of dendritic cell cytokines by probiotics may contribute to the benefit of these molecules in treatment of intestinal diseases.

The role of interleukin 10 in the pathogenesis and potential treatment of skin diseases

Interleukin 10 (IL-10) is a key cytokine produced by a multitude of immune effector cells and possesses distinct regulatory effects on immune functioning in the skin. In this article we report the current understanding of the immunobiology of IL-10 and identify the role of IL-10 in cutaneous infection as well as in autoimmune and neoplastic processes. We reviewed the literature to examine the function of IL-10 in different cutaneous disorders. IL-10 can influence and potentially treat T1/T2 differentiation, antigen-presenting cell functioning, antigen-presenting cell-mediated T-cell activation, and T-cell, B-cell, and mast cell growth and differentiation that is aberrant in various disease processes. The literature consensus is that the multitude of effects of IL-10 contribute to the pathogenesis of different skin disorders. In certain circumstances IL-10 could represent novel therapeutic approaches to treating cutaneous diseases.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be acquainted with the role of IL-10 in many infectious diseases, autoimmune skin disease, inflammatory processes, and malignancy. Its possible role in the resolution of various skin diseases should be better understood.

Increased interleukin-10 mRNA stability in melanoma cells is associated with decreased levels of A + U-rich element binding factor AUF1

Abnormal production of interleukin-10 (IL-10) is observed in some pathologic conditions. For example, compared with normal melanocytes, IL-10 expression is elevated in melanoma cells. IL-10 overexpression could inhibit both immune surveillance and tumor rejection. We investigated a potential posttranscriptional mechanism for IL-10 overexpression in melanoma cells. In normal melanocytes, the half-life of IL-10 mRNA is 7 min, whereas in the melanoma cell line MNT1, the half-life is 75 min. This 10-fold difference could account, at least in part, for IL-10 overexpression in MNT1 cells. Examination of the 3'-untranslated region (3'-UTR) of IL-10 mRNA revealed a suspected A + U-rich element (ARE) that might target the mRNA for rapid degradation. Transfection experiments confirmed that these sequences promote rapid degradation when inserted into a normally stable mRNA, indicating ARE functionality. As AREs act via their interactions with ARE-binding proteins, we examined cytoplasmic proteins from normal melanocytes and MNT1 cells for IL-10 ARE-binding activity. Compared with cytoplasmic extracts of normal melanocytes, cytoplasmic extracts of MNT1 cells possess substantially less ARE-binding activity, consistent with the extended half-life of IL-10 mRNA in MNT1 cells. Finally, we find that the ARE-binding protein AUF1 comprises the major ARE-binding activity in cytoplasmic extracts of normal melanocytes. By contrast, AUF1 is not detectable in cytoplasmic extracts of MNT1 cells but appears restricted to the nuclear fraction. Together, these data suggest a mechanism whereby reduced cytoplasmic levels of AUF1 in MNT1 melanoma cells may lead to IL-10 overexpression, with deleterious consequences for tumor surveillance and rejection.

Results of a phase I clinical study using autologous tumour lysate-pulsed monocyte-derived mature dendritic cell vaccinations for stage IV malignant melanoma patients combined with low dose interleukin-2

We conducted a pilot study to assess the feasibility and efficacy of immunotherapy for stage IV malignant melanoma patients resistant to conventional therapies involving vaccination with mature dendritic cells (mDCs) combined with administration of low dose interleukin-2. Autologous monocytes were harvested from a single apheresis and cultured for 7 days with granulocyte-macrophage colony-stimulating factor and interleukin-4, yielding immature dendritic cells (iDCs), which were then cryopreserved until use. For 4 days prior to vaccination, iDCs were exposed to autologous tumour lysate combined with tumour necrosis factor-alpha to induce terminal differentiation into mDCs. Patients were then vaccinated weekly with 107 mDCs for 10 weeks and given 350-700 kIU of interleukin-2 three times per week. Of the 10 patients in the study, one showed stable disease, seven showed progressive disease, and two showed mixed responses, including partial tumour regression, and were therefore given 20 additional injections. Only minimal adverse events were noted, including localized skin reactions and mild fever (NIH-CTC grade 0-1). Median survival from the first vaccination was 240 days (range 31-735 days). In vitro, melanoma patient-derived dendritic cells (DCs) showed reduced cell surface expression of CD1a antigen on iDCs and reduced CD86 and HLA-DR expression on mDCs. In addition, antigen uptake, chemotaxis and antigen presentation were all attenuated in DCs from the patients. In summary, although improvement of clinical efficacy will require further research, autologous tumour lysate-pulsed monocyte-derived mDCs could be safely harvested, cryopreserved and administrated to patients without obvious complications.

Adenovirus CD40 Ligand Gene Therapy Counteracts Immune Escape Mechanisms in the Tumor Microenvironment

Tumors exhibit immune escape properties that promote their survival. These properties include modulation of Ag presentation, secretion of immunosuppressive factors, resistance to apoptosis, and induction of immune deviation, e.g., shifting from Th1- to Th2-type responses. These escape mechanisms have proven to hamper several immunotherapeutic strategies, and efforts need to be taken to revert this situation. We have studied the immunological effects of introducing CD40 ligand (CD40L), a potent dendritic cell activation molecule, into the tumor micromilieu by adenoviral gene transfer. For this purpose, a murine bladder cancer model (MB49) was used in C57BL/6 mice. The MB49 cells are known to induce IL-10 in the tumor environment. IL-10 potently inhibits the maturation of dendritic cells and thereby also the activation of CTLs. In this paper we show that CD40L immunogene therapy suppresses IL-10 and TGF-beta production (2-fold decrease) and induces a typical Th1-type response in the tumor area (200-fold increase in IL-12 production). The antitumor responses obtained were MB49 cell specific, and the cytotoxicity of the stimulated CD8(+) cells could be blocked by IL-10. Adenovirus CD40L therapy was capable of regressing small tumors (five of six animals were tumor free) and inhibiting the progression of larger tumors even in the presence of other escape mechanisms, such as apoptosis resistance. Furthermore, CD40L-transduced MB49 cells promoted the maturation of dendritic cells (2-fold increase in IL-12) independently of IL-10. Our results argue for using adenovirus CD40L gene transfer, alone or in combination with other modalities, for the treatment of Th2-dominated tumors.

Induction of T cell anergy by the treatment with IL-10-treated dendritic cells

In order to apply for reducing graft versus host disease in allogeneic stem cell transplantation, the study concerning the induction of specific T cell anergy was designed. Normal allogeneic lymphocytes, which were co-cultured with IL-10-treated immature dendritic cells in the first mixed leukocyte culture (MLC), were cultured with mature dendritic cells of the same origin as IL-10-treated immature dendritic cells in the second MLC. By co-culturing with IL-10-treated immature dendritic cells, the response of normal lymphocytes to mature dendritic cells cultured from the same individual as that of IL-10-treated dendritic cells was markedly reduced, compared with the lymphocytes cultured with non-treated dendritic cells or IL-10-treated dendritic cells from a third party individual. The present study demonstrated that antigen specific T cell anergy was generated by priming allogeneic lymphocytes with IL-10-treated immature dendritic cells. These data suggested the applicability of IL-10-treated recipient dendritic cells for the induction of recipient cell-specific donor T cell anergy in donor graft.

Advances in the use of dendritic cells and new adjuvants for the development of therapeutic vaccines

The recent advances in immunology and biotechnology have opened new perspectives for the development of immunotherapy strategies against cancer and infectious diseases. The understanding of the pivotal role of dendritic cells in the initiation and regulation of the immune response has led to an ensemble of preclinical studies and pilot clinical trials, which have provided some evidence on the potential advantages of using dendritic cells as cellular adjuvants for the development of therapeutic vaccines against infectious diseases and malignancies. Current research efforts are focused on the definition of optimal protocols for dendritic cell-based therapies in patients. An additional area of emerging importance in the field of immunotherapy is the identification of safe, selective, and more powerful adjuvants, capable not only of enhancing immune protection against pathogens, but also of breaking tolerance against certain tumor-associated antigens, which is the critical issue for the development of cancer vaccines. The recent recognition of the key role of certain cytokines, such as type I interferons, in linking the innate and adaptive immunity through their action on dendritic cells opens new perspectives for using these natural factors as adjuvants for the development of therapeutic vaccines. We review some of the emerging research aspects in immunotherapy, with special attention to the perspectives of using new adjuvants and dendritic cell-based vaccines for the treatment of cancer and infectious diseases.

Induction of tolerogenic DCs: 'you are what you eat'

Dendritic cells (DCs) take up antigens using antigen receptors that can be divided into three major classes: C-type lectins, integrins and Fc receptors. These receptors facilitate effective presentation of MHC-peptide complexes to T cells, resulting in the induction of immune responses. However, we discuss recent evidence that some receptors also cause induction of tolerance. Signaling motifs within the receptors either block maturation of DCs or induce signals that render DCs tolerogenic. These DCs then either induce regulatory T cells or cause deletion of effector T cells, resulting in the induction of tolerance. Antigen receptors expressed by DCs might therefore have an important role in the induction and maintenance of peripheral tolerance.

IL-10-Conditioned Dendritic Cells, Decommissioned for Recruitment of Adaptive Immunity, Elicit Innate Inflammatory Gene Products in Response to Danger Signals

Dendritic cells (DCs) are the professional APCs of the immune system, enabling T cells to perceive and respond appropriately to potentially dangerous microbes, while also being able to maintain T cell tolerance toward self. In part, such tolerance can be determined by IL-10 released from certain types of regulatory T cells. IL-10 has previously been shown to render DCs unable to activate T cells and it has been assumed that this process represents a general block in maturation. Using serial analysis of gene expression, we show that IL-10 pretreatment of murine bone marrow-derived DCs alone causes significant changes in gene expression. Furthermore, these cells retain the ability to respond to Toll-like receptor agonists, but in a manner skewed toward the selective induction of mediators known to enhance local inflammation and innate immunity, among which we highlight a novel CXCR2 ligand, DC inflammatory protein-1. These data suggest that, while the presence of a protolerogenic and purportedly anti-inflammatory agent such as IL-10 precludes DCs from acquiring their potential as initiators of adaptive immunity, their ability to act as initiators of innate immunity in response to Toll-like receptor signaling is enhanced.

The multifaceted relationship between IL-10 and adaptive immunity: putting together the pieces of a puzzle

Interleukin-10 (IL-10) is a pleiotropic cytokine that modulates the function of several adaptive immunity-related cells. Although generally considered an immunosuppressive molecule, IL-10 possesses immunostimulatory properties in several in vitro and in vivo models. These very different outcomes are believed to depend upon experimental conditions, the dominant immune effector mediating a given immune response, the timing of IL-10 production/administration, and IL-10 dose and/or location of expression. In the present work, we review the current knowledge regarding IL-10 activity on adaptive immunity related cells, emphasize new insights on IL-10 molecular/cellular targets, and summarize the available data on the relationship between IL-10 and some pathological conditions (e.g. infectious diseases, autoimmunity, allergy, cancer and transplantation) involving adaptive immunity.

Paradoxical effects of interleukin-10 on the maturation of murine myeloid dendritic cells

The immunoregulatory cytokine, interleukin-10 (IL-10), has been shown to inhibit the maturation of human myeloid dendritic cells (DC). In the present study, we demonstrate that IL-10 has paradoxical effects on the maturation of murine myeloid bone marrow-derived DC. On the one hand, IL-10 inhibits the maturation of murine myeloid DC. The addition of IL-10 to granulocyte-macrophage colony-stimulating factor (GM-CSF)-supported murine BM-derived DC cultures reduced the frequency of major histocompatibility complex (MHC) class IIbright cells. These IL-10-pretreated DC have a reduced capacity to stimulate T cells in an allogeneic mixed leucocyte reaction. On the other hand, however, and in contrast to the effects of IL-10 on human DC, we found that the addition of IL-10 from the initiation of the culture onwards induced an up-regulation of the expression of the costimulatory molecules CD40, CD80 and CD86 on murine myeloid DC, as compared to DC generated with GM-CSF only. Moreover, a subpopulation of IL-10-pretreated MHC class IIdim DC lacked the capacity to take up dextran-fluorescein isothiocyanate (FITC), a feature of DC maturation. Taken together, our data demonstrate that the generation of murine myeloid DC in the presence of IL-10 results in a population of incompletely matured MHC class IIdim CD80+ CD86+ DC. These DC lack T-cell stimulatory capacity, suggesting a role for IL-10 in conferring tolerogenic properties on murine myeloid DC.

Imatinib mesylate affects the development and function of dendritic cells generated from CD34+ peripheral blood progenitor cells

Imatinib mesylate (STI571) is a competitive Bcr-Abl tyrosine kinase inhibitor and has yielded encouraging results in treatment of chronic myelogenous leukemia (CML) and gastrointestinal stroma tumors (GISTs). Apart from inhibition of the Abl protein tyrosine kinases, it also shows activity against platelet-derived growth factor receptor (PDGF-R), c-Kit, Abl-related gene (ARG), and their fusion proteins while sparing other kinases. In vitro studies have revealed that imatinib mesylate can inhibit growth of cell lines and primitive malignant progenitor cells in CML expressing Bcr-Abl. However, little is known about the effects of imatinib mesylate on nonmalignant hematopoietic cells. In the current study we demonstrate that in vitro exposure of mobilized human CD34+ progenitors to therapeutic concentrations of imatinib mesylate (1-5 microM) inhibits their differentiation into dendritic cells (DCs). DCs obtained after 10 to 16 days of culture in the presence of imatinib mesylate showed concentration-dependent reduced expression levels of CD1a and costimulatory molecules such as CD80 and CD40. Furthermore, exposure to imatinib mesylate inhibited the induction of primary cytotoxic T-lymphocyte (CTL) responses. The inhibitory effects of imatinib mesylate were accompanied by down-regulation of nuclear localized RelB protein. Our results demonstrate that imatinib mesylate can act on normal hematopoietic cells and inhibits the differentiation and function of DCs, which is in part mediated via the nuclear factor kappaB signal transduction pathway.

Treatment of patients with progressive unresectable metastatic melanoma with a heterologous polyvalent melanoma whole cell vaccine

Unresectable metastatic melanoma has no elective treatment. Neither chemotherapy, intravenous IL-2 nor biochemotherapy clearly improves the overall survival. Recent assays with therapeutic vaccines have been recently yielded promising results. Here, we describe the application, clinical tolerance and antitumoural activity of a heterologous polyvalent melanoma whole cell vaccine in patients with metastatic melanoma. Twenty-eight AJCC stage III/IV melanoma patients with progressive unresectable metastatic disease were treated with our heterologous polyvalent melanoma whole cell vaccine between July 1, 1998 and July 1, 2002. All patients had already been unsuccessfully treated with high doses of IFN-alpha2 and/or polychemotherapy and/or biochemotherapy and/or perfusion of extremities, or could not receive other treatments due to their age or underlying illness. Twenty-three were assessable. The vaccine was constituted by 10 melanoma cell lines, derived from primary, lymph node and metastatic melanomas. Prior to intradermal inoculation, the cells were irradiated and mixed with BCG, and 50% were treated with DNFB. After a median follow-up of 19 months, 26% of patients responded: 3 CR (18, 16+, and 26+ months), 2 PR (8 and 22 months) and 1 MR (36+ months). The median survival of the whole group was 20.2 months. None of the 28 patients initially included in the study presented significant toxicity. This vaccination program had specific antitumoural activity in advanced metastatic melanoma patients and was well tolerated. The clinical responses and the median survival of our group of patients, together with the low toxicity of our polyvalent vaccine, suggest that this approach could be applied to earlier metastatic melanoma patients.

A pilot trial of tumor lysate-loaded dendritic cells for the treatment of metastatic renal cell carcinoma

Cultured tumor lysate-loaded dendritic cells (TuLy-DC) have been demonstrated in vitro to stimulate potent immune modulations and generate significant antitumor response. We report the results of a pilot trial of TuLy-DC vaccine for patients with metastatic renal cell carcinoma (mRCC). Fourteen mRCC patients underwent nephrectomy to obtain autologous TuLy prepared by subjecting tumor cells to 3 freeze/thaw cycles. Dendritic cells were generated from peripheral blood CD14+ precursors cultured in the presence of GM-CSF, IL-4, and 10% autologous serum. Patients received one vaccination of TuLy alone as an immunologic control, followed by 3 weekly vaccinations of DC-TuLy injected intradermally in the midaxillary region. Peripheral blood lymphocytes were collected before and after weekly vaccines and were assessed for changes in phenotype, cytotoxicity, and cytokine profile. The TuLy-DC vaccine was successfully prepared and administered to 12 patients, whereas 2 patients did not receive vaccine treatment due to declines in postoperative performance status. The vaccines were well tolerated, with only grade 1 toxicities noted. One patient had a partial response to treatment that did not correspond to any significant change in immunologic profile. This pilot trial demonstrated both the safety and feasibility of reliably preparing a DC-based vaccine for mRCC patients. Our data suggest that autologous TuLy-DC vaccines generate only limited clinical response. Further clinical studies are needed to identify the most potent treatment regimen that can consistently mediate an antitumor immune response in vivo.

T cell anergy

T cell anergy is a tolerance mechanism in which the lymphocyte is intrinsically functionally inactivated following an antigen encounter, but remains alive for an extended period of time in a hyporesponsive state. Models of T cell anergy affecting both CD4(+) and CD8(+) cells fall into two broad categories. One, clonal anergy, is principally a growth arrest state, whereas the other, adaptive tolerance or in vivo anergy, represents a more generalized inhibition of proliferation and effector functions. The former arises from incomplete T cell activation, is mostly observed in previously activated T cells, is maintained by a block in the Ras/MAP kinase pathway, can be reversed by IL-2 or anti-OX40 signaling, and usually does not result in the inhibition of effector functions. The latter is most often initiated in naïve T cells in vivo by stimulation in an environment deficient in costimulation or high in coinhibition. Adaptive tolerance can be induced in the thymus or in the periphery. The cells proliferate and differentiate to varying degrees and then downregulate both functions in the face of persistent antigen. The state involves an early block in tyrosine kinase activation, which predominantly inhibits calcium mobilization, and an independent mechanism that blocks signaling through the IL-2 receptor. Adaptive tolerance reverses in the absence of antigen. Aspects of both of the anergic states are found in regulatory T cells, possibly preventing them from dominating initial immune responses to foreign antigens and shutting down such responses prematurely.

Urinary IL-2 assay for monitoring intravesical bacillus Calmette-Guérin response of superficial bladder cancer during induction course and maintenance therapy

We evaluated the clinical significance of Th1(IL-2)/Th2(IL-10) urinary profiles during a weekly induction course lasting 6 weeks, followed by a weekly maintenance therapy schedule for 3 weeks. Urinary IL-2 and /IL-10 were measured by ELISA in 39 patients receiving BCG for superficial bladder cancer or carcinoma in situ. Measurements were made after each instillation of 81 mg of BCG Connaught (Immucyst) during the induction course and the 3-week maintenance therapy (given at 3, 6, 12, 18, 24, 30 and 36 months). Cytokine levels were correlated with the risk of recurrence, progression, leukocyturia and adverse events. Median follow-up was 35 months (range 7-72 months). Complete responses to BCG were obtained in 30 patients (77%); the remaining 9 patients relapsed (23%), and 4 of these patients progressed (10.2%). Failure to detect urinary IL-2 during BCG induction course and the first extended induction cycle (6+3 schedule) correlated with time to recurrence (p = 0.01) and progression (p = 0.01). During the extended induction cycle, the first instillation was associated with an IL-2 cytokine profile, whereas the second and third instillations were associated with a switch to an IL-10 cytokine profile. This switch was associated with leukocyturia (p = 0.0001) and adverse events (p = 0.03). The 6+3 schedule is associated with urinary IL-2 overproduction and improved recurrence- and progression-free survival. During the BCG extended induction cycle, the favorable IL-2 urinary cytokine pattern gradually switches to an IL-10 profile, suggesting that the schedule based on 3 weekly instillations may be unsuitable for some patients and that the dose and frequency of maintenance BCG instillations may be adapted to individual urinary cytokine levels.

Dendritic cells, engineered to secrete a T-cell receptor mimic peptide, induce antigen-specific immunosuppression in vivo

A T-cell receptor mimic peptide (TCRpep) consisting of an 8-amino-acid peptide, homologous to the transmembrane region of the T-cell receptor (TCR) alpha chain, blocks T-cell activation after systemic application. When dendritic cells (DCs) were transduced to secrete the TCRpep and injected into mice, evidence of immunosuppression was observed. In a CD8-driven allergy model, the injection of DCs transduced with the TCRpep reduced inflammation markedly and in a CD4+ T cell-dependent model of multiple sclerosis (experimental autoimmune encephalitis, EAE), injection of TCRpep-secreting DCs abrogated EAE symptoms and prolonged survival. These effects were antigen specific, because transduced DCs that did not express the respective antigen failed to convey protection in the allergy model as well as in the EAE model. Thus these data show that DCs expressing the TCRpep are able to suppress T-cell activation and might be a useful tool for inducing antigen-specific immune suppression in vivo.

Interplay between human papillomaviruses and dendritic cells

The design of the human papillomavirus (HPV) infection cycle is tightly fitted to the differentiation program of its natural host, the keratinocyte. This has important consequences for the role of antigen-presenting cells in the priming of antiviral immunity. The confinement of HPV infection to epithelia puts the epithelial dendritic cell, the Langerhans cell (LC), in charge of the induction of T cell-dependent immunity. Because HPV-infected keratinocytes cannot reach the regional lymphoid organs, and HPV-infection of LCs does not result in viral gene expression, priming of antiviral T cells exclusively depends on cross-presentation of viral antigens by the LC. Sensitization of the immune system in the regional lymphoid organs elicits systemic anti-HPV immunity as well as intraepithelial immune surveillance by memory-type intraepithelial T cells and locally produced antibodies. The high rate of spontaneous rejections of high-risk HPV-infections and HPV-positive premalignant lesions indicates that in general the LC-driven antigen presentation machinery is capable of raising an effective immune defense against HPV. Epidemiological studies also reveal that a decrease in the vigilance of the immune system is readily exploited by HPV to escape immune destruction, resulting in persistent infections and development of HPV-positive cancers. In view of the inherent antigenicity of HPV, immune intervention strategies constitute a promising approach for both the prevention and the therapeutic treatment of HPV-induced diseases. Importantly, the mechanisms that govern the induction and effector phases of the intraepithelial immune surveillance against HPV must be taken into account when designing such strategies.

Immune regulation by regulatory T cells: implications for transplantation

The induction of antigen-specific T cell tolerance and its maintenance in the periphery are critical for the immune system to prevent autoaggressive immune responses. Our current state of knowledge about the immunoregulatory mechanisms responsible for T cell tolerance in the periphery offers new possibilities for immunomodulation to prevent transplant rejection as well as to diminish autoimmune reaction or chronic allergy. There is growing evidence that dendritic cells, besides their well-known T cell stimulatory functions, also maintain and regulate T cell tolerance in the periphery. This control function is exerted by certain maturation stages and subsets of dendritic cells, and can be further influenced and modulated by immunoregulatory cytokines and drugs. The regulatory functions of dendritic cells include the induction of T cell anergy, of T cells with regulatory properties and of T cells that produce immunosuppressive cytokines such as IL-10 or TGF-beta. Additionally, distinct subsets of resident regulatory T cells generated in the thymus play a central role in maintenance of peripheral tolerance by active suppression of effector T cell populations. These CD4(+)CD25(+) regulatory T cells inhibit a variety of autoimmune and inflammatory diseases and they are also efficient in the suppression of alloantigen responses. This review summarises the current knowledge regarding the immunoregulatory role of dendritic cells and the functional activities of resident regulatory T cells as guardians for peripheral T cell tolerance.

Dendritic cells in peripheral tolerance and immunity

Dendritic cells capable of influencing immunity exist as functionally distinct subsets, T cell-tolerizing and T cell-immunizing subsets. The present paper reviews how these subsets of DCs develop, differentiate and function in vivo and in vitro at the cellular and molecular level. In particular, the role of DCs in the generation of regulatory T cells is highlighted.

Pathogens target DC-SIGN to influence their fate DC-SIGN functions as a pathogen receptor with broad specificity

Dendritic cells (DC) are vital in the defense against pathogens. To sense pathogens DC express pathogen recognition receptors such as toll-like receptors (TLR) and C-type lectins that recognize different fragments of pathogens, and subsequently activate or present pathogen fragments to T cells. It is now becoming evident that some pathogens subvert DC functions to escape immune surveillance. HIV-1 targets the DC-specific C-type lectin DC-SIGN to hijack DC for viral dissemination. HIV-1 binding to DC-SIGN protects HIV-1 from antigen processing and facilitates its transport to lymphoid tissues, where DC-SIGN promotes HIV-1 infection of T cells. Recent studies demonstrate that DC-SIGN is a more universal pathogen receptor that also recognizes Ebola, cytomegalovirus and mycobacteria. Mycobacterium tuberculosis targets DC-SIGN by a mechanism that is distinct from that of HIV-1, leading to inhibition of the immunostimulatory function of DC and pathogen survival. Thus, a better understanding of DC-SIGN-pathogen interactions and their effects on DC function is necessary to combat infections.

Generation and function of antigen-specific suppressor and regulatory T cells

The identification and characterization of regulatory and suppressor T cells that control immune responsiveness to self and non-self antigens has become the focus of innumerable studies. There are two broad categories of naturally occurring and induced CD4(+)CD25(+) regulatory T cells. Naturally occurring T(R) are antigen non-specific and interact directly with other T cells inhibiting their activation. Induced T(R) are either CD4(+)CD25(+) or CD8(+), produce immunosuppressive cytokines such as IL-10, act directly on other T cells or APC and are antigen specific in some but not in all systems. Finally, a distinct subset of T suppressor cells, characterized by their CD8(+)CD28(-) phenotype have been shown to be antigen-specific, recognizing HLA class I/peptide complexes. T(S) act directly on APC inducing the up-regulation of inhibitory receptors ILT3 and ILT4, which render the APC tolerogenic. Tolerized APC, which expresses high ILT3 and ILT4, trigger the generation of antigen-specific CD4(+) T(R) propagating antigen-specific suppression. Up-regulation of ILT3 and ILT4 appears to be a general characteristic of tolerogenic DC since it is also induced by use of vit D3, IL-10 and/or IFN-alpha. The clinical relevance of these inhibitory receptors is in the maintenance of transplantation tolerance as well as in progression of AIDS has been demonstrated.