Tumors promote altered maturation and early apoptosis of monocyte-derived dendritic cells

Restoration by IL-15 of MHC class I antigen-processing machinery in human dendritic cells inhibited by tumor-derived gangliosides

We have recently reported that MHC class I Ag-processing machinery (APM) component expression in dendritic cells (DC) might be down-regulated by tumor cells. However, the tumor-derived factors responsible for inhibition of the APM component expression in DC generated in the tumor microenvironment as well as potential protective mechanism have not yet been investigated. In this article, we demonstrate that expression of several MHC class I APM components, including MB1 (beta5), LMP2, LMP7, LMP10, and ERp57, is significantly down-regulated in human DC generated in the presence of primary oral squamous cell carcinoma cell lines or coincubated with purified gangliosides. Suppression of MHC class I APM component expression in DC generated in the presence of tumor cells was significantly attenuated by the inhibition of glucosyl transferase in tumor cells, suggesting that tumor-induced MHC class I APM component down-regulation in DC was mediated in part by oral squamous cell carcinoma-derived gangliosides. Furthermore, rIL-15 restored both tumor cell-induced and ganglioside-induced MHC class I APM component expression in DC, as well as their ability to present Ags to autologous Ag-specific T cells. These results demonstrate that IL-15 restores MHC class I APM component expression in DC down-regulated by tumor-derived gangliosides.

Tumorangiogenese und Immunsuppression

BACKGROUND

Angiogenesis and tumor-associated immunosuppression are two of the hallmarks of carcinogenesis. In previous studies we demonstrated in vitro that HNSCC tumor cells attract monocytes via monocyte chemotactic protein-1 (MCP-1) and activate them via transforming growth factor-beta 1(TGF-beta1) to secrete interleukin (IL)-1alpha, which in turn stimulates tumor cells to secrete increased levels of the angiogenic and immunosuppressive vascular endothelial growth factor (VEGF). These findings suggest that interaction between the immune system and VEGF-mediated angiogenesis is important for progression of HNSCC. Recent studies in vitro show that retinoic acid (RA) downregulates the release of MCP-1 and TGF-beta1 by tumor cells. Therefore, we investigated the ability of RA to modulate the ability of tumor cells to recruit and activate monocytes for participation in VEGF-mediated angiogenesis and immunosuppression in vivo.

MATERIAL AND METHODS

Mice (ten/group) were injected daily with RA (160 microg/kg) for 3 weeks. After that time mice were sacrificed, and paraffin sections of tumors were obtained and stained for VEGF-A, CD68, and PECAM (CD31) by immunohistochemistry. The lungs, liver, and myocardium were analyzed for macro- and micrometastases. The plasma protein levels of VEGF-A and MCP-1 were determined by ELISA.

RESULTS

In RA-treated mice tumors regressed completely and RA prevented metastases (p=0.00) and macrophage infiltration (p=0.007). Treated mice downregulated VEGF-A (0 pg/ml) and MCP-1 (12 pg/ml) in peripheral blood (p=0.001).

CONCLUSION

Our findings suggest a new therapeutic possibility: the development of treatment protocols that can block each of the ways in which tumors induce new blood vessel growth and immunosuppression of the host.

Tumor cyclooxygenase-2/prostaglandin E2-dependent promotion of FOXP3 expression and CD4+ CD25+ T regulatory cell activities in lung cancer

Cyclooxygenase (COX)-2 and its product prostaglandin (PG) E2 underlie an immunosuppressive network that is important in the pathogenesis of non-small cell lung cancer. CD4+ CD25+ T regulatory (Treg) cells play an important role in maintenance of immunologic self-tolerance. CD4+ CD25+ Treg cell activities increase in lung cancer and appear to play a role in suppressing antitumor immune responses. Definition of the pathways controlling Treg cell activities will enhance our understanding of limitation of the host antitumor immune responses. Tumor-derived COX-2/PGE2 induced expression of the Treg cell-specific transcription factor, Foxp3, and increased Treg cell activity. Assessment of E-prostanoid (EP) receptor requirements revealed that PGE2-mediated induction of Treg cell Foxp3 gene expression was significantly reduced in the absence of the EP4 receptor and ablated in the absence of the EP2 receptor expression. In vivo, COX-2 inhibition reduced Treg cell frequency and activity, attenuated Foxp3 expression in tumor-infiltrating lymphocytes, and decreased tumor burden. Transfer of Treg cells or administration of PGE2 to mice receiving COX-2 inhibitors reversed these effects. We conclude that inhibition of COX-2/PGE2 suppresses Treg cell activity and enhances antitumor responses.

Dendritic cells and vascular endothelial growth factor in colorectal cancer: correlations with clinicobiological findings

OBJECTIVE

Dendritic cells (DC) are central to the development of immune system responses. In a cohort of 54 patients affected by colorectal cancer, we prospectively investigated the number of peripheral blood (PB) DC type 1 (DC1) and type 2 (DC2) and correlated their counts and functionality to the stage of the disease and to vascular endothelial growth factor (VEGF) levels.

RESULTS

At diagnosis, compared with healthy controls, patients presented reduced PBDC1 and PBDC2 numbers (p < 0.001). Moreover, in cancer patients, PBDC showed low levels of DC-associated antigens (HLA DR, p = 0.004; CD11c, p < 0.001; CD83, p = 0.01; CD86, p = 0.007 and Mannose receptor, p = 0.029), an upregulation of CXCR4 (p = 0.017) and a reduced T cell stimulation capability (p < 0.001). DC1 and DC2 loss was higher in stage D versus stage ABC patients (p = 0.003 and p = 0.002, respectively); surgery and chemotherapy appeared to attenuate a DC defect, although the restoration of normal PBDC levels is completed only at 6 and 12 months after diagnosis, respectively. In this series of patients, PBDC1 and PBDC2 numbers inversely correlated with VEGF serum levels (p < 0.001), suggesting a possible effect of this cytokine on DC compartment. In culture, the exposure of monocyte-derived DC to VEGF produced a dramatic alteration of DC differentiation by (1) induction of apoptosis, (2) alteration of DC immunophenotypic profile and (3) increased CXCR4 expression. Exposure to anti-VEGF blocking antibodies reversed VEGF inhibitory effects in all cases.

CONCLUSIONS

These findings suggest that in colorectal cancer patients there is a numerical and functional impairment of PBDC compartment possibly related to the stage of the disease and to VEGF levels.

Treatment of transplanted CT26 tumour with dendritic cell vaccine in combination with blockade of vascular endothelial growth factor receptor 2 and CTLA-4

We investigated the anti CT26 tumour effect of dendritic cell based vaccination with the MuLV gp70 envelope protein-derived peptides AH1 and p320-333. Vaccination lead to generation of AH1 specific cytotoxic lymphocytes (CTL) and some decrease in tumour growth of simultaneously inoculated CT26 cells. After combination with an antibody against VEGF receptor 2 (DC101), a significant increase in survival of the tumour cell recipients was observed. Also, monotherapy with an antibody against CTLA-4 (9H10), led to approximately 100% survival of tumour cell recipients. However, effective treatment of mice with already established tumours was only obtained after combination of vaccination, DC101 and 9H10 treatment in which setting 80% of the mice rejected their tumours.

Immunotherapy of Murine Malignant Mesothelioma Using Tumor Lysate–pulsed Dendritic Cells

RATIONALE

Exploiting the immunostimulatory capacities of dendritic cells holds great promise for cancer immunotherapy. Currently, dendritic cell-based immunotherapy is evaluated clinically in a number of malignancies, including melanoma and urogenital and lung cancer, showing variable but promising results.

OBJECTIVE

To evaluate if pulsed dendritic cells induce protective immunity against malignant mesothelioma in a mouse model.

METHODS

Malignant mesothelioma was induced in mice by intraperitoneal injection of the AB1 mesothelioma cell line, leading to death within 28 days. For immunotherapy, dendritic cells were pulsed overnight either with AB1 tumor cell line lysate, AB1-derived exosomes, or ex vivo AB1 tumor lysate, and injected either before (Days -14 and -7) at the day of (Day 0) or after (Days +1 and +8) tumor implantation.

MAIN RESULTS

Mice receiving tumor lysate-pulsed dendritic cells before tumor implantation demonstrated protective antitumor immunity with prolonged survival (> 3 months) and even resisted secondary tumor challenge. Tumor protection was associated with strong tumor-specific cytotoxic T-lymphocyte responses. Adoptive transfer of splenocytes or purified CD8+ T lymphocytes transferred tumor protection to unimmunized mice in vivo. When given after tumor implantation in a therapeutic setting, pulsed dendritic cells prevented mesothelioma outgrowth. With higher tumor load and delayed administration after tumor implantation, dendritic cells were no longer effective.

CONCLUSIONS

We demonstrate in this murine model that immunotherapy using pulsed dendritic cells may emerge as a powerful tool to control mesothelioma outgrowth. In the future, immunotherapy using dendritic cells could be used as adjuvant to control local recurrence after multimodality treatment for malignant mesothelioma.

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.

Altered Immunity Accompanies Disease Progression in a Mouse Model of Prostate Dysplasia

Increasing evidence suggests that altered immune function accompanies, and indeed may facilitate, cancer progression. In this study, we sought to determine the nature of, and cellular mechanisms underlying, changes in immune status during disease progression in a transgenic mouse model of prostate dysplasia. Immune cells in the tumor microenvironment, as well as in the secondary lymphoid tissues, displayed altered phenotypes. Although evidence of antitumor immunity was detected, there was a paradoxical decrease in the ability of T cells to proliferate in vitro at later stages of disease progression. Detailed analysis of the draining lumbar lymph nodes revealed an increased frequency and number of CD4(+)CD25(+) T cells and an enhanced production of inhibitory cytokines, which correlated with impaired T-cell function. Functional studies confirmed a role for CD4(+)CD25(+) regulatory T cells in suppressing T-cell proliferation as well as regulating the growth of transplanted prostate tumor cells. In addition, our studies show for the first time that anti-CD25 antibody treatment reduces, but does not prevent, tumor growth in a transgenic mouse model of prostate dysplasia. Taken together, this work provides compelling evidence that prostate tumor progression is accompanied by altered immune function and, moreover, that regulatory T cells play an important role in this process. These studies thus provide the impetus for development of specific and effective strategies to deplete regulatory T cells, or suppress their function, as an alternative or adjunct strategy for reducing tumor growth.

Phenotypic and functional characterization of clinical grade dendritic cells generated from patients with advanced breast cancer for therapeutic vaccination

Dendritic cells (DC) are promising candidates for cancer immunotherapy. However, it is not known whether in vitro-generated monocyte-derived DC from cancer patients are altered compared with DC from healthy donors. In a clinical phase I/II study, monocyte-derived DC were generated in vitro utilizing granulocyte macrophage colony-stimulating factor and rh-interleukin-4 (IL-4) and used for cancer immunotherapy. In this study, we tested the effect of various maturation cocktails and performed a comparative evaluation of the DC phenotype and functional characteristics. Polyriboinosinic polyribocytidylic acid (Poly I:C) + tumour necrosis factor-alpha (TNF-alpha) induced significant IL-12 p70 secretion, which was increased after addition of a decoy IL-10 receptor. The lymph node homing chemokine receptor CCR-7 expression was induced by TNF-alpha + IL-1beta + IL-6 + prostaglandin E2 but was not induced by Poly I:C + TNF-alpha. In general, DC from patients had an intermediate maturity phenotype with a significantly higher expression of CD40 and CD54 compared with healthy donors. In vitro analyses showed an unimpaired capacity of the patient-derived DC for antigen-specific (cytomegalovirus, tetanus and keyhole limpet haemocyanin) T-cell stimulation, whereas the allostimulatory capacity of patient-derived DC was significantly decreased. These data suggest that patient-derived DC are more differentiated but are less sensitive to maturation-inducing agents than DC obtained from healthy individuals.

Fusion cell vaccination of patients with metastatic breast and renal cancer induces immunological and clinical responses

PURPOSE

Dendritic cells (DCs) are potent antigen-presenting cells that are uniquely capable of inducing tumor-specific immune responses. We have conducted a Phase I trial in which patients with metastatic breast and renal cancer were treated with a vaccine prepared by fusing autologous tumor and DCs.

EXPERIMENTAL DESIGN

Accessible tumor tissue was disrupted into single cell suspensions. Autologous DCs were prepared from adherent peripheral blood mononuclear cells that were obtained by leukapheresis and cultured in granulocyte macrophage colony-stimulating factor, interleukin 4, and autologous plasma. Tumor cells and DCs were cocultured in the presence of polyethylene glycol to generate the fusions. Fusion cells were quantified by determining the percentage of cells that coexpress tumor and DC markers. Patients were vaccinated with fusion cells at 3-week intervals and assessed weekly for toxicity, and tumor response was assessed at 1, 3, and 6 months after completion of vaccination.

RESULTS

The vaccine was generated for 32 patients. Twenty-three patients were vaccinated with 1 x 10(5) to 4 x 10(6) fusion cells. Fusion cells coexpressed tumor and DC antigens and stimulated allogeneic T-cell proliferation. There was no significant treatment-related toxicity and no clinical evidence of autoimmunity. In a subset of patients, vaccination resulted in an increased percentage of CD4 and CD8+ T cells expressing intracellular IFN-gamma in response to in vitro exposure to tumor lysate. Two patients with breast cancer exhibited disease regressions, including a near complete response of a large chest wall mass. Five patients with renal carcinoma and one patient with breast cancer had disease stabilization.

CONCLUSIONS

Our findings demonstrate that fusion cell vaccination of patients with metastatic breast and renal cancer is a feasible, nontoxic approach associated with the induction of immunological and clinical antitumor responses.

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.

Human mesenchymal stem cells alter antigen-presenting cell maturation and induce T-cell unresponsiveness

Infusion of either embryonic or mesenchymal stem cells prolongs the survival of organ transplants derived from stem cell donors and prevents graft-versus-host-disease (GVHD). An in-depth mechanistic understanding of this tolerization phenomenon could lead to novel cell-based therapies for transplantation. Here we demonstrate that while human mesenchymal stem cells (hMSCs) can promote superantigen-induced activation of purified T cells, addition of antigen-presenting cells (APCs; either monocytes or dendritic cells) to the cultures inhibits the T-cell responses. This contact- and dose-dependent inhibition is accompanied by secretion of large quantities of interleukin (IL)-10 and aberrant APC maturation, which can be partially overridden by the addition of factors that promote APC maturation (ie, lipopolysaccharide [LPS] or anti-CD40 monoclonal antibody [mAb]). Thus, our data support an immunoregulatory mechanism wherein hMSCs inhibit T cells indirectly by contact-dependent induction of regulatory APCs with T-cell-suppressive properties. Our data may reveal a physiologic phenomenon whereby the development of a distinct APC population is regulated by the tissue's cellular microenvironment.

Tumor-derived MUC1 mucins interact with differentiating monocytes and induce IL-10highIL-12low regulatory dendritic cell

Dendritic cells (DC) initiate immunity by the activation of naive T cells and control immunity through their ability to induce unresponsiveness of lymphocytes by mechanisms that include deletion and induction of regulatory cells. An inadequate presentation to T cells by tumor-induced "regulatory" DC, among several mechanisms, can explain tolerance to tumor-associated Ags. In this study, we show that tumor-derived mucin profoundly affects the cytokine repertoire of monocyte-derived DC and switch them into IL-10(high)IL-12(low) regulatory APCs with a limited capacity to trigger protective Th1 responses. In fact, DC cocultured with pancreatic tumor cell lines in a Transwell system did not reach full maturation, had low immunostimulatory functions, did not produce IL-12, and released high levels of IL-10. The involvement of known tumor-derived immune-suppressive factors (e.g., vascular endothelial growth factor, TGF-beta, IL-6, and IL-10) was considered and excluded. We provide evidence that tumor-derived MUC1 mucins are responsible for the impaired DC maturation and function. DC obtained in the presence of tumor microenvironment preferentially polarized IL-4(+) response. Moreover, T cells primed by these regulatory DC became anergic and behaved as suppressor/regulatory cells. These findings identify mucin secretion as a novel mechanism of tumor escape from immune surveillance and provide the basis for the generation of potentially tolerogenic DC.

Anti-tumor effects of dendritic and tumor cell fusions are not dependent on expression of MHC class I and II by dendritic cells

Vaccination of fusion cells (FCs) made from dendritic and tumor cells elicits anti-tumor effects. We investigated whether major histocompatibility complex (MHC) class I and II play an important role in the induction of anti-tumor immunity by FCs. Immunization with fusion cells composed of syngeneic, allogeneic, or MHC I(-/-)II(-/-) DCs and B16 cells inhibited tumor growth. Elispot assay showed a higher population of interferon-gamma secreting T lymphocytes in mice immunized with fusion cells. These data suggest that anti-tumor effects of DCs and tumor cell fusions are not dependent on the expression of MHC class I and II on DCs.

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Nitric oxide confers therapeutic activity to dendritic cells in a mouse model of melanoma

Susceptibility of dendritic cells (DCs) to tumor-induced apoptosis reduces their efficacy in cancer therapy. Here we show that delivery within exponentially growing B16 melanomas of DCs treated ex vivo with nitric oxide (NO), released by the NO donor (z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NO), significantly reduced tumor growth, with cure of 37% of animals. DETA-NO-treated DCs became resistant to tumor-induced apoptosis because DETA-NO prevented tumor-induced changes in the expression of Bcl-2, Bax, and Bcl-xL; activation of caspase-9; and a reduction in the mitochondrial membrane potential. DETA-NO also increased DC cytotoxic activity against tumor cells and DC ability to trigger T-lymphocyte proliferation. All of the effects of DETA-NO were mediated through cGMP generation. NO and NO-generating drugs may therefore be used to increase the anticancer efficacy of DCs.

GPI-defective monocytes from paroxysmal nocturnal hemoglobinuria patients show impaired in vitro dendritic cell differentiation

Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal, acquired hematopoietic disorder characterized by a phosphatidylinositol (PI) glycan-A gene mutation, which impairs the synthesis of the glycosyl-PI (GPI) anchor, thus causing the absence of all GPI-linked proteins on the membrane of the clonal-defective cells. The presence of a consistent GPI-defective monocyte compartment is a common feature in PNH patients. To investigate the functional behavior of this population, we analyzed its in vitro differentiation ability toward functional dendritic cells (DCs). Our data indicate that GPI-defective monocytes from PNH patients are unable to undergo full DC differentiation in vitro after granulocyte macrophage-colony stimulating factor and recombinant interleukin (IL)-4 treatment. In this context, the GPI-defective DC population shows mannose receptor expression, high levels of the CD86 molecule, and impaired CD1a up-regulation. The analysis of lipopolysaccharide and CD40-dependent, functional pathways in these DCs revealed a strong decrease in tumor necrosis factor alpha and IL-12 production. Finally, GPI-defective DCs showed a severe impairment in delivering accessory signals for T cell receptor-dependent T cell proliferation.

Vaccination of prostatectomized prostate cancer patients in biochemical relapse, with autologous dendritic cells pulsed with recombinant human PSA

This study was conducted in prostate cancer patients in biochemical relapse after radical prostatectomy, to assess the feasibility, safety, and immunogenicity of therapeutic vaccination with autologous dendritic cells (DCs) pulsed with human recombinant prostate-specific antigen (PSA) (Dendritophage-rPSA). Twenty-four patients with histologically proven prostate carcinoma and an isolated postoperative rise of serum PSA (>1 ng/ml to 10 ng/ml) after radical prostatectomy were included. The patients received nine administrations of PSA-loaded DCs by combined intravenous, subcutaneous, and intradermal routes over 21 weeks. Postbaseline blood tests were performed at months 1, 3, 6, 9, and 12 (PSA levels), at months 6 and 12 (circulating prostate cancer cells), at month 6 (anti-PSA IgG and IgM antibodies), and at up to eight time points before, during, and after immunization (PSA-specific T cells). Circulating prostate cancer cells detected in six patients at baseline were undetectable at 6 months and remained undetectable at 12 months. Eleven patients had a postbaseline transient PSA decrease on one to three occasions, predominantly occurring at month 1 (7 patients) or month 3 (2 patients). Maximum PSA decrease ranged from 6% to 39%. PSA decrease on at least one occasion was more frequent in patients with low Gleason score ( p=0.016) at prostatectomy and with positive skin tests at study baseline ( p=0.04). PSA-specific T cells were detected ex vivo by ELISpot for IFN-gamma in 7 patients before vaccination and in 11 patients after vaccination. Of the latter 11 patients, 5 had detectable T cells both before and during the vaccination period, 4 only during the vaccination period, while 2 patients could for technical reasons not be assessed prevaccination. No induction of anti-PSA IgG or IgM antibodies was detected. There were no serious adverse events or otherwise severe toxicities observed during the trial. Immunization with Dendritophage-rPSA was feasible and safe in this cohort of patients. An immune response specific for PSA could be detected in some patients. A notable effect was the disappearance of circulating prostate cells in all patients who were RT-PCR positive before vaccination.

Human dendritic cell maturation by adenovirus transduction enhances tumor antigen-specific T-cell responses

Dendritic cells (DCs) have been shown to require a degree of maturation to stimulate antigen-specific, type 1 cytotoxic T lymphocytes in numerous murine models. Limited data in humans suggest that immature DCs (DC) can induce tolerance, yet a variety of nonmatured DC used clinically have induced antigen-specific type 1 T cells in vivo to various tumor-associated antigens. Use of adenovirus to engineer DCs is an efficient method for delivery of entire genes to DC, but the data on the biologic effects of viral transduction are contradictory. The authors demonstrate that DCs transduced with adenovirus (AdV) clearly become more mature by the phenotypic criterion of upregulation of CD83 and downregulation of CD14. Transduced DCs also decrease production of IL-10, and a subset of transduced DCs produce increased levels of IL-12 p70. This level of maturation is superior to that achieved by treatment of these cells with tumor necrosis factor-alpha or interferon-alpha but less pronounced than with CD40L trimer or CD40L + interferon-gamma. Maturation by AdV transduction alone leads to efficient stimulation of antigen-specific T cells from both healthy donors and patients with advanced cancer using two defined human tumor-associated antigens, MART-1 and AFP. Given the pivotal role of DCs in immune activation, it is important to understand the direct biologic effects of AdV on DCs, as well as the impact these biologic changes have on the stimulation of antigen-specific T cells. This study has important implications for the design of DC-based clinical trials.

Murine prostate cancer inhibits both in vivo and in vitro generation of dendritic cells from bone marrow precursors

BACKGROUND

There is increasing evidence to suggest that dendritic cells (DC) are functionally impaired in tumor bearing hosts. However there is little or no data on the effects of murine prostate cancer (CaP) on DC generation from bone marrow precursors.

METHODS

Flow cytometry, mixed leukocyte reactions (MLR), and immunohistochemical analyses were used to characterize DC in CaP.

RESULTS

DC generated in the presence of CaP cell lines RM1 and the cell line C2 from the transgenic adenocarcinoma of the mouse prostate (TRAMP) mouse in a Transwell system expressed significantly lower levels of DC differentiation markers. This effect was confirmed when TK-neo-transfected RM1 cells were directly added to DC cultures and eliminated 5 days later using gancyclovir (GCV). Furthermore, co-incubation of DC with CaP cells resulted in a decrease in the stimulatory capacity of DC to induce T cell proliferation in the MLR assay. These results were further confirmed in vivo in two different murine models of CaP: i) DC generated from mice intrafemorally injected with TK-neo-transfected RM1 cells; and ii) in DC generated from TRAMP mice.

CONCLUSIONS

The generation and function of DC are significantly suppressed in the CaP microenvironment in both in vivo and in vitro murine models.

Identification of Multiple HLA-DR-Restricted Epitopes of the Tumor-Associated Antigen CAMEL by CD4+Th1/Th2 Lymphocytes

CD4(+) Th cells play an important role in the induction and maintenance of adequate CD8(+) T cell-mediated antitumor responses. Therefore, identification of MHC class II-restricted tumor antigenic epitopes is of major importance for the development of effective immunotherapies with synthetic peptides. CAMEL and NY-ESO-ORF2 are tumor Ags translated in an alternative open reading frame from the highly homologous LAGE-1 and NY-ESO-1 genes, respectively. In this study, we investigated whether CD4(+) T cell responses could be induced in vitro by autologous, mature dendritic cells pulsed with recombinant CAMEL protein. The data show efficient induction of CAMEL-specific CD4(+) T cells with mixed Th1/Th2 phenotype in two healthy donors. Isolation of CD4(+) T cell clones from the T cell cultures of both donors led to the identification of four naturally processed HLA-DR-binding CAMEL epitopes: CAMEL(1-20), CAMEL(14-33), CAMEL(46-65), and CAMEL(81-102). Two peptides (CAMEL(1-20) and CAMEL(14-33)) also contain previously identified HLA class I-binding CD8(+) T cell epitopes shared by CAMEL and NY-ESO-ORF2 and are therefore interesting tools to explore for immunotherapy. Furthermore, two CD4(+) T cell clones that recognized the CAMEL(14-33) peptide with similar affinities were shown to differ in recognition of tumor cells. These CD4(+) T cell clones recognized the same minimal epitope and expressed similar levels of adhesion, costimulatory, and inhibitory molecules. TCR analysis demonstrated that these clones expressed identical TCR beta-chains, but different complementarity-determining region 3 loops of the TCR alpha-chains. Introduction of the TCRs into proper recipient cells should reveal whether the different complementarity-determining region 3 alpha loops are important for tumor cell recognition.

Role of immature myeloid Gr-1+ cells in the development of antitumor immunity

One of the mechanisms by which tumor cells evade the immune system is the lack of proper antigen-presenting cells. Improvement in host immunity against tumor cells can be achieved by promoting the differentiation of dendritic cells (DCs) from immature myeloid cells (Gr-1(+)Ly-6C(+)F4/80(+)) that accumulate in the bone marrow and lymphoid organs of mice with large tumor burdens. The enriched immature myeloid cells inhibit T-cell proliferation and tumor-specific T-cell response, which can be reversed by the differentiation of immature myeloid cells or depletion of F4/80(+) cells. Sorted Gr-1(+)/F4/80(+) immature myeloid cells differentiated into CD11c(+) cells that express CD80 and I-A/I-E (MHC class II) in the presence of recombinant murine granulocyte macrophage colony-stimulating factor (GM-CSF). Furthermore, intratumoral gene delivery of GM-CSF not only promoted the differentiation of carboxyfluoroscein succinimidyl ester-labeled immature myeloid cells into CD11c(+) cells with the characteristics of mature DCs (CD80(+), I-A/I-E(+)) but also enhanced innate natural killer and adaptive cytolytic T-cell activities in mice treated with interleukin (IL)-12 and anti-4-1BB combination therapy. More importantly, intratumoral delivery of GM-CSF and IL-12 genes in combination with 4-1BB costimulation greatly improved the long-term survival rate of mice bearing large tumors and eradicated the untreated existing hepatic tumor. The results suggest that inducing the maturation of immature myeloid cells, thus preventing their inhibitory activity and enhancing their antigen-presenting capability, by GM-CSF gene therapy is a critically important step in the development of effective antitumor responses in hosts with advanced tumors.

NK and CD8+ T cell-mediated eradication of poorly immunogenic B16-F10 melanoma by the combined action of IL-12 gene therapy and 4-1BB costimulation

In previous reports, systemic administration of a stimulatory monoclonal antibody directed against the 4-1BB receptor had no effect on survival or tumor burden in mice inoculated with the poorly immunogenic B16-F10 melanoma. We combined IL-12 gene transfer with 4-1BB costimulation to explore a previously noted cooperative anti-tumor effect against this model tumor. We hypothesize that the innate immune response mediated by IL-12-activated natural killer (NK) cells initiates the activation of the immune system, leading to the priming of T cells, whereas 4-1BB costimulation enhances the function of primed tumor-specific T cells. The effect of the combination therapy on the growth of subcutaneous (s.c.) tumors and pulmonary metastasis was examined. The combination therapy significantly retarded the growth of subcutaneously-inoculated tumors, and 50% of tumor-bearing mice survived with complete tumor regression. In contrast, neither IL-12 gene transfer nor anti-4-1BB antibody administration alone was as effective. Enhanced CTL activity against both B16-F10 tumor cells and TRP-2-pulsed EL4 syngeneic tumor cells was observed in tumor-bearing animals treated with the combination therapy 2 weeks after treatment and, in long-term survivors from this combination therapy, at >120 days. In a pulmonary metastatic model, only the combination therapy generated significant protection against metastasis. In vivo depletion of NK or CD8(+) but not CD4(+) subsets eliminated the protective immunity. Furthermore, NK cell depletion significantly reduced both tumor-specific CTL activity and the number of tumor-specific IFN-gamma-producing cells, suggesting that this synergistic effect requires the participation of both NK and CD8(+) T cells.

Altered maturation of peripheral blood dendritic cells in patients with breast cancer

Tumours have at least two mechanisms that can alter dendritic cell (DC) maturation and function. The first affects the ability of haematopoietic progenitors to differentiate into functional DCs; the second affects their differentiation from CD14+ monocytes, promoting an early but dysfunctional maturation. The aim of this study was to evaluate the in vivo relevance of these pathways in breast cancer patients. For this purpose, 53 patients with invasive breast cancer were compared to 68 healthy controls. To avoid isolation or culture procedures for enrichment of DCs, analyses were directly performed by flow cytometry on whole-blood samples. The expression of surface antigens and intracellular accumulation of regulatory cytokines upon LPS stimulation were evaluated. The number of DCs, and in particular of the myeloid subpopulation, was markedly reduced in cancer patients (P<0.001). Patient DCs were characterized by a more mature phenotype compared with controls (P=0.016), and had impaired production of IL-12 (P<0.001). These alterations were reverted by surgical resection of the tumour. To investigate the possible role of some tumour-related immunoactive soluble factors, we measured the plasmatic levels of vascular endothelial growth factor, IL-10 and spermine. A significant inverse correlation between spermine concentration and the percentage of DCs expressing IL-12 was found. Evidence was also obtained that in vitro exposure of monocyte-derived DCs to spermine promoted their activation and maturation, and impaired their function. Taken together, our results suggest that both the above-described mechanisms could concomitantly act in breast cancer to affect DC differentiation, and that spermine could be a mediator of dysfunctional maturation of DCs.

Granulocyte/macrophage-colony stimulating factor and interleukin-4 expand and activate type-1 dendritic cells (DC1) when administered in vivo to cancer patients

Two rare populations of cells with the features of dendritic cell precursors (preDC) can be identified in human peripheral blood. PreDC1 are HLA-DR+/CD11c+ cells which mature into DC1 capable of stimulating Th1 responses. In contrast, preDC2 are HLA-DR+/CD11c-/CD123+ cells that promote Th2 responses when matured into DC2. We hypothesized that administration of GM-CSF and IL-4, growth factors for DC1, would specifically augment the number and function of circulating DC1 in vivo. Patients with advanced metastatic cancer were treated with GM-CSF (2.5 microg/kg/day) and IL-4 (4 or 6 microg/kg/day) for 7 days. Cytokine administration at the highest IL-4 dose produced an average 2.3-fold increase in preDC2 number, but a 6.5-fold increase in preDC1, resulting in an increased ratio of circulating preDC1:preDC2 from 1.4:1 pre-treatment to 4.3:1 after cytokine therapy. DC1 precursors identified after in vivo therapy were larger, more complex and expressed higher levels of HLA-DR, CD11c and CD80 than pre-treatment cells. DC1 isolated from the peripheral blood of patients receiving GM-CSF/IL-4 therapy demonstrated MLR activity comparable to that of monocyte-derived DC generated in vitro from the patients' pre-treatment blood using GM-CSF and IL-4. We conclude that systemic administration of GM-CSF and IL-4 preferentially expands and matures the preDC1 population in vivo. These effects correlate with antigen-presenting activity, providing a mechanism by which systemic GM-CSF and IL-4 might stimulate anti-tumor immunity in vivo.

Immature dendritic cell/tumor cell fusions induce potent antitumour immunity

BACKGROUND

Maturation of dendritic cells (DCs) is important to induce antigen-specific antitumour immunity in cancer immunotherapy with antigen-loaded DCs. However, DCs from tumour-bearing hosts are immature and functionally defective for antigen presentation. We examined whether DCs from tumour-bearing mice could be an effective part of a DC/tumour cell fusion vaccine.

MATERIALS AND METHODS

Dendritic cells from healthy (DC-Hs) or MC38 tumour-bearing mice (DC-TBs) were examined for endocytotic capacity of FITC-labelled dextran, antigen-presenting capacity in allogeneic mixed leucocyte reaction (allo-MLR) and expression of I-Ab, CD80, and CD86. Fusion cells (FCs) of DC-Hs or DC-TBs and MC38 cells (FC-Hs or FC-TBs) were generated by treatment with polyethylene glycol (PEG). Mice vaccinated with FC-Hs or FC-TBs were studied for cytolytic activity of splenocytes and suppressive activity against established MC38 pulmonary metastases.

RESULTS

Dendritic cell-TBs showed higher endocytotic capacity and lower antigen-presenting capacity than did DC-Hs, results indicating that DC-TBs are more immature and functionally defective for antigen presentation than are DC-Hs. Expression of surface molecules, however, was almost same between DC-Hs and DC-TBs. Splenocytes from mice immunized with FC-Hs or FC-TBs induced the same high cytolytic activity against MC38 cells. Vaccination of mice with FC-Hs or FC-TBs resulted in the same significant suppressive effect against established pulmonary metastases of MC38.

CONCLUSION

Dendritic cells from tumour-bearing mice, despite being functionally defective, are effective vehicles for immunotherapy using DC/tumour cell fusion vaccines.

Against the self: dendritic cells versus cancer

The role of host defense in cancer is highly variable. Although there are cases where spontaneous cures of cancer appear to be mediated by immunologic mechanisms, malignant disease generally progresses even in patients where tumor-specific immunity can be demonstrated. It is apparent that there are complex interactions between tumor cells and dendritic cells, the dominant antigen-presenting cells of the immune system. Through their inhibitory actions upon dendritic cells, tumor cells can negatively regulate priming of tumor-specific immunity. Recent work has also shown that dendritic cells have direct cytotoxic effects upon tumor cells. These interactions may impact on the efficacy of current strategies using dendritic cell-based vaccines for tumor immunotherapy.

Melanocyte-specific immune response in melanoma and vitiligo: two faces of the same coin?

The appearance of depigmentation during the course of malignant melanoma has been considered a good prognostic sign. Is it only a side-effect, informative of the immune system's response to the treatment, or does it act as a necessary amplifier of these clinically important anti-tumor responses? The current review will attempt to tackle this question by reviewing the current literature, as well as by posing some novel hypotheses. Understanding the nature of humoral and cellular immune responses directed against normal melanocytes and their malignant counterparts may lead to the design of improved therapeutic strategies relevant to both vitiligo and melanoma.

Neuroblastoma cells inhibit the immunostimulatory function of dendritic cells

PURPOSE

Dendritic cells (DC) are critical for induction of antitumor immunity. Recent studies suggest that tumors may avoid immune destruction by inhibiting DC function. The authors investigated the effect of neuroblastoma (NB) on surface antigen expression and T cell activation by DCs.

METHODS

DCs were generated in the presence of granulocyte and macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4) from peripheral blood of healthy donors. On day 6 of culture, DCs were exposed to human NB cells and were analyzed by flow cytometry.

RESULTS

The proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha) failed to upregulate the expression of HLA-DR and costimulatory molecule CD86 by DCs that were cultured with NB. Conversely, upregulation was preserved when DCs were cultured in the absence of NB. Exposure to NB also led to apoptosis of DCs as shown by 2-fold increase in surface phosphatidylserine. It appears that direct contact was required to inhibit DC maturation, because DCs separated from NB cells using a transwell insert did not suppress surface antigen expression. Finally, DCs exposed to NB inhibited the proliferation of allogeneic T cells in mixed lymphocyte reactions.

CONCLUSIONS

These findings have significant implications for tumor-pulsed DC vaccines in the treatment of NB and suggest a mechanism by which NB escape rejection.

Gangliosides from human melanoma tumors impair dendritic cell differentiation from monocytes and induce their apoptosis

Gangliosides are ubiquitous membrane-associated glycosphingolipids, which are involved in cell growth and differentiation. Most tumor cells synthesize and shed large amounts of gangliosides into their microenvironment, and many studies have unraveled their immunosuppressive properties. In the present study we analyzed the effects of GM3 and GD3 gangliosides, purified from human melanoma tumors, on the differentiation of monocyte-derived dendritic cells (MoDC). At concentrations close to those detected in the sera from melanoma patients, both gangliosides dose-dependently inhibit the phenotypic and functional differentiation of MoDC, as assessed by a strong down-regulation of CD1a, CD54, CD80, and CD40 Ags and impaired allostimulatory function on day 6 of culture. Furthermore, GM3 and GD3 gangliosides decreased the viable cell yield and induced significant DC apoptosis. Finally, addition of GD3 to differentiating DC impaired their subsequent maturation induced by CD154. The resulting DC produced low amounts of IL-12 and large amounts of IL-10, a cytokine pattern that might hamper an efficient antitumor immune response. In conclusion, the results demonstrate that gangliosides impair the phenotypic and functional differentiation of MoDC and induce their apoptosis, which may be an additional mechanism of human melanoma escape.

Modulation of antitumor immune responses by hematopoietic cytokines

BACKGROUND

Advances in immunotherapy for the treatment of patients with malignant disease have led to increasingly successful use of these methods in the clinical setting. This review presents findings from recent studies that have explored improved methods for the presentation of tumor-associated antigens and for the restoration of tumor specific immune responses using cytokine therapy.

METHODS

A review of human clinical trial research on immune cytokines from 1995 (MEDLINE) to the present was conducted. Particular attention was focused on articles that reported results from Phase II or later clinical studies in patients with malignant disease.

RESULTS

The defects in cellular immunity commonly seen in patients with malignancies often are expressed as tumor specific anergy. Reversing patient tolerance to tumor antigens may be accomplished by treatment with immunoregulatory cytokines, such as Flt-3 and granulocyte-macrophage-colony stimulating factor, that mature and activate dendritic cells. Published clinical studies indicate that granulocyte-macrophage-colony stimulating factor stimulates antigen-presenting cells and has promising antitumor activity as an adjunct or as stand-alone therapy for patients with malignant disease, including leukemia, melanoma, breast carcinoma, prostate carcinoma, and renal cell carcinoma.

CONCLUSIONS

Immune-modulating cytokines may be used alone or in combination with other treatments to help restore immune function, improve response to tumor-associated antigens, and reduce the toxic effects of standard antitumor therapies. The evolving understanding of how dendritic cells regulate immune responses and promising results from published studies of immune-enhancing cytokines in the treatment of patients with malignant disease support the conduct of randomized clinical trials to confirm the clinical benefit of these immunotherapeutic strategies.

Transforming growth factor-beta induces apoptosis in antigen-specific CD4+ T cells prepared for adoptive immunotherapy

Transforming growth factor-beta (TGF-beta), found at the site of most tumors, has been recognized as one of the mechanisms involved in tumor immunological escape. To evaluate its impact on adoptive immunotherapy against cancer, we examined the susceptibility of tumor-specific T cells to TGF-beta in the setting of these T cells being prepared for adoptive transfer. Hepatitis B virus (HBV)-specific CD4(+) T cells were ex vivo generated by activating with HBV-transfected dendritic cells and selecting with antibodies to CD25 activation molecules, and then expanded with antibodies to CD3/CD28. These T cells expressed higher levels of the type II TGF-beta receptor than nai;ve T cells and exhibited enhanced apoptosis when exposed to TGF-beta. The underlying apoptotic pathway was linked to the dissipation of the mitochondrial inner membrane potential and activation of caspase-9. The absence of caspase-8 activity in TGF-beta-treated T cells suggests that the death receptor system may not be involved in this type of apoptosis. Interleukin-2 (IL-2), which is concomitantly administered with tumor-specific T cells in adoptive immunotherapy, was unable to protect HBV-specific CD4(+) T cells from the pro-apoptotic effect of TGF-beta when added simultaneously with TGF-beta. Interesting, IL-2-pretreated T cells displayed the type II TGF-beta receptor at lower levels and were more resistant to TGF-beta. Together, our findings indicate that the effectiveness of adoptive cancer immunotherapy may be impaired by tumor-derived TGF-beta and appropriate manipulation of exogenous IL-2 might overcome this hurdle.

Phase I trial of granulocyte macrophage-colony stimulating factor and interleukin-4 as a combined immunotherapy for patients with cancer

Antigen-presenting cells (APC), such as dendritic cells (DC), are the key component of many cancer immunotherapy strategies. However, DCs comprise a rare population of clinically obtainable cells and are compromised in function in cancer-bearing hosts. Clinical trials therefore rely upon DC generated ex vivo. The authors hypothesized that systemic administration of granulocyte-macrophage colony-stimulating factor (GM-CSF) plus interleukin (IL)-4 might lead to the differentiation of DC from their precursors and enhance their number and function in vivo, as it does in vitro. Subjects with advanced malignancies were treated in this phase I, multiple cohort, dose-escalation trial combining GM-CSF (2.5 microgram/kg/d) plus IL-4 (0-6.0 microgram/kg/d). A cycle consisted of 14 days of cytokine therapy and 14 days of observation (cohorts A-D), or alternating 7-day treatment and observation periods (cohort E). Subjects were followed clinically to determine a maximally tolerated dose (MTD), and complimentary in vitro studies were performed to determine a biologically active dose (BAD). Twenty-one subjects received treatment on this outpatient-based protocol. Treatment was well tolerated and generally characterized by Grade 1 and 2 cytokine related toxicities. The MTD was determined to be GM-CSF 2.5 microgram/kg/d plus IL-4 6.0 microgram/kg/d (cohort E). Treatment in cohort D (GM-CSF 2.5 microgram/kg/d plus IL-4 4.0 microgram/kg/d) was well tolerated and resulted in a BAD. Systemic GM-CSF plus IL-4 provides a mechanism for increasing the number and function of APC in cancer patients. Future clinical applications of this strategy are numerous and include the potential as a strong vaccine adjuvant.

Complete loss of HLA class I antigen expression on melanoma cells: a result of successive mutational events

Alterations in the surface expression of HLA class I molecules have been described as a strategy of tumors to evade recognition by cytotoxic T cells. We detected complete loss of HLA class I antigen presentation for 2 tumor cell lines from 1 melanoma patient, the first originated from a regional lymph node lesion diagnosed simultaneously with the primary tumor and the second established 8 months later from a metastatic pleural effusion sample. Antigen presentation was not inducible with IFN-gamma but could be restored after transfection of tumor cells with b2m cDNA, indicating a defect in b2m expression. Analysis of the nature of this defect revealed that it originated from at least 2 mutational events affecting both copies of the b2m gene: a microdeletion of 498 bp in one b2m gene, including its entire exon 1, and a macrodeletion involving the entire copy of the second b2m gene. Microsatellite analysis pointed to the macrodeletion by demonstrating LOH for several specific markers on the long arm (q) of chromosome 15. Structural imbalance of 15q was verified by FISH. FISH studies also indicated the coexistence of a structurally abnormal variant of chromosome 15q with 2 apparently entire chromosomes 15q harboring the homozygous b2m microdeletion. Block of b2m expression in tumor cells builds a barrier to immunotherapy of cancer patients, and its early incidence should be of major consideration in the development and design of immunotherapeutic strategies.

CD4+ Th2 cell recognition of HLA-DR-restricted epitopes derived from CAMEL: a tumor antigen translated in an alternative open reading frame

Tumor Ag NY-ESO-1 is an attractive target for immunotherapy of cancer, since both CD8(+) CTL and CD4(+) Th cells against NY-ESO-1 have been described. Moreover, NY-ESO-1 as well as the highly homologous tumor Ag LAGE-1 are broadly expressed in various tumor types. Interestingly, the NY-ESO-1 and LAGE-1 genes also encode for proteins translated in an alternative open reading frame. These alternatively translated NY-ESO-ORF2 and CAMEL proteins, derived from the NY-ESO-1 and LAGE-1 genes, respectively, have been demonstrated to be immunogenic, since CTL specific for these proteins have been isolated from melanoma patients. In this study a panel of advanced melanoma patients was screened for the presence of Th cells specific for the alternatively translated tumor Ags NY-ESO-ORF2 and CAMEL. PBMC of melanoma patients were stimulated for 4 days with mixes of overlapping peptides covering the entire NY-ESO-ORF2 and CAMEL protein sequences and were tested for the release of type 1 (IFN-gamma) and type 2 (IL-13) cytokines in ELISPOT assays. In three of 15 patients, T cells specific for two CAMEL peptides (CAMEL(71-92) and CAMEL(81-102)) could be detected. From one of these patients, CD4(+) T cell clones specific for CAMEL(81-102) could be generated. These clones recognized a naturally processed epitope presented in both HLA-DR11 and HLA-DR12 and produced high levels of IL-4, IL-5, and IL-13. In conclusion, this study shows the presence of Th cells specific for the alternatively translated tumor Ag CAMEL in melanoma patients and is the first report that describes the isolation of tumor Ag-specific CD4(+) Th 2 clones.

Malignant counterpart of myeloid dendritic cell (DC) belonging to acute myelogenous leukemia (AML) exhibits a dichotomous immunoregulatory potential

Dendritic cells (DCs) play a central role in immune regulation. Some leukemic cells are argued to be malignant counterparts of DC because of their ability to differentiate into leukemic DC. We characterize DC-like leukemia homogenously expressing CD11c+CD86+ in acute myelogenous leukemia patients. They express the Wilms' tumor-1 antigen and common DC phenotypes (i.e., fascin+, CD83+, and DR+) directly. Purified leukemic cells produce interleukin-12 (IL-12) simultaneously with Fas ligand (FasL) and IL-6, which may suppress T cell-mediated immunity. These cells can elicit strong allogeneic T cell responses as well as induce tumor-specific CD8+ cytotoxic T cells, suggesting that they effectively present tumor-associated antigens. In contrast, they drive primary T cells toward apoptosis mediated in a tumor-specific way by a Fas-FasL interaction. Taken together, DC-like leukemia uniquely influences immune surveillance in contradictory ways, some of which may be involved in the mechanism of immune escape.

Human regional lymph nodes draining cancer exhibit a profound dendritic cell depletion as comparing to those from patients without malignancies

Dendritic cells (DCs) are bone-marrow derived 'professional' antigen presenting cells (APC). They are considered as the most potent APC able to induce primary immune responses. DC efficiently capture and process proteic and non-proteic antigens. They are widely distributed throughout the body and occupy sentinel positions such as epithelia. Establishment of an immune response against cancer may depend of the capacity of DCs to transfer (to capture, to process and to present) tumor antigens into regional lymph nodes where they can induce a specific response leading to tumor rejection. Because host 'professional' DCs are one of the most important elements in the induction of specific anti-tumor responses and lymph nodes are the places where the immune response takes place, we investigated the densities of DCs within regional metastasis-free lymph nodes from 47 patients with different malignant epithelial tumors as comparing with lymph nodes from 11 patients without malignancies using an immunohistochemistry method with anti-S100 protein, CD86 and CD1a antibodies. By means of morphometric analysis, we observed that S100+ and CD1a+ DCs densities in regional lymph nodes from cancer patients were significatively decreased as compared with control lymph nodes (P<0.0001 and 0.003, respectively). S100+ DCs and CD86+ DCs densities in lymph nodes draining cancer were similar. Taken together, these data indicated that lymph nodes draining cancer had significantly less CD1a+ DCs than S100+ and possibly CD86+ DCs. These findings may represent another mechanism by which tumors evade the immune recognition.

Cyclopentenone prostaglandins induce caspase activation and apoptosis in dendritic cells by a PPAR-gamma-independent mechanism: regulation by inflammatory and T cell-derived stimuli

OBJECTIVE

Dendritic cells (DC) are professional antigen-presenting cells playing a pivotal role in the induction of immunological responses. There is evidence that DC survival during ongoing immune responses is finite. However, little is known about the mechanisms regulating apoptosis in these cells. Here, we have investigated the effects of the anti-inflammatory cyclopentenone prostaglandins on human monocyte-derived DC.

MATERIALS AND METHODS

Phenotype of DC was determined by flow cytometry and their allostimulatory potential in mixed leukocyte reaction. Induction of apoptosis in DC was monitored by staining with annexin-V-FITC and propidium iodide, propidium iodide staining of cell nuclei, and fluorimetric assay of caspase activity. Induction of maturation in DC was obtained by stimulation with TNF-alpha, LPS, IFN-gamma, CD40-ligand, or different combinations of these stimuli. PPAR-gamma expression in DC was determined by RT-PCR.

RESULTS

Exposure of immature DC to cyclopentenone prostaglandins blunted their allostimulatory capacity and skewed their phenotype by downregulating CD1a and costimulatory molecules. These effects were due to activation of caspases and induction of apoptotic cell death in DC by cyclopentenone prostaglandins. Mature DC showed enhanced susceptibility to apoptosis via cyclopentenone prostaglandins as compared with immature DC. Although DC express PPAR-gamma, the corresponding receptor for some of these metabolites, PPAR-gamma activation by a synthetic high-affinity agonist failed to impair DC viability.

CONCLUSIONS

Cyclopentenone prostaglandins induce apoptosis of human DC by a PPAR-gamma-independent mechanism. Since these compounds are released during an inflammatory event and show anti-inflammatory properties, they may contribute to the downregulation of DC function through apoptotic cell death.

Maturation of dendritic cells induced by Candida beta-D-glucan

We investigated whether Candida beta-D-glucan (CSBG) alters the maturation of dendritic cells (DCs). DC phenotypes were analyzed using FACScan. The expression of surface molecules, including major histocompatibility complex (MHC) classes I and II, as well as CD80 and CD86, increased on DCs that were stimulated with lipopolysaccaride (DCs/LPS), in comparison with unstimulated bone marrow-derived DCs (BM-DCs). Furthermore, the level of surface molecule expression on DCs stimulated with CSBG (DCs/CSBG) was between that of DCs and DCs/LPS. Phagocytosis was assessed by the uptake of FITC-dextran. There were no differences in the uptake of dextran among DCs/LPS and DCs/CSBG. The ability of BM-DCs to uptake dextran was higher than that of DCs/LPS and DCs/CSBG. We analyzed the concentration of IL-12 secreted by DCs using ELISA. BM-DCs secreted a low concentration of IL-12, while DCs/LPS and DCs/CSBG secreted higher levels of IL-12 than BM-DCs. There were no remarkable differences in the concentrations of IL-12 produced by DCs/LPS and DCs/CSBG. This data suggests that CSBG may augment DC maturation.

Interleukin-12-gene transduction makes DCs from tumor-bearing mice an effective inducer of tumor-specific immunity in a peritoneal dissemination model

Dendritic cells (DCs) from cancer patients, as well as tumor-infiltrating DCs, are reported to have suppressed immunostimulatory capacity. One of the major problems in the clinical use of DCs for treating tumors is that the DCs must be autologous ones obtained from patients. Compared with normal DCs (nDCs), flow-cytometric analysis and allogeneic mixed lymphocyte reaction (MLR) have revealed lower expression of the costimulatory molecules and suppressed T-cell-stimulatory activity in DCs derived from tumor-bearing mice (tDCs) despite of culture. We reported previously that the interleukin-12 (IL-12)-gene-transduced nDCs inhibited tumor growth due to induced tumor-specific Th1 and cytotoxic T cells (CTLs) in a murine established subcutaneous tumor model. In the present study, we examined whether tDCs could induce immune responses against tumors after IL-12-gene transduction in an established peritoneal dissemination model. The intraperitoneal injection of IL-12-gene-transduced tDCs resulted in prolonged survival of some treated mice (log-rank test; P=0.001) and tumor-specific Th1 and CTL activity. The injection of IL-12-gene-transduced nDCs prolonged the survival of all treated mice (P<0.0001) and elicited tumor-specific immunity, which were better than those of IL-12-gene-transduced tDCs. Taken together, DC modification of IL-12-gene transduction is an effective and promising approach for cancer therapy even when immunosuppressive tDCs are employed.

Effects of glioma cells on maturation of dendritic cells

We investigated whether glioma cells affected the maturation of dendritic cells (DCs). First, DCs phenotypes were analyzed using FACScan. Incubation of both human and mouse immature DCs with glioma cells altered their expression of cell surface molecules, whereas expression of cell surface molecules by mature mouse and human DCs was not affected by exposure to glioma cells. Subsequently, phagositosis was assessed by uptake of FITC-dextran. Coculture with glioma cells did not inhibit phagositosis of either mature or immature DCs relative to the controls. We also analyzed the concentration of IL-12 secreted by mature DCs using enzyme-linked immunoabsorbent assay (ELISA). IL- 12 production by DCs was inhibited by coculture with glioma cells. However, stimulation with lipopolysaccharide restored the production of IL- 12 by both human and mouse DCs. These data suggest that glioma cells suppress the maturation of DCs.

Prostanoids play a major role in the primary tumor-induced inhibition of dendritic cell differentiation

Production of immunosuppressive factors is one of the mechanisms by which tumors evade immunosurveillance. Soluble factors hampering dendritic cell (DC) development have recently been identified in culture supernatants derived from tumor cell lines. In this study, we investigated the presence of such factors in 24-h culture supernatants from freshly excised solid human tumors (colon, breast, renal cell carcinoma, and melanoma). While primary tumor-derived supernatant (TDSN) profoundly hampered the in vitro DC differentiation from CD14(+) plastic-adherent monocytes or CD34(+) precursors (based on morphology and CD1a/CD14 phenotype), the effects of tested tumor cell line-derived supernatants were minor. Cyclooxygenase (COX)-1- and COX-2-regulated prostanoids present in the primary TDSN were found to be solely responsible for the observed hampered differentiation of monocyte-derived DC (MoDC). In contrast, both prostanoids and IL-6 were found to contribute to the TDSN-induced inhibition of DC differentiation from CD34(+) precursor cells. While the addition of TDSN during differentiation interfered with the ability of CD34-derived DC to stimulate a primary allogeneic T cell response, it actually increased this ability of MoDC. These opposite effects were correlated to different effects of the TDSN on the expression levels of CD86 and HLA-DR on the DC from the different precursor origins. Although TDSN increased the T cell-stimulatory capacity of MoDC, TDSN inhibited the IL-12 production and increased the IL-10 production of MoDC, thus skewing them to a type-2 T cell-inducing phenotype. In conclusion, this study demonstrates that primary tumors negatively impact DC development and function through COX-1 and -2 regulated factors, whereas tumor-derived cell lines may lose this ability upon in vitro propagation.

A large quantity of CD3-/CD19-/CD16- lymphocytes in malignant pleural effusion from a patient with recurrent cholangio cell carcinoma

Tumor infiltrating lymphocytes (TILs) are candidates for adoptive cellular immunotherapy. Here we report on a patient whose TILs presented unusual lymphocyte antigens. Pleural effusions were collected from a 47-year-old man with recurrent cholangio cell carcinoma and malignant effusion. Effusion-associated lymphocytes (EALs) were separated by Ficoll-Hypaque gradient, and the EAL phenotype was determined by flow cytometry. The percentage of positive cells was determined for each lymphocyte-related differentiation antigen. The percentages of CD3+, CD19+, and CD16+ lymphocyte subpopulations among EALs were 20%, 7%, and 3%, respectively. Nearly 70% of EALs were CD3-/CD19-/CD56-/CD16- cells. The phenotypes of peripheral blood lymphocytes (PBLs) collected simultaneously from the patient's peripheral blood were CD3+ (52%), CD19+ (20%), and CD16+ (20%). When EALs were cultured in medium without pleural effusion, T cell-related antigens, but not B cell- or natural killer (NK) cell-related antigens, were newly expressed on EALs, and this expression reached a plateau after 48 h in culture. The proportions of CD3+, CD19+, and CD16+ cells were 69%, 7%, and 3%, respectively. However, when EALs were cultured in medium with pleural effusion, increased expression of T cell-related antigens was not observed; the proportions of CD3+, CD19+, and CD16+ cells were 16%, 6%, and 1%, respectively. Neither total cell numbers nor cellular viability of EALs changed significantly after in-vitro culture, suggesting that significant proliferation or death of EALs did not occur during the culture period. Co-culture of the patient's PBLs with autologous pleural effusion for 96 h did not alter the expression of lymphocyte-related antigens on the PBLs. These results indicate that expression of T cell-related antigens, but not B cell- or NK cell-related antigens, on EALs was blocked temporarily by the malignant pleural effusion. This is the first report concerning the existence of a large quantity of unclassified lymphocytes in which the T cell-related antigens were reversibly masked in the malignant pleural effusion.

Polycyclic aromatic hydrocarbons affect functional differentiation and maturation of human monocyte-derived dendritic cells

Polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene (BP) are environmental carcinogens exhibiting potent immunosuppressive properties. To determine the cellular bases of this immunotoxicity, we have studied the effects of PAHs on differentiation, maturation, and function of monocyte-derived dendritic cells (DC). Exposure to BP during monocyte differentiation into DC upon the action of GM-CSF and IL-4 markedly inhibited the up-regulation of markers found in DC such as CD1a, CD80, and CD40, without altering cell viability. Besides BP, PAHs such as dimethylbenz(a)anthracene and benzanthracene also strongly altered CD1a levels. Moreover, DC generated in the presence of BP displayed decreased endocytic activity. Features of LPS-mediated maturation of DC, such as CD83 up-regulation and IL-12 secretion, were also impaired in response to BP treatment. BP-exposed DC poorly stimulated T cell proliferation in mixed leukocyte reactions compared with their untreated counterparts. In contrast to BP, the halogenated arylhydrocarbon 2,3,7,8-tetrachlorodibenzo-p-dioxin, which shares some features with PAHs, including interaction with the arylhydrocarbon receptor, failed to phenotypically alter differentiation of monocytes into DC, suggesting that binding to the arylhydrocarbon receptor cannot mimic PAH effects on DC. Overall, these data demonstrate that exposure to PAHs inhibits in vitro functional differentiation and maturation of blood monocyte-derived DC. Such an effect may contribute to the immunotoxicity of these environmental contaminants due to the major role that DC play as potent APC in the development of the immune response.

Cell-based therapy approaches using dying cells: from tumour immunotherapy to transplantation tolerance induction

Cell-based therapies are promising approaches to treat uncontrolled pathologies, such as tumours. Apoptotic tumour cells have recently been proposed as a source of tumour-associated antigens to stimulate an efficient immune response. However, a complex relationship exists between apoptosis and the immune system. In this review, the different factors that may influence immune responses against apoptotic cells are detailed and discussed in the light of recent publications. These factors include the nature of the phagocytes and the receptors involved in apoptotic cell uptake, as well as the environment in which cells are dying. A possible distinction between apoptosis and necrosis by immune system sentinels adds a further level of complexity. The potential use of the immunomodulatory properties associated with apoptosis to favour engraftment and induce tolerance in transplantation is then discussed. In conclusion, this review will suggest appropriate conditions to efficiently and safely use apoptotic cells as a new cell therapy product.

Tumor-associated macrophages as a source of functional dendritic cells in ovarian cancer patients

We have generated dendritic cells (DCs) from tumor-associated macrophages (TAMs) obtained from ascites fluid or tumor specimens of ovarian cancer patients, and compared them phenotypically and functionally to DCs derived from the patients' peripheral blood mononuclear cells (PBMCs). Both immature and mature DCs could be generated from TAMs. However, TAM-derived DCs underwent maturation to a lesser degree than PBMC-derived DCs, as measured by DC receptor surface expression. Nonetheless, in allogeneic mixed lymphocyte reactions, TAM-derived DCs stimulated T cell proliferation as efficiently as PBMC-derived DCs. In addition, TAM-derived DCs presenting tumor Ags were capable of stimulating IFN-gamma secretion by tumor-specific T cell lines. Thus, TAMs isolated from ovarian cancer patients can be used to generate significant numbers of DCs. Therefore, TAMs have potential use for either ex vivo or in vivo DC-based immunotherapy, particularly in individuals in which more conventional sources of DCs have been depleted.

Dendritic cell density and activation status in human breast cancer -- CD1a, CMRF-44, CMRF-56 and CD-83 expression

Low CD1a-positive putative dendritic cell numbers in human breast cancer has recently been described and may explain the apparent 'poor immunogenicity' previously reported in breast cancer. Little attention has been given to dendritic cell activation within the tumour microenvironment, which is another reason why the in-situ immune response may be severely deficient. We have therefore examined CD1a expression as a marker for dendritic cells, together with CMRF-44 and -56 as markers of dendritic cell activation status, in 40 human breast cancers. The results demonstrate few or no CD1a-positive putative dendritic cells and minimal or no expression of the dendritic cell activation markers. Both dendritic cell number and dendritic cell activation appear substantially deficient in human breast cancers, regardless of tumour histological grade.

Tumour escape from immune surveillance through dendritic cell inactivation

Dendritic cells (DC) are central to the initiation of immunity. To induce immune reactivity, DC are recruited at the site of antigen expression, uptake antigens and migrate to secondary lymphoid organs while receiving activation signals delivered by pathogens, dying cells, and/or T cells. Tumours can escape the immune system by interfering with the migration of DC or by not providing the necessary activation signals. Moreover, tumours promote the secretion of factors that inhibit DC differentiation and functions. We will review the current knowledge of the physiopathology of DC in cancer, which paves the way for novel strategies of therapeutic intervention.

The generation of immunocompetent dendritic cells from CD34+ acute myeloid or lymphoid leukemia cells

The ability of CD34+ leukemic cells to differentiate to dendritic cells (DCs) was investigated in 18 acute myeloid leukemia (AML) and 4 lymphoid leukemia (ALL) patients. The generation of DCs was determined by the expression of DC-associated CD1a or CD83 (more than 30%) with costimulatory molecules, by CD80 antigens (>20%), and by the exhibition of allostimulatory activity. In the AML patients, allostimulatory mature DCs were generated from 3 of 9 M0 or M1, 2 of 5 M2,2 of 4 M4 or M5, and 3 of 4 ALL (L2) cases. In total, DCs were more efficiently induced from cases expressing over 75% of CD34+ among whole bone marrow mononuclear cells (8 of 12), compared with those under 75% (2 of 10; P < .05). B-cell (CD19), natural killer (NK)-cell (CD56), or T-cell (CD7) lineage markers, which were aberrantly expressed on the blasts, were rarely found on leukemic DCs at the end of the culture period, and myeloid (CD13, CD33), not lymphoid (CD10), markers were shown on ALL-derived DCs. In Philadelphia chromosome-positive ALL or AML patients with t (8;21), DCs were confirmed to be of leukemic origin by fluorescence in situ hybridization analysis.