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

Cytokines and antitumor immunity

Currently, the notion of immunosurveillance against tumors is enjoying something of a renaissance. Even if we still refuse to accept that tumors arising in the normal host are unable to trigger an immune response because of the lack of initiation ("danger") signals, there is no doubt that the immune system can be manipulated experimentally and by implication therapeutically to exert anti-tumor effects. For this activity to be successful, the appropriate cytokine milieu has to be provided, making cytokine manipulation central to immunotherapy. On the other hand, the major hurdle currently preventing successful immunotherapy is the ability of tumors to evolve resistant variants under the pressure of immune selection. Here, too, the cytokine milieu plays an essential role. The purpose of this brief review is to consider the current status of the application of cytokines in facilitating antitumor immunity, as well their role in inhibiting responses to tumors. Clearly, encouraging the former but preventing the latter will be the key to the effective clinical application of cancer immunotherapy.

Apoptosis and transplantation tolerance

Self-tolerance is maintained by several mechanisms including deletion (via apoptosis) and regulation. Acquired tolerance to allogeneic tissues and organs exploits similar strategies. One key difference between alloantigens and peptide antigens is the enormous number of T cells that are alloreactive. Accumulating evidence suggests that in the face of this large mass of potentially graft-destructive T cells, tolerance requires an initial wave of deletion. This creates a more level playing field in which a smaller number of regulatory T cells can then act to maintain an established tolerant state. Deletion of alloreactive T cells by apoptosis actively promotes immunoregulation as well, by interfering with proinflammatory maturation of antigen presenting cells. This article reviews the immune response to alloantigens, the development and use of both necrotic and apoptotic means of cell death during the evolution of the immune response, and the likely role and mechanisms by which apoptosis promotes, and may even be required for, transplantation tolerance.

Dendritic cell vaccination: new hope for the treatment of metastasized endocrine malignancies

Dendritic cells (DCs) are antigen-presenting cells that are involved in the induction of primary immune responses. The unique ability of DCs to activate naive and memory CD4+ and CD8+ T cells suggests that they could be used for the induction of a specific antitumour immunity. In the past few years, several in vitro and in vivo studies in rodents and humans have demonstrated that immunizations with DCs pulsed with tumour antigens result in protective immunity and rejection of established tumours in various malignancies. Here, we focus on recent results of how DCs regulate immune responses that are important for generating antitumour cytotoxic T cells, and summarize clinical vaccination trials for the treatment of endocrine and nonendocrine carcinomas. Preliminary results suggest that DC vaccines might be novel tools for antitumour immunotherapies to treat chemotherapy-resistant and radioresistant endocrine cancers, such as metastasized medullary thyroid carcinomas and other neuroendocrine carcinomas.

Induction of peripheral tolerance to experimental autoimmune myasthenia gravis by acetylcholine receptor-pulsed dendritic cells

Dendritic cells (DC) are usually regarded as antigen-presenting cells involved in T cell activation, but DC also directly and indirectly affect B cell activation, antibody synthesis, and isotype switch. In the present study, bone marrow (BM)-derived DC from healthy rats were pulsed in vitro with acetylcholine receptor (AChR) and injected subcutaneously into healthy Lewis rats. No clinical signs of the first phase of experimental autoimmune myasthenia gravis (EAMG) were observed during 3 weeks of observation. Upon immunization with AChR and complete Freund's adjuvant, the rats that had received AChR-pulsed DC did not develop clinical EAMG. This tolerance of rats injected with AChR-pulsed DC was associated with reduced expression of B cell-activating factor (BAFF) and by reduced numbers of B cells among splenic mononuclear cells (MNC) compared to rats injected with medium or unpulsed DC. Anti-AChR IgG antibody-secreting cells were decreased, while the ratio of IgG1:IgG2b isotypes was enhanced in rats treated with AChR-pulsed DC compared to control EAMG rats. These results demonstrate that AChR-pulsed DC induce peripheral tolerance to EAMG by possibly inhibiting the expression of BAFF and production of anti-AChR antibodies, providing a possible potential for immunotherapy of antibody-mediated autoimmune diseases.

Functional modulation of dendritic cells to suppress adaptive immune responses

In recent years, dendritic cells (DCs) have entered the center court of immune regulation. Dependent on their ontogeny, state of differentiation, and maturation and thereby a variable expression of membrane-bound and soluble molecules, DCs can induce immunostimulatory as well as immunoregulatory responses. This dual function has made them potential targets in vaccine development in cancer and infections as well as for the prevention and treatment of allograft rejection and autoimmune diseases. The present review is focused on the effect of immune-modulatory factors, such as cytokines and immunosuppressive drugs, and on the survival, differentiation, migration, and maturation of DC human subsets. A better understanding of DC immunobiology may lead to the development of specific therapies to prevent or dampen immune responses.

Immunotherapy of malignant melanoma

Several areas of immunotherapeutic research may ultimately improve the effectiveness of active specific immunotherapy for melanoma and other malignancies. Identification of the most relevant tumor antigens will continue to be a vital component of vaccine design. Optimizing delivery of these antigens by use of adjuvants, dendritic cells, or heat shock proteins will enhance the immunogenicity of vaccines. The use of DNA vaccines to deliver nucleotides that encode relevant antigens and immunologic molecules, such as costimulatory molecules, and the use of targeted therapy with immunocytokines have yielded promising results in animal studies. Finally, cutting-edge techniques such as quantitative polymerase chain reaction and gene/protein microarrays will be used to monitor the response to a vaccine and thereby guide management decisions. Although IFN-alpha 2b is the only FDA-approved adjuvant treatment for AJCC stage IIB/III melanoma, recent data failed to show a benefit in overall survival. For patients with AJCC stage IV melanoma, chemotherapy with dacarbazine is currently the standard of care, with modest response rates of 15% to 20%. The encouraging response rates and low toxicities that were reported in phase I/III trials suggest that active immunotherapy may prove to be the most effective adjuvant therapy. At present, there are no FDA-approved cancer vaccines for malignant melanoma, and the results of ongoing randomized phase III clinical trials are greatly anticipated.

Cellular immunotherapy after autologous hematopoietic stem cell transplantation: experimental strategies and clinical experiences

Recurrence of disease after autologous hematopoietic stem cell transplantation is at least partly due to contamination of the reinfused transplant with tumor cells, thereby limiting the clinical outcome after transplantation. On the other hand, immunological effector cells are capable of purging bone marrow transplants in vitro and of destroying disseminated tumor cells in vivo. Cellular immunotherapy subsequent to autologous stem cell transplantation is therefore expected to have a major impact on recurrence rates of the disease. In this review, we present various strategies utilizing immunologic effector cells for elimination of disseminated tumor cells and discuss the advantages and limitations of cellular immunotherapy after autologous hematopoietic stem cell transplantation.

Development of a clinical-scale method for generation of dendritic cells from PBMC for use in cancer immunotherapy

BACKGROUND

There is growing interest in the use of dendritic cells (DCs) for treatment of malignancy and infectious disease. Our goal was to develop a clinical scale method to prepare autologous DCs for cancer clinical trials.

METHODS

PBMC were collected from normal donors or cancer patients by automated leukapheresis, purified by counterflow centrifugal elutriation and placed into culture in polystyrene flasks at 1 x 10(6) cells/mL for 5-7 days at 37 degrees C, with 5% CO(2), with IL-4 and GM-CSF. Conditions investigated included media formulation, supplementation with heat in activated allogeneic AB serum or autologous plasma and time to harvest (Day 5 or Day 7). DCs were evaluated for morphology, quantitative yield, viability, phenotype and function, including mixed leukocyte response and recall response to tetanus toxoid and influenza virus.

RESULTS

DCs with a typical immature phenotype (CD14-negative, CD1a-positive, mannose receptor-positive, CD80-positive, CD83-negative) were generated most consistently in RPMI 1640 supplemented with 10% allogeneic AB serum or 10% autologous plasma. Cell yield was higher at Day 5 than Day 7, without detectable differences in phenotype or function. In pediatric sarcoma patients, autologous DCs had enhanced function compared with monocytes from which they were generated. In this patient group, starting with 8.0 +/- 3.7 x 10(8) fresh or cryopreserved autologous monocytes, DC yield was 2.1 +/- 1.0 x 10(8) cells, or 29% of the starting monocyte number.

DISCUSSION

In the optimized clinical-scale method, purified peripheral monocytes are cultured for 5 days in flasks at 1 x 10(6) cells/mL in RPMI 1640, 10% allogeneic AB serum or autologous plasma, IL-4 and GM-CSF. This method avoids the use of FBS and results in immature DCs suitable for clinical trials.

Mycobacteria target DC-SIGN to suppress dendritic cell function

Mycobacterium tuberculosis represents a world-wide health risk and immunosuppression is a particular problem in M. tuberculosis infections. Although macrophages are primarily infected, dendritic cells (DCs) are important in inducing cellular immune responses against M. tuberculosis. We hypothesized that DCs represent a target for M. tuberculosis and that the observed immuno-suppression results from modulation of DC functions. We demonstrate that the DC-specific C-type lectin DC-SIGN is an important receptor on DCs that captures and internalizes intact Mycobacterium bovis bacillus Calmette-Guérin (BCG) through the mycobacterial cell wall component ManLAM. Antibodies against DC-SIGN block M. bovis BCG infection of DCs. ManLAM is also secreted by M. tuberculosis-infected macrophages and has been implicated as a virulence factor. Strikingly, ManLAM binding to DC-SIGN prevents mycobacteria- or LPS-induced DC maturation. Both mycobacteria and LPS induce DC maturation through Toll-like receptor (TLR) signaling, suggesting that DC-SIGN, upon binding of ManLAM, interferes with TLR-mediated signals. Blocking antibodies against DC-SIGN reverse the ManLAM-mediated immunosuppressive effects. Our results suggest that M. tuberculosis targets DC-SIGN both to infect DCs and to down-regulate DC-mediated immune responses. Moreover, we demonstrate that DC-SIGN has a broader pathogen recognition profile than previously shown, suggesting that DC-SIGN may represent a molecular target for clinical intervention in infections other than HIV-1.

Distinct T cell subsets and cytokine production in cultures derived from transformation zone and squamous intraepithelial lesion biopsies of the uterine cervix

PROBLEM

The characterization of lymphocytes issued from squamous intraepithelial lesions (SIL) and from the transformation zone (TZ), where the majority of SIL occur, is important to understand the role of immunity in SIL development.

METHOD OF STUDY

We compared lymphocyte populations of the TZ and SIL with those of normal exocervix, using a technique allowing for the isolation of lymphocytes, either from the epithelium or from the underlying stroma of small biopsies.

RESULTS

The majority of cells derived from the epithelium of all biopsies were CD8+ T cells. Some SIL-derived cultures were characterized by an increased proportion of activated TCRgammadelta+. The production of the immunosuppressive cytokine IL10 was significantly higher in lymphocyte cultures from the normal TZ in comparison with the exocervix. A decreased percentage of effector T cells was observed in cultures derived from the stroma of normal TZ (TCRgammadelta+) or SIL (CD8+) in comparison with the exocervix.

CONCLUSIONS

Our results suggest that a low proportion of effector T cells and IL10 production could contribute to the predisposition of the TZ to the development of SIL and to the progression of SIL to cervical cancer.

Expression of interleukin-18, interferon-gamma and interleukin-10 in hepatocellular carcinoma

This is the first report on the detection of IL-18, IFN-gamma and IL-10 proteins in hepatocelllular carcinoma. In the apparently normal surrounding tissue, 13 out of 17 paired specimens showed positive immunoreactivity to IL-18 (76.5%) compared with six out of 17 in the tumour portion (35.3% of specimens). Thus, a significantly higher number of IL-18 positive specimens was found in the hepatocytes of apparently normal surrounding tissue compared with the tumour (P=0.018). In contrast, the number of specimens with positive immunoreactivity to the antibody against the Th1 cytokine, IFN-gamma expression in the hepatocytes was lower. Only one specimen from the apparently normal surrounding tissue (one out of 17; 5.9%) and three other specimens from the tumour portion (three out of 17; 17.6%) had positive immunoreactivity. Similarly, the expression of the Th2 cytokine, IL-10 in normal (four out of 17; 23.5%) and tumour portions (five out of 17; 29.4%) was also low. Thus, there did not appear to be predominant Th2 immune response as denoted by IL-10 expression. Using the Spearman correlation rank test, a significant correlation between IL-18 expression in the apparently normal surrounding tissue and high alpha-foetoprotein (AFP) levels of >350 IU/l. No correlation between IL-18 expression in the tumour portion and clinicopathological factors was found. There was also no correlation found between IL-18 and the other cytokines, namely, IFN-gamma and IL-10 expression These new findings provide additional information on the type of cytokines expressed in the tumour microenvironment and give a further insight into the role of cytokines in the pathogenesis of cancer which is critical for the development of effective immunotherapeutic approaches for cancer therapy in the future.

Dendritic cells and apoptosis in mycosis fungoides

BACKGROUND

The existence of an effective antitumour immune response in mycosis fungoides (MF) has been shown by the isolation of tumour-specific T-cell clones from such patients. Dendritic cells (DCs) are considered crucial for the induction of immunity, including resistance to tumours. Apoptotic tumour cells are a major source for tumour antigens processed and presented by DCs via cross-presentation. The production of interleukin (IL)-10 by MF tumour cells is acknowledged and may block DCs maturation leading to tumour tolerance.

OBJECTIVES

Cross-presentation of apoptotic tumour cells by DCs will induce immunity if the DCs mature, but tolerance if maturation does not occur. We now further characterize the DCs in skin infiltrates of patch/plaque-stage MF (PS) and tumour-stage MF (TS) in situ. Secondly, we demonstrate apoptosis in MF infiltrates in situ and analyse the association of apoptotic cells to immature DCs, mature DCs and IL-10-positive cells.

METHODS

Immunohistochemical staining (single, double, triple) employing novel markers specific for immature and mature DCs, IL-10 and a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labelling (TUNEL) test were done on representative skin biopsies from PS and TS.

RESULTS

In PS, the immature DCs are mostly lag/langerin + Langerhans cells (LCs). In the epidermis of PS, LCs predominate over fully mature DCs (non-LC type, CD83+, DC-lamp+). In the dermis of PS and TS, equal numbers of mature and immature (CD1a+, CD1c+) DCs are densely interspersed between the lymphocytic infiltrate. In TS, immature DCs mostly lack lag or langerin expression. Immature DCs with incorporated apoptotic cells were found rarely in PS but increasingly in TS. By triple staining in situ we could now show that strongly IL-10+ cells frequently surround immature DCs, some of them with incorporated apoptotic cells. CONCLUSIONS; DCs in MF perform a dual role, namely induction and maintenance of antitumour immunity, or, under less favourable circumstances such as production of IL-10 downregulation of antitumour immunity. The latter condition was mainly seen in TS, possibly explaining disease progression. Further in vitro studies are now required illuminating the role of DCs for the antitumour immune response in MF.

Dendritic cells: making progress with tumour regression?

Due to their potent ability to activate the immune system, dendritic cells (DC) are showing promise as potential adjuvants for tumour immunotherapy of cancer patients. However, little is known about the effect tumour cells can have on DC function. Indeed, the discovery of different DC subsets with different immunological functions indicates that the relationship between tumour cells and tumour-infiltrating DC subtypes is likely to be complex. There remains a lot to be understood about the effects of tumours on DC before we can expect to benefit from DC-based tumour immunotherapy of cancer patients. Here we review the recent advances being made in understanding DC phenotype and function in relation to interactions with different types of tumours.

Induction of anergic and regulatory T cells by plasmacytoid dendritic cells and other dendritic cell subsets

The induction of antigen-specific tolerance is critical for maintaining immune homeostasis and preventing autoimmunity. Because the central tolerance that eliminates potentially harmful autoreactive T cells is incomplete, peripheral mechanisms for suppressing self-reactive T cells play an important role. Dendritic cells (DCs) are professional antigen-presenting cells, which have an extraordinary capacity to stimulate naïve T cells and initiate primary immune responses. Recent accumulating evidence indicates that several subsets of human DCs also play a critical role in the induction of peripheral tolerance by anergizing effector CD4(+) and CD8(+) T cells or by inducing the differentiation of naïve T cells into T-regulatory cells, which produce interleukin (IL)-10. Human DC subsets with the property of suppressing an antigen-specific T-cell response include plasmacytoid DCs, which are either in an immature state or in a mature state induced by CD40 ligand stimulation, and monocyte-derived DCs, which are either in an immature state or have had their state modulated by treatment with IL-10 or CD8(+)CD28(-) T cells. These "tolerogenic" DCs may be relevant to therapeutic applications for autoimmune and allergic diseases as well as organ transplant rejection.

Gangliosides inhibit the development from monocytes to dendritic cells

Dendritic cell (DC) development and function is critical in the initiation phase of any antigen-specific immune response against tumours. Impaired function of DC is one explanation as to how tumours escape immunosurveillance. In the presence of various soluble tumour-related factors DC precursors lose their ability to differentiate into mature DC and to activate T cells. Gangliosides are glycosphingolipids shed by tumours of neuroectodermal origin such as melanoma and neuroblastoma. In this investigation we address the question of whether gangliosides suppress the development and function of monocyte-derived DC in vitro. In the presence of gangliosides, the monocytic DC precursors showed increased adherence, cell spreading and a reduced number of dendrites. The expression of MHC class II molecules, co-stimulatory molecules and the GM-CSF receptor (CD116) on the ganglioside-treated DC was significantly reduced. Furthermore, the function of ganglioside-treated DC was impaired as observed in endocytosis, chemotactic and T cell proliferation assays. In contrast to monocytic DC precursors, mature DC were unaffected even when higher doses of gangliosides were added to the culture. With regard to their carbohydrate structure, five different gangliosides (GM2, GM3, GD2, GD3, GT1b), which are typically shed by melanoma and neuroblastoma, were tested for their ability to suppress DC development and function. Suppression was induced by GM2, but not by the other gangliosides. These data suggest that certain gangliosides impair DC precursors, implying a possible mechanism for tumour escape.

Reduced virus specific T helper cell induction by autologous dendritic cells in patients with chronic hepatitis B - restoration by exogenous interleukin-12

Insufficient stimulatory capacities of autologous dendritic cells (DC) may contribute in part to impaired T cell stimulation and therefore viral persistence in patients with chronic hepatitis B virus (HBV) infection. In order to characterize the antigen presenting functions of DC from chronic HBV carriers and controls antigen specific T cell responses were analysed. CD34+ peripheral blood progenitor cells were differentiated to immature DC in the presence of GM-CSF, IL-6/IL-6R fusion protein and stem cell factor. Proliferative CD4+ T cell responses and specific cytokine release were analysed in co-cultures of DC pulsed with HBV surface and core antigens or tetanus toxoid and autologous CD4+ T cells. Cultured under identical conditions DC from chronic HBV carriers, individuals with acute resolved hepatitis B and healthy controls expressed similar phenotypical markers but chronic HBV carriers showed less frequent and weaker HBV antigen specific proliferative T helper cell responses and secreted less interferon-gamma while responses to the tetanus toxoid control antigen was not affected. Preincubation with recombinant IL-12 enhanced the HBV specific immune reactivities in chronic HBV patients and controls. In conclusion, the weak antiviral immune responses observed in chronic hepatitis B may result in part from insufficient T cell stimulating capacities of DC. Immunostimulation by IL-12 restored the HBV antigen specific T cell responses and could have some therapeutical benefit to overcome viral persistence.

DNA microarray analysis of the gene expression profiles of naïve versus activated tumor-specific T cells

T cells are a key element in effective cancer immunity, recognizing MHC-antigen peptide complexes on the surface of antigen presenting cells and translating these signals into cytotoxic effector T cell responses. In this study, we systematically investigated by DNA array analysis the expression profiles of 514 immunologically relevant genes in naïve and SP2/0 tumor-specific activated mouse T cell populations. Our data shows that naïve T cells expressed 37 (i.e., 7.6% of the 514) transcripts with expression level (EL) values of > or =2.0, while the activated T cells expressed 101 such transcripts. The expression levels of 9 (1.75% of 514) of the shared transcripts were equivalent in the two populations of T cells. Ninety-six genes were differently expressed upon T cell activation, with 71 (13.81%) being up-regulated and 25 (4.86%) down-regulated. The list of significantly affected genes includes numerous cytokines and their receptors (e.g., IL-2Ralpha, IL-6Ralpha, IL-7Ralpha, IL-16, IL-17R, TGF-beta), chemokines and chemokine receptors (e.g., RANTES, CCR7, CXCR4), alternate surface proteins (e.g., 4-1BB, GITR, integrins-alphaL and -beta7, L-selectin, CD6, CD45 and EMMPRIN), cytoplasmic signaling intermediates (e,g., GATA-3, 14-3-3-eta, CIS1, SMAD4 and JAK1) and an array of other molecules (e.g., NFkappa-B inducing kinase, LTBP3 and persephin), several of which are associated with Th1 responses, and T cell self-regulation or migration. Taken together, our data contribute to our understanding of the generalized processes that accompany T cell activation and, more specifically, to our understanding of the processes associated with T cell activation during antitumor responses.

Leukemic dendritic cells: potential for therapy and insights towards immune escape by leukemic blasts

Dendritic cells (DCs) are a system of potent antigen-presenting cells (APCs) specialized to initiate primary immune responses. DCs are considered important elements in the induction of specific antitumor cytotoxic effectors. At present, because of potential therapeutic implications, the critical role of DCs in cancer patients is under intensive investigation. Interactions between DCs and acute myeloid leukemia cells represent an attractive model for the study of DC physiology. Moreover, DCs can be a valuable therapeutic tool for the adjuvant treatment of leukemic patients. However, DC subsets in vivo may also be affected by leukemogenesis and may contribute to the escape of leukemia from immune control. The aim of this review is to shed further light on this paradoxical picture where the line between immune tolerance and immune defense is narrow.

The natural alliance between type I interferon and dendritic cells and its role in linking innate and adaptive immunity

Dendritic cells (DCs) are the most potent antigen-presenting cells (APCs) and thus play a pivotal role in induction of the immune response. Recent studies in both human and mouse models have shown that type I IFN, cytokines originally characterized for their antiviral activity and exerting multiple biologic effects, efficiently promote the differentiation and activation of DCs. These observations, together with the findings that DCs can express biologically relevant levels of type I interferon (IFN) and, in particular, that high amounts of these cytokines are released by specialized DC precursors (i.e., plasmacytoid DCs) in response to viral infections, strongly suggest the existence of a natural alliance between type I IFN and DCs, which is instrumental in ensuring an efficient immune response to both infectious agents and tumors. Further recent knowledge on the interactions between type I IFN and DCs emphasizes the importance of these cytokines in linking innate and adaptive immunity and may lead to new perspectives in their use as vaccine adjuvants as well as in strategies for the development of DC-based vaccines.

Interleukin-10-treated dendritic cells modulate immune responses of naive and sensitized T cells in vivo

Interleukin-10 is a pleiotropic cytokine known to have inhibitory effects on the accessory functions of dendritic cells. In vitro, interleukin-10 converts immature dendritic cells into tolerizing antigen- presenting cells. To assess whether interleukin-10-treated dendritic cells exert tolerizing effects in vivo, CD4+ T cells from DO11.10 ovalbumin-T cell receptor transgenic mice were transferred to syngeneic BALB/c recipients. Recipient animals were treated with ovalbumin-pulsed/unpulsed, interleukin-10-treated/untreated CD11c+ dendritic cells thereafter and ovalbumin-specific proliferation of lymph node cells was assessed by restimulation with the peptide in vitro. In prophylactic experiments, recipients received naive CD4+ DO11.10 T cells and were immunized with ovalbumin323-339 peptide in incomplete Freund's adjuvant after treatment with various subtypes of dendritic cells. Strong ovalbumin-specific proliferation was observed in animals immunized with control ovalbumin-dendritic cells. Minimal proliferation was found in mice treated with ovalbumin-pulsed, interleukin-10-treated dendritic cells. In therapeutic experiments, preactivated CD4+ DO11.10 T cells were transferred, and recipients were treated with dendritic cells as described. Ovalbumin-specific proliferation was strong in recipients treated with ovalbumin-dendritic cells. CD4+ T cell proliferation from ovalbumin-interleukin-10-dendritic cell treated animals was below background. When delayed type hypersensitivity reactions in the footpads of prophylactically or therapeutically vaccinated animals were tested, mice treated with ovalbumin-interleukin-10-dendritic cells showed no footpad swelling compared with controls. Rechallenge with the antigen in vitro and in vivo did not alter the inhibitory effect of interleukin-10-treated dendritic cells. Thus, interleukin-10-treated dendritic cells inhibit ovalbumin-specific immune responses in naive and sensitized mice.

Immature, but not inactive: the tolerogenic function of immature dendritic cells

The induction of antigen-specific T cell tolerance and its maintenance in the periphery is critical for the prevention of autoimmunity. Recent evidence shows that dendritic cells (DC) not only initiate T cell responses, but are also involved in silencing of T cell immune responses. The functional activities of DC are mainly dependent on their state of activation and differentiation, that is, terminally differentiated mature DC can efficiently induce the development of T effector cells, whereas immature DC are involved in maintenance of peripheral tolerance. The means by which immature DC maintain peripheral tolerance are not entirely clear, however, their functions include the induction of anergic T cells, T cells with regulatory properties as well as the generation of T cells that secrete immunomodulatory cytokines. This review summarizes the current knowledge about the immunoregulatory role of immature DC that might act as guardians for the induction and maintenance of T cell tolerance in the periphery.

Role of dendritic cells in graft-versus-host disease

A major barrier to successful allogeneic hematopoietic stem cell transplantation is graft-versus-host disease (GVHD). Until recently, the role of antigen presentation in the development of this disorder was unknown. The experimental finding that recipient antigen-presenting cells (APCs) were required for the development of CD8(+) T cell-dependent GVHD has led to a fundamental reappraisal of our ideas concerning the pathogenesis of this disease. Following transplantation, the origin (donor or recipient), number, lineage, and function of APCs within the recipient are altered significantly. Studies that test the influence of each of these factors upon graft-versus-host responses, including graft-versus-tumor responses, are beginning to emerge and suggest that APCs, such as dendritic cells, constitute a potential target for therapeutic manipulation.

Human CD4(+)CD25(+) regulatory, contact-dependent T cells induce interleukin 10-producing, contact-independent type 1-like regulatory T cells [corrected]

It has been recently demonstrated that regulatory CD4(+)CD25(+) CD45RO(+) T cells are present in the peripheral blood of healthy adults and exert regulatory function similar to their rodent counterparts. It remains difficult to understand how the small fraction of these T cells that regulate via direct cell-to-cell contact and not via secretion of immunosuppressive cytokines could mediate strong immune suppression. Here we show that human CD4(+)CD25(+) T cells induce long-lasting anergy and production of interleukin (IL)-10 in CD4(+)CD25(-) T cells. These anergized CD4(+)CD25(-) T cells then suppress proliferation of syngenic CD4(+) T cells via IL-10 but independent of direct cell contact, similar to the so-called type 1 regulatory T (Tr1) cells. This 'catalytic' function of CD4(+)CD25(+) T cells to induce Tr1-like cells helps to explain their central role for the maintenance of immune homeostasis.

Involvement of tumour necrosis factor-alpha-related apoptosis-inducing ligand in enhanced cytotoxicity of lipopolysaccharide-stimulated dendritic cells to activated T cells

Dendritic cells (DC) are potent antigen-presenting cells (APC) specialized in T-cell mediated immune responses, and also play critical roles in the homeostasis of T cells for controlling immune responses. In the present study, we demonstrated that during mouse bone-marrow-derived DC activation of ovalbumin (OVA)-specific Ia-kb-restricted T hybridoma cells, MF2.2D9 and OVA257-264-specific H-2kb-restricted RF33.70 T cells, respectively, both hybridomas undergo cell death, partially mediated via apoptotic ligand-tumour necrosis factor-alpha (TNF-alpha)-related apoptosis-inducing ligand (TRAIL). Lipopolysaccharide enhanced the cytotoxic effect on the two activated T hybridoma cells, which was correlated with up-regulation of TRAIL-expression on DC to some extent. The activation of caspase-3 in activated T hybridoma cells cocultured with DC contributed to the programmed cell death pathway T cells underwent. Therefore, our results show that activation-induced cell death of T hybridoma cells can be influenced by DC, suggesting that DC may be involved in elimination of activated T cells at the end of primary immune responses.

Generation of dendritic cell-based vaccines for cancer therapy

Dendritic cells play a major role in the generation of immunity against tumour cells. They can be grown under various culture conditions, which influence the phenotypical and functional properties of dendritic cells and thereby the consecutive immune response mainly executed by T cells. Here we discuss various conditions, which are important during generation and administration of dendritic cells to elicit a tumouricidal T cell-based immune response.

Clinical and immunological efficacy of intradermal vaccine plus lamivudine with or without interleukin-2 in patients with chronic hepatitis B

To evaluate therapeutic immunostimulation nine chronic hepatitis B patients received six monthly intradermal vaccinations with HBsAg in combination with daily lamivudine. Another five patients received six doses of the vaccine and daily lamivudine together with daily Interleukin-2 (IL-2) s.c. within 3 months in an open-labeled trial. Clinical efficacy was assessed by alanine transaminase levels and HBV serology. The induction of specific T and B cell responses was analyzed serially by 3H-thymidine uptake, ELISA and ELISPOT assays. After the therapy was stopped, seven of nine vaccine/lamivudine and two of five vaccine/lamivudine/IL-2 recipients did not have detectable HBV DNA. Four complete responders cleared the virus and had normalized ALT levels, however, one of these patients showed transient disease reactivation followed by spontaneous viral clearance and normal ALT five months later. Low frequencies of anti-HBs producing B cells and HBV specific T helper cells secreting predominantly interferon-gamma were induced by i.d. vaccine therapy. The ELISPOT technique demonstrated transient induction of HBV peptide specific cytotoxic T cells in seven HLA-A2 positive chronic HBV carriers. The preliminary data from this study demonstrate that the HBV surface antigen vaccine in combination with antiviral or immunomodulating drugs induced antiviral immune responses and consequently viral elimination may be achieved in patients with unfavorable prognosis.

Chemokines in cancer

Chemokines participate, by regulating cell trafficking and controlling angiogenesis, in the host response during infection and inflammation. Most of these mechanisms are also operating in cancer. The stimulation of angiogenesis and tumor growth--directly or indirectly through the recruitment of tumor-associated macrophages--are typical situations where chemokines promote tumor development. On the other hand, chemokines could be used to the benefit of cancer patients as they act in the recruitment of dendritic cells (DC) or/and effector cells or for their angiostatic properties. However, chemokine-mediated recruitment of immature DC within tumors, due to factors produced by the tumor milieu, could lead to the induction of immune tolerance and, therefore, novel strategies to eradicate tumors based on chemokines should attempt to avoid this risk.

CD4(+) and CD8(+) anergic T cells induced by interleukin-10-treated human dendritic cells display antigen-specific suppressor activity

Interleukin-10 (IL-10)-treated dendritic cells (DCs) induce an alloantigen- or peptide-specific anergy in various CD4(+) and CD8(+) T-cell populations. In the present study, we analyzed whether these anergic T cells are able to regulate antigen-specific immunity. Coculture experiments revealed that alloantigen-specific anergic CD4(+) and CD8(+) T cells suppressed proliferation of syngeneic T cells in a dose-dependent manner. The same effect was observed when the hemagglutinin-specific CD4(+) T-cell clone HA1.7 or tyrosinase-specific CD8(+) T cells were cocultured with anergic T cells of the same specificity. Anergic T cells did not induce an antigen-independent bystander inhibition. Suppression was dependent on cell-to-cell contact between anergic and responder T cells, required activation by antigen-loaded DCs, and was not mediated by supernatants of anergic T cells. Furthermore, anergic T cells displayed an increased extracellular and intracellular expression of cytotoxic T-lymphocyte antigen (CTLA)-4 molecules, and blocking of the CTLA-4 pathway restored the T-cell proliferation up to 70%, indicating an important role of the CTLA-4 molecule in the suppressor activity of anergic T cells. Taken together, our experiments demonstrate that anergic T cells induced by IL-10-treated DCs are able to suppress activation and function of T cells in an antigen-specific manner. Induction of anergic T cells might be exploited therapeutically for suppression of cellular immune responses in allergic or autoimmune diseases with identified (auto) antigens.

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.

Human peripheral blood monocyte-derived interleukin-10-induced semi-mature dendritic cells induce anergic CD4(+) and CD8(+) T cells via presentation of the internalized soluble antigen and cross-presentation of the phagocytosed necrotic cellular fragments

We examined the ability of human monocyte-derived interleukin (IL)-10-induced semi-mature dendritic cells (semi-mDCs) that had been pulsed with soluble protein and necrotic cellular fragments to induce an antigen (Ag)-specific anergy in CD4(+) and CD8(+) T cells. IL-10 converted normal immature DCs (iDCs) into semi-mDCs during the maturation. In contrast to normal iDCs and mature DCs, IL-10-induced semi-mDCs as well as IL-10-treated iDCs not only had reduced their allogeneic T cell-stimulatory capacity, but also induced an allogeneic Ag-specific anergy in T cells. Normal mDCs that had been pulsed with tetanus toxin (TT) or allogeneic necrotic cellular fragments caused further activation of TT-specific CD4(+) T cells or allogeneic fibroblast-specific CD8(+) T cells, Ag-pulsed IL-10-induced semi-mDCs induced an anergic state in both cell types. Thus, our results suggest that IL-10-induced semi-mDCs induce an Ag-specific anergy in CD4(+) and CD8(+) T cells via presentation of the internalized protein and cross-presentation of the phagocytosed cellular fragments.

Dendritic cells exposed in vitro to TGF-beta1 ameliorate experimental autoimmune myasthenia gravis

Experimental autoimmune myasthenia gravis (EAMG) is an animal model for human myasthenia gravis (MG), characterized by an autoaggressive T-cell-dependent antibody-mediated immune response directed against the acetylcholine receptor (AChR) of the neuromuscular junction. Dendritic cells (DC) are unique antigen-presenting cells which control T- and B-cell functions and induce immunity or tolerance. Here, we demonstrate that DC exposed to TGF-beta1 in vitro mediate protection against EAMG. Freshly prepared DC from spleen of healthy rats were exposed to TGF-beta1 in vitro for 48 h, and administered subcutaneously to Lewis rats (2 x 10(6)DC/rat) on day 5 post immunization with AChR in Freund's complete adjuvant. Control EAMG rats were injected in parallel with untreated DC (naive DC) or PBS. Lewis rats receiving TGF-beta1-exposed DC developed very mild symptoms of EAMG without loss of body weight compared with control EAMG rats receiving naive DC or PBS. This effect of TGF-beta1-exposed DC was associated with augmented spontaneous and AChR-induced proliferation, IFN-gamma and NO production, and decreased levels of anti-AChR antibody-secreting cells. Autologous DC exposed in vitro to TGF-beta1 could represent a new opportunity for DC-based immunotherapy of antibody-mediated autoimmune diseases.

IL-10 alters DC function via modulation of cell surface molecules resulting in impaired T-cell responses

IL-10 is a potent inhibitor of T-cell activation and has tolerizing effects on these cells. These effects are primarily mediated via modulation of antigen presenting cell function. Here, it is demonstrated that IL-10 completely inhibits LPS-induced DC maturation, resulting in altered DC-T-cell interactions and reduced T-cell responses. IL-10 inhibited LPS-induced upregulation of costimulatory molecules, MHC Class II, and the secretion of IL-12, TNF-alpha, IL-6, and IL-1beta by DCs, although it upregulated the SLAM (CD150) expression at both the mRNA and protein levels. IL-10 pre-treated DC did not respond to subsequent LPS activation and its stimulatory ability for allogeneic and antigen-specific T-cells was severely impaired. Importantly, T-cells derived from co-cultures with Ag-pulsed, IL-10-treated DC were impaired in their responses to subsequent Ag-specific restimulation. Transwell and DC-derived plasma membrane experiments indicated that the capacity of IL-10-treated DC to induce T-cell unresponsiveness results from alterations in the cell surface molecules rather than modulation of cytokine secretion.

Dendritic cells pulsed with intact Streptococcus pneumoniae elicit both protein- and polysaccharide-specific immunoglobulin isotype responses in vivo through distinct mechanisms

Immature bone marrow-derived myeloid dendritic cells (BMDCs) are induced to undergo phenotypic maturation and secretion of tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, IL-12, and IL-10 when pulsed in vitro with intact Streptococcus pneumoniae. After transfer to naive mice, pulsed BMDCs induce immunoglobulin (Ig) isotype responses specific for both protein and polysaccharide pneumococcal antigens, having in common the requirement for viable BMDCs, T cells, and B7-dependent costimulation in the recipient mice. Whereas primary Ig isotype responses to bacterial proteins uniformly require BMDC expression of major histocompatibility complex class II, CD40, and B7, and the secretion of IL-6, but not IL-12, similar requirements for antipolysaccharide Ig responses were only observed for the IgG1 isotype.

Antigen-presenting cells and tolerance induction

T cell tolerance induction to foreign and self-antigens has occupied research since the beginning of the understanding of the immune system. Much controversy still exists on this question even though new methods became available to investigate immunoregulatory mechanisms. Antigen-presenting cells play a pivotal role in transferring information from the periphery of the organism to lymphoid organs. There, they initiate not only the activation of naive T cells but seem to deliver important signals which result in T cell unresponsiveness with antigen-specific tolerance induction.

Functional monocyte-derived dendritic cells can be generated in chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) remains an incurable disease. Although modern available treatments are able to induce disease regression, relapse almost inexorably occurs. Therefore, novel therapeutic strategies aimed at reducing the disease relapse rate are very much needed. Among these, the induction of tumour-associated antigen-specific cytotoxic T lymphocytes (CTL), through either DNA vaccines or injection of idiotype pulsed dendritic cells (DCs), has been actively investigated with encouraging preliminary results in B-cell malignancies. As the CLL B lymphocyte characteristically expresses low amounts of surface immunoglobulin (Ig) and T cells from these patients have been reported to display impaired functional activity, there are concerns related to the possibility of generating specific cytotoxic antitumoral T cells in this disease. In addition, no information is presently available regarding the functional ability of CLL-derived DCs. In the present work, freshly purified monocytes from CLL patients and normal donors were induced to differentiate in granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-4 serum-free medium and compared for their morphological, phenotypic and functional characteristics. Our results demonstrate that: (1) functional DCs can be generated from CLL patients with similar phenotype and function to those observed from normal donors; (2) in contrast to normal control subjects, monocyte-derived DCs from CLL patients spontaneously secrete endogenous IL-10; and (3) interferon (IFN)-gamma in combination with CD40L plays a major role in priming DCs from CLL patients for IL-12 and IL-15 production. Overall, these results indicate that it is possible to derive functionally competent DCs from circulating monocytes in CLL patients.

Dendritic cells in cancer vaccines

Dendritic cells (DC) are recognized as the most potent antigen-presenting cells with the ability to stimulate naive resting T cells and to initiate primary immune responses. Encouraging results in vaccination studies in animal models and the development of protocols to generate sufficient numbers of human DC for clinical application have led to attempts to verify the feasibility and efficacy of this approach in patients in the context of Phase I/II vaccination trials. This review aims to present a concise overview of the current knowledge in DC development and biology and describes the recent data of the first published DC-based vaccination studies. These preliminary trials indicate that immunotherapies utilizing DC-presenting tumor-associated antigens can safely be administered to patients with cancer and induce significant immunologic and clinical responses.

Dendritic cells and their emerging clinical applications

Dendritic cells (DC) are now recognised as a unique leukocyte type, consisting of two or more subsets. The origins and functional inter-relationships of these cells are the subject of intense basic scientific investigation. They play important roles in initiating and directing immune responses, defending the host from pathogens and maintaining self tolerance. Fundamental studies are defining new molecules and mechanisms associated with DC function. The first methods for counting these rare blood cell populations are already providing interesting new clinical data. Indeed, abnormal DC function may contribute to deficiencies in the immune response against malignancies. Phase I trial data suggests that DC-based cancer vaccination protocols may contribute an important new biological approach to cancer therapy. Manipulation of DC to facilitate allogeneic transplantation and even to manage autoimmune disease are likely developments.

Generation in vitro of B-cell chronic lymphocytic leukaemia-proliferative and specific HLA class-II-restricted cytotoxic T-cell responses using autologous dendritic cells pulsed with tumour cell lysate

Immunotherapy using dendritic cells has shown encouraging results in both haematological and non-haematological malignancies. In this study, monocyte-derived dendritic cells from patients with B-CLL were cultured for 6 days in the presence of IL-4 and GM-CSF. Autologous B-CLL T-cells were cultured alone or with B-CLL lysate-pulsed and unpulsed autologous dendritic cells. IFN-gamma secretion was assessed using ELISA. Cytotoxicity was assessed, after 21 days in culture and re-stimulation, using flow cytometry with and without blockade by anti-HLA class I, anti-HLA class II, anti-CD4, anti-CD8 and anti-TCRalphabeta monoclonal antibodies. B-CLL T cells stimulated with B-CLL lysate-pulsed autologous dendritic cells showed a significant (P = 0.0004) increase in IFN-gamma secretion and a significant (P = 0.0008) increase in specific cytotoxicity to autologous B-cell targets, but none to autologous T cell or B cell targets from healthy individuals. B-CLL T cells cultured with (non-B-CLL) B-cell lysate-pulsed B-CLL dendritic cells showed no significant response. Pulsing dendritic cells from healthy volunteers with an autologous (non-B-CLL) B-cell lysate did not stimulate proliferation, cytokine production or cytotoxicity by autologous T cells. Pulsing B-CLL dendritic cells with allogeneic B-CLL lysates and culturing with autologous T-cells elicited cytotoxicity against autologous B-CLL targets in some cases, but not in others. Cytotoxicity was significantly reduced by blocking with anti-HLA class II (P = 0.001), anti-TCRalphabeta (P = 0.03) and anti-CD4 (P = 0.046) antibodies. Phenotyping of the responding T-cell population demonstrated the majority to be CD4 positive. Our data demonstrate that HLA class II-restricted proliferative and cytotoxic T-cell responses to B-CLL can be generated using autologous dendritic cells pulsed with tumour cell lysate.

Interleukin-10 promotes the maintenance of antitumor CD8(+) T-cell effector function in situ

Interleukin-10 (IL-10) is a multifunctional cytokine that can exert suppressive and stimulatory effects on T cells. It was investigated whether IL-10 could serve as an immunostimulant for specific CD8(+) cytotoxic T cell (CTL) in vivo after vaccination and, if so, under what conditions. In tumor prevention models, administration of IL-10 before, or soon after, peptide-pulsed primary dendritic cell immunization resulted in immune suppression and enhanced tumor progression. Injection of IL-10, however, just after a booster vaccine significantly enhanced antitumor immunity and vaccine efficacy. Analysis of spleen cells derived from these latter animals 3 weeks after IL-10 treatment revealed that the number of CD8(+) CD44(hi) CD122(+) T cells had increased and that antigen-specific proliferation in vitro was enhanced. Although cytotoxicity assays did not support differences between the various treatment groups, 2 more sensitive assays measuring antigen-specific interferon-gamma production at the single-cell level demonstrated increases in the number of antigen-specific responder T cells in animals in the vaccine/IL-10 treatment group. Thus, IL-10 may maintain the number of antitumor CD8(+) T cells. In adoptive transfer studies, the ability of IL-10 to maintain CTL function could be enhanced by the depletion of CD4(+) T cells. This suggests that IL-10 mediates contrasting effects on both CD4(+) and CD8(+) T cells that result in either immune dampening or immune potentiation in situ, respectively. Appreciation of this dichotomy in IL-10 immunobiology may allow for the design of more effective cancer vaccines designed to activate and maintain specific CD8(+) T-cell effector function in situ.

Dendritic cells and tumor immunity

Researchers and clinicians have tried for decades to use the mechanisms of immunity for the fight against cancer. Early attempts aimed at the instrumentation of soluble immune mediators such as antibodies or cytotoxic proteins for the therapy of malignancies. Major improvements in understanding the induction and regulation of cellular immunity have now made it possible to generate effector cells in cancer patients which are specific for the neoplastic disease. At the beginning of every cellular immune reaction against cancers tumor antigens have to be presented to T cells in order to activate them and drive them into clonal expansion. This is done by antigen presenting cells, the most powerful of which is the dendritic cell (DC). While DC were hard to isolate initially, they can be generated in large numbers in vitro today and manipulated in multiple ways before given back to a patient to induce tumor immunity. Thus, a great amount of hope lies in the use of DC as inducers of tumor immunity. However, the first clinical studies, which have now been completed with only limited success make clear, that still a lot of open questions remain to be answered. This review tries to give an overview of this rapidly developing field, mentioning the major conceptual approaches and techniques, but also discussing important caveats. The next years will show whether we can improve our understanding of DC biology and the mechanisms of immune induction strongly enough to effectively employ DC for immunotherapy of cancer.

Circumventing tolerance to a human MDM2-derived tumor antigen by TCR gene transfer

We identified a tumor-associated cytotoxic T lymphocyte (CTL) epitope derived from the widely expressed human MDM2 oncoprotein and were able to bypass self-tolerance to this tumor antigen in HLA-A*0201 (A2.1) transgenic mice and by generating A2.1-negative, allo-A2.1-restricted human T lymphocytes. A broad range of malignant, as opposed to nontransformed cells, were killed by high-avidity transgenic mouse and allogeneic human CTLs specific for the A2.1-presented MDM2 epitope. Whereas the self-A2.1-restricted human T cell repertoire gave rise only to low-avidity CTLs unable to recognize the natural MDM2 peptide, human A2.1+ T lymphocytes were turned into efficient MDM2-specific CTLs upon expression of wild-type and partially humanized high-affinity T cell antigen receptor (TCR) genes derived from the transgenic mice. These results demonstrate that TCR gene transfer can be used to circumvent self-tolerance of autologous T lymphocytes to universal tumor antigens and thus provide the basis for a TCR gene transfer-based broad-spectrum immunotherapy of malignant disease.

T-cell anergy and peripheral T-cell tolerance

The discovery that T-cell recognition of antigen can have distinct outcomes has advanced understanding of peripheral T-cell tolerance, and opened up new possibilities in immunotherapy. Anergy is one such outcome, and results from partial T-cell activation. This can arise either due to subtle alteration of the antigen, leading to a lower-affinity cognate interaction, or due to a lack of adequate co-stimulation. The signalling defects in anergic T cells are partially defined, and suggest that T-cell receptor (TCR) proximal, as well as downstream defects negatively regulate the anergic T cell's ability to be activated. Most importantly, the use of TCR-transgenic mice has provided compelling evidence that anergy is an in vivo phenomenon, and not merely an in vitro artefact. These findings raise the question as to whether anergic T cells have any biological function. Studies in rodents and in man suggest that anergic T cells acquire regulatory properties; the regulatory effects of anergic T cells require cell to cell contact, and appear to be mediated by inhibition of antigen-presenting cell immunogenicity. Close similarities exist between anergic T cells, and the recently defined CD4+ CD25+ population of spontaneously arising regulatory cells that serve to inhibit autoimmunity in mice. Taken together, these findings suggest that a spectrum of regulatory T cells exists. At one end of the spectrum are cells, such as anergic and CD4+ CD25+ T cells, which regulate via cell-to-cell contact. At the other end of the spectrum are cells which secrete antiinflammatory cytokines such as interleukin 10 and transforming growth factor-beta. The challenge is to devise strategies that reliably induce T-cell anergy in vivo, as a means of inhibiting immunity to allo- and autoantigens.

Predominant Th2/Tc2 polarity of tumor-infiltrating lymphocytes in human cervical cancer

Cytotoxic T lymphocytes (Tc) play a central role in cellular immunity against cancers. The cytotoxic potential of freshly isolated tumor-infiltrating lymphocytes (TILs) is usually not expressed. This suggests the possible existence of as yet unspecified and perhaps complex immunosuppressive factors or cytokines that affect the anti-tumor capacity of these TILs in the tumor milieu. In the present study, we demonstrated for the first time that TILs derived from human cervical cancer tissue consist mainly of Th2/Tc2 phenotypes. In vitro kinetic assays further revealed that cancer cells could direct the tumor-encountered T cells toward the Th2/Tc2 polarity. Cancer cells promote the production of IL-4 and down-regulate the production of IFN-gamma in cancer-encountered T cells. The regulatory effects of cervical cancer cells are mediated mainly by IL-10, and TGF-beta plays only a synergistic role. The cancer-derived effects can be reversed by neutralizing anti-IL-10 and anti-TGF-beta Abs. IL-10 and TGF-beta are present in cancer tissue and weakly expressed in precancerous tissue, but not in normal cervical epithelial cells. Our study strongly suggests important regulatory roles of IL-10 and TGF-beta in cancer-mediated immunosuppression.

Interleukin-10 and the interleukin-10 receptor

Interleukin-10 (IL-10), first recognized for its ability to inhibit activation and effector function of T cells, monocytes, and macrophages, is a multifunctional cytokine with diverse effects on most hemopoietic cell types. The principal routine function of IL-10 appears to be to limit and ultimately terminate inflammatory responses. In addition to these activities, IL-10 regulates growth and/or differentiation of B cells, NK cells, cytotoxic and helper T cells, mast cells, granulocytes, dendritic cells, keratinocytes, and endothelial cells. IL-10 plays a key role in differentiation and function of a newly appreciated type of T cell, the T regulatory cell, which may figure prominently in control of immune responses and tolerance in vivo. Uniquely among hemopoietic cytokines, IL-10 has closely related homologs in several virus genomes, which testify to its crucial role in regulating immune and inflammatory responses. This review highlights findings that have advanced our understanding of IL-10 and its receptor, as well as its in vivo function in health and disease.