Maturation, activation, and protection of dendritic cells induced by double-stranded RNA

Ebola virus-like particles protect from lethal Ebola virus infection

The filovirus Ebola causes hemorrhagic fever with 70-80% human mortality. High case-fatality rates, as well as known aerosol infectivity, make Ebola virus a potential global health threat and possible biological warfare agent. Development of an effective vaccine for use in natural outbreaks, response to biological attack, and protection of laboratory workers is a higher national priority than ever before. Coexpression of the Ebola virus glycoprotein (GP) and matrix protein (VP40) in mammalian cells results in spontaneous production and release of virus-like particles (VLPs) that resemble the distinctively filamentous infectious virions. VLPs have been tested and found efficacious as vaccines for several viruses, including papillomavirus, HIV, parvovirus, and rotavirus. Herein, we report that Ebola VLPs (eVLPs) were immunogenic in vitro as eVLPs matured and activated mouse bone marrow-derived dendritic cells, assessed by increases in cell-surface markers CD40, CD80, CD86, and MHC class I and II and secretion of IL-6, IL-10, macrophage inflammatory protein (MIP)-1alpha, and tumor necrosis factor alpha by the dendritic cells. Further, vaccinating mice with eVLPs activated CD4+ and CD8+ T cells, as well as CD19+ B cells. After vaccination with eVLPs, mice developed high titers of Ebola virus-specific antibodies, including neutralizing antibodies. Importantly, mice vaccinated with eVLPs were 100% protected from an otherwise lethal Ebola virus inoculation. Together, our data suggest that eVLPs represent a promising vaccine candidate for protection against Ebola virus infections and a much needed tool to examine the genesis and nature of immune responses to Ebola virus.

Generation of mature dendritic cells fully capable of T helper type 1 polarization using OK-432 combined with prostaglandin E(2)

Dendritic cell (DC) administration appears to be a very promising approach for the immunotherapy of cancer. The results of clinical studies have suggested that the nature and the magnitude of antitumor immune responses are critically affected by DC functions, including production of T helper type 1 (Th1)-inducing cytokines, activation of T cell subsets and natural killer (NK) cells, and migration from peripheral tissues to the T cell area of the draining lymph nodes. Administration of immature DCs could fail to fully stimulate antigen-specific immune responses and might induce tolerance under some conditions. In this study, we developed a method to obtain fully mature DCs, and we compared in detail the DCs thus obtained with those obtained using a maturation stimulus termed monocyte-derived medium (MCM)-mimic, which is a mixture of recombinant cytokines and prostaglandin E(2) (PGE(2)) mimicking the components of monocyte-conditioned medium. Using DCs derived from monocytes of advanced cancer patients in this study, we found that DCs stimulated with OK-432 alone showed phenotypes similar to those of mature DCs induced using MCM-mimic, though with better secretion of IL-6 and IL-12. However, these DCs were found to have poor migratory capacity associated with the marginal expression of CCR7. When OK-432 was combined with PGE(2), the CCR7 expression and migratory capacity of DCs were significantly improved without impairing other immuno-stimulatory functions. These results suggest that stimulation with the combination of OK-432 and PGE(2) could be applicable as an alternative to MCM-mimic in clinical trials which require fully matured DCs to induce Th1-type immune responses against tumor cells even in patients with advanced cancer.

Salmonella enterica serovar Typhimurium expressing mutant lipid A with decreased endotoxicity causes maturation of murine dendritic cells

A major Salmonella component involved in cellular activation is the lipopolysaccharide (LPS) molecule which can act as a dendritic cell (DC) stimulator. The structure of the lipid A domain of the LPS molecule dictates its immunostimulatory capacity with various cell types. In this study, the role of lipid A as an integral component of Salmonella in stimulating murine DCs was studied by using a Salmonella enterica serovar Typhimurium lpxM mutant with defective lipid A. This study revealed that a mutation in lpxM did not significantly affect the ability of bacteria to activate DCs. Although the lpxM mutant less tumor necrosis factor alpha, interleukin-1beta, and inducible nitric oxide synthase than the parental strain, this was only seen at lower multiplicities of infection (MOIs). Both strains upregulated surface molecule expression on DCs and augmented the T-cell-stimulating capacity of these cells in an MOI-independent manner. Thus, the lpxM mutation did not appear to affect the stimulatory capacity of the Salmonella mutant.

Activation of human dendritic cells is modulated by components of the outer membranes of Neisseria meningitidis

Neisseria meningitidis serogroup B is a major cause of life-threatening meningitis and septicemia worldwide, and no effective vaccine is available. Initiation of innate and acquired immune responses to N. meningitidis is likely to be dependent on cellular responses of dendritic cells (DC) to antigens present in the outer membrane (OM) of the meningococcus. In this study, the responses of human monocyte-derived DC (mo-DC) to OM isolated from parent (lipopolysaccharide [LPS]-replete) meningococci and from a mutant deficient in LPS were investigated. Parent OM selectively up-regulated Toll-like receptor 4 (TLR4) mRNA expression and induced mo-DC maturation, as reflected by increased production of chemokines, proinflammatory cytokines, and CD83, CD80, CD86, CD40, and major histocompatibility complex (MHC) class II molecules. In contrast, LPS-deficient OM selectively up-regulated TLR2 mRNA expression and induced moderate increases in both cytokine production and expression of CD86 and MHC class II molecules. Preexposure to OM, with or without LPS, augmented the allostimulatory properties of mo-DC, which induced proliferation of naive CD4+ CD45RA+ T cells. In addition, LPS-replete OM induced a greater gamma interferon/interleukin-13 ratio in naive T cells, whereas LPS-deficient OM induced the reverse profile. These data demonstrate that components of the OM, other than LPS, are also likely to be involved in determining the levels of DC activation and the nature of the T-helper immune response.

Aspects of the innate and adaptive immune responses to acute infections with BVDV

The immune response can be divided into innate and adaptive components that synergise to effect the clearance of pathogens. Recently, it has been realised that these arms of the immune system do not act independently, the magnitude and quality of the adaptive response is dependent on signals derived from the innate response. Here, we review the innate immune responses to bovine viral diarrhoea virus infections of cattle and relate these changes to immunosuppression and the subsequent development of the adaptive immune response.

Additive inhibition of dendritic cell allostimulatory capacity by alcohol and hepatitis C is not restored by DC maturation and involves abnormal IL-10 and IL-2 induction

BACKGROUND

Excessive alcohol use results in impaired immunity, and it is associated with increased incidence and progression of chronic hepatitis C virus (HCV) infection. Here we investigated the effects of HCV infection and alcohol on myeloid dendritic cells (DC) that are critical in antiviral immunity.

METHODS

Immature and mature DCs were generated from monocytes of chronic HCV infected patients (HCV-DC) and controls (N-DC) with IL-4 plus granulocyte-macrophage colony stimulating factor (GM-CSF) in the presence or absence of alcohol (25 mM). DC allostimulatory capacity was tested in mixed lymphocyte reaction (MLR) and cytokine production by ELISA.

RESULTS

Allostimulatory capacity of HCV-DCs was reduced compared to N-DCs and it was further inhibited by alcohol treatment (p < 0.01). MLR was also decreased with alcohol-treated N-DCs. DC phenotypic markers and apoptosis were comparable between HCV-DCs and N-DCs irrespective of alcohol treatment. However, HCV-DCs and alcohol-treated N-DCs exhibited elevated IL-10 and reduced IL-12 production. Reduced MLR with HCV-DCs and its further inhibition by alcohol coexisted with decreasing IL-2 levels (p < 0.017). DC maturation partially improved but failed to fully restore the reduced allostimulatory function of either alcohol-treated or alcohol-naïve HCV-DCs (p < 0.018).

CONCLUSIONS

Alcohol and HCV independently and together inhibit DC allostimulatory capacity, increase IL-10, reduce IL-12 and IL-2 production that cannot be normalized by DC maturation. HCV and alcohol interact to modulate innate and adaptive immune responses via dendritic cells.

Activation of Discoidin Domain Receptor 1 Facilitates the Maturation of Human Monocyte-Derived Dendritic Cells Through the TNF Receptor Associated Factor 6/TGF-β-Activated Protein Kinase 1 Binding Protein 1β/p38α Mitogen-Activated Protein Kinase Signaling Cascade

Maturation of dendritic cells (DCs) is critical for their ability to stimulate resting naive T cells in primary immune responses. Previous studies demonstrated that collagen, such as type I collagen, could facilitate DC maturation; however, the basis of collagen-mediated DC maturation remains unclear. Discoidin domain receptor 1 (DDR1) is a nonintegrin collagen receptor constitutively expressed in a variety of epithelial cells, including tumor cells, and is inducible in leukocytes. In this study, we evaluated the role of DDR1 in DC maturation using human monocyte-derived DCs. Two DDR1 isoforms, DDR1a and DDR1b, were expressed in both immature and mature DCs. Activation of DDR1 on immature DCs resulted in their partial maturation; however, DDR1 activation markedly amplified TNF-alpha- and LPS-induced phenotypic and functional maturation of DCs through activation of p38 mitogen-activated protein kinase (MAPK), suggesting the involvement of DDR1b in this process. Activation of DDR1b on differentiated DDR1b-overexpressing THP-1 cells or DDR1 on mature DCs induced the formation of TNFR associated factor 6 (TRAF6)/TGF-beta-activated kinase 1 binding protein 1beta/p38alpha MAPK complex and p38alpha autophosphorylation. Transfection of differentiated DDR1b-overexpressing THP-1 cells with dominant negative TRAF6 completely abrogated DDR1b-mediated p38 MAPK phosphorylation, indicating a critical role of TRAF6 in DDR1b-mediated p38 MAPK activation. Taken together, our data suggest that DDR1b-collagen interaction augments the maturation of DCs in a tissue microenvironment through a unique TRAF6/TGF-beta-activated kinase 1 binding protein 1beta/p38alpha MAPK signaling cascade and contributes to the development of adaptive immune responses.

Subcellular localization of Toll-like receptor 3 in human dendritic cells

Toll-like receptor (TLR)3 recognizes dsRNA and transduces signals to activate NF-kappaB and IFN-beta promoter. Type I IFNs (IFN-alpha/beta) function as key cytokines in anti-viral host defense. Human fibroblasts express TLR3 on the cell surface, and anti-TLR3 mAb inhibits dsRNA-induced IFN-beta secretion by fibroblasts, suggesting that TLR3 acts on the cell surface to sense viral infection. In this study, we examined the expression and localization of human TLR3 in various DC subsets using anti-TLR3 mAb. In monocyte-derived immature dendritic cells (iDCs), TLR3 predominantly resided inside the cells but not on the cell surface. iDCs produced IL-12p70 and IFN-alpha and -beta in response to poly(I:C). Similar response was observed in iDCs treated with rotavirus-derived dsRNA. These responses could not be blocked by pretreatment of the cells with anti-TLR3 mAb. In CD11c(+) blood DCs, cytoplasmic retention of TLR3 was also observed as in monocyte-derived iDCs, again endorsing a different TLR3 distribution profile from fibroblasts. In precursor DC2, however, TLR3 could not be detected inside or outside the cells. Of note, there was a putative centrosomal protein that shared an epitope with TLR3 in myeloid DCs and precursor DC2, but not peripheral blood monocytes. Immunoelectron microscopic analysis revealed that TLR3, when stably expressed in the murine B cell line Ba/F3, was specifically accumulated in multivesicular bodies, a subcellular compartment situated in endocytic trafficking pathways. Thus, regulation and localization of TLR3 are different in each cell type, which may reflect participation of cell type-specific multiple pathways in antiviral IFN induction via TLR3.

The polysaccharide capsule of Cryptococcus neoformans interferes with human dendritic cell maturation and activation

The ability of encapsulated and acapsular strains of Cryptococcus neoformans to activate dendritic cells (DC) derived from monocytes stimulated with granulocyte macrophage-colony stimulating factor and interleukin-4 was evaluated. Profound differences in DC response to encapsulated and acapsular C. neoformans strains were observed. In particular, (i) the acapsular strain was easily phagocytosed by immature DC, and the process induced several molecular markers, such as major histocompatibility complex (MHC) class I and class II, CD40, and CD83, which are characteristic of mature DC; (ii) the encapsulated strain did not up-regulate MHC class I and class II and CD83 molecules; (iii) the soluble capsular polysaccharide glucuronoxylomannan (GXM) is unable to regulate MHC class I and class II molecules; (iv) the addition of monoclonal antibody to GXM (anti-GXM) to the encapsulated strain facilitated antigen-presenting cell maturation by promoting ingestion of C. neoformans via Fc receptor for immunoglobulin G (FcgammaR)II (CD32) and FcgammaRIII (CD16); (v) pertubation of FcRgammaII or FcgammaRIII was insufficient to promote DC maturation; and (vi) optimal DC maturation permitted efficient T cell activation and differentiation, as documented by the enhancement of lymphoproliferation and interferon-gamma production. These results indicate that the C. neoformans capsule interferes with DC activation and maturation, indicating a new pathway by which the fungus may avoid an efficient T cell response.

Recent advances in the discovery and delivery of vaccine adjuvants

Adjuvant design has historically had a touch of alchemy at its heart due to its reliance on the complex biology of innate immune activation. However, a new mechanistic understanding of innate immunity, combined with new adjuvant and delivery platforms for exploiting this knowledge, has led to significant advances recently. Although many challenges remain, the field is moving rapidly and the proper tools and methodologies are in place for the use of traditional drug discovery engines in guiding the development of vaccine adjuvants. In this review, we outline the current trends in immune potentiator, delivery system and adjuvant design that will shape the vaccines of the future.

Immunological and regulatory functions of uninfected and virus infected immature and mature subtypes of dendritic cells--a review

In 1868, dendritic cells (DCs) were discovered in human skin by Paul Langerhans using gold staining. These cells were named Langerhans cells (LCs) after their discoverer who, due to their dendrites, regarded them as neurons. One hundred and eleven years were to pass until it was discovered that in vertebrates these cells originate in the bone marrow as monocytes. In the 1980s, DC research was mostly carried out on DCs that are present in different tissues of mice and humans. These studies revealed that after interaction with foreign antigens, skin LCs/DCs migrate through the lymph vessels to the draining lymph nodes and induce the two arms of the immune response. The isolation of DCs from tissue cell suspensions opened the way to studies on the cells' surface proteins and their ability to stimulate immune responses. During the 1990s, studies revealed the role of DCs in the activation of naive T cells in the lymph nodes and the regulatory properties of DCs in lymph nodes, thymus, gut, and spleen. Part A of the review deals with the DC system of human and mice and immunological and regulatory functions of subsets of DCs in the skin with reference to migrating and stationary DCs, as well as the connection between DCs and the nervous system. Furthermore, the origin of both follicular DCs that are present in lymphoid tissues and thymic DCs are discussed. Part B is devoted to virus infections of DCs with an emphasis on infections caused by human herpes viruses. Part C presents the modulation of DC gene expression in response to the influenza virus. Contemporary research focuses on the role of DCs in the immune systems of vertebrates. Moreover, studies are being conducted on the regulatory functions of DCs by tissue cells in different organs of vertebrates.

Dendritic cell uptake of human apoptotic and necrotic neutrophils inhibits CD40, CD80, and CD86 expression and reduces allogeneic T cell responses: relevance to systemic vasculitis

OBJECTIVE

There is a breakdown of tolerance to neutrophil components during systemic vasculitis, which is marked by autoantibodies and T cells with specificity for proteinase 3 or myeloperoxidase, expressed on the surface of apoptotic neutrophils. This study was undertaken to investigate the effects of human apoptotic and necrotic neutrophils on human dendritic cell (DC) phenotype and ability to stimulate allogeneic T cell proliferation.

METHODS

DCs were generated from human peripheral blood mononuclear cells and allowed to interact with human apoptotic and necrotic neutrophils in the presence or absence of tumor necrosis factor alpha (TNFalpha). Effects on DC phenotype and ability to stimulate T cell proliferation were observed.

RESULTS

Immature DCs engulfed apoptotic and necrotic neutrophils, resulting in up-regulation of CD83 and class II major histocompatibility complex molecules, but down-regulation of CD40, CD80, and CD86, and a decreased ability to stimulate T cell proliferation. When TNFalpha was added in combination with apoptotic neutrophils, the inhibitory effects were overcome to some extent.

CONCLUSION

Our results suggest that DC uptake of apoptotic or necrotic neutrophils alone does not shift the immune response from tolerance to autoimmunity in systemic vasculitis. However, cytokines found at sites of inflammation in vasculitis patients may act as maturation factors for DCs, and in combination with apoptotic neutrophils, may lead to an autoimmune phenotype.

Dramatic increase of telomerase activity during dendritic cell differentiation and maturation

Telomerase, the reverse transcriptase that maintains telomere DNA, is usually undetectable in most adult tissues but is positive in embryonic tissues and in cancers. In addition, freshly islolated or in vitro-activated lymphocytes were shown to express high levels of telomerase activity, although its expression in myeloid cells including dendritic cells (DCs) is largely unknown. Here, we investigated telomerase activity during the differentiation and maturation process of DCs. In vitro culture of bone marrow (BM) cells with granulocyte macrophage-colony stimulating factor and interleukin-4 induced a dramatic increase of telomerase activity accompanied with their differentiation into DCs. Furthermore, stimulation with microbial components such as lipopolysaccharide (LPS), which triggers maturation of DCs, augmented the activity. In vivo responses of telomerase activity were also observed in splenic DCs by injection of LPS intraperitoneally. It is interesting that in old mice, telomerase activity of splenic DCs was significantly higher than young mice but rather decreased after LPS stimulation. By measuring expression of cell-surface activation markers, splenic DCs of old mice responded poorly to LPS stimulation. Such poor responses to LPS were also observed in BM-derived DCs. These different features of DCs between young and old mice may contribute to a pathogenesis to microbial infections.

Tumor vaccines: from gene therapy to dendritic cells--the emerging frontier

Gene-modified tumor cells have been employed in a vaccination setting to trigger therapeutic antitumor immunity against metastatic renal cell carcinoma. Recent studies suggest that dendritic cells may be even more potent, because these cells can efficiently present tumor antigens to effector T cells, thereby circumventing the poor antigen-presenting properties of tumor cells. Proof of concept studies using antigen-loaded dendritic cells have been performed, establishing clear evidence of vaccine safety and bioactivity by stimulating immunologic and even clinical responses in cancer patients. Nevertheless, key aspects of such vaccination remain undefined. The critical challenge remains to understand fully the mechanisms of action and to further optimize dendritic cell vaccines to produce effective, durable, and, ultimately, therapeutic antitumor responses.

Immune modulation by silencing IL-12 production in dendritic cells using small interfering RNA

RNA interference is a mechanism of posttranscriptional gene silencing that functions in most eukaryotic cells, including human and mouse. Specific gene silencing is mediated by short strands of duplex RNA of approximately 21 nt in length (termed small interfering RNA or siRNA) that target the cognate mRNA sequence for degradation. We demonstrate here that RNAi can be used for immune modulation by targeting dendritic cell (DC) gene expression. Transfection of DC with siRNA specific for the IL-12 p35 gene resulted in potent suppression of gene expression and blockade of bioactive IL-12 p70 production without affecting unrelated genes or cellular viability. Inhibition of IL-12 was associated with increased IL-10 production, which endowed the DC with the ability to stimulate production of Th2 cytokines from allogenic T cells in vitro. Furthermore, siRNA-silenced DC lacking IL-12 production were poor allostimulators in MLR. IL-12-silenced and KLH-pulsed DC polarized the immune response toward a Th2 cytokine profile in an Ag-specific manner. These data are the first to demonstrate that RNA interference is a potent and specific tool for modulating DC-mediated immune responses.

Influenza virus-induced dendritic cell maturation is associated with the induction of strong T cell immunity to a coadministered, normally nonimmunogenic protein

We evaluated the proposal that during microbial infection, dendritic cells (DCs) undergo maturation and present a mixture of peptides derived from the microbe as well as harmless environmental antigens. Mice were exposed to an aerosol of endotoxin free ovalbumin (OVA) in the absence or presence of influenza virus. In its absence, OVA failed to induce B and T cell responses and even tolerized, but with influenza, OVA-specific antibodies and CD8+ cytolytic T lymphocytes developed. With or without infection, OVA was presented selectively in the draining mediastinal lymph nodes, as assessed by the comparable proliferation of infused, CD8+ and CD4+, TCR transgenic T cells. In the absence of influenza, these OVA-specific T cells produced little IL-2, IL-4, IL-10, and IFN-gamma, but with infection, both CD4+ and CD8+ T cells made high levels of IL-2 and IFN-gamma. The OVA plus influenza-treated mice also showed accelerated recovery to a challenge with recombinant vaccinia OVA virus. CD11c+ DCs from the mediastinal lymph nodes of infected mice selectively stimulated both OVA- and influenza-specific T cells and underwent maturation, with higher levels of MHC class II, CD80, and CD86 molecules. The relatively slow (2-3 d) kinetics of maturation correlated closely to the time at which OVA inhalation elicited specific antibodies. Therefore respiratory infection can induce DC maturation and simultaneously B and T cell immunity to an innocuous antigen inhaled concurrently.

Presentation of exogenous antigens on major histocompatibility complex (MHC) class I and MHC class II molecules is differentially regulated during dendritic cell maturation

During maturation, dendritic cells (DCs) regulate their capacity to process and present major histocompatibility complex (MHC) II-restricted antigens. Here we show that presentation of exogenous antigens by MHC I is also subject to developmental control, but in a fashion strikingly distinct from MHC II. Immature mouse bone marrow-derived DCs internalize soluble ovalbumin and sequester the antigen intracellularly until they receive an appropriate signal that induces cross presentation. At that time, peptides are generated in a proteasome-dependent fashion and used to form peptide-MHC I complexes that appear at the plasma membrane. Unlike MHC II, these events do not involve a marked redistribution of preexisting MHC I molecules from intracellular compartments to the DC surface. Moreover, out of nine stimuli well known to induce the phenotypic maturation of DCs and to promote MHC II presentation, only two (CD40 ligation, disruption of cell-cell contacts) activated cross presentation on MHC I. In contrast, formation of peptide-MHC I complexes from endogenous cytosolic antigens occurs even in unstimulated, immature DCs. Thus, the MHC I and MHC II pathways of antigen presentation are differentially regulated during DC maturation.

Dendritic cell-based immunotherapy

Dendritic cell (DC)-based vaccinations represent a promising approach for the immunotherapy of cancer and infectious diseases as DCs play an essential role in initiating cellular immune responses. A number of clinical trials using ex vivo-generated DCs have been performed so far and only minor toxicity has been reported. Both the induction of antigen-specific T cells and clinical responses have been observed in vaccinated cancer patients. Nevertheless, DC-based immunotherapy is still in its infancy and there are many issues to be addressed such as antigen loading procedures, DC source and maturational state, migration properties, route, frequency, and dosage of DC vaccination. The increasing knowledge of DC biology should be used to improve the efficacy of this new therapy.

Viral vectors for dendritic cell-based immunotherapy

Dendritic cells (DCs) constitute a specialised system of antigen-presenting cells with a high capacity to induce and to modulate the immune response against microbial, tumour and self-antigens. New techniques to generate large amounts of DCs together with the molecular identification of human tumour-associated antigens (TAA) have opened new ways for antigen-specific cancer immunotherapies. DCs loaded either with TAA-derived MHC class I-specific synthetic peptides or with whole tumour cell preparations have been used in numerous clinical trials evaluating the efficacy of DCs in patients with cancer. However, the disadvantages of DCs pulsed with synthetic peptides from TAA include the uncertainty regarding the longevity of antigen presentation, the restriction by the patient's haplotype and the relatively low number of known MHC class I and in particular of MHC class II helper cell-related epitopes. Whole tumour cell preparations are difficult to standardise, and they depend on the availability of tumour cells. Thus the utilisation of viral vectors genetically modified to express TAA for the ex vivo transduction of DCs is an attractive alternative to achieve a MHC I- and MHC II-restricted presentation of tumoural antigens. To induce protective anti-tumoural immune response an increasing number of modified viral vectors have been used to transduce DCs. Although high transduction efficacies were reported for several viruses, analysis of the interaction of viral vectors with DCs has revealed several viral mechanisms that interfere with main functions of DCs, dampening somewhat the initial optimism in the field of DC transduction. However, promising results with different vectors have been achieved. In this review we summarise available data and discuss advantages and drawbacks of currently available vectors.

Dendritic cells and measles virus infection

Measles is a major cause of childhood mortality in developing countries which is mainly attributed to the ability of measles virus (MV) to suppress general immune responses. Paradoxically, virus-specific immunity is efficiently induced, which leads to viral clearance from the host and confers long-lasting protection against reinfection. As sensitisers of pathogen encounter and instructors of the adaptive immune response, dendritic cells (DCs) may play a decisive role in the induction and quality of the MV-specific immune activation. The ability of MV wild-type strains in particular to infect DCs in vitro is dearly established, and the receptor binding haemagglutinin protein of these viruses essentially determines this particular tropism. DC maturation as induced early after MV infection is likely to be of crucial importance for the induction of MV-specific immunity. DCs may, however, be instrumental in MV-induced immunosuppression. (1) T cell depletion could be brought about by DC-T cell fusion or TRAIL-mediated induction of apoptosis. (2) Inhibition of stimulated IL-12 production from MV-infected DCs might affect T cell responses in qualitative terms in favouring Th2 and suppressing Th1 responses. (3) The viral glycoprotein complex expressed at high levels on infected DCs late in infection is able to directly inhibit T cell proliferation by surface contact-dependent negative signalling. This most likely accounts for the failure of infected DC cultures to stimulate allogeneic and inhibit mitogen-stimulated T cell proliferation in vitro and the pronounced proliferative unresponsiveness of T cell ex vivo to polyclonal and antigen-specific stimulation which is a central finding of MV-induced immunosuppression.

Relationships among murine CD11c(high) dendritic cell subsets as revealed by baseline gene expression patterns

The functional relationships and properties of different subtypes of dendritic cells (DC) remain largely undefined. To better characterize these cells, we used global gene analysis to determine gene expression patterns among murine CD11c(high) DC subsets. CD4(+), CD8alpha(+), and CD8alpha(-) CD4(-) (double negative (DN)) DC were purified from spleens of normal C57/BL6 mice and analyzed using Affymetrix microarrays. The CD4(+) and CD8alpha(+) DC subsets showed distinct basal expression profiles differing by >200 individual genes. These included known DC subset markers as well as previously unrecognized, differentially expressed CD Ags such as CD1d, CD5, CD22, and CD72. Flow cytometric analysis confirmed differential expression in nine of nine cases, thereby validating the microarray analysis. Interestingly, the microarray expression profiles for DN cells strongly resembled those of CD4(+) DC, differing from them by <25 genes. This suggests that CD4(+) and DN DC are closely related phylogenetically, whereas CD8alpha(+) DC represent a more distant lineage, supporting the historical distinction between CD8alpha(+) and CD8alpha(-) DC. However, staining patterns revealed that in contrast to CD4(+) DC, the DN subset is heterogeneous and comprises at least two subpopulations. Gene Ontology and literature mining analyses of genes expressed differentially among DC subsets indicated strong associations with immune response parameters as well as cell differentiation and signaling. Such associations offer clues to possible unique functions of the CD11c(high) DC subsets that to date have been difficult to define as rigid distinctions.

Activation by prion peptide PrP106-126 induces a NF-kappaB-driven proinflammatory response in human monocyte-derived dendritic cells

Specific prion peptides have been shown to mimic the pathologic isoform of the prion protein (PrP) and to induce a neurotoxic effect in vitro and in vivo. As monocytic cells are thought to play a role in the transmission and pathogenesis of prion disease, the use of these peptides in regulating monocytic cell function is under intense investigation. In the current study, we characterize the ability of prion peptide PrP(106-126) to activate specific signaling pathways in human monocyte-derived dendritic cells (DCs). Electrophoretic mobility shift assays establish the activation of transcription factor nuclear factor-kappaB within 15 min of exposure, with as little as 25 micro M peptide. This signaling cascade results in the up-regulation of inflammatory cytokines interleukin (IL)-1beta, IL-6, and tumor necrosis factor alpha (TNF-alpha) at the mRNA and protein levels. Phenotypic activation of DCs exposed to PrP(106-126) is partly a result of an autocrine TNF-alpha response and results in an increased ability of these cells to induce lymphocyte proliferation. The effects of PrP(106-126) on DCs were elicited through a receptor complex distinct from that used by human monocytes, demonstrating the ability of this peptide to interact with a multiplicity of receptors on various cell types. Together, these data suggest an involvement of DCs in prion disease pathogenesis.

Intranodal injection of semimature monocyte-derived dendritic cells induces T helper type 1 responses to protein neoantigen

Dendritic cells (DCs) represent the most potent antigen-presenting cells of the immune system capable of initiating primary immune responses to neoantigens. Here we characterize the primary CD4 T-cell immune response to protein keyhole limpet hemocyanin (KLH) in 5 metastatic melanoma patients undergoing a tumor peptide-based dendritic cell vaccination trial. Monocyte-derived dendritic cells displaying a semimature phenotype, as defined by surface markers, were loaded ex vivo with antigen and injected intranodally at weekly intervals for 4 weeks. All patients developed a strong and long-lasting delayed-type hypersensitivity reactivity to KLH, which correlated with the induction of KLH-dependent proliferation of CD4 T cells in vitro. Secondary in vitro stimulation with KLH showed significant increase in interferon-gamma and interleukin-2 (IL-2) but not IL-4, IL-5, nor IL-10 secretion by bulk T cells. On the single-cell level, most TH1 cells among in vitro-generated KLH-specific T-cell lines confirmed the preferential induction of a KLH-specific type 1 T helper immune response. Furthermore, the induction of KLH-specific antibodies of the IgG2 subtype may reflect the induction of a type 1 cytokine profile in vivo after vaccination. Our results indicate that intranodal vaccination with semimature DCs can prime strong, long-lasting CD4 T-cell responses with a TH1-type cytokine profile in cancer patients.

Differential effects of bovine viral diarrhoea virus on monocytes and dendritic cells

Various pathogens have been shown to infect antigen-presenting cells and affect their capacity to interact with and stimulate T-cell responses. We have used an antigenically identical pair of non-cytopathic (ncp) and cytopathic (cp) bovine viral diarrhoea virus (BVDV) isolates to determine how the two biotypes affect monocyte and dendritic cell (DC) function. We have shown that monocytes and DCs are both susceptible to infection with ncp BVDV and cp BVDV in vitro. In addition, monocytes infected with ncp BVDV were compromised in their ability to stimulate allogeneic and memory CD4(+) T cell responses, but DCs were not affected. This was not due to down-regulation of a number of recognized co-stimulatory molecules including CD80, CD86 and CD40. Striking differences in the response of the two cell types to infection with cytopathic virus were seen. Dendritic cells were not susceptible to the cytopathic effect caused by cp BVDV, whereas monocytes were killed. Analysis of interferon (IFN)-alpha/beta production showed similar levels in monocytes and DCs exposed to cp BVDV, but none was detected in cells exposed to ncp BVDV. We conclude that the prevention of cell death in DCs is not associated with enhanced production of IFN-alpha/beta, as proposed for influenza virus, but is by a distinct mechanism.

Interaction of discoidin domain receptor 1 isoform b (DDR1b) with collagen activates p38 mitogen-activated protein kinase and promotes differentiation of macrophages

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase activated by collagen. DDR1 is constitutively expressed in a variety of normal and transformed epithelial cells and plays a role in cell migration and differentiation through as yet unidentified signaling pathways. We previously reported inducible expression of DDR1 in human leukocytes and suggested a role for the DDR1a isoform in leukocyte migration through extracellular matrix. Here, we evaluated the contribution of DDR1 in the differentiation of the human monocytic THP-1 cells overexpressing these isoforms and of primary macrophages. Interestingly, collagen activation of DDR1b, but not DDR1a, further promoted phorbol ester-induced differentiation of THP-1 cells as determined by reduced cell proliferation and up-regulated expression of HLA-DR, CD11c, CD14, and CD40. Collagen activation of DDR1b also induced the recruitment and phosphorylation of Shc and subsequent phosphorylation of p38 mitogen-activated protein (MAP) kinase and its substrate ATF2. A p38 MAP kinase inhibitor, SB203580, completely inhibited DDR1b-mediated HLA-DR expression. Activation of DDR1 endogenously expressed on macrophages also up-regulated their HLA-DR expression in a p38 MAP kinase-dependent manner. Thus, DDR1b in response to collagen transduces signals that promote maturation/differentiation of HLA-DR-positive antigen-presenting cells and contributes to the development of adaptive immunity in a tissue microenvironment.

BCG promotes cord blood monocyte-derived dendritic cell maturation with nuclear Rel-B up-regulation and cytosolic I kappa B alpha and beta degradation

Mycobacterium bovis bacillus Calmette-Guerin (BCG) is given to millions of neonates in developing countries as a vaccine against Mycobacterium tuberculosis; however, little is known about the initiation of response in neonatal dendritic cells (DCs) to BCG. To address this issue, the interaction of BCG with human cord blood monocyte-derived DCs was studied. We showed that BCG could promote cord blood monocyte-derived DC maturation by up-regulation of CD80, CD83, CD86, CD40, and MHC class II molecules and down-regulation of mannose receptor. BCG was able to induce similar levels of tumor necrosis factor-alpha and IL-10 but no bioactive IL-12p70 production from cord blood DCs as from adult blood DCs. Functionally BCG-treated cord blood DCs had higher ability to induce mixed lymphocyte reaction than non-BCG-treated cord blood DCs. Both non-BCG-treated and BCG-treated cord blood DCs efficiently induced a high level of IL-10, medium level of interferon-gamma, but little IL-4 production by cord blood naïve CD4+ T cells. Heat shock protein 65, a key component of BCG, had no effect on cord blood DC maturation in terms of CD86, MHC class II, and mannose receptor up-regulation. During the BCG-induced maturation process of cord blood DCs, nuclear transcription factor Rel-B was up-regulated and cytosolic Rel-B down-regulated with cytosolic IkappaB alpha and beta degradation. These results suggest that BCG can promote cord blood monocyte-derived DC maturation, and that the mechanism is through the up-regulation of nuclear Rel-B secondary to the degradation of cytosolic IkappaB alpha and beta.

Kinetics of the immune response during HBV and HCV infection

The innate immune system has a role not only in protecting the host during the initial period of virus infection, but also in shaping the nature of the adaptive immune response. In this review, we follow the kinetics of the virologic and immunologic events occurring from the time of hepatitis B virus (HBV) and hepatitis C virus (HCV) infection. We primarily discuss how the early events after infection might influence the development of the adaptive immune response in these 2 important viral infections and how new strategies for more efficient preventive and therapeutic vaccines can be derived from this knowledge.

Activation of tumor antigen-specific cytotoxic T lymphocytes (CTLs) by human dendritic cells infected with an attenuated influenza A virus expressing a CTL epitope derived from the HER-2/neu proto-oncogene

The development of cancer vaccines requires approaches to induce expansion and functional differentiation of tumor antigen-specific cytotoxic T lymphocyte (CTL) effectors which posses cytolytic capability and produce cytokines. Efficient induction of such cells is hindered by the poor immunogenicity of tumor antigens and by the poor transduction efficiency of dendritic cells (DCs) with current nonreplicating vectors. We have investigated the use of influenza A virus, a potent viral inducer of CTLs, as a vector expressing the immunodominant HER-2 CTL epitope KIF (E75). For this purpose, an attenuated influenza A/PR8/34 virus with a truncated nonstructural (NS1) gene was generated containing the E75 epitope in its neuraminidase protein (KIF-NS virus). Stimulation of peripheral blood mononuclear cells from healthy donors and of tumor-associated lymphocytes from ovarian and breast cancer patients with DCs infected with KIF-NS virus (KIF-NS DC) induced CTLs that specifically recognized the peptide KIF and HER-2-expressing tumors in cytotoxicity assays and secreted gamma interferon (IFN-gamma) and interleukin-2 at recall with peptide. Priming with KIF-NS DCs increased the number of E75(+) CD45RO(+) cells by more than 10-fold compared to nonstimulated cells. In addition, KIF-NS virus induced high levels of IFN-alpha in DCs. This is the first report demonstrating induction of human epitope-specific CTLs against a tumor-associated antigen with a live attenuated recombinant influenza virus vector. Such vectors may provide a novel approach for tumor antigen delivery, lymphocyte activation, and differentiation in human cancer vaccine development.

Bruton's tyrosine kinase defect in dendritic cells from X-linked agammaglobulinaemia patients does not influence their differentiation, maturation and antigen-presenting cell function

X-linked agammaglobulinaemia (XLA) is a primary immunodeficiency disease characterized by very low levels or even absence of circulating antibodies. The immunological defect is caused by deletions or mutations of Bruton's tyrosine kinase gene (Btk), whose product is critically involved in the maturation of pre-B lymphocytes into mature B cells. Btk is expressed not only in B lymphocytes but also in cells of the myeloid lineage, including dendritic cells (DC). These cells are professional antigen presenting cells (APC) that play a fundamental role in the induction and regulation of T-cell responses. In this study, we analysed differentiation, maturation, and antigen-presenting function of DC derived from XLA patients (XLA-DC) as compared to DC from age-matched healthy subjects (healthy-DC). We found that XLA-DC normally differentiate from monocyte precursors and mature in response to lipopolysaccharide (LPS) as assessed by de novo expression of CD83, up-regulation of MHC class II, B7.1 and B7.2 molecules as well as interleukin (IL)-12 and IL-10 production. In addition, we demonstrated that LPS stimulated XLA-DC acquire the ability to prime naïve T cells and to polarize them toward a Th1 phenotype, as observed in DC from healthy donors stimulated in the same conditions. In conclusion, these data indicate that Btk defect is not involved in DC differentiation and maturation, and that XLA-DC can act as fully competent antigen presenting cells in T cell-mediated immune responses.

Vaccine immunity to pathogenic fungi overcomes the requirement for CD4 help in exogenous antigen presentation to CD8+ T cells: implications for vaccine development in immune-deficient hosts

Systemic fungal infections with primary and opportunistic pathogens have become increasingly common and represent a growing health menace in patients with AIDS and other immune deficiencies. T lymphocyte immunity, in particular the CD4+ Th 1 cells, is considered the main defense against these pathogens, and their absence is associated with increased susceptibility. It would seem illogical then to propose vaccinating these vulnerable patients against fungal infections. We report here that CD4+ T cells are dispensable for vaccine-induced resistance against experimental fungal pulmonary infections with two agents, Blastomyces dermatitidis an extracellular pathogen, and Histoplasma capsulatum a facultative intracellular pathogen. In the absence of T helper cells, exogenous fungal antigens activated memory CD8+ cells in a major histocompatibility complex class I-restricted manner and CD8+ T cell-derived cytokines tumor necrosis factor alpha, interferon gamma, and granulocyte/macrophage colony-stimulating factor-mediated durable vaccine immunity. CD8+ T cells could also rely on alternate mechanisms for robust vaccine immunity, in the absence of some of these factors. Our results demonstrate an unexpected plasticity of immunity in compromised hosts at both the cellular and molecular level and point to the feasibility of developing vaccines against invasive fungal infections in patients with severe immune deficiencies, including those with few or no CD4+ T cells.

Immune responsiveness, tolerance and dsRNA: implications for traditional paradigms

Double-stranded (ds)RNA motifs are central to immune regulation and block tolerance to tumor-associated, self- and foreign antigens. In addition, they could explain why DNA vectors encoding self-replicating mRNA (replicons) are more immunogenic than conventional DNA vaccines. Accumulating evidence on the immunomodulatory roles of dsRNAs warrants a reconsideration of various models of immune homeostasis.

Double-stranded RNA-exposed human keratinocytes promote Th1 responses by inducing a Type-1 polarized phenotype in dendritic cells: role of keratinocyte-derived tumor necrosis factor alpha, type I interferons, and interleukin-18

Dendritic cells play a key role in establishing the class of immune response against invading pathogens. Upon engagement with double-stranded RNA, a major bioactive constituent of many virus types, immature dendritic cells develop into type 1 immunostimulatory dendritic cells that promote Th1 responses. Immature dendritic cells reside in the epithelia and are in close contact with keratinocytes. We studied to what extent dendritic cells can also adopt a type 1 immunostimulatory dendritic cell phenotype indirectly, as a result of the interaction with keratinocytes responding to double-stranded RNA. In contrast to supernatants from keratinocytes activated by the combination of tumor necrosis factor alpha and interleukin-1beta, supernatants from keratinocytes activated by synthetic double-stranded RNA, polyriboinosinic polyribocytidylic acid, comprised tumor necrosis factor alpha and type I interferons, which induced maturation of human monocyte-derived immature dendritic cells. In addition, dendritic cells matured in the presence of these supernatants strongly biased the development of Th1 cells from naive Th cells. This bias was dependent on keratinocyte-derived interferon-alpha/beta and interleukin-18, as neutralization of both interferon-alpha/beta and interleukin-18 in the keratinocyte culture supernatant reduced the development of interferon-gamma-producing Th cells. These findings suggest that keratinocytes can contribute to the development of selective Th1/Th2 responses through the induction of maturation and functional polarization of dendritic cells, indicating a novel role for keratinocytes as initiators and regulators of cutaneous T-cell-mediated inflammation. In addition, these results support the concept that, in addition to direct interaction with pathogens, dendritic cells may also be activated and primed by pathogen indirectly, via the effect of resident tissue cells responding to pathogen.

Apoptosis: programmed cell death at a molecular level

OBJECTIVES

To characterize cell surface receptors, their ligands, and their proteins in the 2 major pathways of apoptosis; the components that promote/suppress these interactions; the noninflammatory removal of apoptotic bodies by dendritic cells; and methods of assay in studies of cell death. To describe: how deregulation of apoptosis may contribute to autoimmunity, cancer, and neurodegenerative disorders and strategies some viruses have evolved that interfere with the host's apoptotic pathways.

METHODS

The authors reviewed and compiled literature on the extrinsic (tumor necrosis factor [TNF] receptor superfamily and ligands) and intrinsic (mitochondria-associated) apoptotic pathways, the pro- and antiapoptotic proteins of the B-cell follicular lymphoma (Bcl)-2 family, the nuclear factor (NF)-kappaB family of proteins, commonly used laboratory methods to distinguish apoptosis from necrosis, the recognition and removal by phagocytosis of apoptotic cells by dendritic cells, and viral strategies to avoid a host's apoptotic response.

RESULTS

The 2 major pathways of apoptosis are (1). FasL and other TNF superfamily ligands induce trimerization of cell-surface death receptors and (2). perturbated mitochondria release cytochrome c, the flavoprotein apoptosis-inducing factor, and second mitochondria-derived activator of caspases/DIABLO (a protein that directly neutralizes inhibitors of apoptotic proteins and activates proteases). Catalytically inactive cysteine proteases, called caspases, and other proteases are activated, ultimately leading to cell death with characteristic cellular chromatin condensation and DNA cleavage to fragments of approximately 180 bp. The inhibitory/promoting action of Bcl-2 family members is involved in the release of cytochrome c, an essential factor for the mitochondrial-associated pathway. A balance between inhibition/promotion determines a cell's fate. The NF-kappaB family in the cytoplasm of cells activates various genes carrying the NF-kappaB response element, such as members of the inhibitor of apoptotic proteins family. A few of the more common methods to detect apoptotic cell death are described, which use immunochemical, morphologic and flow cytometric methods, and genetic markers. Exposed phosphatidylserine at the outer leaflet of the plasma membrane of the apoptotic cell serves as a possible receptor for phagocytosis by immature dendritic cells. These cells phagocytize both apoptotic and necrotic cells, but only the latter induce maturation to become fully functional antigen-presenting cells. Viral inhibitors of apoptosis allow increased virus replication in cells, possibly resulting in their oncogenicity.

CONCLUSIONS

Balanced apoptosis is crucial in development and homeostasis, and all multicellular organisms have a physiologically programmed continuum of pathways to apoptotic cell death. Further studies of the control at the molecular level of key components and promoters/suppressors of apoptosis may provide better approaches to treatment of autoimmune diseases, malignancies, and neurodegenerative disorders. Many important questions remain regarding the advantages of modifying apoptotic programs in clinical situations.

Type I IFNs differentially modulate IL-12p70 production by human dendritic cells depending on the maturation status of the cells and counteract IFN-gamma-mediated signaling

Type I IFNs (IFNalpha/beta) are approved for the treatment of a variety of diseases, including the autoimmune disease multiple sclerosis (MS). The proinflammatory cytokines IL-12 and IFN-gamma have been proposed to contribute to the pathogenesis of MS. Since dendritic cells (DCs) are recognized as major producers of IL-12p70 and promote the development of IFN-gamma-producing Th1 cells, we investigated the direct effect of IFNalpha/beta on monocyte-derived DCs at different stages of development. We demonstrate that IFNalpha/beta enhance IL-12p70 production by immature DCs but inhibit IL-12p70 production by mature DCs. Importantly, IFNalpha/beta strongly counteracted the IL-12-enhancing effect of IFN-gamma on DCs irrespective of their maturation status. Exposure of DCs to IFNalpha/beta during maturation does not affect their maturation or cytokine profile upon CD40 ligation. The differential modulatory effect of IFNalpha/beta on the IL-12-producing capacity of DCs and their cross-regulatory effect on IFN-gamma may reduce inflammatory processes and therefore be therapeutically effective in MS.

The natural killer cell-mediated killing of autologous dendritic cells is confined to a cell subset expressing CD94/NKG2A, but lacking inhibitory killer Ig-like receptors

The cognate NK-DC interaction in inflamed tissues results in NK cell activation and acquisition of cytotoxicity against immature DC (iDC). This may represent a mechanism of DC selection required for the control of downstream adaptive immune responses. Here we show that killing of monocyte-derived iDC is confined to the NK cell subset that expresses CD94/NKG2A, but not killer Ig-like receptors (KIR). Consistent with these data, the expression of HLA-E (i.e. the cellular ligand of CD94/NKG2A) was down-regulated in iDC. On the other hand, HLA-B and HLA-C down-regulation in iDC was not sufficient to induce cytotoxicity in NK cells expressing KIR3DL1 or KIR2DL. Remarkably, CD94/NKG2A(+)KIR(-) NK cells were heterogeneous in their ability to kill iDC and an inverse correlation existed between their CD94/NKG2A surface density and the magnitude of their cytolytic activity. It is conceivable that the reduced CD94/NKG2A surface density enables these cells to efficiently sense the decrease of HLA-E surface expression in iDC. Finally, most NK cells that lysed iDC did not kill mature DC that express higher amounts of HLA class I molecules (including HLA-E)as compared with iDC. However, a small NK cell subset was capable of killing not only iDC but also mature DC.

Glatiramer acetate (copolymer-1, copaxone) promotes Th2 cell development and increased IL-10 production through modulation of dendritic cells

Glatiramer acetate (GA; copolymer-1, Copaxone) suppresses the induction of experimental autoimmune encephalomyelitis and reduces the relapse frequency in relapsing-remitting multiple sclerosis. Although it has become clear that GA induces protective degenerate Th2/IL-10 responses, its precise mode of action remains elusive. Because the cytokine profile of Th cells is often regulated by dendritic cells (DC), we studied the modulatory effects of GA on the T cell regulatory function of human DC. This study shows the novel selective inhibitory effect of GA on the production of DC-derived inflammatory mediators without affecting DC maturation or DC immunostimulatory potential. DC exposed to GA have an impaired capacity to secrete the major Th1 polarizing factor IL-12p70 in response to LPS and CD40 ligand triggering. DC exposed to GA induce effector IL-4-secreting Th2 cells and enhanced levels of the anti-inflammatory cytokine IL-10. The anti-inflammatory effect of GA is mediated via DC as GA does not affect the polarization patterns of naive Th cells activated in an APC-free system. Together, these results reveal that APC are essential for the GA-mediated shift in the Th cell profiles and indicate that DC are a prime target for the immunomodulatory effects of GA.

Respiratory syncytial virus decreases the capacity of myeloid dendritic cells to induce interferon-gamma in naïve T cells

Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis in infants under 6 months of age. Since an RSV infection does not necessarily prevent a reinfection, we asked whether RSV might subvert an effective immune response by interfering with the function of dendritic cells (DCs). Immature DCs cultured from cord blood stem cells and infected with RSV reduced the rate of interferon-gamma (IFN-gamma) production in co-cultured autologous naïve T cells stimulated with the superantigen TSST-1. Maturation of DCs in response to poly(IC) but not to CD40 ligand did overcome the inhibitory effect of RSV. Further experiments demonstrated that induction of apoptosis, a selective increase in CD86 expression and lack of release of pro-inflammatory cytokines were associated with inhibition of IFN-gamma generation. In addition, RSV replication seemed to be essential for modulation of IFN-gamma production because a virus preparation inactivated by UV irradiation had no effect. Hence, one reason for multiple reinfections by RSV might be the subversion of antiviral immune responses by interference of RSV with DC function.

Efficient transduction of human monocyte-derived dendritic cells by chimpanzee-derived adenoviral vector

Using recombinant adenoviruses (Ads) to target host dendritic cells (DCs) presents an attractive prospect for immunization. The efficacy of commonly used human Ad-derived gene transfer vectors for antigen delivery in humans is often compromised by preexisting anti-Ad immunity, acquired by the majority of human population as a result of frequent naturally occurring virus infections. As an alternative vector we propose chimpanzee-derived recombinant adenoviruses, which are poorly neutralized by human sera. In the present study we examine the ability of one such vector, AdC68, to transduce and activate human monocyte-derived DCs in culture. We found that AdC68 could efficiently transduce both immature and mature DCs at levels similar to those by the human serotype 5 Ad recombinant. Exposure of immature DCs to AdC68 did not alter the expression of activation and maturation marker molecules on the cell surface. Nevertheless, the transduction induced DCs to secrete interferon alpha and interleukin (IL)-6, but not IL-12 or tumor necrosis factor alpha. In addition, AdC68-transduced immature DCs could stimulate proliferation of autologous T lymphocytes. This is the first report describing a chimpanzee-derived recombinant Ad as a vector for transduction of human DCs.

Gene-modified dendritic cells for immunotherapy against cancer

Dendritic cells (DCs) are described as professional antigen-presenting cells because of their superior T-cell stimulatory capacity. For this reason, attention is being focused on using DCs for clinical applications to treat cancer patients. Although preclinical studies are promising, the majority of clinical studies with DCs have not fulfilled the expectations, yet. The field of DC biology has progressed rapidly over the past years, leading to several options for the improvement of vaccination. Among the different parameters to investigate, this review focuses on the efficiency and biological and functional consequences of different gene transfer methods into different subsets of human DCs. Another important consideration for DC-based vaccination is the elucidation of the role of maturation and apoptosis during DC differentiation.

Characterizing cellular immune response to kinetoplastid membrane protein-11 (KMP-11) during Leishmania (Viannia) panamensis infection using dendritic cells (DCs) as antigen presenting cells (APCs)

In vitro peptide binding assays and DCs pulsed with recombinant KMP-11 (rKMP-11) plus six 20-mer overlapping peptides covering the entire protein of Leishmania (Viannia) panamensis (L(V)p) promastigotes were used to identify T-cell epitopes in this protein. Such in vitro binding assays, using HLA DRB1* 0101, -0401, -0701 and -1101 alleles, demonstrated that two peptide sequences (DEEFNKKMQEQNAKFFADKP and FKHKFAELLEQQKAAQYPSK) exhibited high HLA DRB1* 0401 allele binding capacity. rKMP-11 specific T-cell proliferation and cytokine production, derived from 13 volunteers exposed to the parasite, suggested that using autologous DCs as APCs becomes advantageous in uncovering T-cell epitopes promoting proliferation and differences in IFN-gamma and IL-4 production in T-cells from volunteers with ACTIVE and CURED undetectable disease when other APCs were used. The two peptides which bound in vitro to the HLA DRB1* 0401 allele were immunogenic in HLA DRB1* 04 volunteers, thus validating the use of in vitro binding assays for predicting epitopes in this protein. The experimental approach used here may prove useful for characterizing T-cell epitopes in a protein useful in designing peptide-based vaccine candidates for Leishmania and other intracellular pathogens.

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.

Mechanisms inducing or controlling CD8+ T cell responses against self- or non-self-antigens

Cytotoxic T lymphocytes (CTLs) generally recognize antigens endogenously synthesized within the cells and presented in the form of peptides on class I molecules. However, a large body of evidence suggests that dendritic cells (DCs) have the capacity to capture and deliver exogenous antigens into the major histocompatibility complex (MHC) class I processing pathway. In this paper, we discuss this function, defined as cross-presentation, and how it is directed, particularly in inducing T cell tolerance, and how it requires special activating signals (such as CD40 ligand) to transform into a mechanism that provides either protective immunity or autoimmunity.

Optimized culture conditions for the generation of dendritic cells from peripheral blood monocytes

BACKGROUND AND OBJECTIVES

Dendritic cells (DCs) are promising adjuvants for clinical immunotherapy, but they are scantily distributed. Therefore, numerous in vitro methods have been developed to expand these cells while maintaining their normal functions. Current culture systems generally require the use of fetal bovine serum (FBS)-supplemented media in order to attain DCs with high immunostimulatory activity. However, the presence of exogenous animal proteins sets limits for their use in clinical trials. The purpose of this study was to establish a simple, efficient and FBS-free method for the generation of human DCs for clinical application.

MATERIALS AND METHODS

We compared monocyte-derived DCs generated in a standard FBS-supplemented medium vs. DCs generated in an autologous plasma (AutoPl)-supplemented medium, with regard to their yield, function and longevity. Peripheral blood monocytes were isolated from buffy coats by two consecutive 2-h adherence steps in tissue culture flasks. The adherent cells were differentiated into DCs within 2 weeks by adding granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-4 (IL-4), c-kit ligand and tumour necrosis factor-alpha (TNF-alpha). Every 2-3 days, the cells in suspension were analysed for their immunophenotype and apoptosis rate by flow cytometry. Their function was demonstrated by their allostimulatory and migratory capacity, as well as by their proteolytic activity.

RESULTS

We show that more than 30 x 10(6) DCs can be achieved per unit of buffy coat using either AutoPl- or FBS-supplemented media. The purity of the DCs was 53.4% and 65% (P > 0.05) in AutoPl- and FBS-based medium, respectively. DCs grown in AutoPl media showed a CD80high CD83+ CD86high CD14neg HLA-DR+ CD1aneg phenotype, while FBS-generated DCs exhibited a CD80high CD83+ CD86high CD14neg HLA-DR+ CD1ahigh phenotype. The apoptosis rate in both culture conditions increased from 10% to 25% over 1 week. AutoPl-generated DCs were shown to be equally strong stimulators for proliferation of allogeneic T lymphocytes as FBS-generated DCs. In addition, the capacity to migrate in response to macrophage inflammatory protein-1alpha (MIP-1alpha) and stromal-cell-derived factor 1alpha (SDF-1alpha) was similar in both groups, whereas the response to MIP-3beta was reduced in AutoPl-derived cells. Zymography analysis of supernatants from 5-day-old cultures demonstrated that AutoPl-generated DCs produced higher amounts of matrix metalloproteinases, suggesting that they have an enhanced capability to traffic through peripheral tissues.

CONCLUSIONS

Our findings indicate that plastic-adherent peripheral blood cells, when cultured with GM-CSF, IL-4, c-kit-ligand and TNF-alpha in autologous human plasma-supplemented media, are a potent source of functional DCS that may be of value for human therapy.

NKT cells provide help for dendritic cell-dependent priming of MHC class I-restricted CD8+ T cells in vivo

Dendritic cells (DC) are potent APCs for naive T cells in vivo. This is evident by inducing T cell responses through adoptive DC transfer. Priming specific CTL responses in vivo often requires "help". We study alternative sources of help in DC-dependent priming of MHC class I-restricted CTL. Priming an anti-viral CTL response in naive B6 mice by adoptive transfer of antigenic peptide-pulsed DC required CD4(+) T cell help. CTL priming was facilitated by providing MHC class II-dependent specific help. Furthermore, transfers of MHC class II-deficient pulsed DC into naive, normal hosts, or DC transfers into naive, CD4(+) T cell-depleted hosts primed CTL inefficiently. Pretreatment of DC with immune-stimulating oligodeoxynucleotides rendered them more efficient for CD4(+) T cell-independent priming of CTL. DC copresenting a K(b)-binding antigenic peptide and the CD1d-binding glycolipid alpha-galactosyl-ceramide efficiently primed CTL in a class II-independent way. To obtain NKT cell-dependent help in CTL priming, the same DC had to present both the peptide and the glycolipid. CTL priming by adoptive DC transfer was largely NK cell-dependent. The requirement for NK cells was only partially overcome by recruiting NKT cell help into DC-dependent CTL priming. NKT cells thus are potent helper cells for DC-dependent CTL priming.

In vitro analysis of the antileukemic effect of tumor necrosis factor-alpha gene therapy with myeloid progenitor cells: the role of dendritic cells

We have previously demonstrated that tumor necrosis factor-alpha (TNF-alpha) gene therapy with transgene-expressing myeloid progenitor cells (32DTNF-alpha) is effective in inhibiting the progression of leukemia with a lethal dose of murine 32Dp210 myeloid leukemia cells. Because TNF-alpha has been shown to induce the activation and maturation of dendritic cells (DCs), we investigated the effect of TNF-alpha secreted by transduced cells (32DTNF-alpha cells) on the activation of DCs and their role in the production of antileukemic cytotoxic T lymphocytes (CTLs). We demonstrate that administration of 32DTNF-alpha cells to the mice enhances the allo-stimulatory capacity of the splenic (CD11c+) and bone marrow-derived DCs in both mixed leukocyte response and CTL development. The enhanced allo-stimulatory capacity of splenic DCs from mice injected with 32DTNF-alpha cells correlated with increase in the cell-surface expression of the costimulatory molecules CD40, CD80, CD86, and major histocompatibility complex (MHC) class II molecules (I-Ak), and production of interleukin-12 (IL-12). Furthermore, administration of 32DTNF-alpha cells during immunization with irradiated 32Dp210 leukemia cells augmented the capacity of splenic DCs to stimulate antileukemic CTL response in spleen cells. Collectively, these data suggest that in vivo production of TNF-alpha by transduced cells enhances the phenotypic and functional activation of DCs, resulting in induction of a stronger antileukemic cytotoxic T-cell immune response.

Accelerated migration of respiratory dendritic cells to the regional lymph nodes is limited to the early phase of pulmonary infection

Respiratory dendritic cells (RDC) are believed to play a central role in the induction of adaptive immune responses to pulmonary infection. Herein we examine the basal migration of RDC from the lungs to secondary lymphoid tissues and their enhanced maturation/migration after pulmonary infection/inflammation. We demonstrate that the accelerated migration of RDC to the draining peribronchial lymph nodes occurs only during the first 24 hr after pulmonary virus infection. RDC are refractory to further migration thereafter in spite of ongoing virus replication and pulmonary inflammation. We further demonstrate that induction of this RDC refractory state suppresses additional RDC mobilization to subsequent pulmonary virus infection and results in concomitant suppression of an antiviral pulmonary CD8(+) T cell response.

TICAM-1, an adaptor molecule that participates in Toll-like receptor 3-mediated interferon-beta induction

Human Toll-like receptor (TLR) 3 recognizes double-stranded (ds) RNA and induces production of interferon (IFN)-beta independent of the adaptor molecules MyD88 and TIRAP. Thus, another adaptor must exist that preferentially mediates TLR3-dependent production of IFN-beta. We have identified an alternative adaptor, designated Toll-interleukin 1 receptor domain (TIR)-containing adaptor molecule (TICAM)-1, that can physically bind the TIR domain of TLR3 and activate the IFN-beta promoter in response to poly(I):poly(C). Thus, dsRNA-TLR3-dependent production of IFN-beta is mediated mainly by TICAM-1. This TICAM-1-dependent pathway may have a role in other TLR-IFN-beta pathways, which form part of the MyD88-independent cellular immune response.

Maternal influenza infection causes marked behavioral and pharmacological changes in the offspring

Maternal viral infection is known to increase the risk for schizophrenia and autism in the offspring. Using this observation in an animal model, we find that respiratory infection of pregnant mice (both BALB/c and C57BL/6 strains) with the human influenza virus yields offspring that display highly abnormal behavioral responses as adults. As in schizophrenia and autism, these offspring display deficits in prepulse inhibition (PPI) in the acoustic startle response. Compared with control mice, the infected mice also display striking responses to the acute administration of antipsychotic (clozapine and chlorpromazine) and psychomimetic (ketamine) drugs. Moreover, these mice are deficient in exploratory behavior in both open-field and novel-object tests, and they are deficient in social interaction. At least some of these behavioral changes likely are attributable to the maternal immune response itself. That is, maternal injection of the synthetic double-stranded RNA polyinosinic-polycytidylic acid causes a PPI deficit in the offspring in the absence of virus. Therefore, maternal viral infection has a profound effect on the behavior of adult offspring, probably via an effect of the maternal immune response on the fetus.

Autocrine type I IFN and contact with endothelium promote the presentation of influenza A virus by monocyte-derived APC

Purified monocytes infected with influenza A virus do not become mature dendritic cells (DCs) and they present viral peptides poorly to autologous memory T cells. In this study, we investigated whether influenza A-infected monocytes matured to DCs with a high capacity to stimulate T cells when they were infected with influenza A virus in a model tissue setting wherein they were cocultured with endothelium grown on a type I collagen matrix. Intercellular interactions with endothelium strongly promoted the Ag-presenting capacity of monocyte-derived cells infected with influenza A virus, and the heterologous coculture system also enhanced production of IFN-alpha by monocytes in the absence of plasmacytoid cells. Production of IFN-alpha in the presence of endothelium correlated with monocyte differentiation to mature DCs and their ability to stimulate proliferation and IFN-gamma production by autologous T cells. Monocyte-derived cells that developed into migratory DCs promoted proliferation of influenza A virus-specific CD4(+) and CD8(+) cells, whereas those that developed into macrophages promoted proliferation of CD8(+) T cells only. This onset of APC activity could be partially blocked with Ab to the IFN-alphabeta receptor when monocytes were infected with UV-treated virus, but neutralizing this pathway was inconsequential when monocytes were infected with live virus. Thus, type I IFN and direct contact with endothelium promote development of influenza A virus-presenting activity in monocyte-derived cells in a setting in which this differentiation does not depend on plasmacytoid cells. However, when infected with live influenza virus, the role of type I IFN in mediating differentiation and Ag-presenting capacity is expendable, apparently due to other mechanisms of virus-mediated activation.