Suppression of endogenous IL-10 gene expression in dendritic cells enhances antigen presentation for specific Th1 induction: potential for cellular vaccine development

A new paradigm for designing vaccines against certain microbial pathogens, including Chlamydia trachomatis, is based on the induction of local mucosal Th1 response. IL-10 is an anti-inflammatory cytokine that exerts negative immunoregulatory influence on Th1 response. This study investigated whether biochemical modulation of endogenous IL-10 expression at the level of APCs is a practical strategy for enhancing the specific Th1 response against pathogens controlled by Th1 immunity. The results revealed that the high resistance of genetically engineered IL-10-/- (IL-10KO) mice to genital chlamydial infection is a function of the predilection of their APCs to rapidly and preferentially activate a high Th1 response. Thus, in microbiological analysis, IL-10KO mice suffered a shorter duration of infection, less microbial burden, and limited ascending infection than immunocompetent wild-type mice. Also, IL-10KO were resistant to reinfection after 8 wk of the primary infection. Cellular and molecular immunologic evaluation indicated that IL-10KO mice induced greater frequency of chlamydial-specific Th1 response following C. trachomatis infection. Moreover, IL-10KO APCs or antisense IL-10 oligonucleotide-treated wild-type APCs were potent activators of Th1 response from naive or immune T cells. Furthermore, both Ag-pulsed dendritic cells from IL-10KO mice and IL-10 antisense-treated dendritic cells from wild-type mice were efficient cellular vaccines in adoptive immunotherapeutic vaccination against genital chlamydial infection. These findings may furnish a novel immunotherapeutic strategy for boosting the Th1 response against T cell-controlled pathogens and tumors, using IL-10-deficient APCs as vaccine delivery agents.     

Involvement of LEK1 in dendritic cell regulation of T cell immunity against Chlamydia

We investigated the hypothesis that the enhanced Ag-presenting function of IL-10-deficient dendritic cells (DCs) is related to specific immunoregulatory cytoskeletal molecules expressed when exposed to Ags. We analyzed the role of a prominent cytoskeletal protein, LEK1, in the immunoregulation of DC functions; specifically cytokine secretion, costimulatory molecule expression, and T cell activation against Chlamydia. Targeted knockdown of LEK1 expression using specific antisense oligonucleotides resulted in the rapid maturation of Chlamydia-exposed DCs as measured by FACS analysis of key activation markers (i.e., CD14, CD40, CD54, CD80, CD86, CD197, CD205, and MHC class II). The secretion of mostly Th1 cytokines and chemokines (IL-1a, IL-9, IL-12, MIP-1a, and GM-CSF but not IL-4 and IL-10) was also enhanced by blocking of LEK1. The function of LEK1 in DC regulation involves cytoskeletal changes, since the dynamics of expression of vimentin and actin, key proteins of the cellular cytoskeleton, were altered after exposure of LEK1 knockdown DCs to Chlamydia. Furthermore, targeted inhibition of LEK1 expression resulted in the enhancement of the immunostimulatory capacity of DCs for T cell activation against Chlamydia. Thus, LEK1 knockdown DCs activated immune T cells at least 10-fold over untreated DCs. These results suggest that the effect of IL-10 deficiency is mediated through LEK1-related events that lead to rapid maturation of DCs and acquisition of the capacity to activate an elevated T cell response. Targeted modulation of LEK1 expression provides a novel strategy for augmenting the immunostimulatory function of DCs for inducing an effective immunity against pathogens.     

A novel chemokine ligand for CCR10 and CCR3 expressed by epithelial cells in mucosal tissues

Mucosae-associated epithelial chemokine (MEC) is a novel chemokine whose mRNA is most abundant in salivary gland, with strong expression in other mucosal sites, including colon, trachea, and mammary gland. MEC is constitutively expressed by epithelial cells; MEC mRNA is detected in cultured bronchial and mammary gland epithelial cell lines and in epithelia isolated from salivary gland and colon using laser capture microdissection, but not in the endothelial, hemolymphoid, or fibroblastic cell lines tested. Although MEC is poorly expressed in skin, its closest homologue is the keratinocyte-expressed cutaneous T cell-attracting chemokine (CTACK; CCL27), and MEC supports chemotaxis of transfected lymphoid cells expressing CCR10, a known CTACK receptor. In contrast to CTACK, however, MEC also supports migration through CCR3. Consistent with this, MEC attracts eosinophils in addition to memory lymphocyte subsets. These results suggest an important role for MEC in the physiology of extracutaneous epithelial tissues, including diverse mucosal organs.     

Double-stranded RNA stimulation or CD40 ligation of monocyte-derived dendritic cells as models to study their activation and maturation process

Monocyte-derived dendritic cells (DCs) were used as an in vitro model of myeloid DCs in order to determine a minimum marker pattern with which to characterize and distinguish different stages of DC activation and maturation. Phenotypic changes induced on immature DCs by two prototypic stimuli, poly I:C and CD40 ligation, were first examined. Both elicited HLA-DR, CD40, CD86 and CXCR4 upregulation, and CCR5 downregulation, but only CD40 ligand-stimulated DCs became CD83(+)\CCR7(+), whereas poly I:C-stimulated DCs expressed lower CD83 levels and were mostly CCR7(--). CD40 ligation and poly I:C elicited increased production of inflammatory cytokines interleukin (IL)-6 and tumor necrosis factor-alpha, of IL-10 and the CCL5 chemokine, but profiles differed as to higher IL-10, IL-12 and CCL22 (a CCR4 ligand important for T cell recruitment) levels for the former, and of CCL4 and CCL5 for the latter. Thus, a limited set of phenotypic markers, cytokine and chemokine production assays, may be used to distinguish the three stages in the life of DCs: immaturity, activation and full maturation. The ability of purified protein derivative-loaded DCs to stimulate autologous T cells to produce IL-2, IL-4 and interferon-gamma indeed depended on their activation stage and endocytic activity, which decreased upon maturation. We then examined whether ligation of CD4, CCR5 and\or CXCR4, the receptor and coreceptors of human immunodeficiency virus envelope gp120, respectively, affected DC activation or maturation, neither a monoclonal antibody to the gp120-binding site on CD4 nor CCL5 nor CXCL12, the natural ligands of CCR5 and CXCR4, respectively, nor gp120 altered the DC activation and maturation processes.     

Differential expression of inflammatory chemokines by Th1- and Th2-cell promoting dendritic cells: a role for different mature dendritic cell populations in attracting appropriate effector cells to peripheral sites of inflammation

Protective immunity to pathogens depends on efficient immune responses adapted to the type of pathogen and the infected tissue. Dendritic cells (DC) play a pivotal role in directing the effector T cell response to either a protective T helper type 1 (Th1) or type 2 (Th2) phenotype. Human monocyte-derived DC can be differentiated into Th1-, Th2- or Th1/Th2-promoting DC in vitro upon activation with microbial compounds or cytokines. Host defence is highly dependent on mobile leucocytes and cell trafficking is largely mediated by the interactions of chemokines with their specific receptors expressed on the surface of leucocytes. The production of chemokines by mature effector DC remains elusive. Here we assess the differential production of both inflammatory and homeostatic chemokines by monocyte-derived mature Th1/Th2-, Th1- or Th2-promoting DC and its regulation in response to CD40 ligation, thereby mimicking local engagement with activated T cells. We show that mature Th1- and Th1/Th2-, but not Th2-promoting DC, selectively express elevated levels of the inflammatory chemokines CCL2/MCP-1, CCL3/MIP-1alpha, CCL4/MIP-1beta and CCL5/RANTES, as well as the homeostatic chemokine CCL19/MIP-3beta. CCL21/6Ckine is preferentially expressed by Th2-promoting DC. Production of the Th1-attracting chemokines, CXCL9/Mig, CXCL10/IP-10 and CXCL11/I-TAC, is restricted to Th1-promoting DC. In contrast, expression of Th2-associated chemokines does not strictly correlate with the Th2-promoting DC phenotype, except for CCL22/MDC, which is preferentially expressed by Th2-promoting DC. Because inflammatory chemokines and Th1-associated chemokines are constitutively expressed by mature Th1-promoting DC and CCL22/MDC is constitutively expressed by mature Th2-promoting DC, we propose a novel role for mature DC present in inflamed peripheral tissues in orchestrating the immune response by recruiting appropriate leucocyte populations to the site of pathogen entry.     

Cross-talk in the innate immune system: neutrophils instruct recruitment and activation of dendritic cells during microbial infection

Type I inflammatory cytokines are essential for immunity to many microbial pathogens, including Toxoplasma gondii. Dendritic cells (DC) are key to initiating type 1 immunity, but neutrophils are also a source of chemokines and cytokines involved in Th1 response ignition. We found that T. gondii triggered neutrophil synthesis of CC chemokine ligand (CCL)3, CCL4, CCL5, and CCL20, chemokines that were strongly chemotactic for immature DC. Moreover, supernatants obtained from parasite-stimulated polymorphonuclear leukocytes induced DC IL-12(p40) and TNF-alpha production. Parasite-triggered neutrophils also released factors that induced DC CD40 and CD86 up-regulation, and this response was dependent upon parasite-triggered neutrophil TNF-alpha production. In vivo evidence that polymorphonuclear leukocytes exert an important influence on DC activation was obtained by examining splenic DC cytokine production following infection of neutrophil-depleted mice. These animals displayed severely curtailed splenic DC IL-12 and TNF-alpha production, as revealed by ex vivo flow cytometric analysis and in vitro culture assay. Our results reveal a previously unrecognized regulatory role for neutrophils in DC function during microbial infection, and suggest that cross-talk between these cell populations is an important component of the innate immune response to infection.     

Chemokine receptor expression and function in CD4+ T lymphocytes with regulatory activity

We have investigated the chemokine receptor expression and migratory behavior of a new subset of nickel-specific skin-homing regulatory CD4(+) T cells (Th(IL-10)) releasing high levels of IL-10, low IFN-gamma, and undetectable IL-4. These cells inhibit in a IL-10-dependent manner the capacity of dendritic cells to activate nickel-specific Tc1 and Th1 lymphocytes. RNase protection assay and FACS analysis revealed the expression of a vast repertoire of chemokine receptors on resting Th(IL-10), including the Th1-associated CXCR3 and CCR5, and the Th2-associated CCR3, CCR4, and CCR8, the latter at higher levels compared with Th2 cells. The most active chemokines for resting Th(IL-10), in terms of calcium mobilization and in vitro migration, were in order of potency: CCL2 (monocyte chemoattractant protein-1, CCR2 ligand), CCL4 (macrophage-inflammatory protein-1beta, CCR5 ligand), CCL3 (macrophage-inflammatory protein-1alpha, CCR1/5 ligand), CCL17 (thymus and activation-regulated chemokine, CCR4 ligand), CCL1 (I-309, CCR8 ligand), CXCL12 (stromal-derived factor-1, CXCR4), and CCL11 (eotaxin, CCR3 ligand). Consistent with receptor expression down-regulation, activated Th(IL-10) exhibited a reduced or absent response to most chemokines, but retained a significant migratory capacity to I-309, monocyte chemoattractant protein-1, and thymus and activation-regulated chemokine. I-309, which was ineffective on Th1 lymphocytes, attracted more efficiently Th(IL-10) than Th2 cells. I-309 and CCR8 mRNAs were not detected in unaffected skin and were up-regulated at the skin site of nickel-allergic reaction, with an earlier expression kinetics compared with IL-10 and IL-4. Results indicate that skin-homing regulatory Th(IL-10) lymphocytes coexpress functional Th1- and Th2-associated chemokine receptors, and that CCR8/I-309-driven recruitment of both resting and activated Th(IL-10) cells may be critically involved in the regulation of Th1-mediated skin allergic disorders.     

CD4+ T cell responses elicited by different subsets of human skin migratory dendritic cells

Skin dendritic cells (DC) are professional APC critical for initiation and control of adaptive immunity. In the present work we have analyzed the CD4+ T cell stimulatory function of different subsets of DC that migrate spontaneously from human skin explants, including CD1a+CD14- Langerhans' cells (LC), CD1a-CD14- dermal DC (DDC), and CD1a-CD14+ LC precursors. Skin migratory DC consisted of APC at different stages of maturation-activation that produced IL-10, TGF-beta1, IL-23p19, and IL-12p40, but did not release IL-12p70 even after exposure to DC1-driving stimuli. LC and DDC migrated as mature/activated APC able to stimulate allogeneic naive CD4+ T cells and to induce memory Th1 cells in the absence of IL-12p70. The potent CD4+ T cell stimulatory function of LC and DDC correlated with their high levels of expression of MHC class II, adhesion, and costimulatory molecules. The Th1-biasing function of LC and DDC depended on their ability to produce IL-23. By contrast, CD1a-CD14+ LC precursors migrated as immature-semimature APC and were weak stimulators of allogeneic naive CD4+ T cells. However, and opposite of a potential tolerogenic role of immature DC, the T cell allostimulatory and Th1-biasing function of CD14+ LC precursors increased significantly by augmenting their cell number, prolonging the time of interaction with responding T cells, or addition of recombinant human IL-23 in MLC. The data presented in this study provide insight into the function of the complex network of skin-resident DC that migrate out of the epidermis and dermis after cutaneous immunizations, pathogen infections, or allograft transplantation.     

IL-12 induction by a TH1-inducing adjuvant in vivo: dendritic cell subsets and regulation by IL-10

IL-12 induction is critical for immune responses against many viruses and intracellular bacterial pathogens. Recent studies suggest that IL-12-secreting dendritic cells (DC) are potent Th1-inducing APC. However, controversy exists concerning the function of DC subsets. Murine studies have suggested that CD8(+) DC preferentially induce Th1 responses, whereas CD8(-) DC induce Th2 development; in this model, different DC subsets prime different responses. Alternatively, the propensity of DC subsets to prime a Th1 response could depend upon the type of initial stimulus. We used a prototypic Th1-inducing adjuvant, heat-killed Brucella abortus (HKBA) to assess stimulation of DC subsets, relationship between Ag burden and IL-12 production, and down-regulation of DC subset IL-12 production by IL-10. In this study, we show that DC were sole producers of IL-12, although most HKBA uptake was by splenic macrophages and granulocytes. More CD8(-) than CD8(+) DC produced IL-12 after HKBA challenge, whereas only CD8(+) DC produced IL-12 after injection of another Th1-promoting microbial substance, soluble Toxoplasma gondii Ags. Studies in IL-10-deficient mice revealed that IL-10 down-regulates frequency and duration of IL-12 production by both DC subsets. In the absence of IL-10, IL-12 expression is enabled in CD11c(low) cells, but not in macrophages or granulocytes. These findings support the concept of DC as the major IL-12 producers in spleens, but challenge the notion that CD8(+) and CD8(-) DC are destined to selectively induce Th1 or Th2 responses, respectively. Thus, the nature of the stimulating substance is important in determining which DC subsets are activated to produce IL-12.     

Impact of bronchial epithelium on dendritic cell migration and function: modulation by the bacterial motif KpOmpA

Mucosal immune response depends on the surveillance network established by dendritic cells (DC), APC localized within the epithelium. Bronchial epithelial cells (BEC) play a pivotal role both in the host defense and in the pathogenesis of inflammatory airway disorders. We previously showed that the outer membrane protein A from Klebsiella pneumoniae (KpOmpA), a pathogen-associated molecular pattern (PAMP) derived from Klebsiella pneumoniae, activates BEC. In this study, we evaluated the consequences of this activation on DC traffic and functions. KpOmpA significantly increased the production of CCL2, CCL5, CXCL10, and CCL20 by BEC. Stimulation of BEC increased their chemotactic activity for monocyte-derived DC (MDDC) precursors, through CCL5 and CXCL10 secretion. BEC/MDDC precursor coculture leads to an ICAM-1-dependent accelerated differentiation and enhanced maturation of MDDC. BEC/DC interactions did not affect the capacity of DC to induce T cell proliferation. However, DC preincubated with BEC increased significantly the IL-10 production by autologous T cells. Basolateral and intraepithelial DC differently enhance IL-4 and/or IL-10 synthesis according to the condition of stimulation. In vivo, intranasal injections of KpOmpA into BALB/c mice induced the recruitment of CD11c(+) and I-A(d+) myeloid DC associated with bronchial epithelium activation as evidenced by CCL20 expression. These data show that KpOmpA-exposed BEC participate in the homeostasis of myeloid DC network, and regulate the induction of local immune response.     

In vivo differentiated cytokine-producing CD4(+) T cells express functional CCR7

Chemokines and their receptors fulfill specialized roles in inflammation and under homeostatic conditions. CCR7 and its ligands, CCL19 and CCL21, are involved in lymphocyte recirculation through secondary lymphoid organs and additionally navigate lymphocytes into distinct tissue compartments. The role of CCR7 in the migration of polarized T effector/memory cell subsets in vivo is still poorly understood. We therefore analyzed murine and human CD4(+) cytokine-producing cells developed in vivo for their chemotactic reactivity to CCR7 ligands. The responses of cells producing cytokines, such as IFN-gamma, IL-4, and IL-10, as well as of subsets defined by memory or activation markers were comparable to that of naive CD4(+) cells, with slightly lower reactivity in cells expressing IL-10 or CD69. This indicates that CCR7 ligands are able to attract naive as well as the vast majority of activated and effector/memory T cell stages. Chemotactic reactivity of these cells toward CCL21 was absent in CCR7-deficient cells, proving that effector cells do not use alternative receptors for this chemokine. Th1 cells generated from CCR7(-/-) mice failed to enter lymph nodes and Peyer's patches, but did enter a site of inflammation. These findings indicate that CD4(+) cells producing effector cytokines upon stimulation retain the capacity to recirculate through lymphoid tissues via CCR7.     

Mice with a selective deletion of the CC chemokine receptors 5 or 2 are protected from dextran sodium sulfate-mediated colitis: lack of CC chemokine receptor 5 expression results in a NK1.1+ lymphocyte-associated Th2-type immune response in the intestine

The chemokine receptors CCR2 and CCR5 and their respective ligands regulate leukocyte chemotaxis and activation. To determine the role of these chemokine receptors in the regulation of the intestinal immune response, we induced colitis in CCR2- and CCR5-deficient mice by continuous oral administration of dextran sodium sulfate (DSS). Both CCR2- and CCR5-deficient mice were susceptible to DSS-induced intestinal inflammation. The lack of CCR2 or CCR5 did not reduce the DSS-induced migration of macrophages into the colonic lamina propria. However, both CCR5-deficient mice and, to a lesser degree, CCR2-deficient mice were protected from DSS-induced intestinal adhesions and mucosal ulcerations. CCR5-deficient mice were characterized by a greater relative infiltration of CD4+ and NK1.1+ lymphocyte in the colonic lamina propria when compared to wild-type and CCR2-deficient mice. In CCR5-deficient mice, mucosal mRNA expression of IL-4, IL-5, and IL-10 was increased, whereas that of IFN-gamma was decreased, corresponding to a Th2 pattern of T cell activation. In CCR2-deficient mice, the infiltration of Th2-type T cells in the lamina propria was absent, but increased levels of IL-10 and decreased levels of IFN-gamma may have down regulated mucosal inflammation. Our data indicate that CCR5 may be critical for the promotion of intestinal Th1-type immune responses in mice.     

IFN-gamma production by Th1 cells generated from naive CD4+ T cells exposed to norepinephrine

During activation in vivo, naive CD4(+) T cells are exposed to various endogenous ligands, such as cytokines and the neurotransmitter norepinephrine (NE). To determine whether NE affects naive T cell differentiation, we used naive CD4(+) T cells sort-purified from either BALB/c or DO11.10 TCR-transgenic mouse spleens and activated these cells with either anti-CD3/anti-CD28 mAbs or APC and OVA(323-329) peptide, respectively, under Th1-promoting conditions. RT-PCR and functional assays using selective adrenergic receptor (AR) subtype antagonists showed that naive CD4(+) T cells expressed only the beta 2AR subtype to bind NE and that stimulation of this receptor generated Th1 cells that produced 2- to 4-fold more IFN-gamma. This increase was due to more IFN-gamma produced per cell upon restimulation instead of more IFN-gamma-secreting cells, as determined by IFN-gamma-specific immunofluorescence and enzyme-linked immunospot. In contrast, Th1 cell differentiation was unaffected when naive T cells were exposed to NE and activated either in the presence of a neutralizing anti-IL-12 mAb or by APC from IL-12-deficient mice. Moreover, the addition of IL-12 to the IL-12-deficient APC cultures restored the ability of NE to increase Th1 differentiation. Taken together, these results indicate that a possible link may exist between the signaling pathways used by NE and IL-12 to increase naive CD4(+) T cell differentiation to a Th1 cell.     

Enhanced Inducible Costimulator Ligand (ICOS-L) Expression on Dendritic Cells in Interleukin-10 Deficiency and Its Impact on T-Cell Subsets in Respiratory Tract Infection

An association between inducible costimulator ligand (ICOS-L) expression and interleukin (IL)-10 production by dendritic cells (DCs) has been commonly found in infectious disease. DCs with higher ICOS-L expression and IL-10 production are reportedly more efficient in inducing regulatory T cells (Tregs). Here we use the Chlamydia muridarum (Cm) lung infection model in IL-10 knockout (KO) mice to test the relationship between IL-10 production and ICOS-L expression by DCs. We examined ICOS-L expression, the development of T-cell subsets, including Treg, Th17 and Th1 cell, in the background of IL-10 deficiency and its relationship with ICOS-L/ICOS signaling after infection. Surprisingly, we found that the IL-10 KO mice exhibited significantly higher ICOS-L expression by DCs. Moreover, IL-10 KO mice showed lower Tregs but higher Th17 and Th1 responses, but only the Th17 response depended on ICOS signaling. Consistently, most of the Th17 cells were ICOS⁺, whereas most of the Th1 cells were ICOS⁻ in the infected mice. Furthermore, neutralization of IL-17 in IL-10 KO mice significantly exacerbated lung infection. The data suggest that ICOS-L expression on DC may be negatively regulated by IL-10 and that ICOS-L expression on DC in the presence or absence of IL-10 costimulation may promote Treg or Th17 response, without significant impact on Th1.     

Exposure of CD34+ precursors to cytostatic anthraquinone-derivatives induces rapid dendritic cell differentiation: implications for cancer immunotherapy

Appropriate activation of dendritic cells (DC) is essential for successful active vaccination and induction of cell-mediated immunity. The scarcity of precursor cells, as well as long culture methods, have hampered wide-scale application of DC vaccines derived from CD34⁺ precursors, despite their suggested superior efficacy over the more commonly applied monocyte-derived DC (MoDC). Here, employing the CD34⁺/CD14⁺ AML-derived human DC progenitor cell line MUTZ3, we show that cytostatic anthraquinone-derivatives (i.e., the anthracenedione mitoxantrone and the related anthracyclin doxorubicin) induce rapid differentiation of CD34⁺ DC precursors into functional antigen-presenting cells (APC) in a three-day protocol. The drugs were found to act specifically on CD34⁺, and not on CD14⁺ DC precursors. Importantly, these observations were confirmed for primary CD34⁺ and CD14⁺ DC precursors from peripheral blood. Mitoxantrone-generated DC were fully differentiated within three days and after an additional 24 h of maturation, were as capable as standard 9-day differentiated and matured DC to migrate toward the lymph node-homing chemokines CCL19 and CCL21, to induce primary allogeneic T cell proliferation, and to prime functional MART1-specific CD8⁺ T lymphocytes. Our finding that anthraquinone-derivatives like mitoxantrone support rapid high-efficiency differentiation of DC precursors may have consequences for in vitro production of DC vaccines as well as for novel immunochemotherapy strategies.     

Cholera toxin promotes the induction of regulatory T cells specific for bystander antigens by modulating dendritic cell activation

It has previously been reported that cholera toxin (CT) is a potent mucosal adjuvant that enhances Th2 or mixed Th1/Th2 type responses to coadministered foreign Ag. Here we demonstrate that CT also promotes the generation of regulatory T (Tr) cells against bystander Ag. Parenteral immunization of mice with Ag in the presence of CT induced T cells that secreted high levels of IL-4 and IL-10 and lower levels of IL-5 and IFN-gamma. Ag-specific CD4(+) T cell lines and clones generated from these mice had cytokine profiles characteristic of Th2 or type 1 Tr cells, and these T cells suppressed IFN-gamma production by Th1 cells. Furthermore, adoptive transfer of bone marrow-derived dendritic cells (DC) incubated with Ag and CT induced T cells that secreted IL-4 and IL-10 and low concentrations of IL-5. It has previously been shown that IL-10 promotes the differentiation or expansion of type 1 Tr cells. Here we found that CT synergized with low doses of LPS to induce IL-10 production by immature DC. CT also enhanced the expression of CD80, CD86, and OX40 (CD134) on DC and induced the secretion of the chemokine, macrophage inflammatory protein-2 (MIP-2), but inhibited LPS-driven induction of CD40 and ICAM-I expression and production of the inflammatory cytokines/chemokines IL-12, TNF-alpha, MIP-1alpha, MIP-1beta, and monocyte chemoattractant protein-1. Our findings suggest that CT induces maturation of DC, but, by inducing IL-10, inhibiting IL-12, and selectively affecting surface marker expression, suppresses the generation of Th1 cells and promotes the induction of T cells with regulatory activity.     

Dendritic cells exposed to MVA-based HIV-1 vaccine induce highly functional HIV-1-specific CD8(+) T cell responses in HIV-1-infected individuals

Currently, MVA virus vectors carrying HIV-1 genes are being developed as HIV-1/AIDS prophylactic/therapeutic vaccines. Nevertheless, little is known about the impact of these vectors on human dendritic cells (DC) and their capacity to present HIV-1 antigens to human HIV-specific T cells. This study aimed to characterize the interaction of MVA and MVA expressing the HIV-1 genes Env-Gag-Pol-Nef of clade B (referred to as MVA-B) in human monocyte-derived dendritic cells (MDDC) and the subsequent processes of HIV-1 antigen presentation and activation of memory HIV-1-specific T lymphocytes. For these purposes, we performed ex vivo assays with MDDC and autologous lymphocytes from asymptomatic HIV-infected patients. Infection of MDDC with MVA-B or MVA, at the optimal dose of 0.3 PFU/MDDC, induced by itself a moderate degree of maturation of MDDC, involving secretion of cytokines and chemokines (IL1-ra, IL-7, TNF-α, IL-6, IL-12, IL-15, IL-8, MCP-1, MIP-1α, MIP-1β, RANTES, IP-10, MIG, and IFN-α). MDDC infected with MVA or MVA-B and following a period of 48 h or 72 h of maturation were able to migrate toward CCL19 or CCL21 chemokine gradients. MVA-B infection induced apoptosis of the infected cells and the resulting apoptotic bodies were engulfed by the uninfected MDDC, which cross-presented HIV-1 antigens to autologous CD8(+) T lymphocytes. MVA-B-infected MDDC co-cultured with autologous T lymphocytes induced a highly functional HIV-specific CD8(+) T cell response including proliferation, secretion of IFN-γ, IL-2, TNF-α, MIP-1β, MIP-1α, RANTES and IL-6, and strong cytotoxic activity against autologous HIV-1-infected CD4(+) T lymphocytes. These results evidence the adjuvant role of the vector itself (MVA) and support the clinical development of prophylactic and therapeutic anti-HIV vaccines based on MVA-B.     

Induction of CTL and nonpolarized Th cell responses by CD8alpha(+) and CD8alpha(-) dendritic cells

Two distinct dendritic cell (DC) subpopulations have been evidenced in mice on the basis of their differential CD8alpha expression and their localization in lymphoid organs. Several reports suggest that CD8alpha(+) and CD8alpha(-) DC subsets could be functionally different. In this study, using a panel of MHC class I- and/or class II-restricted peptides, we analyzed CD4(+) and CD8(+) T cell responses obtained after i.v. injection of freshly purified peptide-pulsed DC subsets. First, we showed that both DC subsets efficiently induce specific CTL responses and Th1 cytokine production in the absence of CD4(+) T cell priming. Second, we showed that in vivo activation of CD4(+) T cells by CD8alpha(+) or CD8alpha(-) DC, injected i.v., leads to a nonpolarized Th response with production of both Th1 and Th2 cytokines. The CD8alpha(-) subset induced a higher production of Th2 cytokines such as IL-4 and IL-10 than the CD8alpha(+) subset. However, IL-5 was produced by CD4(+) T cells activated by both DC subsets. When both CD4(+) and CD8(+) T cells were primed by DC injected i.v., a similar pattern of cytokines was observed, but, under these conditions, Th1 cytokines were mainly produced by CD8(+) T cells, while Th2 cytokines were produced by CD4(+) T cells. Thus, this study clearly shows that CD4(+) T cell responses do not influence the development of specific CD8(+) T cell cytotoxic responses induced either by CD8alpha(+) or CD8alpha(-) DC subsets.