Tuning the volume of the immune response: strength and persistence of stimulation determine migration and cytokine secretion of dendritic cells

P38K and JNK pathways are induced by amyloid-β in astrocyte: Implication of MAPK pathways in astrogliosis in Alzheimer's disease

Astrocyte activation is one of the crucial hallmarks of Alzheimer's disease (AD) along with amyloid-β (Aβ) plaques, neurofibrillary tangles and neuron death. Glial scar and factors secreted from activated astrocytes have important contribution on neuronal health in AD. In this study, we investigated the mechanisms of astrocyte activation both in in vitro and in vivo models of AD. In this regard, mitogen activated protein kinase (MAPK) signalling cascades that control several fundamental and stress related cellular events, has been implicated in astrocyte activation in various neurological diseases. We checked activation of different MAPKs by western blot and immunocytochemistry and found that both JNK and p38K, but not ERK pathways are activated in Aβ-treated astrocytes in culture and in Aβ-infused rat brain cortex. Next, to investigate the downstream consequences of these two MAPKs (JNK and p38K) in Aβ-induced astrocyte activation, we individually blocked these pathways by specific inhibitors in presence and absence of Aβ and checked Aβ-induced cellular proliferation, morphological changes and glial fibrillary acidic protein (GFAP) upregulation. We found that activation of both JNK and p38K signalling cascades are involved in astrocyte proliferation evoked by Aβ, whereas only p38K pathway is implicated in morphological changes and GFAP upregulation in astrocytes exposed to Aβ. To further validate the implication of p38K pathway in Aβ-induced astrocyte activation, we also observed that transcription factor ATF2, a downstream phosphorylation substrate of p38, is phosphorylated upon Aβ treatment. Taken together, our study indicates that p38K and JNK pathways mediate astrocyte activation and both the pathways are involved in cellular proliferation but only p38K pathway contributes in morphological changes triggered by Aβ.

IL-12 from endogenous cDC1, and not vaccine DC, is required for Th1 induction

Success of DC vaccines relies on the quality of antigen presentation, costimulation, lymph node migration, and the release of IL-12, in case of Th1 priming. Here, we provide evidence for interaction between the injected vaccine DCs with endogenous lymph node–resident DCs for Th1 induction. While migration of the injected DCs was essential for antigen delivery to the lymph node, the injected DCs contributed only partially to Th0 priming and were unable to instruct Th1 generation. Instead, we provide evidence that the lymph node–resident XCR1⁺ DCs are activated by the injected DCs to present the cognate antigen and release IL-12 for Th1 polarization. The timing of interactions in the draining lymph nodes appeared step-wise as (a) injected DCs with cognate T cells, (b) injected DCs with bystander DCs, and (c) bystander DCs with T cells. The transcriptome of the bystander DCs showed a downregulation of Treg- and Th2/Th9-inducing genes and self-antigen presentation, as well as upregulation of MHC class II and genes required for Th1 instruction. Together, these data show that injected mature lymph node migratory DCs direct T cell priming and bystander DC activation, but not Th1 polarization, which is mediated by endogenous IL-12p70⁺XCR1⁺ resident bystander DCs. Our results are of importance for clinical DC-based vaccinations against tumors where endogenous DCs may be functionally impaired by chemotherapy.

Successful Th1 priming by DC vaccines in mice depends on IL-12 from endogenous and XCR1⁺ cDC1 population.

Individual combinations of danger signals synergistically increase FVIII product immunogenicity

INTRODUCTION

The most severe side effect in haemophilia A treatment is the development of antifactor VIII antibodies, also called inhibitors. Why inhibitors develop in a proportion of treated patients while others are unaffected still remains unanswered. The presence of immunological danger signals, associated with events such as infection or surgery, has been proposed to play a role. Previous studies demonstrated that the presence of the bacterial molecule lipopolysaccharide (LPS) can synergistically increase the activation of human DC and subsequent T cell activation by FVIII.

AIM AND METHODS

In the present study, we investigated whether a combination of two danger signals can further increase immune cell activation by FVIII. For this, human in vitro differentiated DC that were treated with combinations of danger signals were co-cultured with autologous primary T cells, and T cell proliferation was analysed.

RESULTS

Interestingly, by combining LPS with a second danger signal, lower LPS concentrations were sufficient to synergistically increase DC and subsequent T cell activation by FVIII. Of note, a combination of LPS and the double-stranded RNA, polyinosinic-polycytidylic acid (poly(I:C)), was most potent in increasing FVIII immunogenicity, followed by LPS + R848 (resiquimod). However, a combination of LPS and the bacterial lipopeptide Pam3CysSK4 did not induce increased immune cell activation by FVIII.

CONCLUSION

Thus, individual combinations of danger signals can increase FVIII product immunogenicity. This should be considered in the treatment routine of haemophilia A patients.

NG2, a common denominator for neuroinflammation, blood-brain barrier alteration, and oligodendrocyte precursor response in EAE, plays a role in dendritic cell activation

In adult CNS, nerve/glial-antigen 2 (NG2) is expressed by oligodendrocyte progenitor cells (OPCs) and is an early marker of pericyte activation in pathological conditions. NG2 could, therefore, play a role in experimental autoimmune encephalomyelitis (EAE), a disease associated with increased blood–brain barrier (BBB) permeability, inflammatory infiltrates, and CNS damage. We induced EAE in NG2 knock-out (NG2KO) mice and used laser confocal microscopy immunofluorescence and morphometry to dissect the effect of NG2 KO on CNS pathology. NG2KO mice developed milder EAE than their wild-type (WT) counterparts, with less intense neuropathology associated with a significant improvement in BBB stability. In contrast to WT mice, OPC numbers did not change in NG2KO mice during EAE. Through FACS and confocal microscopy, we found that NG2 was also expressed by immune cells, including T cells, macrophages, and dendritic cells (DCs). Assessment of recall T cell responses to the encephalitogen by proliferation assays and ELISA showed that, while WT and NG2KO T cells proliferated equally to the encephalitogenic peptide MOG35-55, NG2KO T cells were skewed towards a Th2-type response. Because DCs could be responsible for this effect, we assessed their expression of IL-12 by PCR and intracellular FACS. IL-12-expressing CD11c+ cells were significantly decreased in MOG35-55-primed NG2KO lymph node cells. Importantly, in WT mice, the proportion of IL-12-expressing cells was significantly lower in CD11c+ NG2- cells than in CD11c+ NG2+ cells. To assess the relevance of NG2 at immune system and CNS levels, we induced EAE in bone-marrow chimeric mice, generated with WT recipients of NG2KO bone-marrow cells and vice versa. Regardless of their original phenotype, mice receiving NG2KO bone marrow developed milder EAE than those receiving WT bone marrow. Our data suggest that NG2 plays a role in EAE not only at CNS/BBB level, but also at immune response level, impacting on DC activation and thereby their stimulation of reactive T cells, through controlling IL-12 expression.

ERK1 as a Therapeutic Target for Dendritic Cell Vaccination against High-Grade Gliomas

Glioma regression requires the recruitment of potent antitumor immune cells into the tumor microenvironment. Dendritic cells (DC) play a role in immune responses to these tumors. The fact that DC vaccines do not effectively combat high-grade gliomas, however, suggests that DCs need to be genetically modified specifically to promote their migration to tumor relevant sites. Previously, we identified extracellular signal-regulated kinase (ERK1) as a regulator of DC immunogenicity and brain autoimmunity. In the current study, we made use of modern magnetic resonance methods to study the role of ERK1 in regulating DC migration and tumor progression in a model of high-grade glioma. We found that ERK1-deficient mice are more resistant to the development of gliomas, and tumor growth in these mice is accompanied by a higher infiltration of leukocytes. ERK1-deficient DCs exhibit an increase in migration that is associated with sustained Cdc42 activation and increased expression of actin-associated cytoskeleton-organizing proteins. We also demonstrated that ERK1 deletion potentiates DC vaccination and provides a survival advantage in high-grade gliomas. Considering the therapeutic significance of these results, we propose ERK1-deleted DC vaccines as an additional means of eradicating resilient tumor cells and preventing tumor recurrence. Mol Cancer Ther; 15(8); 1975-87. ©2016 AACR.

Synergy between CD40 and MyD88 Does Not Influence Host Survival to Salmonella Infection

Previous studies using purified toll-like receptor (TLR) ligands plus agonistic anti-CD40 antibodies showed that TLRs and CD40 can act synergistically on dendritic cells (DCs) to optimize T cell activation and Th1 differentiation. However, a synergistic effect of TLRs and CD40 during bacterial infection is not known. Here, we show that mice lacking the TLR adaptor MyD88 alone, or lacking both MyD88 and CD40 [double knockout (DKO) mice], are compromised in survival to Salmonella infection but have intact recruitment of neutrophils and inflammatory monocytes as well as unaltered abundance of DC subsets and DC activation in infected tissues. In contrast to infected wildtype and CD40(-/-) mice, both MyD88(-/-) mice and DKO mice lack detectable serum IFN-γ and have elevated IL-10. A synergistic effect of TLRs and CD40 was revealed in co-culture experiments where OT-II T cell proliferation was compromised when DKO DCs were pulsed with OVA protein and OVA323-339 peptide, but not with heat-killed Salmonella expressing OVA (HKSOVA), relative to MyD88(-/-) DCs. By contrast, MyD88(-/-) or DKO DCs pulsed with any of the antigens had a similar ability to induce IFN-γ that was lower than WT or CD40(-/-) DCs. DKO DCs pulsed with HKSOVA, but not with OVA or OVA323-339, had increased IL-10 relative to MyD88(-/-) DCs. Finally, HKSOVA-pulsed MyD88(-/-) and DKO DCs had similar and low induction of NFκB-dependent and -independent genes upon co-culture with OT-II cells. Overall, our data revealed that synergistic effects of CD40 and MyD88 do not influence host survival to Salmonella infection or serum levels of IFN-γ or IL-10. However, synergistic effects of MyD88 and CD40 may be apparent on some (IL-10 production) but not all (OT-II proliferation and IFN-γ production) DC functions and depend on the complexity of the antigen. Indeed, synergistic effects observed using purified ligands and well-defined antigens may not necessarily apply when complex antigens, such as live bacteria, challenge the immune system.

TAM receptor-dependent regulation of SOCS3 and MAPKs contributes to proinflammatory cytokine downregulation following chronic NOD2 stimulation of human macrophages

Microbial-induced cytokine regulation is critical to intestinal immune homeostasis. Acute stimulation of nucleotide-binding oligomerization domain 2 (NOD2), the Crohn's disease-associated sensor of bacterial peptidoglycan, induces cytokines. However, cytokines are attenuated after chronic NOD2 and pattern recognition receptor stimulation of macrophages; similar attenuation is observed in intestinal macrophages. The role of Tyro3, Axl, and Mer (TAM) receptors in regulating chronic pattern recognition receptor stimulation and NOD2-induced outcomes has not been examined. Moreover, TAM receptors have been relatively less investigated in human macrophages. Whereas TAM receptors did not downregulate acute NOD2-induced cytokines in primary human macrophages, they were essential for downregulating signaling and proinflammatory cytokine secretion after chronic NOD2 and TLR4 stimulation. Axl and Mer were similarly required in mice for cytokine downregulation after chronic NOD2 stimulation in vivo and in intestinal tissues. Consistently, TAM expression was increased in human intestinal myeloid-derived cells. Chronic NOD2 stimulation led to IL-10- and TGF-β-dependent TAM upregulation in human macrophages, which, in turn, upregulated suppressor of cytokine signaling 3 expression. Restoring suppressor of cytokine signaling 3 expression under TAM knockdown conditions restored chronic NOD2-mediated proinflammatory cytokine downregulation. In contrast to the upregulated proinflammatory cytokines, attenuated IL-10 secretion was maintained in TAM-deficient macrophages upon chronic NOD2 stimulation. The level of MAPK activation in TAM-deficient macrophages after chronic NOD2 stimulation was insufficient to upregulate IL-10 secretion; however, full restoration of MAPK activation under these conditions restored c-Fos, c-Jun, musculoaponeurotic fibrosarcoma oncogene homolog K, and PU.1 binding to the IL-10 promoter and IL-10 secretion. Therefore, TAM receptors are critical for downregulating proinflammatory cytokines under the chronic NOD2 stimulation conditions observed in the intestinal environment.

Nod2-induced autocrine interleukin-1 alters signaling by ERK and p38 to differentially regulate secretion of inflammatory cytokines

BACKGROUND & AIMS

Stimulation of nucleotide-binding oligomerization domain-containing (Nod)2 and other pattern recognition receptors (PRR) in human monocyte-derived macrophages induces interleukin (IL)-1, which increases mitogen-activated protein kinase (MAPK) activation and cytokine secretion. Activation of MAPK by PRR has varied effects on inflammatory cytokine secretion. We investigated whether different levels of autocrine IL-1 mediate these varied effects.

METHODS

Macrophage responses to PRR ligands were analyzed by enzyme-linked immunosorbent assay and flow cytometry. We overexpressed or reduced MAPK levels (using small inhibitory RNA).

RESULTS

Nod2 and other PRR activated signaling via extracellular signal-related kinase (ERK) and p38 that inhibited inflammatory cytokine production by human monocyte-derived macrophages; autocrine IL-1 production prevented this inhibition. ERK and p38 inhibited inflammatory cytokine production by human macrophages that produce low levels of IL-1 (such as M2, endotoxin-tolerant, and intestinal macrophages); adding exogenous IL-1 caused ERK and p38 to stimulate production of inflammatory cytokines in these cells. In mouse macrophages, which do not produce IL-1 in response to PRR stimulation alone, addition of exogenous IL-1 reversed the ERK-mediated inhibition of IL-12p40. Increasing activation of c-Jun N-terminal kinase in Nod2-stimulated human monocyte-derived macrophages, in the absence of autocrine IL-1 signaling, caused ERK and p38 to stimulate inflammatory cytokines secretion. Importantly, infection of human intestinal macrophages with pathogens that induce IL-1 production reversed the inhibition of inflammatory cytokine production by ERK and p38.

CONCLUSIONS

In response to PRR stimulation of macrophages, the level of MAPK signaling is regulated by autocrine IL-1 and determines whether production of inflammatory cytokines is inhibited or stimulated. This mechanism could account for reported differences in MAPK regulation of inflammatory cytokines and propagate the inflammatory response to pathogens.

MODULATING CO-STIMULATION DURING ANTIGEN PRESENTATION TO ENHANCE CANCER IMMUNOTHERAPY

One of the key roles of the immune system is the identification of potentially dangerous pathogens or tumour cells, and raising a wide range of mechanisms to eliminate them from the organism. One of these mechanisms is activation and expansion of antigen-specific cytotoxic T cells, after recognition of antigenic peptides on the surface of antigen presenting cells such as dendritic cells (DCs). However, DCs also process and present autoantigens. Therefore, antigen presentation has to occur in the appropriate context to either trigger immune responses or establishing immunological tolerance. This is achieved by co-stimulation of T cells during antigen presentation. Co-stimulation consists on the simultaneous binding of ligand-receptor molecules at the immunological synapse which will determine the type and extent of T cell responses. In addition, the type of cytokines/chemokines present during antigen presentation will influence the polarisation of T cell responses, whether they lead to tolerance, antibody responses or cytotoxicity. In this review, we will focus on approaches manipulating co-stimulation during antigen presentation, and the role of cytokine stimulation on effective T cell responses. More specifically, we will address the experimental strategies to interfere with negative co-stimulation such as that mediated by PD-L1 (Programmed cell death 1 ligand 1)/PD-1 (Programmed death 1) to enhance anti-tumour immunity.

Leflunomide induces apoptosis in fludarabine-resistant and clinically refractory CLL cells

PURPOSE

Environmental conditions in lymph node proliferation centers protect chronic lymphocytic leukemia (CLL) cells from apoptotic triggers. This situation can be mimicked by in vitro stimulation with CD40 ligand (CD40L) and interleukin 4 (IL-4). Our study investigates the impact of the drug leflunomide to overcome apoptosis resistance of CLL cells.

EXPERIMENTAL DESIGN

CLL cells were stimulated with CD40L and IL-4 and treated with fludarabine and the leflunomide metabolite A771726.

RESULTS

Resistance to fludarabine-mediated apoptosis was induced by CD40 activation alone stimulating high levels of BCL-XL and MCL1 protein expression. Apoptosis resistance was further enhanced by a complementary Janus-activated kinase (JAK)/STAT signal induced by IL-4. In contrast, CLL proliferation required both a CD40 and a JAK/STAT signal and could be completely blocked by pan-JAK inhibition. Leflunomide (A771726) antagonized CD40L/IL-4-induced proliferation at very low concentrations (3 μg/mL) reported to inhibit dihydroorotate dehydrogenase. At a concentration of 10 μg/mL, A771726 additionally attenuated STAT3/6 phosphorylation, whereas apoptosis of CD40L/IL-4-activated ("resistant") CLL cells was achieved with higher concentrations (IC(50): 80 μg/mL). Apoptosis was also effectively induced by A771726 in clinically refractory CLL cells with and without a defective p53 pathway. Induction of apoptosis involved inhibition of NF-κB activity and loss of BCL-XL and MCL1 expression. In combination with fludarabine, A771726 synergistically induced apoptosis (IC(50): 56 μg/mL).

CONCLUSION

We thus show that A771726 overcomes CD40L/IL-4-mediated resistance to fludarabine in CLL cells of untreated as well as clinically refractory CLL cells. We present a possible novel therapeutic principle for attacking chemoresistant CLL cells.

Acute lymphoblastic leukemia cells treated with CpG oligodeoxynucleotides, IL-4 and CD40 ligand facilitate enhanced anti-leukemic CTL responses

Acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy. Although the majority of patients initially respond to upfront chemotherapy, relapses with poor prognosis occur in approximately 20% of cases. Thus, novel therapeutic strategies are required to improve long-term survival. B-cell precursor (BCP)-ALL cells express low levels of immunogenic molecules and, therefore, are poorly recognized by the immune system. In the present study, we investigated the effect of various combinations of potent B-cell stimulators including CpG, Interleukin (IL)-2 family cytokines and CD40 ligand (CD40L) on the immunogenicity of primary BCP-ALL cells and a series of BCP-ALL cell lines. The combination of CpG, IL-4 and CD40L was identified as most effective to enhance expression of immunogenic molecules on BCP-ALL cells, resulting in an increased capacity to induce both allogeneic and autologous cytotoxic T lymphocytes (CTL). Importantly, such CTL exhibited significant anti-leukemic cytotoxicity not only towards treated, but also towards untreated BCP-ALL cells. Our results demonstrate that the combination of CpG with other B-cell stimulators is more efficient than CpG alone in generating immunogenic BCP-ALL cells and anti-leukemic CTL. Our results may stimulate the development of novel adoptive T cell transfer approaches for the management of BCP-ALL.

Polypyrimidine tract-binding protein is critical for the turnover and subcellular distribution of CD40 ligand mRNA in CD4+ T cells

CD40L (CD154) is regulated at the posttranscriptional level by an activation-induced process that results in a highly stable transcript at extended times of T cell activation. Transcript stability is mediated by polypyrimidine tract-binding protein (PTB)-containing complexes (complex I and II) that bind to three adjacent CU-rich sequences within the 3' untranslated region. To assess the role of PTB in the expression and distribution of CD40L mRNA, PTB was targeted using short hairpin RNA in both primary T cells and a T cell line that recapitulates the stability phase of regulated CD40L mRNA decay. PTB knockdown resulted in a marked decrease in the mRNA stability that resulted in lowered CD40L surface expression. PTB was also critical for appropriate distribution of CD40L mRNA between the nucleus and cytoplasm and in the cytoplasm between the cytosol and the translating polysomes. The activation-induced formation of PTB-specific ribonucleoprotein complexes was observed only with cytoplasmic and not nuclear PTB indicating functional differences in the protein defined by cellular localization. Finally, we observed that cytoplasmic and nuclear PTB isoforms were differentially modified relative to each other and that the changes in cytoplasmic PTB were consistent with activation-induced phosphorylation. Together this work suggests that differentially modified PTB regulates CD40L expression at multiple steps by 1) retaining CD40L mRNA in the nucleus, 2) directly regulating mRNA stability at late times of activation, and 3) forming a ribonuclear complex that preferentially associates with translating ribosomes thus leading to an enhanced level of CD40L protein.

Mitogen-activated protein kinase signalling and ERK1/2 bistability in asthma

Mitogen-activated protein kinases (MAPKs) integrate signals from numerous receptors and translate these signals into cell functions. MAPKs are critical for immune cell metabolism, migration, production of pro-inflammatory mediators, survival and differentiation. We provide a concise review of the involvement of MAPK in important cells of the immune system. Certain cell functions, e.g. production of pro-inflammatory mediators resolve quickly and may require a transient MAPK activation, other processes such as cell differentiation and long-term survival may require persistent MAPK signal. The persistent MAPK signal is frequently a consequence of positive feedback loops or double negative feedback loops which perpetuate the signal after removal of an external cell stimulus. This self-perpetuated activation of a signalling circuit is a manifestation of its bistability. Bistable systems can exist in 'on' and 'off' states and both states are stable. We have demonstrated the existence of self-perpetuated activation mechanism for ERK1/2 in bronchial epithelial cells. This sustained activation of ERK1/2 supports long-term survival of these cells and primes them for cytokine transcription. ERK1/2 bistability arises from repetitive stimulation of the cell. The repeated stimulation (e.g. repeated viral infection or repeated allergen exposure) seems to be a common theme in asthma and other chronic illnesses. We thus hypothesize that the self-perpetuated ERK1/2 signal plays an important role in the pathogenesis of asthma.

Dendritic cells matured by a prostaglandin E2-containing cocktail can produce high levels of IL-12p70 and are more mature and Th1-biased than dendritic cells treated with TNF-α or LPS

Dendritic cells (DCs) play a crucial role in the initiation of an immune response. As maturation is critical for effective antigen presentation, different methods have been used to generate mature DCs (mDCs) ex vivo. The use of a maturation cocktail (MC) consisting of IL-1β, IL-6, TNF-α, and prostaglandin E2 (PGE2) initially showed promising results, but then was challenged because of low production of IL-12p70 and the potential for induction of Th2-type immune responses. To investigate this contention, we compared two of the most commonly used maturation factors, TNF-α and LPS, with MC. Maturation cocktail was superior to TNF-α and LPS with respect to enhancement of mDC-specific surface marker expression (CD83, CD86, and HLA-DR), induction of T cell proliferation by mDCs, and directional motility of mDCs toward CCL19. These results were supported by increased expression of a significant number of additional maturation-related genes by MC in comparison to TNF-α and LPS. In addition, we did not observe a Th2-biased shift in the gene expression profile of mDCs generated by MC. Conversely, MC induced more Th1-promoting transcriptional changes than LPS or TNF-α, including increased transcript levels of Th1-type cytokines such as IL-15, IL-12β, and EBI3 (IL-27β) and MHC class I molecules, Th1-promoting changes in the transcripts of CXCL16, CCL13, and CCL18, and reduced transcript levels of MHC class II molecules. More interestingly, the Th1-promoting characteristics of MC-mDCs were confirmed by their potential to produce large amounts of IL-12p70 after effective stimulation simulating in vivo events.

Dendritic cells for active anti-cancer immunotherapy: targeting activation pathways through genetic modification

Tumour immunotherapy has become a treatment modality for cancer, harnessing the immune system to recognize and eradicate tumour cells specifically. It is based on the expression of tumour associated antigens (TAA) by the tumour cells and aims at the induction of TAA-specific effector T cell responses, whilst overruling various mechanisms that can hamper the anti-tumour immune response, e.g. regulatory T cells (Treg). (Re-) activation of effector T cells requires the completion of a carefully orchestrated series of specific steps. Particularly important is the provision of TAA presentation and strong stimulatory signals, delivered by co-stimulatory surface molecules and cytokines. These can only be delivered by professional antigen-presenting cells, in particular dendritic cells (DC). Therefore, DC need to be loaded with TAA and appropriately activated. It is not surprising that an extensive part of DC research has focused on the delivery of both TAA and activation signals to DC, developing a one step approach to obtain potent stimulatory DC. The simultaneous delivery of TAA and activation signals is therefore the topic of this review, emphasizing the role of DC in mediating T cell activation and how we can manipulate DC for the pill-pose of enhancing tumour immunotherapy. As we gain a better understanding of the molecular and cellular mechanisms that mediate induction of TAA-specific T cells, rational approaches for the activation of T cell responses can be developed for the treatment of cancer.

Release of IL-12 by dendritic cells activated by TLR ligation is dependent on MyD88 signaling, whereas TRIF signaling is indispensable for TLR synergy

Recently, it has been shown that certain combinations of TLR ligands act in synergy to induce the release of IL-12 by DCs. In this study, we sought to define the critical parameters underlying TLR synergy. Our data show that TLR ligands act synergistically if MyD88- and TRIF-dependent ligands are combined. TLR4 uses both of these adaptor molecules, thus activation via TLR4 proved to be a synergistic event on its own. TLR synergy did not affect all aspects of DC activation but enhanced primarily the release of certain cytokines, particularly IL-12, whereas the expression of costimulatory molecules remained unchanged. Consequently, synergistic activation of DC did not affect their ability to induce T cell proliferation but resulted in T(H)1-biased responses in vitro and in vivo. Furthermore, we examined the impact of TLR ligand combinations on primary DC in vitro but observed only modest effects with a combination of CpG + Poly (I:C). However, noticeable synergy in terms of IL-12 production by DCs was detectable in vivo after systemic administration of CpG + Poly (I:C). Finally, we show that synergy is partially dependent on IFNAR signaling but does not require the release of IFNs to the enviroment, suggesting an autocrine action of type I IFNs.

Generation of human dendritic cells that simultaneously secrete IL-12 and have migratory capacity by adenoviral gene transfer of hCD40L in combination with IFN-gamma

Dendritic cells (DCs) are professional antigen presenting cells and have key functions in the initiation of immune responses. Hence, antigen-loaded DCs have become important tools for active-specific immunotherapy. In addition to defining strategies for antigen loading, effective T-cell activation by DCs will depend on vaccination protocols that facilitate DC migration to secondary lymphoid tissues and expression of costimulatory molecules and cytokines. Adenoviral gene transfer has been successfully implemented for genetic antigen loading of DCs. In this study, we exploit an adenoviral vector encoding human CD40 ligand (CD40L), Ad5hCD40L, to establish DCs that feature both migration potential and prolonged secretion of the key T-helper 1 cytokine interleukin-12p70 (IL-12p70). Transduction of human monocyte-derived DCs with Ad5hCD40L resulted in efficient CD40L expression, which was detected only intracellularly, and in secretion of IL-12p70. Addition of recombinant interferon (IFN)-gamma shortly after DC transduction substantially increased IL-12p70 secretion. Maturation of DCs was achieved with a standard cytokine maturation cocktail (MC) containing prostaglandin E2 which, however, abolished IL-12p70 secretion by Ad5hCD40L-transduced cells in the absence of IFN-gamma. Only DCs treated with Ad5hCD40L, MC, and IFN-gamma migrated efficiently towards CCL19 and continued to secrete IL-12p70. Finally, DCs transduced with both Ad5hCD40L and an adenoviral vector encoding the melanoma antigen MelanA/MART-1 and treated with MC and IFN-gamma efficiently primed naive autologous CD8+ T cells into antigen-specific cytotoxic T lymphocyte. This strategy to generate DCs that exert both migration capacity and prolonged IL-12p70 secretion after intracellular CD40L expression and IFN-gamma treatment has the potential to further improve current DC vaccination protocols.

Galectin-1 co-clusters CD43/CD45 on dendritic cells and induces cell activation and migration through Syk and protein kinase C signaling

Galectin-1 is a galactoside-binding lectin expressed in multiple tissues that has pleiotropic immunomodulatory functions. We previously showed that galectin-1 activates human monocyte-derived dendritic cells (MDDCs) and triggers a specific genetic program that up-regulates DC migration through the extracellular matrix, an integral property of mucosal DCs. Here, we identify the galectin-1 receptors on MDDCs and immediate downstream effectors of galectin-1-induced MDDC activation and migration. Galectin-1 binding to surface CD43 and CD45 on MDDCs induced an unusual unipolar co-clustering of these receptors and activates a dose-dependent calcium flux that is abrogated by lactose. Using a kinome screen and a systems biology approach, we identified Syk and protein kinase C tyrosine kinases as mediators of the DC activation effects of galectin-1. Galectin-1, but not lipopolysaccharide, stimulated Syk phosphorylation and recruitment of phosphorylated Syk to the CD43 and CD45 co-cluster on MDDCs. Inhibitors of Syk and protein kinase C signaling abrogated galectin-1-induced DC activation as monitored by interleukin-6 production; and MMP-1, -10, and -12 gene up-regulation; and enhanced migration through the extracellular matrix. The latter two are specific features of galectin-1-activated DCs. Interestingly, we also found that galectin-1 can prime DCs to respond more quickly to low dose lipopolysaccharide stimulation. Finally, we underscore the biological relevance of galectin-1-enhanced DC migration by showing that intradermal injection of galectin-1 in MRL-fas mice, which have a defect in skin DC emigration, increased the in vivo migration of dermal DCs to draining lymph nodes.

Ex vivo generation of mature equine monocyte-derived dendritic cells

Dendritic cells (DCs) are innate immune cells specialized in antigen detection and presentation. They perform an essential role in initiating and guiding the immune response, the direction of which largely depends upon the activation state of the DCs. The objective of this study was to generate mature equine monocyte-derived DCs and, in doing so, to develop a method for measuring the activation state of these cells. Equine DCs were stimulated with UV-inactivated Escherichia coli (E. coli), and the activation status was measured by analyzing cell surface marker expression, cytokine production, and endocytic capacity. Comparisons for each parameter measured were performed between macrophages, non-stimulated DCs and stimulated DCs. Equine monocyte-derived DCs may be distinguished from macrophages based on cell surface expression of MHC class II (p<0.0001) and CD206 (p<0.0001), their capacity for endocytosis of FITC-dextran (p<0.05), and production of TNF-alpha upon stimulation (p<0.001). Furthermore, stimulated DCs can be distinguished from non-stimulated DCs based on increased cell surface expression of MHC class II (p<0.0001) and upregulation of pro-inflammatory cytokine mRNA, particularly IL-12/IL-23p40 (p<0.05) and IL-23p19 (p<0.05). The ability to measure DC activation state will facilitate future investigations of equine DC function.

Activin-A attenuates several human natural killer cell functions

Dendritic-cell (DC) and natural killer (NK)-cell interactions are critical in sculpting the adaptive immune response. However, the mechanisms by which DCs down-regulate NK-cell functions are not well understood. NK-cell function is inhibited by transforming growth factor beta (TGF-beta), but DCs do not appear to produce TGF-beta. We have previously shown that activated human DCs produce large amounts of activin-A, a TGF-beta superfamily member, which autoregulates DC function. The present report shows that NK-cells express type I and II activin receptors and that activin-A triggers NK-cell Smad 2/3 signaling. Furthermore, activin-A directly regulates NK cell functions by (1) down-regulating the T-box transcription factor T-bet and interferon gamma (IFN-gamma) but not perforin or granzyme mRNA; (2) suppressing NK-cell IFN-gamma production as potently as TGF-beta; and (3) suppressing NK-cell CD25 expression and proliferation and sculpting NK-cell cytokine and chemokine profiles. Interestingly, unlike TGF-beta, activin-A weakly down-regulates the NK-cell natural cytotoxicity receptors (NCRs) NKp30 and NKG2D but does not attenuate their cytotoxic function. These findings provide the first evidence for a novel immune regulatory role of activin-A during DC-mediated NK-cell regulation, highlighting the potential of antagonizing activin-A signaling in vivo to enhance NK cell-mediated immune functions and adaptive immunity.

Cofilin activation in peripheral CD4 T cells of HIV-1 infected patients: a pilot study

Cofilin is an actin-depolymerizing factor that regulates actin dynamics critical for T cell migration and T cell activation. In unstimulated resting CD4 T cells, cofilin exists largely as a phosphorylated inactive form. Previously, we demonstrated that during HIV-1 infection of resting CD4 T cells, the viral envelope-CXCR4 signaling activates cofilin to overcome the static cortical actin restriction. In this pilot study, we have extended this in vitro observation and examined cofilin phosphorylation in resting CD4 T cells purified from the peripheral blood of HIV-1-infected patients. Here, we report that the resting T cells from infected patients carry significantly higher levels of active cofilin, suggesting that these resting cells have been primed in vivo in cofilin activity to facilitate HIV-1 infection. HIV-1-mediated aberrant activation of cofilin may also lead to abnormalities in T cell migration and activation that could contribute to viral pathogenesis.

Maximizing dendritic cell migration in cancer immunotherapy

BACKGROUND

The success of dendritic cell (DC)-based immunotherapy in inducing cellular immunity against tumors is highly dependent on accurate delivery and trafficking of the DC to T-cell-rich areas of secondary lymphoid tissues.

OBJECTIVE

To provide an overview of DC migration in vivo and how migration to peripheral lymph nodes might be improved to optimize DC therapy.

METHODS

We focused on DC migration in preclinical models and human skin explants and on clinical vaccination trials studying migration of in vitro-generated DC.

RESULTS/CONCLUSIONS

DC migration requires an intricate interplay between the cell and its environment. To maximize migration for cellular therapy, it is important to optimize the generation of migratory DC as well as treatment strategies.

The adjuvants aluminum hydroxide and MF59 induce monocyte and granulocyte chemoattractants and enhance monocyte differentiation toward dendritic cells

Aluminum hydroxide (alum) and the oil-in-water emulsion MF59 are widely used, safe and effective adjuvants, yet their mechanism of action is poorly understood. We assessed the effects of alum and MF59 on human immune cells and found that both induce secretion of chemokines, such as CCL2 (MCP-1), CCL3 (MIP-1alpha), CCL4 (MIP-1beta), and CXCL8 (IL-8), all involved in cell recruitment from blood into peripheral tissue. Alum appears to act mainly on macrophages and monocytes, whereas MF59 additionally targets granulocytes. Accordingly, monocytes and granulocytes migrate toward MF59-conditioned culture supernatants. In monocytes, both adjuvants lead to increased endocytosis, enhanced surface expression of MHC class II and CD86, and down-regulation of the monocyte marker CD14, which are all phenotypic changes consistent with a differentiation toward dendritic cells (DCs). When monocyte differentiation into DCs is induced by addition of cytokines, these adjuvants enhanced the acquisition of a mature DC phenotype and lead to an earlier and higher expression of MHC class II and CD86. In addition, MF59 induces further up-regulation of the maturation marker CD83 and the lymph node-homing receptor CCR7 on differentiating monocytes. Alum induces a similar but not identical pattern that clearly differs from the response to LPS. This model suggests a common adjuvant mechanism that is distinct from that mediated by danger signals. We conclude that during vaccination, adjuvants such as MF59 may increase recruitment of immune cells into the injection site, accelerate and enhance monocyte differentiation into DCs, augment Ag uptake, and facilitate migration of DCs into tissue-draining lymph nodes to prime adaptive immune responses.

Migration of dendritic cell subsets and their precursors

The ability of dendritic cells (DCs) to initiate and orchestrate immune responses is a consequence of their localization within tissues and their specialized capacity for mobilization. The migration of a given DC subset is typified by a restricted capacity for recirculation, contrasting markedly with T cells. Routes of DC migration into lymph nodes differ notably for distinct DC subsets. Here, we compare the distinct migratory patterns of plasmacytoid DCs (pDCs), CD8alpha(+) DCs, Langerhans cells, and conventional myeloid DCs and discuss how the highly regulated patterns of DC migration in vivo may affect their roles in immunity. Finally, to gain a more molecular appreciation of the specialized migratory properties of DCs, we review the signaling cascades that govern the process of DC migration.

Human lymphocyte activation gene-3 molecules expressed by activated T cells deliver costimulation signal for dendritic cell activation

Data have been reported on the in vivo adjuvant role of soluble lymphocyte activation gene-3 (LAG-3) recombinant protein in mouse models and on its ability to support the in vitro generation of human, tumor-specific CTLs. In this study, we show that soluble human rLAG-3 protein (hLAG-3Ig) used in vitro as a single maturation agent induces phenotypic maturation of monocyte-derived dendritic cells and promoted the production of chemokines and TNF-alpha inflammatory cytokine. When given in association with optimal or suboptimal doses of CD40/CD40L, hLAG-3Ig functions as a strong costimulatory factor and induces full functional activation of monocyte-derived dendritic cells that includes the production of high level of IL-12p70. Moreover, evidence is here provided that this costimulatory function licensing dendritic cells to produce IL-12p70 is also a functional property of LAG-3 molecules when expressed in a physiological context by CD4(+) activated T cells. Altogether, these data show for the first time a role of LAG-3 in mediating dendritic cell activation when expressed on the T cell surface or released after specific Ag stimulation in the interspaces of immunological synapses.

Plasmacytoid and myeloid dendritic cells with a partial activation phenotype accumulate in lymphoid tissue during asymptomatic chronic HIV-1 infection

Dendritic cells (DCs) from HIV-1-infected individuals display numeric and functional defects, and recent evidence suggests that HIV-1 can directly and indirectly activate DCs in vitro. The in vivo activation state and compartmentalization of DC subsets during HIV-1 infection remain poorly understood, however. We evaluated phenotypic and functional characteristics of myeloid dendritic cells (mDCs) and plasmacytoid dendritic cells (pDCs) directly ex vivo in peripheral blood and lymphoid tissue from HIV-1-infected and HIV-seronegative individuals. Analysis of a wide range of chemokine receptors and activation/maturation markers on circulating DCs from viremic HIV-1-infected donors revealed a phenotype indicative of partial activation. Yet, blood DCs from viremic subjects still achieved full maturation when stimulated in vitro. In addition, blood pDCs from viremic individuals had a reduced capacity to migrate to CXCL12 in vitro. Total numbers of both DC subsets were increased in lymph nodes of asymptomatic untreated HIV-1-infected subjects, consistent with DC accumulation in the lymphoid compartment. Lymph node DCs also expressed high levels of CD40 in the absence of increases of other typical activation/maturation markers. Activation and depletion of DCs in blood with accumulation in lymphoid tissue may contribute to HIV-associated chronic immune activation and T-cell dysfunction.

Maturing dendritic cells depend on RAGE for in vivo homing to lymph nodes

The mobilization of dendritic cells (DCs) from peripheral tissues is critical for the establishment of T cell-dependent immune responses or tolerance, because the physical interaction of DCs with naive T cells takes place in the T cell areas of lymph nodes. The autocrine/paracrine release of the high mobility group box 1 (HMGB1) nuclear protein by DCs controls the outcome of the DC-T cell interaction, influencing the priming/Th1 polarization of naive T cells. We herein present evidence that the receptor for advanced glycation end products (RAGE), a multiligand member of the Ig superfamily of cell-surface molecules that acts as a receptor for HMGB1, plays a nonredundant role in DC homing to lymph nodes. We used noninvasive imaging by magnetic resonance and immunohistochemistry to track DCs after s.c. injection in the footpad of wild-type(+/+) or RAGE(-/-) mice. Maturing DCs expressing RAGE effectively migrated in both conditions. In contrast, RAGE(-/-) DCs failed to reach the draining popliteal lymph nodes of +/+ and -/- mice, indicating that the integrity of RAGE is required for DC mobilization. Thus the HMGB1-RAGE pathway is a checkpoint in DC maturation and function and a candidate for targeted therapies.

Comparative evaluation of techniques for the manufacturing of dendritic cell-based cancer vaccines

Manufacturing procedures for cellular therapies are continuously improved with particular emphasis on product safety. We previously developed a dendritic cell (DC) cancer vaccine technology platform that uses clinical grade lipopolysaccharide (LPS) and interferon (IFN)-y for the maturation of monocyte derived DCs. DCs are frozen after 6 hrs exposure at a semi-mature stage (smDCs) retaining the capacity to secret interleukin (IL)-12 and thus support cytolytic T-cell responses, which is lost at full maturation. We compared closed systems for monocyte enrichment from leucocyte apheresis products from healthy individuals using plastic adherence, CD14 selection, or CD2/19 depletion with magnetic beads, or counter flow centrifugation (elutriation) using a clinical grade in comparison to a research grade culture medium for the following DC generation. We found that elutriation was superior compared to the other methods showing 36 ± 4% recovery, which was approximately 5-fold higher as the most frequently used adherence protocol (8 ± 1%), and a very good purity (92 ± 5%) of smDCs. Immune phenotype and IL-12 secretion (adherence: 1.4 ± 0.4; selection: 20 ± 0.6; depletion: 1 ±0.5; elutriation: 3.6 ± 1.5 ng/ml) as well as the potency of all DCs to stimulate T cells in an allogeneic mixed leucocyte reaction did not show statistically significant differences. Research grade and clinical grade DC culture media were equally potent and freezing did not impair the functions of smDCs. Finally, we assessed the functional capacity of DC cancer vaccines manufactured for three patients using this optimized procedure thereby demonstrating the feasibility of manufacturing DC cancer vaccines that secret IL-12 (9.4 ± 6.4 ng/ml). We conclude that significant steps were taken here towards clinical grade DC cancer vaccine manufacturing.

Recruitment of dendritic cells and macrophages during T cell-mediated synovial inflammation

Adoptive transfer of adjuvant-induced arthritis was used in this study to examine local macrophages and dendritic cells (DCs) during T cell-mediated synovial inflammation. We studied the influx of CD11b⁺CD11c⁺ putative myeloid DCs and other non-lymphoid CD45⁺ cells into synovium-rich tissues (SRTs) of the affected hind paws in response to a pulse of autoreactive thoracic duct cells. Cells were prepared from the SRTs using a collagenase perfusion-digestion technique, thus allowing enumeration and phenotypic analysis by flow cytometry. Numbers of CD45⁺ cells increased during the first 6 days, with increases in CD45⁺MHC (major histocompatibility complex) II⁺ monocyte-like cells from as early as day 3 after transfer. In contrast, typical MHC II^- monocytes, mainly of the CD4^- subset, did not increase until 12 to 14 days after cell transfer, coinciding with the main influx of polymorphonuclear cells. By day 14, CD45⁺MHC II^hi cells constituted approximately half of all CD45⁺ cells in SRT. Most of the MHC II^hi cells expressed CD11c and CD11b and represented putative myeloid DCs, whereas only approximately 20% were CD163⁺ macrophages. Less than 5% of the MHC II^hi cells in inflamed SRT were CD11b^-, setting a maximum for any influx of plasmacytoid DCs. Of the putative myeloid DCs, a third expressed CD4 and both the CD4⁺ and the CD4^- subsets expressed the co-stimulatory molecule CD172a. Early accumulation of MHC II^hiCD11c⁺ monocyte-like cells during the early phase of T cell-mediated inflammation, relative to typical MHC II^- blood monocytes, suggests that recruited monocytes differentiate rapidly toward the DC lineage at this stage in the disease process. However, it is possible also that the MHC II^hiCD11c⁺ cells originate from a specific subset of DC-like circulating mononuclear cells.

Activin-A: a novel dendritic cell–derived cytokine that potently attenuates CD40 ligand–specific cytokine and chemokine production

Activin-A is a transforming growth factor-β (TGF-β) superfamily member that plays a pivotal role in many developmental and reproductive processes. It is also involved in neuroprotection, apoptosis of tumor and some immune cells, wound healing, and cancer. Its role as an immune-regulating protein has not previously been described. Here we demonstrate for the first time that activin-A has potent autocrine effects on the capacity of human dendritic cells (DCs) to stimulate immune responses. Human monocyte-derived DCs (MoDCs) and the CD1c+ and CD123+ peripheral blood DC populations express both activin-A and the type I and II activin receptors. Furthermore, MoDCs and CD1c+ myeloid DCs rapidly secrete high levels of activin-A after exposure to bacteria, specific toll-like receptor (TLR) ligands, or CD40 ligand (CD40L). Blocking autocrine activin-A signaling in DCs using its antagonist, follistatin, enhanced DC cytokine (IL-6, IL-10, IL-12p70, and tumor necrosis factor-α [TNF-α]) and chemokine (IL-8, IP-10, RANTES, and MCP-1) production during CD40L stimulation, but not TLR-4 ligation. Moreover, antagonizing DC-derived activin-A resulted in significantly enhanced expansion of viral antigen-specific effector CD8+ T cells. These findings establish an immune-regulatory role for activin-A in DCs, highlighting the potential of antagonizing activin-A signaling in vivo to enhance vaccine immunogenicity.

Immunotherapy with dendritic cells for cancer

Dendritic cells are professional antigen-presenting cells with a key role in both immunity induction and tolerance maintenance. Dendritic cells are highly specialized in antigen capture, processing and presentation, and express co-stimulation signals which activate T lymphocytes and NK cells. Dendritic cells generated in culture and loaded with an antigen efficiently induce antigen-specific immunity after injection. More recently, methods have been developed that target antigens to dendritic cells in vivo, bypassing the need for ex vivo cell manipulations. Numerous ongoing studies aim to evaluate the effectiveness of dendritic cell vaccines in preventing tumor relapses and extending patients' survival. Further implementation of this form of immunotherapy is expected following the identification of the mechanisms controlling dendritic cell immunogenicity, and from a better understanding of the cell dynamics whereby immune responses are orchestrated. Here, we discuss these new insights together with an overview of the dendritic cell-based clinical studies carried out to date.

The phenotypical and functional characteristics of cord blood monocytes and CD14(-/low)/CD16(+) dendritic cells can be relevant to the development of cellular immune responses after transplantation

Umbilical cord blood (UCB) has been used as an alternative source of haematopoietic progenitors for transplantation presenting advantages over bone marrow (BM) that are related with known shortages of newborns' immune system at adaptive and innate levels. Using flow cytometry, we studied the expression of Toll-like receptors (TLRs) and chemokine receptors (CKRs) and the production of pro-inflammatory cytokines by monocytes and CD14(-/low)/CD16(+)DCs from peripheral blood (PB; n=10), and umbilical cord blood (UCB; n=10). CKRs and cytokines were studied before and after stimulation of cells with LPS plus IFN-gamma. We also identified the two populations in normal bone marrow samples (BM; n=5). BM presented lower frequencies of both studied populations when compared to UCB and PB. CD14(-/low)/CD16(+)DCs presented a pattern of TLR expression different from mature monocytes reflecting distinct functions for these two populations. UCB cells presented reduced expression of TLR-4 and lower capability to produce cytokines prior stimulation. The populations studied presented different patterns of CKR expression reflecting distinct migratory pathways. Moreover, UCB cells presented higher expressions of CXCR4 and CCR7 that may be involved in immune system maturation and stem cell homing. Monocytes and CD14(-/low)/CD16(+)DCs present functional and phenotypical characteristics that may contribute to the lower incidence and severity of GVHD.

The clinical grade maturation cocktail monophosphoryl lipid A plus IFNgamma generates monocyte-derived dendritic cells with the capacity to migrate and induce Th1 polarization

Ex vivo generated monocyte-derived dendritic cells (DCs) are used as a cellular vaccine against cancer in clinical trials. In order to be able to induce an efficient tumour-specific CTL response during immunotherapy, DCs have to be able to migrate to the lymph node and produce the Th1 polarizing cytokine, IL-12p70, upon encounter of T cells in the lymph node. However, most clinically used DCs do not produce IL-12p70 upon T cell contact. In this study, we compared a newly developed clinical grade DC maturation cocktail consisting of MPLA and IFNgamma with two clinically available maturation cocktails, the 'gold standard' (TNFalpha, IL-1beta, IL-6 and PGE(2)) and the 'alpha type 1 polarizing' (TNFalpha, IL-1beta, IFNalpha, IFNgamma and pI:C) cocktail. All three cocktails induced phenotypically mature DCs. However, in contrast to 'gold standard' DCs, which produce no IL-12p70 and as a result induce mainly Th2 cells, DCs matured with MPLA and IFNgamma produce high levels of IL-12p70 upon CD40 triggering. Subsequently, these DCs induce mainly Th1 cells in vitro, even slightly more than by the alpha type 1 polarized DCs. In addition, MPLA plus IFNgamma matured DCs have an intermediate migratory capacity towards CCL21. In conclusion, we here present MPLA plus IFNgamma as a simple clinical grade maturation cocktail to generate immunostimulatory DCs with superior capacity to induce type 1 immunity.

Monocytes immunoselected via the novel monocyte specific molecule, CD300e, differentiate into active migratory dendritic cells

Monocytes, immunoselected using MMRI-1, a monoclonal antibody specific for CD300e, were used to generate dendritic cells (DC). These CD300e immunoselected monocyte-derived DC (MoDC) were compared phenotypically and functionally to CD14 immunoselected MoDC. CD300e and CD14 immunoselected mature MoDC expressed similar levels of the DC marker, CD83 and costimulatory molecules, CD80, CD86, and CD40. Both preparations took up soluble antigen with similar efficiency by pinocytosis and receptor mediated uptake. The CD300e and CD14 immunoselected MoDC also induced comparable CD4+ T lymphocyte allogeneic responses and recall responses to tetanus toxoid. Similar magnitude CD8 T lymphocyte responses to the naive antigen, MART-1 and the recall antigen, FMP, were induced by both MoDC preparations. Cytokine secretion by each type of MoDC preparation was similar; each secreted interleukin-12, tumor necrosis factor-alpha, and low levels of interferon-gamma but in most cases no interleukin-10. Migration studies confirmed that both types of MoDC migrated towards the chemokine, CCL21 although CD300e immunoselected showed greater migration. Overall, the CD14 immunoselected MoDC had higher spontaneous background migration, compared with the CD300e immunoselected MoDC. Differential signaling from the antibodies used to immunoselect the monocytes may account for the slight differences in migratory capacity. These data identify the CD300e antigen as another monocyte-specific marker that can be used to purify monocytes for differentiation into functionally active MoDC.

Efficient chemokine-dependent migration and primary and secondary IL-12 secretion by human dendritic cells stimulated through Toll-like receptors

Recent findings have demonstrated the properties of cell migration and cytokine secretion to be mutually exclusive and linked them to different functional subpopulations of dendritic cells (DCs). We studied human monocyte-derived DCs after stimulation with peptidoglycan (PGN), poly(I:C), lipopolysaccharide (LPS), and R848 (resiquimod) and found the resulting mature DCs to express CCR7, to migrate toward CCL19 and to be efficient primary interleukin (IL)-12 producers. Importantly, the potential for secondary production of large amounts of IL-12p70 in response to CD40 ligation was also preserved after stimulation by all Toll-like receptor (TLR) ligands. Differences between the TLR ligands were seen in the primary secretion of IL-12 and IL-23, in the survival of the DCs and in the expression of CD38. Finally, DCs stimulated by R848 were efficient in expanding peptide-specific CD8-positive T cells capable of peptide-specific target cell lysis. Together, our data suggest that TLR ligands induce the generation of mature DCs that integrate migratory and cytokine secretory capacity as well as cytotoxic T lymphocyte (CTL) stimulatory properties.

Cholera toxin promotes the generation of semi-mature porcine monocyte-derived dendritic cells that are unable to stimulate T cells

Cholera toxin (Ctx) is a powerful mucosal adjuvant with potential applications for oral vaccination of swine. Dendritic cells (DC) play a key role in the decision between immunity and tolerance, and are likely target cells for mediating Ctx functions in vivo. Therefore, we examined the capacity of Ctx to enhance stimulatory activity of porcine monocyte-derived DC (MoDC). Ctx promoted the development of a semi-mature DC phenotype, with decreased levels of MHC class II and CD40, but increased CD80/86 expression. These changes were associated with activation of extracellular signal-regulated kinase (ERK), but not NFkappaB or c-Jun N-terminal kinase (JNK). Functionally, Ctx-priming greatly diminished T cell stimulatory capacity both in antigen-specific and superantigen-induced proliferation assays. The lower proliferation rate was not due to increased apoptosis of either DC or T cells. Ctx suppressed TNFalpha secretion by MoDC, but induced IL-10 production. The observed effects on T cell proliferation could only be partially mimicked by IL-10 alone. However, addition of recombinant TNFalpha to co-cultures of Ctx-primed MoDC and lymphocytes restored lymphocyte proliferation in a concentration-dependent manner. Ctx-primed DC were not actively tolerogenic, since they could not suppress proliferative T cell reactions induced by untreated DC.

DC research in Australia

Australian researchers have contributed significantly to the understanding of DC biology and clinical application over the past 25 years. Active DC research programs are in place in all major centers, pursuing the key questions of DC phylogeny, physiology and clinical applicability. Pre-clinical and clinical research include the pathophysiology of DC in malignancy, autoimmunity, chronic viral infection, chronic renal failure and transplantation medicine. In addition, Australian laboratories have uncovered some of the subtle complexities of DC subsets, often utilizing novel investigational tools discovered in their laboratories. Above all, Australian DC research has benefited from the existence of a potent culture of active collaboration, which has led to key interactions between cellular immunologists, clinician scientists and clinical researchers. These collaborations have led to the emergence of DC research programs that extend from in vitro and animal models of DC biology through each step of clinical translation and into active clinical trials.

Duration, combination and timing: the signal integration model of dendritic cell activation

The activation of resting dendritic cells (DCs) is a crucial step in the initiation of adaptive immunity because it links peripheral events initiated by the encounter with pathogens to the activation and expansion of antigen-specific T lymphocytes in secondary lymphoid organs. It is well recognized that a wide variety of microbial products and endogenous signals can trigger DC activation, and that different DC subsets are specialized in inducing different classes of immune responses. In this review, we will focus on how different aspects of DC maturation are regulated not only by the nature of the DC maturation stimuli, but also by their duration, combination and timing, and provide an overview of how different modes of DC activation can affect T cell responses.

Prostaglandin I2 analogs inhibit proinflammatory cytokine production and T cell stimulatory function of dendritic cells

Signaling through the PGI(2) receptor (IP) has been shown to inhibit inflammatory responses in mouse models of respiratory syncytial viral infection and OVA-induced allergic responses. However, little is known about the cell types that mediate the anti-inflammatory function of PGI(2.) In this study, we determined that PGI(2) analogs modulate dendritic cell (DC) cytokine production, maturation, and function. We report that PGI(2) analogs (iloprost, cicaprost, treprostinil) differentially modulate the response of murine bone marrow-derived DC (BMDC) to LPS in an IP-dependent manner. The PGI(2) analogs decreased BMDC production of proinflammatory cytokines (IL-12, TNF-alpha, IL-1alpha, IL-6) and chemokines (MIP-1alpha, MCP-1) and increased the production of the anti-inflammatory cytokine IL-10 by BMDCs. The modulatory effect was associated with IP-dependent up-regulation of intracellular cAMP and down-regulation of NF-kappaB activity. Iloprost and cicaprost also suppressed LPS-induced expression of CD86, CD40, and MHC class II molecules by BMDCs and inhibited the ability of BMDCs to stimulate Ag-specific CD4 T cell proliferation and production of IL-5 and IL-13. These findings suggest that PGI(2) signaling through the IP may exert anti-inflammatory effects by acting on DC.

CD11c+ blood dendritic cells induce antigen-specific cytotoxic T lymphocytes with similar efficiency compared to monocyte-derived dendritic cells despite higher levels of MHC class I expression

Dendritic cell (DC) immunotherapy for cancer has shown promising results in phase I and II clinical trials. Most studies have used monocyte-derived DCs (MoDCs) but their poor migratory capacity in vivo has emerged as a key issue. The natural circulating peripheral blood CD11c+ DC precursors (BDCs) may be an attractive alternative to MoDCs, as they can be isolated rapidly in sufficient quantities, and have superior migratory and T helper-1-inducing capacity in vitro. We performed the first comparative analysis of the ability of autologous BDCs and MoDCs in healthy donors to induce tumor-specific cytotoxic T lymphocytes (CTLs). BDCs expressed significantly higher levels of major histocompatibility complex class I and CD83 in the absence of exogenous stimuli compared with MoDCs. After activation with polyinosinic-polycytidylic acid, BDCs expressed higher levels of major histocompatibility complex class I, CD40, CD80, and CD83, and secreted higher levels of tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6, and IL-8 compared with MoDCs. Despite these differences, both preparations secreted similar levels of IL-12 in response to polyinosinic-polycytidylic acid and, importantly, induced CTL responses of similar magnitude and affinity against influenza matrix protein and MART-1. The ability of BDCs to induce efficient CTL responses, combined with their migratory capacity, makes them an appealing alternative to be investigated in clinical immunotherapy research protocols.