DEC-205 mediates antigen uptake and presentation by both resting and activated human plasmacytoid dendritic cells

PI3K-PKB hyperactivation augments human plasmacytoid dendritic cell development and function

Plasmacytoid dendritic cells (pDCs) are considered potential tools or targets for immunotherapy. However, current knowledge concerning methodologies to manipulate their development or function remains limited. Here, we investigated the role of the phosphatidylinositol 3-kinase (PI3K)-protein kinase B (PKB)-mammalian target of rapamycin (mTOR) axis in human pDC development, survival, and function. In vitro pDC generation from human cord blood-derived CD34(+) hematopoietic progenitors was reduced by pharmacologic inhibition of PI3K, PKB, or mTOR activity, and peripheral blood pDCs required PI3K-PKB-mTOR signaling to survive. Accordingly, activity of this pathway in circulating pDCs correlated with their abundance in peripheral blood. Importantly, introduction of constitutively active PKB or pharmacologic inhibition of negative regulator phosphatase and tensin homolog (PTEN) resulted in increased pDC numbers in vitro and in vivo. Furthermore, MHC class II and costimulatory molecule expression, and production of IFN-α and TNF-α, were augmented, which could be explained by enhanced IRF7 and NF-κB activation. Finally, the numerically and functionally impaired pDCs of chronic hepatitis B patients demonstrated reduced PI3K-PKB-mTOR activity. In conclusion, intact PI3K-PKB-mTOR signaling regulates development, survival, and function of human pDCs, and pDC development and functionality can be promoted by PI3K-PKB hyperactivation. Manipulation of this pathway or its downstream targets could be used to improve the generation and function of pDCs to augment immunity.

Comparative analysis of inflammatory infiltrates in collagen-induced arthritis, kidney graft rejection and delayed-type hypersensitivity in non-human primates

OBJECTIVES

Non-human primates are immunologically closely related to humans providing relevant models of inflammatory disorders often used to evaluate new immunomodulating therapies. The aim of the study was to compare inflammatory infiltrates of acute graft rejection (AR) and collagen-induced arthritis (CIA) to delayed-type hypersensitivity (DTH) reactions as the latter model may serve as a less invasive animal model.

MATERIALS AND METHODS

Tissue samples of AR, CIA and DTH were obtained from rhesus monkeys used in several pre-clinical studies. The infiltrate composition was determined by immunohistochemical analysis.

RESULTS

The infiltrates in AR consisted of T cells, macrophages and B cells. The presence of lymphoid structures in AR suggested ongoing intragraft immune activation. The synovia of CIA contained predominantly macrophages and few T cells. The DTH infiltrates were dominated by T cells when the challenged was ovalbumin (OVA) and by macrophages when the challenge was tetanus toxoid (TT).

CONCLUSIONS

The histology of AR resembles aspects of DTH to OVA while that of CIA showed similarities of the DTH to TT. The DTH reaction could serve as a model to study immunomodulating drugs for acute rejection and the acute inflammatory phase of autoimmunity.

Harnessing human plasmacytoid dendritic cells as professional APCs

The plasmacytoid dendritic cell (pDC) constitutes a unique DC subset that links the innate and adaptive arm of the immune system. Whereas the unique capability of pDCs to produce large amounts of type I IFNs in response to pathogen recognition is generally accepted, their antigen-presenting function is often neglected since most studies on antigen presentation are aimed at other DC subsets. Recently, pDCs were demonstrated capable to present antigen leading to protective tumor immunity. In this review, we discuss how pDCs could be exploited in the fight against cancer by analyzing their capacity to capture, process and (cross-) present antigen.

DEC-205 is a cell surface receptor for CpG oligonucleotides

Synthetic CpG oligonucleotides (ODN) have potent immunostimulatory properties exploited in clinical vaccine trials. How CpG ODN are captured and delivered to the intracellular receptor TLR9, however, has been elusive. Here we show that DEC-205, a multilectin receptor expressed by a variety of cells, is a receptor for CpG ODN. When CpG ODN are used as an adjuvant, mice deficient in DEC-205 have impaired dendritic cell (DC) and B-cell maturation, are unable to make some cytokines such as IL-12, and display suboptimal cytotoxic T-cell responses. We reveal that DEC-205 directly binds class B CpG ODN and enhances their uptake. The CpG-ODN binding function of DEC-205 is conserved between mouse and man, although human DEC-205 preferentially binds a specific class B CpG ODN that has been selected for human clinical trials. Our findings identify an important receptor for class B CpG ODN and reveal a unique function for DEC-205.

Deciphering the message broadcast by tumor-infiltrating dendritic cells

Human dendritic cells (DCs) infiltrate solid tumors, but this infiltration occurs in favorable and unfavorable disease prognoses. The statistical inference is that tumor-infiltrating DCs (TIDCs) play no conclusive role in predicting disease progression. This is remarkable because DCs are highly specialized antigen-presenting cells linking innate and adaptive immunity. DCs either boost the immune system (enhancing immunity) or dampen it (leading to tolerance). This dual effect explains the dual outcomes of cancer progression. The reverse functional characteristics of DCs depend on their maturation status. This review elaborates on the markers used to detect DCs in tumors. In many cases, the identification of DCs in human cancers relies on staining for S-100 and CD1a. These two markers are mainly expressed by Langerhans cells, which are one of several functionally different DC subsets. The activation status of DCs is based on the expression of CD83, DC-SIGN, and DC-LAMP, which are nonspecific markers of DC maturation. The detection of TIDCs has not kept pace with the increased knowledge about the identification of DC subsets and their maturation status. Therefore, it is difficult to draw a conclusion about the performance of DCs in tumors. We suggest a novel selection of markers to distinguish human DC subsets and maturation states. The use of these biomarkers will be of pivotal importance to scrutinize the prognostic significance of TIDCs.

Monocytes differentiation upon treatment with a peptide corresponding to the C-terminus of activated T cell-expressed Tirc7 protein

Atp6v0a3 gene encodes for two alternative products, Tirc7 and a3 proteins, which are differentially expressed in activated T cells and resorbing osteoclasts, respectively. Tirc7 plays a central role in T cell activation, while a3 protein is critical for osteoclast-mediated bone matrix resorption. Based on the large body of evidences documenting the relationships between T cells and osteoclasts, we hypothesized that the extracellular C-terminus of Tirc7 protein could directly interact with osteoclast precursor cells. To address this issue, we performed the molecular cloning of a mouse Atp6v0a3 cDNA segment encoding the last 40 amino acids of Tirc7 protein, and we used this peptide as a ligand added to mouse osteoclast precursor cells. We evidenced that Tirc7-Cter peptide induced the differentiation of RAW264.7 cells into osteoclast-like cells, stimulated an autocrine/paracrine regulatory loop potentially involved in osteoclastic differentiation control, and strongly up-regulated F4/80 protein expression within multinucleated osteoclast-like cells. Using a mouse bone marrow-derived CD11b(+) cell line, or total bone marrow primary cells, we observed that similarly to Rankl, Tirc7-Cter peptide induced the formation of TRACP-positive large multinucleated cells. At last, using mouse primary monocytes purified from total bone marrow, we determined that Tirc7-Cter peptide induced the appearance of small multinucleated cells (3-4 nuclei), devoid of resorbing activity, and which displayed modulations of dendritic cell marker genes expression. In conclusion, we report for the first time on biological effects mediated by a peptide corresponding to the C-terminus of Tirc7 protein, which interfere with monocytic differentiation pathways.

The C-type lectin receptor CLEC9A mediates antigen uptake and (cross-)presentation by human blood BDCA3+ myeloid dendritic cells

CLEC9A is a recently discovered C-type lectin receptor involved in sensing necrotic cells. In humans, this receptor is selectively expressed by BDCA3+ myeloid dendritic cells (mDCs), which have been proposed to be the main human cross-presenting mDCs and may represent the human homologue of murine CD8+ DCs. In mice, it was demonstrated that antigens delivered with antibodies to CLEC9A are presented by CD8+ DCs to both CD4+ and CD8+ T cells and induce antitumor immunity in a melanoma model. Here we assessed the ability of CLEC9A to mediate antigen presentation by human BDCA3+ mDCs, which represent < 0.05% of peripheral blood leukocytes. We demonstrate that CLEC9A is only expressed on immature BDCA3+ mDCs and that cell surface expression is lost after TLR-mediated maturation. CLEC9A triggering via antibody binding rapidly induces receptor internalization but does not affect TLR-induced cytokine production or expression of costimulatory molecules. More importantly, antigens delivered via CLEC9A antibodies to BDCA3+ mDCs are presented by both MHC class I (cross-presentation) and MHC class II to antigen-specific T cells. We conclude that CLEC9A is a promising target for in vivo antigen delivery in humans to increase the efficiency of vaccines against infectious or malignant diseases.

Targeting Dendritic Cells in vivo for Cancer Therapy

Monoclonal antibodies that recognize cell surface molecules have been used deliver antigenic cargo to dendritic cells (DC) for induction of immune responses. The encouraging anti-tumor immunity elicited using this immunization strategy suggests its suitability for clinical trials. This review discusses the complex network of DC, the functional specialization of DC subsets, the immunological outcomes of targeting different DC subsets and their cell surface receptors, and the requirements for the induction of effective anti-tumor CD4 and CD8 T cell responses that can recognize tumor-specific antigens. Finally, we review preclinical experiments and the progress toward targeting human DC in vivo.

Targeted delivery of CpG ODN to CD32 on human and monkey plasmacytoid dendritic cells augments IFNα secretion

Atopic diseases are characterized by the presence of Th2 cells. Recent studies, in mice and man, demonstrated that allergen-specific Th2 responses can be shifted to Th0/Th1 responses. Plasmacytoid dendritic cells (pDCs) produce large amounts of type I interferons (IFNs) after stimulation of Toll Like Receptor 9 (TLR9) and are likely to play an important role in the reorientation of these Th2 cells. The expression of CD32a on the cell surface of pDCs makes this cell type attractive for targeted delivery of antigen and TLR agonists to revert Th2 responses. Therefore we sought to determine the efficacy of targeted delivery of CpG-C ODN to CD32a on the ability of human and monkey pDCs to secrete inflammatory cytokines. Here we demonstrate that targeted delivery of 3'-biotinylated CpG-C to CD32a on pDC induced phenotypical maturation as determined by CD80, CD83 and CD86 expression. Furthermore, targeting both monkey and human pDCs strongly augmented the secretion of IFNα compared to the delivery of CpG-C in an untargeted fashion (p<0.001). TLR9 induced activation hampers the ability of human pDCs to internalize CD32a. Therefore we opted for targeted delivery of CpG-ODNs to CD32a, which reduces the risk of undesired side effects of systemic TLR treatment and in addition delivers a superior signal for the activation of pDCs. This approach opens new treatment principles for allergic patients.

Vaccination with filamentous bacteriophages targeting DEC-205 induces DC maturation and potent anti-tumor T-cell responses in the absence of adjuvants

The efficacy of a new vaccine-delivery vector, based on the filamentous bacteriophage fd displaying a single-chain antibody fragment known to bind the mouse DC surface molecule DEC-205, is reported. We demonstrate both in vitro and in vivo an enhanced receptor-mediated uptake of phage particles expressing the anti-DEC-205 fragment by DCs. We also report that DCs targeted by fd virions in the absence of other stimuli produce IFN-α and IL-6, and acquire a mature phenotype. Moreover, DC-targeting with fd particles double-displaying the anti-DEC-205 fragment on the pIII protein and the OVA(257-264) antigenic determinant on the pVIII protein induced potent inhibition of the growth of the B16-OVA tumor in vivo. This protection was much stronger than other immunization strategies and similar to that induced by adoptively transferred DCs. Since targeting DEC-205 in the absence of DC activation/maturation agents has previously been described to result in tolerance, the ability of fd bacteriophages to induce a strong tumor-specific immune response by targeting DCs through DEC-205 is unexpected, and further validates the potential employment of this safe, versatile and inexpensive delivery system for vaccine formulation.