The dendritic cell receptor for endocytosis, DEC-205, can recycle and enhance antigen presentation via major histocompatibility complex class II-positive lysosomal compartments

Serum IgE clearance is facilitated by human FcεRI internalization

The high-affinity IgE receptor FcεRI is constitutively expressed in mast cells and basophils and is required for transmitting stimulatory signals upon engagement of IgE-bound allergens. FcεRI is also constitutively expressed in dendritic cells (DCs) and monocytes in humans; however, the specific functions of the FcεRI expressed by these cells are not completely understood. Here, we found that FcεRI expressed by human blood DC antigen 1-positive (BDCA1+) DCs and monocytes, but not basophils, traffics to endolysosomal compartments under steady-state conditions. Furthermore, IgE bound to FcεRI on BDCA1+ DCs was rapidly endocytosed, transported to the lysosomes, and degraded in vitro. IgE injected into mice expressing human FcεRIα (FCER1A-Tg mice) was endocytosed by conventional DCs and monocytes, and endocytosis was associated with rapid clearance of circulating IgE from these mice. Importantly, this rapid IgE clearance was dependent on monocytes or DCs but not basophils. These findings strongly suggest that constitutive internalization of human FcεRI by DCs and monocytes distinctively contributes to serum IgE clearance.

Complex determinants in specific members of the mannose receptor family govern collagen endocytosis

Members of the well-conserved mannose receptor (MR) protein family have been functionally implicated in diverse biological and pathological processes. Importantly, a proposed common function is the internalization of collagen for intracellular degradation occurring during bone development, cancer invasion, and fibrosis protection. This functional relationship is suggested by a common endocytic capability and a candidate collagen-binding domain. Here we conducted a comparative investigation of each member's ability to facilitate intracellular collagen degradation. As expected, the family members uPARAP/Endo180 and MR bound collagens in a purified system and internalized collagens for degradation in cellular settings. In contrast, the remaining family members, PLA2R and DEC-205, showed no collagen binding activity and were unable to mediate collagen internalization. To pinpoint the structural elements discriminating collagen from non-collagen receptors, we constructed a series of receptor chimeras and loss- and gain-of-function mutants. Using this approach we identified a critical collagen binding loop in the suggested collagen binding region (an FN-II domain) in uPARAP/Endo180 and MR, which was different in PLA2R or DEC-205. However, we also found that an active FN-II domain was not a sufficient determinant to allow collagen internalization through these receptors. Nevertheless, this ability could be acquired by the transfer of a larger segment of uPARAP/Endo180 (the Cys-rich domain, the FN-II domain and two CTLDs) to DEC-205. These data underscore the importance of the FN-II domain in uPARAP/Endo180 and MR-mediated collagen internalization but at the same time uncover a critical interplay with flanking domains.

Flavivirus entry receptors: an update

Flaviviruses enter host cells by endocytosis initiated when the virus particles interact with cell surface receptors. The current model suggests that flaviviruses use at least two different sets of molecules for infectious entry: attachment factors that concentrate and/or recruit viruses on the cell surface and primary receptor(s) that bind to virions and direct them to the endocytic pathway. Here, we present the currently available knowledge regarding the flavivirus receptors described so far with specific attention to C-type lectin receptors and the phosphatidylserine receptors, T-cell immunoglobulin and mucin domain (TIM) and TYRO3, AXL and MER (TAM). Their role in flavivirus attachment and entry as well as their implication in the virus biology will be discussed in depth.

Recent progress in adjuvant discovery for peptide-based subunit vaccines

Peptide-based subunit vaccines are of great interest in modern immunotherapy as they are safe, easy to produce and well defined. However, peptide antigens produce a relatively weak immune response, and thus require the use of immunostimulants (adjuvants) for optimal efficacy. Developing a safe and effective adjuvant remains a challenge for peptide-based vaccine design. Recent advances in immunology have allowed researchers to have a better understanding of the immunological implication of related diseases, which facilitates more rational design of adjuvant systems. Understanding the molecular structure of the adjuvants allows the establishment of their structure-activity relationships which is useful for the development of next-generation adjuvants. This review summarizes the current state of adjuvants development in the field of synthetic peptide-based vaccines. The structural, chemical and biological properties of adjuvants associated with their immunomodulatory effects are discussed.

Chemokines as Cancer Vaccine Adjuvants

We are witnessing a new era of immune-mediated cancer therapies and vaccine development. As the field of cancer vaccines advances into clinical trials, overcoming low immunogenicity is a limiting step in achieving full success of this therapeutic approach. Recent discoveries in the many biological roles of chemokines in tumor immunology allow their exploitation in enhancing recruitment of antigen presenting cells (APCs) and effector cells to appropriate anatomical sites. This knowledge, combined with advances in gene therapy and virology, allows researchers to employ chemokines as potential vaccine adjuvants. This review will focus on recent murine and human studies that use chemokines as therapeutic anti-cancer vaccine adjuvants.

Oligomannose-coated liposome as a novel adjuvant for the induction of cellular immune responses to control disease status

Professional phagocytic cells, such as dendritic cells, are mainly responsible for phagocytosis, antigen presentation, and cytokine secretion, which induce subsequent activation of T cell-mediated immunity. Thus, strategies that deliver antigens and stimulatory signals to the cells have significant implications for vaccine design. In this paper, we summarize the potential for liposomes coated with the neoglycolipids containing oligomannose residues (OMLs) as a novel adjuvant for induction of Th1 immune responses and CTLs specific for the encased antigen. OMLs preferentially take up peripheral phagocytic cells. In response to OML uptake, the cells secrete IL-12 selectively, enhance the expression of costimulatory molecules, and migrate into lymphoid tissues from peripheral tissues. OMLs also have the ability to deliver encapsulated protein antigens to the MHC class I and class II pathways to generate antigen-specific CTLs and Th1 cells, respectively, and lipid antigen to CD1d to activate NKT cells. Since administration of OML-based vaccines can eliminate an established tumor, inhibit elevation of the serum IgE level, and prevent progression of protozoan infections in several murine, human, and bovine models, OML-based vaccines have revealed their potential for clinical use in vaccination for a variety of diseases in which CTLs and/or Th1 cells act as effector cells.

Targeting antigens to dendritic cell receptors for vaccine development

Dendritic cells (DCs) are highly specialized antigen presenting cells of the immune system which play a key role in regulating immune responses. Depending on the method of antigen delivery, DCs stimulate immune responses or induce tolerance. As a consequence of the dual function of DCs, DCs are studied in the context of immunotherapy for both cancer and autoimmune diseases. In vaccine development, a major aim is to induce strong, specific T-cell responses. This is achieved by targeting antigen to cell surface molecules on DCs that efficiently channel the antigen into endocytic compartments for loading onto MHC molecules and stimulation of T-cell responses. The most attractive cell surface receptors, expressed on DCs used as targets for antigen delivery for cancer and other diseases, are discussed.

DEC-205-mediated antigen targeting to steady-state dendritic cells induces deletion of diabetogenic CD8⁺ T cells independently of PD-1 and PD-L1

CD8⁺ T cells specific for islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) have been implicated in type 1 diabetes in both humans and non-obese diabetic (NOD) mice, in which T cells specific for IGRP₂₀₆₋₂₁₄ are highly prevalent. We sought to manipulate these pathogenic T cells by exploiting the ability of steady-state dendritic cells (DCs) to present antigens in a tolerogenic manner. The endocytic receptor DEC-205 was utilized to deliver an IGRP₂₀₆₋₂₁₄ mimotope to DCs in NOD mice, and the impact of this delivery on a polyclonal population of endogenous islet-reactive cognate T cells was determined. Assessment of islet-infiltrating CD8⁺ T cells showed a decrease in the percentage, and the absolute number, of endogenous IGRP₂₀₆₋₂₁₄-specific T cells when the mimotope was delivered to DCs, compared with delivery of a specificity control. Employing an adoptive transfer system, deletion of CD8⁺ T cells as a result of DEC-205-mediated antigen targeting was found to occur independently of programmed death-1 (PD-1) and its ligand (PD-L1), both often implicated in the regulation of peripheral T-cell tolerance. Given its promise for the manipulation of self-reactive polyclonal T cells demonstrated here, the distinctive characteristics of this antigen delivery system will be important to appreciate as its potential as an intervention for autoimmune diseases continues to be investigated.

Inducing immune tolerance: a focus on Type 1 diabetes mellitus

Tolerogenic strategies that specifically target diabetogenic immune cells in the absence of complications of immunosuppression are the desired treatment for the prevention or even reversal of Type 1 diabetes (T1D). Antigen (Ag)-based therapies must not only suppress disease-initiating diabetogenic T cells that are already activated, but, more importantly, prevent activation of naive auto-Ag-specific T cells that may become autoreactive through epitope spreading as a result of Ag liberation from damaged islet cells. Therefore, identification of auto-Ags relevant to T1D initiation and progression is critical to the design of effective Ag-specific therapies. Animal models of T1D have been successfully employed to identify potential diabetogenic Ags, and have further facilitated translation of Ag-specific tolerance strategies into human clinical trials. In this review, we highlight important advances using animal models in Ag-specific T1D immunotherapies, and the application of the preclinical findings to human subjects. We provide an up-to-date overview of the strengths and weaknesses of various tolerance-inducing strategies, including infusion of soluble Ags/peptides by various routes of delivery, genetic vaccinations, cell- and inert particle-based tolerogenic approaches, and various other strategies that target distinct tolerance-inducing pathways.

Targeting of autoantigens to DEC205⁺ dendritic cells in vivo suppresses experimental allergic encephalomyelitis in mice

The dendritic and epithelial cell receptor with a m.w. of 205 kDa (DEC205) is expressed by dendritic cells (DCs) and facilitates Ag presentation. After injection of Ags coupled to Abs specific for DEC205 into mice, Ag presentation occurs by nonactivated DCs, which leads to induction of regulatory T cells (Tregs). To test this system for tolerance induction in experimental allergic encephalomyelitis (EAE), we created single-chain fragment variables (scFv) specific for DEC205 and fused the scFv to the self-Ag myelin oligodendrocyte glycoprotein (MOG; scFv DEC:MOG). An anti-β-galactosidase scFv:MOG fusion protein (scFv GL117:MOG) served as isotype control. After staining of DCs in vitro with purified scFv DEC:MOG, binding to DCs and colocalization with MHC class II was apparent, whereas isotype controls did not bind. We next injected scFv DEC:MOG into mice and observed elevated numbers of highly activated, IL-10-producing CD4⁺CD25⁺Foxp3⁺ Tregs (17% of CD4) in spleens, as compared with isotype controls and uninjected mice (12% of CD4). Furthermore, DCs isolated from scFv DEC:MOG-injected animals produced significantly increased levels of TGF-β. Most importantly, when EAE was induced in scFv DEC:MOG-injected mice, 90% of the mice were protected from EAE, whereas all mice in the isotype controls (scFv GL117:MOG) experienced development of EAE. When applying scFv DEC:MOG to mice that had already experienced EAE symptoms, abrogation of the disease in 90% of the animals was apparent, whereas all animals in the control groups experienced development of severe EAE. Thus, these data indicate that targeting of MOG to "steady-state" DCs in vivo may provide a tool to prevent and to treat EAE by a DC/Treg-driven mechanism.

Granuloma cells in chronic inflammation express CD205 (DEC205) antigen and harbor proliferating T lymphocytes: similarity to antigen-presenting cells

Granulomas are classified as immune or foreign body granulomas. Of these, the immune granulomas, a hallmark of granulomatous inflammation, are closely related to cell-mediated immune responses. The aim of the present study is to characterize immune granuloma cells in 33 patients with granulomatous inflammation focusing on the expression of CD205 (DEC205), a cell surface marker of antigen presenting cells, and their spatial relationship to T cells. CD205 was frequently expressed by immune granuloma cells, in contrast to foreign body granuloma cells that lacked CD205 expression. T cells were not only distributed in a lymphocyte collar around the granuloma, but also present among the granuloma cells (termed 'intra-granuloma T cells'). Intra-granuloma T cells stained positive for Ki-67 (median positivity = 9.4%) by double immunostaining for CD3 and Ki-67. This indicated the presence of proliferative stimuli within the granuloma that could activate the intra-granuloma T cells. The labeling index of Ki-67 in intra-granuloma T cells was significantly higher than that of T cells in the lymphocyte collar (P < 0.0001) or T cells in the T cell zone (paracortex) of chronic tonsillitis or reactive lymphadenitis (P = 0.002). These data indicate a close similarity between immune granulomas and antigen presenting cells.

Sensing of cell death by myeloid C-type lectin receptors

Molecules associated with dead or dying cells can be detected by receptors on macrophages and dendritic cells. Signals from these receptors impact myeloid cell function and play a role in determining whether death is silent or proinflammatory, tolerogenic or immunogenic. Prominent among myeloid receptors detecting dead cells are C-type lectin receptors (CLRs). Signals from these receptors variably induce endocytosis of cell corpses, corpse degradation, retrieval of dead cell-associated antigens and/or modulation of immune responses. The sensing of tissue damage by myeloid CLRs complements detection of pathogens in immunity and represents an ancient response aimed at restoring tissue homeostasis.

Expression of chicken DEC205 reflects the unique structure and function of the avian immune system

The generation of appropriate adaptive immune responses relies critically on dendritic cells, about which relatively little is known in chickens, a vital livestock species, in comparison with man and mouse. We cloned and sequenced chicken DEC205 cDNA and used this knowledge to produce quantitative PCR assays and monoclonal antibodies to study expression of DEC205 as well as CD83. The gene structure of DEC205 was identical to those of other species. Transcripts of both genes were found at higher levels in lymphoid tissues and the expression of DEC205 in normal birds had a characteristic distribution in the primary lymphoid organs. In spleen, DEC205 was seen on cells ideally located to trap antigen. In thymus it was found on cells thought to participate in the education of T cells, and in the bursa on cells that may be involved in presentation of antigen to B cells and regulation of B cell migration. The expression of DEC205 on cells other than antigen presenting cells (APC) is also described. Isolated splenocytes strongly expressing DEC205 but not the KUL01 antigen have morphology similar to mammalian dendritic cells and the distinct expression of DEC205 within the avian-specific Bursa of Fabricius alludes to a unique function in this organ of B cell diversification.

Robust T-cell stimulation by Epstein-Barr virus-transformed B cells after antigen targeting to DEC-205

DEC-205 is a type I transmembrane multilectin receptor that is predominantly expressed on dendritic cells (DCs). Therefore, previous studies primarily focused on processing of DEC-205–targeted antigens by this potent antigen presenting cell type. Here we show that Epstein-Barr virus (EBV) transformed lymphoblastoid B-cell lines (LCLs) not only express DEC-205 at similar levels to DCs, but also efficiently present targeted EBV nuclear antigen 1 (EBNA1) and EBV-latent membrane protein 1 (LMP1) to EBNA1- and LMP1-specific CD4+ and CD8+ T-cell clones in vitro. Targeting of antigens to DEC-205 on B cells led to more efficient MHC class II than I loading, and stimulated T cells more efficiently than targeting to DEC-205 on DCs. Although LCLs internalized DEC-205–targeted antigens less efficiently than DCs, they retained them for longer time periods and delivered them to endosomal compartments that receive also B-cell receptor targeted proteins. This could facilitate prolonged T-cell stimulation and efficient MHC class II loading, and, indeed, CD4+ T-cell expansion by DEC-205–targeted vaccination was significantly compromised in B-cell deficient mice. These studies suggest that B cells, activated by virus transformation or other means, can contribute to T-cell stimulation after DEC-205 targeting of antigens during vaccination.

Normal T cell selection occurs in CD205-deficient thymic microenvironments

The thymus imparts a developmental imprint upon T cells, screening beneficial and self-tolerant T cell receptor (TCR) specificities. Cortical thymic epithelial cells (CTEC) present self-peptide self-MHC complexes to thymocytes, positively selecting those with functional TCRs. Importantly, CTEC generate diverse self-peptides through highly specific peptide processing. The array of peptides utilized for positive selection appears to play a key role in shaping TCR repertoire and influencing T cell functionality. Whilst self-peptide diversity influences T cell development, the precise source of proteins generating such self-peptide arrays remains unknown, the abundance of apoptotic thymocytes failing thymic selection may provide such a pool of self-proteins. In relation to this notion, whilst it has been previously demonstrated that CTEC expression of the endocytic receptor CD205 facilitates binding and uptake of apoptotic thymocytes, the possible role of CD205 during intrathymic T cell development has not been studied. Here, we directly address the role of CD205 in normal thymocyte development and selection. Through analysis of both polyclonal and monoclonal transgenic TCR T-cell development in the context of CD205 deficiency, we demonstrate that CD205 does not play an overt role in T cell development or selection.

Targeted antigen delivery to DEC-205⁺ dendritic cells for tolerogenic vaccination

Dendritic cells (DCs) and Foxp3-expressing CD4⁺ regulatory T (Treg) cells play non-redundant roles in the maintenance of peripheral tolerance to self-antigens, thereby preventing fatal autoimmunity. A common hallmark of intra- and extra-thymic Treg cell lineage commitment is the induction of Foxp3 expression as a consequence of appropriate T cell receptor engagement with MHC class II:agonist ligand. It has now become increasingly clear that agonist ligand presentation by immature DCs in the steady state induces T cell tolerance by both recessive and dominant mechanisms, rather than promoting productive T helper cell responses. In this context, the ability of steady-state DCs to promote the extrathymic conversion of initially naïve CD4⁺Foxp3⁻ T cells into Foxp3⁺ Treg cells is of particular interest as it provides novel perspectives to enhance antigen-specific Treg cell function in clinical settings of unwanted immunity, such as β-cell autoimmunity.

The specialized roles of immature and mature dendritic cells in antigen cross-presentation

Exogenous antigen cross-presentation is integral to the stimulation of cytotoxic T-lymphocytes against viruses and tumors. Central to this process are dendritic cells (DCs), which specialize in cross-presentation. DCs may be considered to exist in two radically different states of activation, generally referred to as immature and mature. In each of these states, the cell has a series of separate and specialized abilities for the induction of T-cell immunity. In the immature state, the DC is adept in surveying the periphery, acquiring and storing antigen, but has a limited capacity for direct T-cell activation. During a brief and defined window of time following DC stimulation, nearly every aspect of antigen handling changes, as it transitions from an entity focused on protein preservation to one capable of efficient cross-presentation. It is this time period and the underlying molecular mechanisms active here, which form the core of our studies on cross-presentation.

Generation of hypoallergenic neoglycoconjugates for dendritic cell targeted vaccination: a novel tool for specific immunotherapy

The incidence of allergic disorders and asthma continuously increased over the past decades, consuming a considerable proportion of the health care budget. Allergen-specific subcutaneous immunotherapy represents the only intervention treating the underlying causes of type I allergies, but still suffers from unwanted side effects and low compliance. There is an urgent need for novel approaches improving safety and efficacy of this therapy. In the present study we investigated carbohydrate-mediated targeting of allergens to dermal antigen-presenting cells and its influence on immunogenicity and allergenicity. Mannan, high (40 kDa) and low (6 kDa) molecular weight dextran, and maltodextrin were covalently attached to ovalbumin and papain via mild carbohydrate oxidation resulting in neoglycocomplexes of various sizes. In particular, mannan-conjugates were efficiently taken up by dendritic cells in vivo leading to elevated humoral immune responses against the protein moiety and a shift from IgE to IgG. Beyond providing an adjuvant effect, papain glycocomplexes also proved to mask B-cell epitopes, thus rendering the allergen derivative hypoallergenic.

The present data demonstrate that carbohydrate-modified allergens combine targeting of antigen presenting cells with hypoallergenicity, offering the potential for low dose allergen-specific immunotherapy while concomitantly reducing the risk of side effects.

Differential immunogenicity and allergenicity of native and recombinant human lactoferrins: role of glycosylation

Human native milk lactoferrin (LF) and recombinant forms of lactoferrin (rLF) are available with identical aa sequences, but different glycosylation patterns. Native lactoferrin (NLF) possesses the intrinsic ability to stimulate vigorous IgG and IgE antibody responses in BALB/c mice, whereas recombinant forms (Aspergillus or rice) are 40-fold less immunogenic and 200-fold less allergenic. Such differences are independent of endotoxin or iron content and the glycans do not contribute to epitope formation. A complex glycoprofile is observed for NLF, including sialic acid, fucose, mannose, and Lewis (Le)(x) structures, whereas both rLF species display a simpler glycoprofile rich in mannose. Although Le(x) type sugars play a Th2-type adjuvant role, endogenous expression of Le(x) on NLF did not completely account for the more vigorous IgE responses it provoked. Furthermore, coadminstration of rLF downregulated IgE and upregulated IgG2a antibody responses provoked by NLF, but was without effect on responses to unrelated peanut and chicken egg allergens. These results suggest glycans on rLF impact the induction phase to selectively inhibit IgE responses and that differential glycosylation patterns may impact on antigen uptake, processing and/or presentation, and the balance between Th1 and Th2 responses.

Antibodies and carbohydrate ligands binding to DC-SIGN differentially modulate receptor trafficking

DCs are regarded as key APCs that initiate humoral and cellular immune responses. Consequently, targeted delivery of Ag toward DC-specific receptors enhances vaccine efficacy. DC-SIGN is a C-type lectin receptor that facilitates DC-specific delivery of Ag. This is accomplished by conjugating Ag to receptor-specific Ab or carbohydrate ligands that bind to its carbohydrate recognition domain. Here, we investigated the fate of DC-SIGN following receptor triggering with Ab. Both whole and single-chain Ab induced rapid internalization of about half of the surface receptor molecules. Biochemical studies showed that about half of the receptor molecules were still intracellular after 3 h, while minimal or no resurfacing of internalized or newly synthesized unbound DC-SIGN molecules was observed. Prolonged exposure of DCs to DC-SIGN Ab, but not carbohydrate ligands, resulted in reduced receptor expression levels, which lasted up to 2 days following removal of the Ab. In addition, exposure to DC-SIGN Ab reduced the ability of the receptor to internalize. Consequently, DC-SIGN showed a poor ability to accumulate targeting Abs within DCs. Vaccine efficacy may therefore be enhanced by strategies increasing the amount of Ag entering via a single receptor molecule, such as the use of targeting moieties allowing DC-SIGN recycling or Ab-coated vaccine carriers.

A simple approach for enhanced immune response using engineered dendritic cell targeted nanoparticles

In this study, we demonstrate a simple strategy for enhanced immune response using a two-component dendritic cell (DC) targeted antigen delivery system. One component consists of a recombinant bifunctional fusion protein (bfFp) used for DC targeting, whereas, the other component is made of biotinylated PLGA nanoparticles that encapsulate the antigen. The fusion protein (bfFp) made of a truncated core-streptavidin fused to anti-DEC-205 single chain antibody (scFv) was mixed with ovalbumin-loaded biotinylated NPs that were formulated using biotin-PEG (2000)-PLGA, and the combination, bfFp functionalized NPs was used for DC targeted antigen delivery. In vitro DC uptake studies revealed a 2-fold higher receptor-mediated uptake of bfFp functionalized NPs when compared to non-targeted NPs. Immunization of the mice with the bfFp functionalized NPs in conjunction with DC maturation stimulus (anti-CD40 mAb) enhanced OVA-specific IgG and IgG subclass responses. Splenocytes of these mice secreted significantly higher levels of Th1 (IFN-γ and IL-2) cytokines upon ex vivo restimulation with OVA. The promising outcomes of the bfFp functionalized DC targeted system support its use as a versatile vaccine delivery system for the design of monovalent or polyvalent vaccines.

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.

Autoimmunity in chronic obstructive pulmonary disease: clinical and experimental evidence

Over the past few decades, neutrophils and macrophages had co-occupied center stage as the critical innate immune cells underlying the pathobiology of cigarette smoke-induced chronic obstructive pulmonary disease and lung parenchymal destruction (i.e., emphysema). While chronic exposure to smoke facilitates the recruitment of innate immune cells into the lung, a clear role for adaptive immunity in emphysema has emerged. Evidence from human studies specifically point to a role for recruitment and activation of pathogenic lymphocytes and lung antigen-presenting cells in emphysema; similarly, animal models have confirmed a significant role for autoimumnity in progressive smoke-induced emphysema. Increased numbers of activated antigen-presenting cells, Th1 and Th17 cells, have been associated with smoke-induced lung inflammation and production of the canonical cytokines of these cells, IFN-γ and IL-17, correlates with disease severity. These exciting new breakthroughs could open new avenues for developing effective new therapies for smoke-induced emphysema.

Internalization and endosomal degradation of receptor-bound antigens regulate the efficiency of cross presentation by human dendritic cells

Dendritic cells (DCs) can capture extracellular antigens and load resultant peptides on to MHC class I molecules, a process termed cross presentation. The mechanisms of cross presentation remain incompletely understood, particularly in primary human DCs. One unknown is the extent to which antigen delivery to distinct endocytic compartments determines cross presentation efficiency, possibly by influencing antigen egress to the cytosol. We addressed the problem directly and quantitatively by comparing the cross presentation of identical antigens conjugated with antibodies against different DC receptors that are targeted to early or late endosomes at distinct efficiencies. In human BDCA1+ and monocyte-derived DCs, CD40 and mannose receptor targeted antibody conjugates to early endosomes, whereas DEC205 targeted antigen primarily to late compartments. Surprisingly, the receptor least efficient at internalization, CD40, was the most efficient at cross presentation. This did not reflect DC activation by CD40, but rather its relatively poor uptake or intra-endosomal degradation compared with mannose receptor or DEC205. Thus, although both early and late endosomes appear to support cross presentation in human DCs, internalization efficiency, especially to late compartments, may be a negative predictor of activity when selecting receptors for vaccine development.

Functional crosstalk between dendritic cells and Foxp3(+) regulatory T cells in the maintenance of immune tolerance

Peripheral immune tolerance requires a controlled balance between the maintenance of self-tolerance and the capacity to engage protective immune responses against pathogens. Dendritic cells (DCs) serve as sentinels of the immune system by sensing environmental and inflammatory signals, and play an essential role in the maintenance of immune tolerance. To achieve this, DC play a key role in dictating the outcome of immune responses by influencing the balance between inflammatory or Foxp3(+) regulatory T (T(reg)) cell responses. At the heart of this immunological balance is a finely regulated DC and T(reg) cell crosstalk whereby T(reg) cells modulate DC phenotype and function, and DC drive the differentiation of Foxp3(+) T(reg) cells in order to control immune responses. This review will focus on recent advances, which highlight the importance of this bidirectional DC and T(reg) cell crosstalk during the induction of tolerance and organ-specific autoimmunity. More specifically, we will discuss how T(reg) cells modulate DC function for the suppression of inflammatory responses and how DC subsets employ diverse mechanisms to drive differentiation of T(reg) cells. Finally, we will discuss the therapeutic potential of tolerogenic DCs for the induction of tolerance in autoimmune diseases.

Immunogenicity of DNA vaccines encoding simian immunodeficiency virus antigen targeted to dendritic cells in rhesus macaques

BACKGROUND

Targeting antigens encoded by DNA vaccines to dendritic cells (DCs) in the presence of adjuvants enhances their immunogenicity and efficacy in mice.

METHODOLOGY/PRINCIPAL FINDINGS

To explore the immunogenicity of this approach in non-human primates, we generated a single chain antibody to the antigen uptake receptor DEC-205 expressed on rhesus macaque DCs. DNA vaccines encoding this single chain antibody fused to the SIV capsid protein were delivered to six monkeys each by either intramuscular electroporation or conventional intramuscular injection co-injected or not with poly ICLC, a stabilized poly I: C analogue, as adjuvant. Antibodies to capsid were induced by the DC-targeting and non-targeting control DNA delivered by electroporation while conventional DNA immunization at a 10-fold higher dose of DNA failed to induce detectable humoral immune responses. Substantial cellular immune responses were also observed after DNA electroporation of both DNAs, but stronger responses were induced by the non-targeting vaccine. Conventional immunization with the DC-targeting DNA at a 10-fold higher dose did not give rise to substantial cellular immune responses, neither when co-injected with poly ICLC.

CONCLUSIONS/SIGNIFICANCE

The study confirms the potent immunogenicity of DNA vaccines delivered by electroporation. Targeting the DNA via a single chain antibody to DEC-205 expressed by DCs, however, does not improve the immunogenicity of the antigens in non-human primates.

Selective increase in blood dendritic cell antigen-3-positive dendritic cells in bronchoalveolar lavage fluid in allergic patients

Dendritic cells (DCs) are specific antigen-presenting cells that play critical roles in the initiation and polarization of immune responses. DCs residing in the lungs might be detected in the bronchoalveolar lavage fluid (BALF). We analysed DC compartment in the peripheral blood and BALF of patients with allergy and in controls. Plasmacytoid and four distinct subsets of myeloid DCs [characterized by the expression of blood dendritic cell antigen (BDCA)-1+ and -3+ and CD16 positivity or negativity] were detected in both tested compartments. We further evaluated the expression of C-type lectins [mannose receptor (MR), dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) and dendritic and epithelial cells (DEC)-205] relevant to the pathogenesis of asthma. Interestingly, we found a selective increase in the frequency of myeloid DC-expressing BDCA-3 and MR particularly in BALF from allergic patients. Specific and highly statistically significant increase in BDCA-3+ and/or MR+ DCs brings a novel characteristic to BAL analysis in allergic patients.

Targeting of the hNC16A collagen domain to dendritic cells induces tolerance to human type XVII collagen

Antibodies, specific to murine DEC205, can be used to target antigens to dendritic cells. The immunodominant domain of human type XVII collagen, hNC16A, was fused to this antibody (DEC-hNC16A) and was administered as expression plasmid by gene gun transfection with the aim of inducing tolerance to human type XVII collagen in a skin transplantation model. Mice transfected with DEC-hNC16A were challenged with skin grafts from transgenic mice engineered to express human type XVII collagen. Graft survival was either prolonged or grafts were accepted infinitely (33% and 16%, respectively) upon treatment with DEC-hNC16A while 100% of grafts were rejected in untreated controls. Graft acceptance was associated with the absence of a CD4+ infiltrate and a dense CD8+ T-cell infiltrate and was not strictly dependent on antibody production. Our results show that DEC-hNC16A targets dendritic cells in vivo leading to prolonged survival of transgenic skin grafts. This indicates that DEC205-targeting may be used for the induction of tolerance to skin antigens, which would increase the chances of successful skin gene therapy of epidermolysis bullosa patients.

Toll-like receptor gene expression in fresh and archived ovine pseudoafferent lymph DEC205+ dendritic cells

Toll-like receptors (TLRs) are key regulators of the innate and adaptive immune response to bacterial, viral and fungal pathogens. To date, 10 human TLRs and 13 mouse TLRs have been identified and they exhibit tissue-specific mRNA/protein expression patterns. We recently cloned and characterized 10 ovine TLR genes. The present study was carried out to determine the expression profile of TLRs 1-10 in fresh and archived ovine pseudoafferent lymph (pAL) cells and pAL dendritic cells (pALDCs) using two-step quantitative reverse transcriptase polymerase chain reaction (RT-PCR) with ovine specific primer/probe sets. Dendritic cells are important in the initiation and maintenance of immune responses and express a spectrum of pattern-recognition receptors (that includes the TLRs). Fresh and archived total pAL cells expressed all 10 ovine TLRs to a broadly similar extent and TLR1-10 mRNA expression was observed in DEC205(hi) pALDCs. In addition, there were changes in particular TLR transcript levels in DEC205(hi) pALDC in archived lymph samples at two time points after orf virus reinfection. The results show that frozen archived cells can be used for retrospective TLR gene expression analysis. Furthermore, changes in TLR gene expression in DEC205(hi) pALDC after orf virus reinfection in the skin of sheep suggests that more detailed analyses of TLR gene expression changes during disease processes are worthwhile. These data will be useful to inform future studies on the role of TLRs in disease pathogenesis and control.

Dendritic cell targeted chitosan nanoparticles for nasal DNA immunization against SARS CoV nucleocapsid protein

This work investigates the formulation and in vivo efficacy of dendritic cell (DC) targeted plasmid DNA loaded biotinylated chitosan nanoparticles for nasal immunization against nucleocapsid (N) protein of severe acute respiratory syndrome coronavirus (SARS-CoV) as antigen. The induction of antigen-specific mucosal and systemic immune response at the site of virus entry is a major challenge for vaccine design. Here, we designed a strategy for noninvasive receptor mediated gene delivery to nasal resident DCs. The pDNA loaded biotinylated chitosan nanoparticles were prepared using a complex coacervation process and characterized for size, shape, surface charge, plasmid DNA loading and protection against nuclease digestion. The pDNA loaded biotinylated chitosan nanoparticles were targeted with bifunctional fusion protein (bfFp) vector for achieving DC selective targeting. The bfFp is a recombinant fusion protein consisting of truncated core-streptavidin fused with anti-DEC-205 single chain antibody (scFv). The core-streptavidin arm of fusion protein binds with biotinylated nanoparticles, while anti-DEC-205 scFv imparts targeting specificity to DC DEC-205 receptor. We demonstrate that intranasal administration of bfFp targeted formulations along with anti-CD40 DC maturation stimuli enhanced magnitude of mucosal IgA as well as systemic IgG against N protein. The strategy led to the detection of augmented levels of N protein specific systemic IgG and nasal IgA antibodies. However, following intranasal delivery of naked pDNA no mucosal and systemic immune responses were detected. A parallel comparison of targeted formulations using intramuscular and intranasal routes showed that the intramuscular route is superior for induction of systemic IgG responses compared with the intranasal route. Our results suggest that targeted pDNA delivery through a noninvasive intranasal route can be a strategy for designing low-dose vaccines.

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 of the non-mutated tumor antigen HER2/neu to mature dendritic cells induces an integrated immune response that protects against breast cancer in mice

INTRODUCTION

Given their relative simplicity of manufacture and ability to be injected repeatedly, vaccines in a protein format are attractive for breast and other cancers. However, soluble human epidermal growth factor receptor (HER2)/neu protein as a vaccine has not been immunogenic. When protein is directly targeted to antigen uptake receptors, such as DEC205 (DEC), efficient processing and presentation of antigen take place. The aim of this study was to determine the immunogenicity of a HER2 protein vaccine that directly targets to DEC+ dendritic cells (DCs) in a mouse breast cancer model.

METHODS

We genetically engineered the HER2 extracellular domain into a monoclonal antibody specific for DEC (DEC-HER2). Mice of various genetic backgrounds were immunized with DEC-HER2 in combination with DC maturation stimuli (poly IC ± CD40 Ab). Vaccine-induced T cell immunity was determined by analyzing the ability of CD4+/CD8+ T cell to produce interferon (IFN)-gamma and proliferate upon antigen rechallenge. Sera were assessed for the presence of antigen specific antibody (Ab). For vaccine efficacy, FVB/N mice were immunized with DEC-HER2 in combination with poly IC and protection against neu-expressing mammary tumors was assessed. Protection mechanisms and tumor-specific T cell responses were also evaluated.

RESULTS

We demonstrate that DEC-HER2 fusion mAb, but not Ctrl Ig-HER2, elicits strong, broad and multifunctional CD4+ T cell immunity, CD8+ T cell responses, and humoral immunity specific for HER2 antigen. Cross-reactivity to rat neu protein was also observed. Importantly, mice xeno-primed with DEC-HER2 were protected from a neu-expressing mammary tumor challenge. Both CD4+ and CD8+ T cells mediated the tumor protection. Robust anti-tumor T cell immunity was detected in tumor protected mice.

CONCLUSIONS

Immunization of mice with HER2 protein vaccine targeting DEC+ DCs in vivo induced high levels of T- and B-cell immunity. Non-targeted HER2 protein was poorly immunogenic for CD4+ and CD8+ T cells. This vaccination approach provided long-term survival benefit for mice challenged with neu-expressing tumor following as little as 2.7 μg of HER2 protein incorporated in the vaccine. Vaccine-induced CD4+ and CD8+ T cells were both essential for tumor protection. This immunization strategy demonstrates great potential towards the development of vaccines for breast cancer patients.

Directed antigen targeting in vivo identifies a role for CD103+ dendritic cells in both tolerogenic and immunogenic T-cell responses

The αE integrin chain CD103 identifies a subset of migratory dendritic cells (DCs) in the gut, lung, and skin. To gain further understanding of the function of CD103(+) DCs in regulating adaptive immunity in vivo, we coupled ovalbumin (OVA) to the CD103 antibody M290 (M290.OVA). Intraperitoneal injection of M290.OVA induced OVA-specific CD8(+) and CD4(+) T-cell proliferation in lymph nodes (LNs) of wild-type but not CD103(-/-) mice, or in mice depleted of CD11c(+) cells. In the absence of maturation stimuli, systemic antigen targeting to CD103(+) DCs led to tolerance of CD8(+) T cells, whereas coadministration of adjuvant induced cytotoxic T-lymphocyte (CTL) immunity and antibody production. Mucosal intratracheal application of M290.OVA also induced T-cell proliferation in mediastinal LNs, yet the functional outcome was tolerance that inhibited subsequent development of allergic airway inflammation and immunoglobulin E (IgE) responses to inhaled OVA. These findings identify antigen targeting to CD103(+) DCs as a potential strategy to regulate immune responses in nonlymphoid mucosal tissues.

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.

Development and characterization of a monoclonal antibody against porcine CD205

The aim of this work was to develop mAbs against porcine CD205 and to conduct a comparative analysis of the CD205 protein expression on lymphoid tissues, monocyte-derived dendritic cells (DCs) and DCs isolated from the porcine skin. To conduct this study, we generated a monoclonal antibody, designated 1.F6F6, against the C-type lectin-like domain-5 of the porcine CD205 and showed that it recognizes a protein band of ∼200 kDa by Western Blot analysis in mesenteric lymph nodes cells. Flow cytometric analysis showed that the mAb 1.F6F6 recognized 28.5%, 28.1% and 34.1% of cells from tonsil, inguinal and mesenteric lymph nodes, respectively, and 6% of cells from thymus. Analysis of monocyte-derived DCs showed that approximately 20% were positive and activation of the cells with LPS increased the positive population to 36%. Analysis of DCs isolated from the porcine skin showed that approximately 70% of the cell population expressed the CD205 receptor. The development of a monoclonal antibody capable of recognizing the CD205 receptor in swine opens up possibilities of applying new strategies for enhancing vaccine efficacy by using the anti-CD205 antibody for DC antigen-targeting to enhance priming of immune responses.

Generation of anti-human DEC205/CD205 monoclonal antibodies that recognize epitopes conserved in different mammals

DEC205/CD205 is a C-type multilectin receptor, expressed highly in dendritic cells (DCs). Previous efforts to generate anti-human DEC205 (anti-hDEC205) monoclonal antibodies (mAbs) from mice immunized with subdomain proteins of hDEC205 resulted in a few mAbs. Recently, we expressed and utilized a full-length extracellular domain protein of hDEC205 to successfully generate 5 strong anti-hDEC205 mAbs from mice. In this study, DEC205 knockout (KO) mice were immunized with this full-length extracellular domain protein of hDEC205. One of the 3 immunized DEC205 KO mice was chosen for the highest anti-hDEC205 titer by flow cytometric analysis of serum samples on CHO cells stably expressing hDEC205 (CHO/hDEC205 cells) and used for hybridoma fusion. From a single fusion, more than 400 anti-hDEC205 hybridomas were identified by flow cytometric screen with CHO/hDEC205 cells, and a total of 115 hybridomas secreting strong anti-hDEC205 mAb were saved and named HD1 through HD115. To characterize in detail, 10 HD mAbs were chosen for superior anti-hDEC205 reactivity and further subjected to cloning and purification. Interestingly, out of those 10 chosen anti-hDEC205 HD mAbs, 5 mAbs were also strongly reactive to mouse DEC205 while 8 mAbs were found to stain DEC205(+) DCs on monkey spleen sections. In addition, we also identified that HD83, one of the 10 chosen HD mAbs, stains DEC205(+) DCs in rat spleen and lymph node. Therefore, by immunizing DEC205 KO mice with a full-length extracellular domain protein of hDEC205, we generated a large number of strong anti-hDEC205 mAbs many of which are cross-species reactive and able to visualize DEC205(+) DCs in lymphoid tissues of other mammals.

The effect of azithromycin on the maturation and function of murine bone marrow-derived dendritic cells

Dendritic cells (DCs) are professional antigen-presenting cells capable of initiating primary/adaptive immune responses and tolerance. DC functions are regulated by their state of maturation. However, the molecular pathways leading to DC development and maturation remain poorly understood. We attempted to determine whether inhibition of nuclear factor kappa B (NF-κB), which is one of the pivotal pathways underlying these processes, could induce immunophenotypic and functional changes in lipopolysaccharide-induced mature DCs derived from murine bone marrow. A comparative in vitro study of five clinically used drugs that are known to inhibit NF-κB demonstrated that azithromycin, a macrolide antibiotic, significantly inhibited expression of co-stimulatory molecules (CD40 and CD86) and major histocompatibility complex (MHC) class II by DCs. It also reduced Toll-like receptor 4 expression, interleukin-12 production and the allostimulatory capacity of DCs. These data suggest that azithromycin, as not only an NF-κB inhibitor but also an antibiotic, has potential as a novel drug for manipulation of allogeneic responses.

Signaling by myeloid C-type lectin receptors in immunity and homeostasis

Myeloid cells are key drivers of physiological responses to pathogen invasion or tissue damage. Members of the C-type lectin receptor (CLR) family stand out among the specialized receptors utilized by myeloid cells to orchestrate these responses. CLR ligands include carbohydrate, protein, and lipid components of both pathogens and self, which variably trigger endocytic, phagocytic, proinflammatory, or anti-inflammatory reactions. These varied outcomes rely on a versatile system for CLR signaling that includes tyrosine-based motifs that recruit kinases, phosphatases, or endocytic adaptors as well as nontyrosine-based signals that modulate the activation of other pathways or couple to the uptake machinery. Here, we review the signaling properties of myeloid CLRs and how they impact the role of myeloid cells in innate and adaptive immunity.

Targeting skin dendritic cells to improve intradermal vaccination

Vaccinations in medicine are typically administered into the muscle beneath the skin or into the subcutaneous fat. As a consequence, the vaccine is immunologically processed by antigen-presenting cells of the skin or the muscle. Recent evidence suggests that the clinically seldom used intradermal route is effective and possibly even superior to the conventional subcutaneous or intramuscular route. Several types of professional antigen-presenting cells inhabit the healthy skin. Epidermal Langerhans cells (CD207/langerin(+)), dermal langerin(neg), and dermal langerin(+) dendritic cells (DC) have been described, the latter subset so far only in mouse skin. In human skin langerin(neg) dermal DC can be further classified based on their reciprocal expression of CD1a and CD14. The relative contributions of these subsets to the generation of immunity or tolerance are still unclear. Yet, specializations of these different populations have become apparent. Langerhans cells in human skin appear to be specialized for induction of cytotoxic T lymphocytes; human CD14(+) dermal DC can promote antibody production by B cells. It is currently attempted to rationally devise and improve vaccines by harnessing such specific properties of skin DC. This could be achieved by specifically targeting functionally diverse skin DC subsets. We discuss here advances in our knowledge on the immunological properties of skin DC and strategies to significantly improve the outcome of vaccinations by applying this knowledge.

Expression of DEC205 in the gastric mucosa of Helicobacter pylori-infected patients

AIM: To investigate the expression of DEC205 in the gastric mucosa of Helicobacter pylori (H. pylori)-infected patients.

METHODS: Thirteen H. pylori-positive patients with gastritis received eradication therapy. Gastroscopy was performed in all the 13 patients before eradication therapy and in 7 seven patients after treatment to take gastric mucosa samples, which were used to prepare frozen section to detect the expression of DEC205 and CD14 in human gastric mucosa by immunofluorescence.

RESULTS: Cells which were positive for both DEC205 and CD14 in the gastric mucosa significantly increased in H. pylori-infected patients. Furthermore, DEC205-positive macrophages invaded into gastric pits in the gastric mucosa of H. pylori-positive patients.

CONCLUSION: Macrophage expressing DEC205 in the gastric mucosa may play an immunological role in H. pylori infection.

Targeting mucosal immunity in the battle to develop a mastitis vaccine

The mucosal immune system encounters antigens that enhance and suppress immune function, and serves as a selective barrier against invading pathogens. The mammary gland not only encounters antigens but also produces a nutrient evolved to protect and enhance mucosal development in the neonate. Efforts to manipulate antibody concentrations in milk to prevent mastitis, an infection of the mammary gland, have been hampered both by complexity and variation in target pathogens and limited knowledge of cellular immunity in the gland. Successful vaccination strategies must overcome the natural processes that regulate types and concentrations of milk antibodies for neonatal development, and enhance cellular immunity. Furthermore, the need to overcome dampening of immunity caused by non-pathogenic encounters to successfully prevent establishment of infection is an additional obstacle in vaccine development at mucosal sites. A significant mastitis pathogen, Staphylococcus aureus, not only resides as a normal flora on a multitude of species, but also causes clinical disease with limited treatment options. Using the bovine model of S. aureus mastitis, researchers can decipher the role of antigen selection and presentation by mammary dendritic cells, enhance development of central and effector memory function, and subsequently target specific memory cells to the mammary gland for successful vaccine development. This brief review provides an overview of adaptive immunity, previous vaccine efforts, current immunological findings relevant to enhancing immune memory, and research technologies that show promise in directing future vaccine efforts to enhance mammary gland immunity and prevent mastitis.

Decisions about dendritic cells: past, present, and future

A properly functioning adaptive immune system signifies the best features of life. It is diverse beyond compare, tolerant without fail, and capable of behaving appropriately with a myriad of infections and other challenges. Dendritic cells are required to explain how this remarkable system is energized and directed. I frame this article in terms of the major decisions that my colleagues and I have made in dendritic cell science and some of the guiding themes at the time the decisions were made. As a result of progress worldwide, there is now evidence of a central role for dendritic cells in initiating antigen-specific immunity and tolerance. The in vivo distribution and development of a previously unrecognized white cell lineage is better understood, as is the importance of dendritic cell maturation to link innate and adaptive immunity in response to many stimuli. Our current focus is on antigen uptake receptors on dendritic cells. These receptors enable experiments involving selective targeting of antigens in situ and new approaches to vaccine design in preclinical and clinical systems.

The actin regulatory protein HS1 is required for antigen uptake and presentation by dendritic cells

The hematopoietic actin regulatory protein hematopoietic lineage cell-specific protein 1 (HS1) is required for cell spreading and signaling in lymphocytes, but the scope of HS1 function in Ag presentation has not been addressed. We show that dendritic cells (DCs) from HS1(-/-) mice differentiate normally and display normal LPS-induced upregulation of surface markers and cytokines. Consistent with their normal expression of MHC and costimulatory molecules, HS1(-/-) DCs present OVA peptide efficiently to CD4(+) T cells. However, presentation of OVA protein is defective. Similarly, MHC class I-dependent presentation of VSV8 peptide to CD8(+) T cells occurs normally, but cross-presentation of GRP94/VSV8 complexes is defective. Analysis of Ag uptake pathways shows that HS1 is required for receptor-mediated endocytosis, but not for phagocytosis or macropinocytosis. HS1 interacts with dynamin 2, a protein involved in scission of endocytic vesicles. However, HS1(-/-) DCs showed decreased numbers of endocytic invaginations, whereas dynamin-inhibited cells showed accumulation of these endocytic intermediates. Taken together, these studies show that HS1 promotes an early step in the endocytic pathway that is required for efficient Ag presentation of exogenous Ag by DCs.

HIV-1 N-glycan composition governs a balance between dendritic cell-mediated viral transmission and antigen presentation

The natural function of dendritic cells (DCs) is to capture and degrade pathogens for Ag presentation. However, HIV-1 can evade viral degradation by DCs and hijack DCs for migration to susceptible CD4(+) T lymphocytes. It is unknown what factors decide whether a virus is degraded or transmitted to T cells. The interaction of DCs with HIV-1 involves C-type lectin receptors, such as DC-specific ICAM-3-grabbing nonintegrin, which bind to the envelope glycoprotein complex (Env), which is decorated heavily with N-linked glycans. We hypothesized that the saccharide composition of the Env N-glycans is involved in avoiding viral degradation and Ag presentation, as well as preserving infectious virus for the transmission to target cells. Therefore, we studied the fate of normally glycosylated virus versus oligomannose-enriched virus in DCs. Changing the heterogeneous N-linked glycan composition of Env to uniform oligomannose N-glycans increased the affinity of HIV-1 for DC-specific ICAM-3-grabbing nonintegrin and enhanced the capture of HIV-1 by immature DCs; however, it decreased the subsequent transmission to target cells. Oligomannose-enriched HIV-1 was directed more efficiently into the endocytic pathway, resulting in enhanced viral degradation and reduced virus transfer to target cells. Furthermore, Env containing exclusively oligomannose N-glycans was presented to Env-specific CD4(+) T cells more efficiently. Taken together, our results showed that the HIV-1 N-glycan composition plays a crucial role in the balance between DC-mediated Ag degradation and presentation and DC-mediated virus transmission to target cells. This finding may have implications for the early events in HIV-1 transmission and the induction of antiviral immune responses.

Inhibitory C-type lectin receptors in myeloid cells

C-type lectin receptors encoded by the natural killer gene complex play critical roles in enabling NK cell discrimination between self and non-self. In recent years, additional genes at this locus have been identified with patterns of expression that extend to cells of the myeloid lineage where many of the encoded inhibitory receptors have equally important functions as regulators of immune homeostasis. In the present review we highlight the roles of some of these receptors including recent insights gained with regard to the identification of exogenous and endogenous ligands, mechanisms of cellular inhibition and activation, regulated expression within different cellular and immune contexts, as well as functions that include the regulation of bone homeostasis and involvement in autoimmunity.

A novel non-toxic combined CTA1-DD and ISCOMS adjuvant vector for effective mucosal immunization against influenza virus

Here we demonstrate that by using non-toxic fractions of saponin combined with CTA1-DD we can achieve a safe and above all highly efficacious mucosal adjuvant vector. We optimized the construction, tested the requirements for function and evaluated proof-of-concept in an influenza A virus challenge model. We demonstrated that the CTA1-3M2e-DD/ISCOMS vector provided 100% protection against mortality and greatly reduced morbidity in the mouse model. The immunogenicity of the vector was superior to other vaccine formulations using the ISCOM or CTA1-DD adjuvants alone. The versatility of the vector was best exemplified by the many options to insert, incorporate or admix vaccine antigens with the vector. Furthermore, the CTA1-3M2e-DD/ISCOMS could be kept 1 year at 4°C or as a freeze-dried powder without affecting immunogenicity or adjuvanticity of the vector. Strong serum IgG and mucosal IgA responses were elicited and CD4 T cell responses were greatly enhanced after intranasal administration of the combined vector. Together these findings hold promise for the combined vector as a mucosal vaccine against influenza virus infections including pandemic influenza. The CTA1-DD/ISCOMS technology represents a breakthrough in mucosal vaccine vector design which successfully combines immunomodulation and targeting in a safe and stable particulate formation.