Transfer of antigen between migrating and lymph node-resident DCs in peripheral T-cell tolerance and immunity

A rational designed multi-epitope vaccine elicited robust protective efficacy against Klebsiella pneumoniae lung infection

BACKGROUND

The emergence of drug-resistant strains of Klebsiella pneumoniae (K. pneumoniae) has become a significant challenge in the field of infectious diseases, posing an urgent need for the development of highly protective vaccines against this pathogen.

METHODS AND RESULTS

In this study, we identified three immunogenic extracellular loops based on the structure of five candidate antigens using sera from K. pneumoniae infected mice. The sequences of these loops were linked to the C-terminal of an alpha-hemolysin mutant (mHla) from Staphylococcus aureus to generate a heptamer, termed mHla-EpiVac. In vivo studies confirmed that fusion with mHla significantly augmented the immunogenicity of EpiVac, and it elicited both humoral and cellular immune responses in mice, which could be further enhanced by formulation with aluminum adjuvant. Furthermore, immunization with mHla-EpiVac demonstrated enhanced protective efficacy against K. pneumoniae channeling compared to EpiVac alone, resulting in reduced bacterial burden, secretion of inflammatory factors, histopathology and lung injury. Moreover, mHla fusion facilitated antigen uptake by mouse bone marrow-derived cells (BMDCs) and provided sustained activation of these cells.

CONCLUSIONS

These findings suggest that mHla-EpiVac is a promising vaccine candidate against K. pneumoniae, and further validate the potential of mHla as a versatile carrier protein and adjuvant for antigen design.

Cotransfer of antigen and contextual information harmonizes peripheral and lymph node conventional dendritic cell activation

T cell responses against infections and cancer are directed by conventional dendritic cells (cDCs) in lymph nodes distant from the site of challenge. Migratory cDCs, which travel from the tissue to the lymph node, not only drive initial T cell activation but also transfer antigen to lymph node-resident cDCs. These resident cells have essential roles defining the character of the resulting T cell response; however, it is unknown how they can appropriately process and present antigens to suitably direct responses given their spatial separation. Here, using a novel strain of influenza A and a modified melanoma model, we show that tissue and lymph node cDC activation is harmonized and that this is driven by cotransfer of contextual cues. In the tumor, incomplete cDC activation in the tumor microenvironment is mirrored by lymph node-resident cDCs, whereas during influenza infection, pathogen-associated molecular patterns cotransferred with antigen drive TLR signaling in resident cDCs and their subsequent robust activation. This cotransfer mechanism explains how individual antigens can be handled distinctly by resident cDCs and how signals driving poor tumoral cDC activation further impact the lymph node. Our findings clarify how tissue context dictates antigenic and, consequently, T cell fate in the lymph node.

Effect of Autoclaving on the Physicochemical Properties and Biological Activity of Aluminum Oxyhydroxide Used as an Adjuvant in Vaccines

The long-term biodistribution of non-biodegradable microstructures or nanostructures used in vaccinations is widely unknown. This is the case for aluminum oxyhydroxide, the most widely used vaccine adjuvant, which is a nanocrystalline compound that spontaneously forms nanoprecipitates. Although generally well-tolerated, aluminum oxyhydroxide is detected in macrophages a long time after vaccination in individuals predisposed to the development of systemic and neurological aspects of the autoimmune (inflammatory) syndrome induced by modified adjuvant. In the present study, we established that the terminal sterilization of aluminum oxyhydroxide by autoclaving in final container vials produced measurable changes in its physicochemical properties. Moreover, we found that these changes included (1) a decreasing in the pH of aluminum oxyhydroxide solutions, (2) a reduction in the adsorption capacity of bovine serum albumin, (3) a shift in the angle of X-ray diffraction, (4) a reduction in the lattice spacing, causing the crystallization and biopersistence of modified aluminum oxyhydroxide in the macrophage, as well as in muscle and the brain.

Heat-inactivated modified vaccinia virus Ankara boosts Th1 cellular and humoral immunity as a vaccine adjuvant

Protein or peptide-based subunit vaccines have generated excitement and renewed interest in combating human cancer or COVID-19 outbreak. One major concern for subunit vaccine application is the weak immune responses induced by protein or peptides. Developing novel and effective vaccine adjuvants are critical for the success of subunit vaccines. Here we explored the potential of heat-inactivated MVA (heat-iMVA) as a vaccine adjuvant. Heat-iMVA dramatically enhances T cell responses and antibodies responses, mainly toward Th1 immune responses when combined with protein or peptide-based immunogen. The adjuvant effect of Heat-iMVA is stronger than live MVA and is dependent on the cGAS/STING-mediated cytosolic DNA-sensing pathway. In a therapeutic vaccination model based on tumor neoantigen peptide vaccine, Heat-iMVA significantly extended the survival and delayed tumor growth. When combined with SARS-CoV-2 spike protein, Heat-iMVA induced more robust spike-specific antibody production and more potent neutralization antibodies. Our results support that Heat-iMVA can be developed as a safe and potent vaccine adjuvant for subunit vaccines against cancer or SARS-CoV-2.

Antigen Presentation in the Lung

The lungs are constantly exposed to environmental and infectious agents such as dust, viruses, fungi, and bacteria that invade the lungs upon breathing. The lungs are equipped with an immune defense mechanism that involves a wide variety of immunological cells to eliminate these agents. Various types of dendritic cells (DCs) and macrophages (MACs) function as professional antigen-presenting cells (APCs) that engulf pathogens through endocytosis or phagocytosis and degrade proteins derived from them into peptide fragments. During this process, DCs and MACs present the peptides on their major histocompatibility complex class I (MHC-I) or MHC-II protein complex to naïve CD8⁺ or CD4⁺ T cells, respectively. In addition to these cells, recent evidence supports that antigen-specific effector and memory T cells are activated by other lung cells such as endothelial cells, epithelial cells, and monocytes through antigen presentation. In this review, we summarize the molecular mechanisms of antigen presentation by APCs in the lungs and their contribution to immune response.

Immune Responses to Varicella-Zoster Virus Vaccines

The live attenuated varicella vaccine is intended to mimic the tempo and nature of the humoral and cell-mediated immune responses to varicella infection. To date, two doses of varicella vaccine administered in childhood have been very effective in generating varicella-zoster virus (VZV) immune responses that prevent natural infection for at least several decades. After primary infection, the infecting VZV establishes latency in sensory and cranial nerve ganglia with the potential to reactivate and cause herpes zoster. Although, the immune responses developed during varicella are important for preventing herpes zoster they wane with increasing age (immune senescence) or with the advent of immune suppression. Protection can be restored by increasing cell-mediated immune responses with two doses of an adjuvanted recombinant VZV glycoprotein E vaccine that stimulates both VZV-and gE-specific immunity. This vaccine provides ~85-90% protection against herpes zoster for 7-8 years (to date).

Revisiting Current Concepts on the Tolerogenicity of Steady-State Dendritic Cell Subsets and Their Maturation Stages

The original concept stated that immature dendritic cells (DC) act tolerogenically whereas mature DC behave strictly immunogenically. Meanwhile, it is also accepted that phenotypically mature stages of all conventional DC subsets can promote tolerance as steady-state migratory DC by transporting self-antigens to lymph nodes to exert unique functions on regulatory T cells. We propose that in vivo 1) there is little evidence for a tolerogenic function of immature DC during steady state such as CD4 T cell anergy induction, 2) all tolerance as steady-state migratory DC undergo common as well as subset-specific molecular changes, and 3) these changes differ by quantitative and qualitative markers from immunogenic DC, which allows one to clearly distinguish tolerogenic from immunogenic migratory DC.

The cryo-EM structure of the endocytic receptor DEC-205

DEC-205 (CD205), a member of the macrophage mannose receptor protein family, is the prototypic endocytic receptor of dendritic cells, whose ligands include phosphorothioated cytosine-guanosine oligonucleotides, a motif often seen in bacterial or viral DNA. However, despite growing biological and clinical significance, little is known about the structural arrangement of this receptor or any of its family members. Here, we describe the 3.2 Å cryo-EM structure of human DEC-205, thereby illuminating the structure of the mannose receptor protein family. The DEC-205 monomer forms a compact structure comprising two intercalated rings of C-type lectin-like domains, where the N-terminal cysteine-rich and fibronectin domains reside at the central intersection. We establish a pH-dependent oligomerization pathway forming tetrameric DEC-205 using solution-based techniques and ultimately solved the 4.9 Å cryo-EM structure of the DEC-205 tetramer to identify the unfurling of the second lectin ring which enables tetramer formation. Furthermore, we suggest the relevance of this oligomerization pathway within a cellular setting, whereby cytosine-guanosine binding appeared to disrupt this cell-surface oligomer. Accordingly, we provide insight into the structure and oligomeric assembly of the DEC-205 receptor.

Migratory dendritic cells in skin-draining lymph nodes have nickel-binding capabilities

Nickel (Ni) is the most frequent metal allergen and induces Th1-dependent type-IV allergies. In local skin, epidermal Langerhans cells (LCs) and/or dermal dendritic cells (DCs) uptake antigens and migrate to draining lymph nodes (LNs). However, the subsets of antigen-presenting cells that contribute to Ni presentation have not yet been identified. In this study, we analyzed the Ni-binding capabilities of murine DCs using fluorescent metal indicator Newport Green. Elicitation of Ni allergy was assessed after intradermal (i.d.) injection of Ni-treated DCs into ear pinnae of Ni-sensitized mice. The Ni-binding capabilities of MHC class II^hi CD11c^int migratory DCs were significantly stronger than those of MHC class II^int CD11c^hi resident DCs and CD11c^int PDCA1⁺ MHC class II^int B220⁺ plasmacytoid DCs. Migratory DCs in skin-draining and mandibular LNs showed significantly stronger Ni-binding capabilities than those in mesenteric and medial iliac LNs. An i.d. injection of IL-1β induced the activation of LCs and dermal DCs with strong Ni-binding capabilities. Ni-binding LCs were detected in draining LNs after i.d. challenge with IL-1β and Ni. Moreover, an i.d. injection of Ni-treated DCs purified from skin-draining LNs elicited Ni-allergic inflammation. These results demonstrated that migratory DCs in skin-draining LNs have strong Ni-binding capabilities and elicit Ni allergy.

Re-Emergence of Dendritic Cell Vaccines for Cancer Treatment

Dendritic cells (DCs) are essential in immunity owing to their role in activating T cells, thereby promoting antitumor responses. Tumor cells, however, hijack the immune system, causing T cell exhaustion and DC dysfunction. Tumor-induced T cell exhaustion may be reversed through immune checkpoint blockade (ICB); however, this treatment fails to show clinical benefit in many patients. While ICB serves to reverse T cell exhaustion, DCs are still necessary to prime, activate, and direct the T cells to target tumor cells. In this review we provide a brief overview of DC function, describe mechanisms by which DC functions are disrupted by the tumor microenvironment, and highlight recent developments in DC cancer vaccines.

Sustained accumulation of antigen-presenting cells after infection promotes local T-cell immunity

Antigen-presenting cells (APC), such as dendritic cells (DC) and macrophages, are critical for T-cell-mediated immunity. Although it is established that memory T cells accumulate and persist in peripheral tissues after the resolution of infection, whether this is also the case for APC remains unclear. Here, we report that CCR2-dependent cells infiltrate skin during acute infection with herpes simplex virus (HSV)-1 and subsequently give rise to localized populations of DCs and macrophages. These APC are found at elevated numbers at sites of resolved infection or inflammation compared with unaffected regions of skin. Importantly, this local accumulation of APC is sustained for prolonged periods of time and has important functional consequences, as it promotes interferon-γ responses by virus-specific CD4⁺ T cells upon localized challenge infection with HSV-1. Thus, our results highlight how infection history determines long-term changes in immune cell composition in skin and how different types of immune cells accumulate, persist and co-operate to provide optimal immunity at this critical barrier site.

Plasmacytoid dendritic cells induce tolerance predominantly by cargoing antigen to lymph nodes

Plasmacytoid dendritic cells (pDCs) have been shown to induce tolerance to innocuous antigens. Their migratory properties allow them to take up antigens from the periphery and transport them to the draining lymph nodes or to the thymus. However, pDC‐T‐cell interaction in the primary and secondary lymphoid organs still remains poorly defined. In this study, we show that resting pDCs loaded with exogenous antigen could induce tolerance when transferred intralymphatically into a single lymph node of wild‐type C57BL/6 mice. However, this was a result of antigen transfer from pDCs to endogenous antigen presenting cells and subsequent abortive proliferation of cognate CD4⁺ T cells. pDCs could not directly induce the proliferation of CD4⁺ T cells, as observed in mice lacking MHC class II gene. Moreover, pDCs failed to make physical contacts with OT‐II cells as revealed by two‐photon imaging. Thus, the role of resting pDCs in tolerance induction seems to be independent of its direct interaction with cognate CD4⁺ T cells.

Functional Specialization of Skin Dendritic Cell Subsets in Regulating T Cell Responses

Dendritic cells (DC) are a heterogeneous family of professional antigen-presenting cells classically recognized as most potent inducers of adaptive immune responses. In this respect, Langerhans cells have long been considered to be prototypic immunogenic DC in the skin. More recently this view has considerably changed. The generation of in vivo cell ablation and lineage tracing models revealed the complexity of the skin DC network and, in particular, established the existence of a number of phenotypically distinct Langerin⁺ and negative DC populations in the dermis. Moreover, by now we appreciate that DC also exert important regulatory functions and are required for the maintenance of tolerance toward harmless foreign and self-antigens. This review summarizes our current understanding of the skin-resident DC system in the mouse and discusses emerging concepts on the functional specialization of the different skin DC subsets in regulating T cell responses. Special consideration is given to antigen cross-presentation as well as immune reactions toward contact sensitizers, cutaneous pathogens, and tumors. These studies form the basis for the manipulation of the human counterparts of the murine DC subsets to promote immunity or tolerance for the treatment of human disease.

Modulation of Dendritic Cell Activation and Subsequent Th1 Cell Polarization by Lidocaine

Dendritic cells play an essential role in bridging innate and adaptive immunity by recognizing cellular stress including pathogen- and damage-associated molecular patterns and by shaping the types of antigen-specific T cell immunity. Although lidocaine is widely used in clinical settings that trigger cellular stress, it remains unclear whether such treatment impacts the activation of innate immune cells and subsequent differentiation of T cells. Here we showed that lidocaine inhibited the production of IL–6, TNFα and IL–12 from dendritic cells in response to toll-like receptor ligands including lipopolysaccharide, poly(I:C) and R837 in a dose-dependent manner. Notably, the differentiation of Th1 cells was significantly suppressed by the addition of lidocaine while the same treatment had little effect on the differentiation of Th17, Th2 and regulatory T cells in vitro. Moreover, lidocaine suppressed the ovalbumin-specific Th1 cell responses in vivo induced by the adoptive transfer of ovalbumin-pulsed dendritic cells. These results demonstrate that lidocaine inhibits the activation of dendritic cells in response to toll-like receptor signals and subsequently suppresses the differentiation of Th1 cell responses.

Identification of Teleost Skin CD8α+ Dendritic-like Cells, Representing a Potential Common Ancestor for Mammalian Cross-Presenting Dendritic Cells

Although fish constitute the most ancient animal group in which an acquired immune system is present, the presence of dendritic cells (DCs) in teleosts has been addressed only briefly, and the identification of a specific DC subset in teleosts remained elusive because of the lack of specific Abs. In mice, DCs expressing CD8α(+) in lymphoid tissues have the capacity to cross-present extracellular Ags to T cells through MHC I, similarly to tissue-derived CD103(+) DCs and the human CD141(+) DC population. In the current study, we identified a large and highly complex subpopulation of leukocytes coexpressing MHC class II and CD8α. This CD8α(+) MHC II(+) DC-like subpopulation constituted ∼1.2% of the total leukocyte population in the skin, showing phenotypical and functional characteristics of semimature DCs that seem to locally regulate mucosal immunity and tolerance in a species lacking lymph nodes. Furthermore, we identified trout homologs for CD141 and CD103 and demonstrated that, in trout, this skin CD8(+) DC-like subpopulation expresses both markers. To our knowledge, these results provide the first evidence of a specific DC-like subtype in nonimmune tissue in teleosts and support the hypothesis of a common origin for all mammalian cross-presenting DCs.

A subset of human plasmacytoid dendritic cells expresses CD8α upon exposure to herpes simplex virus type 1

Classical and plasmacytoid dendritic cells (DC) play important roles in the defense against murine and human infections with herpes simplex virus (HSV). So far, CD8α expression has only been reported for murine DC. CD8α⁺ DC have prominent cross-presenting activities, which are enhanced by murine CD8α⁺ PDC. The human orthologue of murine CD8α⁺ DC, the CD141 (BDCA3)⁺ DC, mainly cross-present after TLR3 ligation. We report here the serendipitous finding that a subset of human PDC upregulates CD8α upon HSV-1 stimulation, as shown by gene array and flow cytometry analyses. CD8α, not CD8ß, was expressed upon exposure. Markers of activation, migration, and costimulation were upregulated on CD8α-expressing human PDC. In these cells, increased cytokine and chemokine levels were detected that enhance development and function of T, B, and NK cells, and recruit immature DC, monocytes, and Th1 cells, respectively. Altogether, human CD8α⁺ PDC exhibit a highly activated phenotype and appear to recruit other immune cells to the site of inflammation. Further studies will show whether CD8α-expressing PDC contribute to antigen cross-presentation, which may be important for immune defenses against HSV infections in vitro and in vivo.

Fibroblastic reticular cells: organization and regulation of the T lymphocyte life cycle

The connective tissue of any organ in the body is generally referred to as stroma. This complex network is commonly composed of leukocytes, extracellular matrix components, mesenchymal cells, and a collection of nerves, blood, and lymphoid vessels. Once viewed primarily as a structural entity, stromal cells of mesenchymal origin are now being intensely examined for their ability to directly regulate various components of immune cell function. There is particular interest in the ability of stromal cells to influence the homeostasis, activation, and proliferation of T lymphocytes. One example of this regulation occurs in the lymph node, where fibroblastic reticular cells support the maintenance of naive T cells, induce Ag-specific tolerance, and restrict the expansion of newly activated T cells. In an effort to highlight the varied immunoregulatory properties of fibroblastic reticular cells, we reviewed the most recent advances in this field and provide some insights into potential future directions.

The mechanisms of action of vaccines containing aluminum adjuvants: an in vitro vs in vivo paradigm

Adjuvants such as the aluminum compounds (alum) have been dominantly used in many vaccines due to their immunopotentiation and safety records since 1920s. However, how these mineral agents influence the immune response to vaccination remains elusive. Many hypotheses exist as to the mode of action of these adjuvants, such as depot formation, antigen (Ag) targeting, and the induction of inflammation. These hypotheses are based on many in vitro and few in vivo studies. Understanding how cells interact with adjuvants in vivo will be crucial to fully understanding the mechanisms of action of these adjuvants. Interestingly, how alum influences the target cell at both the cellular and molecular level, and the consequent innate and adaptive responses, will be critical in the rational design of effective vaccines against many diseases. Thus, in this review, mechanisms of action of alum have been discussed based on available in vitro vs in vivo evidences to date.

A brief glimpse over the horizon for type 1 diabetes nanotherapeutics

The pace at which nanotherapeutic technology for human disease is evolving has accelerated exponentially over the past five years. Most of the technology is centered on drug delivery which, in some instances, offers tunable control of drug release. Emerging technologies have resulted in improvements in tissue and cell targeting while others are at the initial stages of pairing drug release and drug release kinetics with microenvironmental stimuli or changes in homeostasis. Nanotherapeutics has only recently been adopted for consideration as a prophylaxis/treatment approach in autoimmunity. Herein, we summarize the current state-of-the art of nanotherapeutics specifically for type 1 diabetes mellitus and offer our view over the horizon of where we envisage this modality evolving towards.

Generation of antigen-specific Foxp3+ regulatory T-cells in vivo following administration of diabetes-reversing tolerogenic microspheres does not require provision of antigen in the formulation

We have developed novel antisense oligonucleotide-formulated microspheres that can reverse hyperglycemia in newly-onset diabetic mice. Dendritic cells taking up the microspheres adopt a restrained co-stimulation ability and migrate to the pancreatic lymph nodes when injected into an abdominal region that is drained by those lymph nodes. Furthermore, we demonstrate that the absolute numbers of antigen-specific Foxp3+ T regulatory cells are increased only in the lymph nodes draining the site of administration and that these T-cells proliferate independently of antigen supply in the microspheres. Taken together, our data add to the emerging model where antigen supply may not be a requirement in "vaccines" for autoimmune disease, but the site of administration - subserved by lymph nodes draining the target organ - is in fact critical to foster the generation of antigen-specific regulatory cells. The implications of these observations on "vaccine" design for autoimmunity are discussed and summarized.

The role of dendritic cells in immunity against primary herpes simplex virus infections

Herpes simplex virus (HSV) is a DNA virus with tropism for infecting skin and mucosal epithelia during the lytic stages of its complex life cycle. The immune system has evolved a multitude of strategies to respond to primary HSV infections. These include rapid innate immune responses largely driven by pattern recognition systems and protective anti-viral immunity. Dendritic cells (DC) represent a versatile and heterogenic group of antigen presenting cells that are important for pathogen recognition at sites of infection and for priming of protective HSV-specific T cells. Here we will review the current knowledge on the role of DCs in the host immune response to primary HSV infection. We will discuss how DCs integrate viral cues into effective innate immune responses, will dissect how HSV infection of DCs interferes with their capacity to migrate from sites of infection to the draining lymph nodes and will outline how migratory DCs can make antigens available to lymph node resident DCs. The role of distinct DC subsets and their relevant contribution to antigen presentation on MHC class I and MHC class II molecules will be detailed in the context of T cell priming in the lymph node and the elicitation of effector function in infected tissues. An improved understanding of the fundamental mechanisms of how DCs recognize HSV, process and present its antigens to naïve and effector T cells will not only assist in the improvement of vaccine-based preventions of this important viral disease, but also serves as a paradigm to resolve basic immunological principles.

Human immunity in vitro - solving immunogenicity and more

It has been widely recognised that the phylogenetic distance between laboratory animals and humans limits the former's predictive value for immunogenicity testing of biopharmaceuticals and nanostructure-based drug delivery and adjuvant systems. 2D in vitro assays have been established in conventional culture plates with little success so far. Here, we detail the status of various 3D approaches to emulate innate immunity in non-lymphoid organs and adaptive immune response in human professional lymphoid immune organs in vitro. We stress the tight relationship between the necessarily changing architecture of professional lymphoid organs at rest and when activated by pathogens, and match it with the immunity identified in vitro. Recommendations for further improvements of lymphoid tissue architecture relevant to the development of a sustainable adaptive immune response in vitro are summarized. In the end, we sketch a forecast of translational innovations in the field to model systemic innate and adaptive immunity in vitro.

Dendritic cells of the oral mucosa

The oral cavity contains distinct mucosal surfaces, each with its own unique distribution of dendritic cell (DC) subsets. In addition to tissue-specific properties, such organization might confer differential immune outcomes guided by tissue-resident DCs, which translate in the lymph node into an overall immune response. This process is further complicated by continual exposure and colonization of the oral cavity with enormous numbers of diverse microbes, some of which might induce destructive immunity. As a central cell type constantly monitoring changes in oral microbiota and orchestrating T-cell function, oral DCs are of major importance in deciding whether to induce immunity or tolerance. In this review, an overview of the phenotype and distribution of DCs in the oral mucosa is provided. In addition, the role of the various oral DC subsets in inducing immunity vs. tolerance, as well as their involvement in several oral pathologies is discussed.

Priming of T follicular helper cells by dendritic cells

T follicular helper cells (Tfh) are required to generate long-lived antibody responses, which confer long-term protection to pathogens following vaccination or infection. Despite significant advances in the field, however, little is known about the early steps that drive Tfh cell differentiation. In this review, we will discuss the mechanisms by which dendritic cells promote the initial commitment of activated CD4(+) T cells to the Tfh cell differentiation pathway.

Diminished Memory T-Cell Expansion Due to Delayed Kinetics of Antigen Expression by Lentivectors

Memory CD8⁺ T lymphocytes play a central role in protective immunity. In attempt to increase the frequencies of memory CD8⁺ T cells, repeated immunizations with viral vectors are regularly explored. Lentivectors have emerged as a powerful vaccine modality with relatively low pre-existing and anti-vector immunity, thus, thought to be ideal for boosting memory T cells. Nevertheless, we found that lentivectors elicited diminished secondary T-cell responses that did not exceed those obtained by priming. This was not due to the presence of anti-vector immunity, as limited secondary responses were also observed following heterologous prime-boost immunizations. By dissecting the mechanisms involved in this process, we demonstrate that lentivectors trigger exceptionally slow kinetics of antigen expression, while optimal activation of lentivector-induced T cells relays on durable expression of the antigen. These qualities hamper secondary responses, since lentivector-encoded antigen is rapidly cleared by primary cytotoxic T cells that limit its presentation by dendritic cells. Indeed, blocking antigen clearance by cytotoxic T cells via FTY720 treatment, fully restored antigen presentation. Taken together, while low antigen expression is expected during secondary immunization with any vaccine vector, our results reveal that the intrinsic delayed expression kinetics of lentiviral-encoded antigen, further dampens secondary CD8⁺ T-cell expansion.

Slow CCL2-dependent translocation of biopersistent particles from muscle to brain

BACKGROUND

Long-term biodistribution of nanomaterials used in medicine is largely unknown. This is the case for alum, the most widely used vaccine adjuvant, which is a nanocrystalline compound spontaneously forming micron/submicron-sized agglomerates. Although generally well tolerated, alum is occasionally detected within monocyte-lineage cells long after immunization in presumably susceptible individuals with systemic/neurologic manifestations or autoimmune (inflammatory) syndrome induced by adjuvants (ASIA).

METHODS

On the grounds of preliminary investigations in 252 patients with alum-associated ASIA showing both a selective increase of circulating CCL2, the major monocyte chemoattractant, and a variation in the CCL2 gene, we designed mouse experiments to assess biodistribution of vaccine-derived aluminum and of alum-particle fluorescent surrogates injected in muscle. Aluminum was detected in tissues by Morin stain and particle induced X-ray emission) (PIXE) Both 500 nm fluorescent latex beads and vaccine alum agglomerates-sized nanohybrids (Al-Rho) were used.

RESULTS

Intramuscular injection of alum-containing vaccine was associated with the appearance of aluminum deposits in distant organs, such as spleen and brain where they were still detected one year after injection. Both fluorescent materials injected into muscle translocated to draining lymph nodes (DLNs) and thereafter were detected associated with phagocytes in blood and spleen. Particles linearly accumulated in the brain up to the six-month endpoint; they were first found in perivascular CD11b+ cells and then in microglia and other neural cells. DLN ablation dramatically reduced the biodistribution. Cerebral translocation was not observed after direct intravenous injection, but significantly increased in mice with chronically altered blood-brain-barrier. Loss/gain-of-function experiments consistently implicated CCL2 in systemic diffusion of Al-Rho particles captured by monocyte-lineage cells and in their subsequent neurodelivery. Stereotactic particle injection pointed out brain retention as a factor of progressive particle accumulation.

CONCLUSION

Nanomaterials can be transported by monocyte-lineage cells to DLNs, blood and spleen, and, similarly to HIV, may use CCL2-dependent mechanisms to penetrate the brain. This occurs at a very low rate in normal conditions explaining good overall tolerance of alum despite its strong neurotoxic potential. However, continuously escalating doses of this poorly biodegradable adjuvant in the population may become insidiously unsafe, especially in the case of overimmunization or immature/altered blood brain barrier or high constitutive CCL-2 production.

Delivery of viral-vectored vaccines by B cells represents a novel strategy to accelerate CD8+ T-cell recall responses

Using B cells to target antigens into the follicular regions represents a novel approach to accelerate CD8+ T-cell recall responses.

Multivalent glycopeptide dendrimers for the targeted delivery of antigens to dendritic cells

Dendritic cells are the most powerful type of antigen presenting cells. Current immunotherapies targeting dendritic cells have shown a relative degree of success but still require further improvement. One of the most important issues to solve is the efficiency of antigen delivery to dendritic cells in order to achieve an appropriate uptake, processing, and presentation to Ag-specific T cells. C-type lectins have shown to be ideal receptors for the targeting of antigens to dendritic cells and allow the use of their natural ligands - glycans - instead of antibodies. Amongst them, dendritic cell-specific ICAM-3-grabbing non-integrin (DC-SIGN) is an interesting candidate due to its biological properties and the availability of its natural carbohydrate ligands. Using Le(b)-conjugated poly(amido amine) (PAMAM) dendrimers we aimed to characterize the optimal level of multivalency necessary to achieve the desired internalization, lysosomal delivery, Ag-specific T cell proliferation, and cytokine response. Increasing DC-SIGN ligand multivalency directly translated in an enhanced binding, which might also be interesting for blocking purposes. Internalization, routing to lysosomal compartments, antigen presentation and cytokine response could be optimally achieved with glycopeptide dendrimers carrying 16-32 glycan units. This report provides the basis for the design of efficient targeting of peptide antigens for the immunotherapy of cancer, autoimmunity and infectious diseases.

Site-specific dynamics of CD11b+ and CD103+ dendritic cell accumulations following ozone exposure

Pulmonary dendritic cells (DCs) are among the first responders to inhaled environmental stimuli such as ozone (O(3)), which has been shown to activate these cells. O(3) reacts with epithelial lining fluid (ELF) components in an anatomically site-specific manner dictated by O(3) concentration, airway flow patterns, and ELF substrate concentration. Accordingly, the anatomical distribution of ELF reaction products and airway injury are hypothesized to produce selective DC maturation differentially within the airways. To investigate how O(3) affects regional airway DC populations, we utilized a model of O(3)-induced pulmonary inflammation, wherein C57BL/6 mice were exposed to 0.8 ppm O(3) 8 h/day for 1, 3, and 5 days. This model induced mild inflammation and no remarkable epithelial injury. Tracheal, but not more distant airway sites, and mediastinal lymph node (MLN) DC numbers were increased significantly after the third exposure day. The largest increase in each tissue was of the CD103(+) DC phenotype. After 3 days of exposure, fewer DCs expressed CD80, CD40, and CCR7, and, at this same time point, total MLN T cell numbers increased. Together, these data demonstrate that O(3) exposure induced site-specific and phenotype changes in the pulmonary and regional lymph node DC populations. Possibly contributing to ozone-mediated asthma perturbation, the phenotypic changes to DCs within pulmonary regions may alter responses to antigenic stimuli. Decreased costimulatory molecule expression within the MLN suggests induction of tolerance mechanisms; increased tracheal DC number may raise the potential for allergic sensitization and asthmatic exacerbation, thus overcoming O(3)-induced decrements in costimulatory molecule expression.

Dendritic cell science: more than 40 years of history

Over 40 years of research into the field of DCs has revolutionized our understanding into the activation and regulation of the immune system. This minireview discusses the major breakthroughs in DC science that have paved the way to the 2011 Nobel Prize in Physiology-Medicine awarded to Bruce A. Beutler and Jules A. Hoffmann (for their discoveries in innate immune recognition) and Ralph M. Steinman (for his discovery of the DC).

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.

Thioperamide induces CD4 CD25 Foxp3 regulatory T lymphocytes in the lung mucosa of allergic mice through its action on dendritic cells

Background:

Histamine is an important mediator in the development of allergic reactions. The biological effects of histamine are mediated through four histaminergic receptors. In recent years, an important role has been assigned to the proinflammatory functions of histamine regarding the H4 receptor. Previously, we have demonstrated that injection of immature dendritic cells treated with histamine into allergic mice promotes an increase in CD8⁺ Tc2 lymphocytes, which are involved in the worsening of allergy symptoms during the chronic phase of the disease. The aim of this study was to evaluate the role of the H3/H4 receptor antagonist, thioperamide, in allergy.

Methods:

Ovalbumin-allergized mice and nonallergized mice were injected with phosphate-buffered saline, dendritic cells, or thioperamide-treated dendritic cells. After treatment, the lungs of the mice were obtained and analyzed for changes in the populations of dendritic cells and T lymphocytes, as well as the expression of H and H4 receptors in mononuclear lung cells.

Results:

We found an increase in regulatory T cells in the lungs of allergic mice intratracheally injected with dendritic cells which had their H3/H4 receptors blocked with thioperamide. We also found an increase in the production of interleukin-10 by dendritic cells of the lung. Finally, we observed a decrease in serum levels of specific anti-IgE and a reduction of eosinophils in bronchoalveolar lavage from allergic mice.

Conclusion:

Thioperamide induces a significant improvement in symptoms of allergic reaction perhaps via induction of regulatory T lymphocytes. These findings may become relevant in the understanding of type 1 hypersensivity reactions.

The role of the lymphatic system in vaccine trafficking and immune response

The development and improvement of vaccines has been a significant endeavor on the part of the medical community for more than the last two centuries, and the success of these efforts is obvious when one considers the millions of lives that have been saved. Recent work in the field of vaccines, however, indicates that vaccines may be developed for even more challenging diseases than those previously addressed. It will be important in achieving this feat to account for the physical and chemical processes related to vaccine trafficking, rather than solely relying on our knowledge of the pathogen and our empirical experience. A thorough understanding of the lymphatic system is essential considering the role it plays in antigen trafficking and all immunological activity. This review describes the results of recent work that provides insight into the physiological processes of the lymphatic system and its various components with an emphasis on vaccine antigen trafficking from the administration site to secondary lymphoid tissues and the ensuing immune response. The review also discusses current challenges in designing vaccines and presents modern strategies for designing vaccines to better interface with the lymphatic system.

Lung dendritic cells at the innate-adaptive immune interface

This review updates the basic biology of lung DCs and their functions. Lung DCs have taken center stage as cellular therapeutic targets in new vaccine strategies for the treatment of diverse human disorders, including asthma, allergic lung inflammation, lung cancer, and infectious lung disease. The anatomical distribution of lung DCs, as well as the division of labor between their subsets, aids their ability to recognize and endocytose foreign substances and to process antigens. DCs can induce tolerance in or activate naïve T cells, making lung DCs well-suited to their role as lung sentinels. Lung DCs serve as a functional signaling/sensing unit to maintain lung homeostasis and orchestrate host responses to benign and harmful foreign substances.

Complexity of dendritic cell subsets and their function in the host immune system

Dendritic cells (DCs) are professional antigen-presenting cells that are critical for induction of adaptive immunity and tolerance. Traditionally DCs have been divided into two discrete subtypes, which comprise conventional and non-conventional DCs. They are distributed across various organs in the body and comprise a heterogeneous population, which has been shown to display differences in terms of surface marker expression, function and origins. Recent studies have shed new light on the process of DC differentiation and distribution of DC subtypes in various organs. Although monocytes, macrophages and DCs share a common macrophage-DC progenitor, a common DC progenitor population has been identified that exclusively gives rise to DCs and not monocytes or macrophages. In this review, we discuss the recent advances in our understanding of DC differentiation and subtypes and provide a comprehensive overview of various DC subtypes with emphasis on their function and origins. Furthermore, in light of recent developments in the field of DC biology, we classify DCs based on the precursor populations from which the various DC subsets originate. We classify DCs derived from common DC progenitor and pre-DC populations as conventional DCs, which includes both migratory and lymphoid-resident DC subsets and classify monocyte-derived DCs and plasmacytoid DCs as non-conventional DCs.

Pathogenic aspects of dermatomyositis, polymyositis and overlap myositis

Inflammatory myopathies (IMs) often have distinct histopathologic features suggesting humorally mediated involvement of the microcirculation in dermatomyositis (DM), including early capillary deposition of the complement C5b-9 membranolytic attack complex (MAC) and secondary ischaemic changes; and CD8 T-cell-mediated and MHC1-restricted autoimmune attack of myofibers in polymyositis (PM) and inclusion body myositis. Novel insights in these specific diseases include emerging evidence that capillary loss involves whole microvascular units in DM, and that regulatory T-cells strongly protect myofibers from experimental autotoxic attack in PM. However, all IMs do not exhibit pathophysiology-relevant histopathologic features of DM or PM. Autoimmune necrotizing myopathies (AINM) occur in the absence of endomysial inflammatory cells and may be specifically associated with anti-SRP autoantibodies. Moreover, IM histopathological features may be scarce, unspecific and overlapping. Therefore, increasing attention is paid to features shared by IMs regardless of their type, relevant to the innate immune response and to non-immune mechanisms. Innate immune responses to myodamage (and/or as yet unknown stimuli), involves release of chemokines, activation of specific Toll-like receptors (TLRs) and complex Th-1, Th-17 and other cytokine interplays; it triggers DC recruitment and maturation, and is associated with type 1 IFN signature (especially in DM where type 1 IFN-producing cells called plasmacytoid DCs are mainly detected). Non-immune mechanisms mainly include endoplasmic reticulum (ER) stress induced in myofibers by up-regulation of MHC-class I antigens (as typically observed in PM with a diffuse pattern and in DM with perifascicular predominance). ER stress may favour autoimmune reactions but may also be associated with myofiber damage and dysfunction in the absence of lymphocytes. Overlap myositis (OM) may be associated with other connective tissue diseases and a variety of autoantibodies, such as those directed against tRNA synthetase. Myositis specific autoantibodies are mainly expressed by regenerating myofibers, that may also express MHC-1 and endogenous ligand-binding TLRs, thus drawing a picture in which the regenerating myofiber plays a central pathophysiologic role.

Murine melanoma-infiltrating dendritic cells are defective in antigen presenting function regardless of the presence of CD4CD25 regulatory T cells

Tumor-infiltrating dendritic cells are often ineffective at presenting tumor-derived antigen in vivo, a defect usually ascribed to the suppressive tumor environment. We investigated the effects of depleting CD4⁺CD25⁺ “natural” regulatory T cells (Treg) on the frequency, phenotype and function of total dendritic cell populations in B16.OVA tumors and in tumor-draining lymph nodes. Intraperitoneal injection of the anti-CD25 monoclonal antibody PC61 reduced Treg frequency in blood and tumors, but did not affect the frequency of tumor-infiltrating dendritic cells, or their expression of CD40, CD86 and MHCII. Tumor-infiltrating dendritic cells from PC61-treated or untreated mice induced the proliferation of allogeneic T cells in vitro, but could not induce proliferation of OVA-specific OTI and OTII T cells unless specific peptide antigen was added in culture. Some proliferation of naïve, OVA-specific OTI T cells, but not OTII T cells, was observed in the tumor-draining LN of mice carrying B16.OVA tumors, however, this was not improved by PC61 treatment. Experiments using RAG1^−/− hosts adoptively transferred with OTI and CD25-depleted OTII cells also failed to show improved OTI and OTII T cell proliferation in vivo compared to C57BL/6 hosts. We conclude that the defective presentation of B16.OVA tumor antigen by tumor-infiltrating dendritic cells and in the tumor-draining lymph node is not due to the presence of “natural” CD4⁺CD25⁺ Treg.

Accelerated dendritic cell differentiation from migrating Ly6C(lo) bone marrow monocytes in early dermal West Nile virus infection

No study has investigated the participation of Ly6C(+) monocytes in the earliest phase of skin infection with the mosquito-borne West Nile virus. In a novel murine model mimicking natural dermal infection, CCL2-dependent bone marrow (BM)-derived monocyte migration, differentiation into Ly6C(+) dendritic cells (DC), and accumulation around dermal deposits of infected fibroblasts by day 1 postinfection were associated with increasing numbers of monocyte-derived TNF/inducible NO synthase-producing DC by day 2 postinfection in draining auricular lymph nodes (ALN). Adoptive transfer demonstrated simultaneous migration of bone marrow-derived Ly6C(lo) monocytes to virus-infected dermis and ALN, where they first become Ly6C(hi) DC within 24 h and then Ly6C(lo) DC by 72 h. DC migration from the infected dermis to the ALN derived exclusively from Ly6C(lo) BM monocytes. This demonstrates that Ly6C(hi) and Ly6C(lo) BM-derived monocytes have different fates in vivo and suggests that BM may be a reservoir of preinflammatory monocytes for rapid deployment as inflammatory DC during virus infection.

Lymph node stroma broaden the peripheral tolerance paradigm

Research into how self-reactive T cells are tolerized in lymph nodes has focused largely on dendritic cells (DCs). We now know that lymph node stromal cells (LNSC) are important mediators of deletional tolerance to peripheral tissue-restricted antigens (PTAs), which are constitutively expressed and presented by LNSCs. Of the major LNSC subsets, fibroblastic reticular cells and lymphatic endothelial cells are known to directly induce tolerance of responding naïve CD8 T cells. The biological outcome of this interaction fills a void otherwise not covered by DCs or thymic stromal cells. These findings, we suggest, necessitate a broadening of peripheral tolerance theory to include steady-state presentation of clinically relevant PTA to naïve CD8 T cells by lymph node-resident stroma.

Dynamics of dendritic cell-T cell interactions: a role in T cell outcome

Antigen-specific dendritic cells (DC)-T cell encounters occur in lymph nodes (LNs) and are essential for the induction of both priming and tolerance. In both cases, T cells are rapidly activated and proliferate. However, the subsequent outcome of T cell activation depends on the modulation of different DC- and T cell-intrinsic signals. Recent advances in two-photon (2P) microscopy have furthered our understanding regarding the complex choreography of DCs and T cells in intact LNs, and established differences in the dynamics of DC-T cell contacts during priming and tolerance induction. The mechanisms that favour DC-T cell encounters, as well as the contribution of the frequency and the duration of such encounters in dictating the T cell response, are discussed in this review.

Naturally arising human CD4 T-cells that recognize islet autoantigens and secrete interleukin-10 regulate proinflammatory T-cell responses via linked suppression

OBJECTIVE

Regulatory T-cells (Tregs) recognizing islet autoantigens are proposed as a key mechanism in the maintenance of self-tolerance and protection from type 1 diabetes. To date, however, detailed information on such cells in humans, and insight into their mechanisms of action, has been lacking. We previously reported that a subset of CD4 T-cells secreting high levels of the immunosuppressive cytokine interleukin-10 (IL-10) is significantly associated with late onset of type 1 diabetes and is constitutively present in a majority of nondiabetic individuals. Here, we test the hypothesis that these T-cells represent a naturally generated population of Tregs capable of suppressing proinflammatory T-cell responses.

RESEARCH DESIGN AND METHODS

We isolated and cloned islet-specific IL-10-secreting CD4(+) T-cells from nondiabetic individuals after brief ex vivo exposure to islet autoantigens using cytokine capture technology and examined their phenotype and regulatory potential.

RESULTS

Islet-specific IL-10(+) CD4 T-cells are potent suppressors of Th1 effector cells, operating through a linked suppression mechanism in which there is an absolute requirement for the cognate antigen of both the regulatory and effector T-cells to be presented by the same antigen-presenting cell (APC). The regulatory T-cells secrete perforin and granzymes, and suppression is associated with the specific killing of APCs presenting antigen to effector T-cells.

CONCLUSIONS

This hitherto undescribed population of islet autoantigen-specific Tregs displays unique characteristics that offer exquisite specificity and control over the potential for pathological autoreactivity and may provide a suitable target with which to strengthen beta-cell-specific tolerance.

Langerhans cells and more: langerin-expressing dendritic cell subsets in the skin

Langerhans cells (LCs) are antigen-presenting dendritic cells (DCs) that reside in epithelia. The best studied example is the LC of the epidermis. By electron microscopy, their identifying feature is the unique rod- or tennis racket-shaped Birbeck granule. The phenotypic hallmark is their expression of the C-type lectin receptor langerin/CD207. Langerin, however, is also expressed on a recently discovered population of DC in the dermis and other tissues of the body. These 'dermal langerin(+) dendritic cells' are unrelated to LCs. The complex field of langerin-negative dermal DCs is not dealt with here. In this article, we briefly review the history, ontogeny, and homeostasis of LCs. More emphasis is laid on the discussion of functional properties in vivo. Novel models using genetically engineered mice are contributing tremendously to our understanding of the role of LCs in eliciting adaptive immune responses against pathogens or tumors and in inducing and maintaining tolerance against self antigens and innocuous substances in vivo. Also, innate effector functions are increasingly being recognized. Current activities in this area are reviewed, and possibilities for future exploitation of LC in medicine, e.g. for the improvement of vaccines, are contemplated.

Langerhans cells: critical regulators of skin immunity?

Langerhans cells (LC) are members of the heterogenous family of professional antigen presenting dendritic cells (DC). They are identified by the C-type lectin receptor Langerin and form a contiguous network in the epidermis. Consequently, LC are an integral part of the skin barrier to the environment and were considered to be critical inducers of skin immunity, whereas dermal DC were largely overlooked. However, with the identification of a distinct subset of Langerin expressing dermal DC, the situation in the skin has become more complex and the relative contribution of the different cutaneous DC populations in balancing immunity and tolerance has become a matter of active debate. Here, we briefly review the classical paradigm and recent challenges of LC function, before focusing on advances concerning their role in contact hypersensitivity and ultraviolet radiation-induced immunosuppression obtained with in vivo LC ablation models. We then discuss novel LC/DC-specific gene targeting approaches currently used to dissect the role of the regulatory cytokines transforming growth factor-beta and interleukin-10 to govern LC and DC function in vivo. This second generation of LC-specific genetically engineered mice will considerably extend our understanding of the molecular control of LC function in regulating skin immunity and tolerance in the near future.

Disentangling the complexity of the skin dendritic cell network

Using 'knockin' mice to track and ablate dendritic cells (DCs) expressing notably the langerin (Cd207) gene, it has been possible to identify five DC subsets within the skin and to assess whether functional specialization exists among them. The present review summarizes recent information concerning the phenotype and the function of these five DC subsets before and after their migration to cutaneous draining lymph nodes. Moreover, it integrates this information into a unifying model that emphasizes the similarities that exist among the mouse DC subsets that are found in both lymphoid and nonlymphoid tissues.