Identification of three distinct subsets of migrating dendritic cells from oral mucosa within the regional lymph nodes

Discovery of an theranostic functional mAb for visualizing the sensitivity and effectiveness of PD-L1 checkpoint therapy

To address the challenges of inconsistent efficacy, low sensitivity, and subjective screening methods faced by PD-L1-targeted immune checkpoint therapies in the clinic. We propose to construct a therapeutic functional monoclonal antibody with tracking capability using tetrazolium-based bioorthogonal reaction turn-on fluorescence technology, focusing on the molecular biomarker PD-L1 for easy visualisation of therapeutic response. This therapeutic monoclonal antibody enables bioorthogonal reaction turn-on fluorescence to monitoring of tumors with varying degrees of PD-L1 expression, while preserving the activity of the PDL1 monoclonal antibody and improve the immune activation rate and achieve efficient anti-tumor effects. In conclusion, our proposed family of bio-orthogonal reaction-driven fluorescence turn-on methods can be used to identify therapeutic bifunctional monoclonal antibodies to PD-L1, which can be employed alongside the screening of PD-L1 antibodies for therapeutic effects. Abbreviations: CRT, Calreticulin; DCs, Dendritic cells; ELISA, Enzyme-linked immunosorbent assay; IFN-γ, Interferon-γ; IL-2, Interleukin-2; IHC, Immunohistochemistry; WB, Western blot.

Effect of chronic ethanol ingestion on dendritic cell population during oral mucosal repair: An experimental study

The aim of this study was to analyze the effect of chronic ethanol ingestion on dendritic cell repopulation during the repair process of rat oral mucosa and in the rat spleen by analyzing the immunohistochemical expression of dendritic cell markers. Wistar rats ingested 20% ethanol solution for 28 days; a surgical wound was performed on the rat tongue after this period. The repair process and the number of CD1a+, CD11c+, and CD207+ cells in the regions adjacent to the wound were determined at day 1, 3, and 7 following the wound as well as in the rat spleen. The wound-only group (no ethanol exposure) had complete reepithelization after 7 days, but this did not occur in the ethanol + wound group at this time point. The inflammatory infiltrate was significantly reduced in animals exposed to ethanol, which also showed significantly lower counts of CD1a+, CD11c+, and CD207+ cells than the wound-only group at all experimental time points. In addition, ethanol exposure also resulted in lower densities of CD11c+ and CD207+ cells in the rat spleen. In conclusion, chronic ethanol intake had a negative impact on dendritic cell numbers, a fact that may contribute to delay in oral mucosa repair.

Hapten sensitization to vaginal mucosa induces less recruitment of dendritic cells accompanying TGF-β-expressing CD206+ cells compared with skin

INTRODUCTION

Contact hypersensitivity (CHS), a type of delayed-type hypersensitivity, is induced by hapten exposure to the skin and mucosa. We previously reported that, in a murine model of CHS, the vaginal mucosa (VM) sensitization showed lower T-cell responses as compared with the abdominal skin sensitization. To investigate mechanisms of impaired CHS by the VM sensitization, we compared migration of hapten-captured dendritic cells (DCs) in the draining lymph nodes (dLNs) and recruitment of DCs at the sensitized local sites.

METHODS

Fluorescein isothiocyanate (FITC) or 2,4-dinitrofluorobenzene (DNFB) was used as hapten, and migration of FITC+ DCs in the dLNs and local recruitment of MHC class II+ and CD11c+ cells were compared between abdominal skin and VM sensitization by flow cytometric analyses and immunohistochemistry. Expression of tumor growth factor (TGF)-β at mRNA and protein levels, and local recruitment of CD206+ cells were examined after VM sensitization.

RESULTS

VM sensitization showed less numbers of FITC+ MHC class IIhigh CD11c+ migratory DCs in the dLNs at 6 and 24 h, as compared with skin sensitization. Both skin and VM sensitization induced the recruitment of dermal/submucosal DCs at 6 h, but the number of submucosal DCs in the VM was significantly decreased at 24 h. VM showed persistently higher mRNA levels of TGF-β2/β3 expression than those of the skin before and after sensitization. In the VM sensitization, increment of CD206+ MHC class II+ cells was observed especially at the deep lamina propria at 24 h. Most of CD206+ cells were also positive for the binding to Fc chimeric TGF-β receptor that interacts with all TGF-β isoforms, suggesting TGF-β expression.

CONCLUSION

DC migration to dLNs and localization of DCs at the sensitized sites are limited in the VM sensitization. Our results suggest that the existence of TGF-β-expressing CD206+ cells may contribute less sensitization ability and CHS responses in the VM.

Tolerogenic properties of CD206+ macrophages appeared in the sublingual mucosa after repeated antigen-painting

The sublingual mucosa (SLM) in the oral cavity is utilized as the site for sublingual immunotherapy to induce tolerance against allergens. We previously reported that CD206+ round-type macrophage-like cells were induced in the SLM after repeated antigen (e.g. cedar pollen or fluorescein isothiocyanate (FITC))-painting. In this study, we examined the phenotypic and functional properties of CD206+ cells induced by repeated FITC-painting on the SLM. CD206+ cells after the repeated FITC-painting possessed a macrophage-like CD11b+Ly6C+ F4/80+CD64+ phenotype and expressed TIM-4, which was expressed in tolerogenic tissue-resident macrophages, at a high level. SLM CD206+ cells preferentially expressed molecules related to endocytosis and homeostatic processes, including the novel B7 family of immune checkpoint molecules, as assessed by microarray analyses. SLM CD206+ cells showed preferential expression of M2-related genes such as Fizz1, Aldh1a1 and Aldh1a2 but not Ym-1 and Arginase-1. A CD206+ cell-rich status inhibited OVA-specific CD4+ T-cell responses but reciprocally enhanced the proportion of both IL-10+CD4+ cells and Foxp3+ regulatory T-cells in regional lymph nodes. Co-culture of CD206+ cells with dendritic cells (DCs) showed that IL-12 production was suppressed in DCs concurrent with the decline of the MHC class IIhiCD86+ population, which was restored by neutralization of IL-10. These results demonstrate SLM CD206+ cells show the feature of tolerogenic macrophages and down-regulate the antigen-presenting cell function of mature DCs resulting in the inhibition of CD4+ T-cell responses.

Silencing of PD-L2/B7-DC by Topical Application of Small Interfering RNA Inhibits Elicitation of Contact Hypersensitivity

PD-L2 is a ligand for the immune checkpoint receptor PD-1; however, its regulatory function is unclear. We previously reported that silencing of CD86 in cutaneous dendritic cells by topical application of small interfering RNA (siRNA) inhibits the elicitation of contact hypersensitivity (CHS). Here, we investigated the effects of topical application of PD-L2 siRNA on allergic skin disease. PD-L2 was induced in dendritic cells concurrently with the elevation of major histocompatibility complex class II and CD86 expression. Topical application of PD-L2 siRNA inhibited the elicitation of CHS by suppressing early proinflammatory cytokine expression and migration of hapten-carrying dendritic cells into lymph nodes. Local injection of neutralizing anti-PD-L2 mAb inhibited CHS to the same extent. PD-L2 siRNA treatment inhibited CHS in PD-1/PD-L1 double knockout mice and in the sensitized T-cell-transferred skin. These results suggest that the effects of PD-L2 silencing are independent of PD-1 but dependent on local memory T cells. Most of the inhibitory effects of PD-L2 and CD86 silencing on CHS were comparable, but PD-L2 siRNA treatment did not inhibit atopic disease-like manifestations and T helper type 2 responses in NC/Nga mice. Our results suggest that PD-L2 in cutaneous dendritic cells acts as a costimulator rather than a regulator. Local PD-L2 silencing by topical application of siRNA represents a therapeutic approach for contact allergy.

Systemic administration of a TLR7 agonist attenuates regulatory T cells by dendritic cell modification and overcomes resistance to PD-L1 blockade therapy

Research on immune checkpoint blockade therapy has made great progress in cancer immunotherapy, but the number of patients who benefit from this therapy remains limited. In this study, we examined the effects of monotherapy with systemic low-dose resiquimod, a synthesized TLR7 agonist, and examined its combined effects with PD-L1 blockade in two PD-L1 blockade-resistant tumor models (SCCVII and Colon 26). Resiquimod monotherapy in SCCVII tumors, representing impaired CD8⁺ T cell function and accelerated regulatory T cells (Tregs) within the tumors, efficiently reduced tumor growth with more recruitment of CD8⁺ T cells and a reduction of Treg. The results of resiquimod monotherapy in Colon 26, representing impaired Treg recruitment, were inferior to that in SCCVII. Combined resiquimod treatment with PD-L1 blockade exerted clear additional effects, as it was associated with reduced tumor size, attenuation of Tregs, and an increased ratio of CD8⁺ T cells/Tregs in both tumors. Systemic administration of low-dose resiquimod induced a transient and rapid activation of plasmacytoid and conventional dendritic cells, resulting in enhanced priming of T cells in regional lymph nodes. Experiments with more limited doses of resiquimod that did not yield beneficial effects after single treatment, showed additional effects to PD-L1 blockade and comparable antitumor effects when the frequency of anti-PD-L1 therapy was decreased. Our results suggest that systemic administration of low-dose resiquimod is useful as a companion drug to PD-1/PD-L1 blockade therapy.

Unique B7-H1 expression on masticatory mucosae in the oral cavity and trans-coinhibition by B7-H1-expressing keratinocytes regulating CD4+ T cell-mediated mucosal tissue inflammation

The PD-1/B7-H1 pathway regulates immune responses and maintains homeostasis. Here, we identified a unique expression of B7 homolog 1 (B7-H1) on masticatory mucosae in the oral cavity. B7-H1 was physiologically expressed on the dorsal surface of the tongue, gingiva, and hard palate. Other squamous epithelia and other structures of the epithelia did not express B7-H1 in the steady state. Physiological B7-H1 expression on masticatory mucosae was limited on prickle cells, and its expression on basal keratinocytes (KCs) was strictly regulated. B7-H1 on prickle cells was upregulated by external topical stimuli, but B7-H1 on basal KCs was induced only by internal stimuli via infiltrating cells. The blocking of KC-associated B7-H1 or the lack of programmed cell death-1 (PD-1) on tissue effector CD4⁺ T cells in mice lacking B7-H1 on immune cells drastically exacerbated the tissue inflammation induced by topical OVA painting as an exogenous antigen, indicating direct interaction with KCs and CD4⁺ T cells. Trans-coinhibitory signals by KCs may modulate local T-cell/dendritic cell activation, resulting in inhibition of T-cell responses in both peripheral and secondary lymphoid tissues. Careful control of B7-H1 induction in KCs may play a crucial role in the protection from CD4⁺ T cell-mediated tissue inflammation by exogenous antigens delivered from the mucosal surface.

Pattern of circulation of MCMV mimicking natural infection upon oronasal inoculation

Cytomegaloviruses may infect mammals via oronasal route. However, up till now it remains unclear how this exposure leads to a general infection and shedding. To address this issue, BALB/c female mice were oronasally inoculated with either the highly passaged murine cytomegalovirus (MCMV) Smith or the low passaged MCMV HaNa1. Virus titration showed a productive virus replication of both strains in the nasal mucosa from 1 dpi until the end of the experiment (14 dpi), in lungs from 5 until 14 dpi, and in submandibular glands from 7 until 14 dpi. In contrast to MCMV HaNa1, MCMV Smith also established a low level productive infection in abdominal organs (spleen, liver and kidneys) from 5 dpi (spleen), 7 dpi (liver), and 10 dpi (kidneys) until the end of the experiment. Co-culture showed that for both strains, cell-associated virus was detected in a non-infectious form in nasopharynx-associated lymphoid tissues (NALT) from 1 until 14 dpi, in submandibular lymph nodes from 3 until 5 dpi, in deep cervical lymph nodes from 3 until 14 dpi, in mediastinal lymph nodes from 7 until 14 dpi, in spleen from 5 until at least 10 dpi and in the peripheral blood mononuclear cells (PBMC) at 7 and 10 dpi. The present study shows that upon oronasal exposure, MCMV first enters the nasal mucosa and NALT, from where the virus disseminates to the spleen possibly via the draining lymphatic system and blood; a subsequent cell-associated viremia transports MCMV to submandibular glands and for MCMV Smith also to liver and kidneys, where a second productive replication starts.

Repeated antigen painting and sublingual immunotherapy in mice convert sublingual dendritic cell subsets

The sublingual mucosa (SLM) is utilized as the site for sublingual immunotherapy (SLIT) to induce tolerance against allergens. The contribution of SLM-dendritic cells (SLM-DCs) has not been clarified. The aim of this study was to examine the dynamics and phenotype of SLM-DCs after topical antigen painting and SLIT. SLM-DCs were histologically evaluated after FITC painting. A novel murine Japanese cedar pollinosis (JCP) model was generated and change in SLM-DCs after SLIT was examined. The density of SLM-DCs was clearly lower compared with the buccal mucosa and dorsal surface of the tongue. Topical FITC painting on the SLM induced maximal recruitment of submucosal DCs (smDCs) at 6h, but most smDCs had vanished at 24h. Repeated painting on the SLM induced exhaustion and conversion of the smDC phenotype. CD206(high)CD11c(low) round-type cells with fewer dendrites and less lymph node migration capacity became dominant. In the murine model of JCP, SLIT efficiently inhibited clinical symptoms and allergen-mediated immunological responses. SLIT markedly reduced the number of SLM-DCs, converted to the round-type dominant phenotype and inhibited the activation of regional lymph node DCs. Topical antigen painting on the SLM induced rapid exhaustion and conversion of smDCs. The unique dynamics of SLM-DCs may contribute to tolerance induction in SLIT.

CD207⁺ cells recruitment to the vaccination site and draining lymph nodes after the administration of DC-Apo/Nec vaccine in mice

De novo ectopic lymphoid tissue formation is known to occur in certain disease and inflammatory settings. After an effective vaccination with dendritic cells (DC) charged with melanoma apoptotic/necrotic cells (Apo/Nec), a subcutaneous tertiary lymphoid structure was organized, where retained vaccine cells interacted with recruited inflammatory and T cells. In this work we report for the first time the recruitment of two morphologically different CD207(+) cells to vaccination site. The time-course behavior of CD207(+) cells was reciprocal between vaccination site and draining lymph nodes (DLNs). After 6-10 days, CD207(+) cells localized at the paracortical region of DLNs, in close contact with T cell population. DLNs were enriched in a peculiar MHCII(+) CD11c((-)) CD207(+) population, whose role remains to be determined. Whether CD207(+) cells migration to the vaccination site can be associated with a differential anti-tumoral response remains as an open and exciting question.

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.

Dental Pulp Dendritic Cells Migrate to Regional Lymph Nodes

Dendritic cell (DC) migration to regional lymph nodes (RLNs) is an essential step in adaptive immunity, and cell-surface antigens on migrating DCs greatly affect the quality and quantity of subsequent immune responses. Although MHC class II+ DC-like cells exist in the dental pulp, the lineage and function of these cells remain unknown. Here, we identified migratory DCs from the dental pulp after cusp trimming and acid etching in KikGR mice, in which the photoconvertible fluorescent protein changed from green to red upon violet light exposure. Two major cell fractions from the dental pulp had migrated to the RLNs at 16 hrs after cusp treatment, which showed the following lineage markers in the main and second fractions: CD11chighCD11b++Ly6Clow Ly6Glow F4/80+ and CD11cmedCD11b+++Ly6C++Ly6G+++F4/80-, respectively. These lineage markers indicate that the former cells were DCs that had migrated through afferent lymphoid vessels, and the latter were granulocytes recruited via blood circulation. Migratory dental pulp DCs were mature, expressing the highest levels of CD273 (B7-DC) and CD86 co-stimulators and MHC class II. Our results suggest that cariogenic-bacteria-exposed dental pulp DCs migrate to RLNs and there trigger adaptive immune responses.

Dendritic cells in the periphery control antigen-specific natural and induced regulatory T cells

Dendritic cells (DCs) are specialized antigen-presenting cells that regulate both immunity and tolerance. DCs in the periphery play a key role in expanding naturally occurring Foxp3⁺ CD25⁺ CD4⁺ regulatory T cells (Natural T-regs) and inducing Foxp3 expression (Induced T-regs) in Foxp3⁻ CD4⁺ T cells. DCs are phenotypically and functionally heterogeneous, and further classified into several subsets depending on distinct marker expression and their location. Recent findings indicate the presence of specialized DC subsets that act to expand Natural T-regs or induce Foxp3⁺ T-regs from Foxp3⁻ CD4⁺ T cells. For example, two major subsets of DCs in lymphoid organs act differentially in inducing Foxp3⁺ T-regs from Foxp3⁻ cells or expanding Natural T-regs with model-antigen delivery by anti-DC subset monoclonal antibodies in vivo. Furthermore, DCs expressing CD103 in the intestine induce Foxp3⁺ T-regs from Foxp3⁻ CD4⁺ T cells with endogenous TGF-β and retinoic acid. In addition, antigen-presenting DCs have a capacity to generate Foxp3⁺ T-regs in the oral cavity where many antigens and commensals exist, similar to intestine and skin. In skin and skin-draining lymph nodes, at least six DC subsets have been identified, suggesting a complex DC-T-reg network. Here, we will review the specific activity of DCs in expanding Natural T-regs and inducing Foxp3⁺ T-regs from Foxp3⁻ precursors, and further discuss the critical function of DCs in maintaining tolerance at various locations including skin and oral cavity.

Epicutaneous Immunotherapy Compared with Sublingual Immunotherapy in Mice Sensitized to Pollen (Phleum pratense)

Background. The aim of this study was to compare the efficacy of epicutaneous immunotherapy (EPIT) to sublingual immunotherapy (SLIT) in a model of mice sensitized to Phleum pratense pollen. Methods. BALB/c mice were sensitized by sub-cutaneous route to pollen protein extract mixed treated for 8 weeks, using sham, EPIT, or SLIT. Measurements involved the serological response and cytokine profile from reactivated splenocytes, plethysmography after aerosol challenge to pollen, cell, and cytokine contents in the bronchoalveolar lavages (BALs). Results. After immunotherapy, sIgE was significantly decreased in the treated groups compared to sham (P < 0.001), whereas sIgG2a increased with EPIT and SLIT (P < 0.001 and P < 0.005 versus sham). Reactivated splenocytes secreted higher levels of Th2 cytokines with sham (P < 0.01). Penh values were higher in sham than EPIT and SLIT. Eosinophil recruitment in BAL was significantly reduced only by EPIT (P < 0.01). Conclusion. In this model of mice sensitized to pollen, EPIT was at least as efficient as SLIT.

Enhanced antigen uptake by dendritic cells induced by the B pentamer of the type II heat-labile enterotoxin LT-IIa requires engagement of TLR2

The potent mucosal adjuvant properties of the type II heat-labile enterotoxin LT-IIa of Escherichia coli are dependent upon binding of the B pentamer of the enterotoxin (LT-IIa-B(5)) to ganglioside receptors on immunocompetent cells. To evaluate the immunomodulatory activities of LT-IIa-B(5), in vitro experiments employing bone marrow-derived dendritic cells (BMDC) were performed. Uptake of OVA-FITC, a model antigen (Ag), was enhanced by treatment of BMDC with LT-IIa-B5, but not by treatment of cells with the B pentamer of cholera toxin (CTB). Expression of co-stimulatory molecules (CD40, CD80, CD86, and MHC-II) and cytokines (IL-12p40, TNF-alpha, and IFN-gamma) was increased in BMDC treated with LT-IIa-B(5). The capacity of LT-IIa-B(5) to enhance Ag uptake and to induce expression of co-stimulatory receptors and cytokines by BMDC was dependent upon expression of TLR2 by the cell. Increased Ag uptake induced by LT-IIa-B(5) was correlated with increased Ag-specific proliferation of CD4(+) T cells in an in vitro syngeneic DO11.10 CD4(+) T cell proliferation assay. These experiments confirm that LT-IIa-B(5) exhibits potent immunomodulatory properties which may be exploitable as a non-toxic mucosal adjuvant.