Early antitumor activity of oral Langerhans cells is compromised by a carcinogen.

Early diagnosis of oral squamous cell carcinoma (OSCC) remains an unmet clinical need. Therefore, elucidating the initial events of OSCC preceding tumor development could benefit OSCC prognosis. Here, we define the Langerhans cells (LCs) of the tongue and demonstrate that LCs protect the epithelium from carcinogen-induced OSCC by rapidly priming αßT cells capable of eliminating γH2AX+ epithelial cells, whereas γδT and natural killer cells are dispensable. The carcinogen, however, dysregulates the epithelial resident mononuclear phagocytes, reducing LC frequencies, while dendritic cells (DCs), macrophages, and plasmacytoid DCs (pDCs) populate the epithelium. Single-cell RNA-sequencing analysis indicates that these newly differentiated cells display an immunosuppressive phenotype accompanied by an expansion of T regulatory (Treg) cells. Accumulation of the Treg cells was regulated, in part, by pDCs and precedes the formation of visible tumors. This suggests LCs play an early protective role during OSCC, yet the capacity of the carcinogen to dysregulate the differentiation of mononuclear phagocytes facilitates oral carcinogenesis.

Guidelines for DC preparation and flow cytometry analysis of mouse nonlymphoid tissues.

This article is part of the Dendritic Cell Guidelines article series, which provides a collection of state-of-the-art protocols for the preparation, phenotype analysis by flow cytometry, generation, fluorescence microscopy and functional characterization of mouse and human dendritic cells (DC) from lymphoid organs and various nonlymphoid tissues. DC are sentinels of the immune system present in almost every mammalian organ. Since they represent a rare cell population, DC need to be extracted from organs with protocols that are specifically developed for each tissue. This article provides detailed protocols for the preparation of single-cell suspensions from various mouse nonlymphoid tissues, including skin, intestine, lung, kidney, mammary glands, oral mucosa and transplantable tumors. Furthermore, our guidelines include comprehensive protocols for multiplex flow cytometry analysis of DC subsets and feature top tricks for their proper discrimination from other myeloid cells. With this collection, we provide guidelines for in-depth analysis of DC subsets that will advance our understanding of their respective roles in healthy and diseased tissues. While all protocols were written by experienced scientists who routinely use them in their work, this article was also peer-reviewed by leading experts and approved by all coauthors, making it an essential resource for basic and clinical DC immunologists.

Antigen targeting to dendritic cells: Still a place in future immunotherapy?

The hallmark of DCs is their potent and outstanding capacity to activate naive resting T cells. As such, DCs are the sentinels of the immune system and instrumental for the induction of immune responses. This is one of the reasons, why DCs became the focus of immunotherapeutical strategies to fight infections, cancer, and autoimmunity. Besides the exploration of adoptive DC-therapy for which DCs are generated from monocytes or purified in large numbers from the blood, alternative approaches were developed such as antigen targeting of DCs. The idea behind this strategy is that DCs resident in patients' lymphoid organs or peripheral tissues can be directly loaded with antigens in situ. The proof of principle came from mouse models; subsequent translational studies confirmed the potential of this therapy. The first clinical trials demonstrated feasibility and the induction of T-cell immunity in patients. This review will cover: (i) the historical aspects of antigen targeting, (ii) briefly summarize the biology of DCs and the immunological functions upon which this concept rests, (iii) give an overview on attempts to target DC receptors with antibodies or (glycosylated) ligands, and finally, (iv) discuss the translation of antigen targeting into clinical therapy.

Mouse dendritic cells and other myeloid subtypes in healthy lymph nodes and skin: 26-Color flow cytometry panel for immune phenotyping.

This novel 26-color flow cytometry panel allows the detailed immune phenotyping of the complex network of myeloid cells in murine lymph nodes and skin. With the optimized panel the different murine DC-subsets and other myeloid cell types can be identified and further characterized for co-stimulatory and inhibitory surface molecules.

Targeted delivery of a vaccine protein to Langerhans cells in the human skin via the C-type lectin receptor Langerin.

Human skin is a preferred vaccination site as it harbors multiple dendritic cell (DC) subsets, which display distinct C-type lectin receptors (CLR) that recognize pathogens. Antigens can be delivered to CLR by antibodies or ligands to boost antigen-specific immune responses. This concept has been established in mouse models but detailed insights into the functional consequences of antigen delivery to human skin DC in situ are sparse. In this study, we cloned and produced an anti-human Langerin antibody conjugated to the EBV nuclear antigen 1 (EBNA1). We confirmed specific binding of anti-Langerin-EBNA1 to Langerhans cells (LC). This novel LC-based vaccine was then compared to an existing anti-DEC-205-EBNA1 fusion protein by loading LC in epidermal cell suspensions before coculturing them with autologous T cells. After restimulation with EBNA1-peptides, we detected elevated levels of IFN-γ- and TNF-α-positive CD4+ T cells with both vaccines. When we injected the fusion proteins intradermally into human skin explants, emigrated skin DC targeted via DEC-205-induced cytokine production by T cells, whereas the Langerin-based vaccine failed to do so. In summary, we demonstrate that antibody-targeting approaches via the skin are promising vaccination strategies, however, further optimizations of vaccines are required to induce potent immune responses.

Guidelines for mouse and human DC functional assays.

This article is part of the Dendritic Cell Guidelines article series, which provides a collection of state-of-the-art protocols for the preparation, phenotype analysis by flow cytometry, generation, fluorescence microscopy, and functional characterization of mouse and human dendritic cells (DC) from lymphoid organs and various non-lymphoid tissues. Recent studies have provided evidence for an increasing number of phenotypically distinct conventional DC (cDC) subsets that on one hand exhibit a certain functional plasticity, but on the other hand are characterized by their tissue- and context-dependent functional specialization. Here, we describe a selection of assays for the functional characterization of mouse and human cDC. The first two protocols illustrate analysis of cDC endocytosis and metabolism, followed by guidelines for transcriptomic and proteomic characterization of cDC populations. Then, a larger group of assays describes the characterization of cDC migration in vitro, ex vivo, and in vivo. The final guidelines measure cDC inflammasome and antigen (cross)-presentation activity. While all protocols were written by experienced scientists who routinely use them in their work, this article was also peer-reviewed by leading experts and approved by all co-authors, making it an essential resource for basic and clinical DC immunologists.

CD73 contributes to anti-inflammatory properties of afferent lymphatic endothelial cells in humans and mice.

CD73 is an important ectoenzyme responsible for the production of extracellular adenosine. It is involved in regulating inflammatory responses and cell migration and is overexpressed in various cancers. The functions of CD73 in blood endothelial cells are understood in detail, but its role on afferent lymphatics remains unknown. Moreover, anti-CD73 antibodies are now used in multiple clinical cancer trials, but their effects on different endothelial cell types have not been studied. This study reveals that a previously unknown role of CD73 on afferent lymphatics is to dampen immune responses. Knocking it out or suppressing it by siRNA leads to the upregulation of inflammation-associated genes on lymphatic endothelial cells and a more pro-inflammatory phenotype of interacting dendritic cells in vitro and in vivo. In striking contrast, anti-CD73 antibodies had only negligible effects on the gene expression of lymphatic- and blood-endothelial cells. Our data thus reveal new functions of lymphatic CD73 and indicate a low likelihood of endothelial cell-related adverse effects by CD73 targeting therapeutic antibodies.

BRAF and MEK inhibition in melanoma patients enables reprogramming of tumor infiltrating lymphocytes.

BACKGROUND: Combined inhibition of BRAF/MEK is an established therapy for melanoma. In addition to its canonical mode of action, effects of BRAF/MEK inhibitors on antitumor immune responses are emerging. Thus, we investigated the effect of these on adaptive immune responses. PATIENTS, METHODS AND RESULTS: Sequential tumor biopsies obtained before and during BRAF/MEK inhibitor treatment of four (n = 4) melanoma patients were analyzed. Multiplexed immunofluorescence staining of tumor tissue revealed an increased infiltration of CD4+ and CD8+ T cells upon therapy. Determination of the T-cell receptor repertoire usage demonstrated a therapy induced increase in T-cell clonotype richness and diversity. Application of the Grouping of Lymphocyte Interactions by Paratope Hotspots algorithm revealed a pre-existing immune response against melanoma differentiation and cancer testis antigens that expanded preferentially upon therapy. Indeed, most of the T-cell clonotypes found under BRAF/MEK inhibition were already present in lower numbers before therapy. This expansion appears to be facilitated by induction of T-bet and TCF7 in T cells, two transcription factors required for self-renewal and persistence of CD8+ memory T cells. CONCLUSIONS: Our results suggest that BRAF/MEK inhibition in melanoma patients allows an increased expansion of pre-existing melanoma-specific T cells by induction of T-bet and TCF7 in these.

Laser-assisted epicutaneous immunization to target human skin dendritic cells.

Dendritic cells (DC) are promising targets for immunotherapy of cancer. Clinically, immunization against cancer antigens by means of the most potent antigen-presenting cells, that is DC, remains an important treatment option in combination with the modern immune checkpoint approaches. Instead of adoptively transferring in vitro monocyte-derived DC, they can also be loaded in situ by antibody-mediated targeting of antigen. Conventionally, these vaccines are delivered by classical intradermal injections. Here, we tested an alternative approach, namely laser-assisted epicutaneous immunization. With an infrared laser ("Precise Laser Epidermal System"/P.L.E.A.S.E.® Laser System), we created micropores in human skin and applied monoclonal antibodies (mAbs) against C-type lectins, for example DEC-205/CD205 and Langerin/CD207. Optimal parameters for formation of pores in epidermis and dermis were determined. We could induce pores of defined depths without enhanced apoptosis around them. Antibodies applied epicutaneously to the laser-porated skin could be detected both in Langerhans cells (LC) in situ in the epidermis and in migratory skin DC subsets from short term human skin explant culture, demonstrating uptake and transport of Langerin and DEC-205 mAbs. Efficacy of targeting was similar between the different laser treatments and pore depths. Thus, laser-assisted epicutaneous immunization may be a valuable alternative to intradermal injection, yet the loading efficacy of DC needs to be further improved.

Langerhans cells come in waves.

It is unclear how the Langerhans cell (LC) network is maintained in adult epidermis. In this issue of Immunity, Seré et al. (2012) show that LCs are replenished in two waves. Monocyte-derived, short-lived LCs come first. A second wave follows, and these LCs of nonmonocytic origin are long-lived.

A TLR7 agonist strengthens T and NK cell function during BRAF-targeted therapy in a preclinical melanoma model.

Therapeutic success of targeted therapy with BRAF inhibitors (BRAFi) for melanoma is limited by resistance development. Observations from preclinical mouse models and recent insights into the immunological effects caused by BRAFi give promise for future development of combination therapy for human melanoma. In our study, we used the transplantable D4M melanoma mouse model with the BRAFV600E mutation and concomitant PTEN loss in order to characterize alterations in tumor-infiltrating effector immune cells when tumors become resistant to BRAFi. We found that BRAFi-sensitive tumors displayed a pronounced inflammatory milieu characterized by high levels of cytokines and chemokines accompanied by an infiltration of T and NK cells. The tumor-infiltrating effector cells were activated and produced high levels of IFN-γ, TNF-α and granzyme B. When tumors became resistant and progressively grew, they reverted to a low immunogenic state similar to untreated tumors as reflected by low mRNA levels of proinflammatory cytokines and chemokines and fewer tumor-infiltrating T and NK cells. Moreover, these T and NK cells were functionally impaired in comparison to their counterparts in BRAFi-sensitive tumors. Their effector cell function could be restored by additional peritumoral treatment with the TLR7 agonist imiquimod, a clinically approved agent for nonmelanoma skin cancer. Indeed, resistance to BRAFi therapy was delayed and accompanied by high numbers of activated T and NK cells in tumors. Thus, combining BRAFi with an immune stimulating agent such as a TLR ligand could be a promising alternative approach for the treatment of melanoma.

Langerin+ DCs regulate innate IL-17 production in the oral mucosa during Candida albicans-mediated infection.

The opportunistic fungal pathogen Candida albicans frequently causes diseases such as oropharyngeal candidiasis (OPC) in immunocompromised individuals. Although it is well appreciated that the cytokine IL-17 is crucial for protective immunity against OPC, the cellular source and the regulation of this cytokine during infection are still a matter of debate. Here, we directly visualized IL-17 production in the tongue of experimentally infected mice, thereby demonstrating that this key cytokine is expressed by three complementary subsets of CD90+ leukocytes: RAG-dependent αß and γδ T cells, as well as RAG-independent ILCs. To determine the regulation of IL-17 production at the onset of OPC, we investigated in detail the myeloid compartment of the tongue and found a heterogeneous and dynamic mononuclear phagocyte (MNP) network in the infected tongue that consists of Zbtb46-Langerin- macrophages, Zbtb46+Langerin+ dendritic cells (DCs) and Ly6C+ inflammatory monocytes. Of those, the Langerin+ DC population stands out by its unique capacity to co-produce the cytokines IL-1ß, IL-6 and IL-23, all of which promote IL-17 induction in response to C. albicans in the oral mucosa. The critical role of Langerin+ DCs for the innate IL-17 response was confirmed by depletion of this cellular subset in vivo, which compromised IL-17 induction during OPC. In conclusion, our work revealed key regulatory factors and their cellular sources of innate IL-17-dependent antifungal immunity in the oral mucosa.

Combining chemotherapy and autologous peptide-pulsed dendritic cells provides survival benefit in stage IV melanoma patients.

BACKGROUND AND OBJECTIVES: We examined retrospectively whether the combination of standard dacarbazine (DTIC) and/or fotemustine chemotherapy and autologous peptide-loaded dendritic cell (DC) vaccination may improve survival of stage IV melanoma patients. Furthermore, a small cohort of long-term survivors was studied in more detail. PATIENTS AND METHODS: Between 1998 and 2008, 41 patients were vaccinated at least three times with DCs while receiving chemotherapy and compared to all other 168 patients in our database who only received chemotherapy (1993-2008). RESULTS: Median life expectancy of patients receiving additional DC-vaccination was 18 months, compared to eleven months for patients under standard chemotherapy alone. In contrast to patients with other haplotypes, the HLA-A1/A1 subset of DC-treated patients showed significantly lower median survival (12 vs. 25 months). Autoantibodies were frequently detected in serum of both vaccinated and non-vaccinated patients, and there was no correlation between titers, loss or appearance of autoantibodies and survival. Additionally, phenotyping of DCs and PBMCs also did not reveal any conspicuous correlation with survival. CONCLUSIONS: Combining standard chemotherapy and DC vaccination appears superior to chemotherapy alone. The impact of HLA haplotypes on survival emphasizes the importance of a careful selection of patients with specific, well-defined HLA haplotypes for future vaccination trials using peptide-pulsed DCs, possibly combined with checkpoint inhibitors.

A Liposomal Platform for Delivery of a Protein Antigen to Langerin-Expressing Cells.

The skin is an attractive site for vaccination and harbors a dense network of Langerhans cells that are the prime target for antigen delivery approaches in the epidermis. While specific targeting of Langerhans cells has been shown to elicit the necessary T-cell response using antibody-based delivery approaches, the targeted administration of particulate antigens in the form of nanoparticle-based vaccine formulations has been challenging. We previously reported on a specific targeting ligand for human Langerin, a C-type lectin expressed on Langerhans cells. This ligand is presented on liposomes and renders them highly specific for the uptake by Langerhans cells. Here we show a detailed study of the uptake and intracellular routing of the particles in model cell lines by confocal and live cell imaging as well as flow cytometric assays. Liposomes are internalized into early endosomal compartments and accumulate in late endosomes and lysosomes, shortly followed by a release of the cargo. Furthermore, we show the encapsulation of protein antigens and their delivery to cell lines and primary human Langerhans cells. These data further support the applicability of the targeted liposomal particles for protein vaccine applications.

Oncolytic virotherapy enhances the efficacy of a cancer vaccine by modulating the tumor microenvironment.

The efficacy of cancer vaccines has been limited by the immunosuppressive tumor microenvironment, which can be alleviated by immune checkpoint inhibitor (ICI) therapy. Here, we tested if oncolytic viruses (OVs), similar to ICI, can also synergize with cancer vaccines by modulating the tumor microenvironment. VSV-GP, a chimeric vesicular stomatitis virus (VSV) pseudotyped with the glycoprotein (GP) of the lymphocytic choriomeningitis virus, is a promising new OV candidate. Here, we show that in mouse B16-OVA melanoma, combination treatment of VSV-GP with an ovalbumin (OVA) peptide-loaded dendritic cell (DC) vaccine (DCVacc) significantly enhanced survival over the single agent therapies, although both DCVacc and DCVacc/VSV-GP treatments induced comparable levels of OVA-specific CD8 T cell responses. Virus replication was minimal so that direct viral oncolysis in B16-OVA did not contribute to this synergism. The strong therapeutic effect of the DCVacc/VSV-GP combination treatment was associated with high numbers of tumor-infiltrating, highly activated T cells and the relative reduction of regulatory T cells in treated and contra-lateral nontreated tumors. Accordingly, depletion of CD8 T cells but not natural killer cells abrogated the therapeutic effect of DCVacc/VSV-GP supporting the crucial role of CD8 T cells. In addition, a drastic increase in several proinflammatory cytokines was observed in VSV-GP-treated tumors. Taken together, OVs, similar to ICI, have the potential to markedly increase the efficacy of cancer vaccines by alleviating local immune suppression in the tumor microenvironment.

The late endosomal adaptor molecule p14 (LAMTOR2) represents a novel regulator of Langerhans cell homeostasis.

Langerhans cells (LCs) are dendritic cells (DCs) residing in epithelia, where they critically regulate immunity and tolerance. The p14 adaptor molecule is part of the late endosomal/LAMTOR (lysosomal adaptor and mitogen-activated protein kinase and mammalian target of rapamycin [mTOR] activator/regulator) complex, thereby contributing to the signal transduction of the extracellular signaling-regulated kinase (ERK) and the mTOR cascade. Furthermore, p14 represents an important regulator for endosomal sorting processes within the cell. Mutated, dysfunctional p14 leads to a human immunodeficiency disorder with endosomal/lysosomal defects in immune cells. Because p14 participates in the regulation of endosomal trafficking, growth factor signaling, and cell proliferation, we investigated the role of p14 in mouse DCs/LCs using a conditional knockout mouse model. p14-deficient animals displayed a virtually complete loss of LCs in the epidermis early after birth due to impaired proliferation and increased apoptosis of LCs. Repopulation analysis after application of contact sensitizer leads to the recruitment of a transient LC population, predominantly consisting of short-term LCs. The underlying molecular mechanism involves the p14-mediated disruption of the LAMTOR complex which results in the malfunction of both ERK and mTOR signal pathways. Hence, we conclude that p14 acts as a novel and essential regulator of LC homeostasis in vivo.

NK cells are required for dendritic cell-based immunotherapy at the time of tumor challenge.

Increasing evidence suggests that NK cells act to promote effective T cell-based antitumor responses. Using the B16-OVA melanoma model and an optimized Gram-positive bacteria-dendritic cell (DC) vaccination strategy, we determined that in vivo depletion of NK cells at time of tumor challenge abolished the benefit of DC immunotherapy. The contribution of NK cells to DC immunotherapy was dependent on tumor Ag presentation by DC, suggesting that NK cells act as helper cells to prime or reactivate tumor-specific T cells. The absence of NK cells at tumor challenge resulted in greater attenuation of tumor immunity than observed with selective depletion of either CD4 or CD8 T cell subsets. Although successful DC immunotherapy required IFN-γ, perforin expression was dispensable. Closer examination of the role of NK cells as helper cells in enhancing antitumor responses will reveal new strategies for clinical interventions using DC-based immunotherapy.

Lapatinib and doxorubicin enhance the Stat1-dependent antitumor immune response.

The dual erbB1/2 tyrosine kinase inhibitor lapatinib as well as the anthracycline doxorubicin are both used in the therapy of HER2-positive breast cancer. Using MMTV-neu mice as an animal model for HER2-positive breast cancer, we observed enhanced tumor infiltration by IFN-γ-secreting T cells after treatment with doxorubicin and/or lapatinib. Antibody depletion experiments revealed a contribution of CD8⁺ but not CD4⁺ T cells to the antitumor effect of these drugs. Doxorubicin treatment additionally decreased the content of immunosuppressive tumor-associated macrophages (TAMs) in the tumor bed. In contrast, Stat1-deficient mice were resistant to tumor growth inhibition by lapatinib and/or doxorubicin and exhibited impaired T-cell activation and reduced T-cell infiltration of the tumor in response to drug treatment. Furthermore, Stat1-deficiency resulted in reduced expression of the T-cell chemotactic factors CXCL9, CXCL10, and CXCL11 in the tumor epithelium. The inhibition of TAM infiltration of the tumor by doxorubicin and the immunosuppressive function of TAMs were found to be Stat1 independent. Taken together, the results point to an important contribution toward enhancing T-cell and IFN-γ-based immunity by lapatinib as well as doxorubicin and emphasize the role of Stat1 in building an effective antitumor immune response.

Anatomical distribution analysis reveals lack of Langerin+ dermal dendritic cells in footpads and tail of C57BL/6 mice.

Epidermal Langerhans cells (LCs) and dermal dendritic cells (dDCs) capture cutaneous antigens and present them to T-cells in lymph nodes (LNs). The function of LCs and Langerin+ dDCs was extensively studied in the mouse, but their anatomical repartition is unknown. Here, we found LCs in back skin, footpads and tail skin of C57BL/6, BALB/c, 129/Sv and CBA/J mice. Langerin+ dDCs were readily observed in back skin of all strains, but only in footpads and tail of BALB/c and CBA/J mice. Similarly, while LCs were equally present in all LNs and strains, Langerin+ dDCs were found in popliteal LNs (draining footpads) only in BALB/c and CBA/J mice. The sciatic LNs, which we identified as the major tail-draining lymphoid organ, were devoid of Langerin+ dDCs in all strains. Thus, functionally different DCs reside in different skin areas, with variations among mouse strains, implying a potential impact on the cutaneous immune reaction.