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Hidradenitis suppurativa (HS) is a recurrent inflammatory skin disease with a complex etiopathogenesis whose treatment poses a challenge in the clinical practice. Here, we present a novel integrated pipeline produced by the European consortium BATMAN (Biomolecular Analysis for Tailored Medicine in Acne iNversa) aimed at investigating the molecular pathways involved in HS by developing new diagnosis algorithms and building cellular models to pave the way for personalized treatments. The objectives of our european Consortium are the following: (1) identify genetic variants and alterations in biological pathways associated with HS susceptibility, severity and response to treatment; (2) design in vitro two-dimensional epithelial cell and tri-dimensional skin models to unravel the HS molecular mechanisms; and (3) produce holistic health records HHR to complement medical observations by developing a smartphone application to monitor patients remotely. Dermatologists, geneticists, immunologists, molecular cell biologists, and computer science experts constitute the BATMAN consortium. Using a highly integrated approach, the BATMAN international team will identify novel biomarkers for HS diagnosis and generate new biological and technological tools to be used by the clinical community to assess HS severity, choose the most suitable therapy and follow the outcome.

The relative roles of Langerhans cells (LC), dermal dendritic cells (DC), and, in particular, the recently discovered Langerin+ dermal DC subset in the induction and control of contact hypersensitivity (CHS) responses remain controversial. Using an inducible mouse model, in which LC and other Langerin+ DC can be depleted by injection of diphtheria toxin, we previously reported impaired transport of topically applied antigen to draining lymph nodes and reduced CHS in the absence of all Langerin+ skin DC. In this study, we demonstrate that mice with a selective depletion of LC exhibit attenuated CHS only upon sensitization with a low hapten dose but not with a high hapten dose. In contrast, when painting a higher concentration of hapten onto the skin, which leads to increased antigen dissemination into the dermis, CHS is still diminished in mice lacking all Langerin+ skin DC. Taken together, these data suggest that the magnitude of a CHS reaction depends on the number of skin DC, which have access to the hapten, rather than on the presence or absence of a particular skin DC population. LC and (Langerin+) dermal DC thus seem to have a redundant function in regulating CHS.

Vaccinations in medicine are commonly administered through the skin. Therefore, the vaccine is immunologically processed by antigen‐presenting cells of the skin. There is recent evidence that the clinically less often used intradermal route is effective; in cases even superior to the conventional subcutaneous or intramuscular route. Professional antigen‐presenting cells of the skin comprise epidermal Langerhans cells (CD207/langerin+), dermal langerin– and dermal langerin+ dendritic cells (DCs). In human skin, langerin– dermal DCs can be further subdivided on the basis of their reciprocal CD1a and CD14 expression. The relative contributions of these subsets to the generation of immunity or tolerance are still unclear. Langerhans cells in human skin seem to be specialized for induction of cytotoxic T lymphocytes. Likewise, mouse Langerhans cells are capable of cross‐presentation and of protecting against experimental tumours. It is desirable to harness these properties for immunotherapy. A promising strategy to dramatically improve the outcome of vaccinations is ‘antigen targeting’. Thereby, the vaccine is delivered directly and selectively to defined types of skin DCs. Targeting is achieved by means of coupling antigen to antibodies that recognize cell surface receptors on DCs. This approach is being widely explored. Little is known, however, about the events that take place in the skin and the DCs subsets involved therein. This topic will be discussed in this article.

Dengue virus (DENV) is responsible for the most prevalent arthropod-borne viral infection in humans. Events decisive for disease development occur in the skin after virus inoculation by the mosquito. Yet, the role of human dermis–resident immune cells in dengue infection and disease remains elusive. Here we investigated how dermal dendritic cells (dDCs) and macrophages (dMs) react to DENV and impact on immunopathology. We show that both CD1c+ and CD14+ dDC subsets were infected, but viral load greatly increased in CD14+ dDCs upon IL-4 stimulation, which correlated with upregulation of virus-binding lectins Dendritic Cell–Specific Intercellular adhesion molecule-3–Grabbing Nonintegrin (DC-SIGN/CD209) and mannose receptor (CD206). IL-4 also enhanced T-cell activation by dDCs, which was further increased upon dengue infection. dMs purified from digested dermis were initially poorly infected but actively replicated the virus and produced TNF-α upon lectin upregulation in response to IL-4. DC-SIGN+ cells are abundant in inflammatory skin with scabies infection or Th2-type dermatitis, suggesting that skin reactions to mosquito bites heighten the risk of infection and subsequent immunopathology. Our data identify dDCs and dMs as primary arbovirus target cells in humans and suggest that dDCs initiate a potent virus-directed T-cell response, whereas dMs fuel the inflammatory cascade characteristic of dengue fever.

Skin dendritic cells (DCs) control the immunogenicity of cutaneously administered vaccines. Antigens targeted to DCs via the C‐type lectin Langerin/CD207 are cross‐presented to CD8 + T cells in vivo . We investigated the relative roles of Langerhans cells (LCs) and Langerin + dermal DCs (dDCs) in different vaccination settings. Poly(I:C) and anti‐CD40 agonist antibody promoted cytotoxic responses upon intradermal immunization with ovalbumin (OVA)‐coupled anti‐Langerin antibodies (Langerin/OVA). This correlated with CD70 upregulation in Langerin + dDCs, but not LCs. In chimeric mice where Langerin targeting was restricted to dDCs, CD8 + T‐cell memory was enhanced. Conversely, providing Langerin/OVA exclusively to LCs failed to prime cytotoxicity, despite initial antigen cross‐presentation to CD8 + T cells. Langerin/OVA combined with imiquimod could not prime CD8 + T cells and resulted in poor cytotoxicity in subsequent responses. This tolerance induction required targeting and maturation of LCs. Altogether, Langerin + dDCs prime long‐lasting cytotoxic responses, while cross‐presentation by LCs negatively influences CD8 + T‐cell priming. Moreover, this highlights that DCs exposed to TLR agonists can still induce tolerance and supports the existence of qualitatively different DC maturation programs. Synopsis The properties of two murine skin antigen‐presenting dendritic cell (DC) subsets were investigated in vivo . Following adjuvanted OVA‐immunization, functional differences were found between the DC subsets that may bear translational relevance for vaccination in the skin. Both Langerin + dermal DCs and epidermal Langerhans cells (LC) can present exogenous antigen to CD8 + T cells. Langerin + dermal DCs prime long‐lasting cytotoxic responses, while cross‐presentation by LCs negatively influences CD8 + T‐cell priming. Specific adjuvants can be used to independently harness the different potential of distinct DC subsets simultaneously targeted by an antigen. Treatment of skin with imiquimod, an agonist of TLR7, does not result in potent immune responses when the antigen is targeted to Langerin, thereby relativizing the paradigm stating that mature DCs always promote immunity. Graphical Abstract The properties of two murine skin antigen‐presenting dendritic cell (DC) subsets were investigated in vivo . Following adjuvanted OVA‐immunization, functional differences were found between the DC subsets that may bear translational relevance for vaccination in the skin.

Dengue virus (DENV) is responsible for the most prevalent arthropod-borne viral infection in humans. Events decisive for disease development occur in the skin after virus inoculation by the mosquito. Yet, the role of human dermis-resident immune cells in dengue infection and disease remains elusive. Here we investigated how dermal dendritic cells (dDCs) and macrophages (dMs) react to DENV and impact on immunopathology. We show that both CD1c super(+) and CD14 super(+) dDC subsets were infected, but viral load greatly increased in CD14 super(+) dDCs upon IL-4 stimulation, which correlated with upregulation of virus-binding lectins Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Nonintegrin (DC-SIGN/CD209) and mannose receptor (CD206). IL-4 also enhanced T-cell activation by dDCs, which was further increased upon dengue infection. dMs purified from digested dermis were initially poorly infected but actively replicated the virus and produced TNF- alpha upon lectin upregulation in response to IL-4. DC-SIGN super(+) cells are abundant in inflammatory skin with scabies infection or Th2-type dermatitis, suggesting that skin reactions to mosquito bites heighten the risk of infection and subsequent immunopathology. Our data identify dDCs and dMs as primary arbovirus target cells in humans and suggest that dDCs initiate a potent virus-directed T-cell response, whereas dMs fuel the inflammatory cascade characteristic of dengue fever.

Murine tumor models that closely reflect human diseases are important tools to investigate carcinogenesis and tumor immunity. The transgenic (tg) mouse strain tg(Grm1)EPv develops spontaneous melanoma due to ectopic overexpression of the metabotropic glutamate receptor 1 (Grm1) in melanocytes. In the present study, we characterized the immune status and functional properties of immune cells in tumor-bearing mice. Melanoma development was accompanied by a reduction in the percentages of CD4+ T cells including regulatory T cells (Tregs) in CD45+ leukocytes present in tumor tissue and draining lymph nodes (LNs). In contrast, the percentages of CD8+ T cells were unchanged, and these cells showed an activated phenotype in tumor mice. Endogenous melanoma-associated antigen glycoprotein 100 (gp100)-specific CD8+ T cells were not deleted during tumor development, as revealed by pentamer staining in the skin and draining LNs. They, however, were unresponsive to ex vivo gp100-peptide stimulation in late-stage tumor mice. Interestingly, immunosuppressive myeloid-derived suppressor cells (MDSCs) were recruited to tumor tissue with a preferential accumulation of granulocytic MDSC (grMDSCs) over monocytic MDSC (moMDSCs). Both subsets produced Arginase-1, inducible nitric oxide synthase (iNOS), and transforming growth factor-β and suppressed T-cell proliferation in vitro. In this work, we describe the immune status of a spontaneous melanoma mouse model that provides an interesting tool to develop future immunotherapeutical strategies.

Langerhans cells, a subset of skin dendritic cells in the epidermis, survey peripheral tissue for invading pathogens. In recent functional studies it was proven that Langerhans cells can present exogenous antigen not merely on major histocompatibility complexes (MHC)-class II molecules to CD4⁺ T cells, but also on MHC-class I molecules to CD8⁺ T cells. Immune responses against topically applied antigen could be measured in skin-draining lymph nodes. Skin barrier disruption or co-application of adjuvants was required for maximal induction of T cell responses. Cytotoxic T cells induced by topically applied antigen inhibited tumor growth in vivo, thus underlining the potential of Langerhans cells for immunotherapy. Here we review recent work and report novel observations relating to the potential use of Langerhans cells for immunotherapy. We investigated the potential of epicutaneous immunization strategies in which resident skin dendritic cells are loaded with tumor antigen in situ. This contrasts with current clinical approaches, where dendritic cells generated from progenitors in blood are loaded with tumor antigen ex vivo before injection into cancer patients. In the current study, we applied either fluorescently labeled protein antigen or targeting antibodies against DEC-205/CD205 and langerin/CD207 topically onto barrier-disrupted skin and examined antigen capture and transport by Langerhans cells. Protein antigen could be detected in Langerhans cells in situ, and they were the main skin dendritic cell subset transporting antigen during emigration from skin explants. Potent in vivo proliferative responses of CD4⁺ and CD8⁺ T cells were measured after epicutaneous immunization with low amounts of protein antigen. Targeting antibodies were mainly transported by langerin⁺ migratory dendritic cells of which the majority represented migratory Langerhans cells and a smaller subset the new langerin⁺ dermal dendritic cell population located in the upper dermis. The preferential capture of topically applied antigen by Langerhans cells and their ability to induce potent CD4⁺ and CD8⁺ T cell responses emphasizes their potential for epicutaneous immunization strategies.

Murine tumor models that closely reflect human diseases are important tools to investigate carcinogenesis and tumor immunity. The transgenic (tg) mouse strain tg(Grm1)EPv develops spontaneous melanoma due to ectopic overexpression of the metabotropic glutamate receptor 1 (Grm1) in melanocytes. In the present study, we characterized the immune status and functional properties of immune cells in tumor-bearing mice. Melanoma development was accompanied by a reduction in the percentages of CD4 super(+) T cells including regulatory T cells (Tregs) in CD45 super(+) leukocytes present in tumor tissue and draining lymph nodes (LNs). In contrast, the percentages of CD8 super(+) T cells were unchanged, and these cells showed an activated phenotype in tumor mice. Endogenous melanoma-associated antigen glycoprotein 100 (gp100)-specific CD8 super(+) T cells were not deleted during tumor development, as revealed by pentamer staining in the skin and draining LNs. They, however, were unresponsive to ex vivo gp100-peptide stimulation in late-stage tumor mice. Interestingly, immunosuppressive myeloid-derived suppressor cells (MDSCs) were recruited to tumor tissue with a preferential accumulation of granulocytic MDSC (grMDSCs) over monocytic MDSC (moMDSCs). Both subsets produced Arginase-1, inducible nitric oxide synthase (iNOS), and transforming growth factor- beta and suppressed T-cell proliferation in vitro. In this work, we describe the immune status of a spontaneous melanoma mouse model that provides an interesting tool to develop future immunotherapeutical strategies.