xenograft-skin-model-to-manipulate-human-immune-responses-in-vivo

Xenograft Skin Model to Manipulate Human Immune Responses <em>In Vivo</em>

The human skin xenograft model, in which human donor skin is transplanted onto an immunodeficient mouse host, is an important option for translational ...

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Mesenchymal chondrosarcoma (MC) is an aggressive small, round, blue cell tumor with chondrogenic differentiation that typically arises in bony sites. Approximately, a third of these tumors develop in extraskeletal sites such as the meninges, and somatic soft tissue. The MCs are well-circumscribed, lobulated masses, with focal calcification. Histologically, 2 distinct populations of neoplastic cells characterize MC: sheets of primitive small, round, blue cells surrounding islands of well-developed hyaline cartilage with mature chondrocytes in lacunae. Involvement of the gastrointestinal tract and pancreas by primary or metastatic MC is a relatively rare occurrence. We identified 8 patients with MC in our departmental archives from 1990 to 2015, two of which had pancreatic involvement. The patients were young women who developed masses in the distal pancreas. Molecular testing demonstrated that both tumors harbored the recently described HEY1-NCOA2 gene fusion. These cases illustrate that pancreatic involvement can occur in MC, and the demonstration of HEY1-NCOA2 fusion can be helpful to confirm the diagnosis.

Pancreatic involvement by mesenchymal chondrosarcoma harboring the HEY1-NCOA2 gene fusion.

Heavily pigmented melanocytic neoplasms are genotypically and phenotypically diverse. Recently, a subset of this histopathologic spectrum was shown to harbor recurrent genetic alterations in the gene-encoding protein kinase A regulatory subunit-α (PRKAR1A). To date, no histopathologic descriptions of melanomas arising from this pathway have been described. We present a case of a darkly pigmented papule arising on the posterior neck of a 28-year-old man. Microscopically, the heavily pigmented compound melanocytic proliferation was centered in the dermis with permeation into the superficial subcutis. Tumor cells were arranged in large confluent nests and fascicles and lacked maturation with descent. The epithelioid melanocytes were characterized by enlarged vesicular nuclei with prominent nucleoli, nuclear pleomorphism, and plentiful gray-brown granular cytoplasm. Mitotic figures were readily identified. By immunohistochemistry, melanocytes were positive for mutant BRAF V600E and showed loss of Prkar1α and p16 expression. A multiplex MART-1/tyrosinase/phosophohistone-H3 immunostain demonstrated an increased mitotic index in melanocytes. The combination of highly atypical cytomorphology and architecture, increased mitoses, and p16 expression loss compelled the diagnosis of melanoma. Overall, we present the first clinicopathologic description of a PRKAR1A-inactivated melanoma to highlight morphological features and discuss mimics that may enter the differential diagnosis.

Heavily Pigmented Epithelioid Melanoma With Loss of Protein Kinase A Regulatory Subunit-α Expression.

Cutaneous warts have high prevalence and cause significant morbidity. Understanding the mechanisms by which warts evade the immune system could lead to targeted and improved treatments.

Expression of programmed cell death ligand 1 and programmed cell death 1 in cutaneous warts.

Restoration of barrier-tissue integrity after injury is dependent on the function of immune cells and stem cells (SCs) residing in the tissue. In response to skin injury, hair-follicle stem cells (HFSCs), normally poised for hair generation, are recruited to the site of injury and differentiate into cells that repair damaged epithelium. We used a SC fate-mapping approach to examine the contribution of regulatory T (Treg) cells to epidermal-barrier repair after injury. Depletion of Treg cells impaired skin-barrier regeneration and was associated with a Th17 inflammatory response and failed HFSC differentiation. In this setting, damaged epithelial cells preferentially expressed the neutrophil chemoattractant CXCL5, and blockade of CXCL5 or neutrophil depletion restored barrier function and SC differentiation after epidermal injury. Thus, Treg-cell regulation of localized inflammation enables HFSC differentiation and, thereby, skin-barrier regeneration, with implications for the maintenance and repair of other barrier tissues.

Treg-Cell Control of a CXCL5-IL-17 Inflammatory Axis Promotes Hair-Follicle-Stem-Cell Differentiation During Skin-Barrier Repair.

Melanotic schwannoma is a pigmented tumor of peripheral nerve differentiation. Primary cutaneous presentations are extremely rare, as the bulk of melanotic schwannomas tend to develop in paraspinal and axial sites. Tumors arise sporadically and in the setting of the Carney complex. Alterations in the gene encoding protein kinase A regulatory subunit-α (PRKAR1A) underlie most patients with the Carney complex and mediate melanotic schwannoma tumorigenesis. Melanotic schwannomas from noncutaneous sites can locally recur and metastasize widely, leading to a recent proposal to change the nomenclature to "malignant melanotic schwannian tumor." However, the clinicopathologic features of primary cutaneous melanotic schwannomas are relatively unexplored. We present a case of a nodule arising on the vulva of a 34-year-old woman. Microscopically, a dermal-based, heavily pigmented proliferation of plump spindled and epithelioid cells arrayed in nodules and fascicles was seen. Lesional cells stained positively for S100, Melan-A, and BAP1 but were negative for Prkar1α. Next-generation sequencing of a panel of 480 cancer-associated genes revealed that the tumor harbored a PRKAR1A p.S299fs truncating mutation and copy neutral loss of heterozygosity of chromosome 17q, the locus at which PRKAR1A resides. Importantly, no other genetic abnormalities or chromosomal copy number changes were identified. On the basis of combined histopathologic, immunohistochemical, and genetic features, a diagnosis of melanotic schwannoma was rendered. Overall, we present the first clinicopathologic description of a vulvar melanotic schwannoma, review the literature concerning cutaneous presentations of melanotic schwannoma, and propose that melanotic schwannian tumors native to skin may behave more indolently than their noncutaneous counterparts.

Melanotic Schwannoma of the Vulva: A Case Report and Review of the Literature.

At the center of fibrosing diseases is the aberrant activation of tissue fibroblasts. The cellular and molecular mechanisms of how the immune system augments fibroblast activation have been described; however, little is known about how the immune system controls fibroblast function in tissues. Here, we identify regulatory T cells (T) as important regulators of fibroblast activation in skin. Bulk cell and single-cell analysis of T in murine skin and lungs revealed that T in skin are transcriptionally distinct and skewed toward T helper 2 (T2) differentiation. When compared with T in lung, skin T preferentially expressed high levels of GATA3, the master T2 transcription factor. Genes regulated by GATA3 were highly enriched in skin "T2 T" subsets. In functional experiments, T depletion resulted in a preferential increase in T2 cytokine production in skin. Both acute depletion and chronic reduction of T resulted in spontaneous skin fibroblast activation, profibrotic gene expression, and dermal fibrosis, all of which were exacerbated in a bleomycin-induced murine model of skin sclerosis. Lineage-specific deletion of  in T resulted in an exacerbation of T2 cytokine secretion that was preferential to skin, resulting in enhanced fibroblast activation and dermal fibrosis. Together, we demonstrate that T play a critical role in regulating fibroblast activation in skin and do so by expressing a unique tissue-restricted transcriptional program that is mediated, at least in part, by GATA3.

Regulatory T cells in skin are uniquely poised to suppress profibrotic immune responses.

T helper (Th) type 17 and Th2 cells mediate psoriasis and eczema, respectively. Some dermatoses exhibit overlapping clinicopathologic features, and their immunopathology is relatively unexplored.

Clinicopathologic overlap of psoriasis, eczema, and psoriasiform dermatoses: A retrospective study of T helper type 2 and 17 subsets, interleukin 36, and β-defensin 2 in spongiotic psoriasiform dermatitis, sebopsoriasis, and tumor necrosis factor α inhibitor-associated dermatitis.

Skin injury is a highly inflammatory process that is carefully regulated to mitigate tissue damage and allow for proper barrier repair. Regulatory T cells (T) are crucial coordinators of the immune response to injury in several organs. Here, we review the emerging role of T in facilitating skin repair after injury. We focus on recently discovered interactions between lymphocytes and nonhematopoietic cells during wound healing and discuss how these interactions are regulated both by "classical" suppressive mechanisms of T and by "nonclassical" reparative T functions.

Regulatory T cells in skin injury: At the crossroads of tolerance and tissue repair.

Keratinocytes regulate circulating CD8 T cell memory after cutaneous infection.

Y'all comeback now.

Lymphocytes in barrier tissues play critical roles in host defense and homeostasis. These cells take up residence in tissues during defined developmental windows, when they may demonstrate distinct phenotypes and functions. Here, we utilized mass and flow cytometry to elucidate early features of human skin immunity. Although most conventional αβ T (Tconv) cells in fetal skin have a naive, proliferative phenotype, a subset of CD4 Tconv and CD8 cells demonstrate memory-like features and a propensity for interferon (IFN)γ production. Skin regulatory T cells dynamically accumulate over the second trimester in temporal and regional association with hair follicle development. These fetal skin regulatory T cells (Tregs) demonstrate an effector memory phenotype while differing from their adult counterparts in expression of key effector molecules. Thus, we identify features of prenatal skin lymphocytes that may have key implications for understanding antigen and allergen encounters  and in infancy.

Developing Human Skin Contains Lymphocytes Demonstrating a Memory Signature.

Regulatory T cells (T) use multiple mechanisms to attenuate inflammation and prevent autoimmunity. T residing in peripheral (i.e., nonlymphoid) tissues have specialized functions; specifically, skin T promote wound healing, suppress dermal fibrosis, facilitate epidermal regeneration, and augment hair follicle cycling. Here, we demonstrated that skin T were transcriptionally attuned to interact with their tissue environment through increased expression of integrin and TGF-β pathway genes that influence epithelial cell biology. We identified a molecular pathway where skin T license keratinocytes to promote innate inflammation after skin barrier breach. Using a single-cell discovery approach, we identified preferential expression of the integrin αvβ8 on skin T Upon skin injury, T used this integrin to activate latent TGF-β, which acted directly on epithelial cells to promote CXCL5 production and neutrophil recruitment. Induction of this circuit delayed epidermal regeneration but provided protection from  infection across a compromised barrier. Thus, αvβ8-expressing T in the skin, somewhat paradoxical to their canonical immunosuppressive functions, facilitated inflammation acutely after loss of barrier integrity to promote host defense against infection.

Regulatory T cells promote innate inflammation after skin barrier breach via TGF-β activation.

Inflammation early in life can prime the local immune milieu of peripheral tissues, which can cause lasting changes in immunological tone that confer disease protection or susceptibility. The cellular and molecular mechanisms that prompt changes in immune tone in many nonlymphoid tissues remain largely unknown. Here we find that time-limited neonatal inflammation induced by a transient reduction in neonatal regulatory T cells causes a dysregulation of subcutaneous tissue in mouse skin. This is accompanied by the selective accumulation of type 2 helper T (T2) cells within a distinct microanatomical niche. T2 cells are maintained into adulthood through interactions with a fibroblast population in skin fascia that we refer to as T2-interacting fascial fibroblasts (TIFFs), which expand in response to T2 cytokines to form subcutaneous fibrous bands. Activation of the T2-TIFF niche due to neonatal inflammation primes the skin for altered reparative responses to wounding. Furthermore, we identify fibroblasts in healthy human skin that express the TIFF transcriptional signature and detect these cells at high levels in eosinophilic fasciitis, an orphan disease characterized by inflammation and fibrosis of the skin fascia. Taken together, these data define a previously unidentified T2 cell niche in skin and functionally characterize a disease-associated fibroblast population. The results also suggest a mechanism of immunological priming whereby inflammation early in life creates networks between adaptive immune cells and stromal cells to establish an immunological set-point in tissues that is maintained throughout life.

Early-life inflammation primes a T helper 2 cell-fibroblast niche in skin.

Decades of work have elucidated cytokine signalling and transcriptional pathways that control T cell differentiation and have led the way to targeted biologic therapies that are effective in a range of autoimmune, allergic and inflammatory diseases. Recent evidence indicates that obesity and metabolic disease can also influence the immune system, although the mechanisms and effects on immunotherapy outcomes remain largely unknown. Here, using two models of atopic dermatitis, we show that lean and obese mice mount markedly different immune responses. Obesity converted the classical type 2 T helper (T2)-predominant disease associated with atopic dermatitis to a more severe disease with prominent T17 inflammation. We also observed divergent responses to biologic therapies targeting T2 cytokines, which robustly protected lean mice but exacerbated disease in obese mice. Single-cell RNA sequencing coupled with genome-wide binding analyses revealed decreased activity of nuclear receptor peroxisome proliferator-activated receptor-γ (PPARγ) in T2 cells from obese mice relative to lean mice. Conditional ablation of PPARγ in T cells revealed that PPARγ is required to focus the in vivo T response towards a T2-predominant state and prevent aberrant non-T2 inflammation. Treatment of obese mice with a small-molecule PPARγ agonist limited development of T17 pathology and unlocked therapeutic responsiveness to targeted anti-T2 biologic therapies. These studies reveal the effects of obesity on immunological disease and suggest a precision medicine approach to target the immune dysregulation caused by obesity.

Obesity alters pathology and treatment response in inflammatory disease.

Resident microbes in skin and gut predominantly impact local immune cell function during homeostasis. However, colitis-associated neutrophilic skin disorders suggest possible breakdown of this compartmentalization with disease. Using a model wherein neonatal skin colonization by Staphylococcus epidermidis facilitates generation of commensal-specific tolerance and CD4 regulatory T cells (Tregs), we ask whether this response is perturbed by gut inflammation. Chemically induced colitis is accompanied by intestinal expansion of S. epidermidis and reduces gut-draining lymph node (dLN) commensal-specific Tregs. It also results in reduced commensal-specific Tregs in skin and skin-dLNs and increased skin neutrophils. Increased CD4 circulation between gut and skin dLN suggests that the altered cutaneous response is initiated in the colon, and resistance to colitis-induced effects in Cd4Il1r1 mice implicate interleukin (IL)-1 in mediating the altered commensal-specific response. These findings provide mechanistic insight into observed connections between inflammatory skin and intestinal diseases.

Article	Year
Pancreatic involvement by mesenchymal chondrosarcoma harboring the HEY1-NCOA2 gene fusion. Human pathology\| PubMed ID: 27544802	2016
Heavily Pigmented Epithelioid Melanoma With Loss of Protein Kinase A Regulatory Subunit-α Expression. The American Journal of dermatopathology\| PubMed ID: 29771690	2018
Expression of programmed cell death ligand 1 and programmed cell death 1 in cutaneous warts. Journal of the American Academy of Dermatology\| PubMed ID: 30872155	2019
Treg-Cell Control of a CXCL5-IL-17 Inflammatory Axis Promotes Hair-Follicle-Stem-Cell Differentiation During Skin-Barrier Repair. Immunity\| PubMed ID: 30893588	2019
Melanotic Schwannoma of the Vulva: A Case Report and Review of the Literature. The American Journal of dermatopathology\| PubMed ID: 31268928	2020
Regulatory T cells in skin are uniquely poised to suppress profibrotic immune responses. Science immunology\| PubMed ID: 31492709	2019
Clinicopathologic overlap of psoriasis, eczema, and psoriasiform dermatoses: A retrospective study of T helper type 2 and 17 subsets, interleukin 36, and β-defensin 2 in spongiotic psoriasif... Journal of the American Academy of Dermatology\| PubMed ID: 31859047	2020
Regulatory T cells in skin injury: At the crossroads of tolerance and tissue repair. Science immunology\| PubMed ID: 32358172	2020
Y'all comeback now. Science immunology\| PubMed ID: 32619187	2019
Developing Human Skin Contains Lymphocytes Demonstrating a Memory Signature. Cell reports. Medicine\| PubMed ID: 33294857	2020
Regulatory T cells promote innate inflammation after skin barrier breach via TGF-β activation. Science immunology\| PubMed ID: 34452925	2021
Early-life inflammation primes a T helper 2 cell-fibroblast niche in skin. Nature\| PubMed ID: 34707292	2021
Obesity alters pathology and treatment response in inflammatory disease. Nature\| PubMed ID: 35355021	2022
Intestinal inflammation alters the antigen-specific immune response to a skin commensal. Cell reports\| PubMed ID: 35649365	2022

Jarish N. Cohen

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