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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Commensal-specific T cells dually possess type-2 and type-17 effector potential, allowing plasticity in orchestrating tissue immunity.

Inflammatory T cells maintain a healing disposition.

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.

Tumor-infiltrating CD8+ T cells mediate antitumor immune responses. However, the mechanisms by which T cells remain poised to kill cancer cells despite expressing high levels of inhibitory receptors are unknown. Here, we report that layilin, a C-type lectin domain-containing membrane glycoprotein, is selectively expressed on highly activated, clonally expanded, but phenotypically exhausted CD8+ T cells in human melanoma. Lineage-specific deletion of layilin on murine CD8+ T cells reduced their accumulation in tumors and increased tumor growth in vivo. Congruently, gene editing of LAYN in human CD8+ T cells reduced direct tumor cell killing ex vivo. On a molecular level, layilin colocalized with integrin αLβ2 (LFA-1) on T cells, and cross-linking layilin promoted the activated state of this integrin. Accordingly, LAYN deletion resulted in attenuated LFA-1-dependent cellular adhesion. Collectively, our results identify layilin as part of a molecular pathway in which exhausted or "dysfunctional" CD8+ T cells enhance cellular adhesiveness to maintain their cytotoxic potential.

Layilin augments integrin activation to promote antitumor immunity.

B cells were long presumed to be a minor and functionally unimportant component of cutaneous immunobiology. However, it is now clear that these lymphocytes are present in healthy skin and accumulate during inflammatory disease. Aira and Debes (2021) identify ⍺4ꞵ1 integrin-mediated recruitment of IL-10 B cells as a key pathway in attenuating skin inflammation. Their work provides valuable insight into the potential for B cells to regulate skin pathology.

B Home or You Are In Trouble: B Cell Integrin-Mediated Recruitment Attenuates Skin Inflammation.

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.

Regulatory T cells (Tregs) reside in nonlymphoid tissues where they carry out unique functions. The molecular mechanisms responsible for Treg accumulation and maintenance in these tissues are relatively unknown. Using an unbiased discovery approach, we identified  (layilin), a C-type lectin-like receptor, to be preferentially and highly expressed on a subset of activated Tregs in healthy and diseased human skin. Expression of layilin on Tregs was induced by TCR-mediated activation in the presence of IL-2 or TGF-β. Mice with a conditional deletion of layilin in Tregs had reduced accumulation of these cells in tumors. However, these animals somewhat paradoxically had enhanced immune regulation in the tumor microenvironment, resulting in increased tumor growth. Mechanistically, layilin expression on Tregs had a minimal effect on their activation and suppressive capacity in vitro. However, expression of this molecule resulted in a cumulative anchoring effect on Treg dynamic motility in vivo. Taken together, our results suggest a model whereby layilin facilitates Treg adhesion in skin and, in doing so, limits their suppressive capacity. These findings uncover a unique mechanism whereby reduced Treg motility acts to limit immune regulation in nonlymphoid organs and may help guide strategies to exploit this phenomenon for therapeutic benefit.

Layilin Anchors Regulatory T Cells in Skin.

The diverse populations of tissue-resident and transitory T cells present in the skin share a common functional need to enter, traverse, and interact with their environment. These processes are largely dependent on the regulated expression of adhesion molecules, such as selectins and integrins, which mediate bidirectional interactions between immune cells and skin stroma. Dysregulation and engagement of adhesion pathways contribute to ectopic T-cell activity in tissues, leading to the initiation and/or exacerbation of chronic inflammation. In this paper, we review how the molecular interactions supported by adhesion pathways contribute to T-cell dynamics and function in the skin. A comprehensive understanding of the molecular mechanisms underpinning T-cell adhesion in inflammatory skin disorders will facilitate the development of novel tissue-specific therapeutic strategies.

T-Cell Adhesion in Healthy and Inflamed Skin.

Layilin is a small type I transmembrane receptor thought to bridge extracellular ligands with the cytoskeleton through its intracellular interactions with the scaffolding protein talin. Recent bulk- and single-cell RNA sequencing experiments have repeatedly found layilin to be highly upregulated in key T cell sub-populations in multiple disease states, suggesting its importance to the adaptive immune response. Despite this prevalence, little is known about layilin's precise role in mediating extracellular interactions or how these interactions can be modulated in disease states. Here we take advantage of layilin's dependence on calcium ions to discover its interactions with highly glycosylated type II, IV, V, and VI collagens. Toward exploring layilin's role in disease, we exploited the Ca dependence in a differential phage display strategy to engineer species cross-reactive antibodies that block this interaction.

Article	Year
Inflammatory T cells maintain a healing disposition. Science immunology\| PubMed ID: 30610014	2019
Regulatory T cells in skin are uniquely poised to suppress profibrotic immune responses. Science immunology\| PubMed ID: 31492709	2019
Layilin augments integrin activation to promote antitumor immunity. The Journal of experimental medicine\| PubMed ID: 32539073	2020
B Home or You Are In Trouble: B Cell Integrin-Mediated Recruitment Attenuates Skin Inflammation. The Journal of investigative dermatology\| PubMed ID: 34303469	2021
Regulatory T cells promote innate inflammation after skin barrier breach via TGF-β activation. Science immunology\| PubMed ID: 34452925	2021
Layilin Anchors Regulatory T Cells in Skin. Journal of immunology (Baltimore, Md. : 1950)\| PubMed ID: 34470859	2021
T-Cell Adhesion in Healthy and Inflamed Skin. JID innovations : skin science from molecules to population health\| PubMed ID: 35024681	2021
Identifying and antagonizing the interactions between layilin and glycosylated collagens. Cell chemical biology\| PubMed ID: 35104453	2022

Joshua M. Moreau

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