Epidermal Niche Research Articles

Competition between T Cells for a Finite Epidermal Niche Promotes Selective Retention of Antigen-specific Memory T Cells in the Epidermis

Tissue-resident memory T cells are a highly abundant, non-blood circulating subset of memory T cells. These appear to be the most protective population of memory T cells at barrier surfaces. Long-term retention and survival of tissue-resident memory CD8+ T cells (Trm) is determined by tissue-derived signals, such as keratinocyte-mediated activation of transforming growth factor β (TGFβ) in the epidermis. We found that T cell clones compete for limited amounts of active TGFβ and pre-existing Trm could be replaced with newly recruited effector T cells in the epidermis. On the other hand, when effector T cells transition into Trm, the presence of cutaneous cognate antigen increases the fitness of individual Trm clones in the epidermal niche. Thus, antigen-specific Trm are more efficiently retained than bystander Trm that have not encountered cognate antigens when they compete with newly recruited effector T cells for limited active TGFβ. Therefore, competition between T cells for active TGFβ represents a selective pressure that promotes the accumulation of antigen-specific Trm cells in the epidermal niche. Furthermore, our model implies that the epidermis offers a finite niche for maintaining Trm. Although the epidermal niche of Trm cannot represent the capacity of T cell-mediated immune memory in our body, these findings might suggest a challenge for the accommodation of memory T cells specific to multiple pathogens throughout a lifetime.

042 Competition for active TGFβ augments accumulation of antigen-specific CD8+ T cells in murine melanoma

Melanoma is the least common skin cancer but is responsible for the majority of skin-cancer related mortality. Successful anti-tumor immunity is mediated in part by tumor antigen specific CD8+ T cells. Our group has shown that competition for limiting amounts of active TGFβ allows antigen-specific CD8+ resident memory T cells (Trm) to persist in the epidermal niche at the expense of bystander Trm. Whether or not competition for active TGFβ affects T cells in the context of chronic antigen is unknown.

Clone Wars: Survival of the Fittest CD8+ Trm Cells

In this issue of Immunity, Hirai etal. illuminate competition for the cytokine TGFβ as a key regulator of CD8+ tissue-resident memory Tcell persistence and occupancy in the skin epidermal niche.

Competition for Active TGFβ Cytokine Allows for Selective Retention of Antigen-Specific Tissue- Resident Memory T Cells in the Epidermal Niche

Following antigen-driven expansion in lymph node, transforming growth factor-β (TGFβ) is required for differentiation of skin-recruited CD8+ Tcell effectors into epidermal resident memory T (Trm) cells and their epidermal persistence. We found that the source of TGFβ -supporting Trm cells was autocrine. In addition, antigen-specific Trm cells that encountered cognate antigen in the skin, and bystander Trm cells that did not, both displayed long-term persistence in the epidermis under steady-state conditions. However, when the active-TGFβ was limited or when new Tcell clones were recruited into the epidermis, antigen-specific Trm cells were more efficiently retained than bystander Trm cells. Genetically enforced TGFβR signaling allowed bystander Trm cells to persist in the epidermis as efficiently as antigen-specific Trm cells in both contexts. Thus, competition between Tcells for active TGFβ represents an unappreciated selective pressure that promotes the accumulation and persistence of antigen-specific Trm cells in the epidermal niche.

099 Competition for active TGFβ eliminates bystander CD8+ TRM from the epidermal niche

Epidermal resident memory CD8+ T cell (TRM) provide efficient host defense against neoplasia and pathogens. After antigen-driven expansion in lymph node, differentiation of T cell effectors into TRM and their persistence in the epidermis is independent of cognate antigen but requires TGFβ. TRM that do encounter cognate antigen in the skin outcompete ‘bystander’ TRM that do not encounter antigen in the skin by unknown mechanisms. We examined the effect of antigen encounter in the skin by comparing Ova-specific OT-I TRM recruited to skin by Vaccinia virus-Ova (VV-Ova) infection where antigen is present with ‘bystander’ TRM recruited by epicutaneous application of the chemical sensitizer DNFB at a different site within the same animal.

Pathogenic CD8+ Epidermis-Resident Memory T Cells Displace Dendritic Epidermal T Cells in Allergic Dermatitis

The skin is our interface with the outside world, and consequently it is exposed to a wide range of microbes and allergens. Recent studies have indicated that allergen-specific skin-resident memory T (TRM) cells play a role in allergic contact dermatitis (ACD). However, the composition and dynamics of the epidermal T-cell subsets during ACD are not known. Here we show that exposure of the skin to the experimental contact allergen DNFB results in a displacement of the normally occurring dendritic epidermal T cells (DETC) concomitant with an accumulation of epidermal CD8+CD69+CD103+ TRM cells in mice. By studying knockout mice, we provide evidence that CD8+ T cells are required for the displacement of the DETC and that DETC are not required for recruitment of CD8+ TRM cells to the epidermis following allergen exposure. We demonstrate that the magnitude of the allergic reaction correlates with the number of CD8+ epidermal TRM cells, which again correlates with allergen dose and number of allergen exposures. Finally, in an attempt to elucidate why CD8+ epidermal TRM cells persist in the epidermis, we show that CD8+ epidermal TRM cells have a higher proliferative capability and are bioenergetically more stable, displaying a higher spare respiratory capacity than DETC.

Niches for the Long-Term Maintenance of Tissue-Resident Memory T Cells

Tissue-resident memory T cells (TRM cells) are a population of immune cells that reside in the lymphoid and non-lymphoid organs without recirculation through the blood. These important cells occupy and utilize unique anatomical and physiological niches that are distinct from those for other memory T cell populations, such as central memory T cells in the secondary lymphoid organs and effector memory T cells that circulate through the tissues. CD8+ TRM cells typically localize in the epithelial layers of barrier tissues where they are optimally positioned to act as sentinels to trigger antigen-specific protection against reinfection. CD4+ TRM cells typically localize below the epithelial layers, such as below the basement membrane, and cluster in lymphoid structures designed to optimize interactions with antigen-presenting cells upon reinfection. A key feature of TRM populations is their ability to be maintained in barrier tissues for prolonged periods of time. For example, skin CD8+ TRM cells displace epidermal niches originally occupied by γδ T cells, thereby enabling their stable persistence for years. It is also clear that the long-term maintenance of TRM cells in different microenvironments is dependent on multiple tissue-specific survival cues, although the specific details are poorly understood. However, not all TRM persist over the long term. Recently, we identified a new spatial niche for the maintenance of CD8+ TRM cells in the lung, which is created at the site of tissue regeneration after injury [termed repair-associated memory depots (RAMD)]. The short-lived nature of RAMD potentially explains the short lifespans of CD8+ TRM cells in this particular tissue. Clearly, a better understanding of the niche-dependent maintenance of TRM cells will be important for the development of vaccines designed to promote barrier immunity. In this review, we discuss recent advances in our understanding of the properties and nature of tissue-specific niches that maintain TRM cells in different tissues.

Persistence of skin-resident memory T cells within an epidermal niche

Barrier tissues such as the skin contain various populations of immune cells that contribute to protection from infections. These include recently identified tissue-resident memory T cells (TRM). In the skin, these memory CD8(+) T cells reside in the epidermis after being recruited to this site by infection or inflammation. In this study, we demonstrate prolonged persistence of epidermal TRM preferentially at the site of prior infection despite sustained migration. Computational simulation of TRM migration within the skin over long periods revealed that the slow rate of random migration effectively constrains these memory cells within the region of skin in which they form. Notably, formation of TRM involved a concomitant local reduction in dendritic epidermal γδ T-cell numbers in the epidermis, indicating that these populations persist in mutual exclusion and may compete for local survival signals. Accordingly, we show that expression of the aryl hydrocarbon receptor, a transcription factor important for dendritic epidermal γδ T-cell maintenance in skin, also contributes to the persistence of skin TRM. Together, these data suggest that skin tissue-resident memory T cells persist within a tightly regulated epidermal T-cell niche.

Circulating Tumor Cells With Markers of Epithelial-Mesenchymal Transition Are Associated With Distant Metastatic Failures in Lung Cancer Patients Treated With Definitive Chemoradiation

repopulation kinetics. Analyses utilized WT C57Bl/6 mice and B6.S129 p21-/mice. Results: We found that LCs do not undergo apoptosis following IR as do other DC subsets, but instead persist and migrate to skin-draining lymph nodes. Subsequent analysis in migration deficient CCR7-/mice revealed a constant number of epidermal LCs, indicating that changes in LC number following IR is due solely to migration and not to cell death. Further, the percentage of BrdU+ LCs doubles in the epidermis by day 7, contributing to full LC repopulation at day 14-post IR. Moreover, we show for the first time that LCs are resistant to the formation of DNA damage as measured by induction of H2AX foci and COMET assay. In contrast, other members of the myeloid lineage, notably lymphoid tissue-resident DCs, are exquisitely sensitive to IR-induced DNA damage. In addition, both steady state and post-lethal IR LCs express a unique repertoire of pro-survival and stress related proteins (Foxo3, p21, Bcl-xL, FGFR2) and diminished levels of pro-apoptotic molecules (Casp3, p53, Bim, Bid) by microarray analysis. Of interest, we found that LCs uniquely express p21 in the steady state myeloid compartment. Accordingly, we extended our analysis of the cellular effects of IR on LCs from p21-/-. We found that p21-/LCs had an impaired recovery following IR and were more radiosensitive. Conclusions: These data suggest that LCs uniquely express an IR-resistance module of genes that permit LCs to persist and repopulate the epidermal niche following IR. Future analyses will seek to elaborate the functional implications of LC and IR-sensitive DC IR-exposure as it relates to the priming and development of GVHD and local anti-tumor immunity following radiation therapy. Author Disclosure: J. Price: None. B. Hogstad: None. J. Idoyaga: None. M. LeBoeuf: None. C. Bigarella: None. S. Ghaffari: None. M.Merad: None.

ATM Gene Variations Predict Differences in Pretreatment Lung Inflammation in Non-Small Cell Lung Cancer (NSCLC) Patients

repopulation kinetics. Analyses utilized WT C57Bl/6 mice and B6.S129 p21-/mice. Results: We found that LCs do not undergo apoptosis following IR as do other DC subsets, but instead persist and migrate to skin-draining lymph nodes. Subsequent analysis in migration deficient CCR7-/mice revealed a constant number of epidermal LCs, indicating that changes in LC number following IR is due solely to migration and not to cell death. Further, the percentage of BrdU+ LCs doubles in the epidermis by day 7, contributing to full LC repopulation at day 14-post IR. Moreover, we show for the first time that LCs are resistant to the formation of DNA damage as measured by induction of H2AX foci and COMET assay. In contrast, other members of the myeloid lineage, notably lymphoid tissue-resident DCs, are exquisitely sensitive to IR-induced DNA damage. In addition, both steady state and post-lethal IR LCs express a unique repertoire of pro-survival and stress related proteins (Foxo3, p21, Bcl-xL, FGFR2) and diminished levels of pro-apoptotic molecules (Casp3, p53, Bim, Bid) by microarray analysis. Of interest, we found that LCs uniquely express p21 in the steady state myeloid compartment. Accordingly, we extended our analysis of the cellular effects of IR on LCs from p21-/-. We found that p21-/LCs had an impaired recovery following IR and were more radiosensitive. Conclusions: These data suggest that LCs uniquely express an IR-resistance module of genes that permit LCs to persist and repopulate the epidermal niche following IR. Future analyses will seek to elaborate the functional implications of LC and IR-sensitive DC IR-exposure as it relates to the priming and development of GVHD and local anti-tumor immunity following radiation therapy. Author Disclosure: J. Price: None. B. Hogstad: None. J. Idoyaga: None. M. LeBoeuf: None. C. Bigarella: None. S. Ghaffari: None. M.Merad: None.

The Touch Dome Defines an Epidermal Niche Specialized for Mechanosensory Signaling

In mammalian skin, Merkel cells are mechanoreceptor cells that are required for the perception of gentle touch. Recent evidence indicates that mature Merkel cells descend from the proliferative layer of skin epidermis; however, the stem cell niche for Merkel cell homeostasis has not been reported. Here, we provide genetic evidence for maintenance of mature Merkel cells during homeostasis by Krt17+ stem cells located in epidermal touch domes of hairy skin and in the tips of the rete ridges of glabrous skin. Lineage tracing analysis indicated that the entire pool of mature Merkel cells is turned over every 7-8 weeks in the adult epidermis and that Krt17+ stem cells also maintain squamous differentiation in the touch dome and in glabrous skin. Finally, selective genetic ablation of Krt17+ touch-dome keratinocytes indicates that these cells, and not mature Merkel cells, are primarily responsible for maintaining innervation of the Merkel cell-neurite complex.

In vivo benefits of a compound that modulates basal epidermal niche components during aging or following solar stress

In vivo benefits of a compound that modulates basal epidermal niche components during aging or following solar stress

The aneurogenic limb identifies developmental cell interactions underlying vertebrate limb regeneration

The removal of the neural tube in salamander embryos allows the development of nerve-free aneurogenic limbs. Limb regeneration is normally nerve-dependent, but the aneurogenic limb regenerates without nerves and becomes nerve-dependent after innervation. The molecular basis for these tissue interactions is unclear. Anterior Gradient (AG) protein, previously shown to rescue regeneration of denervated limbs and to act as a growth factor for cultured limb blastemal cells, is expressed throughout the larval limb epidermis and is down-regulated by innervation. In an aneurogenic limb, the level of AG protein remains high in the epidermis throughout development and regeneration, but decreases after innervation following transplantation to a normal host. Aneurogenic epidermis also shows a fivefold difference in secretory gland cells, which express AG protein. The persistently high expression of AG in the epithelial cells of an aneurogenic limb ensures that regeneration is independent of the nerve. These findings provide an explanation for this classical problem, and identify regulation of the epidermal niche by innervation as a distinctive developmental mechanism that initiates the nerve dependence of limb regeneration. The absence of this regulation during anuran limb development might suggest that it evolved in relation to limb regeneration.

PW1 gene/paternally expressed gene 3 (PW1/Peg3) identifies multiple adult stem and progenitor cell populations

A variety of markers are invaluable for identifying and purifying stem/progenitor cells. Here we report the generation of a murine reporter line driven by Pw1 that reveals cycling and quiescent progenitor/stem cells in all adult tissues thus far examined, including the intestine, blood, testis, central nervous system, bone, skeletal muscle, and skin. Neurospheres generated from the adult PW1-reporter mouse show near 100% reporter-gene expression following a single passage. Furthermore, epidermal stem cells can be purified solely on the basis of reporter-gene expression. These cells are clonogenic, repopulate the epidermal stem-cell niches, and give rise to new hair follicles. Finally, we demonstrate that only PW1 reporter-expressing epidermal cells give rise to follicles that are capable of self-renewal following injury. Our data demonstrate that PW1 serves as an invaluable marker for competent self-renewing stem cells in a wide array of adult tissues, and the PW1-reporter mouse serves as a tool for rapid stem cell isolation and characterization.

31 The epidermal niche: a regulator for normal and skin tumour stem cells

CD8+ tissue-resident memory T (TRM) cells play crucial roles in defense against infections and cancer and have been implicated in autoimmune diseases such as psoriasis. In mice and humans, they exist in all nonlymphoid organs and share key characteristics across all tissues, including downregulation of tissue egress and lymph node homing pathways. However, recent studies demonstrate considerable heterogeneity across TRM cells lodged in different tissues – linked to the activity of tissue-specific molecules, including chemokines, cytokines, and transcription factors. Current work indicates that transforming growth factor (TGF)-β plays a major role in generating TRM heterogeneity at phenotypic and functional levels. Here, we review common and unique features of TRM cells in different tissues and discuss putative strategies aimed at harnessing TRM cells for site-specific protection against infectious and malignant diseases.

The adult hair follicle: cradle for pluripotent neural crest stem cells.

This review focuses on the recent identification of two novel neural crest-derived cells in the adult mammalian hair follicle, pluripotent stem cells, and Merkel cells. Wnt1-cre/R26R compound transgenic mice, which in the periphery express beta-galactosidase in a neural crest-specific manner, were used to trace neural crest cells. Neural crest cells invade the facial epidermis as early as embryonic day 9.5. Neural crest-derived cells are present along the entire extent of the whisker follicle. This includes the bulge area, an epidermal niche for keratinocyte stem cells, as well as the matrix at the base of the hair follicle. We have determined by in vitro clonal analysis that the bulge area of the adult whisker follicle contains pluripotent neural crest stem cells. In culture, beta-galactosidase-positive cells emigrate from bulge explants, identifying them as neural crest-derived cells. When these cells are resuspended and grown in clonal culture, they give rise to colonies that contain multiple differentiated cell types, including neurons, Schwann cells, smooth muscle cells, pigment cells, chondrocytes, and possibly other types of cells. This result provides evidence for the pluripotentiality of the clone-forming cell. Serial cloning showed that bulge-derived neural crest cells undergo self-renewal, which identifies them as stem cells. Pluripotent neural crest cells are also localized in the back skin hair of adult mice. The bulge area of the whisker follicle is surrounded by numerous Merkel cells, which together with innervating nerve endings form slowly adapting mechanoreceptors that transduce steady skin indentation. Merkel cells express beta-galactosidase in double transgenic mice, which confirms their neural crest origin. Taken together, our data indicate that the epidermis of the adult hair follicle contains pluripotent neural crest stem cells, termed epidermal neural crest stem cells (eNCSCs), and one newly identified neural crest derivative, the Merkel cell. The intrinsic high degree of plasticity of eNCSCs and the fact that they are easily accessible in the skin make them attractive candidates for diverse autologous cell therapy strategies.

IL-04 The role of kit-ligand presentation in the development of the epidermal melanocyte niche

IL-04 The role of kit-ligand presentation in the development of the epidermal melanocyte niche