Lymphocyte-mediated alopecia in C57BL/6 mice following successful immunotherapy for melanoma

The clinical and immunological features of alopecia areata following SARS-CoV-2 infection or COVID-19 vaccines

INTRODUCTION

Alopecia areata (AA) is an autoimmune disease induced by viral infection or vaccination. With the increased incidence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the incidence of AA has also increased. Recently the incidence was found to be 7.8% from a previously reported rate of 2.1%. The physical and psychological damage caused by AA could seriously affect patients' lives, while AA is a challenging dermatological disease owing to its complex pathogenesis.

AREAS COVERED

This paper presents a comprehensive review of the prevalence, pathogenesis and potential therapeutic targets for AA after infection with SARS-CoV-2 or SARS-CoV-2 vaccine.

EXPERT OPINION

The treatment of AA remains challenging because of the complexity of its pathogenesis. For patients with AA after SARS-CoV-2 infection or vaccination, the use of sex hormones and alternative regenerative therapies may be actively considered in addition to conventional treatments. For preexisting disease, therapeutic agents should be adjusted to the patient's specific condition.

A virtual memory CD8+ T cell-originated subset causes alopecia areata through innate-like cytotoxicity

Virtual memory T (TVM) cells are a T cell subtype with a memory phenotype but no prior exposure to foreign antigen. Although TVM cells have antiviral and antibacterial functions, whether these cells can be pathogenic effectors of inflammatory disease is unclear. Here we identified a TVM cell-originated CD44super-high(s-hi)CD49dlo CD8+ T cell subset with features of tissue residency. These cells are transcriptionally, phenotypically and functionally distinct from conventional CD8+ TVM cells and can cause alopecia areata. Mechanistically, CD44s-hiCD49dlo CD8+ T cells could be induced from conventional TVM cells by interleukin (IL)-12, IL-15 and IL-18 stimulation. Pathogenic activity of CD44s-hiCD49dlo CD8+ T cells was mediated by NKG2D-dependent innate-like cytotoxicity, which was further augmented by IL-15 stimulation and triggered disease onset. Collectively, these data suggest an immunological mechanism through which TVM cells can cause chronic inflammatory disease by innate-like cytotoxicity.

Autoantigen Discovery in the Hair Loss Disorder, Alopecia Areata: Implication of Post-Translational Modifications

Alopecia areata (AA) is a chronic, multifactorial, polygenic, and heterogeneous disorder affecting growing hair follicles in susceptible individuals, which results in a non-scarring and reversible hair loss with a highly unpredictable course. Despite very considerable research effort, the nature of the precipitating factor(s) responsible for initiating AA in any given hair follicle remains unclear, due largely to significant gaps in our knowledge of the precise sequence of the etiopathogenic events in this dermatosis. However, disease-related changes in the immune-competence of the lower growing hair follicle, together with an active immune response (humoral and cellular) to hair follicle-associated antigens, are key associated phenomena. Confirmation of the hair follicle antigen(s) implicated in AA disease onset has remained stubbornly elusive. While it may be considered somewhat philosophical by some, it is also unclear whether immune-mediated hair loss in AA results from a) an ectopic (i.e., in an abnormal location) immune response to native (unmodified) self-antigens expressed by the healthy hair follicle, b) a normal immune response against modified self-antigens (or neoantigens), or c) a normal immune response against self-antigens (modified/non-modified) that were not previously visible to the immune system (because they were conformationally-hidden or sequestered) but become exposed and presentable in an MHC-I/-II molecule-restricted manner. While some candidate hair follicle antigen target(s) in AA are beginning to emerge, with a potential role for trichohyalin, it is not yet clear whether this represents the initial and immunodominant antigenic focus in AA or is simply one of an expanding repertoire of exposed hair follicle tissue damage-associated antigens that are secondary to the disease. Confirmation of autoantigen identity is essential for our understanding of AA etiopathogenesis, and consequently for developing a more informed therapeutic strategy. Major strides have been made in autoantigen discovery in other autoimmune conditions. In particular, some of these conditions may provide insights into how post-translational modifications (e.g., citrullination, deamidation, etc.) of hair follicle-restricted proteins may increase their antigenicity and so help drive the anti-hair follicle immune attack in AA.

Frontiers in alopecia areata pathobiology research

This current review explores selected and as yet insufficiently investigated frontiers in current alopecia areata (AA) pathobiology research, with an emphasis on potential "new" players in AA pathobiology that deserve more systematic exploration and therapeutic targeting. Indeed, new evidence suggests that CD8⁺ T cells, which have long been thought to be the central players in AA pathobiology, are not the only drivers of disease. Instead, subsets of natural killer (NK) and so-called "unconventional" T cells (invariant NK T cells, γδ T cells, classic NK cells, and type 1 innate lymphoid cells), all of which can produce large amounts of IFN-γ, might also drive AA pathobiology independent of classical, autoantigen-dependent CD8⁺ T-cell functions. Another important new frontier is the role of regulatory lymphocyte subsets, such as regulatory T cells, γδ regulatory T cells, NKT10 cells, and perifollicular mast cells, in maintaining physiologic hair follicle immune privilege (IP); the extent to which these functions are defective in patients with AA; and how this IP-protective role could be restored therapeutically in patients with established AA. Broadening our AA research horizon along the lines suggested above promises not only to open the door to innovative and even more effective immunotherapy strategies for AA but will also likely be relevant for other autoimmune disorders in which pathobiology, ectopic MHC class I expression, and IP collapse play an important role.

Evaluation of the Relationship between Alopecia Areata and Viral Antigen Exposure

BACKGROUND

Alopecia areata (AA) is an autoimmune disease characterized by non-scarring alopecia with T-cell infiltration at the affected hair follicle.

OBJECTIVE

Our aim was to study the potential link between hepatitis B virus (HBV) antigen exposure and AA.

METHODS

Two pediatric patients with AA following hepatitis B vaccination were identified in a general dermatology clinic. A bioinformatics analysis and an electronic medical record (EMR) database query were performed at the University of Rochester Medical Center to identify patients with AA, coexisting viral infections, vaccinations, or interferon (IFN) therapy in order to determine if the presence of AA and these conditions was higher than in AA patients without these associated conditions or therapy.

RESULTS

An increased frequency of AA among those who received the HBV surface protein antigen [odds ratio (OR) 2.7, p < 0.0001] was identified, and an independent analysis revealed an increased frequency of AA in those receiving IFN-β treatment (OR 8.1, p < 0.05). One potential antigenic target identified was SLC45A2, a melanosomal transport protein important in skin and hair pigmentation. The longest potential vaccine peptide fragment match (8-mer) was to a segment of natural killer (NK) cell inhibitory receptors, KIR3DL2 and KIR3DL1. Predictive modeling of major histocompatibility complex (MHC)-peptide binding demonstrated potential binding of this peptide to MHC relevant to AA.

LIMITATIONS

The results will need to be verified in additional patient databases allowing analysis of temporal relationships, and with molecular experiments of the identified antigens.

CONCLUSIONS

Our data confirm associations between viral infection and IFN treatment with AA. It establishes that the hepatitis B surface protein antigen has shared epitopes with human killer immunoglobulin-like receptors.

The role of lymphocytes in the development and treatment of alopecia areata

Alopecia areata (AA) development is associated with both innate and adaptive immune cell activation, migration to peri- and intra-follicular regions, and hair follicle disruption. Both CD4(+) and CD8(+) lymphocytes are abundant in AA lesions; however, CD8(+) cytotoxic T lymphocytes are more likely to enter inside hair follicles, circumstantially suggesting that they have a significant role to play in AA development. Several rodent models recapitulate important features of the human autoimmune disease and demonstrate that CD8(+) cytotoxic T lymphocytes are fundamentally required for AA induction and perpetuation. However, the initiating events, the self-antigens involved, and the molecular signaling pathways, all need further exploration. Studying CD8(+) cytotoxic T lymphocytes and their fate decisions in AA development may reveal new and improved treatment approaches.

Combination of interleukin-12 gene therapy, metronomic cyclophosphamide and DNA cancer vaccination directs all arms of the immune system towards tumor eradication

In this work a combination therapy that acts upon the immune suppressive, the innate and specific arms of the immune system is proposed. This combination therapy, which consists of intratumoral interleukin-12 (IL-12) gene therapy, human tyrosinase (hTyr) DNA vaccination and metronomic cyclophosphamide (CPX), was evaluated in a B16-F10 mouse model. The following groups were compared: (1) no treatment, (2) control vector, (3) intratumoral IL-12 gene therapy, (4) intratumoral IL-12 gene therapy+metronomic CPX, (5) intratumoral IL-12 gene therapy+metronomic CPX+hTyr DNA vaccination. Next to clinical efficacy and safety, we characterized acute effects of IL-12 and anti-tumor immune response after a second tumor challenge. All treatment groups showed increased survival and higher cure rates than control groups. Survival of non-cured mice was increased when metronomic CPX was combined with IL-12 gene therapy. Furthermore, mice that received metronomic CPX had significantly lower percentages of regulatory T cells. Addition of the hTyr DNA vaccine increased cure rate and resulted in increased survival compared to other treatment groups. We also demonstrated that the manifest necrosis within days after IL-12 gene therapy is at least partly due to IL-12 mediated activation of NK cells. All cured mice were resistant to a second challenge. A humoral memory response against the tumor cells was observed in all groups that received IL-12 gene therapy, while a cellular memory response was observed only in the vaccinated mice. In conclusion, every component of this combination treatment contributed a unique immunologic trait with associated clinical benefits.

What causes alopecia areata?

The pathobiology of alopecia areata (AA), one of the most frequent autoimmune diseases and a major unsolved clinical problem, has intrigued dermatologists, hair biologists and immunologists for decades. Simultaneously, both affected patients and the physicians who take care of them are increasingly frustrated that there is still no fully satisfactory treatment. Much of this frustration results from the fact that the pathobiology of AA remains unclear, and no single AA pathogenesis concept can claim to be universally accepted. In fact, some investigators still harbour doubts whether this even is an autoimmune disease, and the relative importance of CD8(+) T cells, CD4(+) T cells and NKGD2(+) NK or NKT cells and the exact role of genetic factors in AA pathogenesis remain bones of contention. Also, is AA one disease, a spectrum of distinct disease entities or only a response pattern of normal hair follicles to immunologically mediated damage? During the past decade, substantial progress has been made in basic AA-related research, in the development of new models for translationally relevant AA research and in the identification of new therapeutic agents and targets for future AA management. This calls for a re-evaluation and public debate of currently prevalent AA pathobiology concepts. The present Controversies feature takes on this challenge, hoping to attract more skin biologists, immunologists and professional autoimmunity experts to this biologically fascinating and clinically important model disease.

A mouse model of vitiligo with focused epidermal depigmentation requires IFN-γ for autoreactive CD8⁺ T-cell accumulation in the skin

Vitiligo is an autoimmune disease of the skin causing disfiguring patchy depigmentation of the epidermis and, less commonly, hair. Therapeutic options for vitiligo are limited, reflecting in part limited knowledge of disease pathogenesis. Existing mouse models of vitiligo consist of hair depigmentation but lack prominent epidermal involvement, which is the hallmark of human disease. They are thus unable to provide a platform to fully investigate disease mechanisms and treatment. CD8⁺ T cells have been implicated in the pathogenesis of vitiligo and expression of interferon-gamma (IFN-γ) is increased in the lesional skin of patients, however it is currently unknown what role IFN-γ plays in disease. Here, we have developed an adoptive transfer mouse model of vitiligo using melanocyte-specific CD8⁺ T cells, which recapitulates the human condition by inducing epidermal depigmentation while sparing the hair. Like active lesions in human vitiligo, histology of depigmenting skin reveals a patchy mononuclear infiltrate and single-cell infiltration of the epidermis. Depigmentation is accompanied by accumulation of autoreactive CD8⁺ T cells in the skin, quantifiable loss of tyrosinase transcript, and local IFN-γ production. Neutralization of IFN-γ with antibody prevents CD8⁺ T cell accumulation and depigmentation, suggesting a therapeutic potential for this approach.

A mouse model of clonal CD8+ T lymphocyte-mediated alopecia areata progressing to alopecia universalis

Alopecia areata is among the most prevalent autoimmune diseases, yet compared with other autoimmune conditions, it is not well studied. This in part results from limitations in the C3H/HeJ mouse and DEBR rat model systems most commonly used to study the disease, which display a low frequency and late onset. We describe a novel high-incidence model for spontaneous alopecia areata. The 1MOG244 T cell expresses dual TCRA chains, one of which, when combined with the single TCRB present, promotes the development of CD8(+) T cells with specificity for hair follicles. Retroviral transgenic mice expressing this TCR develop spontaneous alopecia areata at nearly 100% incidence. Disease initially follows a reticular pattern, with regionally cyclic episodes of hair loss and regrowth, and ultimately progresses to alopecia universalis. Alopecia development is associated with CD8(+) T cell activation, migration into the intrafollicular region, and hair follicle destruction. The disease may be adoptively transferred with T lymphocytes and is class I and not class II MHC-dependent. Pathologic T cells primarily express IFNG and IL-17 early in disease, with dramatic increases in cytokine production and recruitment of IL-4 and IL-10 production with disease progression. Inhibition of individual cytokines did not significantly alter disease incidence, potentially indicating redundancy in cytokine responses. These results therefore characterize a new high-incidence model for alopecia areata in C57BL/6J mice, the first to our knowledge to apply a monoclonal TCR, and indicate that class I MHC-restricted CD8(+) T lymphocytes can independently mediate the pathologic response.

The role of T cells in cutaneous autoimmune disease

T cells assume a fundamental function in immunosurveillance and maintenance of the cutaneous immune barrier, yet derangement of their requisite role effects a range of cutaneous autoimmune diseases with significant associated morbidity. While blistering skin diseases, such as pemphigus vulgaris (PV), pemphigus foliaceus (PF) and bullous pemphigoid (BP) are mediated by antibodies directed against autoantigens found in the skin, recent evidence has shown that T cell activation is crucial for the initiation and coordination of this humoral response. Non-blistering skin diseases, such as alopecia areata (AA), vitiligo (VL) and psoriasis (PS) are increasingly believed to be directly mediated by the activities of autoreactive T cells. Here, we examine T lymphocyte control of antibody-mediated and cell-mediated processes involved in the pathoimmunology of the above mentioned skin diseases.

Old wine in new bottles: reviving old therapies for alopecia areata using rodent models

Alopecia areata is regarded as a tissue-restricted autoimmune disease of hair follicles in which follicular activity is arrested because of the continued activity of lymphocytic infiltrates. Actual loss of hair follicles does not occur, even in hairless lesions. A variety of immunomodulating therapies, including contact sensitizers and immunomodulators, are part of the usual armamentarium for this disorder. None of these treatments have been consistent in their efficacy, and many have untoward side effects. Nevertheless, their uses in valid animal models provide a tool to dissect out molecular mechanisms of therapeutic effects. For several decades, both mechlorethamine (for the treatment of cutaneous T cell lymphoma) and anthralin (for the treatment of psoriasis) have been used successfully. When these therapies were tested in rat and mouse alopecia areata models, we found anthralin and mechlorethamine to be the most effective topical modalities, respectively. The underlying cellular mechanisms may act through targeting infiltrative lymphocytes, and the molecular mechanisms may involve specific cytokine expression changes. These visible, accessible, and unilaterally treated animal model systems are ideal for studying novel alopecia areata therapies, particularly in terms of their in vivo molecular mechanisms of action.

Hypopigmentary Skin Disorders

Alterations of skin and hair pigmentation are important features that have warranted treatment from ancient history on up to modern time. In some cultures, even today patients with vitiligo are regarded as social outcasts and are affected considerably both emotionally and physically. This article presents current options and future directions for the treatment of hypopigmentary disorders. Whereas with congenital disorders, such as albinism and phenylketonuria, no causal therapy has been established up to now, several treatment options for acquired hypopigmentary disorders have been investigated. In particular, in vitiligo, one of the most prevalent hypopigmentary disorders, a number of treatment modalities have been employed in the past 30 years. However, most of them are only able to palliate, not cure, the disease. Depending on the distribution of the hypopigmented lesions (localised or generalised) and the state of the disease (active or stable), several therapeutic options, for example phototherapy, surgical skin grafts, autologous melanocyte transplantation and immunomodulators, can be applied alone or in combination. For phototherapy, because of unfavourable results and adverse effects, ultraviolet (UV) A has been largely replaced by narrow-band UVB for repigmentation of generalised vitiligo. Although immunomodulators, such as corticosteroids, have been used both topically and systemically over the past 3 decades for the treatment of disseminated vitiligo, they are only suitable for the treatment of acrofacial and localised forms because of adverse effects. Hence, new immunomodulatory agents, such as calcineurin antagonists, have recently been introduced as new promising tools to treat acquired hypopigmentary disorders. However, all therapeutic approaches are hampered by the fact that the pathophysiology of hypopigmentary disorders is still poorly understood.

Alopecia Areata: Autoimmunity—The Evidence Is Compelling

There is strong evidence indicating that alopecia areata is a tissue-specific, autoimmune disease. Hair loss is associated with a perifollicular lymphocytic infiltrate made up primarily of CD4+ cells, along with a CD8+ intrafollicular infiltrate. Evidence of immune activation includes expression of HLA-DR; HLA-A,B,C; and ICAM-1 on the follicular epithelium. It is likely that the follicular expression of HLA-DR and ICAM-1 is induced by interferon-gamma produced by T cells. Antibodies to follicular epithelium are often present, but their significance is not known. Lesional scalp from alopecia areata patients grafted onto nude mice regrows hair coincident with a loss of infiltrating lymphocytes from the graft. Hair loss can be transferred to human scalp explants on SCID mice by injection of lesional T cells. It is necessary to activate the T cells by culture with follicular autoantigens. Melanocyte-associated antigens are also capable of activating T cells to induce hair loss, suggesting that they are capable of functioning as autoantigens for alopecia areata. Parallel evidence in rodent models of spontaneous alopecia areata also strongly supports a role for T cells in the pathogenesis of this condition.

Topical mechlorethamine restores autoimmune-arrested follicular activity in mice with an alopecia areata-like disease by targeting infiltrated lymphocytes

Alopecia areata is an autoimmune disease targeted at hair follicles with infiltrated T lymphocytes probably playing an important role in the pathogenesis. It was reported in 1985 that mechlorethamine was effective on alopecia areata patients. This has never been confirmed since. The aims of the study were to investigate the effects of mechlorethamine on balding C3H/HeJ mice affected with an alopecia-areata-like disease and to study the underlying mechanisms. Mice were treated on half of the dorsal skin with mechlorethamine and the contralateral side was treated with the vehicle ointment. After 10 wk of mechlorethamine therapy, a full pelage of hair covered the treated side in all the mice and was maintained during the study, whereas the vehicle-treated sides showed either no change or continued hair loss. Immunohistochemistry revealed that infiltrated CD4+ and CD8+ lymphocytes were eliminated from the treated side. In vitro cell viability assay showed that lymphocytes were much more sensitive to the cytotoxic effects of mechlorethamine than skin and hair follicular cells. RNase protection assay and real-time reverse transcription polymerase chain reaction showed that tumor necrosis factor alpha/beta, interleukin-12, and interferon-gamma were inhibited by mechlorethamine upon successful treatment. Our findings support that mechlorethamine restores follicular activity by selectively targeting infiltrated lymphocytes in vivo in alopecia-areata-affected mice.

Melanocyte-associated T cell epitopes can function as autoantigens for transfer of alopecia areata to human scalp explants on Prkdc(scid) mice

Alopecia areata is a tissue restricted autoimmune condition affecting the hair follicle, resulting in hair loss. The goal of this study was to test the hypothesis that the autoantigen of alopecia areata is melanocyte associated. Potential autoantigens were tested in the human scalp explant/Prkd(scid) CB-17 mouse transfer system. Scalp T cells from lesional (bald) alopecia areata scalp were cultured with antigen-presenting cells, and antigen, along with interleukin-2. The T cells were then injected into autologous lesional scalp grafts on SCID mice, and hair regrowth was measured. Hair follicle homogenate was used as an autoantigen control. T cells cultured with melanoma homogenate induced statistically significant reduction in hair growth (p <0.01 by ANOVA). HLA-A2-restricted melanocyte peptide epitopes were then tested with lesional scalp T cells from HLA-A2-positive alopecia areata patients. Melanocyte-peptide-activated T cells significantly reduced the number of hairs regrowing in two experiments with six patients (p <0.001 by ANOVA). Injected scalp grafts showed histologic and immunochemical changes of alopecia areata. The most consistent peptide autoantigens were the Gp100-derived G9-209 and G9-280 peptides, as well as MART-1 (27-35). Melanocyte peptide epitopes can function as autoantigens for alopecia areata. Multiple peptides were recognized, suggesting epitope spreading.

Alopecia areata update

Alopecia areata (AA) is a nonscarring hair loss condition. Among the many factors under investigation in the pathogenesis of AA, the main areas of concentration have been genetic constitution as well as nonspecific immune and organ-specific autoimmune reactions. Treatment with intralesional corticosteroid injections for localized patchy AA and topical immunotherapy for extensive AA have proven successful in the majority of patients, although all treatments are palliative and do not change the prognosis of the disease.

The human hair follicle immune system: cellular composition and immune privilege

The immunology of the hair follicle, its relationship with the 'skin immune system' and its role in hair diseases remain biologically intriguing and clinically important. In this study, we analysed the immunoreactivity patterns of 15 immunodermatological markers to determine the cellular composition and immune privilege of the human hair follicle immune system in anagen VI (growth phase). The most prominent cells located in or around the hair follicle were Langerhans cells, CD4+ or CD8+ T cells, macrophages and mast cells, whereas B cells, natural killer cells and gammadelta T cells were found very rarely. Langerhans cells (CD1a+, major histocompatibility complex, MHC class II+), and T cells (CD4+ or CD8+) were predominantly distributed in the distal hair follicle epithelium, whereas macrophages (CD68+, MHC class II+) and mast cells (Giemsa+) were located in the perifollicular connective tissue sheath. Transmission electron microscopy confirmed low numbers of immune cells in the proximal hair follicle epithelium, and very few macrophages and Langerhans cells were seen in the dermal papilla. Melanophages were observed in the connective tissue sheath and dermal papilla. MHC class I (HLA-A, -B, -C) and beta2-microglobulin immunoreactivity was found on most skin cells, but was substantially reduced on isthmus keratinocytes and virtually absent in the proximal hair follicle epithelium. Apart from the absence of Fas ligand immunoreactivity, the sharply reduced numbers of T cells and Langerhans cells, and the virtual absence of MHC class I expression all suggest that the anagen proximal hair follicle constitutes an area of immune privilege within the hair follicle immune system, whose collapse may be crucial for the pathogenesis of alopecia areata.

Accumulation of identical T cells in melanoma and vitiligo-like leukoderma

The cloning of genes encoding melanoma antigens has opened new possibilities for the treatment of patients with cancer; however, most tumor rejection antigens recognized by tumor infiltrating lymphocytes are the products of genes that are also expressed by normal melanocytes. Hence, a large set of antigenic determinants of the self have not induced self-tolerance and these peptide determinants furnish target structures for immune responses directed against tumors. The notion that the immunotherapeutic targets involved in cancer regression comprise normal differentiation antigens is stressed by the association between vitiligo-like leukoderma, due to destruction of normal melanocytes, and melanoma regression, due to destruction of cancer cells. Nevertheless, this is the first report to demonstrate by means of a new technique based on reverse transcription polymerase chain reaction and denaturing gradient gel electrophoresis, the presence of clonally expanded T cells with identical BV regions in areas of destruction of both normal and neoplastic cells.

Alopecia areata: an autoimmune disease?

A wide range of hypotheses such as focal infection, trophoneuroses, and endocrine dysfunction, have been previously proposed to explain the pathogenesis of alopecia areata (AA). Currently, the most widely held belief is that AA is an autoimmune disease with cellular and/or humoral immunity directed against anagen hair follicle antigen(s). However, until recently evidence in support of an autoimmune mechanism of AA has been largely circumstantial. More fundamental evidence has recently been amassed in support of AA as an autoimmune disease by using animal models. These data include: 1) identification of cross-species hair follicle specific IgG autoantibodies, 2) The ability to induce AA in an animal model with transfer of skin from affected to naive individuals, and 3) the induction of disease by transfer of lymphocytes to human skin grafted to severe combined immunodeficiency mutant mice. A review of the previous and current data related to the autoimmune basis of AA is provided to put into perspective the future studies needed to definitively determine whether AA is an autoimmune disease.

Experimental induction of alopecia areata-like hair loss in C3H/HeJ mice using full-thickness skin grafts

Alopecia areata (AA)-like hair loss in C3H/HeJ mice provides an excellent model for human AA disease research. The potential to induce mouse AA in normal haired C3H/HeJ mice at an early age or serially passage the AA phenotype was investigated by exchange of full-thickness skin grafts. Skin grafts from normal male and female C3H/HeJ, or severe combined immunodeficient C3H/SmnC Prkdc(scid)/J, mice onto AA-affected C3H/HeJ mice became inflamed and lost hair (28 of 28). Successful grafts from AA-affected C3H/HeJ mice induced hair loss in histocompatible C3H/OuJ mice (four of 13) and normal C3H/HeJ mice dependent on age (four of 17 at <31 d and 15 of 15 at >70 d). The AA phenotype was serially transmitted from induced AA mice to normal C3H/HeJ mice (nine of nine). Grafts from AA-affected C3H/HeJ mice onto C3H/SmnC Prkd(scid)/J mice resulted in depigmented hair fiber regrowth and perifollicular neutrophil and eosinophil infiltrates but no hair loss (15 of 15). Sham grafting did not induce AA (none of 10). The finding that AA can be serially transferred from AA-affected C3H/HeJ mice to normal littermates and C3H/ OuJ mice, indicates that an immune response against hair follicles can be induced with suitable stimuli. Conversely, skin grafts from normal C3H/HeJ, or C3H/SmnC Prkd(scid)/J, mice rapidly lose hair due to lymphocyte, but not neutrophil and eosinophil, mediated inflammation. This AA induction method reproducibly provides large numbers of AA-affected mice to study the pathogenesis and treatment of human AA.

Activation of preexisting T cell clones by targeted interleukin 2 therapy

The induction of an immunological antitumor response capable of eradicating metastatic tumors is the ultimate goal of immunotherapy. We have recently shown that this can be achieved by interleukin 2 (IL-2) therapy directed to the tumor microenvironment by a recombinant antibody-IL-2 fusion protein. It is not known, however, whether this curative treatment is associated with a predominance of T cells carrying specific T cell receptor variable beta regions (TCRBV) or the presence of clonally expanded T cells. To address this question, we have used a quantitative reverse transcriptase-coupled PCR method to analyze the TCRBV region repertoire in tumor-infiltrating lymphocytes of treated and untreated animals. As controls the TCRBV region repertoire was analyzed in blood and skin from disease-free animals. The results indicate an overexpression of TCRBV5 in the tumors of all treated mice and an additional overexpression of individual regions in each tumor. Direct sequencing of these TCRBV regions did not reveal any evidence of clonal expansions. However, since clonal expansions could exist as subpopulations in highly expressed regions, not detectable by direct sequencing, a denaturing gradient gel electrophoresis assay was used for clonal analysis of TCRBV PCR products. Denaturing gradient gel electrophoresis analysis of selected TCRBV regions revealed the presence of clonotypic T cells in tumors from both treated and untreated animals. These data indicate that targeted IL-2 therapy in this model does not induce clonal T cell responses de novo, rather it acts as an activator for an already existing population of clonotypic T cells.

Generation and cyclic remodeling of the hair follicle immune system in mice

In this immunohistomorphometric study, we have defined basic characteristics of the hair follicle (HF) immune system during follicle morphogenesis and cycling in C57BL/6 mice, in relation to the skin immune system. Langerhans cells and gammadelta T cell receptor immunoreactive lymphocytes were the predominant intraepithelial hematopoietic cells in neonatal mouse skin. After their numeric increase in the epidermis, these cells migrated into the HF, although only when follicle morphogenesis was almost completed. In contrast to Langerhans cells, gammadelta T cell receptor immunoreactive lymphocytes entered the HF only via the epidermis. Throughout HF morphogenesis and cycling, both cell types remained strikingly restricted to the distal outer root sheath. On extremely rare occasions, CD4+ or CD8+ alphabetaTC were detected within the HF epithelium or the sebaceous gland. Major histocompatibility complex class II+, MAC-1+ cells of macrophage phenotype and numerous mast cells appeared very early on during HF development in the perifollicular dermis, and the percentage of degranulated mast cells significantly increased during the initiation of synchronized HF cycling (first catagen). During both depilation- and cyclosporine A-induced HF cycling, the numbers of intrafollicular Langerhans cells, gammadelta T cell receptor immunoreactive lymphocytes, and perifollicular dermal macrophages fluctuated significantly. Yet, no numeric increase of perifollicular macrophages was detectable during HF regression, questioning their proposed role in catagen induction. In summary, the HF immune system is generated fairly late during follicle development, shows striking differences to the extrafollicular skin immune system, and undergoes substantial hair cycle-associated remodeling. In addition, synchronized HF cycling is accompanied by profound alterations of the skin immune system.

MHC class I expression in murine skin: developmentally controlled and strikingly restricted intraepithelial expression during hair follicle morphogenesis and cycling, and response to cytokine treatment in vivo

Hair bulb keratinocytes generate one of the few "immune privileged" tissue compartments of the mammalian organism by suppressing classical MHC class I (MHC Ia) antigens. Expression of non-classical MHC class I (MHC Ib) antigens in the follicle has been found, but only in its distal epithelium. Here, we have defined when during murine hair follicle morphogenesis these peculiar MHC Ia and Ib expression patterns are established, how they change during the murine hair cycle, and how different MHC I modulatory agents alter follicular MHC Ia and Ib expression in vivo. During neonatal hair follicle morphogenesis in C57BL/6 mice, distal follicle keratinocytes began to express MHC Ia (H2b) only late in development. The MHC Ib antigens, Qa-1 and Qa-2, did not become visible until the initiation of follicle cycling, with Qa-1 expression being more widespread than that of Qa-2. H2b, Qa-1, and TAP-1 immunoreactivity on previously negative keratinocytes of the proximal anagen hair bulb was upregulated by intradermal injection of the proinflammatory cytokine interferon-gamma, but not by tumor necrosis factor-alpha or interleukin-1beta. Injection of the reportedly MHC class I downregulating agents interleukin-10, insulin-like growth factor-1, transforming growth factor-beta, alpha-melanocyte stimulating hormone, or dexamethasone, however, all failed to downregulate constitutive or interferon-gamma-induced follicular MHC Ia expression. This shows that the hair follicle is a previously unrecognized site of Qa-1 expression and that interferon-gamma is a key regulator of follicular MHC I expression in vivo. It also suggests that the developmental and immunologic controls of MHC I expression by follicle keratinocytes differ from those of other epithelial cells.