Reduced expression of interleukin-2 decreases the frequency of alopecia areata onset in C3H/HeJ mice

Efficacy and safety of tofacitinib for treatment of alopecia areata in children: A systematic review and meta-analysis

BACKGROUND

Tofacitinib, a potent JAK inhibitor, has gained increasing interest, in recent years, among dermatologists for the management of refractory alopecia areata. Despite a growing number of studies on its safety and efficacy, there is still a lack of clarity, especially in the pediatric population, in treatment considerations such as proper dosage, treatment duration, side-effect profile, and therapeutic strategies to guide clinicians.

METHODS

Multiple databases were systematically searched. Following the PRISMA diagram, of a pool of 601 papers, seven met a checklist of inclusion criteria. These were observational studies including a total of 59 patients from four to 19 years of age.

RESULTS

In the evaluated studies, tofacitinib was administered either orally at a 2.5 to 15 mg daily (mostly 5 mg twice a day) dosage for 2 to 38 months or in the form of a 2% topical solution for 3-17 months. Metanalysis showed that 49% (95% CI: 29%-69%, I²  = 59.94%) of patients experienced a reversal of alopecia after a minimum of 3 to 9 months of therapy. Fifty-five percent (95% CI: 23%-86%, I²  = 75.07%) and 41% (95% CI: 23%-59%, I²  = 0.00%) showed Good/complete and partial response rates, respectively. Oral administration was significantly more efficacious than topical application (73% vs 23%, p-Value = 0.04). Few side effects such as diarrhea and mild liver transaminases abnormalities were noted in several patients.

CONCLUSION

Results of this review suggest that tofacitinib at 2.5-15 mg daily (especially 5 mg twice daily) oral formulation or 2% topical solution can be regarded as a viable alternative or adjunct to the conventional treatment options for moderate to severe forms of alopecia areata in children owing to its acceptable efficacy and side-effect profile. However, uncertainties continue to exist around treatment strategies including initial and maintenance dosages, route of administration, dose adjustments, the timing of tapering or discontinuation, and associated treatment modalities.

An overview of JAK/STAT pathways and JAK inhibition in alopecia areata

Alopecia Areata (AA) is a common autoimmune disease characterized by non-scarring hair loss ranging from patches on the scalp to complete hair loss involving the entire body. Disease onset is hypothesized to follow the collapse of immune privilege of the hair follicle, which results in an increase in self-peptide/MHC expression along the follicular epithelium. Hair loss is associated with infiltration of the hair follicle with putatively self-reactive T cells. This process is thought to skew the hair follicle microenvironment away from a typically homeostatic immune state towards one of active inflammation. This imbalance is mediated in part by the dominating presence of specific cytokines. While interferon-γ (IFNγ) has been identified as the key player in AA pathogenesis, many other cytokines have also been shown to play pivotal roles. Mechanistic studies in animal models have highlighted the contribution of common gamma chain (γ_c) cytokines such as IL-2, IL-7, and IL-15 in augmenting disease. IFNγ and γ_c cytokines signal through pathways involving receptor activation of Janus kinases (JAKs) and signal transducers and activators of transcription (STATs). Based on these findings, JAK/STAT pathways have been targeted for the purposes of therapeutic intervention in the clinical setting. Case reports and series have described use of small molecule JAK inhibitors leading to hair regrowth among AA patients. Furthermore, emerging clinical trial results show great promise and position JAK inhibitors as a treatment strategy for patients with severe or recalcitrant disease. Demonstrated efficacy from large-scale clinical trials of the JAK inhibitor baricitinib led to the first-in-disease FDA-approved treatment for AA in June of 2022. This review aims to highlight the JAK/STAT signaling pathways of various cytokines involved in AA and how targeting those pathways may impact disease outcomes in both laboratory and clinical settings.

The current state of knowledge of the immune ecosystem in alopecia areata

Alopecia areata (AA) is an autoimmune disease that affects approximately 2% of the general population. Patients with AA most commonly present with one or more patches of hair loss on the scalp in defined circular areas. A fraction of patients progress to more severe forms of the disease, in some cases with involvement of all body surfaces. The healthy anagen stage hair follicle is considered an immune privileged site, described as an environment that suppresses inflammatory immune responses. However, in AA, this immune privileged state collapses and marks the hair follicle as a target for the immune system, resulting in peri- and intrafollicular infiltration by lymphocytes. The complexity of the inflammatory ecosystem of the immune response to the hair follicle, and the relationships between the cellular and soluble participants, in AA remains incompletely understood. Many studies have demonstrated the presence of various immune cells around diseased hair follicles; however, often little is known about their respective contributions to AA pathogenesis. Furthering our understanding of the mechanisms of disease in AA is essential for the novel identification of targeted therapeutics that are efficacious and have few unintended effects.

Alopecia areata is driven by cytotoxic T lymphocytes and is reversed by JAK inhibition

Alopecia areata (AA) is a common autoimmune disease resulting from damage of the hair follicle by T cells. The immune pathways required for autoreactive T cell activation in AA are not defined limiting clinical development of rational targeted therapies. Genome-wide association studies (GWAS) implicated ligands for the NKG2D receptor (product of the KLRK1 gene) in disease pathogenesis. Here, we show that cytotoxic CD8(+)NKG2D(+) T cells are both necessary and sufficient for the induction of AA in mouse models of disease. Global transcriptional profiling of mouse and human AA skin revealed gene expression signatures indicative of cytotoxic T cell infiltration, an interferon-γ (IFN-γ) response and upregulation of several γ-chain (γc) cytokines known to promote the activation and survival of IFN-γ-producing CD8(+)NKG2D(+) effector T cells. Therapeutically, antibody-mediated blockade of IFN-γ, interleukin-2 (IL-2) or interleukin-15 receptor β (IL-15Rβ) prevented disease development, reducing the accumulation of CD8(+)NKG2D(+) T cells in the skin and the dermal IFN response in a mouse model of AA. Systemically administered pharmacological inhibitors of Janus kinase (JAK) family protein tyrosine kinases, downstream effectors of the IFN-γ and γc cytokine receptors, eliminated the IFN signature and prevented the development of AA, while topical administration promoted hair regrowth and reversed established disease. Notably, three patients treated with oral ruxolitinib, an inhibitor of JAK1 and JAK2, achieved near-complete hair regrowth within 5 months of treatment, suggesting the potential clinical utility of JAK inhibition in human AA.

Tolerance induction by hair-specific keratins in murine alopecia areata

AA is a presumptive autoimmune disease, severely damaging the hair follicle. Hair- and nail-specific keratins are discussed as potential candidates, which we controlled in C3H/HeJ mice that develop AA spontaneously or after skin transplantation. From nine keratins, K71 and K31 peptides supported T cell activation when presented by DCs to syngeneic naive T cells, and young C3H/HeJ mice receiving s.c. injections of peptide-loaded DC developed AA. The frequency of K71- and K31-specific CD4(+) and CD8(+) T cells increased four- to fivefold by vaccination, which corresponds with the frequency seen in skin transplantation-induced AA mice. Also, accessory molecule expression, the cytokine profile with a dominance of IFN-γ-expressing T cells, the proliferative response against AA lysate or peptide-loaded DCs, as well as peptide-specific cytotoxic T cells were similar in keratin peptide- and skin transplantation-induced AA. Instead, vaccination with soluble K71 or K31 peptides significantly retarded AA induction and prevented progression. Soluble peptide vaccination did not provoke immunosuppression but induced long-lasting T cell anergy with unresponsiveness to DC-presented K71 and K31 peptides. Thus, keratins K71 and K31 contribute to AA induction, and peptide application in a nonimmunogenic form serves as an efficient therapeutic.

Endogenous retinoids in the pathogenesis of alopecia areata

Alopecia areata (AA) is an autoimmune disease that attacks anagen hair follicles. Gene array in graft-induced C3H/HeJ mice revealed that genes involved in retinoic acid (RA) synthesis were increased, whereas RA degradation genes were decreased in AA compared with sham controls. This was confirmed by immunohistochemistry in biopsies from patients with AA and both mouse and rat AA models. RA levels were also increased in C3H/HeJ mice with AA. C3H/HeJ mice were fed a purified diet containing one of the four levels of dietary vitamin A or an unpurified diet 2 weeks before grafting and disease progression followed. High vitamin A accelerated AA, whereas mice that were not fed vitamin A had more severe disease by the end of the study. More hair follicles were in anagen in mice fed high vitamin A. Both the number and localization of granzyme B-positive cells were altered by vitamin A. IFNγ was also the lowest and IL13 highest in mice fed high vitamin A. Other cytokines were reduced and chemokines increased as the disease progressed, but no additional effects of vitamin A were seen. Combined, these results suggest that vitamin A regulates both the hair cycle and immune response to alter the progression of AA.

Etiopathogenesis of alopecia areata: Why do our patients get it?

Alopecia areata (AA) is a nonscarring, inflammatory skin disease that results in patchy hair loss. AA is unpredictable in its onset, severity, and duration making it potentially very stressful for affected individuals. Currently, the treatment options for AA are limited and the efficacy of these treatments varies from patient to patient. The exact etiology of AA is unknown. This article provides some insights into the etiopathogenesis of AA and why some people develop it. The current knowledge on the pathogenesis of AA is summarized and some of the recent hypotheses and studies on AA are presented to allow for a fuller understanding of the possible biological mechanisms of AA.

Maintenance of hair follicle immune privilege is linked to prevention of NK cell attack

Hair follicles (HFs) enjoy a relative immune privilege (IP) that is characterized by downregulation of major histocompatibility complex (MHC) class I and local expression of potent immunosuppressants. Normally, natural killer (NK) cells attack cells with absent/low MHC class I expression. However, because few perifollicular NK cells are found around healthy human anagen HFs, we asked how HFs escape from NK cell attack. This study suggests that this happens via an active NK cell suppression. Alopecia areata (AA), an organ-specific autoimmune disease thought to result from a collapse of HF-IP, in contrast, shows striking defects in NK cell inhibition/containment. We show that the NK cell inhibitor macrophage migration inhibitory factor is strongly expressed by the HF epithelium, and very few CD56(+)/NKG2D(+) NK cells are observed in and around normal anagen HFs compared to AA with prominent aggregations of CD56(+)/NKG2D(+) NK around AA-HFs. By flow cytometry, many fewer NK function-activating receptors (NKG2D, NKG2C) and significantly more killer cell Ig-like receptors-2D2/2D3 were found to be expressed on peripheral blood CD56(+) NK cells of healthy controls than on those of AA patients. In addition, only weak immunoreactivity for MHC class I chain-related A gene was observed in normal anagen HFs compared to AA. To our knowledge, this defect is previously unreported and must be taken into account in AA pathogenesis and its management.

Lymphocytes, neuropeptides, and genes involved in alopecia areata

Many lessons in autoimmunity - particularly relating to the role of immune privilege and the interplay between genetics and neuroimmunology - can be learned from the study of alopecia areata, the most common cause of inflammation-induced hair loss. Alopecia areata is now understood to represent an organ-restricted, T cell-mediated autoimmune disease of hair follicles. Disease induction is associated with collapse of hair follicle immune privilege in both humans and in animal models. Here, the role of HLA associations, other immunogenetic factors, and neuroendocrine parameters in alopecia areata pathogenesis are reviewed. This instructive and clinically significant model disease deserves more widespread interest in the immunology community.

Alopecia universalis associated with impaired interleukin-4 production and low serum IgE level

A 17-year-old female presented with alopecia universalis, which appeared following widespread eczematous dermatitis. An immunohistochemical study demonstrated that CD8(+) T cells infiltrated into hair follicles with satellite cell necrosis of keratinocytes. The precedence of the autosensitization dermatitis suggested that T cells concerned with the eczematous reaction also attacked hair follicles, or alternatively, that those T cells sequentially activated another population of cytotoxic T cells. We found that she had a continuously low level of serum IgE (<1 units/ml), and this abnormality urged us to investigate interleukin (IL)-4 production of T cells. Although the patient had a normal number of CD4(+) T cells, the production of IL-4, but not IL-10, was profoundly impaired as assessed by a reverse transcriptase polymerase chain reaction analysis, suggesting the possible relationship between the baldness and IL-4 reduction. The autoimmune hair loss might occur via activation of cytotoxic T cells and Th(1) cells as a result of a relief from IL-4 control.

Alopecia areata

Alopecia areata (AA) is a nonscarring, autoimmune, inflammatory, hair loss on the scalp, and/or body. Etiology and pathogenesis are still unknown. The most common site affected is the scalp. Histopathology is characterized by an increased number of the catagen and telogen follicles, the presence of inflammatory lymphocytic infiltrate in the peribulbar region ("swarm of bees"). Corticosteroids are the most popular drugs for the treatment of this disease. Etiologic and pathogenic mechanisms, as well as other current treatments available will be discussed in this article.

Interferon-gamma-deficient mice are resistant to the development of alopecia areata

BACKGROUND

Alopecia areata (AA) is a T-cell mediated putative autoimmune disease of hair follicles, which can be transferred by CD4(+) T cells. However, whether T-helper (Th) 1 or Th2 cytokines are predominant has not yet been defined.

OBJECTIVES

To elucidate the importance of Th1 cells in the pathogenesis of AA we investigated the functional role of interferon (IFN)-gamma in the experimental induction of AA.

METHODS

AA was experimentally induced by grafting full-thickness skin from AA-affected C3H/HeJ mice on to C3H/HeJ mice with a targeted deletion of the Th1 cytokine IFN-gamma gene (IFNgamma(-/-)) and on to wild-type mice (IFNgamma(+/+)).

RESULTS

While 90% of wild-type mice developed AA, none of the IFNgamma(-/-) mice exhibited hair loss. Immunohistochemistry of skin sections revealed a dense perifollicular and intrafollicular infiltrate of CD4(+) and CD8(+) T cells in controls, while in IFNgamma(-/-) mice skin-infiltrating CD8(+) T cells were absent and the number of CD4(+) cells was significantly reduced. Aberrant expression of major histocompatibility complex class I and II molecules in the putative immune-privileged infrainfundibular site of the hair follicle was found to be weaker in AA-resistant IFNgamma(-/-) mice than in control mice with AA. Flow cytometry revealed that leucocytes of IFNgamma(-/-) mice did not respond to the transfer of AA-affected skin. As distinct from IFNgamma(+/+) mice, neither T-cell activation markers nor Th1 cytokines were upregulated in draining lymph node cells or skin-infiltrating leucocytes of AA-resistant IFNgamma(-/-) mice. However, there was no evidence for a shift towards a Th2 cytokine profile, nor for upregulation of regulatory T cells in IFNgamma(-/-) mice.

CONCLUSIONS

IFNgamma(-/-) mice fail to activate Th1 cells in response to the transplanted (auto)antigens, which suggests an essential requirement for IFN-gamma-mediated Th1 activation in the induction of AA.