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 therapies1. Genome-wide association studies (GWAS)2 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.

This Feature Article is part of a series identified by the Editorial Board as reporting findings of exceptional significance.Edited by Zena Werb, University of California, San Francisco, CA, and approved September 5, 2013 (received for review May 28, 2013) De novo organ regeneration has been observed in several lower organisms, as well as rodents; however, demonstrating these regenerative properties in human cells and tissues has been challenging. In the hair follicle, rodent hair follicle-derived dermal cells can interact with local epithelia and induce de novo hair follicles in a variety of hairless recipient skin sites. However, multiple attempts to recapitulate this process in humans using human dermal papilla cells in human skin have failed, suggesting that human dermal papilla cells lose key inductive properties upon culture. Here, we performed global gene expression analysis of human dermal papilla cells in culture and discovered very rapid and profound molecular signature changes linking their transition from a 3D to a 2D environment with early loss of their hairinducing capacity. We demonstrate that the intact dermal papilla transcriptional signature can be partially restored by growth of papilla cells in 3D spheroid cultures. This signature change translates to a partial restoration of inductive capability, and we show that human dermal papilla cells, when grown as spheroids, are capable of inducing de novo hair follicles in human skin.

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IntroductionAlopecia areata (AA) is a major medical problem and is among the most prevalent autoimmune disease in the US, with a lifetime risk of 1.7% (1). AA affects both sexes across all ethnicities and represents the second most common form of human hair loss, second only to androgenetic alopecia (2). AA usually presents with patchy hair loss. One-third of these patients will experience spontaneous remissions within the first year. However, many patients' disease will progress to alopecia totalis (AT, total scalp hair loss) or alopecia universalis (AU, loss of all body hair). Persistent moderate-to-severe AA causes significant disfigurement and psychological distress in affected individuals (3). In clinical practice, there are no evidence-based treatments for AA (4), yet various treatments are offered, most commonly topical and intralesional steroids, which have limited efficacy.Our recent mechanistic studies demonstrated a dominant role for type I cellular immunity in AA pathogenesis, mediated by IFN-γ-producing NKG2D-bearing CD8 + cytotoxic T lymphocytes (CTLs) (5). The central role of type I cellular immunity is also reflected in the transcriptional landscape of AA lesional skin in humans and mice, which is dominated by IFN response genes and a CTL signature. These findings provided BACKGROUND. Alopecia areata (AA) is a common autoimmune disease with a lifetime risk of 1.7%; there are no FDA-approved treatments for AA. We previously identified a dominant IFN-γ transcriptional signature in cytotoxic T lymphocytes (CTLs) in human and mouse AA skin and showed that treatment with JAK inhibitors induced durable hair regrowth in mice by targeting this pathway. Here, we investigated the use of the oral JAK1/2 inhibitor ruxolitinib in the treatment of patients with moderate-to-severe AA.

Topical treatment of mouse and human skin with small-molecule inhibitors of the JAK-STAT pathway results in hair growth.

BackgroundAlopecia areata (AA) is an autoimmune disease resulting in hair loss with devastating psychosocial consequences. Despite its high prevalence, there are no FDA-approved treatments for AA. Prior studies have identified a prominent interferon signature in AA, which signals through JAK molecules.MethodsA patient with AA was enrolled in a clinical trial to examine the efficacy of baricitinib, a JAK1/2 inhibitor, to treat concomitant CANDLE syndrome. In vivo, preclinical studies were conducted using the C3H/HeJ AA mouse model to assess the mechanism of clinical improvement by baricitinib.FindingsThe patient exhibited a striking improvement of his AA on baricitinib over several months. In vivo studies using the C3H/HeJ mouse model demonstrated a strong correlation between resolution of the interferon signature and clinical improvement during baricitinib treatment.InterpretationBaricitinib may be an effective treatment for AA and warrants further investigation in clinical trials.

Alopecia areata (AA) is a common autoimmune disease with a lifetime risk of ∼2%. In AA, the immune system targets the hair follicle, resulting in clinical hair loss. The prognosis of AA is unpredictable, and currently there is no definitive treatment. Our previous whole genome expression studies identified active immune circuits in AA lesions, including common γ-chain cytokine and IFN pathways. Because these pathways are mediated through JAK kinases, we prioritized clinical exploration of small molecule JAK inhibitors. In preclinical trials in mice, tofacitinib successfully prevented AA development and reversed established disease. In our tofacitinib trial in 12 patients with moderate to severe AA, 11 patients completed a full course of treatment with minimal adverse events. Following limited response to the initial dose (5 mg b.i.d.), the dose was escalated (10 mg b.i.d.) for nonresponding subjects. Eight of 12 patients demonstrated ≥50% hair regrowth, while three patients demonstrated <50% hair regrowth, as measured by Severity in Alopecia Tool scoring. One patient demonstrated no regrowth. Gene expression profiles and Alopecia Areata Disease Activity Index scores correlated with clinical response. Our open-label studies of ruxolitinib and tofacitinib have shown dramatic clinical responses in moderate to severe AA, providing strong rationale for larger clinical trials using JAK inhibitors in AA. ClinicalTrials.gov ID NCT02299297.

The t-distributed stochastic neighbor embedding t-SNE is a new dimension reduction and visualization technique for high-dimensional data. t-SNE is rarely applied to human genetic data, even though it is commonly used in other data-intensive biological fields, such as single-cell genomics. We explore the applicability of t-SNE to human genetic data and make these observations: (i) similar to previously used dimension reduction techniques such as principal component analysis (PCA), t-SNE is able to separate samples from different continents; (ii) unlike PCA, t-SNE is more robust with respect to the presence of outliers; (iii) t-SNE is able to display both continental and sub-continental patterns in a single plot. We conclude that the ability for t-SNE to reveal population stratification at different scales could be useful for human genetic association studies.