JAK1/2 inhibition impairs the development and function of inflammatory dendritic epidermal cells in atopic dermatitis.

BACKGROUND: Janus kinase (JAK) inhibitors are a new class of therapeutic compounds for dermatological diseases. In atopic dermatitis (AD), data of clinical phase III trials show rapid improvement of pruritus and significant reduction of inflammation within the first weeks with a favorable safety profile. However, their mode of action in AD is not fully understood. OBJECTIVES: In our study, we investigate the effect of different JAK inhibitors on cell differentiation, phenotype, and function of inflammatory dendritic epidermal cells (IDECs). METHODS: We analyzed the JAK expression in IDEC from ex vivo skin and in vitro generated IDECs using flow cytometry and PCR. Further, we studied in vitro the effect of different JAK inhibitors on IDEC cell differentiation, phenotype, and maturation. RESULTS: IDECs express JAK1 and JAK2 ex vivo and in vitro. We found that JAK1 and JAK2 were upregulated during the differentiation from monocytes to IDECs. Conversely, JAK2 inhibition by ruxolitinib (JAK1/2 inhibitor) or BMS-911543 (JAK2 inhibitor) abrogated the differentiation from monocytes into IDECs. Differentiated IDECs can redifferentiate into a more monocyte-like phenotype in the presence of ruxolitinib or BMS-911543. Furthermore, we showed that concomitant inhibition of JAK1/2 rather than blocking JAK1 or JAK2 alone, impaired maturation and the release of proinflammatory cytokines on lipopolysaccharide stimulation. CONCLUSIONS: Our results suggest that inhibition of JAK1/2 impairs IDEC differentiation and function. We provide new insight into the mode of action of JAK inhibitors in AD and highlight the role of JAK1/2 inhibitors for the treatment of patients with AD.

JAK inhibitor ruxolitinib inhibits the expression of cytokines characteristic of cutaneous lupus erythematosus.

This study was stimulated by the clinical observation of a rapid response of a chilblain lupus patient to treatment with JAK1/2-kinase inhibitor ruxolitinib. We investigated the in vivo expression of phospho-JAK2 in CLE skin samples as well as the immunomodulatory in vitro effect of ruxolitinib in cultured immortalized keratinocytes and in a 3D human epidermis model (epiCS). Our results demonstrate that ruxolitinib significantly decreases the production of CLE-typical cytokines (CXCL10, CXCL9, MxA) and might be a promising drug for future clinical studies in patients with CLE and related autoimmune skin diseases.

Upcoming therapeutic targets in cutaneous lupus erythematous.

Novel insights into molecular mechanisms have altered our understanding of the pathogenesis of autoimmune skin disorders. Cutaneous lupus erythematosus (CLE) is an autoimmune skin disease characterized by auto-aggressive skin inflammation which histologically presents with interface dermatitis. This inflammation is driven by interferon (IFN)-regulated proinflammatory cytokines that orchestrate the B- and T-cell mediated lesional inflammation. During the last years, therapeutic strategies have focused on these players: biologicals targeting type I IFNs and their receptors as well as anti-B-cell drugs have been investigated in clinical trials with variable success. Very recently, CLE gene expression analyses revealed lesional activation of several pathways of the immune system, thus providing potential new therapeutic targets. In this article, we review the current knowledge concerning pathways and key mediators involved in the pathogenesis of cutaneous lupus erythematosus (including TLR-dependent and TLR-independent immune activation, NfkB, TBK1, PI3K, MAPK, JAK/STAT-pathway) and their inhibitors (e.g. chloroquine, bufalin, duvelisib, rapamycin, R788, KN-93, amlexanox, tofacitinib, ruxolitinib, baricitinib), and discuss emerging strategies for the treatment of CLE and related diseases.