Whereas atopic dermatitis (AD) is considered as a T helper 2 (Th2)-centered disease, IL-17eproducing Th (Th17) cells are also activated in AD lesional skin. However, the relationship between Th17 responses and Th2 responses in AD is still to be elucidated. Although Th17 cells are increased in AD skin, the expression and function of IL-26, which is also produced by Th17 cells, in AD are still unknown. In this report, we demonstrated that IL-26 mRNA expression levels were elevated in AD lesional skin compared with healthy controls and that IL-26-producing cells were increased in AD lesional skin by immunohistochemistry. Furthermore, IL-26 promoted IL-8, IL-1b, chemokine (C-C motif) ligand 20, IL-33, and b-defensin 2 production in keratinocytes through phosphorylation of signal transducer and activator of transcription 1 and signal transducer and activator of transcription 3. Selective JAK inhibitors for JAK1, JAK2, and tyrosine kinase 2 blocked IL-26einduced cytokine production in keratinocytes. We also showed that injection of IL-26 exacerbated an oxazolone-induced AD mouse model and upregulated Th2 and Th17 cytokine expression in vivo. Because previous studies indicate that the above molecules induced by IL-26 can promote Th17 and/or Th2 immune responses, IL-26 may play an important role for bridging between Th17 and Th2 responses, resulting in the development of AD.

CD137 and its ligand, CD137L, are expressed on activated T cells and antigen-presenting cells, respectively. Recent studies have shown that CD137L and CD137 are aberrantly expressed by tumor cells, especially in some hematopoietic malignancies, and interactions between these molecules on tumor cells promote tumor growth. In this study, we investigated the roles of CD137L and CD137 in cutaneous T-cell lymphoma (CTCL), represented by mycosis fungoides and Sézary syndrome. Flow cytometric analysis showed that primary Sézary cells and CTCL cell lines (Hut78, MyLa, HH, SeAx, and MJ) aberrantly expressed CD137L. CD137L expression by tumor cells in CTCL was also confirmed by immunohistochemistry. Anti-CD137L-neutralizing antibody inhibited proliferation, survival, CXCR4-mediated migration, and in vivo growth in CTCL cell lines through inhibition of phosphorylation of AKT, extracellular signal-regulated kinase 1/2, p38 MAPK, and JNK. Moreover, suppression of CD137L signaling decreased antiapoptotic proteins Bcl-2 and phosphorylated Bad. We also explored the transcription factor regulating CD137L expression. Because GATA6 has been proposed as an oncogene in many types of tumors with aberrant CD137L expression, we examined GATA6 expression and the involvement of GATA6 in CD137L expression in CTCL. DNA hypomethylation and histone acetylation induced GATA6 overexpression in CTCL cells. Furthermore, chromatin immunoprecipitation, luciferase reporter assay, and knockdown by short hairpin RNA showed that GATA6 directly upregulated CD137L expression. Inhibition of GATA6 resulted in decreased survival and in vivo growth in CTCL cells. Collectively, our findings prompt a novel therapeutic approach to CTCL based on the discovery that the GATA6/CD137L axis plays an important role in the tumorigenesis of CTCL.

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SIGNIFICANCECutaneous T-cell lymphomas are a heterogeneous group of extranodal non-Hodgkin's lymphomas that are characterized by a cutaneous infiltration of malignant monoclonal T lymphocytes. Tumor cells in cutaneous T-cell lymphoma express limited numbers of chemokine receptors on their cell surface. We analyzed the expression patterns of CXCR3, CCR3, CCR4 and CCR10 in skin samples from patients with cutaneous T-cell lymphoma. In addition, we investigated the relationship between chemokine receptor expression and survival prognosis. Differential patterns of CXCR3, CCR3, CCR4 and CCR10 expression were useful for the diagnosis of cutaneous T cell lymphoma. Moreover, expression of CCR3 or CCR4 suggested a poor prognosis in cutaneous T-cell lymphoma.Tumor cells in cutaneous T-cell lymphoma express limited numbers of chemokine receptors. We investigated the expression patterns of CXCR3, CCR3, CCR4 and CCR10 in mycosis fungoides, Sézary syndrome, lymphomatoid papulosis and anaplastic large cell lymphoma in 121 skin biopsy samples. CXCR3 was expressed in 86% of mycosis fungoides cases but in no anaplastic large cell lymphoma cases. CCR3 was expressed in 73% of cases of CD30 + lymphoproliferative disorders such as lymphomatoid papulosis and anaplastic large cell lymphoma. Mycosis fungoides/Sézary syndrome patients with high CCR3 or CCR4 expression had a poorer survival prognosis than mycosis fungoides/Sézary syndrome patients whose tumor cells did not express these receptors. CCR10 was expressed in 50% of mycosis fungoides/Sézary syndrome cases and in 13% of cases with CD30 + lymphoproliferative disorders. These results suggest that differential patterns of CXCR3, CCR3, CCR4 and CCR10 expression are useful for the diagnosis of cutaneous T-cell lymphoma. Moreover, expression of CCR3 or CCR4 suggests a poor prognosis in mycosis fungoides/Sézary syndrome.

CD147, a transmembrane glycoprotein that belongs to the immunoglobulin superfamily, and cyclophilin A (CypA), one of the binding partners of CD147, are overexpressed in tumor cells and associated with the progression of several malignancies, including both solid and hematological malignancies. However, CD147 and CypA involvement in cutaneous T-cell lymphoma (CTCL) has not been reported. In this study, we examined CD147 and CypA expression and function using clinical samples of mycosis fungoides (MF) and Sézary syndrome (SS) and CTCL cell lines. CD147 and CypA were overexpressed by tumor cells of MF/SS, and CypA was also expressed by epidermal keratinocytes in MF/SS lesional skin. Serum CypA levels were increased and correlated with disease severity markers in MF/SS patients. Anti-CD147 antibody and/or anti-CypA antibody suppressed the proliferation of CTCL cell lines, both in vitro and in vivo, via downregulation of phosphorylated extracellular-regulated kinase 1/2 and Akt. These results suggest that CD147-CypA interactions can contribute to the proliferation of MF/SS tumor cells in both a autocrine and paracrine manner, and that the disruption of CD147-CypA interactions could be a new therapeutic strategy for the treatment of MF/SS.

Bromodomain and external domain (BET) proteins regulate cell growth, proliferation, cell cycle, and differentiation in various cancers. Therefore, they have emerged as interesting targets. The effect of BET inhibitor on cutaneous T-cell lymphoma (CTCL), however, is yet to be known. Here, we examined the effect of BET inhibitor JQ1 on four cell lines (MyLa, SeAx, Hut78 and HH cells). CTCL cell lines were treated with JQ1 and cell number, cell cycle, frequency of apoptosis, and expressions of CD25, CD30 and CCR4 on the cell surface were evaluated by flow cytometry. Cell surface molecules were also analyzed by quantitative RT-PCR. JQ1 dose-dependently decreased the cell number of CTCL cells through G1 arrest concomitantly with downregulation of c-Myc expression. JQ1 induced senescence in MyLa cells and apoptosis in Hut78 and HH cells. We also showed that JQ1 inhibited tumor growth of HH cells in vivo. Moreover, JQ1 downregulated CD30 and CCR4 expression both on the cell surface and at mRNA levels. Thus, BET bromodomain inhibitor JQ1 may be useful for treatment of CTCL.

Mycosis fungoides (MF) is the most frequent type of cutaneous T‐cell lymphoma. Folliculotropic MF (fMF) and erythrodermic MF (eMF) are two distinct variants of MF. Both variants have been considered aggressive and most cases are less responsive to standard skin‐directed therapies than classical MF. We, however, experienced many cases with fMF or eMF who showed indolent clinical courses. In this article, we reviewed 10 cases with fMF and 13 cases with eMF who came to our department between 2005 and 2017. In patients with fMF, monotherapy with topical corticosteroid was effective in two cases (20%) and ultraviolet phototherapy with oral retinoid controlled disease activity in two cases (20%). Five patients with eMF (38%) responded well to ultraviolet phototherapy. In conclusion, patients with early fMF and a subgroup of eMF patients have an indolent disease course, as was proposed among the specialists. Skin‐directed therapies are preferable rather than aggressive treatment in those cases.