CCR4+T cell recruitment to the skin in mycosis fungoides: potential contributions by thymic stromal lymphopoietin and interleukin-16

The Tumor Microenvironment as a Therapeutic Target in Cutaneous T Cell Lymphoma

Cutaneous T cell lymphomas (CTCLs) are a heterogeneous group of non-Hodgkin lymphomas, with mycosis fungoides and Sézary syndrome being the two common subtypes. Despite the substantial improvement in early-stage diagnosis and treatments, some patients still progress to the advanced stage with an elusive underpinning mechanism. While this unsubstantiated disease mechanism coupled with diverse clinical outcomes poses challenges in disease management, emerging evidence has implicated the tumor microenvironment in the disease process, thus revealing a promising therapeutic potential of targeting the tumor microenvironment. Notably, malignant T cells can shape their microenvironment to dampen antitumor immunity, leading to Th2-dominated responses that promote tumor progression. This is largely orchestrated by alterations in cytokines expression patterns, genetic dysregulations, inhibitory effects of immune checkpoint molecules, and immunosuppressive cells. Herein, the recent insights into the determining factors in the CTCL tumor microenvironment that support their progression have been highlighted. Also, recent advances in strategies to target the CTCL tumor micromovement with the rationale of improving treatment efficacy have been discussed.

CCL17, CCL22 and their receptor CCR4 in hematologic malignancies

Hematological malignancies (HM) are common malignant tumors with high morbidity and mortality rates, and are malignant diseases that seriously affect human health, with chemotherapy prone to recurrence and toxic side effects. Therefore, the development of precise, effective, and safe targeted therapeutic agents has become a hotspot in the current research of antitumor technology. More and more studies have shown that the interaction of C-C chemokine ligand 17 (CCL17) and C-C chemokine ligand 22 (CCL22) with the receptor C-C chemokine receptor type 4 (CCR4) promotes the immune escape of tumors and is closely related to the occurrence, development, and prognosis of hematological tumors. In this regard, we present a review on the expression and role of the CCL17/CCL22-CCR4 axis in HM, including lymphoma, leukemia, and multiple myeloma, with the aim of providing latest ideas and directions for the diagnosis and treatment of HM. In addition, we discuss the role and related mechanisms of HM therapeutic agents targeting the CCL17/CCL22-CCR4 axis and the potential of humanized anti-CCR4 antibodies for the treatment of HM.

From Molecules to Microbes: Tracing Cutaneous T-Cell Lymphoma Pathogenesis through Malignant Inflammation

The etiology of CTCL is a subject of extensive investigation. Researchers have explored links between CTCL and environmental chemical exposures, such as aromatic hydrocarbons (eg, pesticides and benzene), as well as infectious factors, including various viruses (eg, human T-lymphotropic virus [HTLV]-I and HTLV-II) and bacteria (eg, Staphylococcus aureus). There has been growing emphasis on the role of malignant inflammation in CTCL development. In this review, we synthesize studies of environmental and infectious exposures, along with research on the aryl hydrocarbon receptor and the involvement of pathogens in disease etiology, providing insight into the pathogenesis of CTCL.

A Narrative Review of the State of the Art of CCR4-Based Therapies in Cutaneous T-Cell Lymphomas: Focus on Mogamulizumab and Future Treatments

The CCR4 receptor is a pivotal target in cutaneous T-cell lymphoma (CTCL) therapy due to its role in impairing immune responses against malignant T-cells and expression profiles. Monoclonal antibodies like mogamulizumab effectively bind to CCR4, reducing tumour burden and enhancing patient outcomes by inhibiting the receptor's interaction with ligands, thereby hindering malignant T-cell migration and survival. Combining CCR4 antibodies with chemotherapy, radiation, and other drugs is being explored for synergistic effects. Additionally, small-molecular inhibitors, old pharmacological agents interacting with CCR4, and CAR-T therapies are under investigation. Challenges include drug resistance, off-target effects, and patient selection, addressed through ongoing trials refining protocols and identifying biomarkers. Despite advancements, real-life data for most of the emerging treatments are needed to temper expectations. In conclusion, CCR4-targeted therapies show promise for CTCL management, but challenges persist. Continued research aims to optimise treatments, enhance outcomes, and transform CTCL management. This review aims to elucidate the biological rationale and the several agents under various stages of development and clinical evaluation with the actual known data.

The Role of Cytokines in Cutaneous T Cell Lymphoma: A Focus on the State of the Art and Possible Therapeutic Targets

Cutaneous T cell lymphomas (CTCLs), encompassing mycosis fungoides (MF) and Sézary syndrome (SS), present a complex landscape influenced by cytokines and cellular responses. In this work, the intricate relationship between these inflammatory proteins and disease pathogenesis is examined, focusing on what is known at the clinical and therapeutic levels regarding the most well-known inflammatory mediators. An in-depth look is given to their possible alterations caused by novel immunomodulatory drugs and how they may alter disease progression. From this narrative review of the actual scientific landscape, Interferon-gamma (IFN-γ) emerges as a central player, demonstrating a dual role in both promoting and inhibiting cancer immunity, but the work navigates through all the major interleukins known in inflammatory environments. Immunotherapeutic perspectives are elucidated, highlighting the crucial role of the cutaneous microenvironment in shaping dysfunctional cell trafficking, antitumor immunity, and angiogenesis in MF, showcasing advancements in understanding and targeting the immune phenotype in CTCL. In summary, this manuscript aims to comprehensively explore the multifaceted aspects of CTCL, from the immunopathogenesis and cytokine dynamics centred around TNF-α and IFN-γ to evolving therapeutic modalities. Including all the major known and studied cytokines in this analysis broadens our understanding of the intricate interplay influencing CTCL, paving the way for improved management of this complex lymphoma.

Role of IL-4 and IL-13 in Cutaneous T Cell Lymphoma

The interleukins IL-4 and IL-13 are increasingly recognized contributors to the pathogenesis of cutaneous T cell lymphomas (CTCLs), and their role in disease-associated pruritus is accepted. The prevailing Th2 profile in advanced CTCL underscores the significance of understanding IL-4/IL-13 expression dynamics from the early stages of disease, as a shift from Th1 to Th2 may explain CTCL progression. Targeted agents blocking key cytokines of type 2 immunity are established therapeutics in atopic disorders and have a promising therapeutic potential in CTCL, given their involvement in cutaneous symptoms and their contribution to the pathogenesis of disease. IL-4, IL-13, and IL-31 are implicated in pruritus, offering therapeutic targets with dupilumab, tralokinumab, lebrikizumab, and nemolizumab. This review analyzes current knowledge on the IL-4/IL-13 axis in mycosis fungoides and Sezary syndrome, the most common types of CTCL, examining existing literature on the pathogenetic implications with a focus on investigational treatments. Clinical trials and case reports are required to shed light on novel uses of medications in various diseases, and ongoing research into the role of IL-4/IL-13 axis blockers in CTCL therapy might not only improve the management of disease-related pruritus but also provide in-depth insights on the pathophysiologic mechanisms of CTCL.

An update on mechanisms of pruritus and their potential treatment in primary cutaneous T-cell lymphoma

Primary cutaneous T-cell lymphomas (CTCL), which include mycosis fungoides (MF) and Sézary syndrome (SS), are a group of lymphoproliferative disorders characterized by clonal accumulation of neoplastic T-lymphocytes in the skin. Severe pruritus, one of the most common and distressing symptoms in primary CTCL, can significantly impair emotional well-being, physical functioning, and interpersonal relationships, thus greatly reducing quality of life. Unfortunately, effectively managing pruritus remains challenging in CTCL patients as the underlying mechanisms are, as of yet, not fully understood. Previous studies investigating the mechanisms of itch in CTCL have identified several mediators and their corresponding antagonists used for treatment. However, a comprehensive overview of the mediators and receptors contributing to pruritus in primary CTCL is lacking in the current literature. Here, we summarize and review the mediators and receptors that may contribute to pruritus in primary CTCL to explore the mechanisms of CTCL pruritus and identify effective therapeutic targets using the PubMed and Web of Science databases. Studies were included if they described itch mediators and receptors in MF and SS. Overall, the available data suggest that proteases (mainly tryptase), and neuropeptides (particularly Substance P) may be of greatest interest. At the receptor level, cytokine receptors, MRGPRs, and TRP channels are most likely important. Future drug development efforts should concentrate on targeting these mediators and receptors for the treatment of CTCL pruritus.

Molecular pathogenesis of Cutaneous T cell Lymphoma: Role of chemokines, cytokines, and dysregulated signaling pathways

Cutaneous T cell lymphomas (CTCLs) are a heterogeneous group of lymphoproliferative neoplasms that exhibit a wide spectrum of immune-phenotypical, clinical, and histopathological features. The biology of CTCL is complex and remains elusive. In recent years, the application of next-generation sequencing (NGS) has evolved our understanding of the pathogenetic mechanisms, including genetic aberrations and epigenetic abnormalities that shape the mutational landscape of CTCL and represent one of the important pro-tumorigenic principles in CTCL initiation and progression. Still, identification of the major pathophysiological pathways including genetic and epigenetic components that mediate malignant clonal T cell expansion has not been achieved. This is of prime importance given the role of malignant T cell clones in fostering T helper 2 (Th2)-bias tumor microenvironment and fueling progressive immune dysregulation and tumor cell growth in CTCL patients, manifested by the secretion of Th2-associated cytokines and chemokines. Alterations in malignant cytokine and chemokine expression patterns orchestrate the inflammatory milieu and influence the migration dynamics of malignant clonal T cells. Here, we highlight recent insights about the molecular mechanisms of CTCL pathogenesis, emphasizing the role of cytokines, chemokines, and associated downstream signaling networks in driving immune defects, malignant transformation, and disease progression. In-depth characterization of the CTCL immunophenotype and tumoral microenvironment offers a facile opportunity to expand the therapeutic armamentarium of CTCL, an intractable malignant skin disease with poor prognosis and in dire need of curative treatment approaches.

Expression of Thymic Stromal Lymphopoietin in Immune-Related Dermatoses

Thymic stromal lymphopoietin (TSLP), long known to be involved in Th2 response, is also implicated in multiple inflammatory dermatoses and cancers. The purpose of this study was to improve our understanding of the expression of TSLP in the skin of those dermatoses. Lesional specimens of representative immune-related dermatoses, including lichen planus (LP), discoid lupus erythematosus (DLE), eczema, bullous pemphigoid (BP), psoriasis vulgaris (PsV), sarcoidosis, and mycosis fungoides (MF), were retrospectively collected and analyzed by immunohistochemistry. Morphologically, TSLP was extensively expressed in the epidermis of each dermatosis, but the expression was weak in specimens of DLE. In a semiquantitative analysis, TSLP was significantly expressed in the epidermis in LP, BP, eczema, PsV, sarcoidosis, and MF. TSLP expression was higher in the stratum spinosum in LP, eczema, BP, PsV, and MF and higher in the stratum basale in sarcoidosis and PsV. Moreover, we found positive TSLP staining in the dermal infiltrating inflammatory cells of BP, PsV, and sarcoidosis. Our observation of TSLP in different inflammatory dermatoses might provide a novel understanding of TSLP in the mechanism of diseases with distinctly different immune response patterns and suggest a potential novel therapeutic target of those diseases.

Inhibition of integrin αVβ3 signaling improves the antineoplastic effect of bexarotene in cutaneous T-cell lymphoma

Bexarotene is a specific RXR agonist that has been used for the treatment of cutaneous T-cell lymphoma (CTCL). Since bexarotene causes hypothyroidism, it requires the administration of levothyroxine. However, levothyroxine, in addition to its ubiquitous nuclear receptors, can activate the αVβ3 integrin that is overexpressed in CTCL, potentially interfering the antineoplastic effect of bexarotene. We thus investigated the biological effect of levothyroxine in relation to bexarotene treatment. Although in isolated CTCL cells levothyroxine decreased, in an αVβ3 -dependent manner, the antineoplastic effect of bexarotene; levothyroxine supplementation in pre-clinical models was necessary to avoid suppression of lymphoma immunity. Accordingly, selective genetic and pharmacologic inhibition of integrin αVβ3 3 improved the antineoplastic effect of bexarotene plus levothyroxine replacement while maintaining lymphoma immunity. Our results provide a mechanistic rationale for clinical testing of integrin αVβ3 inhibitors as part of CTCL regimens based on bexarotene administration.

Pathogenesis of cutaneous T cell lymphoma: Involvement of Staphylococcus aureus

Mycosis fungoides (MF) and Sézary syndrome (SS) are representative cutaneous lymphomas. In their early stage, a small number of tumor cells and a large number of non-malignant cells form a Th1-dominant tumor microenvironment. Increase in malignant T cells is accompanied by a decrease in CD8-positive T cells, with a shift toward a Th2-dominant milieu in advanced-stage lesions. The etiologies of MF/SS are diverse, and the underlying pathogenetic mechanisms are yet to be elucidated. Advanced MF/SS is known to be highly sensitive to Staphylococcus aureus, and the majority of deaths are caused by severe infections. The susceptibility to infection is associated with barrier dysfunction and immunosuppression, which are the main symptoms of MF. In recent years, skin-colonizing S. aureus has been identified to not only cause severe infections but also play an important role in the pathogenesis of MF/SS. Staphylococcal superantigens activate the proliferation of tumor cells and induce CD25 upregulation, FOXP3 expression, IL-17 expression, and miR-155 expression. Alpha-toxin eliminates non-neoplastic CD4-positive cells and CD8-positive cells and plays a major role in tumor cell selection. Lipoprotein may also be associated with the induction of Th2-dominant milieu. Antibiotic therapy for S. aureus eradication has been reported to cause considerable clinical improvement in the majority of individuals with advanced cutaneous T-cell lymphoma. Therefore, S. aureus may be a novel target for the treatment of advanced-stage MF/SS in the future.

The Microenvironment's Role in Mycosis Fungoides and Sézary Syndrome: From Progression to Therapeutic Implications

BACKGROUND

Mycosis fungoides (MF) and Sezary Syndrome (SS) are the most common cutaneous T-cell lymphomas. It has been hypothesized that the interaction between the immune system, cutaneous cells, and neoplastic elements may play a role in MF/SS pathogenesis and progression.

METHODS

This paper aims to revise in a narrative way our current knowledge of the microenvironment's role in MF/SS.

RESULTS AND CONCLUSIONS

Literature data support a possible implication of microenvironment cells in MF/SS pathogenesis and progression, opening up new therapeutic avenues.

Single-cell RNA sequencing reveals markers of disease progression in primary cutaneous T-cell lymphoma

Background

In early-stage mycosis fungoides (MF), the most common primary cutaneous T-cell lymphoma, limited skin involvement with patches and plaques is associated with a favorable prognosis. Nevertheless, approximately 20–30% of cases progress to tumors or erythroderma, resulting in poor outcome. At present, factors contributing to this switch from indolent to aggressive disease are only insufficiently understood.

Methods

In patients with advanced-stage MF, we compared patches with longstanding history to newly developed plaques and tumors by using single-cell RNA sequencing, and compared results with early-stage MF as well as nonlesional MF and healthy control skin.

Results

Despite considerable inter-individual variability, lesion progression was uniformly associated with downregulation of the tissue residency markers CXCR4 and CD69, the heat shock protein HSPA1A, the tumor suppressors and immunoregulatory mediators ZFP36 and TXNIP, and the interleukin 7 receptor (IL7R) within the malignant clone, but not in benign T cells. This phenomenon was not only found in conventional TCR-αβ MF, but also in a case of TCR-γδ MF, suggesting a common mechanism across MF subtypes. Conversely, malignant cells in clinically unaffected skin from MF patients showed upregulation of these markers.

Conclusions

Our data reveal a specific panel of biomarkers that might be used for monitoring MF disease progression. Altered expression of these genes may underlie the switch in clinical phenotype observed in advanced-stage MF.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12943-021-01419-2.

Cellular Interactions and Inflammation in the Pathogenesis of Cutaneous T-Cell Lymphoma

Cutaneous T-cell lymphoma (CTCL) comprises a group of lymphoproliferative diseases characterized by the accumulation of malignant T cells in chronically inflamed skin lesions. In early stages, the disease presents as skin patches or plaques covering a limited area of the skin and normally follows an indolent course. However, in a subset of patients the cutaneous lesions develop into tumors and the malignant T cells may spread to the lymphatic system, blood and internal organs with fatal consequences. Despite intensive research, the mechanisms driving disease progression remain incompletely understood. While most studies have focused on cancer cell-intrinsic oncogenesis, such as genetic and epigenetic events driving malignant transformation and disease progression, an increasing body of evidence shows that the interplay between malignant T cells and non-malignant cells plays a crucial role. Here, we outline some of the emerging mechanisms by which tumor, stromal and epidermal interactions may contribute to the progression of CTCL with particular emphasis on the crosstalk between fibroblasts, keratinocytes and malignant T cells.

Angiogenesis in cutaneous T-cell lymphoma - proteomic approaches

Neoangiogenesis plays an important role in cutaneous lymphoma pathogenesis. Cutaneous T-cell lymphoma (CTCL) is characterized by the presence of malignant T-cell clones in the skin. Vascular microenvironment of lymphomas accelerates neoangiogenesis through several factors released by tumoral cells: VEGF family, bFGF and PIGF. Tumor stroma (fibroblasts, inflammatory and immune cells) also plays a crucial role, by providing additional angiogenic factors. The angiogenic process through the VEGF-VEGFR axis can promote survival, proliferation and metastasis via autocrine mechanisms in cutaneous lymphomas. Microvascular density (MVD) measures the neo-vascularization of cutaneous lymphoma, generated by the response of tumor cells, proangiogenic stromal cells, and benign T/B lymphocytes within the tumor inflammatory infiltrate. Pro-angiogenic proteins have been found to indicate the evolution and prognosis in patients with CTCL. In conclusion, anti-angiogenic therapeutic protocols can target tumor vasculature or malignant tumor cells directly or through a large number of combinations with other drugs. The integration of proteomics into clinical practice based on high-throughput technologies leads to the development of personalized medicine, adapting the specific biomarkers to the application of cancer-type specific individual drug targets.

Molecular and Genomic Landscape of Peripheral T-Cell Lymphoma

Peripheral T-cell lymphoma (PTCL) is an uncommon group of lymphoma covering a diverse spectrum of entities. Little was known regarding the molecular and genomic landscapes of these diseases until recently but the knowledge is still quite spotty with many rarer types of PTCL remain largely unexplored. In this chapter, the recent findings from gene expression profiling (GEP) studies, including profiling data on microRNA, where available, will be presented with emphasis on the implication on molecular diagnosis, prognostication, and the identification of new entities (PTCL-GATA3 and PTCL-TBX21) in the PTCL-NOS group. Recent studies using next-generation sequencing have unraveled the mutational landscape in a number of PTCL entities leading to a marked improvement in the understanding of their pathogenesis and biology. While many mutations are shared among PTCL entities, the frequency varies and certain mutations are quite unique to a specific entity. For example, TET2 is often mutated but this is particularly frequent (70-80%) in angioimmunoblastic T-cell lymphoma (AITL) and IDH2 R172 mutations appear to be unique for AITL. In general, chromatin modifiers and molecular components in the CD28/T-cell receptor signaling pathways are frequently mutated. The major findings will be summarized in this chapter correlating with GEP data and clinical features where appropriate. The mutational landscape of cutaneous T-cell lymphoma, specifically on mycosis fungoides and Sezary syndrome, will also be discussed.

New Therapies and Immunological Findings in Cutaneous T-Cell Lymphoma

Primary cutaneous lymphomas comprise a group of lymphatic malignancies that occur primarily in the skin. They represent the second most common form of extranodal non-Hodgkin’s lymphoma and are characterized by heterogeneous clinical, histological, immunological, and molecular features. The most common type is mycosis fungoides and its leukemic variant, Sézary syndrome. Both diseases are considered T-helper cell type 2 (Th2) diseases. Not only the tumor cells but also the tumor microenvironment can promote Th2 differentiation, which is beneficial for the tumor cells because a Th1 environment enhances antitumor immune responses. This Th2-dominant milieu also underlies the infectious susceptibility of the patients. Many components, such as tumor-associated macrophages, cancer-associated fibroblasts, and dendritic cells, as well as humoral factors, such as chemokines and cytokines, establish the tumor microenvironment and can modify tumor cell migration and proliferation. Multiagent chemotherapy often induces immunosuppression, resulting in an increased risk of serious infection and poor tolerance. Therefore, overtreatment should be avoided for these types of lymphomas. Interferons have been shown to increase the time to next treatment to a greater degree than has chemotherapy. The pathogenesis and prognosis of cutaneous T-cell lymphoma (CTCL) differ markedly among the subtypes. In some aggressive subtypes of CTCLs, such as primary cutaneous gamma/delta T-cell lymphoma and primary cutaneous CD8⁺ aggressive epidermotropic cytotoxic T-cell lymphoma, hematopoietic stem cell transplantation should be considered, whereas overtreatment should be avoided with other, favorable subtypes. Therefore, a solid understanding of the pathogenesis and immunological background of cutaneous lymphoma is required to better treat patients who are inflicted with this disease. This review summarizes the current knowledge in the field to attempt to achieve this objective.

Detection of Minimal Bone Marrow involvement of Blastic Plasmacytoid Dendritic Cell Neoplastic Cells - CD303 immunostaining as a diagnostic tool

Blastic plasmacytoid dendritic cell (pDC) neoplasm (BPDCN) is a relatively rare hematological malignancy with significantly complex clinicopathological features that are still unclear. This study aimed to analyze the clinicopathological data of BPDCN and evaluate immunohistochemical detection of minimal bone marrow (BM) involvement. In this study, we examined skin and BM lesions from 6 patients with BPDCN. Neoplastic cells tested positive for CD303 (polyclonal, 100%; monoclonal, 40%) in the skin lesions and for CD303 (polyclonal, 100%; monoclonal, 67%) in the BM clots. Although immunostaining of CD4, CD56, CD123, CD303, and TCLl detected minimal BM involvement in 3 patients, morphological identification was challenging in the BM clots stained with hematoxylin-eosin. In conclusion, our results demonstrate the significance of observing BM smears to detect neoplastic cells and that immunohistochemical examination, including CD303 antibodies, is useful to detect minimal BM involvement. This study is the first to report the expression of thymic stromal lymphopoietin (TSLP) and its receptor in BPDCN cells. Therefore, the TSLP/TSLP receptor axis may be associated with the proliferation of BPDCN, and consequently, the survival of patients.

Malignant inflammation in cutaneous T-cell lymphoma-a hostile takeover

Cutaneous T-cell lymphomas (CTCL) are characterized by the presence of chronically inflamed skin lesions containing malignant T cells. Early disease presents as limited skin patches or plaques and exhibits an indolent behavior. For many patients, the disease never progresses beyond this stage, but in approximately one third of patients, the disease becomes progressive, and the skin lesions start to expand and evolve. Eventually, overt tumors develop and the malignant T cells may disseminate to the blood, lymph nodes, bone marrow, and visceral organs, often with a fatal outcome. The transition from early indolent to progressive and advanced disease is accompanied by a significant shift in the nature of the tumor-associated inflammation. This shift does not appear to be an epiphenomenon but rather a critical step in disease progression. Emerging evidence supports that the malignant T cells take control of the inflammatory environment, suppressing cellular immunity and anti-tumor responses while promoting a chronic inflammatory milieu that fuels their own expansion. Here, we review the inflammatory changes associated with disease progression in CTCL and point to their wider relevance in other cancer contexts. We further define the term "malignant inflammation" as a pro-tumorigenic inflammatory environment orchestrated by the tumor cells and discuss some of the mechanisms driving the development of malignant inflammation in CTCL.

Thymic Stromal Chemokine TSLP Acts through Th2 Cytokine Production to Induce Cutaneous T-cell Lymphoma

Thymic stromal lymphopoietin (TSLP) activates dendritic cells to induce Th2-mediated inflammation. Periostin, an extracellular matrix protein produced by fibroblasts, induces chronic inflammation by stimulating TSLP production. Recently, a reinforcing cycle linking Th2-type immune responses with periostin-induced keratinocyte activation has been proposed in atopic dermatitis pathogenesis. In this study, we investigated the role of TSLP and periostin in the development of cutaneous T-cell lymphoma (CTCL), where Th2 cytokines and chemokines are also dominant. TSLP and periostin mRNA expression levels were elevated in CTCL lesional skin, both of which correlated with IL4 expression levels. In vitro and ex vivo, IL4 or IL13 stimulated periostin expression by dermal fibroblasts, and fibroblasts from CTCL lesional skin expressed higher levels of periostin than those from control skin. Serum periostin levels of CTCL patients were also significantly higher than those of healthy individuals. Hut78 and MJ, CTCL cell lines, and peripheral blood mononuclear cells from leukemic CTCL patients expressed the TSLP receptor. TSLP induced production of IL4 and IL13 by Hut78 and MJ cells through the activation of STAT5. Moreover, TSLP induced proliferation of CTCL cells both in vitro and in vivo These data suggest that periostin-mediated TSLP production by keratinocytes directly stimulates CTCL tumor cell growth in addition to inducing a Th2-dominant tumor environment in CTCL. Cancer Res; 76(21); 6241-52. ©2016 AACR.