Discovery of somatic STAT5b mutations in large granular lymphocytic leukemia

Ontogeny, Genetics, Molecular Biology, and Classification of B- and T-Cell Non-Hodgkin Lymphoma

Mature B- and T-cell lymphomas are diverse in their biology, etiology, genetics, clinical behavior, and response to specific therapies. Here, we review the principles of diagnostic classification for non-Hodgkin lymphomas, summarize the characteristic features of major entities, and place recent biological and molecular findings in the context of principles that are applicable across the spectrum of mature lymphoid cancers.

Structural and functional consequences of the STAT5BN642H driver mutation

Hyper-activated STAT5B variants are high value oncology targets for pharmacologic intervention. STAT5BN642H, a frequently-occurring oncogenic driver mutation, promotes aggressive T-cell leukemia/lymphoma in patient carriers, although the molecular origins remain unclear. Herein, we emphasize the aggressive nature of STAT5BN642H in driving T-cell neoplasia upon hematopoietic expression in transgenic mice, revealing evidence of multiple T-cell subset organ infiltration. Notably, we demonstrate STAT5BN642H-driven transformation of γδ T-cells in in vivo syngeneic transplant models, comparable to STAT5BN642H patient γδ T-cell entities. Importantly, we present human STAT5B and STAT5BN642H crystal structures, which propose alternative mutation-mediated SH2 domain conformations. Our biophysical data suggests STAT5BN642H can adopt a hyper-activated and hyper-inactivated state with resistance to dephosphorylation. MD simulations support sustained interchain cross-domain interactions in STAT5BN642H, conferring kinetic stability to the mutant anti-parallel dimer. This study provides a molecular explanation for the STAT5BN642H activating potential, and insights into pre-clinical models for targeted intervention of hyper-activated STAT5B.

IL-2 and IL-15 blockade by BNZ-1, an inhibitor of selective γ-chain cytokines, decreases leukemic T-cell viability

Interleukin-15 (IL-15) and IL-2 drive T-cell malignancies including T-cell large granular lymphocyte leukemia (T-LGLL) and HTLV-1 driven adult T-cell leukemia (ATL). Both cytokines share common γ-chain receptors and downstream signaling pathways. T-LGLL is characterized by clonal expansion of cytotoxic T cells and is associated with abnormal JAK/STAT signaling. ATL is an aggressive CD4+ T-cell neoplasm associated with HTLV-1. T-LGLL and ATL share dependence on IL-2 and IL-15 for survival and both diseases lack effective therapies. BNZ-1 is a pegylated peptide designed to specifically bind the γc receptor to selectively block IL-2, IL-15, and IL-9 signaling. We hypothesized that treatment with BNZ-1 would reduce cytokine-mediated proliferation and viability. Our results demonstrated that in vitro treatment of a T-LGLL cell line and ex vivo treatment of T-LGLL patient cells with BNZ-1 inhibited cytokine-mediated viability. Furthermore, BNZ-1 blocked downstream signaling and increased apoptosis. These results were mirrored in an ATL cell line and in ex vivo ATL patient cells. Lastly, BNZ-1 drastically reduced leukemic burden in an IL-15-driven human ATL mouse xenograft model. Thus, BNZ-1 shows great promise as a novel therapy for T-LGLL, ATL, and other IL-2 or IL-15 driven hematopoietic malignancies.

Fine-Tuning Cytokine Signals

Cytokines are secreted or otherwise released polypeptide factors that exert autocrine and/or paracrine actions, with most cytokines acting in the immune and/or hematopoietic system. They are typically pleiotropic, controlling development, cell growth, survival, and/or differentiation. Correspondingly, cytokines are clinically important, and augmenting or attenuating cytokine signals can have deleterious or therapeutic effects. Besides physiological fine-tuning of cytokine signals, altering the nature or potency of the signal can be important in pathophysiological responses and can also provide novel therapeutic approaches. Here, we give an overview of cytokines, their signaling and actions, and the physiological mechanisms and pharmacologic strategies to fine-tune their actions. In particular, the differential utilization of STAT proteins by a single cytokine or by different cytokines and STAT dimerization versus tetramerization are physiological mechanisms of fine-tuning, whereas anticytokine and anticytokine receptor antibodies and cytokines with altered activities, including cytokine superagonists, partial agonists, and antagonists, represent new ways of fine-tuning cytokine signals.

The Signal Transducer and Activator of Transcription 5B (STAT5B) Gene Promotes Proliferation and Drug Resistance of Human Mantle Cell Lymphoma Cells by Activating the Akt Signaling Pathway

Background

Mantle cell lymphoma (MCL) is a high-grade B-cell lymphoma with poor prognosis. Fludarabine is used alone or in combination for relapsed and advanced-stage MCL. The expression of the signal transducer and activator of transcription 5B (STAT5B) gene is associated with tumorigenesis in solid tumors, but its role in MCL remains unknown. The aims of this study were to investigate the role of STAT5B in GRANTA-519 human mantle cell lymphoma cells and drug resistance.

Material/Methods

GRANTA-519 human mantle cell lymphoma cells were cultured with and without 10 μM fludarabine dephosphorylated 9-β-D-arabinofuranosyl-2-fluoroadenine, (2-F-araA) or 10 μM 4-hydroperoxycyclophosphamide (4-HC). The MTT assay assessed cell proliferation. Flow cytometry was used to investigate the cell cycle in MCL cells treated with the specific inhibitor of the Akt pathway, LY294002, and assessed cell cycle and cell apoptosis. Western blot was used to detect the expression levels of p-Akt/Akt and STAT5B/p-STAT5B. The gene expression profiles of lymph node (LN)-derived MCL cells were compared with peripheral blood (PB)-derived lymphocytes using bioinformatics and hierarchical cluster analysis. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) was performed to determine the expression of the marker of proliferation Ki-67 (MKI67) gene.

Results

STAT5B was significantly upregulated in LN-derived MCL cells compared with PB lymphocytes. Increased expression of STAT5B was associated with increased MCL cell proliferation and reduced cell apoptosis and was associated with drug resistance and activation of Akt.

Conclusions

STAT5B promoted cell proliferation and drug resistance in human MCL cells by activating the Akt signaling pathway.

Flow Cytometry Applications in the Diagnosis of T/NK-Cell Lymphoproliferative Disorders

This article provides an overview of the role of flow cytometry in the diagnosis, prognosis, and follow-up of T and NK-cell lymphoproliferative disorders. For each category, we will briefly discuss the immunophenotypic features of normal T and NK cells, and address technical issues in flow cytometry, the approach to diagnosis in various contexts, pitfalls in interpretation, and its use in follow-up and post-therapy management. In addition to reviewing the diagnostic, prognostic, and therapeutic utility of flow cytometric immunophenotyping in several of specific T and NK cell entities, we will also cover some of the new immunophenotypic markers. Furthermore, we will touch upon incorporation of flow cytometry in the final diagnosis, including correlation with other ancillary tests. © 2019 International Clinical Cytometry Society.

Recurrent activating STAT5B N642H mutation in myeloid neoplasms with eosinophilia

Determining the underlying cause of persistent eosinophilia is important for effective clinical management but remains a diagnostic challenge in many cases. We identified STAT5B N642H, an established oncogenic mutation, in 27/1715 (1.6%) cases referred for investigation of eosinophilia. Of the 27 mutated cases, a working diagnosis of hypereosinophilic syndrome (HES; n = 7) or a myeloid neoplasm with eosinophilia (n = 20) had been made prior to the detection of STAT5B N642H. Myeloid panel analysis identified a median of 2 additional mutated genes (range 0–4) with 4 cases having STAT5B N642H as a sole abnormality. STAT5B N642H was absent in cultured T cells of 4/4 positive cases. Individuals with SF3B1 mutations (9/27; 33%) or STAT5B N642H as a sole abnormality had a markedly better overall survival compared to cases with other additional mutations (median 65 months vs. 14 months; hazard ratio = 8.1; P < 0.001). The overall survival of STAT5B-mutated HES cases was only 30 months, suggesting that these cases should be reclassified as chronic eosinophilic leukemia, not otherwise specified (CEL-NOS). The finding of STAT5B N642H as a recurrent mutation in myeloid neoplasia with eosinophilia provides a new diagnostic and prognostic marker as well as a potential target for therapy.

Vitamin D pathway activation selectively deactivates signal transducer and activator of transcription (STAT) proteins and inflammatory cytokine production in natural killer leukemic large granular lymphocytes

Calcitriol, the active form of vitamin D, has been well documented to act directly on immune cells and malignant cells. Activated T cells are one of the best characterized targets of calcitriol, with effects including decreasing inflammatory cytokine output and promoting anti-inflammatory cytokine production. However, the effects of calcitriol on natural killer (NK) cells are less clear. Reports suggest that only immature NK cell populations are affected by calcitriol treatment resulting in impaired cytotoxic function and cytokine production, while mature NK cells may have little or no response. NK cell large granular lymphocyte leukemia (NK-LGLL) is a rare leukemia with CD3-CD16+CD56+NK cell clonal expansion. The current standard treatments are immunosuppressant therapies, which are not curative. The Janus kinase (JAK) - signal transducer and activator of transcription (STAT) pathway is hyperactivated in LGLL and is one pathway of interest in new drug target investigations. We previously demonstrated the ability of calcitriol to decrease STAT1 tyrosine 701 (p-STAT1) and STAT3 tyrosine 705 (p-STAT3) phosphorylation as well as inflammatory cytokine output of T cell large granular lymphocyte leukemia cells, but did not determine the effects of calcitriol on NK-LGLL. Therefore, in the present study, we investigated whether NKL cells, a model of NK-LGLL, and NK-LGLL patient peripheral blood mononuclear cells (PBMCs) are susceptible to treatment with calcitriol or seocalcitol (EB1089), a potent analog of calcitriol. NKL cells are dependent on interleukin (IL)-2 for survival and we show here for the first time that treatment with IL-2 induced tyrosine phosphorylation of STATs 1 through 6. Both calcitriol and EB1089 caused significant upregulation of the vitamin D receptor (VDR). IL-2 induction of p-STAT1 and p-STAT3 phosphorylation was significantly decreased after calcitriol or EB1089 treatment. Additionally, IL-10, interferon (IFN)-γ, and FMS-like tyrosine kinase 3 ligand (Flt-3L) extracellular output was significantly decreased at 100 nM EB1089 and intracellular IL-10 was decreased with either calcitriol or EB1089 treatment. We treated NK-LGLL patient PBMCs with calcitriol or EB1089 and found decreased p-STAT1 and p-STAT3 while VDR increased, which matched the NKL cell line data. We then measured 75 serum cytokines in NK-LGLL patients (n = 8) vs. age- and sex-matched normal healthy donors (n = 8), which is the first serum cytokine study for this LGLL subtype. We identified 15 cytokines, including IL-10 and Flt-3L, which were significantly different between normal donors and NK-LGLL patients. Overall, our results suggest that activating the vitamin D pathway could be a mechanism to decrease STAT1 and 3 activation and inflammatory cytokine output in NK-LGLL patients.

Latest Advances in the Diagnosis and Treatment of Large Granular Lymphocytic Leukemia

Large granular lymphocyte (LGL) leukemia has been recognized in the World Health Organization classifications among mature T cell and natural killer cell neoplasms and is divided into three categories. Chronic T cell leukemia and natural killer cell lymphocytosis can be considered as a similar spectrum of an indolent disease characterized by cytopenias and autoimmune conditions. The last category, aggressive natural killer cell LGL leukemia is very rare, related to Epstein-Barr virus, and seen mainly in young Asian people. Clonal LGL expansion arises from chronic antigenic stimulation sustained by interleukin-15 and platelet-derived growth factor cytokine signal. Those leukemic cells are resistant to apoptosis, mainly because of constitutive activation of survival pathways including Jak/Stat, MapK, Pi3k-Akt, RasRaf-1, MEK1/ERK, sphingolipid, and NFκB. Stat3 constitutive activation is the hallmark of this lymphoproliferative disorder. Socs3 is downregulated, but no mutation could be found to explain this status. However, several somatic mutations, including Stat3, Stat5b, and tumor necrosis factor alpha-induced protein 3, have been demonstrated recently in LGL leukemia; they are identified in half of patients and cannot explain by themselves LGL leukemogenesis. Recurrent infections as a result of chronic neutropenia, anemia, and autoimmune disorders are the main complications related to LGL leukemia. Despite an indolent presentation, 10% of patients die, mainly because of infectious complications. Current treatments are based on immunosuppressive therapies. A better mechanistic understanding of LGL leukemia will allow future consideration of a personalized therapeutic approach perhaps based on Jak/Stat inhibitors, which may offer better results than current immunosuppressive therapy.

The 2017 WHO update on mature T- and natural killer (NK) cell neoplasms

Over the last decade, there has been a significant body of information regarding the biology of the lymphoid neoplasms. This clearly supports the need for updating the 2008 WHO (World Health Organization) classification of haematopoietic and lymphoid tumours. The 2017 WHO classification is not a new edition but an update and revision of the 4th edition. New provisional entities but not new definitive entities are included, and novel molecular data in most of the entities and changes in the nomenclature in few of them have been incorporated. In the context of the mature T- and NK-cell neoplasms, the most relevant updates concern to: 1-dysregulation of the JAK/STAT pathway due to gene mutations which are common to various aggressive and indolent neoplasms; 2-incorporation of new molecular players that are relevant to the pathogenesis of these neoplasms and/or have prognostic implications; 3-inclusion of new provisional entities within the subgroups of anaplastic, primarily intestinal and cutaneous lymphomas such as breast implant-associated anaplastic large cell lymphoma, indolent T-cell lymphoproliferative disorder of the gastrointestinal tract and primary cutaneous acral CD8⁺ T-cell lymphoma; 4-identification of poor prognostic subtypes of peripheral T-cell lymphomas not otherwise specified (PTCL, NOS) characterized by overexpression of certain genes and of a subgroup PTCL, NOS with a T follicular phenotype that now is included together with angioimmunoblastic T-cell lymphoma under the umbrella of lymphomas with a T follicular helper phenotype; and 5-refinement on the designation and definition of already established entities. A review of the major changes will be outlined.

The Cooperative Relationship between STAT5 and Reactive Oxygen Species in Leukemia: Mechanism and Therapeutic Potential

Reactive oxygen species (ROS) are now recognized as important second messengers with roles in many aspects of signaling during leukemogenesis. They serve as critical cell signaling molecules that regulate the activity of various enzymes including tyrosine phosphatases. ROS can induce inactivation of tyrosine phosphatases, which counteract the effects of tyrosine kinases. ROS increase phosphorylation of many proteins including signal transducer and activator of transcription-5 (STAT5) via Janus kinases (JAKs). STAT5 is aberrantly activated through phosphorylation in many types of cancer and this constitutive activation is associated with cell survival, proliferation, and self-renewal. Such leukemic activation of STAT5 is rarely caused by mutation of the STAT5 gene itself but instead by overactive mutant receptors with tyrosine kinase activity as well as JAK, SRC family protein tyrosine kinases (SFKs), and Abelson murine leukemia viral oncogene homolog (ABL) kinases. Interestingly, STAT5 suppresses transcription of several genes encoding antioxidant enzymes while simultaneously enhancing transcription of NADPH oxidase. By doing so, STAT5 activation promotes an overall elevation of ROS level, which acts as a feed-forward loop, especially in high risk Fms-related tyrosine kinase 3 (FLT3) mutant leukemia. Therefore, efforts have been made recently to target ROS in cancer cells. Drugs that are able to either quench ROS production or inversely augment ROS-related signaling pathways both have potential as cancer therapies and may afford some selectivity by activating feedback inhibition of the ROS-STAT5 kinome. This review summarizes the cooperative relationship between ROS and STAT5 and explores the pros and cons of emerging ROS-targeting therapies that are selective for leukemia characterized by persistent STAT5 phosphorylation.

Aggressive B-cell lymphomas in patients with myelofibrosis receiving JAK1/2 inhibitor therapy

Inhibition of Janus-kinase 1/2 (JAK1/2) is a mainstay to treat myeloproliferative neoplasms (MPN). Sporadic observations reported the co-incidence of B-cell non-Hodgkin lymphomas during treatment of MPN with JAK1/2 inhibitors. We assessed 626 patients with MPN, including 69 with myelofibrosis receiving JAK1/2 inhibitors for lymphoma development. B-cell lymphomas evolved in 4 (5.8%) of 69 patients receiving JAK1/2 inhibition compared with 2 (0.36%) of 557 with conventional treatment (16-fold increased risk). A similar 15-fold increase was observed in an independent cohort of 929 patients with MPN. Considering primary myelofibrosis only (N = 216), 3 lymphomas were observed in 31 inhibitor-treated patients (9.7%) vs 1 (0.54%) of 185 control patients. Lymphomas were of aggressive B-cell type, extranodal, or leukemic with high MYC expression in the absence of JAK2 V617F or other MPN-associated mutations. Median time from initiation of inhibitor therapy to lymphoma diagnosis was 25 months. Clonal immunoglobulin gene rearrangements were already detected in the bone marrow during myelofibrosis in 16.3% of patients. Lymphomas occurring during JAK1/2 inhibitor treatment were preceded by a preexisting B-cell clone in all 3 patients tested. Sequencing verified clonal identity in 2 patients. The effects of JAK1/2 inhibition were mirrored in Stat1^-/- mice: 16 of 24 mice developed a spontaneous myeloid hyperplasia with the concomitant presence of aberrant B cells. Transplantations of bone marrow from diseased mice unmasked the outgrowth of a malignant B-cell clone evolving into aggressive B-cell leukemia-lymphoma. We conclude that JAK/STAT1 pathway inhibition in myelofibrosis is associated with an elevated frequency of aggressive B-cell lymphomas. Detection of a preexisting B-cell clone may identify individuals at risk.

Dominant-negative STAT5B mutations cause growth hormone insensitivity with short stature and mild immune dysregulation

Growth hormone (GH) insensitivity syndrome (GHIS) is a rare clinical condition in which production of insulin-like growth factor 1 is blunted and, consequently, postnatal growth impaired. Autosomal-recessive mutations in signal transducer and activator of transcription (STAT5B), the key signal transducer for GH, cause severe GHIS with additional characteristics of immune and, often fatal, pulmonary complications. Here we report dominant-negative, inactivating STAT5B germline mutations in patients with growth failure, eczema, and elevated IgE but without severe immune and pulmonary problems. These STAT5B missense mutants are robustly tyrosine phosphorylated upon stimulation, but are unable to nuclear localize, or fail to bind canonical STAT5B DNA response elements. Importantly, each variant retains the ability to dimerize with wild-type STAT5B, disrupting the normal transcriptional functions of wild-type STAT5B. We conclude that these STAT5B variants exert dominant-negative effects through distinct pathomechanisms, manifesting in milder clinical GHIS with general sparing of the immune system.

Severe growth hormone insensitivity syndrome (GHIS) with immunodeficiency is caused by autosomal recessive mutations in STAT5B. Here the authors report heterozygous STAT5B mutations with dominant-negative effects, causing mild GHIS without immune defects.

STAT5 inhibition induces TRAIL/DR4 dependent apoptosis in peripheral T-cell lymphoma

Peripheral T-cell lymphoma (PTCL) is a rare, aggressive, heterogeneous, Non-Hodgkin's lymphoma with poor prognosis and inadequate response to current therapies. Recent sequencing studies indicate a prevalence of activating mutations in the JAK/STAT signaling pathway. Oncogenic mutations in STAT5B, observed in approximately one third of cases of multiple different PTCL subtypes, correlate with inferior patient outcomes. Therefore, interest in the development of therapeutic strategies for targeting STAT5 in PTCL is warranted. In this study, we show that the drug pimozide inhibits STAT5 in PTCL, leading to apoptotic cell death by means of the TRAIL/DR4 dependent extrinsic apoptotic pathway. Pimozide induced PTCL cell death is caspase 8 dependent, increases the expression of the TRAIL receptor, DR4, on the surface of pre-apoptotic PTCL cells, and enhances TRAIL induced apoptosis in a TRAIL dependent manner. In parallel, we show that mRNA and protein levels of intrinsic pathway BCL-2 family members and mitochondrial membrane potential remain unaffected by STAT5 knockdown and/or inhibition. In primary PTCL patient samples, pimozide inhibits STAT5 activation and induces apoptosis. Our data support a role for STAT5 inhibition in PTCL and implicate potential utility for inhibition of STAT5 and activation of the extrinsic apoptotic pathway as combination therapy in PTCL.

Primary atopic disorders

Important insights from monogenic disorders into the immunopathogenesis of allergic diseases and reactions are discussed.

Monogenic disorders have provided fundamental insights into human immunity and the pathogenesis of allergic diseases. The pathways identified as critical in the development of atopy range from focal defects in immune cells and epithelial barrier function to global changes in metabolism. A major goal of studying heritable single-gene disorders that lead to severe clinical allergic diseases is to identify fundamental pathways leading to hypersensitivity that can be targeted to provide novel therapeutic strategies for patients with allergic diseases, syndromic and nonsyndromic alike. Here, we review known single-gene disorders leading to severe allergic phenotypes in humans, discuss how the revealed pathways fit within our current understanding of the atopic diathesis, and propose how some pathways might be targeted for therapeutic benefit.

Mutations in the signal transducer and activator of transcription family of genes in cancer

In recent years, it has become clear that members of the signal transducer and activator of transcription (STAT) family of genes play an important role in cancer. The STAT family consists of seven genes, STAT1‐4,STAT5A, STAT5B and STAT6, that are involved in regulating cellular proliferation, apoptosis, angiogenesis and the immune system response. Constitutive activation of STAT3, via mutational changes, is important in oncogenesis in both solid and hematopoietic cancers. In the case of hematopoietic neoplasms, STAT3 driver mutations have been described in T‐cell large granular lymphocytic (T‐LGL) leukemia and chronic natural killer lymphoproliferative disorders (CLPD‐NK) and are seen in 30%‐40% of T‐LGL leukemia patients. STAT5B is also mutated in T‐LGL leukemia and CLPD‐NK, but in a much smaller proportion. Here we review past and current research on STAT genes in hematopoietic and solid cancers with emphasis on STAT3 and STAT5B and their roles in the pathogenesis of hematopoietic malignancies, particularly T‐LGL leukemia and CLPD‐NK.

Divergent roles for antigenic drive in the aetiology of primary versus dasatinib-associated CD8+ TCR-Vβ+ expansions

CD8+ T-cell expansions are the primary manifestation of T-cell large granular lymphocytic leukemia (T-LGLL), which is frequently accompanied by neutropenia and rheumatoid arthritis, and also occur as a secondary phenomenon in leukemia patients treated with dasatinib, notably in association with various drug-induced side-effects. However, the mechanisms that underlie the genesis and maintenance of expanded CD8+ T-cell receptor (TCR)-Vβ+ populations in these patient groups have yet to be fully defined. In this study, we performed a comprehensive phenotypic and clonotypic assessment of expanded (TCR-Vβ+) and residual (TCR-Vβ-) CD8+ T-cell populations in T-LGLL and dasatinib-treated chronic myelogenous leukemia (CML) patients. The dominant CD8+ TCR-Vβ+ expansions in T-LGLL patients were largely monoclonal and highly differentiated, whereas the dominant CD8+ TCR-Vβ+ expansions in dasatinib-treated CML patients were oligoclonal or polyclonal, and displayed a broad range of memory phenotypes. These contrasting features suggest divergent roles for antigenic drive in the immunopathogenesis of primary versus dasatinib-associated CD8+ TCR-Vβ+ expansions.

Evolution of Cytogenetically Normal Acute Myeloid Leukemia During Therapy and Relapse: An Exome Sequencing Study of 50 Patients

Purpose: To study mechanisms of therapy resistance and disease progression, we analyzed the evolution of cytogenetically normal acute myeloid leukemia (CN-AML) based on somatic alterations.Experimental Design: We performed exome sequencing of matched diagnosis, remission, and relapse samples from 50 CN-AML patients treated with intensive chemotherapy. Mutation patterns were correlated with clinical parameters.Results: Evolutionary patterns correlated with clinical outcome. Gain of mutations was associated with late relapse. Alterations of epigenetic regulators were frequently gained at relapse with recurring alterations of KDM6A constituting a mechanism of cytarabine resistance. Low KDM6A expression correlated with adverse clinical outcome, particularly in male patients. At complete remission, persistent mutations representing preleukemic lesions were observed in 48% of patients. The persistence of DNMT3A mutations correlated with shorter time to relapse.Conclusions: Chemotherapy resistance might be acquired through gain of mutations. Insights into the evolution during therapy and disease progression lay the foundation for tailored approaches to treat or prevent relapse of CN-AML. Clin Cancer Res; 24(7); 1716-26. ©2018 AACR.

Hepatosplenic T-cell Lymphoma: a review of clinicopathologic features, pathogenesis, and prognostic factors

Hepatosplenic T-cell lymphoma (HSTCL) is a rare and clinically aggressive type of T-cell lymphoma that arises most often in adolescents and young adults. Patients with HSTCL commonly present with B-symptoms and cytopenias, which may suggest a diagnosis of acute leukemia initially. Patients present with extranodal disease involving the spleen, liver and bone marrow; lymphadenopathy is usually absent. The lymphoma cells can show a spectrum of cell sizes and are of T-cell lineage, often negative for CD4 and CD8 and positive for T-cell receptor γδ or, less often, αβ. Recent studies have identified gene mutations in oncogenic pathways that are likely involved in pathogenesis and may be targets for therapy. Mutations in STAT3 or STAT5B lead to activation of the JAK/STAT pathway, and mutations involving SETD2, IN080 and ARID1 are involved in chromatin modification. Currently, there is no consensus standard of care for HSTCL patients, although several studies support a role for allogeneic hematopoietic stem cell transplant. Although patients with HSTCL are best treated in the context of clinical trials, the rarity of these neoplasms likely necessitates a multi-institutional approach. In this review, we focus on the clinicopathologic and genetic characteristics of HSTCL. We also discuss the differential diagnosis and therapeutic approaches.

Responses to Cytokines and Interferons that Depend upon JAKs and STATs

Many cytokines and all interferons activate members of a small family of kinases (the Janus kinases [JAKs]) and a slightly larger family of transcription factors (the signal transducers and activators of transcription [STATs]), which are essential components of pathways that induce the expression of specific sets of genes in susceptible cells. JAK-STAT pathways are required for many innate and acquired immune responses, and the activities of these pathways must be finely regulated to avoid major immune dysfunctions. Regulation is achieved through mechanisms that include the activation or induction of potent negative regulatory proteins, posttranslational modification of the STATs, and other modulatory effects that are cell-type specific. Mutations of JAKs and STATs can result in gains or losses of function and can predispose affected individuals to autoimmune disease, susceptibility to a variety of infections, or cancer. Here we review recent developments in the biochemistry, genetics, and biology of JAKs and STATs.

Chronic neutropenia in LGL leukemia and rheumatoid arthritis

This section reviews the diagnostic criteria and pathogenesis of large granular lymphocyte (LGL) leukemia. There is a particular focus on the overlap of LGL leukemia and rheumatoid arthritis (Felty's syndrome). Current understanding of the mechanisms of neutropenia in these disorders is discussed. Finally, treatment indications and therapeutic recommendations are outlined.

Somatic STAT3 mutations in Felty syndrome: an implication for a common pathogenesis with large granular lymphocyte leukemia

Felty syndrome is a rare disease defined by neutropenia, splenomegaly, and rheumatoid arthritis. Sometimes the differential diagnosis between Felty syndrome and large granular lymphocyte leukemia is problematic. Recently, somatic STAT3 and STAT5B mutations were discovered in 30–40% of patients with large granular lymphocyte leukemia. Herein, we aimed to study whether these mutations can also be detected in Felty syndrome, which would imply the existence of a common pathogenic mechanism between these two disease entities. We collected samples and clinical information from 14 Felty syndrome patients who were monitored at the rheumatology outpatient clinic for Felty syndrome. Somatic STAT3 mutations were discovered in 43% (6/14) of Felty syndrome patients with deep amplicon sequencing targeting all STAT3 exons. Mutations were located in the SH2 domain of STAT3, which is a known mutational hotspot. No STAT5B mutations were found. In blood smears, overrepresentation of large granular lymphocytes was observed, and in the majority of cases the CD8⁺ T-cell receptor repertoire was skewed when analyzed by flow cytometry. In bone marrow biopsies, an increased amount of phospho-STAT3 positive cells was discovered. Plasma cytokine profiling showed that ten of the 92 assayed cytokines were elevated both in Felty syndrome and large granular lymphocyte leukemia, and three of these cytokines were also increased in patients with uncomplicated rheumatoid arthritis. In conclusion, somatic STAT3 mutations and STAT3 activation are as frequent in Felty syndrome as they are in large granular lymphocyte leukemia. Considering that the symptoms and treatment modalities are also similar, a unified reclassification of these two syndromes is warranted.

Rare mutations provide unique insight into oncogenic potential of STAT transcription factors

The inappropriate activation of transcription factors, including STATs, is known to promote tumor initiation and progression. The most common mechanisms of misregulation lead to constitutive activation of WT STATs. However, the recent discovery of rare STAT mutations in hematopoietic malignancies suggests that STAT mutants may be oncogenic. In this issue of the JCI, Pham et al. use a transgenic mouse model to demonstrate that STAT5BN642H is sufficient for the development of T cell neoplasia. This study, along with other studies of constitutively active STAT mutants, provides insight into the pathogenesis and treatment of STAT5-driven cancer.

STAT5BN642H is a driver mutation for T cell neoplasia

STAT5B is often mutated in hematopoietic malignancies. The most frequent STAT5B mutation, Asp642His (N642H), has been found in over 90 leukemia and lymphoma patients. Here, we used the Vav1 promoter to generate transgenic mouse models that expressed either human STAT5B or STAT5B^N642H in the hematopoietic compartment. While STAT5B-expressing mice lacked a hematopoietic phenotype, the STAT5B^N642H-expressing mice rapidly developed T cell neoplasms. Neoplasia manifested as transplantable CD8⁺ lymphoma or leukemia, indicating that the STAT5B^N642H mutation drives cancer development. Persistent and enhanced levels of STAT5B^N642H tyrosine phosphorylation in transformed CD8⁺ T cells led to profound changes in gene expression that were accompanied by alterations in DNA methylation at potential histone methyltransferase EZH2-binding sites. Aurora kinase genes were enriched in STAT5B^N642H-expressing CD8⁺ T cells, which were exquisitely sensitive to JAK and Aurora kinase inhibitors. Together, our data suggest that JAK and Aurora kinase inhibitors should be further explored as potential therapeutics for lymphoma and leukemia patients with the STAT5B^N642H mutation who respond poorly to conventional chemotherapy.

Emerging therapeutic targets in myeloproliferative neoplasms and peripheral T-cell leukemia and lymphomas

Introduction: Hematopoietic neoplasms are often driven by gain-of-function mutations of the JAK-STAT pathway together with mutations in chromatin remodeling and DNA damage control pathways. The interconnection between the JAK-STAT pathway, epigenetic regulation or DNA damage control is still poorly understood in cancer cell biology.

Areas covered: Here, we focus on a broader description of mutational insights into myeloproliferative neoplasms and peripheral T-cell leukemia and lymphomas, since sequencing efforts have identified similar combinations of driver mutations in these diseases covering different lineages. We summarize how these pathways might be interconnected in normal or cancer cells, which have lost differentiation capacity and drive oncogene transcription.

Expert opinion: Due to similarities in driver mutations including epigenetic enzymes, JAK-STAT pathway activation and mutated checkpoint control through TP53, we hypothesize that similar therapeutic approaches could be of benefit in these diseases. We give an overview of how driver mutations in these malignancies contribute to hematopoietic cancer initiation or progression, and how these pathways can be targeted with currently available tools.

New Insights into Lymphoma Pathogenesis

Lymphomas represent clonal proliferations of lymphocytes that are broadly classified based upon their maturity (peripheral or mature versus precursor) and lineage (B cell, T cell, and natural killer cell). Insights into the pathogenetic mechanisms involved in lymphoma impact the classification of lymphoma and have significant implications for the diagnosis and clinical management of patients. Serial scientific and technologic advances over the last 30 years in immunology, cytogenetics, molecular biology, gene expression profiling, mass spectrometry-based proteomics, and, more recently, next-generation sequencing have contributed to greatly enhance our understanding of the pathogenetic mechanisms in lymphoma. Novel and emerging concepts that challenge our previously accepted paradigms about lymphoma biology and how these impact diagnosis, molecular testing, disease monitoring, drug development, and personalized and precision medicine for lymphoma are discussed.

Expression of the JAK/STAT Signaling Pathway in Bullous Pemphigoid and Dermatitis Herpetiformis

A family of eleven proteins comprises the Janus kinases (JAK) and signal transducers and activators of transcription (STAT) signaling pathway, which enables transduction of signal from cytokine receptor to the nucleus and activation of transcription of target genes. Irregular functioning of the cascade may contribute to pathogenesis of autoimmune diseases; however, there are no reports concerning autoimmune bullous diseases yet to be published. The aim of this study was to evaluate the expression of proteins constituting the JAK/STAT signaling pathway in skin lesions and perilesional area in dermatitis herpetiformis (DH) and bullous pemphigoid (BP), as well as in the control group. Skin biopsies were collected from 21 DH patients, from 20 BP patients, and from 10 healthy volunteers. The localization and expression of selected STAT and JAK proteins were examined by immunohistochemistry and immunoblotting. We found significantly higher expression of JAK/STAT proteins in skin lesions in patients with BP and DH, in comparison to perilesional skin and the control group, which may be related to proinflammatory cytokine network and induction of inflammatory infiltrate in tissues. Our findings suggest that differences in the JAK and STAT expression may be related to distinct cytokines activating them and mediating neutrophilic and/or eosinophilic infiltrate.

HIV-1-mediated insertional activation of STAT5B and BACH2 trigger viral reservoir in T regulatory cells

HIV-1 insertions targeting BACH2 or MLK2 are enriched and persist for decades in hematopoietic cells from patients under combination antiretroviral therapy. However, it is unclear how these insertions provide such selective advantage to infected cell clones. Here, we show that in 30/87 (34%) patients under combination antiretroviral therapy, BACH2, and STAT5B are activated by insertions triggering the formation of mRNAs that contain viral sequences fused by splicing to their first protein-coding exon. These chimeric mRNAs, predicted to express full-length proteins, are enriched in T regulatory and T central memory cells, but not in other T lymphocyte subsets or monocytes. Overexpression of BACH2 or STAT5B in primary T regulatory cells increases their proliferation and survival without compromising their function. Hence, we provide evidence that HIV-1-mediated insertional activation of BACH2 and STAT5B favor the persistence of a viral reservoir in T regulatory cells in patients under combination antiretroviral therapy.

HIV insertions in hematopoietic cells are enriched in BACH2 or MLK2 genes, but the selective advantages conferred are unknown. Here, the authors show that BACH2 and additionally STAT5B are activated by viral insertions, generating chimeric mRNAs specifically enriched in T regulatory cells favoring their persistence.

JAK/STAT disruption induces immuno-deficiency: Rationale for the development of JAK inhibitors as immunosuppressive drugs

Cytokines are mediating immune cells responses through the activation of the JAK/STAT signaling pathway. Being critical for immune cells, a defective JAK/STAT signaling leads to various immune disorders, such as immunodeficiency. In contrast, hyperactivation of JAK/STAT signaling is linked to autoimmunity and cancer. Targeting the JAK/STAT proteins by small protein inhibitors impedes immune cell function by uncoupling cells from cytokine effects and by interfering with functional immune cell hallmarks, such as cell migration. This review will explore immune syndromes driven by JAK/STAT deregulation and discuss the emerging role of JAK inhibitors as immunosuppressive drugs used in autoimmunity and transplantation medicine.

The Challenges of Precision Medicine and New Advances in Molecular Diagnostic Testing in Hematolymphoid Malignancies: Impact on the VHA

The Hematopathology Molecular Genetics subcommittee presents recommendations for molecular diagnostic testing in acute myeloid leukemia, myeloproliferative neoplasms, myelodysplastic syndrome, and lymphomas and for the development of an interfacility consultation service.

Clinicopathologic Characterization of Aggressive Natural Killer Cell Leukemia Involving Different Tissue Sites

Aggressive natural killer cell leukemia (ANKL) is a rare disease with an extremely aggressive clinical course. The etiology of ANKL is unclear with few genetic/epigenetic aberrations described to date. Moreover, misdiagnosis of ANKL is a frequent problem. Clinicopathologic characteristics of 35 retrospective cases of ANKL were investigated with the aim of improving diagnosis and to find the genetic/epigenetic aberrations associated with ANKL etiology. Because of the relatively low number of leukemic cells in the peripheral blood and bone marrow, diagnosis of ANKL can be missed; therefore, it is important to perform biopsy on solid tissues, if necessary. We describe the pathology of ANKL in the lymph nodes, bone marrow, spleen, liver, and skin, with focus on diagnosis and differentiated diagnosis. We observed young male predominance in our cohort, and the clinical course was more aggressive than reported previously. Low lactate dehydrogenase (<712 IU/L), chemotherapy or L-asparaginase administration were found to be associated with more favorable outcomes. SH2 domains of STAT5B and STAT3 also were screened for the presence of activating mutations. Moreover, CpG island methylation status of HACE1, a candidate tumor-suppressor gene, was determined in ANKL samples. We observed activating STAT5B mutations (1/5) and hypermethylation of HACE1 (3/4) in ANKL cases, suggesting that these aberrations may contribute to ANKL pathogenesis.

EBV-negative Aggressive NK-cell Leukemia/Lymphoma: Clinical, Pathologic, and Genetic Features

Aggressive natural killer cell leukemia (ANKL) is a systemic NK-cell neoplasm, almost always associated with Epstein-Barr virus (EBV). Rare cases of EBV-negative ANKL have been described, and some reports suggested more indolent behavior. We report the clinicopathologic, immunophenotypic, and molecular characteristics of 7 EBV-negative ANKL. All patients were adults, with a median age of 63 years (range 22 to 83 y) and an M:F ratio of 2.5:1. Five patients were White, 1 Black, and 1 Asian. All patients presented acutely, with fever (6/7), cytopenias (6/7), and splenomegaly (4/7). Four patients had lymphadenopathy, 4 had extranodal disease. Bone marrow involvement was present in 5, with hemophagocytosis in 3. Peripheral blood was involved in 5 with the neoplastic cells containing prominent azurophilic granules. By immunohistochemistry and/or flow cytometry, the tumor cells lacked surface CD3 and were positive for CD56 (7/7), CD2 (5/5), CD8 (3/7), CD30 (4/5), and granzyme-B (6/6). They were negative for CD4, CD5, βF1, TCRγ, LMP1, and EBV-encoded RNA. Polymerase chain reaction for TCRG clonality was polyclonal. Mutational analysis revealed missense mutations in the STAT3 gene in both cases studied. Median survival was 8 weeks from the onset of disease. One patient received allogeneic bone marrow transplant and is alive with no disease (follow-up 15 mo). EBV-negative ANKL exists but is rare. It tends to occur in older patients and is indistinguishable clinically and pathologically from EBV-positive ANKL, with a similar fulminant clinical course. The high prevalence of Asian patients seen with EBV-positive disease seems less evident with EBV-negative cases.

STAT3 mutation impacts biological and clinical features of T-LGL leukemia

STAT3 mutations have been described in 30-40% of T-large granular lymphocyte (T-LGL) leukemia patients, leading to STAT3 pathway activation. Considering the heterogeneity of the disease and the several immunophenotypes that LGL clone may express, the aim of this work was to evaluate whether STAT3 mutations might be associated with a distinctive LGL immunophenotype and/or might be indicative for specific clinical features. Our series of cases included a pilot cohort of 101 T-LGL leukemia patients (68 CD8+/CD4- and 33 CD4+/CD8±) from Padua Hematology Unit (Italy) and a validation cohort of additional 20 patients from Rennes Hematology Unit (France). Our results indicate that i) CD8+ T-LGL leukemia patients with CD16+/CD56- immunophenotype identify a subset of patients characterized by the presence of STAT3 mutations and neutropenia, ii) CD4+/CD8± T-LGL leukemia are devoid of STAT3 mutations but characterized by STAT5b mutations, and iii) a correlation exists between STAT3 activation and presence of Fas ligand, this molecule resulting highly expressed in CD8+/CD16+/CD56- patients. Experiments with stimulation and inhibition of STAT3 phosphorylation confirmed this relationship. In conclusion, our data show that T-LGL leukemia with specific molecular and phenotypic patterns is associated with discrete clinical features contributing to get insights into molecular bases accounting for the development of Fas ligand-mediated neutropenia.

Somatic mutations in clonally expanded cytotoxic T lymphocytes in patients with newly diagnosed rheumatoid arthritis

Somatic mutations contribute to tumorigenesis. Although these mutations occur in all proliferating cells, their accumulation under non-malignant conditions, such as in autoimmune disorders, has not been investigated. Here, we show that patients with newly diagnosed rheumatoid arthritis have expanded CD8+ T-cell clones; in 20% (5/25) of patients CD8+ T cells, but not CD4+ T cells, harbour somatic mutations. In healthy controls (n=20), only one mutation is identified in the CD8+ T-cell pool. Mutations exist exclusively in the expanded CD8+ effector-memory subset, persist during follow-up, and are predicted to change protein functions. Some of the mutated genes (SLAMF6, IRF1) have previously been associated with autoimmunity. RNA sequencing of mutation-harbouring cells shows signatures corresponding to cell proliferation. Our data provide evidence of accumulation of somatic mutations in expanded CD8+ T cells, which may have pathogenic significance for RA and other autoimmune diseases.

Accumulation of somatic mutations in lymphocytes is a feature of some cancers. Here the authors show that patients with recent onset of rheumatoid arthritis also accumulate mutations in their expanded CD8+ effector memory T cell pool independent of cancer association.

Mechanisms and consequences of Jak-STAT signaling in the immune system

Kinases of the Jak ('Janus kinase') family and transcription factors (TFs) of the STAT ('signal transducer and activator of transcription') family constitute a rapid membrane-to-nucleus signaling module that affects every aspect of the mammalian immune system. Research on this paradigmatic pathway has experienced breakneck growth in the quarter century since its discovery and has yielded a stream of basic and clinical insights that have profoundly influenced modern understanding of human health and disease, exemplified by the bench-to-bedside success of Jak inhibitors ('jakinibs') and pathway-targeting drugs. Here we review recent advances in Jak-STAT biology, focusing on immune cell function, disease etiology and therapeutic intervention, as well as broader principles of gene regulation and signal-dependent TFs.

Dysregulated signaling, proliferation and apoptosis impact on the pathogenesis of TCRγδ+ T cell large granular lymphocyte leukemia

TCRγδ+ T-LGL leukemia is a rare form of chronic mature T cell disorders in elderly, which is generally characterized by a persistently enlarged CD3+CD57+TCRγδ+ large granular lymphocyte population in the peripheral blood with a monoclonal phenotype. Clinically, the disease is heterogeneous, most patients being largely asymptomatic, although neutropenia, fatigue and B symptoms and underlying diseases such as autoimmune diseases or malignancies are also often observed. The etiology of TCRγδ+ T-LGL proliferations is largely unknown. Here, we aimed to investigate underlying molecular mechanisms of these rare proliferations by performing gene expression profiling of TCRγδ+ T-LGL versus normal TCRγδ+ T cell subsets. From our initial microarray dataset we observed that TCRγδ+ T-LGL leukemia forms a separate group when compared with different healthy control TCRγδ+ T cell subsets, correlating best with the healthy TemRA subset. The lowest correlation was seen with the naive subset. Based on specific comparison between healthy control cells and TCRγδ+ T-LGL leukemia cells we observed up-regulation of survival, proliferation and hematopoietic system related genes, with a remarkable down-regulation of apoptotic pathway genes. RQ-PCR validation of important genes representative for the dataset, including apoptosis (XIAP, CASP1, BCLAF1 and CFLAR), proliferation/development (ID3) and inflammation (CD28, CCR7, CX3CR1 and IFNG) processes largely confirmed the dysregulation in proliferation and apoptosis. Based on these expression data we conclude that TCRγδ+ T-LGL leukemia is likely the result of an underlying aberrant molecular mechanisms leading to increased proliferation and reduced apoptosis.

Disorders of the JAK/STAT Pathway in T Cell Lymphoma Pathogenesis: Implications for Immunotherapy

Common gamma receptor-dependent cytokines and their JAK/STAT pathways play pivotal roles in T cell immunity. Abnormal activation of this system was pervasive in diverse T cell malignancies assessed by pSTAT3/pSTAT5 phosphorylation. Activating mutations were described in some but not all cases. JAK1 and STAT3 were required for proliferation and survival of these T cell lines whether or not JAKs or STATs were mutated. Activating JAK and STAT mutations were not sufficient to initiate leukemic cell proliferation but rather only augmented signals from upstream in the cytokine pathway. Activation required the full pathway, including cytokine receptors acting as scaffolds and docking sites for required downstream JAK/STAT proteins. JAK kinase inhibitors have depressed leukemic T cell line proliferation. The insight that JAK/STAT system activation is pervasive in T cell malignancies suggests novel therapeutic approaches that include antibodies to common gamma cytokines, inhibitors of cytokine-receptor interactions, and JAK kinase inhibitors that may revolutionize therapy for T cell malignancies.

Lymphoma classification update: T-cell lymphomas, Hodgkin lymphomas, and histiocytic/dendritic cell neoplasms

INTRODUCTION

Lymphomas are classified based on the normal counterpart, or cell of origin, from which they arise. Because lymphocytes have physiologic immune functions that vary both by lineage and by stage of differentiation, the classification of lymphomas arising from these normal lymphoid populations is complex. Recent genomic data have contributed additional depth to this complexity. Areas covered: Lymphoma classification follows the World Health Organization (WHO) system, which reflects international consensus and is based on pathological, genetic, and clinical factors. The present review focuses on the classification of T-cell lymphomas, Hodgkin lymphomas, and histiocytic and dendritic cell neoplasms, summarizing changes reflected in the 2016 revision to the WHO classification. These changes are critical to hematologists and other clinicians who care for patients with these disorders. Expert commentary: Lymphoma classification is a continually evolving field that needs to be responsive to new clinical, pathological, and molecular understanding of lymphoid neoplasia. Among the entities covered in this review, the 2016 revisions in the WHO classification particularly impact T-cell lymphomas, including a new umbrella category of T-follicular helper cell-derived lymphomas and evolving recognition of indolent T-cell lymphomas and lymphoproliferative disorders.