Mast Cell-Targeting Therapies in Mast Cell Activation Syndromes

PURPOSE OF REVIEW

Provide an overview of the expanding landscape of mast cell (MC)-targeting treatments in mast cell activation syndromes (MCAS).

RECENT FINDINGS

Tyrosine-kinase inhibitors (TKIs) targeting wild-type and mutated KIT can efficiently induce MC depletion. Avapritinib and midostaurin can also temper IgE-mediated degranulation. Avapritinib has been recently approved by the FDA for the treatment of indolent systemic mastocytosis (ISM). Targeting activation pathways and inhibitory receptors is a promising therapeutic frontier. Recently, the anti Siglec-8 antibody lirentelimab showed promising results in ISM. MCAS is a heterogeneous disorder demanding a personalized therapeutic approach and, especially when presenting as anaphylaxis, has not been formally captured as outcome in prospective clinical trials with TKI. Long-term safety of TKI needs to be addressed. New drugs under investigation in diseases in which non-neoplastic MCs play a pivotal role can provide important inputs to identify new efficient and safe treatments for MCAS.

The Expressions of CD30 and CD123 of Mastocytosis in Taiwan

Mastocytosis is a rare disease with a low incidence in Asia-Pacific populations. CD30 and CD123 may have potential prognostic and therapeutic value, but the results are inconsistent. Because racial disparities may exist, we aim to evaluate the expressions of CD30 and CD123 in a series of mastocytosis cases in Taiwan. Twelve patients with systemic and 7 with cutaneous forms of mastocytosis were studied. The expressions of CD30 and CD123 were correlated with the clinical features of the patients. Eighty-three percent (10/12) of patients with systemic mastocytosis (SM) had an associated hematological neoplasm. Four of the SM patients had both "B" and "C" findings, and they had a median survival time of 0.9 months. CD30 expression was positive in 50% (6/12) of SM cases and 100% (6/6) of cutaneous mastocytosis cases. CD123 was expressed focally or weakly in only 2 SM-associated hematological neoplasm cases. The distribution of mastocytosis subtypes and the expression of CD30 and CD123 in Taiwan differed from those reported in North America and Europe. However, mastocytosis, especially indolent forms, is easily overlooked as its heterogeneous and nonspecific clinical manifestations. A high index of suspicion and improved diagnostic methods can be helpful.

Refined diagnostic criteria for bone marrow mastocytosis: a proposal of the European competence network on mastocytosis

In the current classification of the World Health Organization (WHO), bone marrow mastocytosis (BMM) is a provisional variant of indolent systemic mastocytosis (ISM) defined by bone marrow involvement and absence of skin lesions. However, no additional diagnostic criteria for BMM have been proposed. Within the registry dataset of the European Competence Network on Mastocytosis, we compared characteristics and outcomes of 390 patients with BMM and 1175 patients with typical ISM. BMM patients were significantly older, predominantly male, had lower tryptase and lower burden of neoplastic mast cells, and displayed a higher frequency of allergic reactions, mainly triggered by Hymenoptera, than patients with typical ISM. The estimated 10-year progression-free survival of BMM and typical ISM was 95.9% and 92.6%, respectively. In BMM patients defined by WHO-based criteria, the presence of one B-Finding and tryptase level ≥125 ng/mL were identified as risk factors for progression in multivariate analyses. BMM patients without any of these risk factors were found to have better progression-free survival (p < 0.05) and better overall survival (p < 0.05) than other ISM patients. These data support the proposal to define BMM as a separate SM variant characterized by SM criteria, absence of skin lesions, absence of B-Findings, and tryptase levels <125 ng/mL.

GlcNAc is a mast-cell chromatin-remodeling oncometabolite that promotes systemic mastocytosis aggressiveness

Systemic mastocytosis (SM) is a KIT-driven hematopoietic neoplasm characterized by the excessive accumulation of neoplastic mast cells (MCs) in various organs and, mainly, the bone marrow (BM). Multiple genetic and epigenetic mechanisms contribute to the onset and severity of SM. However, little is known to date about the metabolic underpinnings underlying SM aggressiveness, which has thus far impeded the development of strategies to leverage metabolic dependencies when existing KIT-targeted treatments fail. Here, we show that plasma metabolomic profiles were able to discriminate indolent from advanced forms of the disease. We identified N-acetyl-d-glucosamine (GlcNAc) as the most predictive metabolite of SM severity. High plasma levels of GlcNAc in patients with advanced SM correlated with the activation of the GlcNAc-fed hexosamine biosynthesis pathway in patients BM aspirates and purified BM MCs. At the functional level, GlcNAc enhanced human neoplastic MCs proliferation and promoted rapid health deterioration in a humanized mouse model of SM. In addition, in the presence of GlcNAc, immunoglobulin E-stimulated MCs triggered enhanced release of proinflammatory cytokines and a stronger acute response in a mouse model of passive cutaneous anaphylaxis. Mechanistically, elevated GlcNAc levels promoted the transcriptional accessibility of chromatin regions that contain genes encoding mediators of receptor tyrosine kinases cascades and inflammatory responses, thus leading to a more aggressive phenotype. Therefore, GlcNAc is an oncometabolite driver of SM aggressiveness. This study suggests the therapeutic potential for targeting metabolic pathways in MC-related diseases to manipulate MCs effector functions.

Mast cell differentiation of leukemic blasts in diverse myeloid neoplasms: A potential pre-myelomastocytic leukemia condition

INTRODUCTION

Myeloid neoplasm with blasts showing mast cell (MC)-differentiation and MC-component less than 10% of all nucleated cells but not fulfilling the criteria for systemic mastocytosis with associated hematological neoplasm (SM-AHN) or myelomastocytic leukemia (MML) has not been described in the literature. Herein, we report a study of diverse myeloid malignancies with blasts showing MC-differentiation but not meeting the criteria for SM-AHN or MML. We also evaluated the utility of flow-cytometric immunophenotyping (FCI) in the characterization of immature-MCs (iMCs).

METHODS

We identified nine patients of myeloid neoplasms and studied their morphological, FCI, immunohistochemistry, cytogenetic and molecular characteristics. We also compared the immunophenotypic features of MCs from patient samples with control samples.

RESULTS

The study included patients with newly-diagnosed acute myeloid leukemia (n = 4), chronic myelomonocytic leukemia (n = 1), and chronic myeloid leukemia on follow-up (n = 4) showing MC differentiation in leukemic-blasts. These patients had mildly increased MCs (range, 0.5%-3%) in bone-marrow morphology, including immature-forms and did not meet the criteria for either SM-AHN or MML. On FCI, iMCs were positive for bright-CD117, heterogeneous-CD34, dim-to-negative-HLADR, and moderate-CD203c expression. Expression-levels of CD123 and CD38 were higher (p < 0.001) but CD33 and CD45 were lower in iMCs compared to mature-MC from control samples (p = 0.019 and p = 0.0037).

CONCLUSION

We reported a rare finding of MC differentiation of leukemic blasts in diverse myeloid neoplasms and proposed it as a potential pre-myelomastocytic leukemia condition. We described the distinct immunophenotypic signature of immature-MCs using commonly used markers and highlighted the utility of FCI for the diagnosis of this entity.

Clinical Impact of Inherited and Acquired Genetic Variants in Mastocytosis

Mastocytosis is a rare and complex disease characterized by expansion of clonal mast cells (MC) in skin and/or various internal organ systems. Involvement of internal organs leads to the diagnosis of systemic mastocytosis (SM). The WHO classification divides SM into indolent SM, smoldering SM and advanced SM variants, including SM with an associated hematologic neoplasm, aggressive SM, and MC leukemia. Historically, genetic analysis of individuals with pure cutaneous mastocytosis (CM) and SM have focused primarily on cohort studies of inherited single nucleotide variants and acquired pathogenic variants. The most prevalent pathogenic variant (mutation) in patients with SM is KIT p.D816V, which is detectable in most adult patients. Other somatic mutations have also been identified-especially in advanced SM-in TET2, SRSF2, ASXL1, RUNX1, CBL and JAK2, and shown to impact clinical and cellular phenotypes. Although only small patient cohorts have been analyzed, disease associations have also been identified in several germline variants within genes encoding certain cytokines or their receptors (IL13, IL6, IL6R, IL31, IL4R) and toll-like receptors. More recently, an increased prevalence of hereditary alpha-tryptasemia (HαT) caused by increased TPSAB1 copy number encoding alpha-tryptase has been described in patients with SM. Whereas HαT is found in 3-6% of general Western populations, it is identified in up to 17% of patients with SM. In the current manuscript we review the prevalence, functional role and clinical impact of various germline and somatic genetic variants in patients with mastocytosis.

KIT D816 mutated/CBF-negative acute myeloid leukemia: a poor-risk subtype associated with systemic mastocytosis

KIT D816 mutations (KIT D816mut) are strongly associated with systemic mastocytosis (SM) but are also detectable in acute myeloid leukemia (AML), where they represent an adverse prognostic factor in combination with core binding factor (CBF) fusion genes. Here, we evaluated the clinical and molecular features of KIT D816mut/CBF-negative (CBFneg) AML, a previously uncharacterized combination. All KIT D816mut/CBFneg cases (n = 40) had histologically proven SM with associated AML (SM-AML). Molecular analyses revealed at least one additional somatic mutation (median, n = 3) beside KIT D816 (e.g., SRSF2, 38%; ASXL1, 31%; RUNX1, 34%) in 32/32 (100%) patients. Secondary AML evolved in 29/40 (73%) patients from SM ± associated myeloid neoplasm. Longitudinal molecular and cytogenetic analyses revealed the acquisition of new mutations and/or karyotype evolution in 15/16 (94%) patients at the time of SM-AML. Median overall survival (OS) was 5.4 months. A screen of two independent AML databases (AMLdatabases) revealed remarkable similarities between KIT D816mut/CBFneg SM-AML and KIT D816mut/CBFneg AMLdatabases (n = 69) with regard to KIT D816mut variant allele frequency, mutation profile, aberrant karyotype, and OS suggesting underlying SM in a significant proportion of AMLdatabases patients. Bone marrow histology and reclassification as SM-AML has important clinical implications regarding prognosis and potential inclusion of KIT inhibitors in treatment concepts.

Longitudinal Evaluation of Bone Mineral Density and Bone Metabolism Markers in Patients with Indolent Systemic Mastocytosis Without Osteoporosis

Systemic Mastocytosis has been long identified as a potential cause of osteoporosis; nevertheless, data regarding longitudinal variation of bone mineral density (BMD) in patients with indolent systemic mastocytosis (ISM) are missing . We studied BMD variation at lumbar spine and proximal hip after 30-month (±6 months) follow-up in a large cohort of patients (83) with ISM without osteoporosis, supplementated with vitamin D and/or calcium when needed. We also analyzed the correlation between variation of BMD, basal serum tryptase levels and bone turnover markers (BTM). Sixty-four percent of our population was male; mean age was 52.1 (±11.5) years. Vitamin D insufficiency (serum levels of 25-OH-vitamin D, 25OHD, lower than 75 nmol/L) was found in more than 70 % of patients. After a follow-up of 30 ± 6 months with only vitamin D (5000-7500 IU weekly of oral cholecalciferol) or calcium (500 mg/die) supplementation when needed, we observed 2.1 % increase in BMD at lumbar spine, with no significant changes at hip. At the end of follow-up, almost 60 % of patients showed 25OHD serum levels still lower than recommended, despite vitamin D supplementation. Reduction in BMD after follow-up significantly correlated with high C-telopeptide of type I collagen serum levels at the time of diagnosis. In patients with ISM without osteoporosis, a routinary BMD evaluation within a time <2 years is not justified, except in the presence of elevated BTM. In these patients, vitamin D supplementation is frequently needed.

Well-differentiated systemic mastocytosis showed excellent clinical response to imatinib in the absence of known molecular genetic abnormalities: A case report

INTRODUCTION

Well-differentiated systemic mastocytosis (WDSM) is a rare, recently recognized provisional subvariant of systemic mastocytosis (SM). We report a case of WDSM that showed excellent clinical and cutaneous response to imatinib in the absence of known molecular genetic abnormalities.

CLINICAL FINDINGS/DIAGNOSES

We present a 24-year-old woman with childhood onset of skin manifestations that progressed to mediator-related systemic events, and a gastrointestinal tract mastocytoma. A subsequent bone marrow examination showed WDSM. Treatment with imatinib resulted in complete resolution of cutaneous lesions and systemic symptoms, which relapsed with the discontinuation of the drug. Targeted next-generation sequencing-based mutation analysis did not demonstrate any mutations in the coding regions of KIT or other genes commonly associated with myeloid neoplasms.

CONCLUSIONS

The diagnosis of WDSM is challenging in the absence of spindle-shaped mast cells, CD2 or CD25 expression, and KIT D816 mutation. This case illustrated the need for recognizing this unique variant of SM for diagnostic and therapeutic implications.

Endocrine manifestations of systemic mastocytosis in bone

Systemic Mastocytosis (SM) is characterized by accumulation of clonal, neoplastic proliferations of abnormal mast cells (MC) in one or more organ system other than skin. Presence of these multifocal clusters of abnormal mast cells is an essential feature of SM. Frequently associated with D816V (KIT) mutation, the presence of this mutation and elevated serum tryptase are minor criteria for diagnosis. SM manifestations depend on the degree of mast cell proliferation, activation and degranulation. SM has a variable prognosis and presentation, from indolent to "smoldering" to life-threatening disease. Bone manifestations of SM include: osteopenia with or without lytic lesions, osteoporosis with or without atraumatic fracture, osteosclerosis with increased bone density, and isolated lytic lesions. Male sex, older age, higher bone resorption markers, lower DKK1 level, lower BMD, absence of urticaria pigmentosa, and alcohol intake are all associated with increased risk of fracture. Treatment of SM is generally palliative. Most therapy is symptom-directed; and, infrequently, chemotherapy for refractory symptoms is indicated. Anti-histamines may alleviate direct bone effects of histamine. Bisphosphonates, including alendronate, clodronate, pamidronate and zoledronic acid are recommended as a first line treatment of SM and osteoporosis. Interferon α may act synergistically with bisphosphonates. As elevation of RANKL and OPG is reported in SM, denosumab could be an effective therapy for bone manifestations of SM.

Pharmacological treatment options for mast cell activation disease

Mast cell activation disease (MCAD) is a term referring to a heterogeneous group of disorders characterized by aberrant release of variable subsets of mast cell (MC) mediators together with accumulation of either morphologically altered and immunohistochemically identifiable mutated MCs due to MC proliferation (systemic mastocytosis [SM] and MC leukemia [MCL]) or morphologically ordinary MCs due to decreased apoptosis (MC activation syndrome [MCAS] and well-differentiated SM). Clinical signs and symptoms in MCAD vary depending on disease subtype and result from excessive mediator release by MCs and, in aggressive forms, from organ failure related to MC infiltration. In most cases, treatment of MCAD is directed primarily at controlling the symptoms associated with MC mediator release. In advanced forms, such as aggressive SM and MCL, agents targeting MC proliferation such as kinase inhibitors may be provided. Targeted therapies aimed at blocking mutant protein variants and/or downstream signaling pathways are currently being developed. Other targets, such as specific surface antigens expressed on neoplastic MCs, might be considered for the development of future therapies. Since clinicians are often underprepared to evaluate, diagnose, and effectively treat this clinically heterogeneous disease, we seek to familiarize clinicians with MCAD and review current and future treatment approaches.

The role of Lin28b in myeloid and mast cell differentiation and mast cell malignancy

Mast cells (MCs) are critical components of the innate immune system and important for host defense, allergy, autoimmunity, tissue regeneration and tumor progression. Dysregulated MC development leads to systemic mastocytosis (SM), a clinically variable but often devastating family of hematologic disorders. Here we report that induced expression of Lin28, a heterochronic gene and pluripotency factor implicated in driving a fetal hematopoietic program, caused MC accumulation in adult mice in target organs such as the skin and peritoneal cavity. In vitro assays revealed a skewing of myeloid commitment in LIN28B-expressing hematopoietic progenitors, with increased levels of LIN28B in common myeloid and basophil-MC progenitors altering gene expression patterns to favor cell fate choices that enhanced MC specification. In addition, LIN28B-induced MCs appeared phenotypically and functionally immature, and in vitro assays suggested a slowing of MC terminal differentiation in the context of LIN28B upregulation. Finally, interrogation of human MC leukemia samples revealed upregulation of LIN28B in abnormal MCs from patients with SM. This work identifies Lin28 as a novel regulator of innate immune function and a new protein of interest in MC disease.

Metabolomics approach in allergic and rheumatic diseases

Metabolomics is the analysis of the concentration profiles of low molecular weight compounds present in biological fluids. Metabolites are nonpeptide molecules representing the end products of cellular activity. Therefore, changes in metabolite concentrations reveal the range of biochemical effects induced by a disease or its therapeutic intervention. Metabolomics has recently become feasible with the accessibility of new technologies, including mass spectrometry and high-resolution proton nuclear magnetic resonance, and has already been applied to several disorders. Indeed, it has the advantage of being a nontargeted approach for identifying potential biomarkers, which means that it does not require a preliminary knowledge of the substances to be studied. In this review, we summarize the main studies in which metabolomic approach was used in some allergic (asthma, atopic dermatitis) and rheumatic diseases (rheumatoid arthritis, systemic lupus erythematosus) to explore the feasibility of this technique as a novel diagnostic tool in these complex disorders.

Loss of function of TET2 cooperates with constitutively active KIT in murine and human models of mastocytosis

Systemic Mastocytosis (SM) is a clonal disease characterized by abnormal accumulation of mast cells in multiple organs. Clinical presentations of the disease vary widely from indolent to aggressive forms, and to the exceedingly rare mast cell leukemia. Current treatment of aggressive SM and mast cell leukemia is unsatisfactory. An imatinib-resistant activating mutation of the receptor tyrosine kinase KIT (KIT D816V) is most frequently present in transformed mast cells and is associated with all clinical forms of the disease. Thus the etiology of the variable clinical aggressiveness of abnormal mast cells in SM is unclear. TET2 appears to be mutated in primary human samples in aggressive types of SM, suggesting a possible role in disease modification. In this report, we demonstrate the cooperation between KIT D816V and loss of function of TET2 in mast cell transformation and demonstrate a more aggressive phenotype in a murine model of SM when both mutations are present in progenitor cells. We exploit these findings to validate a combination treatment strategy targeting the epigenetic deregulation caused by loss of TET2 and the constitutively active KIT receptor for the treatment of patients with aggressive SM.

Systemic mastocytosis with associated myeloproliferative neoplasm with t(8;19)(p12;q13.1) and abnormality of FGFR1: report of a unique case

Systemic mastocytosis is a neoplastic proliferation of mast cells that frequently presents with associated clonal hematological non-mast cell lineage disease. Myeloid and lymphoid neoplasms with abnormalities of the FGFR1 gene are a heterogenous group of rare and aggressive hematopoietic stem cell disorders. About a dozen of chromosome changes involving the FGFR1 gene, presenting as myeloid or lymphoid neoplasms, have been described in the literature. To date, only 2 cases of myeloid and lymphoid neoplasms with abnormalities of the FGFR1 gene have been reported in association with systemic mastocytosis, one with t(8;13) and one with t(8;17) involving the FGFR1 gene. Here we describe another case of myeloproliferative neoplasm with chromosome translocation t(8;19) involving FGFR1 gene associated with systemic mastocytosis.

Ki-67 proliferation index in renal biopsy samples of patients with systemic lupus erythematosus and its correlation with clinical findings

INTRODUCTION

Systemic lupus erythematosus is an autoimmune disease that may affect almost all organ systems. Renal involvement is the most significant prognostic factor. Renal biopsy findings play an important role in treatment decision. Ki-67 is a monoclonal antibody that is only found in proliferative cells. This study aimed to investigate the proliferative activity in renal biopsy specimens of patients with lupus nephritis using the Ki-67 monoclonal antibody, and to compare the proliferative index between different subgroups of patients.

MATERIALS AND METHODS

Renal biopsy specimens of 29 patients with systemic lupus erythematosus were retrospectively evaluated. Type of lupus nephritis and activity and chronicity indexes were determined. Ki-67 immunostaining was performed. For each patient, 1000 cells were counted and the number of Ki-67 positive cells was determined. The Ki-67 activity index was compared between different subgroups of lupus nephritis and correlated with systemic lupus erythematosus disease activity index, serum creatinine, proteinuria, anticardiolipin antibodies, and complement levels.

RESULTS

A positive correlation between Ki-67 proliferation index, serum creatinine levels, and systemic lupus erythematosus disease activity index were found. Although conventional activity indexes were low, in 3 of 9 patients with class II lupus nephritis, Ki-67 proliferation indexes were high, indicating proliferation.

CONCLUSIONS

Ki-67 can be used as a proliferation marker in renal biopsy specimens for patients diagnosed with systemic lupus erythematosus.

Polo-like kinase-1 as a novel target in neoplastic mast cells: demonstration of growth-inhibitory effects of small interfering RNA and the Polo-like kinase-1 targeting drug BI 2536

BACKGROUND

In advanced systemic mastocytosis the response of neoplastic mast cells to conventional drugs is poor and the prognosis is bad. Current research is, therefore, attempting to identify novel drug targets in neoplastic mast cells. Polo-like kinase-1 is a serine/threonine kinase that plays an essential role in mitosis and has recently been introduced as a new target in myeloid leukemias and solid tumors.

DESIGN AND METHODS

In the present study, we analyzed the expression and function of Polo-like kinase-1 in neoplastic mast cells in systemic mastocytosis.

RESULTS

As determined by immunostaining, primary neoplastic mast cells as well as the human mast cell leukemia cell line HMC-1 displayed phosphorylated Polo-like kinase-1. In addition, neoplastic mast cells expressed Polo-like kinase-1 mRNA. Polo-like kinase-1-specific small interfering RNA induced apoptosis in neoplastic mast cells, whereas no effect was seen with a control small interfering RNA. BI 2536, a drug targeting Polo-like kinase-1, was found to inhibit proliferation in HMC-1 cells in a dose-dependent manner. BI 2536 also inhibited the growth of primary neoplastic mast cells and cells of the canine mastocytoma cell line C2. The growth-inhibitory effects of BI 2536 on neoplastic mast cells were found to be associated with mitotic arrest and subsequent apoptosis. Finally, BI 2536 was found to synergize with the KIT-targeting kinase inhibitor midostaurin (PKC412) in inhibiting the growth of neoplastic mast cells. In control experiments, BI 2536 did not induce apoptosis in normal cultured mast cells.

CONCLUSIONS

Collectively, our data show that Polo-like kinase-1 is a potential therapeutic target in neoplastic mast cells. Targeting Polo-like kinase-1 may be an attractive pharmacological concept in the management of advanced systemic mastocytosis.

Interleukin-9 (IL-9) and NPM-ALK each generate mast cell hyperplasia as single 'hit' and cooperate in producing a mastocytosis-like disease in mice

Mast cell neoplasms are characterized by abnormal growth and focal accumulation of mast cells (MC) in one or more organs. Although several cytokines, including stem cell factor (SCF) and interleukin-9 (IL-9) have been implicated in growth of normal MC, little is known about pro-oncogenic molecules and conditions triggering differentiation and growth of MC far enough to lead to the histopathological picture of overt mastocytosis. The anaplastic lymphoma kinase (ALK) has recently been implicated in growth of neoplastic cells in malignant lymphomas. Here, we describe that transplantation of NPM-ALK-transplanted mouse bone marrow progenitors into lethally irradiated IL-9 transgenic mice not only results in lymphoma-formation, but also in the development of a neoplastic disease exhibiting histopathological features of systemic mastocytosis, including multifocal dense MC-infiltrates, occasionally with devastating growth in visceral organs. Transplantation of NPM-ALK-transduced progenitors into normal mice or maintenance of IL-9-transgenic mice without NPM-ALK each resulted in MC hyperplasia, but not in mastocytosis. Neoplastic MC in mice not only displayed IL-9, but also the IL-9 receptor, and the same was found to hold true for human neoplastic MC. Together, our data show that neoplastic MC express IL-9 receptors, that IL-9 and NPM-ALK upregulate MC-production in vivo, and that both'hits' act in concert to induce a mastocytosis-like disease in mice. These data may have pathogenetic and clinical implications and fit well with the observation that neoplastic MC in advanced SM strongly express NPM and multiple "lymphoid" antigens including CD25 and CD30.

Tryptase is not cleared by the kidneys into the urine

BACKGROUND

Patients with chronic kidney disease have been reported to have increased concentrations of blood tryptase. Detection of tryptase in the urine of healthy subjects has been reported.

OBJECTIVE

The objective is to determine whether tryptase is indeed cleared by the kidneys.

METHODS

Blood and urine collections were performed in healthy and systemic mastocytosis subjects. Total and mature tryptase concentrations in blood and total tryptase concentrations in urine were determined.

RESULTS

Total tryptase levels in urine were below the limit of detection in both healthy subjects and those with systemic mastocytosis, even after concentrating the urine 10-fold. Thus, both mature and protryptase levels in urine are <0.2 ng/ml.

CONCLUSION

Tryptase is not cleared by the kidneys into the urine.

Biochemical diagnosis of systemic mast cell disorders

Systemic mastocytosis is characterized by an abnormal proliferation of tissue mast cells. Symptoms of mastocytosis are primarily attributed to the release of mast cell mediators during episodes of systemic activation of the excessive numbers of mast cells. Thus, biochemical evidence for the release of increased quantities of mast cell secretory products can suggest or confirm, depending on the clinical situation, a diagnosis of systemic mastocytosis. A major advantage of the biochemical approach to the diagnosis of systemic mast cell disease is that it has allowed the recognition of a class of patients in whom episodes of systemic mastocyte activation can be unequivocally documented biochemically but in whom clear-cut evidence of abnormal mast cell proliferation is lacking by current histologic criteria. Although the release of increased quantities of mast cell mediators can be demonstrated during episodes of mast cell activation in such patients, mediator levels are usually normal at quiescent times. By contrast, patients with proliferative mast cell disease (mastocytosis) usually exhibit chronic overproduction of mast cell mediators. Mast cell secretory products that can be measured in an attempt to obtain biochemical evidence of systemic mast cell activation include histamine, prostaglandin D2, tryptase, and heparin. The analytical approaches to assessing release of those individual mast cell products are evaluated. In general, the diagnosis and investigation of patients with systemic mast cell activation can best be accomplished by concerted use of histologic examination of key tissues together with analysis of chemical markers of the mast cell.

Identification of MCL1 as a novel target in neoplastic mast cells in systemic mastocytosis: inhibition of mast cell survival by MCL1 antisense oligonucleotides and synergism with PKC412

MCL-1 is a Bcl-2 family member that has been described as antiapoptotic in various myeloid neoplasms. Therefore, MCL-1 has been suggested as a potential new therapeutic target. Systemic mastocytosis (SM) is a myeloid neoplasm involving mast cells (MCs) and their progenitors. In the present study, we examined the expression and functional role of MCL-1 in neoplastic MCs and sought to determine whether MCL-1 could serve as a target in SM. As assessed by RT-PCR and immunohistochemical examination, primary neoplastic MCs expressed MCL-1 mRNA and the MCL-1 protein in all SM patients examined. Moreover, MCL-1 was detectable in both subclones of the MC line HMC-1--HMC-1.1 cells, which lack the SM-related KIT mutation D816V, and HMC-1.2 cells, which carry KIT D816V. Exposure of HMC-1.1 cells or HMC-1.2 cells to MCL-1-specific antisense oligonucleotides (ASOs) or MCL-1-specific siRNA resulted in reduced survival and increased apoptosis compared with untreated cells. Moreover, MCL-1 ASOs were found to cooperate with various tyrosine kinase inhibitors in producing growth inhibition in neoplastic MCs, with synergistic effects observed with PKC412, AMN107, and imatinib in HMC-1.1 cells and with PKC412 in HMC-1.2 cells. Together, these data show that MCL-1 is a novel survival factor and an attractive target in neoplastic MCs.

Juxtamembrane-type c-kit gene mutation found in aggressive systemic mastocytosis induces imatinib-resistant constitutive KIT activation

Aggressive systemic mastocytosis (ASM) is a very rare form of mast cell neoplasm that does not benefit from conventional chemotherapy. The majority of adult mast cell neoplasms and gastrointestinal stromal tumors (GISTs) have mutations in the proto-oncogene c-kit, which encodes the KIT receptor tyrosine kinase. The c-kit gene mutations are generally confined to the tyrosine kinase II domain in mast cell neoplasms, but are often observed at the juxtamembrane domain in GISTs. We found a case of ASM with a juxtamembrane-type mutation, Val559Ile, and in this report the mutation was characterized through transfection of the mutated c-kit cDNA into human embryonic kidney cells. Phosphorylation of KIT and its possible downstream signaling molecules were examined in the presence or absence of imatinib, a selective tyrosine kinase inhibitor. Ligand-independent autophosphorylation was observed in the mutant KIT with Val559Ile as well as that with Val559Asp, as found in GISTs. Imatinib, at a concentration of 10 microM, inhibited autophosphorylation of the mutant KIT with Val559Asp, but not that with the Val559Ile. Phosphorylation of MAPK and STAT5 was also inhibited by imatinib at the same concentration, in cells expressing Val559Asp but not in those expressing Val559Ile. These results suggest that different mutations, even at the same codon, in juxtamembrane domain of the c-kit gene show different inhibitory effects of imatinib, and that patients with GISTs or mast cell neoplasms possessing this Val559Ile mutation are resistant to imatinib therapy.

Novel approaches in the treatment of systemic mastocytosis

In the absence of curative options, therapy for aggressive forms of systemic mastocytosis (SM) has relied in the use of cytoreductive agents, mainly interferon-alpha (IFN-alpha) and cladribine. However, responses are transient and only occur in a subset of patients. Gain-of-function mutations at codon 816 of the KIT protooncogene lead to constitutively active Kit receptor molecules, which are central to the pathogenesis of SM. Recent advances in the understanding of the molecular underpinnings of SM have led to the development of small molecules targeting mutant Kit tyrosine kinase isoforms that significantly have widened the range of therapeutic options for patients with SM. Some of these promising agents, such as dasatinib, AMN107, and PKC412, currently are under investigation in clinical trials whereas, others are at different stages of preclinical development. In addition, monoclonal antibodies directed to neoplastic mast cell-restricted surface antigens constitute a viable option for the treatment of SM that warrants further investigation.

Urticaria pigmentosa and mastocytosis: the role of immunophenotyping in diagnosis and determining response to treatment

Recent advances in our understanding of mast cell biology and disease resulted in identification of important differences in expression of mast cell surface antigens in normal and neoplastic mast cells. Most notably, detection of aberrant expression of CD25 and CD2 on the surface of neoplastic mast cells but not on their normal counterparts leads to the inclusion of this immunophenotypic abnormality in the World Health Organization's diagnostic criteria for systemic mastocytosis. Aberrant mast cell surface marker expression can be detected in the bone marrow aspirate by flow cytometry, even in patients with limited disease that lacks histopathologically detectable aggregates of mast cells in bone marrow biopsy sections. Flow cytometric analysis of bone marrow mast cells is therefore a sensitive method of diagnosis of mast cell disease and is expected to find increasing use in determining response to emerging mast cell cytoreductive therapies.

Delineation of patterns of bone marrow mast cell infiltration in systemic mastocytosis: value of CD25, correlation with subvariants of the disease, and separation from mast cell hyperplasia

In most cases, the diagnosis of systemic mastocytosis (SM) is based on histomorphologic evaluation of the bone marrow. We analyzed mast cell (MC) infiltration patterns in 57 cases of SM and 31 cases of mast cell hyperplasia (MCH). Tryptase immunohistochemical analysis was used for MC detection and CD25 to distinguish neoplastic from normal MCs. The following infiltration patterns were found: I, diffuse interstitial; II, focal, dense; III, focal, dense with an additional diffuse component, located preferentially around focal infiltrates; IV, focal, dense with an additional diffuse component evenly distributed throughout; and V, diffuse, dense. In 29 cases of MCH, MCs formed the type I pattern. The majority of SM cases exhibited patterns II to V; type IV was the most frequent (n = 36). Type V was seen in 3 cases of MC leukemia and 1 case of smoldering SM. In 1 case of SM, type I infiltration was found; the SM diagnosis was based on 3 minor SM criteria. Our data show that the infiltration pattern in SM correlates with the disease subtype and should be recognized as an important aspect in the histomorphologic evaluation of the bone marrow.

Vesicular monoamine transporter 2 (VMAT2) expression in hematopoietic cells and in patients with systemic mastocytosis

Uptake of monoamines into secretory granules is mediated by the vesicular monoamine transporters VMAT1 and VMAT2. In this study, we analyzed their expression in inflammatory and hematopoietic cells and in patients suffering from systemic mastocytosis (SM) and chronic myelogenous leukemia (CML). Normal human and monkey tissue specimens and tissues from patients suffering from SM and CML were analyzed by means of immunohistochemistry, radioactive in situ hybridization, real time RT-PCR, double fluorescence confocal laser scanning microscopy, and immunoelectron microscopy. In normal tissue specimens, VMAT2, but not VMAT1, was expressed in mast cells, megakaryocytes, thrombocytes, basophil granulocytes, and cutaneous Langerhans cells. Further hematopoietic and lymphoid cells showed no expression of VMATs. VMAT2 was expressed in all types of SM, as indicated by coexpression with the mast cell marker tryptase. In CML, VMAT2 expression was retained in neoplastic megakaryocytes and basophil granulocytes. In conclusion, the identification of VMAT2 in mast cells, megakaryocytes, thrombocytes, basophil granulocytes, and cutaneous Langerhans cells provides evidence that these cells possess molecular mechanisms for monoamine storage and handling. VMAT2 identifies normal and neoplastic mast cells, megakaryocytes, and basophil granulocytes and may therefore become a valuable tool for the diagnosis of mastocytosis and malignant systemic diseases involving megakaryocytes and basophil granulocytes.

The faces of mast cell disease: bone marrow infiltrates in 3 patients with systemic mastocytosis

The clinical spectrum of mast cell disease ranges from relatively innocuous and histologically subtle urticarial skin lesions to an aggressive and fatal leukemic form of mast cell proliferation. Not surprisingly, mast cell infiltrates may show significant microscopic heterogeneity, particularly in the bone marrow, the most common site of involvement in systemic mastocytosis (SM). Herein, 3 cases are presented to illustrate the clinical and morphologic heterogeneity of mast cell disease: the first patient, with long standing urticaria pigmentosa, developed anemia and thrombocytopenia; the second patient presented with a pathologic fracture; and the third patient was suspected to have refractory anemia. Upon bone marrow examination, all 3 patients showed mast cell infiltration with distinct morphologic features and all met the WHO criteria for aggressive systemic mastocytosis. Histochemical methods continue to play a role in the identification of mast cells, with some limitations depending on the degree of differentiation of the mast cells and tissue processing methods. Immunohistochemistry has contributed to the identification of mast cells. Coexpression of CD117 and CD25, as well as expression of the more specific immunohistochemical marker tryptase, is seen in systemic SM. The latter may also be employed as a serum marker in the diagnosis and follow-up of patients with SM. The mast cells, in the majority adults with SM, have somatic point mutations of KIT.

Evaluation of normal and neoplastic human mast cells for expression of CD172a (SIRPα), CD47, and SHP-1

Signal regulatory proteins (SIRPs) and tyrosine phosphatases have recently been implicated in the control of receptor tyrosine kinase (RTK)-dependent cell growth. In systemic mastocytosis (SM), neoplastic cells are driven by the RTK KIT, which is mutated at codon 816 in most patients. We examined expression of SIRPalpha, SIRPalpha ligand CD47, and Src homology 2 domain-containing protein tyrosine phosphatase-1 (SHP-1), a tyrosine phosphatase-type, negative regulator of KIT-dependent signaling, in normal human lung mast cells (HLMC) and neoplastic MC obtained from nine patients with SM. As assessed by multicolor flow cytometry, normal LMC expressed SIRPalpha, CD47, and SHP-1. In patients with SM, MC also reacted with antibodies against SIRPalpha and CD47. By contrast, the levels of SHP-1 were low or undetectable in MC in most cases. Corresponding data were obtained from mRNA analysis. In fact, whereas SIRPalpha mRNA and CD47 mRNA were detected in all samples, the levels of SHP-1 mRNA varied among donors. To demonstrate adhesive functions for SIRPalpha and CD47 on neoplastic MC, an adhesion assay was applied using the MC leukemia cell line HMC-1, which was found to bind to immobilized extracellular domains of SIRPalpha1 (SIRPalpha1ex) and CD47 (CD47ex), and binding of these cells to CD47ex was inhibited by the CD172 antibody SE5A5. In summary, our data show that MC express functional SIRPalpha and CD47 in SM, whereas expression of SHP-1 varies among donors and is low compared with LMC. It is hypothesized that CD172 and CD47 contribute to MC clustering and that the "lack" of SHP-1 in MC may facilitate KIT-dependent signaling in a subgroup of patients.

Clonality and molecular pathogenesis of mastocytosis

Mast cell is a hematopoietic lineage dependent on Kit signaling for growth, differentiation, and survival. Mast cells are found in excessive numbers in tissues in a heterogeneous group of disorders collectively known as mastocytosis. Last decade has witnessed important advancements in our understanding of the molecular pathology of mastocytosis. First, systemic mastocytosis has been found to be associated with activating codon 816 mutations of the c-kit gene. Second, this mutation was used as a tracking marker to elucidate the clonal nature of mastocytosis. These findings have resulted in consideration of systemic mastocytosis as a clonal neoplastic disorder of a hematopoietic progenitor cell. Improved knowledge of the mechanisms causing pathological mast cell growth will lead to the discovery of novel treatment options including drugs targeting the mutated Kit protein.

A novel NF-kappaB inhibitor, IMD-0354, suppresses neoplastic proliferation of human mast cells with constitutively activated c-kit receptors

Constitutive phosphorylation of c-kit tyrosine kinase is the major cause of factor-independent proliferation of mast cells. Recently available tyrosine kinase inhibitors have shown marked activity against mast cell lines that carry wild-type c-kit, and some, but not others, carry mutant c-kit. Here we clearly demonstrated that a novel NF-kappaB inhibitor, IMD-0354, restrained factor-independent proliferation of mast cells with c-kit mutations but not of normal mast cells. In HMC-1 cells with the Asp816Val and Val560Gly mutations, we found that NF-kappaB was constitutively activated without exogenous stimulation. When the DNA-binding activity of NF-kappaB was inhibited by treatment with IMD-0354, cell proliferation was completely suppressed. We detected the expression of cyclin D2, D3, and E in HMC-1 cells and observed that cyclin D3 expression was dramatically decreased by treatment with IMD-0354. Abolishing protein kinase C or phosphatidylinositol 3 kinase pathways also inhibited NF-kappaB translocation to the nucleus, indicating the involvement of these signaling cascades in NF-kappaB activation in HMC-1 cells. Our findings indicated that autophosphorylated c-kit receptors induced NF-kappaB activation, resulting in the up-regulation of cyclin D3 expression and cell cycle progression. The observations from the current study suggest a therapeutic potential, in systemic mastocytosis, for compounds that interfere with NF-kappaB signaling.

CD25 Indicates the Neoplastic Phenotype of Mast Cells

The diagnosis of systemic mastocytosis (SM) is based primarily on the histologic and immunohistochemical evaluation of a bone marrow trephine biopsy specimen. Although mast cell (MC) specific antigens like tryptase and chymase are detectable in routinely processed tissue, no immunohistochemical markers that can be used to discriminate between normal and neoplastic MCs are yet available. We have investigated the diagnostic value of an antibody against CD25 for the immunohistochemical detection of MCs in bone marrow sections in 73 patients with SM and 75 control cases (reactive marrow, n = 54; myelogenous neoplasms, n = 21) and correlated the results with the presence of c-kit mutations. While MCs in almost all patients with SM (72 of 73) expressed CD25, none of the control samples contained CD25-positive MCs. Irrespective of the SM subtype, most of neoplastic MCs expressed CD25. In 3 patients with advanced MC disease, pure populations of neoplastic MCs were obtained and found to express CD25 mRNA by RT-PCR analysis. In addition, all patients with CD25-positive MCs contained c-kit mutations, while all control cases exhibited wild type c-kit. CD25 therefore appears to be a reliable immunohistochemical marker for the discrimination of neoplastic from normal/reactive MCs, with potential as a diagnostic tool in SM.

I?B? is expressed in mast cells

IkappaBgamma (IkappaBgamma) is a 70-kDa protein that is encoded by the C-terminal part of the NF-kappaB p105 gene and acts as an inhibitor of the transcription factor NF-kappaB. Until now, IkappaBgamma expression has only been described in cell-culture models of B-lymphocytes and enterocytes but not in tissues. In a model of radiation-induced pulmonary damage, we found that mast cells accumulating after irradiation are the only cells in the rat lung that are positive for IkappaBgamma. The mast cells were characterised by their metachromatic staining with toluidine blue and by double immunofluorescence labelling with mast-cell tryptase. Western blotting revealed that the lung mast cells expressed the 70-kDa form of IkappaBgamma cytoplasmatically and that no alternative splicing variants were expressed. In addition, we studied 11 cases of systemic mastocytosis, as well as 5 cases of mast-cell hyperplasia. In all cases, the mast cells stained strongly with IkappaBgamma. Rat peritoneal mast cells also contained high levels of IkappaBgamma. Since NF-kappaB is an important regulator of mast-cell functions, IkappaBgamma is likely to play a central role in the maintenance of the mast-cell phenotype and possibly in the modification of mast-cell-dependent immune responses.

Cladribine therapy for systemic mastocytosis

Patients with systemic mastocytosis (SM) can suffer from disabling symptoms related to mast cell mediator release or mast cell infiltration, requiring mast cell eradication. In the present absence of any curative therapy, a recent case report describing the efficacy of cladribine showed promising results. In a pilot study, the efficacy of cladribine (0.10-0.13 mg/kg in a 2-hour infusion, days 1-5; repeated at 4-8 weeks until 6 cycles) was studied. Ten patients with SM with severe symptoms were treated. Four patients were classified as having indolent or smoldering mastocytosis, 3 as having aggressive systemic mastocytosis, and 3 as having SM with an accompanying hematologic malignancy. Nine patients received 6 courses, 1 patient stopped because of toxicodermia. All responded concerning signs, symptoms, and mast cell parameters (serum tryptase and urinary histamine metabolite excretion), although none achieved a complete remission. Prolonged follow-up is required, as response is ongoing in most cases. One patient relapsed within 11 months and showed a second response. Side effects were mainly related to bone marrow suppression. Single-agent cladribine is an effective and relatively safe treatment for severe systemic mastocytosis. The optimal dose and schedule need to be explored.

Expression of Bcl-2 and Bcl-xL in cutaneous and bone marrow lesions of mastocytosis

Mastocytosis is a rare disease characterized by accumulation of mast cells in tissues. To investigate whether an altered regulation of mast cell apoptosis might be involved in the pathogenesis of mastocytosis, expression of the apoptosis-preventing molecules bcl-2 and bcl-xL was studied by immunohistochemistry in skin and bone marrow lesions of mastocytosis patients. In addition, reverse transcription-polymerase chain reaction was used to investigate levels of bcl-2 and bcl-xL mRNA in cutaneous mastocytosis lesions. Since activating mutations of c-kit are known to be associated with some forms of mastocytosis, human mast cell cultures were also stimulated via c-kit and the expression of bcl-2 and bcl-xL was assessed by immunoblotting. In patients with mastocytosis, the expression of bcl-2 protein but not bcl-xL in cutaneous mast cells was significantly enhanced, compared to healthy controls. Evaluating different subgroups of adult and pediatric mastocytosis patients, all groups were found to express significantly increased levels of bcl-2 protein, and none of the patient groups was found to overexpress bcl-xL, with the exception of solitary mastocytomas that showed a tendency for up-regulated bcl-xL protein. Furthermore, the expression of bcl-2 mRNA was significantly enhanced in cutaneous lesions of adult and pediatric patients, while bcl-xL mRNA levels were only slightly increased in pediatric, but not in adult patients with mastocytosis. In contrast to the skin lesions, bone marrow infiltrates of patients with systemic mastocytosis showed only low or absent immunoreactivity for bcl-2, but marked expression of bcl-xL. In vitro, stimulation of two different mast cell culture systems by activation of c-kit resulted in up-regulation of bcl-2 and also in an increase of bcl-xL, although less pronounced. Thus, overexpression of bcl-2 and bcl-xL leading to prolonged survival of mast cells may contribute to the pathogenesis of mastocytosis. Our findings may help to develop new strategies for the treatment of this disease.

Differential expression of CD2 on neoplastic mast cells in patients with systemic mast cell disease with and without an associated clonal haematological disorder

Recently, aberrant coexpression of CD2 and CD25 has been reported to reliably distinguish neoplastic mast cells from normal or so-called reactive mast cells. Such expression is included in the consensus diagnostic criteria for systemic mast cell disease (SMCD). In our study of patients with SMCD, we found CD2 expression to be more prevalent on mast cells from patients without an associated haematological disorder (P = 0.04). Furthermore, no correlation was found between mast cell CD2 expression and other clinicopathological features in these patients.

Treatment of adult systemic mastocytosis with interferon-alpha: results of a multicentre phase II trial on 20 patients

Systemic mastocytosis (SM) is characterized by proliferation of mast cells in various organs, which may release a wide variety of mediators, thereby explaining the broad clinical spectrum of disease manifestations. The potentially life-threatening systemic symptoms and tumoral proliferation are poorly controlled despite the use of several cytotoxic chemotherapies and/or symptomatic treatments. Twenty consecutive adult SM patients with histologically confirmed bone marrow (BM) involvement received interferon-alpha subcutaneously (1-5 million units/m2/d, with progressive dose intensification over the first month of treatment) and were evaluated after 6 months of therapy. Seven of them had previously received symptomatic treatments, including steroids, which were ineffective. Among the 13 patients treated for at least 6 months, seven partial and six minor responses, mainly concerning vascular congestion and skin lesions, were obtained, while BM infiltration remained unchanged in 12 patients. The significant reduction of mast-cell mediator levels after 6 months of treatment was not predictive of clinical remission. The rate of depression was unexpectedly high (seven patients; 35%). Two patients died soon after starting therapy (one myocardial infarction, one septic shock). Six months of interferon-alpha may relieve vascular congestion in adults with SM, probably by inhibiting mast-cell degranulation.