Mastocytosis: an unusual clonal disorder of bone marrow-derived hematopoietic progenitor cells

Description and Characterization of Three-Dimensional Human Mast Cell Progenitor Spheroids In Vitro

Human mast cells (MC) are an essential component of the immune system as they uniquely store and release a wide range of soluble mediators through IgE and non-IgE mechanisms. Several tissue sources can be used to differentiate functional MC for in vitro and in vivo studies. Here we describe an improved method for obtaining large numbers of human MC from adipose tissue with advantages over current methods. We analyzed donor parameters (e.g. age, race) on MC-isolation following adipose and skin tissue digestion from healthy donors. Adipose and skin-derived MC were morphologically and immunophenotypically similar in all donors regardless of age. However, donor-dependent variations in MC numbers were observed following tissue digestion. In addition, we identified and characterized three-dimensional structures from which mature MC emerged in vitro using peripheral blood and human tissue sources. MC progenitor spheroids (MCPS) appeared approximately one week following progenitor isolation and were consistently observed to have mature MC attached, emerging, or nearby when cultured in a stem cell factor-containing medium. The overall characteristics of the MCPS were similar from each tissue source. We propose that these MCPS serve as the common source of human MC in vitro.

Protease profile of normal and neoplastic mast cells in the human bone marrow with special emphasis on systemic mastocytosis

Mast cells (MC) are immune cells that produce a variety of mediators, such as proteases, that are important in the body's immune responses. MC proteases have pronounced multifunctionality and in many respects determine the biological characteristics of the organ-specific MC population. Although, increased numbers of MC are one of the objective mastocytosis signs, a detailed assessment of the proteases biogenesis and excretion mechanisms in the bone marrow (BM) has not yet been carried out. Here, we performed an analysis of the expression of proteases in patients with various forms of systemic mastocytosis. We presented data on intracellular protease co-localization in human BM MCs and discussed their implication in secretory pathways of MCs in the development of the disease. Systemic mastocytosis, depending on the course, is featured by the formation of definite profiles of specific proteases in various forms of atypical mast cells. Intragranular accumulation of tryptase, chymase and carboxypeptidases in the hypochromic phenotype of atypical mast cells is characterized. Characterization of MC proteases expression during mastocytosis can be used to refine the MC classification, help in a prognosis, and increase the effectiveness of targeted therapy.

Classic Hodgkin lymphoma with initial extranodal osseous presentation: a case report and literature review

Initial extranodal osseous presentation of Classic Hodgkin lymphoma (CHL) is extremely rare. The present study describes a case of CHL in an 11-year-old male presenting with lower back and right hip pain. Radiologic imaging showed a solitary lytic lesion involving the L5 vertebrae and sacrum. Pathologic examination led to a diagnosis of extranodal osseous CHL and further workup proved bone marrow and nodal disease. Diagnosis of extranodal osseous CHL is challenging, especially in this age group and location. When confronted with a solitary lytic bone lesion in a young patient, more common benign and neoplastic entities enter the differential diagnosis and include osteomyelitis, Langerhans cell histiocytosis, epithelioid hemangioma of bone, leukemia, and anaplastic large cell lymphoma (ALCL) among others, with extranodal osseous CHL being one of the less common entities in the differential diagnosis. This case report raises the awareness of extranodal osseous CHL as one of the entities to consider when confronted with a solitary lytic bone lesion in a young patient.

Splenomegaly: A Combined Clinical and Radiologic Approach to the Differential Diagnosis

An enlarged spleen (splenomegaly) is a common imaging finding and may be related to a broad array of underlying conditions. The multifaceted functions of the spleen make it susceptible to involvement by a variety of pathophysiologic processes. Understanding these conditions and incorporating all relevant clinical and radiologic data allow narrowing the differential diagnosis.

A new humanized in vivo model of KIT D816V+ advanced systemic mastocytosis monitored using a secreted luciferase

Systemic mastocytosis are rare neoplasms characterized by accumulation of mast cells in at least one internal organ. The majority of systemic mastocytosis patients carry KIT D816V mutation, which activates constitutively the KIT receptor. Patient with advanced forms of systemic mastocytosis, such as aggressive systemic mastocytosis or mast cell leukemia, are poorly treated to date. Unfortunately, the lack of in vivo models reflecting KIT D816V+ advanced disease hampers pathophysiological studies and preclinical development of new therapies for such patients. Here, we describe a new in vivo model of KIT D816V+ advanced systemic mastocytosis developed by transplantation of the human ROSAKIT D816V-Gluc mast cell line in NOD-SCID IL-2R γ-/- mice, using Gaussia princeps luciferase as a reporter. Intravenous injection of ROSAKIT D816V-Gluc cells led, in 4 weeks, to engraftment in all injected primary recipient mice. Engrafted cells were found at high levels in bone marrow, and at lower levels in spleen, liver and peripheral blood. Disease progression was easily monitored by repeated quantification of Gaussia princeps luciferase activity in peripheral blood. This quantification evidenced a linear relationship between the number of cells injected and the neoplastic mast cell burden in mice. Interestingly, the secondary transplantation of ROSAKIT D816V-Gluc cells increased their engraftment capability. To conclude, this new in vivo model mimics at the best the features of human KIT D816V+ advanced systemic mastocytosis. In addition, it is a unique and convenient tool to study the kinetics of the disease and the potential in vivo activity of new drugs targeting neoplastic mast cells.

A fractal analysis of the spatial distribution of tumoral mast cells in lymph nodes and bone marrow

The spatial distribution of mast cells inside the tumor stroma has been little investigated. In this study, we have evaluated tumor mast cells distribution through the analysis of the morphological features of the spatial patterns generated by these cells, including size, shape, and architecture of the cell pattern. We have compared diffuse large B cells lymphoma (DLBCL) and systemic mastocytosis in two different anatomical localizations (lymph nodes for DLBCL and, respectively, bone marrow for mastocytosis). Results have indicated that, despite the high difference in size exhibited by the mast cells patterns in the two conditions, the spatial relationship between the mast cells forming the aggregates resulted similar, characterized by a significant tendency of the mast cells to self-organize in clusters.

Advances in anti-IgE therapy

Omalizumab depletes free IgE in the blood and interstitial space and inhibits IgE binding to FcεRI on basophils, mast cells, and dendritic cells. We stopped omalizumab treatment after four years. Recurrences of urticaria symptoms were found to be higher in patients with chronic urticaria than recurrences of asthmatic symptoms in severe persistent asthma patients. For the very first time, we used omalizumab in symptomatic therapy of recurrent laryngeal oedema and urticaria attacks in a patient with postoperative pulmonary carcinoid tumor for eight months. During the four years of follow-up, no recurrence was noted in pulmonary carcinoid tumor. Control PET CT results revealed normal findings. After omalizumab treatment, laryngeal oedema and urticaria symptoms were decreased. The most common adverse reaction from omalizumab is injection site induration, injection site itching, injection site pain, and bruising but the package insert contains warnings regarding parasitic infections. While there are no reports of fatal anaphylaxis as a result of omalizumab, some cases have been serious and potentially life-threatening. Therefore, the FDA requires that people receiving omalizumab be monitored in the physician's office for a period of time after their injections.

Mast cell leukemia: a review

SUMMARY 

Mast cell leukemia (MCL) is a rare subtype of systemic mastocytosis. In MCL the numbers of mast cells exceed 19% of nucleated cells in bone marrow and/or 10% of circulating leukocytes in peripheral blood. Primary MCL must be distinguished from secondary MCL evolving from another subvariant of systemic mastocytosis or from mast cell sarcoma. Acute MCL with a poor prognosis is distinguished from the more indolent chronic MCL. Serum tryptase is significantly elevated in almost all MCL patients and activating point mutations at codon 816 of KIT (usually KIT D816V) are encountered in about 70%. Regarding differential diagnosis, other ‘tryptase-positive’ or ‘metachromatic’ leukemias must be considered, including myelomastocytic leukemia and tryptase-positive acute myeloid leukemia but also acute and chronic basophilic leukemias.

An overview of the effects of anti-IgE therapies

Omalizumab, a humanized mAb that binds to the CH3 domain near the binding site for the high-affinity type-I IgE Fc receptors of human IgE, can neutralize free IgE and inhibit the IgE allergic pathway without sensitizing mast cells and basophils. We found that omalizumab in patients with severe persistent asthma (SPA) was an effective therapy for asthma and the following co-morbid conditions: chronic urticaria (CU), bee venom allergy, latex allergy, atopic dermatitis, food allergy and Samter's syndrome. Information on the use of omalizumab in treatment of asthma and other allergic diseases has improved our understanding that treatment acts on many levels, including regulating levels of inflammatory proteins, including cytokines (copper-containing alpha- 2-glycoprotein, total antioxidant capacity, MDA, NO, H2O2, CXCL8, IL-10, TGF-β, GMCSF, IL-17, IL-1β), MPV, Hs-CRP, eosinophil cationic peptide, vitamin-D (25(OH)D), homocysteine (Hcy), OX-2, d- dimer, albumin, and sApo-2L. The decrease in Hcy concentrations and increase in 25(OH)D also support the existence of a vascular endothelial protection mechanism. Mediators and cells classically involved in pro-coagulant and anticoagulant pathways together play a role in SPA and CU pathophysiology and omalizumab effect. The mechanism of action of omalizumab in the treatment of asthma is believed to be multifactorial, and includes effects mediated through altered production of redox metabolites, extrinsic coagulation pathway, oxidative markers-related mi RNA, TRAIL-related mi RNA, and regulation of production of known inflammatory proteins.

Elevated levels of mast cells are involved in pruritus associated with polycythemia vera in JAK2V617F transgenic mice

Pruritus occurs frequently in patients with polycythemia vera (PV), and the pathophysiology of PV-associated pruritus is unclear. We have previously demonstrated that transgenic mice expressing JAK2V617F displayed clear PV-like phenotypes. In the current study, we found frequent occurrence of pruritus with aged JAK2V617F transgenic mice and further investigated the underlying mechanisms by studying mast cells, key players in allergic reactions and anaphylaxis. Massive accumulations of mast cells were observed in the skin of pruritic JAK2V617F transgenic mice. In vitro culture yielded much higher mast cell counts from the bone marrow, spleen, peripheral blood, and peritoneal cavity of JAK2V617F transgenic mice than from controls. Cultured mast cells from JAK2V617F transgenic mice exhibited enhanced proliferative signals, relative resistance to cell death upon growth factor deprivation, and a growth advantage over control cells under suboptimal growth conditions. However, these mast cells displayed normal morphology and contained normal levels of mast cell proteases before and after degranulation. Finally, the JAK2 inhibitor G6 effectively reduced mast cell numbers and alleviated pruritus in JAK2V617F transgenic mice. Collectively, these data demonstrate that mast cells are involved in PV-associated pruritogenesis and that JAK2 inhibitors are potential antipruritus drugs.

A new human mast cell line expressing a functional IgE receptor converts to tumorigenic growth by KIT D816V transfection

In systemic mastocytosis (SM), clinical problems arise from factor-independent proliferation of mast cells (MCs) and the increased release of mediators by MCs, but no human cell line model for studying MC activation in the context of SM is available. We have created a stable stem cell factor (SCF) -dependent human MC line, ROSA(KIT WT), expressing a fully functional immunoglobulin E (IgE) receptor. Transfection with KIT D816V converted ROSA(KIT WT) cells into an SCF-independent clone, ROSA(KIT D816V), which produced a mastocytosis-like disease in NSG mice. Although several signaling pathways were activated, ROSA(KIT D816V) did not exhibit an increased, but did exhibit a decreased responsiveness to IgE-dependent stimuli. Moreover, NSG mice bearing ROSA(KIT D816V)-derived tumors did not show mediator-related symptoms, and KIT D816V-positive MCs obtained from patients with SM did not show increased IgE-dependent histamine release or CD63 upregulation. Our data show that KIT D816V is a disease-propagating oncoprotein, but it does not activate MCs to release proinflammatory mediators, which may explain why mediator-related symptoms in SM occur preferentially in the context of a coexisting allergy. ROSA(KIT D816V) may provide a valuable tool for studying the pathogenesis of mastocytosis and should facilitate the development of novel drugs for treating SM patients.

Systemic mastocytosis accompanied by a non-secretory plasma cell dyscrasia and nephrotic syndrome-level proteinuria in a 76-year-old patient

We report here the interesting case of a 76-year-old man with severe proteinuria who was diagnosed with systemic mastocytosis accompanied by a clonal non-mast-cell lineage haematological disorder (a non-secretory plasma cell dyscrasia). This is a unique report of systemic mastocytosis with a non-secretory plasma cell dyscrasia and nephrotic syndrome. The pathophysiological relevance between these entities along with the probability of occult amyloidosis is discussed.

Advanced systemic mastocytosis: the impact of KIT mutations in diagnosis, treatment, and progression

Apart from indolent systemic mastocytosis (SM), which is associated with a favorable prognosis, other subtypes of SM (SM with associated clonal hematologic non–mast cell lineage disease, aggressive SM, and mast cell leukemia – collectively referred to in this review as advanced SM) can be debilitating. The complexity of SM makes both the diagnosis and design of response criteria challenging for clinical studies. The tyrosine kinase KIT has been shown to play a crucial role in the pathogenesis of SM and has been a focal point in the development of targeted therapy. Mutations within various domains of the KIT receptor that lead to constitutive activation have been identified in patients, and those involving the activation loop of the KIT receptor are the mutations most frequently detected in patients with mastocytosis. Aberrant activation of the KIT receptor results in increased production of mast cells in extracutaneous organs that may lead to organ failure or early death. This review discusses the diagnosis and management of patients with advanced SM, including the relevance of KIT in this disease, potential therapies targeting this kinase, and criteria for measuring responses to these therapies.

Mastocytosis in children and adults: clinical disease heterogeneity

Mastocytosis is a clonal disease of the hematopoietic stem cell. The condition consists of a heterogeneous group of disorders characterized by a pathological accumulation of mast cells in tissues including the skin, bone marrow, liver, spleen and the lymph nodes. Mastocytosis is a rare disease which occurs both in children and adults. Childhood onset mastocytosis is usually cutaneous and transient while in adults the condition commonly progresses to a systemic form. The heterogeneity of clinical presentation of mastocytosis is typically related to the tissue mast cell burden, symptoms due to the release of mast cell mediators, the type of skin lesions, the patient's age at the onset and associated haematological disorders. Therefore, a multidisciplinary approach is recommended. The present article provides an overview of clinical symptoms, diagnostic criteria and treatment of mastocytosis to facilitate the diagnosis and management of mastocytosis patients in clinical practice.

CADM1 isoforms differentially regulate human mast cell survival and homotypic adhesion

Cell adhesion molecule 1 (CADM1), expressed by human lung mast cells (HLMCs), mediates their adhesion to airway smooth muscle (ASM), and contributes to ASM-dependent HLMC proliferation and survival. CADM1 is expressed in alternatively spliced isoforms, but those present in HLMCs and their function are not known. We cloned three functional and one cryptic non-functional isoform with alternative splicing between exons 7/11 and 1/2, respectively, from HLMCs and human MC lines (HMC-1 and LAD2). Differentiated HLMCs and LAD2 cells expressed the functional isoform SP4 containing exons 7/8/11 (~80% of clones), as well as SP1 (exons 7/8/9/11) and a novel SP6 (exons 7/8/9/10/11). In contrast, immature HMC-1 cells expressed only functional SP4. SP4 overexpression in HMC-1 cells and HLMCs augmented homotypic adhesion to a greater extent than SP1 in various conditions. In contrast, CADM1 downregulation abolished homotypic adhesion, indicating that CADM1 is the sole receptor mediating mast cell aggregation. CADM1-mediated adhesion was enhanced by the presence of cell survival factors. SP1 overexpression in HMC-1 cells compromised survival compared to SP4 overexpression or control. CADM1 downregulation resulted in reduced viability and decreased expression of the pro-survival protein Mcl-1_L, but not Blc-2 or Bcl-X_L, and increased caspase-3/7 activity in both HMC-1 cells and HLMCs. This coincided with decreased basal Kit levels in HLMCs. In summary, human MCs express multiple CADM1 isoforms which exhibit differential regulation of survival and homotypic adhesion. The most highly expressed SP4 isoform is likely to contribute to MC aggregation and longevity in mastocytosis, and augment the pathophysiology of allergic diseases.

Neuropeptide blood levels correlate with mast cell load in patients with mastocytosis

BACKGROUND

Mastocytosis is characterized by abnormal growth and accumulation of mast cells (MCs) in different organs. MCs have been shown to express receptors for neuropeptides. Furthermore, neuropeptides can activate MCs inducing cytokine production and MC mediator release, which further contribute to MC chemotaxis and stimulate the release of vasoactive peptides from sensory nerves. Thus, a contribution of neuropeptides to mastocytosis seems highly conceivable, but has not been investigated sufficiently yet. This study aimed to analyse blood levels of the neuropeptides substance P (SP), somatostatin (SST), vasoactive intestinal peptide (VIP), calcitonine gene--related peptide (CGRP) and expression of the SP receptor NK-1R in the skin of patients with mastocytosis (n = 46) compared to healthy controls (n = 69).

METHODS

Substance P, SST, VIP and CGRP plasma levels were analysed by ELISA, serum tryptase levels with the UniCAP System and NK-1R expression in the skin by immunohistochemistry.

RESULTS

Plasma levels of SP (P < 0.0001), SST, (P = 0.007), VIP (P < 0.0001) and CGRP (P = 0.003) were significantly increased in patients with mastocytosis compared to controls. Tryptase serum levels correlated significantly with neuropeptide levels, implying a link between MC load and neuropeptide blood levels in mastocytosis. NK-1R was expressed on the majority of MCs, and NK-1R-positive cells were increased in lesional mastocytosis skin compared to control skin (P = 0.01).

CONCLUSIONS

Elevated blood levels of the neuropeptides SP, SST, VIP and CGRP correlate with MC load and together with an increased expression of NK-1R in the skin of patients with mastocytosis indicate a role of neuropeptides in the pathophysiology of mastocytosis.

Tyrosine kinase inhibitors in the treatment of systemic mastocytosis

Systemic mastocytosis (SM) is a heterogeneous disease, vast majority of these patients have a gain of function mutation in the gene encoding the tyrosine kinase KIT (KIT(D816V)). A small subset of SM patients with KIT(D816V) mutation require cytoreductive therapy. In these patients, tyrosine kinase inhibitors (TKIs) have been actively investigated over the last decade because of codon 816 KIT mutations causing constitutive activation of tyrosine kinase activity of the molecule. The main question has been whether the success story with imatinib in chronic myeloid leukemia (CML), another disease associated with a constitutively active tyrosine kinase, could be mimicked in mastocytosis. However, the results from various TKIs in SM with KIT(D816V) mutation have been disappointing to date. Only a few of the TKIs sufficiently block KIT(D816V) activity and have shown promising clinical results. The data from these studies indicate that, apart from KIT(D816V), other kinase targets and target pathways may play a role in disease evolution and progression, especially in patients with SM with an associated clonal hematological non-mast cell lineage disease (SM-AHNMD). Imatinib is effective in patients with increased mast cells and eosinophils associated with FIP1L1/PDGFRA+ (e.g., myeloid neoplasm with eosinophilia and rearrangement of PDGFRA) or rare patients with SM associated with KIT mutations outside of exon 17. This review will focus on the KIT receptor, KIT mutations, and the effects of the mutations in SM. The preclinical and clinical activities of FDA approved TKIs (for CML) as well as novel TKIs in SM will be evaluated.

Systemic Mastocytosis

An unusual disease, mastocytosis challenges the pathologist with a variety of morphologic appearances and heterogeneous clinical presentations ranging from skin manifestations (pruritus, urticaria, dermatographism) to systemic signs and symptoms indicative of mast cell mediator release, including flushing, hypotension, headache, and anaphylaxis among others. In this article, we focus on recognizing the cytology, histopathology, clinical features, and prognostic implications of systemic mastocytosis, a clonal and neoplastic mast cell proliferation infiltrating extracutaneous organ(s) with or without skin involvement. Diagnostic pitfalls are reviewed with ancillary studies to help unmask the mast cell and exclude morphologic mimics.

Lesional and nonlesional skin from patients with untreated juvenile dermatomyositis displays increased numbers of mast cells and mature plasmacytoid dendritic cells

OBJECTIVE

To investigate the distribution of mast cells and dendritic cell (DC) subsets in paired muscle and skin (lesional/nonlesional) from untreated children with juvenile dermatomyositis (DM).

METHODS

Muscle and skin biopsy samples (4 skin biopsy samples with active rash) from 7 patients with probable/definite juvenile DM were compared with muscle and skin samples from 10 healthy pediatric controls. Mast cell distribution and number were assessed by toluidine blue staining and analyzed by Student's t-test. Immunohistochemical analysis was performed to identify mature DCs, myeloid DCs (MDCs), and plasmacytoid DCs (PDCs) by using antibodies against DC-LAMP, blood dendritic cell antigen 1 (BDCA-1), and BDCA-2, respectively. Myxovirus resistance protein A (MxA) staining indicated active type I interferon (IFN) signaling; positive staining was scored semiquantitatively and analyzed using the Mann-Whitney U test.

RESULTS

Both inflamed and nonlesional skin from patients with juvenile DM contained more mast cells than did skin from pediatric controls (P = 0.029), and comparable numbers of mast cells were present in lesional and nonlesional skin. Interestingly, mast cell numbers were greater in skin than in paired muscle tissue from patients with juvenile DM (P = 0.014) and were not increased in muscle from patients with juvenile DM compared with control muscle. Both muscle and skin from patients with juvenile DM showed more mature PDCs and MxA staining than did their corresponding control tissues (P < 0.05). In both muscle and skin from patients with juvenile DM and in pediatric control muscle, there were fewer MDCs than PDCs, and the distributions of MDCs and PDCs were similar in pediatric control skin samples.

CONCLUSION

The identification of mast cells in skin (irrespective of rash) from patients with juvenile DM, but not in paired muscle tissue, suggests that they have a specific role in juvenile DM skin pathophysiology. In skin from patients with juvenile DM, increased numbers of PDCs and increased expression of type I IFN-induced protein suggest a selective influence on T cell differentiation and subsequent effector function.