John-Hendrik Jordan

Mutation analysis of C-KIT in patients with myelodysplastic syndromes without mastocytosis and cases of systemic mastocytosis

The proto‐oncogene C‐KIT encodes a tyrosine kinase receptor that is expressed on mast cells and haematopoietic stem cells and can show somatic mutations in patients with mastocytosis. Only scattered information is available about mutations in C‐KIT in patients with other myeloid neoplasms. Moreover, the prevalence of mutations in C‐KIT in bone marrow specimens of individuals with systemic mastocytosis is largely unknown. Using sequence analysis, we have screened cDNAs of the C‐KIT domain encompassing codon 510–626 and codon 763–858 in bone marrow (BM) mononuclear cells (MNCs) of patients with myelodysplastic syndromes (n = 28) and patients with systemic mastocytosis (n = 12) for the presence of mutations. Furthermore, restriction fragment length polymorphism analysis was applied for identification of the C‐KIT 2468A→T and the C‐KIT 1700T→G mutation, as well as the C‐KIT 1642A→C polymorphism. All 11 patients with systemic indolent mastocytosis tested positive for C‐KIT 2468A→T. In contrast, no mutation was identified in the case of aggressive mastocytosis. Among patients with myelodysplastic syndromes, no patient showed a somatic mutation in C‐KIT. The allele frequency for C‐KIT 1642A→C among the entire patient population was 0·038 and was 0·125 among age‐ and sex‐matched healthy controls. Our data demonstrate that myelodysplastic syndromes without histological or cytological evidence of mastocytosis do not exhibit somatic mutations in exons 10, 11, 12, 16, 17 and 18 of C‐KIT. In contrast, BM MNCs of patients with systemic indolent mastocytosis were all positive for C‐KIT 2468A→T and negative for additional mutations in these exons. The C‐KIT 1642A→C polymorphism is not associated with myelodysplastic syndrome or systemic mastocytosis.

Serum Tryptase Levels in Patients with Mastocytosis: Correlation with Mast Cell Burden and Implication for Defining the Category of Disease

Background: The serum tryptase level is used as a diagnostic marker in mastocytosis and is considered to reflect the burden of (neoplastic) mast cells (MC). Methods: In the present study, serum tryptase levels were measured in patients with mastocytosis by fluoroenzyme immunoassay and compared with the extent of infiltration of the bone marrow (BM) by neoplastic MC, determined by tryptase immunohistochemistry. Sixteen patients with cutaneous mastocytosis (CM) and 43 patients with systemic mastocytosis (SM) were examined. Results: In most patients with CM (defined by the absence of dense compact MC infiltrates in tryptase-stained BM sections), normal or near-normal serum tryptase levels (median 10 ng/ml, range 2–23 ng/ml) were measured. By contrast, in the vast majority of patients with SM, elevated serum tryptase levels (median 67 ng/ml) were found. In addition, there was a significant correlation between the grade of infiltration of the BM by neoplastic MC and tryptase levels in patients with SM (r = 0.8). Moreover, enzyme levels differed significantly among the groups of patients with different types of SM. The highest levels (>900 ng/ml) were detected in the patient with MC leukemia, 2 patients with slowly progressing SM and high MC burden (smoldering SM) and 1 patient with indolent SM. In contrast, in all 3 patients with isolated BM mastocytosis (no skin lesions and no signs of multiorgan involvement), serum tryptase levels were <20 ng/ml. Conclusions: In summary, our data suggest that the measurement of serum tryptase is a reliable noninvasive diagnostic approach to estimate the burden of MC in patients with mastocytosis and to distinguish between categories of disease.

Serum tryptase measurements in patients with myelodysplastic syndromes.

Abnormal differentiation and maturation of hemopoietic cells are characteristic features of myelodysplastic syndromes (MDS). Tryptases (α- and β-type) are lineage-restricted serine proteases primarily expressed in mast cells (MC). We have analyzed expression of tryptase in 89 de novo MDS patients (refractory anemia (RA), n = 30; RA with ringed sideroblasts (RARS), n = 21; RA with excess of blasts (RAEB/RAEB-t), n = 27; chronic myelomonocytic leukemia (CMML), n = 11). Serum levels of total tryptase (α – protryptase + β – tryptase) were measured by FIA. The numbers of tryptase+ cells were determined in paraffin-embedded bone marrow (bm) sections by immunohistochemistry and morphometry. In healthy individuals, serum total tryptase levels ranged between < 1 and 15 ng/ml (5.6 ± 2.8 ng/ml). Tryptase levels of > 20 ng/ml were detected in 5/22 patients with RA (22.7%), 4/17 with RARS (23.5%), 0/16 with RAEB/RAEB-t, and 3/8 with CMML (37.5%). Thus, serum tryptase concentrations were higher in RA (16.6 ± 14.3 ng/ml), RARS (12.9 ± 8.2), and CMML (16.5 ± 7.6) compared to RAEB/-t (8.7 ± 3.8). By morphometry, elevated numbers of tryptase+ bm cells were detected in all MDS groups (RA: 139 ± 131; RARS: 118 ± 98; RAEB/RAEB-t: 80 ± 79; CMML: 105 ± 114 cells/mm2) compared to controls (54 ± 51 cells/mm2). As assessed by Northern blotting and protein analysis, bm cells in MDS primarily produced α-(pro)tryptase, but little or no β-tryptase. Together, our data show that elevated levels of tryptase are detectable in a group of patients with MDS probably because of an increase in neoplastic (mast) cells producing the enzyme(s). In addition, serum tryptase levels appear to correlate with MDS variants. Follow up studies should clarify whether an elevated tryptase concentration in MDS is of prognostic significance.

Activation of human mast cells through stem cell factor receptor (KIT) is associated with expression of bcl-2

Background: Mast cells (MCs) are multifunctional effector cells of the immune system. These cells originate from pluripotent hemopoietic progenitors. In contrast to basophils and other leukocytes, MCs exhibit a remarkably long life span (years) in vivo. Although a role for stem cell factor (SCF) and SCF receptor (KIT) in long-term survival of MCs has been proposed, the underlying biochemical mechanisms remain unknown. Materials and Methods:We have examined expression of ‘survival-related’ molecules of the bcl-2 family including bcl-2 and bcl-xL, in primary human MCs and the human MC line HMC-1. Primary MCs were isolated from dispersed lung tissue by cell sorting using an antibody against KIT. mRNA expression was analyzed by RT-PCR and Northern blotting. Results: As assessed by RT-PCR, purified unstimulated lung MCs (>98% pure) exhibited KIT- and bcl-xL mRNA, but did not express bcl-2 mRNA. However, exposure of lung MCS to SCF (100 ng/ml) for 8 h resulted in expression of bcl-2 mRNA. Corresponding results were obtained by immunocytochemistry. In fact, exposure of MC to SCF resulted in expression of the bcl-2 protein whereas unstimulated MCs displayed only the bcl-xL protein without expressing the bcl-2 protein. The human MC leukemia cell line HMC-1, which contains a mutated and intrinsically activated SCF receptor, showed constitutive expression of both bcl-2 and bcl-xL at the mRNA and protein level. Conclusion: Our data show that human MCs can express members of the bcl-2 family. It is hypothesized that bcl-xL plays a role in KIT-independent growth of MCs, whereas bcl-2 may be involved in KIT-dependent functions of MCs.

Increased Angiogenesis in the Bone Marrow of Patients with Systemic Mastocytosis

Recent data suggest that angiogenesis in the bone marrow (BM) is augmented and associated with growth of neoplastic cells in various hematological malignancies. Systemic mastocytosis (SM) is a neoplasm affecting multilineage and mast cell (MC)-committed hemopoietic progenitors. In the present study, we have assessed the BM microvessel density (MVD) by CD34 immunohistochemistry in 21 patients with SM, 5 with cutaneous mastocytosis (no BM infiltrates), and 5 control cases (normal BM). The median BM MVD was significantly higher in SM compared to cutaneous mastocytosis or controls (P < 0.05). In addition, a significant correlation (r = 0.74) between the BM MVD and grade of MC infiltration (percent tryptase(+) BM infiltrates) was found in SM. Moreover, the MVD was higher in MC infiltrates compared to the nonaffected adjacent marrow (P < 0.05). Immunohistochemical staining revealed expression of vascular endothelial growth factor in MC infiltrates. The notion that SM is associated with increased BM angiogenesis and vascular endothelial growth factor expression may have implications for the biology of disease and development of new treatment strategies.

A case of smouldering mastocytosis with peripheral blood eosinophilia and lymphadenopathy

Systemic mastocytosis (SM) is a clonal hematologic disease showing abnormal growth and accumulation of mast cells (MC) in visceral organs with or without skin involvement. The clinical course in SM is variable. In fact, indolent and aggressive variants have been described. In addition, SM patients may acquire an associated hematologic clonal non-MC lineage disease (AHNMD). In some cases, hematologic parameters are indicative of slowly progressing SM although the clinical course remains indolent over years. These cases have been referred to as smouldering SM. We report on a smouldering patient presenting with typical skin lesions, hypercellular marrow with focal MC aggregates, persistent leukocytosis (20,000-30,000/microl) with eosinophilia (5-10%), marked lymphadenopathy, and splenomegaly. The C-KIT mutation Asp-816-Val confirmed the diagnosis of SM. The clinical picture remained stable during an observation period of 10 years without signs of progression to an AHNMD or a high grade MC disease. These data show that some patients with SM can remain in a clinically indolent smouldering state over years even when presenting with marked eosinophilia and lymphadenopathy.

Prognostic value of lactate dehydrogenase activity in myelodysplastic syndromes

Several prognostic factors for patients with myelodysplastic syndromes (MDS) have been defined in the past. One of these factors appears to be the serum lactate dehydrogenase (LDH) activity. However, the precise predictive value of an elevated LDH level with regard to AML transformation remains uncertain. In this study, the prognostic value of the LDH activity was examined in a cohort of 180 patients with de novo MDS (median age 71 years [27-93]; f/m-ratio 1:1.2; RA: n=53; RARS: n=37; RAEB: n=50; RAEBT: n=19; CMML: n=21). Significant differences in LDH activities were found among FAB groups (P<0.05), and especially among IPSS groups (HIGH: 411+/-574; INT-2: 221+/-90; INT-1: 254+/-145; LOW: 192+/-47 U/l; P<0.05). An LDH level of >/=300 U/l was found to be associated with a significantly shorter median survival (10.3 months) when compared to <300 U/l (33.7 months; P<0.01). Moreover, an LDH activity of >/=300 U/l indicated a reduced AML-free survival in our MDS patients (P<0.01). As assessed by Cox regression, the inclusion of LDH as additional variable into the IPSS system resulted in an improved prediction concerning survival, but not with regard to AML evolution. Together, our data show that a serum LDH activity of >/=300 U/l in MDS is associated with a significantly shorter survival and higher risk to transform to AML. The LDH activity should be considered as an important prognostic factor in MDS.

Chymase expressing bone marrow mast cells in mastocytosis and myelodysplastic syndromes: an immunohistochemical and morphometric study

Background: Two cell specific neutral proteases, tryptase and chymase, are produced by human mast cells (MC). Tryptase is constitutively expressed by all MC, whereas chymase is found only in an MC subset. Very little is known about chymase expression in MC proliferative disorders (mastocytosis). Aims and Methods: Routinely processed, formalin fixed, and paraffin wax embedded bone marrow trephine biopsy specimens obtained from patients with various subtypes of mastocytosis (n = 47) and myelodysplastic syndromes (MDS; n = 28) were immunostained with antibodies against chymase and tryptase. Normal/reactive bone marrow specimens with intact haemopoiesis (n = 31) served as controls. The numbers of chymase expressing (C+) and of tryptase expressing (T+) MC were assessed morphometrically using a computer assisted video camera system. Results: In normal/reactive bone marrow, the numbers of C+ MC (median, 8/mm2; maximum, 159/mm2) were in the same range as those of T+ MC (median, 4/mm2; maximum, 167/mm2). Because normal MC express both chymase and tryptase, these findings indicate that the common phenotype of bone marrow MC in normal/reactive states is MCTC (MC expressing both tryptase and chymase). In contrast, in MDS and mastocytosis, the bone marrow exhibited far more T+ MC than C+ MC in almost all cases. Conclusions: According to these findings, the predominant MC type in the bone marrow in neoplastic states such as MDS and mastocytosis is MCT (MC expressing only tryptase). Although the pathophysiological basis of this apparent lack of chymase expression in most neoplastic MC in mastocytosis and MC involved in MDS remains unknown, this study has produced further evidence of the superior value of antitryptase antibodies in the diagnosis of mastocytosis.

Stem Cell Factor-induced Bone Marrow Mast Cell Hyperplasia Mimicking Systemic Mastocytosis (SM): Histopathologic and Morphologic Evaluation with Special Reference to Recently Established SM-criteria

Although systemic mastocytosis (SM) is a well-defined hematologic neoplasm, it is sometimes difficult to discriminate between SM and a reactive mast cell (MC) hyperplasia. We describe a patient with aplastic anemia who was treated with recombinant stem cell factor (SCF). In response to SCF, the patient showed transient hematologic improvement and developed a marked increase in MC as well as a transient increase in serum tryptase. Histologic and immunohistochemical examination revealed a huge increase in MC in the bone marrow with focal infiltrates similar to SM. However, most of the SM-criteria were not met: First, MC showed normal cytomorphological characteristics without significant atypias (no cytoplasmic extensions, no oval nuclei, no hypogranulated cytoplasm). Furthermore, bone marrow MC were CD2- and CD25-negative and did not exhibit the C-KIT 2468 A → T mutation (Asp-816-Val). After discontinuation of SCF the MC hyperplasia resolved confirming its reactive nature. Based on our case and similar cases mimicking mastocytosis, it seems of importance to apply recently established SM criteria in order to discriminate between reactive MC hyperplasia and true mastocytosis with certainty.

Numbers of colony-forming progenitors in patients with systemic mastocytosis: potential diagnostic implications and comparison with myeloproliferative disorders.

Background An increase in colony‐forming progenitor cells (CFU) is typically seen in myeloproliferative disorders (MPD). Systemic mastocytosis (SM) is a haemopoietic neoplasm involving myeloid progenitors similar to MPD. In the present study, we measured the levels of peripheral blood (pb) and bone marrow (bm) CFU in patients with different categories of SM, and compared them with those obtained in MPD patients and healthy controls.