Alemtuzumab-BEAM as conditioning for allogeneic hematopoietic stem cell transplantation in relapsed/refractory Hodgkin lymphoma: a single-center analysis.

PURPOSE: Treatment of refractory Hodgkin disease deserves specific considerations. Recently, alemtuzumab-BEAM has been introduced in allogeneic hematopoietic stem cell transplantation (HSCT) in these patients. METHODS: We retrospectively analyzed the outcome of 20 patients with relapsed/refractory Hodgkin's lymphoma (HL) who received allogeneic HSCT following conditioning therapy with alemtuzumab-BEAM. RESULTS: Treatment-related toxicity was tolerable. Half of the patients (50 %) had infections. Of these, 50 % were found to have pneumonia or catheter-related infections. In 20 %, an oral mucositis was observed. Acute graft-versus-host disease (GvHD) (≥grade 2) was seen in three patients. Complete remission (CR) could be achieved in 17 patients (85 %), 2 patients had persistent Hodgkin disease, and 1 patient died from infection prior to CR evaluation. Median progression-free survival and overall survival were 17.9 and 67.5 months, respectively. From the 17 CR patients, 8 had a relapse after a median of 10 months. Notably, of the eight patients relapsing after HSCT, all patients received another salvage treatment and four patients are still alive, whereas the other four patients died due to further progress. Six out of the remaining nine patients are still in CR, whereas the other three died from chronic GvHD and multi-organ failure. Overall, seven patients experienced chronic GvHD. CONCLUSION: In summary, alemtuzumab-BEAM is a well-tolerated conditioning therapy for allogeneic HSCT with high response rates in refractory HL.

Immunosuppression and atypical infections in CML patients treated with dasatinib at 140 mg daily.

BACKGROUND: The multikinase inhibitor dasatinib exerts growth-inhibitory effects in patients with imatinib-resistant chronic myeloid leukaemia (CML). In first clinical trials, side effects of dasatinib, 140 mg daily, were reported to be mild and tolerable. PATIENTS AND METHODS: We examined the side effect profile in 16 patients with imatinib-resistant CML who received 140 mg dasatinib daily in our center. RESULTS: Dasatinib produced substantial and sometimes severe or even life-threatening side effects with > or = 10% body weight loss (6/16 patients), pleural effusions grade II or higher (12/16) and infectious complications (12/16), including atypical infections not seen in imatinib-treated patients. One patient developed Epstein-Barr-Virus-positive mucosal leucoplakia, one died from pneumonia caused by pneumocystis carinii and three patients developed a skin-cancer. Most events were recorded within the first 2 years of therapy, only skin tumours developed after the second year. In ex vivo experiments performed in dasatinib-treated patients, transient suppression of IgE-dependent activation of blood basophils and TcR-dependent activation of T-lymphocytes was found. Moreover, in drug-binding studies, dasatinib was found to bind to several key kinase-targets of the immune system including Lyn and Btk, in mast cell, basophil, B-cell and T-cell lines. CONCLUSION: Dasatinib acts not only anti-neoplastic in CML but may also act as an immunosuppressive agent when applied at 140 mg daily, and produces frequent pleural effusions and weight loss in advanced CML.

Targeting of Hsp32 in solid tumors and leukemias: a novel approach to optimize anticancer therapy.

Heat shock protein 32 (Hsp32), also known as heme oxygenase-1 (HO-1), is a stress-related anti-apoptotic molecule, that has been implicated in enhanced survival of neoplastic cells and in drug-resistance. We here show that Hsp32 is expressed in most solid tumors and hematopoietic neoplasms and may be employed as a new therapeutic target as evidenced by experiments using specific siRNA and a Hsp32-targeting pharmacologic inhibitor. This Hsp-32 targeting drug, SMA-ZnPP, was found to inhibit the proliferation of neoplastic cells with IC(50) values ranging between 1 and 50 microM. In addition, SMA-ZnPP induced apoptosis in all neoplastic cells examined. Furthermore, SMA-ZnPP was found to synergize with other targeted and conventional drugs in producing growth-inhibition. Resulting synergistic effects were observed in all tumor and leukemia cells examined. Interestingly, several of the drug partners, when applied as single agents, induced the expression of Hsp32 in neoplastic cells, suggesting that synergistic effects resulted from SMA-ZnPP-induced ablation of a Hsp32-mediated survival-pathway that is otherwise used by tumor cells to escape drug-induced apoptosis. Together, Hsp32 is an important survival factor and target in solid tumors and hematopoietic neoplasms, and may be used to optimize anticancer therapy by combining conventional or targeted drugs with Hsp32-inhibitors. Based on these data, it seems desirable to explore the value of Hsp32-targeting drugs as anti-cancer agents in clinical trials.

Elevated tryptase levels selectively cluster in myeloid neoplasms: a novel diagnostic approach and screen marker in clinical haematology.

BACKGROUND: Recent data suggest that tryptase, a mast cell enzyme, is expressed in neoplastic cells in myeloid leukaemias. In several of these patients, increased serum tryptase levels are detectable. MATERIALS AND METHODS: We have determined serum tryptase levels in 914 patients with haematological malignancies, including myeloproliferative disorders (n = 156), myelodysplastic syndromes (MDS, n = 241), acute myeloid leukaemia (AML, n = 317), systemic mastocytosis (SM, n = 81), non-Hodgkin's lymphoma (n = 59) and acute lymphoblastic leukaemia (n = 26). Moreover, tryptase was measured in 136 patients with non-neoplastic haematological disorders, 102 with non-haematological disorders and 164 healthy subjects. RESULTS: In healthy subjects, the median serum tryptase was 5.2 ng mL(-1). Elevated serum tryptase levels were found to cluster in myeloid neoplasm, whereas almost all patients with lymphoid neoplasms exhibited normal tryptase. Among myeloid neoplasms, elevated tryptase levels (> 15 ng mL(-1)) were recorded in > 90% of patients with SM, 38% with AML, 34% with CML and 25% with MDS. The highest tryptase levels, often > 1000 ng mL(-1), were found in advanced SM and core-binding-factor leukaemias. In most patients with non-neoplastic haematological disorders and non-haematological disorders analysed in our study, tryptase levels were normal, the exception being a few patients with end-stage kidney disease and helminth infections, in whom a slightly elevated tryptase was found. CONCLUSIONS: In summary, tryptase is a new diagnostic marker of myeloid neoplasms and a useful test in clinical haematology.

Evaluation of antileukaemic effects of rapamycin in patients with imatinib-resistant chronic myeloid leukaemia.

BACKGROUND: Recent data suggest that the mammalian target of rapamycin (mTOR) is involved in the regulation of growth of neoplastic cells in chronic myeloid leukaemia (CML). PATIENTS AND METHODS: We treated six patients with imatinib-resistant CML in haematological relapse (leukocytes > 20,000 microL(-1)) with rapamycin at 2 mg per os daily for 14 consecutive days, with dose-adjustment allowed to reach a target rapamycin serum concentration of 10-20 pg mL(-1). RESULTS: A major leukocyte response with decrease to less than 10,000 microL(-1) was obtained in two patients, and a minor transient response was seen in two other patients. In responding patients, we also observed a decrease in vascular endothelial growth factor (VEGF) mRNA levels in circulating leukaemic cells. Side effects during rapamycin treatment were mild in most patients. In one patient, pneumonia developed. Rapamycin was also found to counteract growth of CML cells in vitro as determined by (3)H-thymidine incorporation. Moreover, rapamycin inhibited the growth of Ba/F3 cells exhibiting various imatinib-resistant mutants of BCR/ABL, including the T315I variant that exhibits resistance against most currently available BCR/ABL kinase inhibitors. CONCLUSIONS: Rapamycin shows antileukaemic effects in imatinib-resistant CML in vitro and in vivo. Larger trials with rapamycin or rapamycin-derivatives in combination with other targeted drugs are warranted to further determine clinical efficacy in CML.

Clinical and prognostic significance of histamine monitoring in patients with CML during treatment with imatinib (STI571).

BACKGROUND: Although imatinib is highly effective in chronic myeloid leukemia (CML), drug-resistance may occur. Therefore, monitoring of minimal residual disease (MRD) during treatment with imatinib is important. However, most MRD-parameters are expensive and require special technology. We determined the value of histamine as MRD-marker in CML. PATIENTS AND METHODS: Histamine levels were measured serially in whole blood samples before and during imatinib therapy in 80 CML patients by radioimmunoassay. RESULTS: Histamine levels were highly upregulated in CML at diagnosis compared to healthy controls, and correlated with the presence of basophils. During treatment with imatinib, histamine levels decreased and returned to normal levels in those achieving a complete cytogenetic response (CCR). Loss of CCR during therapy was invariably accompanied by an increase in histamine. Moreover, a histamine level of >100 ng/ml three or six months after start of imatinib was associated with a significantly reduced probability of survival (p<0.05). Whereas basophils were found to correlate well with histamine during imatinib, no correlations were found between histamine and Ph+ metaphases or histamine and BCR/ABL. CONCLUSION: Histamine-monitoring during treatment with imatinib is of prognostic significance.

Liposomal cytarabine for treatment of myeloid central nervous system relapse in chronic myeloid leukaemia occurring during imatinib therapy.

BACKGROUND: Central nervous system (CNS) relapse in chronic myeloid leukaemia (CML) is rare and if recorded is usually found to occur in patients with lymphoblastic transformation. The BCR/ABL tyrosine kinase inhibitor imatinib is highly effective in patients with CML, but hardly crosses the blood-brain barrier. PATIENTS AND METHODS: We report on two CML patients who developed a myeloid CNS relapse during treatment with imatinib. One patient was in major cytogenetic response at the time of CNS relapse. In both cases, the myeloid origin of neoplastic cells in the cerebrospinal fluid (CSF) was demonstrable by immunophenotyping, and their leukaemic origin by detection of the BCR/ABL oncoprotein. No BCR/ABL kinase domain mutations were found. Both patients received intrathecal liposomal cytarabine (50 mg each cycle; 6 cycles). In one patient, additional CNS radiation was performed, whereas in the other, consecutive treatment with dasatinib (70 mg per os twice daily) was started. RESULTS: In response to therapy, the clinical symptoms resolved, and the leukaemic cells in the CSF disappeared in both cases. After three months of observation, both patients are in complete cytogenetic and major molecular response, without evidence for a systemic or a CNS relapse. CONCLUSIONS: 'Anatomic' resistance against imatinib in the CNS can lead to a myeloid CNS relapse. Liposomal cytarabine with or without radiation is effective as local therapy in these patients. For systemic treatment and prophylaxis, BCR/ABL kinase inhibitors crossing the blood-brain barrier such as dasatinib should be considered in patients with CNS relapse.

Mesenchymal stem cells in patients with chronic myelogenous leukaemia or bi-phenotypic Ph+ acute leukaemia are not related to the leukaemic clone.

BACKGROUND: Human mesenchymal stem cells (MSCs) are thought to be multipotent cells which primarily reside in the bone marrow. Besides their well-known ability to replicate as undifferentiated cells and to differentiate into diverse lineages of mesenchymal tissues, they were recently suggested to also give rise to haematopoietic and leukaemic/cancer stem cells. In this study, the relationship between MSCs and leukemic stem cells in patients with either chronic myelogenous leukaemia (CML) or the more primitive variant, Ph+ bi-phenotypic leukaemia was investigated. PATIENTS AND METHODS: Cultured MSCs from 5 patients with CML and 3 patients with bi-phenotypic Ph+ leukaemia, all of them positive for BCP-ABL, were analysed with conventional cytogenetics, fluorescence in situ hybridisation (FISH) and polymerase chain reaction (PCR) for the presence of t(9;22) and BCR-ABL. MSCs were characterised phenotypically with surface markers (+CD73, +CD90, +CD105, -CD34, -CD45) and functionally through their potential to differentiate into both adipocytes and osteoblasts. RESULTS: MSCs could be cultivated from seven patients. These cells were BCR-ABL negative when analysed with conventional cytogenetics and FISH. Further cytogenetic analysis revealed a normal set of chromosomes without any aberrations. Two patients were BCR-ABL-positive when analysed with PCR, probably as a result of MSC contamination with macrophages. CONCLUSION: MSCs in patients with CML or Ph+ bi-phenotypic leukaemia are not related to the malignant cell clone.

In vivo effects of imatinib mesylate on human haematopoietic progenitor cells.

BACKGROUND: Imatinib mesylate has considerable antineoplastic activity in patients with chronic myeloid leukaemia (CML) and some solid tumours. Although originally regarded as nontoxic for normal haematopoiesis, mild to moderate myelosuppression is a commonly observed side-effect of this treatment. Recently, this molecule has been shown to suppress normal haematopoietic progenitor cells in vitro. This is the first study that has investigated the effect of imatinib on haematopoietic progenitor cells in vivo. MATERIALS AND METHODS: We investigated the number of circulating haematopoietic progenitor cells in 79 patients with CML and five patients with solid tumours who were treated with imatinib for at least 3 months. Bone marrow progenitor cells were assessed in a subgroup of 18 patients with CML after 12 months of imatinib treatment. Results were compared with haematopoietic progenitor cell numbers of normal controls. RESULTS: Circulating progenitors of all classes were significantly decreased in CML up to 24 months of imatinib therapy compared with healthy controls (median progenitor cells in CML after 12 months: CFU-GM 62, range 0-2543; BFU-E 216, range 0-3259; CFU-GEMM 0, range 0-139; versus controls: CFU-GM 208, range 50-936; BFU-E 690, range 120-1862; CFU-GEMM 20, range 4-77; P < 0.001). Similar reductions in the number of progenitor cells derived from bone marrow were found in a subgroup of 18 patients with CML. In patients with solid tumours the number of circulating progenitor cells was significantly lower under treatment with imatinib when compared with the controls. Withdrawal of imatinib in a patient with a malignant brain tumour resulted in a prompt normalization of circulating progenitors. CONCLUSIONS: This study suggests that imatinib exerts myelosuppressive effects through inhibition of haematopoietic progenitor cells.

Expression of angiogenic factors in chronic myeloid leukaemia: role of the bcr/abl oncogene, biochemical mechanisms, and potential clinical implications.

Chronic myeloid leukaemia (CML) is a stem cell disease characterized by an increased production and accumulation of clonal BCR/ABL-positive cells in haematopoietic tissues. The chronic phase of CML is inevitably followed by an accelerated phase of the disease, with consecutive blast crisis. However, depending on genetic stability, epigenetic events, and several other factors, the clinical course and survival appear to vary among patients. Recent data suggest that angiogenic cytokines such as vascular endothelial growth factor (VEGF), are up-regulated in CML, and play a role in the pathogenesis of the disease. These factors appear to be produced and released in leukaemic cells in patients with CML. In line with this notion, increased serum-levels of angiogenic growth factors are measurable in CML patients. In this study we provide an overview of angiogenic growth factors expressed in CML cells, discuss the possible pathogenetic role of these cytokines, the biochemical basis of their production in leukaemic cells, and their potential clinical implications.

Low dose thalidomide in patients with relapsed or refractory multiple myeloma.

Remarkable results of the treatment of refractory multiple myeloma with thalidomide have been reported. In most preceding studies, the given thalidomide dose was escalated to a maximum tolerated dose of up to 800 mg/d. The frequency of adverse effects correlates with dose intensity. Since a significant gain of therapeutic effects could not be observed as thalidomide dosage was escalated, the optimal dose of thalidomide remains to be determined. We report the results of a study with low dose thalidomide (median administered dose 100 mg/d, range 50-400 mg/d). Twenty-four relapsed (n = 19) or resistant (n = 5) multiple myeloma patients were included in the study. Twelve patients (50%) received thalidomide as monotherapy, 8 patients (33%) received a combination of thalidomide and dexamethasone (every 4 weeks 40 mg/day for 4 days) and 4 patients (17%) who were resistant to vincristine, doxorubicin, dexamethasone (VAD) received VAD combined with thalidomide. Overall, a response was observed in 12 patients (50%). Of the 12 patients treated with low dose thalidomide alone 5 (42%) responded, of the 8 patients who received a combination of thalidomide and dexamethasone 5 (63%) responded and of the 4 patients who had thalidomide in addition to VAD 2 patients (50%) responded. In 3 patients, thalidomide treatment had to be discontinued because of side effects and 1 patient died before response could be assessed. We conclude that low dose thalidomide is an effective and safe rescue therapy in relapsing or refractory multiple myeloma. Response to thalidomide might be dependent on prognostic parameters and tumor burden. To answer these questions larger prospective studies are necessary.

New aspects in thrombosis research: possible role of mast cells as profibrinolytic and antithrombotic cells.

Venous thromboembolism represents a significant cause of morbidity worldwide. The factors that underly thrombophilia are manifold. The concept of Virchow defines the well known triad of stasis, humoral factors, and pathologies of the vascular wall. In the current article, an additional factor, the "accumulation of repair cells" is discussed. This novel concept highlights the mast cell that accumulates around thrombosed vessels and provides a number of important repair molecules including heparin, profibrinolytic tPA, and fibrinogenolytic beta-tryptase. Thus, mast cell recruitment and activation may result in local thrombolysis and prevention of coagulation. In line with this concept, mast cell-deficient mice are more susceptible to lethal thrombogenic stimuli compared to normal mice. The factors (cytokines) that trigger mast cell accumulation and release of repair molecules have also been identified - the most important one appears to be stem cell factor (SCF). All in all. our novel concept suggests that the patho-physiology of thrombosis may involve a "physiologic" cell that provides the same repair molecules that are used for treatment of thrombotic disorders by the physician. Whether an altered availability of components of this cellular repair system can predispose for thrombophilia remains to be determined.

STAT5 activation contributes to growth and viability in Bcr/Abl-transformed cells.

The transcription factor STAT5 is constitutively tyrosine phosphorylated and activated after transformation of hematopoietic cells by p210Bcr/Abl. A truncated form of STAT5B (triangle upSTAT5; aa, 1-683) that lacks tyrosine 699 and the transcriptional activation domain was introduced into Ba/F3p210 cells under the control of a tetracycline-inducible promoter. Treatment of these cells with doxycycline, a tetracycline analogue, induced expression of triangle upSTAT5 and inhibited STAT5-dependent transcription. triangle upSTAT5 coprecipitated with STAT5 and decreased Bcr/Abl-dependent tyrosine phosphorylation of endogenous STAT5. Induction of triangle upSTAT5 inhibited growth of Ba/F3p210 cells (26%-52% of control levels at 4 days) but did not cause cell-cycle arrest. triangle upSTAT5 reduced viability of Ba/F3p210 cells and increased sensitivity of the cells to the cytotoxic drugs hydroxyurea and cytarabine. These results indicate that high-level expression of triangle upSTAT5, as achieved here by using a tetracycline-inducible promoter, inhibits STAT5 activity, reduces the growth rate of Ba/F3p210 cells by inhibiting viability, and results in increased sensitivity to chemotherapeutic drugs. It is therefore likely that STAT5 activation plays a role in the transformation of hematopoietic cell lines by p210Bcr/Abl. (Blood. 2000;95:2118-2125)

Effects of interferon-alpha2b treatment on ex vivo differentiation of mast cells from circulating progenitor cells in a patient with systemic mastocytosis.

Interferon (IFN)-alpha, a known inhibitor of myelopoiesis, is increasingly used to treat patients with systemic mastocytosis (SM). However, the mechanisms of IFN-alpha effects on mast cell (MC) growth remain unknown, and the treatment responses may be variable. In the present study, factor-dependent ex-vivo differentiation of MCs from peripheral blood mononuclear cells (PBMNCs) was analyzed in a patient with SM treated with IFN-alpha2b (3 million U/day). The patient exhibited an extensive MC infiltration in his bone marrow (BM) and increasing serum total tryptase levels (spiking to > 1,400 ng/ml). PBMNCs were collected before and during IFN-alpha2b treatment and cultured in the presence or absence of stem cell factor (SCF, 100 ng/ml) for 42 days. In the absence of SCF, no MC growth was detectable. However, in the presence of SCF, MC containing tryptase appeared in the cultures. Treatment with IFN-alpha2b resulted in a time-dependent decrease in SCF-inducible formation of MCs from PB progenitor cells in vitro. Also, during IFN-alpha2b treatment, blood histamine concentrations decreased. Serum total tryptase levels initially increased despite IFN-alpha2b treatment. However, after a latency period of a few months, tryptase concentrations declined and then reached a plateau. In healthy individuals, the SCF-induced in vitro growth of MCs from their progenitor cells was also inhibitable by the addition of IFN-alpha2b. In summary, our data show that IFN-alpha2b can exhibit inhibitory effects on factor-dependent growth of MC progenitor cells. However, it still remains open which of the patients with mastocytosis can benefit from long-term IFN-alpha treatment.

Immunophenotypic characterization of human bone marrow endosteal cells.

In order to determine the relationship between bone marrow (bm) endosteal cells (EDC) and hemopoietic progenitors, we have analyzed the immunophenotype of EDC using various antibodies (Ab) against mesenchymal antigens. The Ab were applied on paraffin sections of normal bm (iliac crest, n=17; talus, n=1; phalanx, n=1), myeloregenerative bm (after chemotherapy), and hematologic disorders (acute myeloid leukemia (AML), n=8; chronic myeloid leukemia (CML), n=6; myelodysplastic syndromes (MDS), n=14; severe aplastic anemia (SAA), n=4; essential thrombocythemia (ET), n=2; idiopathic (primary) osteomyelo-fibrosis (IMF), n=1; polycythemia vera (PV), n=1). In normal bm, EDC were found to react with Ab against vimentin, tenascin, alpha-smooth muscle actin, osteocalcin, CD51, and CD56, but did not react with Ab against CD3, CD15, CD20, CD34, CD45, CD68, or CD117. An identical phenotype of EDC was found in AML, MDS, SAA, ET, IMF, PV, myeloregenerative bm, and peripheral bones lacking active hemopoiesis (talus, phalanx). In patients with CML, EDC reacted with Ab to CD51, but did not react with Ab to CD56. Based on their unique antigen profile, EDC were enriched from normal bm by enzyme digestion and cell sorting. However, these enriched cells (CD56+, CD45-, CD34-) did not give rise to hemopoietic cells under the culture conditions used, i.e. in the presence of the growth factors IGF-1, bFGF, SCF, IL-3, and GM-CSF Together, our data do not support the hypothesis that EDC are totipotent mesenchymal progenitors giving rise to hemopoietic cells.

An in vitro model for the allergen-IgE-FcARI interaction.

BACKGROUND: The interaction of immune complexes consisting of allergens and allergen-specific IgE with the high-affinity Fcepsilon receptor represents the key event in the induction of symptoms in type I allergic individuals. Immediate-type symptoms result from the release of biological mediators due to allergen-induced cross-linking of FcepsilonRI receptors on mast cells and basophils, whereas FcepsilonRI-mediated presentation of allergen-IgE complexes may contribute to late-phase symptoms through enhanced T cell activation. The interaction of allergens/allergen-specific IgE/FcepsilonRI represents, therefore, an important target for therapeutic intervention strategies in type I allergy. METHODS AND RESULTS: A molecular model of the allergen-IgE-FcepsilonRI interaction was established. It consists of recombinant purified Bet v 1, the major birch pollen allergen, a chimeric Bet v 1 specific monoclonal IgE antibody, and the baculovirus-expressed purified human alpha chain of FcepsilonRI. The chimeric Bet v 1-specific IgE antibody consists of the light chain and the heavy chain variable region of a mouse monoclonal Bet v 1 specific antibody, Bip 1, and the constant region of human IgE. The interaction of rBet v 1, chimeric Bip 1, and human alpha chain was investigated by overlay experiments. Nitrocellulose-immobilized recombinant alpha chains was incubated with chimeric Bip 1 and, for control purposes, with mouse-derived Bip 1. Bound chimeric Bip 1 was detected with 125I-labeled rBet v 1. The specific interaction of rBetv 1, chimeric Bip 1, and recombinant human alpha chain is demonstrated. We thus establish a molecular model of the allergen/IgE/alpha chain interaction. The usefulness of the described in vitro system is exemplified by the identification of a mouse monoclonal antihuman IgE antibody which blocked the IgE-alpha chain interaction. CONCLUSIONS: The module system consisting of rBet v 1, chimeric Bip 1, and recombinant alpha chain may be used for the identification of competitors of the allergic effector reaction by means of high throughput screening of compounds or by combinatorial chemistry.

The mast cell as site of tissue-type plasminogen activator expression and fibrinolysis.

Recent data suggest that mast cells (MC) and their products (heparin, proteases) are involved in the regulation of coagulation and fibrino(geno)lysis. The key enzyme of fibrinolysis, plasmin, derives from its inactive progenitor, plasminogen, through catalytic action of plasminogen activators (PAs). In most cell systems, however, PAs are neutralized by plasminogen activator inhibitors (PAIs). We report that human tissue MC as well as the MC line HMC-1 constitutively produce, express, and release tissue-type plasminogen activator (tPA) without producing inhibitory PAIs. As assessed by Northern blotting, highly enriched lung MC (>98% pure) as well as HMC-1 expressed tPA mRNA, but did not express mRNA for PAI-1, PAI-2, or PAI-3. The tPA protein was detectable in MC-conditioned medium by Western blotting and immunoassay, and the MC agonist stem cell factor (c-Kit ligand) was found to promote the release of tPA from MC. In addition, MC-conditioned medium induced fibrin-independent plasmin generation as well as clot lysis in vitro. These observations raise the possibility that MC play an important role in endogenous fibrinolysis.

Systemic mastocytosis associated with acute myeloid leukaemia: report of two cases and detection of the c-kit mutation Asp-816 to Val.

A subset of patients with systemic mastocytosis (SM) develop acute myeloid leukaemia (AML). However, little is known about the biology of such leukaemias and their relationship to the mast cell (MC) lineage. We report on two female patients who suffered from SM and AML. According to FAB criteria, the leukaemias were classified as AML-M4 (patient 1) and AML-MO (patient 2). The coexistence of the two distinct neoplasms (AML and SM) was demonstrable by immunostaining of serial bone marrow (BM) sections with monoclonal antibodies (mAb). In particular, the MC infiltrates were found to react with mAb against MC-tryptase and MC growth factor receptor c-kit (CD117), but not with mAb to CD15 or CD34. In contrast, the AML blasts were immunoreactive for CD15 (patient 1) or CD34 (patient 2), but did not express tryptase. The c-kit point mutation Asp-->Val at codon 816, considered to play a role in the transformation of MC progenitors, was detected in patient 1 in a BM cell fraction containing 4% MC. However, no c-kit mutation was found in pure AML blasts (<1% MC). These findings argue against an evolution of the AML clone from neoplastic MC or MC-committed progenitors.

Phenotypic characterization of human skin mast cells by combined staining with toluidine blue and CD antibodies.

Mast cells (MC) are important cellular components of the immune network in diverse organs. The skin MC has likewise been implicated in IgE- and complement-mediated cutaneous reactions. Such reactions supposedly involve specific cell surface membrane receptors. In this study, the cell surface marker profile of human skin MC was established using monoclonal antibodies (MoAb) against defined CD antigens. MC were isolated from juvenile foreskin (n = 55) and adult mammary skin (n = 5). The reactivity of MC with MoAb was assessed by a combined toluidine blue/immunofluorescence staining technique. Confirming our previous analyses on lung MC, foreskin MC reacted with MoAb against CD9, CD29, CD33, CD43, CD44, CD45, CD46, CD51, CD54, CD55, CD58, CD59, CD61, and CD117 (c-kit). Foreskin MC were also recognized by MoAb to CD47, CD48, CD49d, CD53, CD60, CD63, CD81, CD82, CD84, CD87, CD92, CD97, CD98, and CD99. Recently clustered CD antigens detectable on foreskin MC were CD147 (neurothelin), CD149 (MEM133), CD151 (PETA-3), and CD157 (BST-1). In contrast to lung MC and MC from adult skin, foreskin MC were found to express CD88 (C5aR). Also, cutaneous MC (from both juvenile foreskin and adult mammary skin), but not lung MC, were found to bind the CD32 MoAb IV.3, 2E1, and FLI8.26 (Fc gammaRII). The CD50 antigen (ICAM-3) was detectable on lung MC, but not on foreskin MC or MC of adult mammary skin. In summary, our data show that cutaneous MC and lung MC express an almost identical phenotype; however, in contrast to lung MC, cutaneous MC appear to express substantial amounts of CD32 and to lack CD50. In addition, foreskin MC, unlike MC from adult skin or lung, express CD88.