Identification of CD203c as a New Basophil-Specific Flow-Marker in Ph+ Chronic Myeloid Leukemia

Basophilia is a crucial prognostic variable in Ph-chromosome-positive chronic myeloid leukemia (CML). The ectoenzyme CD203c is an activation-linked surface antigen that is expressed specifically on basophil-committed progenitor cells and mature basophils. We examined the expression of CD203c on progenitors and/or basophils in 21 healthy donors and 44 patients with CML. As expected, the numbers of CD203c⁺ blood leukocytes were significantly higher in CML patients compared to controls (percentage of CD203c⁺ cells among viable cells in CML at diagnosis: 4.19 ± 3.68% vs. controls: 0.53 ± 0.23%, p < 0.05). Moreover, CML basophils expressed higher levels of CD203c compared to normal basophils (median staining-index in CML at diagnosis: 29.41 ± 19.14 versus controls: 20.44 ± 13.45). We also found that the numbers and percentage of circulating CD203c⁺ cells at diagnosis correlate with the disease-related risk-profile. Incubation of CML basophils with an anti-IgE-antibody resulted in further upregulation of CD203c. After successful treatment with imatinib and/or other BCR::ABL1 inhibitors leading to major or complete molecular responses, the numbers of CD203c⁺ basophils decreased substantially in our CML patients compared to pre-treatment values. Together, CD203c is overexpressed on CML basophils, is further upregulated by IgE receptor cross-linking, and may serve as a biomarker to quantify basophilia in patients with CML at diagnosis and during therapy.

Functional Precision Medicine Provides Clinical Benefit in Advanced Aggressive Hematologic Cancers and Identifies Exceptional Responders

Personalized medicine aims to match the right drug with the right patient by using specific features of the individual patient's tumor. However, current strategies of personalized therapy matching provide treatment opportunities for less than 10% of patients with cancer. A promising method may be drug profiling of patient biopsy specimens with single-cell resolution to directly quantify drug effects. We prospectively tested an image-based single-cell functional precision medicine (scFPM) approach to guide treatments in 143 patients with advanced aggressive hematologic cancers. Fifty-six patients (39%) were treated according to scFPM results. At a median follow-up of 23.9 months, 30 patients (54%) demonstrated a clinical benefit of more than 1.3-fold enhanced progression-free survival compared with their previous therapy. Twelve patients (40% of responders) experienced exceptional responses lasting three times longer than expected for their respective disease. We conclude that therapy matching by scFPM is clinically feasible and effective in advanced aggressive hematologic cancers. SIGNIFICANCE: This is the first precision medicine trial using a functional assay to instruct n-of-one therapies in oncology. It illustrates that for patients lacking standard therapies, high-content assay-based scFPM can have a significant value in clinical therapy guidance based on functional dependencies of each patient's cancer.See related commentary by Letai, p. 290.This article is highlighted in the In This Issue feature, p. 275.

Successful treatment of vaccine-induced prothrombotic immune thrombocytopenia (VIPIT)

Cases of unusual thrombosis and thrombocytopenia after administration of the ChAdOx1 nCoV-19 vaccine (AstraZeneca) have been reported. The term vaccine-induced prothrombotic immune thrombocytopenia (VIPIT) was coined to reflect this new phenomenon. In vitro experiments with VIPIT patient sera indicated that high-dose intravenous immunoglobulins (IVIG) competitively inhibit the platelet-activating properties of ChAdOx1 nCoV-19 vaccine induced antibodies. Here, we report a case of a 62-year-old woman who had received this vaccine and developed VIPIT. She visited the emergency ward because of petechiae and hematomas. In the laboratory work-up, thrombocytopenia, low fibrinogen, elevated D-dimer, and positivity in the platelet factor 4/heparin-enzyme-immunoassay were present. Signs and symptoms of thrombosis were absent. Upon immediate therapy with non-heparin anticoagulation, high-dose IVIG, and prednisolone, laboratory parameters steadily improved and the patient was discharged from hospital without thrombotic complications. We conclude that early initiation of VIPIT treatment results in a swift response without thrombotic complications.

The pan-BCL-2-blocker obatoclax (GX15-070) and the PI3-kinase/mTOR-inhibitor BEZ235 produce cooperative growth-inhibitory effects in ALL cells

Acute lymphoblastic leukemia (ALL) is characterized by leukemic expansion of lymphoid blasts in hematopoietic tissues. Despite improved therapy only a subset of patients can be cured. Therefore, current research is focusing on new drug-targets. Members of the BCL-2 family and components of the PI3-kinase/mTOR pathway are critically involved in the regulation of growth and survival of ALL cells. We examined the effects of the pan-BCL-2 blocker obatoclax and the PI3-kinase/mTOR-inhibitor BEZ235 on growth and survival of ALL cells. In ³H-thymidine uptake experiments, both drugs suppressed the in vitro proliferation of leukemic cells in all patients with Philadelphia chromosome-positive (Ph⁺) ALL and Ph⁻ ALL (obatoclax IC₅₀: 0.01-5 μM; BEZ235, IC₅₀: 0.01-1 μM). Both drugs were also found to produce growth-inhibitory effects in all Ph⁺ and all Ph⁻ cell lines tested. Moreover, obatoclax and BEZ235 induced apoptosis in ALL cells. In drug-combination experiments, obatoclax and BEZ235 exerted synergistic growth-inhibitory effects on ALL cells. Finally, we confirmed that ALL cells, including CD34⁺/CD38⁻ stem cells and all cell lines express transcripts for PI3-kinase, mTOR, BCL-2, MCL-1, and BCL-xL. Taken together, this data shows that combined targeting of the PI3-kinase/mTOR-pathway and BCL-2 family-members is a potent approach to counteract growth and survival of ALL cells.

Monoclonal B-cell lymphocytosis (MBL) with normal lymphocyte counts is associated with decreased numbers of normal circulating B-cell subsets

Monoclonal B-cell lymphocytosis (MBL) with normal lymphocyte counts is associated with decreased numbers of normal circulating B-cell subsets.Little is known about the distribution of normal lymphoid cells and their subsets in the peripheral blood (PB) of subjects with monoclonal B-cell lymphocytosis (MBL). In our study, we compared the absolute number of PB lymphoid cells and their subpopulations in 95 MBL cases with normal lymphocyte counts vs. 617 age-/sex-matched non-MBL healthy subjects (controls), using highly sensitive flow cytometry. MBL cases showed significantly reduced numbers of normal circulating B-cells, at the expense of immature and naive B-cells; in addition, CD4+CD8+ double-positive T-cells and CD8+ T-cells were significantly lower and higher vs. controls, respectively. Moreover, most normal B-cell subsets were significantly decreased in PB at >1% MBL-counts, vs. "low-count" MBL cases, and lower amounts of immature/naive B-cells were detected in biclonal (particularly in cases with coexisting CLL-like- and non-CLL-like B-cell clones) vs. monoclonal MBL subjects. In summary, our results show imbalanced (reduced) absolute numbers of recently produced normal circulating B-cells (e.g., immature and naıve B-cells) in MBL, which becomes more pronounced as the MBL cell count increases.

Prolonged progression-free survival in patients with chronic lymphocytic leukemia receiving granulocyte colony-stimulating factor during treatment with fludarabine, cyclophosphamide, and rituximab

The clinical benefit of the addition of granulocyte colony-stimulating factor (G-CSF) to standard immunochemotherapy of chronic lymphocytic leukemia (CLL) with fludarabine, cyclophosphamide, and rituximab (FCR) is still unclear. In this retrospective study we analyzed the outcome of 32 consecutive patients with CLL during treatment with FCR. Sixteen patients received G-CSF for treatment of CTC grade 3 or 4 neutropenia or febrile neutropenia at some point during therapy and 16 did not. Both groups were well balanced for clinical and biological risk factors. Overall response rates were not significantly different (94% vs. 75%; p=0.144). Interestingly, a significantly better progression-free survival (100% vs. 35.4% at 24 months; p<0.001) and even overall survival (100% vs. 77.8% at 24 months; p=0.022) was observed in patients receiving G-CSF. While the underlying cause remains to be elucidated, these data strongly suggest an association of the addition of G-CSF to FCR therapy with final patient outcome.

Autoimmune hemolytic anemias, Evans' syndromes, and pure red cell aplasia in non-Hodgkin lymphomas

We analyzed 108 cases of non-CLL non-Hodgkin lymphoma (NHL) associated with autoimmune hemolytic anemia (AIHA) (+/- pure red cell aplasia (PRCA)) or Evans' syndrome. The analysis was based on cases reported in the literature, which were retrieved by means of Pubmed and Medline searches and of an original series of 121 patients with NHL as well as reference lists of papers in the field. The number of cases in various NHL subtypes was small (n = 6-25). Nevertheless, interesting and sometimes unexpected differences in sex prevalence, temporal relationship between onset of lymphoma and AIHA, stage of lymphoma, relative frequency of warm antibody-AIHA (WA-AIHA) and cold antibody (CA-AIHA), association with PRCA and response of AIHA to treatments were noted for various lymphoma entities. WA-AIHA was more frequent in B-cell lymphomas, while CA-AIHA and PRCA predominantly occurred in T-cell lymphomas. Anti-lymphoma treatment seemed to be more effective against AIHA than conventional therapy with steroids or immunoglobulin. Although generated by a literature survey, this compilation of data indicates a complex relation of lymphoma and AIHA and warrants more attention and specific studies.

CD203c is overexpressed on neoplastic mast cells in systemic mastocytosis and is upregulated upon IgE receptor cross-linking

The ectoenzyme E-NPP3 (CD203c) has recently been identified as a novel activation-linked cell surface antigen on basophils. In the present study, we examined expression of CD203c on normal mast cells (MC)and bone marrow (bm) MC derived from 85 patients with systemic mastocytosis (SM), including cases with indolent SM (ISM, n=72), SM with associated clonal hematologic non-MC-lineage disease (SM-AHNMD, n=6), aggressive SM (ASM, n=3), and mast cell leukemia (MCL, n=4). Surface expression of CD203c was analyzed by multicolor flow cytometry. In patients with SM, bm MC expressed significantly higher amounts of CD203c compared to normal bm MC (median MFI in controls: 260 versus median MFI in SM: 516, p<0.05). Slightly lower amounts of CD203c were detected on MC in SM-AHNMD and ASM compared to ISM. To demonstrate CD203c expression in MC at the mRNA level, neoplastic MC were highly enriched by cell sorting, and were found to express CD203c mRNA in RT-PCR analysis. Cross-linking of the IgE receptor on MC resulted in a substantial upregulation of CD203c, whereas the KIT-ligand stem cell factor (SCF) showed no significant effects. In conclusion, CD203c is a novel activation-linked surface antigen on MC that is upregulated in response to IgE receptor cross-linking and is overexpressed on neoplastic MC in patients with SM.

Immunohistochemical assessment of CD25 is equally sensitive and diagnostic in mastocytosis compared to flow cytometry

BACKGROUND

Systemic mastocytosis (SM) is a clonal myeloid disorder characterized by abnormal accumulation and growth of mast cells (MC) in internal organs. In most cases, the bone marrow is involved. Expression of CD25 in bone marrow MC, with or without coexpression of CD2, is an important minor SM criterion. So far, most studies have examined CD25-expression on MC by flow cytometry.

MATERIALS AND METHODS

We examined the expression of CD25 in MC in patients with SM (n = 25) by immunohistochemistry (IHC) and compared these data with results obtained by flow cytometric assessment of CD25-expression. In addition, we compared CD25-staining results with that obtained with an antibody against CD2.

RESULTS

In a majority of all patients (> 80%), CD25 was detectable by both staining techniques. However, in one patient, CD25 was only detectable on MC by IHC, but not by flow cytometry, and in two patients in whom IHC could not be applied because of lack of compact MC infiltrates, flow cytometry revealed aberrant expression of CD25. The antibody against CD2 produced diagnostic staining results in a smaller group of patients (flow cytometry: 65%; IHC: 28% of SM cases) compared to CD25 (> 80%).

CONCLUSIONS

CD25-IHC is equally diagnostic and sensitive in SM compared to flow cytometry and thus can be recommended as a diagnostic test. Our data also suggest that the diagnostic value of CD25 exceeds that of CD2, and that optimal assessment of CD25-expression in neoplastic MC in all patients requires the application of both techniques, flow cytometry and IHC.

Interleukin-3 promotes the expression of E-NPP3/CD203C on human blood basophils in healthy subjects and in patients with birch pollen allergy

We recently identified the ectoenzyme CD203c as a novel basophil activation antigen that is upregulated in response to FcepsilonRI cross-linkage. We investigated the effects of various interleukins (ILs) on expression of CD203c on blood basophils using an antibody against CD203c and flow cytometry. Of all cytokines tested, only IL-3 was found to upregulate expression of CD203c on basophils above baseline levels. The effects of IL-3 were dose- and time-dependent (EC(50): 0.1-1 ng/ml) without differences observed between healthy and allergic donors. Whereas anti-IgE induced maximum upregulation of CD203c within 15 minutes, the IL-3-induced upregulation showed a maximum after 180 minutes. IgE-receptor cross-linking resulted in enhanced expression of both CD63 and CD203c, whereas IL-3 enhanced the levels of CD203c without promoting expression of CD63. The IL-3-induced upregulation of CD203c was also observed in highly enriched basophils and was counteracted by a blocking antibody against the alpha chain of the IL-3 receptor (CD123). The IL-3-induced upregulation of CD203c was also found to depend on the presence of calcium. To analyze signaling pathways involved in IL-3-induced upregulation of CD203c, pharmacologic inhibitors were applied. The PI3-kinase inhibitors, wortmannin and LY294002 counteracted the IL-3-induced expression of CD203c, whereas MEK- and PKC inhibitors showed no effects. In conclusion, IL-3 upregulates expression of CD203c on basophils through a specific receptor and via a PI3-kinase-dependent signaling-pathway. Compared to FcepsilonRI-mediated cell activation, IL-3-induced upregulation of CD203c is a late(r) event and is not accompanied by upregulation of CD63.

Standards and standardization in mastocytosis: consensus statements on diagnostics, treatment recommendations and response criteria

Although a classification for mastocytosis and diagnostic criteria are available, there remains a need to define standards for the application of diagnostic tests, clinical evaluations, and treatment responses. To address these demands, leading experts discussed current issues and standards in mastocytosis in a Working Conference. The present article provides the resulting outcome with consensus statements, which focus on the appropriate application of clinical and laboratory tests, patient selection for interventional therapy, and the selection of appropriate drugs. In addition, treatment response criteria for the various clinical conditions, disease-specific symptoms, and specific pathologies are provided. Resulting recommendations and algorithms should greatly facilitate the management of patients with mastocytosis in clinical practice, selection of patients for therapies, and the conduct of clinical trials.

Expression of the target receptor CD33 in CD34+/CD38-/CD123+ AML stem cells

BACKGROUND

CD33 (Siglec-3) is becoming increasingly important as a target of antibody-mediated therapy in acute myeloid leukaemia (AML). In normal myelopoiesis, expression of CD33 is restricted to advanced stages of differentiation, whereas primitive stem cells do not express CD33. In the present study, we asked whether leukaemic stem cells in patients with AML express CD33.

MATERIALS AND METHODS

A multicolour-staining technique was applied in 11 patients with AML, and leukaemic progenitors defined as CD34(+)/CD38(-)/CD123(+) cells. AML stem cells were purified by cell sorting and were examined for expression of CD33 mRNA by reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

In all patients in whom the majority of myeloblasts expressed CD33 (n = 8), AML progenitors reacted with the CD33 antibody P67.6. Repopulation experiments utilizing irradiated NOD/SCID mice confirmed that AML stem cells in these patients reside within the CD33(+) subpopulation of the leukaemic clone. Moreover, highly purified AML stem cells (> 98% purity) from patients with CD33(+) AML were found to express CD33 mRNA in RT-PCR analyses. CD33 was neither detectable on CD34(+)/CD38(-) cells in normal bone marrow nor on leukaemic stem cells in patients with CD33-negative AML.

CONCLUSIONS

Leukaemic stem cells in patients with CD33(+) AML express CD33. This observation is in favour of novel treatment concepts employing CD33-targeting antibodies in AML.

Evaluation of biologic activity of tryptase secreted from blast cells in acute myeloid leukemia

A number of autocrine and paracrine growth regulators are considered to be involved in the survival and proliferation of blast cells in acute myeloid leukemia (AML). We have recently shown that blast cells in a group of patients with AML produce and secrete the mitogenic enzyme tryptase. In the present study, we examined functional effects of tryptase in the context of AML. As assessed by 3H-thymidine uptake experiments, tryptase-containing serum from patients with AML as well as heparin-complexed recombinant tryptase were found to promote the proliferation of cultured bone marrow- and lung fibroblasts in a dose-dependent manner. A neutralizing antibody against human beta-tryptase was found to diminish these growth-stimulatory effects of serum-tryptase in all patients examined. Tryptase also induced the expression of mRNA for GM-CSF and SCF, two cytokines known to promote growth of AML cells, in cultured bone marrow fibroblasts. Neither recombinant tryptase nor tryptase-rich serum of AML patients, showed an effect on the growth of leukemic blast cells irrespective of the FAB category or expression of protease-activated receptor (PAR)-2, a putative molecular target of tryptase. Together, tryptase is secreted from AML blasts as a biologically active molecule that may exhibit paracrine rather than autocrine effects in AML.

Detection of novel leukocyte differentiation antigens on basophils and mast cells by HLDA8 antibodies

BACKGROUND

Basophils (BA) and mast cells (MC) are important effector cells in allergic reactions. Development, growth and effector cell functions are regulated by a network of cytokines, other ligands, and respective cell surface antigens.

METHODS

We examined the expression of novel CD antigens on human BA, lung MC, the BA cell line KU-812, and the MC line HMC-1. Expression of surface antigens was analyzed by monoclonal antibodies (mAb) of the HLDA8 workshop and flow cytometry.

RESULTS

Basophils were found to stain positive for CXCR1 (CD181), CCR1 (CD191), CCR2 (CD192), CCR7 (CD197), IL-18Ralpha (CDw218a), IL-18Rbeta (CDw218b), TRAIL-R1 (CD261), TRAIL-R2 (CD262), TACI (CD267), TLR-4 (CD284), LAIR1 (CD305), EMR-2 (CD312), JAM1 (CD321), and JAM2 (CD322). Lung MC were found to react with mAb against EMR-2 (CD312) and JAM1 (CD321). KU-812 cells were found to stain positive for CXCR1 (CD181), TRAIL-R2 (CD262), B7H2 (CD275), TLR-4 (CD284), JAM1 (CD321), and E-Cadherin (CD324). HMC-1 cells were recognized by mAb against TRAIL-R2 (CD262), B7H2 (CD275), LAIR1 (CD305), EMR-2 (CD312), JAM1 (CD321), and Siglec-6 (CDw327).

CONCLUSIONS

Extensive phenotyping with antibodies against novel CD antigens provides further evidence that BA and MC represent two separate hematopoietic cell lineages with unique phenotypic properties observed in mature cells as well as malignant immature cells. Further studies are required to define the functional role of these CD antigens expressed in BA and MC.

Detection of molecular targets on the surface of CD34+/CD38-- stem cells in various myeloid malignancies

Recent data suggest that myeloid neoplasms are organized hierarchically in terms of self-renewal and maturation of early progenitor cells, similar to normal myelopoiesis. In acute myeloid leukemia (AML), the NOD/SCID mouse-repopulating leukemic stem cells usually co-express CD123 with CD34, but lack CD38. So far, however, little is known about expression of other markers and targets on these progenitors. In the present study, expression of target antigens on CD34+/CD38- cells was analysed by multi-color flow cytometry in patients with AML (n = 18), myelodysplastic syndromes (MDS, n = 6), chronic myeloid leukemia (CML, n = 8) and systemic mastocytosis (SM, n = 9). The IL-3Ralpha chain (CD123) was found to be expressed on CD34+/CD38- cells in a majority of the patients in all disease categories. Independent of the type of disease, the vast majority of these stem cells co-expressed aminopeptidase-N (CD13) and CD44 in all patients. By contrast, the CD34+/CD38- progenitor cells expressed variable amounts of the target receptor CD33, c-kit (CD117) and AC133 (CD133). In conclusion, neoplastic stem cells in various myeloid neoplasms appear to express a similar phenotype including target antigens such as CD13, CD33 and CD44. Since many of these targets are not expressed on all stem cells in all patients, the elimination of the entire clone may require combinations of targeted antibodies or use of additional drugs.

CD 33 as a target of therapy in acute myeloid leukemia: current status and future perspectives

CD 33 is a myeloid cell surface antigen that is expressed on blast cells in acute myeloid leukemia (AML) in a majority of all patients regardless of age or subtype of disease. The antigen is also expressed on leukemic stem cells in many cases, but is not expressed on normal hematopoietic stem cells. In an attempt to improve therapy in AML, a CD 33-targeted drug has been developed. The drug, gemtucumab ozogamicin (GO; Mylotarg), consists of a humanized CD 33 antibody (hP 67.6), a pH-dependent linker, and a highly potent chemotherapy agent, calicheamicin 1,2,-dimethyl hydrazine dichloride. Based on its clinical activity, GO has been approved for application in chemotherapy-refractory AML in various countries and is effective as a mono-substance as well as in combination with conventional chemotherapy. However, despite high efficacy and a certain specificity for leukemic (as opposed to normal) stem cells, the drug does not work in all patients, and can produce significant side-effects, including veno-occlusive disease (VOD), especially in patients who undergo stem cell transplantation. These side-effects have to be balanced against the benefit of GO therapy in patients with relapsed or refractory AML.

Immunological characterization and antibacterial function of persisting granulocytes in leukemic patients receiving pulse cytosine arabinoside-consolidation chemotherapy on days 1, 3, and 5

High-dose cytosine arabinoside (HiDAC) and intermediate-dose cytosine arabinoside (IDAC) have been introduced as effective and safe consolidation chemotherapy in acute myeloid leukemia, with relatively low rates of life-threatening infections despite the high total dose of the cytostatic drug. To explore the biological background of low toxicity, we examined the numbers, immunophenotype, and functional properties of granulocytes in patients with acute myeloid leukemia receiving HiDAC or IDAC. Interestingly, the absolute numbers of neutrophils remained >500/microl until day 10 in 92 of 125 (74%) HiDAC cycles and in 106 of 113 (94%) IDAC cycles. As assessed by electron microscopy, these day-10 granulocytes surviving chemotherapy were found to be mature cells containing secondary granules and phagolysosomes. They also expressed opsonization- and phagocytosis-linked surface Ags (C3biR, CR1, C1qR, C5aR, FcgammaRI, FcgammaRII, FcgammaRIII, and G-CSF and GM-CSF receptors) like neutrophils in healthy controls. Moreover, these day-10 neutrophils exhibited oxidative burst activity and took up and digested bacteria in the same way as neutrophils in healthy controls. There was a negative correlation between absolute neutrophil counts and severe infections in HiDAC- and IDAC-treated patients with a later onset of infections in IDAC patients (median: IDAC, day 18; HiDAC, day 16). Together, functionally mature neutrophils are detectable at least until day 10 in patients treated with HiDAC or IDAC, and may explain the relatively low hematologic toxicity of these consolidation protocols. IDAC is a superior protocol in this regard and may therefore be most suitable for elderly patients and those at high risk for severe infections.

Effects of various statins on cytokine-dependent growth and IgE-dependent release of histamine in human mast cells

BACKGROUND

Statins are inhibitors of hydroxymethylglutaryl coenzyme A (HMG CoA) reductase, a key enzyme in mevalonic acid (MVA)-dependent signaling. Recent data suggest that statins exhibit profound inhibitory effects on growth and function of various immune cells. In the present study, we examined the in vitro effects of five different statins on primary human mast cells (MCs), MC progenitors, and the human MC line HMC-1.

METHODS

Histamine release experiments were conducted on isolated MCs using statins and an anti-immunoglobulin E (IgE) antibody. Culture experiments were performed with stem cell factor (SCF) and interleukin (IL)-6, and cord blood-derived progenitors.

RESULTS

Preincubation of primary lung MCs with cerivastatin or atorvastatin (1-50 microM) for 24 h resulted in inhibition of anti-IgE-induced release of histamine. The effects of both statins were dose-dependent. Moreover, both statins, and to a lesser degree lovastatin, were found to inhibit the SCF-induced differentiation of MCs from their progenitors. The other statins tested (simvastatin, pravastatin) did not affect mediator release or growth of MCs.

CONCLUSIONS

Cerivastatin and atorvastatin act as inhibitors of growth and function of human MCs.

Expression of cell surface antigens on mast cells: mast cell phenotyping

During the past few decades, a number of functionally important cell surface antigens have been detected on human mast cells (MCs). These antigens include the stem cell factor receptor (SCFR/CD117), the high-affinity immunoglobulin E receptor, adhesion molecules, and activation-linked membrane determinants. Several of these antigens (CD2, CD25, CD35, CD88, CD203c) appear to be upregulated on MCs in patients with systemic mastocytosis and therefore are used as diagnostic markers. Quantitative measurement of these markers on MCs is thus of diagnostic value and is usually performed by multicolor-based flow cytometry techniques utilizing a PE- or APC-labeled antibody against CD117 for MCs detection. This chapter gives an overview about the methods of staining of MC in various tissues with special reference to novel diagnostic markers applied in patients with suspected systemic mastocytosis.

Myelomastocytic Leukemia: Evidence for the Origin of Mast Cells from the Leukemic Clone and Eradication by Allogeneic Stem Cell Transplantation

PURPOSE

Myelomastocytic leukemia is a term used for patients with advanced myeloid neoplasms, in whom elevated numbers of immature atypical mast cells are found, but criteria for a primary mast cell disease are not met. The origin of mast cells in these patients is presently unknown.

PATIENT AND METHODS

We have analyzed clonality of mast cells in an 18-year-old patient suffering from acute myeloid leukemia with a complex karyotype including a t(8;21) and mastocytic transformation with a huge increase in immature mast cells and elevated serum tryptase level, but no evidence for a primary mast cell disease/mastocytosis.

RESULTS

As assessed by in situ fluorescence hybridization combined with tryptase staining, both the tryptase-negative blast cells and the tryptase-positive mast cells were found to contain the t(8;21)-specific AML1/ETO fusion gene. Myeloablative stem cell transplantation resulted in complete remission with consecutive disappearance of AML1/ETO transcripts, decrease of serum tryptase to normal range, and disappearance of neoplastic mast cells.

CONCLUSION

These data suggest that mast cells directly derive from the leukemic clone in patients with myelomastocytic leukemia.

Detection of differentiation- and activation-linked cell surface antigens on cultured mast cell progenitors

BACKGROUND

Mast cells (MC) are multifunctional effector cells of the immune system. They derive from uncommitted CD34(+) hemopoietic progenitor cells (HPC). Depending on the stage of maturation and the environment, MC variably express differentiation- and activation-linked antigens. Little is known, however, about the regulation of expression of such antigens in immature human MC.

METHODS

We analyzed expression of CD antigens on human MC grown from cord blood-derived CD34(+) HPC. The HPC were isolated by magnetic cell sorting (MACS) and FACS to >97% purity, and were cultured in stem cell factor (SCF) and interleukin (IL)-6 with or without additional cytokines (IL-4 or IL-10) in serum-free medium. The cell surface phenotype of MC was determined by monoclonal antibodies and flow cytometry.

RESULTS

Cultured MC progenitors were found to react with antibodies against various CD antigens including CD58, CD63, CD117, CD147, CD151, CD203c, and CD172a, independent of the growth factors used and time-point investigated (days 14-42). CD116 [granulocyte-macrophage colony-stimulating factor receptor alpha (GM-CSFRalpha)] and CD123 (IL-3Ralpha) were expressed on MC precursors on day 14, but disappeared thereafter. Cultured MC did not express CD2, CD3, CD5, CD10, CD19, or CD25. Addition of IL-10 to MC cultures showed no effect on expression of CD antigens. However, IL-4 was found to promote expression of CD35 and CD88 on cultured MC without changing expression of other CD antigens.

CONCLUSIONS

Most MC antigens may already be expressed at an early stage of mastopoiesis. Whereas IL-3R and GM-CSFRs are lost during differentiation of MC, these cells may acquire complement receptors (CD35, CD88) under the influence of distinct cytokines.

Cell surface membrane antigen phenotype of human gastrointestinal mast cells

BACKGROUND

Mast cells (MC) are important effector cells of allergic and inflammatory reactions in diverse organs. These cells interact with a number of other immune cells and structural cells in the tissues as well as with proinflammatory mediators and cytokines. The various interactions are considered to be mediated through distinct cell surface membrane receptors on MC.

METHODS

In the present study, we have established the cell surface membrane phenotype of human gastrointestinal MC (HGMC) using a panel of monoclonal antibodies and indirect immunofluorescence staining techniques.

RESULTS

HGMC were found to react with antibodies against CD29, CD33, CD44, CD45, CD47, CD54, CD55, CD58, CD63, CD117, CD147, CD151, CD172a, and CD203c. By contrast, HGMC did not express detectable amounts of CD1, CD2, CD4, CD5, CD14, CD15, CD16, CD22, CD24, CD25, CD26, CD27, CD28, CD31, CD32, CD34, CD35, CD88, or CD116. The alpha-chain of the IL-3 receptor (CD123) was detectable neither in resting HGMC nor in HGMC exposed to stem cell factor and interleukin-4.

CONCLUSIONS

HGMC express a unique profile of surface antigens including the receptor for mast cell growth factor, adhesion-related molecules, and activation-linked membrane antigens.

Identification of mTOR as a novel bifunctional target in chronic myeloid leukemia: dissection of growth‐inhibitory and VEGF‐suppressive effects of rapamycin in leukemic cells

The mammalian target of rapamycin (mTOR) has recently been described to be constitutively activated in Bcr-Abl-transformed cells and to mediate rapamycin-induced inhibition of growth in respective cell lines. We have recently shown that rapamycin down-regulates expression of vascular endothelial growth factor (VEGF), a mediator of leukemia-associated angiogenesis, in primary CML cells. In the present study, we analyzed growth-inhibitory in vitro and in vivo effects of rapamycin on primary CML cells and asked whether rapamycin-induced suppression of VEGF in leukemic cells is related to growth inhibition. Rapamycin dose dependently inhibited growth of primary CML cells obtained from patients with imatinib-responsive or imatinib-resistant disease as well as growth of Bcr-Abl-transformed imatinib-resistant cell lines. Moreover, we observed potent cytoreductive effects of rapamycin in a patient with imatinib-resistant Bcr-Abl+ leukemia. The growth-inhibitory effects of rapamycin on CML cells were found to be associated with G1 cell cycle arrest and with induction of apoptosis. In all cell types tested, rapamycin was found to down-regulate expression of VEGF. However, exogenously added VEGF did not counteract the rapamycin-induced decrease in proliferation. In conclusion, rapamycin inhibits growth of CML cells in vitro and in vivo and, in addition, down-regulates expression of VEGF. Both effects may contribute to the antileukemic activity of the drug in CML.

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.

Gain of structure and IgE epitopes by eukaryotic expression of the major Timothy grass pollen allergen, Phl p 1

Approximately 400 million allergic patients are sensitized against group 1 grass pollen allergens, a family of highly cross-reactive allergens present in all grass species. We report the eukaryotic expression of the group 1 allergen from Timothy grass, Phl p 1, in baculovirus-infected insect cells. Domain elucidation by limited proteolysis and mass spectrometry of the purified recombinant glycoprotein indicates that the C-terminal 40% of Phl p 1, a major IgE-reactive segment, represents a stable domain. This domain also exhibits a significant sequence identity of 43% with the family of immunoglobulin domain-like group 2/3 grass pollen allergens. Circular dichroism analysis demonstrates that insect cell-expressed rPhl p 1 is a folded species with significant secondary structure. This material is well behaved and is adequate for the growth of crystals that diffract to 2.9 A resolution. The importance of conformational epitopes for IgE recognition of Phl p 1 is demonstrated by the superior IgE recognition of insect-cell expressed Phl p 1 compared to Escherichia coli-expressed Phl p 1. Moreover, insect cell-expressed Phl p 1 induces potent histamine release and leads to strong up-regulation of CD203c in basophils from grass pollen allergic patients. Deglycosylated Phl p 1 frequently exhibits higher IgE binding capacity than the recombinant glycoprotein suggesting that rather the intact protein structure than carbohydrate moieties themselves are important for IgE recognition of Phl p 1. This study emphasizes the important contribution of conformational epitopes for the IgE recognition of respiratory allergens and provides a paradigmatic tool for the structural analysis of the IgE allergen interaction.

Assays for measuring in vitro basophil activation induced by recombinant allergens

The diagnosis of type I allergy is essentially based on clinical data, skin tests, and measurements of allergen-specific IgE. However, the determination of specific IgE per se does not permit a definitive conclusion concerning the response of effector cells to the respective allergen(s) and consecutive clinical symptoms in all patients. In an attempt to overcome this problem, a number of basophil-activation assays have been developed during the last few years. Today, allergen-induced activation of blood basophils can be employed as a specific and reliable measure of IgE-dependent responses in sensitized individuals. Using recombinant allergens and basophil-specific markers, these novel assays appear to serve as simple and useful tests in component-resolved diagnosis of type I allergies. In the current article, the biochemical, functional, and technical background of these basophil tests is discussed.

Human leukaemic stem cells: a novel target of therapy

Acute myeloid leukaemia (AML) is a life-threatening haematopoietic disease that is characterized by clonal growth and the accumulation of myelopoietic progenitor cells. Although AML cells only have a limited potential to undergo differentiation and maturation, each AML clone is organized in a hierarchical manner similar to normal haematopoiesis. Recent data have shown that each AML clone consists of leukaemic stem cells and their progeny, and that AML stem cells differ from more mature cells in several aspects, including survival and target antigen profiles. Most importantly, AML stem cells, but not their progeny, have the capacity to repopulate haematopoietic tissues with leukaemias in NOD/SCID mice. Furthermore, AML stem cells are thought to be responsible for the infinite growth of leukaemias in patients with AML. The phenotypic properties of AML stem cells have also been described. In most cases, these cells are detectable within the CD34+, CD38-, Lin-, CD123+ subpopulation of AML cells. Because of their AML-initiating and -renewing capacity and their unique phenotype, which includes several molecular targets of drug therapy, AML stem cells have recently been proposed as novel important target cell populations in the context of curative therapies. The present article gives an overview of our knowledge about AML stem cells, their phenotype, and their role as a 'therapy-target' in new concepts to treat and to cure patients with AML.

Response to therapy with interferon alpha-2b and prednisolone in aggressive systemic mastocytosis: report of five cases and review of the literature

Aggressive systemic mastocytosis (ASM) is a hematopoietic neoplasm characterized by infiltration of visceral organs by neoplastic mast cells (MCs) with consecutive organopathy and respective clinical and laboratory findings (so called C-Findings). Whereas, it is generally appreciated that patients with ASM are candidates for pharmacological intervention, no ideal drug or drug combination have been identified yet. One drug proposed to work in ASM is interferon alpha-2b (IFN-alpha2b). However, little is known so far about the quality of responses to IFN-alpha2b and actual response rates. We here report on five ASM patients treated with either a combination of IFN-alpha2b (3x3 million units per week) and prednisolone (n=4), or IFN-alpha2b alone (n=1). During therapy, two of the five patients showed a major response defined by complete resolution of C-Finding(s), one a partial response (partial regression of C-Findings), and one a stable disease (no changes in C-Findings). In one patient, progression to mast cell leukemia was seen after 3 months. In contrast to the other patients, this patient exhibited >10% MCs in his bone marrow (bm) smear at first presentation. In summary, our data confirm beneficial effects of IFN-alpha2b (plus prednisolone) for a group of patients with ASM, whereas patients with mast cell leukemia may require more aggressive therapy. Prospective trials with more patients are now required to further document these drug effects and to better define subgroups of patients with ASM who show good and long-lasting responses to IFN-alpha2b.

Characterization of recombinant cat albumin

BACKGROUND

Indoor allergens derived from animals and mites often contribute to exacerbation of skin manifestations in atopic dermatitis (AD) patients.

OBJECTIVE

To produce and characterize recombinant cat albumin, a cross-reactive animal allergen.

METHODS

A complete cDNA coding for cat albumin was obtained by RT-PCR amplification from cat liver RNA. Recombinant cat albumin was expressed in Escherichia coli as hexahistidine-tagged protein, purified by nickel affinity chromatography and studied for IgE reactivity with sera from cat-allergic patients by ELISA and immunoblotting. Furthermore, CD203c expression of basophils from cat-allergic patients upon exposure to recombinant cat albumin was analysed.

RESULTS

Recombinant cat albumin, a cross-reactive animal allergen sharing most IgE epitopes with its natural counterpart, was produced in E. coli. It was recognized preferentially by IgE from AD patients and elicited IgE-dependent basophil activation in sensitized patients.

CONCLUSIONS

Recombinant cat albumin may be used as a paradigmatic tool to analyse mechanisms of allergen-triggered exacerbation of AD, for diagnostic and, perhaps for therapeutic purposes.

Treatment concepts for elderly patients with acute myeloid leukemia

The majority of patients with acute myeloid leukemia (AML) are over 60 years of age at diagnosis. Unlike treatment options for younger adults, those for older patients are limited to non-myeloablative therapy, and many patients are not treatable because of poor performance status. In those who are treatable, long-term survival can be achieved using intensive induction and consolidation chemotherapy. Such curative treatment can be administered in about 70% of elderly patients with AML. In responding patients (up to 60%) the disease-free survival may be almost comparable to that of younger adults. However, treatment-related toxicity results in a higher mortality rate in the elderly patients. Moreover, aggressive chemotherapy cannot be used for 30% of the patients, due to their poor performance status. Currently, palliative cytoreductive treatment and supportive care are considered appropriate for these patients. Recently, however, targeting antileukemic antibodies and inhibitors of signal transduction have been introduced as promising new treatment options. The therapeutic efficiency and toxicity-profiles of these novel drugs are currently under investigation in clinical trials.

Immunohistochemical detection of VEGF in the bone marrow of patients with acute myeloid leukemia. Correlation between VEGF expression and the FAB category

We studied vascular endothelial growth factor (VEGF) expression in bone marrow sections obtained from 3 healthy donors and 41 patients with acute myeloid leukemia (AML) of various French-American-British (FAB) subtypes by immunohistochemical analysis using an anti-VEGF antibody. In normal bone marrow, the anti-VEGF antibody reacted with myeloid progenitor cells and megakaryocytes but not with erythroid cells or mature granulocytic cells. High levels of VEGF were found in the bone marrow in patients with AML-M1, -M2, -M3, -M4, -M4Eo, and -M5. In these leukemias, the vast majority of myeloblasts (> 90%) expressed VEGF. By contrast, in AML-M0, the percentage of VEGF-positive blasts was lower in most cases (median, 42%), and if at all detectable, these blast cells contained only trace amounts of VEGF. In AML-M3 and -M4Eo, maturing granulocytes failed to express VEGF similar to granulocytes in normal bone marrow. In AML-M6, myeloblasts exhibited VEGF, whereas erythroid cells did not. In AML-M7, blast cells and megakaryocytes were identified as major sources of VEGF. In summary, VEGF expression in the bone marrow is restricted to certain stages of differentiation and maturation of myeloid cells and correlates with the FAB category.

Cerivastatin and atorvastatin inhibit IL-3-dependent differentiation and IgE-mediated histamine release in human basophils and downmodulate expression of the basophil-activation antigen CD203c/E-NPP3

Recent data suggest that the statins, apart from their lipid-lowering activity, exhibit profound anti-inflammatory effects. Basophils are major proinflammatory effector cells in diverse pathologic reactions. We have examined the in vitro effects of five different statins on primary human basophils, their progenitors, and the basophil cell line KU-812. Preincubation of blood basophils with cerivastatin or atorvastatin (0.1-100 microM) for 24 h reduced their capacity to release histamine on immunoglobulin E (IgE)-dependent stimulation in a dose-dependent manner. These statins also inhibited IgE-dependent up-regulation of the basophil-activation antigen CD203c. Moreover, both statins suppressed interleukin-3-induced differentiation of basophils from their progenitors as well as (3)H-thymidine uptake in KU-812 cells. All inhibitory effects of cerivastatin and atorvastatin were reversed by mevalonic acid (200 microM). The other statins tested (lovastatin, simvastatin, pravastatin) did not show significant inhibitory effects on basophils. Together, these data identify cerivastatin and atorvastatin as novel inhibitors of growth and activation of human basophils.

Tryptase a novel biochemical marker of acute myeloid leukemia

Despite maturation arrest, blast cells in acute myeloid leukemia (AML) are often capable of expressing lineage-restricted (granulomonocytic or myelomastocytic) differentiation antigens. Tryptases are lineage-associated serine proteases primarily expressed in mast cells, and less abundantly in blood basophils. We have recently shown that myeloblasts in a group of patients with AML (approximately 40%) produce significant amounts of tryptase(s). In these patients, serum tryptase levels are elevated (> 15 ng/ml) and reflect the total burden of leukemic cells. In most cases, myeloblasts express alpha-tryptase mRNA in excess over beta-tryptase mRNA, and secrete the respective protein (= pro-alpha-tryptase) in a constitutive manner. It was also found that these AML blasts frequentlyco-express tryptase with additional mast cell lineage- and/or basophil-related differentiation antigens including KIT (CD117), histamine, and 2D7. We hypothesize that tryptase-positive AMLs arise from a leukemic progenitor that exhibits a limited potential to differentiate into mast cells and/or basophils.

C5a stimulates production of plasminogen activator inhibitor-1 in human mast cells and basophils

We have recently shown that resting human mast cells (MCs) produce tissue-type plasminogen activator (t-PA) without simultaneously expressing plasminogen activator inhibitor 1 (PAI-1). In the present study we have identified the anaphylatoxin rhC5a as a potent inducer of PAI-1 expression in human MCs and basophils. In primary human skin MCs and primary blood basophils, exposure to rhC5a was followed by an increase from undetectable to significant levels of PAI-1. In addition, rhC5a induced a concentration- and time-dependent increase in PAI-1 antigen in the MC line HMC-1 and the basophil cell line KU-812 and increased the expression of PAI-1 mRNA in HMC-1. In conditioned media of HMC-1 treated with rhC5a, active PAI-1 could be detected. A simultaneous loss of t-PA activity in conditioned media from the same cells indicated that rhC5a-induced PAI-1 was capable of inhibiting the enzymatic activity of coproduced t-PA. Correspondingly, the levels of t-PA-PAI-1 complexes increased in rhC5a-treated cells. When HMC-1 cells were incubated with pertussis toxin or anti-C5a receptor antibodies, the effect of rhC5a on PAI-1 production was completely abolished. Treatment of C5a with plasmin resulted in loss of its ability to induce PAI-1 production in MCs. Considering the suggested role for MCs and components of the complement system in the development of cardiovascular diseases, we hypothesize that MCs, by producing t-PA in a resting state and by expressing PAI-1 when activated by C5a, might participate in the modulation of the balance between proteases and protease inhibitors regulating tissue injury and repair in such disease processes.

Recombinant allergens promote expression of CD203c on basophils in sensitized individuals

BACKGROUND

Traditionally, the diagnosis of type I allergies is based on clinical data, skin test results, and laboratory test results with allergen extracts. During the past few years, several attempts have been made to refine diagnostic assays in clinical allergy by introducing recombinant allergens and novel markers of IgE-dependent cell activation.

OBJECTIVES

We have identified the ectoenzyme CD203c as a novel basophil antigen that is upregulated on IgE receptor cross-linkage. In this study we applied CD203c and a panel of recombinant allergens to establish a novel basophil test that allows for a reliable quantification of IgE-dependent responses at the effector cell level.

METHODS

Patients allergic to birch (Bet v 1, n = 15; Bet v 2, n = 8) and grass (Phl p 1, n = 15; Phl p 2, n = 10; Phl p 5, n = 14) pollen allergens, as well as 10 nonallergic donors, were examined. Basophils were exposed to various concentrations of recombinant allergens for 15 minutes and then examined for expression of CD203c by means of flow cytometry. CD203c upregulation was correlated with the increase in CD63.

RESULTS

Exposure to recombinant allergens resulted in a dose-dependent increase in expression of CD203c on peripheral blood basophils in sensitized individuals, whereas no increase was seen in healthy control subjects. The effects of the recombinant allergens on CD203c expression were also time dependent. There was a good correlation between allergen-induced upregulation of CD203c and upregulation of CD63 (R = 0.76).

CONCLUSION

Flow cytometric quantitation of CD203c on blood basophils exposed to recombinant allergens is a useful approach to determine the allergic state in sensitized individuals and represents a basis for a sensitive novel allergy test.

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.

Signal transduction-associated and cell activation-linked antigens expressed in human mast cells

Mast cells (MCs) are multifunctional hematopoietic effector cells that produce and release an array of biologically active mediator substances. Growth and functions of MCs are regulated by cytokines, other extracellular factors, surface and cytoplasmic receptors, oncogene products, and a complex network of signal transduction cascades. Key regulators of differentiation of MCs appear to be stem cell factor (SCF) and its tyrosine kinase receptor KIT (c-kit proto-oncogene product=CD117), downstream-acting elements, and the mi transcription factor (MITF). Signaling through KIT is negatively regulated by the signal regulatory protein (SIRP)-alpha (CD172a)-SHP-1-pathway that is disrupted in neoplastic MCs in MC proliferative disorders. Both KIT and FcepsilonRI are involved in MC activation and mediator release. Activation of MCs through FcepsilonRI is associated with increased expression of activation-linked membrane antigens as well as with signaling events involving Lyn and Syk kinases, the phosphatidylinositol-3-kinase-pathway, Ras pathway, and the phospholipase C-protein kinase C pathway. A similar network of signaling is found in SCF-activated MCs. The current article gives an overview on signal transduction-associated and activation-linked antigens expressed in human MCs. Wherever possible the functional implication of signaling pathways and antigen expression are discussed.

Detection of novel CD antigens on the surface of human mast cells and basophils

BACKGROUND

Mast cells (MC) and basophils are effector cells of allergic reactions. Growth and function of these cells are regulated by a network of cytokines, other ligands, and respective cell surface membrane receptors.

METHODS

In the present study, we examined the expression of novel CD antigens on human lung MC, skin MC, blood basophils, the MC line HMC-1, and the basophil cell line KU-812. Expression of surface antigens was analyzed by monoclonal antibodies (mAbs) and indirect immunofluorescence staining techniques.

RESULTS

Primary MC were found to react with mAbs against KIT (CD117), the signal regulatory protein SIRP-alpha (CD172a), and the ectoenzyme E-NPP3 (CD203c). Human basophils were found to express large amounts of E-NPP3 and lower levels of Siglec-5 (CD170), CXCR4 (CD184) and SIRP-alpha. The HMC-1 cell line was recognized by mAbs against SIRP-alpha, CXCR4, endothelial protein C receptor (CD201) and E-NPP3. KU-812 cells were found to react with mAbs against E-NPP3, CXCR4 and glycophorin C (CD236R), but did not react with mAb against endothelial protein C receptor. Most of the other CD antigens tested disclosed negative results.

CONCLUSIONS

In summary, our data provide further evidence that MC and basophils express a unique composition of surface antigens. The use of novel CD antibodies may help to isolate MC and basophils and to study their functional properties.