Human mast cells express receptors for IL-3, IL-5 and GM-CSF; a partial map of receptors on human mast cells cultured in vitro

MEDI-563, a humanized anti-IL-5 receptor alpha mAb with enhanced antibody-dependent cell-mediated cytotoxicity function

BACKGROUND

Peripheral blood eosinophilia and lung mucosal eosinophil infiltration are hallmarks of bronchial asthma. IL-5 is a critical cytokine for eosinophil maturation, survival, and mobilization. Attempts to target eosinophils for the treatment of asthma by means of IL-5 neutralization have only resulted in partial removal of airway eosinophils, and this warrants the development of more effective interventions to further explore the role of eosinophils in the clinical expression of asthma.

OBJECTIVE

We sought to develop a novel humanized anti-IL-5 receptor alpha (IL-5Ralpha) mAb with enhanced effector function (MEDI-563) that potently depletes circulating and tissue-resident eosinophils and basophils for the treatment of asthma.

METHODS

We used surface plasmon resonance to determine the binding affinity of MEDI-563 to FcgammaRIIIa. Primary human eosinophils and basophils were used to demonstrate antibody-dependent cell-mediated cytotoxicity. The binding epitope of MEDI-563 on IL-5Ralpha was determined by using site-directed mutagenesis. The consequences of MEDI-563 administration on peripheral blood and bone marrow eosinophil depletion was investigated in nonhuman primates.

RESULTS

MEDI-563 binds to an epitope on IL-5Ralpha that is in close proximity to the IL-5 binding site, and it inhibits IL-5-mediated cell proliferation. MEDI-563 potently induces antibody-dependent cell-mediated cytotoxicity of both eosinophils (half-maximal effective concentration = 0.9 pmol/L) and basophils (half-maximal effective concentration = 0.5 pmol/L) in vitro. In nonhuman primates MEDI-563 depletes blood eosinophils and eosinophil precursors in the bone marrow.

CONCLUSIONS

MEDI-563 might provide a novel approach for the treatment of asthma through active antibody-dependent cell-mediated depletion of eosinophils and basophils rather than through passive removal of IL-5.

Both interleukin-3 and interleukin-6 are necessary for better ex vivo expansion of CD133+ cells from umbilical cord blood

Umbilical cord blood (UCB), an ideal source for transplantable hematopoietic stem cells (HSC), is readily available and is rich in progenitor cells. Identification of conditions favoring UCB-HSC ex vivo expansion and of repopulating potential remains a major challenge in hematology. CD133+ cells constitute an earlier, less-differentiated HSC group with a potentially higher engraftment capacity. The presence of SCF, Flt3-L, and TPO are essential for CD133+ and/or CD34+ cells ex vivo expansion; however, IL-3 and IL-6 influence has not yet been clearly established. We investigated this influence on CD133+ cells from UCB ex vivo expansion and the effect of these cytokines upon cell phenotype. Immediately after isolation an 85% of CD133+ cell purity was obtained, diminishing after 4 and 8 days of ex vivo expansion. CD133+ fold-increase was higher using IMDM with SCF, Flt3-L, and TPO (BM)+IL-3 or BM+IL-3+IL-6 on day 8 (13.83- and 17.47-fold increase, respectively). BM+IL-6 presented no significant difference from BM alone. We demonstrated that 5.1% of the CD133+ cells expressed IL-6 receptor (IL-6R) after isolation. After 4 and 8 days in culture, the percentage of CD133+ cells that expressed IL-6R was as follows: BM alone (9.8% and 22.02%, respectively); BM+IL-3 (8.33% and 16.74%); BM+IL-6 (9.2% and 17.67%); and BM+IL-3+IL-6 (12.5% and 61.20%). Cell cycle analysis revealed quiescent cells after isolation, 95.5% CD133+ cells in the G0/G1 phase. Regardless of culture period or cytokine incubation, CD133+ cell cycle altered to 70% of CD133+ in the G0/G1 phase. Colony-forming unit (CFU) doubled in BM+IL-3+IL-6 after 8 days of incubation compared with BM group. SOX-2 and NANOG-relative gene expression was detected on day 0 after isolation. BM+IL-6 prevented the decrease in NANOG and SOX-2 gene expression level compared to BM+IL-3 or BM+IL-3+IL-6 incubated cells. Our results indicated that UCB-isolated CD133+ cells were better ex vivo expanded in the presence of SCF, Flt3-L, TPO, IL-3+IL-6. IL-3 probably promotes higher CD133+ cell expansion and IL-6 maintains immature phenotype.

FIP1L1/PDGFR alpha-associated systemic mastocytosis

Since the identification of the FIP1L1/PDGFRA fusion gene as a pathogenic cause of the hypereosinophilic syndrome (HES), the importance of the molecular classification of HES leading to the diagnosis of chronic eosinophilic leukemia (CEL) has been recognized. As a result, a new category, 'myeloid and lymphoid neoplasm with eosinophilia and abnormalities in PDGFRA, PDGFRB or FGFR1', has recently been added to the new WHO criteria for myeloid neoplasms. FIP1L1/PDGFR alpha-positive disorders are characterized by clonal hypereosinophilia, multiple organ dysfunctions due to eosinophil infiltration, systemic mastocytosis (SM) and a dramatic response to treatment with imatinib mesylate. A murine HES/CEL model by the introduction of FIP1L1/PDGFR alpha and IL-5 overexpression also shows SM, representing patients with FIP1L1/PDGFR alpha-positive HES/CEL/SM. The murine model and the in vitro development system of FIP1L1/PDGFR alpha-positive mast cells revealed the interaction between FIP1L1/PDGFR alpha, IL-5 and stem cell factor in the development of HES/CEL/SM. Current findings of FIP1L1/PDGFR alpha-positive HES/CEL are reviewed focusing on aberrant mast cell development leading to SM.

Induction of IL-4 release and upregulated expression of protease activated receptors by GM-CSF in P815 cells

GM-CSF has been showed to be able to induce up-regulated receptor and cytokine expression in mast cells in inflammatory conditions. However, little is known of its effects on protease activated receptor (PAR) expression and Th2 cytokine secretion from mast cells. In the present study, we examined potential influence of GM-CSF on mast cell PAR expression and IL-4 and IL-10 release by using flow cytometry analysis, quantitative real time PCR, ELISA and cellular activation of signaling ELISA (CASE) techniques. The results showed that GM-CSF induced up to 3.0-fold increase in IL-4 release from P815 cells, and FSLLRY-NH(2) and trans-cinnamoyl (tc)-YPGKF-NH(2) did not affect GM-CSF induced IL-4 release. GM-CSF reduced tryptase and trypsin induced IL-4 release by up to approximately 55.8% and 70.3%, respectively. GM-CSF elicited the upregulated expression of PAR-1, PAR-2, PAR-3 and PAR-4 mRNAs, but enhanced only PAR-4 protein expression in P815 cells. U0126, PD98059 and LY204002 almost completely abolished GM-CSF induced IL-4 release when they were preincubated with P815 cells for 30 min, indicating ERK and Akt cell signaling pathways may be involved in the event. In conclusion, GM-CSF can stimulate IL-4 release from mast cells through an ERK and Akt cell signaling pathway dependent, but PAR independent mechanism. GM-CSF may serve as a regulator for IL-4 production in mast cells and through which participates in the mast cell related inflammation.

CXCR2 antagonists for the treatment of pulmonary disease

Chemokines have long been implicated in the initiation and amplification of inflammatory responses by virtue of their role in leukocyte chemotaxis. The expression of one of the receptors for these chemokines, CXCR2, on a variety of cell types and tissues suggests that these receptors may have a broad functional role under both constitutive conditions and in the pathophysiology of a number of acute and chronic diseases. With the development of several pharmacological, immunological and genetic tools to study CXCR2 function, an important role for this CXC chemokine receptor subtype has been identified in chronic obstructive pulmonary disease (COPD), asthma and fibrotic pulmonary disorders. Interference with CXCR2 receptor function has demonstrated different effects in the lungs including inhibition of pulmonary damage induced by neutrophils (PMNs), antigen or irritant-induced goblet cell hyperplasia and angiogenesis/collagen deposition caused by lung injury. Many of these features are common to inflammatory and fibrotic disorders of the lung. Clinical trials evaluating small molecule CXCR2 antagonists in COPD, asthma and cystic fibrosis are currently underway. These studies hold considerable promise for identifying novel and efficacious treatments of pulmonary disorders.

Potential mechanism for recruitment and migration of CD133 positive cells to areas of vascular inflammation

OBJECTIVE

Mast cells are found in large numbers in atherosclerotic plaques. The present study was conducted to determine whether tryptase stimulation of human coronary artery endothelial cells (HCAEC) would lead to an increase in transmigration of CD133 positive cells (CD133+). In vitro these cells can differentiate into mast cells under the influence of specific cytokines and growth factors.

METHODS AND RESULTS

CD133+ cells were isolated from umbilical cord blood. They express mRNA for several adhesion molecules that are also utilized in neutrophil migration and can migrate across an HCAEC monolayer. Migration increased significantly when HCAEC were stimulated with tryptase and decreased when CD133+ cells were pretreated with CV3988, a platelet activating factor receptor (PTAFR) antagonist. Following long-term cell culture, these cells stained positively for the presence of tryptase, a mast cell enzyme.

CONCLUSION

CD133+ cells can be utilized as a mast cell precursor population. The transendothelial migration is facilitated by the presence of tryptase and may utilize the PAF/PTAFR interaction in a manner similar to that involved in neutrophil transmigration. Following transmigration, a subset of these progenitor cells may mature into mast cells in the subendothelial space and play a role in propagation of the inflammatory process in atherosclerosis.

Generation of a considerable number of functional mast cells with a high basal level of FcepsilonRI expression from cord blood CD34+ cells by co-culturing them with bone marrow stromal cell line under serum-free conditions

The number of mast cells (MC) that can be obtained from tissue is limited, making it difficult to study the role of MC. Cultured MC derived from cord blood (CB)-CD34(+) cells proliferate well compared with those derived from adult CD34(+) cells; however, they have been reported to be phenotypically or functionally immature regardless of culture system. For example, very few cells express FcepsilonRI. To resolve this problem, we addressed the effect of human bone marrow stromal cell line on the development of cultured MC. CB-CD34(+) (1 x 10(4)) cells were cultured for 8 weeks in a serum-free medium containing rhIL-6 and rhSCF with or without a human bone marrow stromal cell line, namely, co-culture and liquid culture, and were compared in various regards. MC were basically determined by metachromatic staining of granules. The number of MC obtained (60.3 +/- 15.8 x 10(5) versus 2.0 +/- 1.0 x 10(5)), percentage of FcepsilonRI(+) cells (29.3 +/- 9.4% versus 1.9 +/- 0.8%), histamine content (9.7 +/- 2.8 pg/cell versus 5.8 +/- 2.3 pg/cell), and IgE-mediated histamine release (46 +/- 10% versus 17 +/- 7%) were higher (P < 0.01 and P < 0.05) in the co-culture than in the liquid culture. When CB-CD34(+) cells were developed in liquid culture with the co-culture supernatant (CM), a significant increase (P < 0.01) in the percentage of FcepsilonRI(+) cells and in cell number was observed but these values were lower than those of co-cultured MC. We concluded that this co-culture system was useful for obtaining a considerable number of mature MC with a high basal level of functional FcepsilonRI expression from CB-CD34(+) cells. Yet unknown humoral factors in CM may partly mediate this effect.

Role of mast cells in allergic and non-allergic immune responses: comparison of human and murine data

The versatile role of mast cells in allergy, in innate immune responses and in the regulation of tissue homeostasis is well recognized. However, it is often not made clear that most mast-cell data derive solely from experiments in mice or rats, species that obviously never suffer from allergic and most other mast-cell-associated human diseases. Data on human mast cells are limited, and the mast-cell source and species from which findings derive are frequently not indicated in the titles and summaries of research publications. This Review summarizes recent data on human mast cells, discusses differences with murine mast cells, and describes new tools to study this increasingly meaningful cell type in humans.

Modulation of Chemokine Gene Expression in CD133+Cord Blood-Derived Human Mast Cells by Cyclosporin A and Dexamethasone

We have recently developed a protocol for generating huge numbers of mature and functional mast cells from in vitro differentiated umbilical cord blood cells. Using CD133 as a positive selection marker to isolate haematopoietic progenitors we routinely expand the number of recovered cells at least 150-fold, which vastly exceeds the yields of conventional protocols using CD34+ cells as a source of progenitors. Taking advantage of the large quantities of in vitro differentiated mast cells, here we assess at the levels of transcription and translation the kinetics of chemokine gene induction following receptor mediated mast cell activation or following pharmacological activation of specific signal transduction cascades that become activated upon classical FcepsilonRI receptor crosslinking. We demonstrate that chemokine genes encoding IL-8, MCP-1, MIP-1alpha, and MIP-1beta are induced with different kinetics and with different amplitudes in a receptor activation dependent manner, and that these events can be mimicked using pharmacological agents which activate distinct signal transduction pathways. These findings were corroborated by adding immunomodulators such as cyclosporin A and dexamethasone prior to mast cell activation. Finally, we demonstrate that the same modulators added after mast cell activation can differentially quench ongoing chemokine gene induction. Thus, considering the vast yields of mast cells, our protocol is valuable not only for studying regulation of gene expression in mast cells in general, but also as an experimental tool to develop better and more balanced treatments of mast cell related disorders.

Generation and characterization of bone marrow-derived cultured canine mast cells

Disorders of mast cells, particularly mast cell tumors (MCTs), are common in dogs. There now is evidence that many of these disorders exhibit breed predilections, suggesting an underlying heritable component. In comparison to humans and mice, little is known regarding the biology of canine mast cells. To facilitate the study of mast cell biology in other species, bone marrow-derived cultured mast cells (BMCMCs) often are used because these represent a ready source of large numbers of cells. We have developed a protocol to successfully generate canine BMCMCs from purified CD34(+) cells. After 5-7 weeks of culture with recombinant canine stem cell factor (rcSCF), greater than 90% of the cell population consisted of mast cells as evidenced by staining with Wright's-Giemsa, as well as production of chymase, tryptase, IL-8 and MCP-1. These cells expressed cell surface markers typical of mast cells including Kit, Fc epsilonRI, CD44, CD45 and CD18/CD11b. The canine BMCMCs were dependent on rcSCF for survival and proliferation, and migrated in response to rcSCF gradients. Cross-linking of cell surface-bound IgE induced the release of histamine and TNFalpha. Histamine release could also be stimulated by ConA, compound 48/80, and calcium ionophore. In summary, canine BMCMCs possess phenotypic and functional properties similar to mast cells found in vivo. These cells represent a novel, valuable resource for investigating normal canine mast cell biology as well as for identifying factors that lead to mast cell dysregulation in the dog.

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.

Gene expression and regulation of transcription factor activator protein-2 alpha in human mast cells

BACKGROUND

The transcription factor activator protein (AP)-2 regulates cell-type specific gene expression during development and differentiation, but its role in mast cell development has so far not been explored.

METHODS

Gene expression and regulation of AP2 was assessed in normal skin, diseases with increased mast cell numbers, and in vitro models of mast cell differentiation.

RESULTS

AP-2alpha-protein was not detectable in normal skin but in mastocytoma lesional mast cells. AP-2alpha-mRNA and -protein were also detected in leukemic mast cells (HMC-1), in the adherent fraction of peripheral blood (PBMC) and umbilical cord blood mononuclear cells (CBMC), and AP-2alpha-mRNA at low levels in isolated-purified mast cells. During culture with fibroblast supernatants or SCF, AP-2alpha-mRNA was de novo expressed in KU812-cells, maintained at about the same level in PBMC and CBMC, and upregulated in HMC-1-cells. On extended culture, a down-regulation was noted at mRNA and/or protein levels. In contrast, tryptase expression increased in all cells throughout culture, as did c-Kit in normal cells, whereas in both leukemic cell lines, c-Kit was maintained unchanged at about the same level.

CONCLUSIONS

These findings suggest a continuous activation of AP-2alpha in mastocytomas and mast cell leukemia and its transient upregulation during c-Kit dependent early steps of normal mast cell differentiation.