Siglec-8 antibody reduces eosinophils and mast cells in a transgenic mouse model of eosinophilic gastroenteritis

Aberrant accumulation and activation of eosinophils and potentially mast cells (MCs) contribute to the pathogenesis of eosinophilic gastrointestinal diseases (EGIDs), including eosinophilic esophagitis (EoE), gastritis (EG), and gastroenteritis (EGE). Current treatment options, such as diet restriction and corticosteroids, have limited efficacy and are often inappropriate for chronic use. One promising new approach is to deplete eosinophils and inhibit MCs with a monoclonal antibody (mAb) against sialic acid-binding immunoglobulin-like lectin 8 (Siglec-8), an inhibitory receptor selectively expressed on MCs and eosinophils. Here, we characterize MCs and eosinophils from human EG and EoE biopsies using flow cytometry and evaluate the effects of an anti-Siglec-8 mAb using a potentially novel Siglec-8-transgenic mouse model in which EG/EGE was induced by ovalbumin sensitization and intragastric challenge. MCs and eosinophils were significantly increased and activated in human EG and EoE biopsies compared with healthy controls. Similar observations were made in EG/EGE mice. In Siglec-8-transgenic mice, anti-Siglec-8 mAb administration significantly reduced eosinophils and MCs in the stomach, small intestine, and mesenteric lymph nodes and decreased levels of inflammatory mediators. In summary, these findings suggest a role for both MCs and eosinophils in EGID pathogenesis and support the evaluation of anti-Siglec-8 as a therapeutic approach that targets both eosinophils and MCs.

AK002, a Humanized Sialic Acid-Binding Immunoglobulin-Like Lectin-8 Antibody that Induces Antibody-Dependent Cell-Mediated Cytotoxicity against Human Eosinophils and Inhibits Mast Cell-Mediated Anaphylaxis in Mice

INTRODUCTION

Pathologic accumulation and activation of mast cells and eosinophils are implicated in allergic and inflammatory diseases. Sialic acid-binding immunoglobulin-like lectin (Siglec)-8 is an inhibitory receptor selectively expressed on mast cells, eosinophils and, at a lower extent, basophils. When engaged with an antibody, Siglec-8 can induce apoptosis of activated eosinophils and inhibit mast cell activation. AK002 is a humanized, non-fucosylated IgG1 anti-Siglec-8 antibody undergoing clinical investigation for treatment of allergic, inflammatory, and proliferative diseases. Here we examine the human tissue selectivity of AK002 and evaluate the in vitro, ex vivo, and in vivo activity of AK002 on eosinophils and mast cells.

METHODS

The affinity of AK002 for Siglec-8 and CD16 was determined by biolayer interferometry. Ex vivo activity of AK002 on human eosinophils from blood and dissociated human tissue was tested in apoptosis and antibody-dependent cell-mediated cytotoxicity (ADCC) assays. The in vivo activity of a murine precursor of AK002 (mAK002) was tested in a passive systemic anaphylaxis (PSA) humanized mouse model.

RESULTS

AK002 bound selectively to mast cells, eosinophils and, at a lower level, to basophils in human blood and tissue and not to other cell types examined. AK002 induced apoptosis of interleukin-5-activated blood eosinophils and demonstrated potent ADCC activity against blood eosinophils in the presence of natural killer cells. AK002 also significantly reduced eosinophils in dissociated human lung tissue. Furthermore, mAK002 prevented PSA in humanized mice through mast cell inhibition.

CONCLUSION

AK002 selectively evokes potent apoptotic and ADCC activity against eosinophils and prevents systemic anaphylaxis through mast cell inhibition.

Sialic acid-binding immunoglobulin-like lectin (Siglec) 8 in patients with eosinophilic disorders: Receptor expression and targeting using chimeric antibodies

BACKGROUND

Sialic acid-binding immunoglobulin-like lectin (Siglec) 8 is selectively expressed on eosinophils, mast cells, and basophils and, when engaged on eosinophils, can cause cell death.

OBJECTIVE

We sought to characterize surface and soluble Siglec-8 (sSiglec-8) levels in normal donors (NDs) and eosinophilic donors (EOs) and assess the efficacy of anti-Siglec-8 antibodies in inducing eosinophil cell death in vitro.

METHODS

Eosinophil expression of Siglec-8 was assessed by using flow cytometry and quantitative PCR. Serum sSiglec-8 levels were measured by means of ELISA. Induction of eosinophil death by IgG₄ (chimeric 2E2 IgG₄) and afucosylated IgG₁ (chimeric 2E2 IgG₁ [c2E2 IgG₁]) anti-Siglec-8 antibodies was evaluated in vitro by using flow cytometry and in vivo in humanized mice.

RESULTS

Siglec-8 was consistently expressed on eosinophils from NDs and EOs and did not correlate with absolute eosinophil count or disease activity. sSiglec-8 levels were measurable in sera from most donors unrelated to absolute eosinophil counts or Siglec-8 surface expression. c2E2 IgG₁ and chimeric 2E2 IgG₄ were equally effective at inducing cell death (Annexin-V positivity) of purified eosinophils from NDs and EOs after overnight IL-5 priming. In contrast, killing of purified eosinophils without IL-5 was only seen in EOs, and natural killer cell-mediated eosinophil killing was seen only with c2E2 IgG₁. Finally, treatment of humanized mice with anti-Siglec antibody led to robust depletion of IL-5-induced eosinophilia in vivo.

CONCLUSIONS

Siglec-8 is highly expressed on blood eosinophils from EOs and NDs and represents a potential therapeutic target for eosinophilic disorders. Enhanced killing of eosinophils in the presence of IL-5 might lead to increased efficacy in patients with IL-5-driven eosinophilia.

Targeting EphA3 inhibits cancer growth by disrupting the tumor stromal microenvironment

Eph receptor tyrosine kinases are critical for cell-cell communication during normal and oncogenic tissue patterning and tumor growth. Somatic mutation profiles of several cancer genomes suggest EphA3 as a tumor suppressor, but its oncogenic expression pattern and role in tumorigenesis remain largely undefined. Here, we report unexpected EphA3 overexpression within the microenvironment of a range of human cancers and mouse tumor xenografts where its activation inhibits tumor growth. EphA3 is found on mouse bone marrow-derived cells with mesenchymal and myeloid phenotypes, and activation of EphA3(+)/CD90(+)/Sca1(+) mesenchymal/stromal cells with an EphA3 agonist leads to cell contraction, cell-cell segregation, and apoptosis. Treatment of mice with an agonistic α-EphA3 antibody inhibits tumor growth by severely disrupting the integrity and function of newly formed tumor stroma and microvasculature. Our data define EphA3 as a novel target for selective ablation of the tumor microenvironment and demonstrate the potential of EphA3 agonists for anticancer therapy.

A high affinity recombinant antibody to the human EphA3 receptor with enhanced ADCC activity

EphA3 is expressed in solid tumors and leukemias and is an attractive target for the therapy. We have generated a panel of Humaneered® antibodies to the ligand-binding domain using a Fab epitope-focused library that has the same specificity as monoclonal antibody mIIIA4. A high-affinity antibody was selected that competes with the mIIIA4 antibody for binding to EphA3 and has an improved affinity of ∼1 nM. In order to generate an antibody with potent cell-killing activity the variable regions were assembled with human IgG1k constant regions and expressed in a Chinese hamster ovary (CHO) cell line deficient in fucosyl transferase. Non-fucosylated antibodies have been reported to have enhanced binding affinity for the IgG receptor CD16a (FcγRIIIa). The affinity of the antibody for recombinant CD16a was enhanced approximately 10-fold. This resulted in enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) activity against EphA3-expressing leukemic cells, providing a potent antibody for the evaluation as a therapeutic agent.

The use of UCOE vectors in combination with a preadapted serum free, suspension cell line allows for rapid production of large quantities of protein

UCOE vectors contain non-tissue specific chromatin-opening-elements that permit rapid expression of a protein in anintegration independent manner. Efficient expression can bederived from a single copy of an integrated gene site resulting ina higher percentage of cells expressing the marker gene in theselected pool in comparison to standard non-UCOE containingvectors. This, in combination with the utilization of a serum-free, suspension adapted parent cell line allows for rapidproduction of large quantities of protein in a short period oftime. Utilizing this system more than 300 mg of a recombinantantibody has been produced in less than 1 month from transfectionpools in shake flask. Selected subclones have been scaled intosmall bioreactors in less than 2 months, producing significantquantities of monoclonal antibody using a protocol generic for theparent cell line. The increased efficiency obtained with the UCOEvector reduces the number of transfectants which need to bescreened in order to obtain high productivity subclones.Transfection of a standard host cell line, preadapted to grow in alarge-scale setting, allows for rapid cell line developmentdecreasing the transition time from research into development andmanufacturing. Alternatively, the traditional approach of using aparent cell line which requires serum-free and suspensionadaptation after transfection further increases the need forscreening a large number of subclones, because many of thesubclones will not be able to grow under conditions that allowlarge-scale protein production. The use of a preadapted cell linecan reduce the time required to develop a cell line from months toweeks.

Granulocyte-macrophage colony-stimulating factor antibody suppresses microglial activity: implications for anti-inflammatory effects in Alzheimer's disease and multiple sclerosis

The objective of our study was to determine granulocyte-macrophage colony-stimulating factor (GM-CSF) activity in the brain following GM-CSF induction. We injected recombinant mouse GM-CSF into the brains of 8-month-old C57BL6 mice via intracerebroventricular injections and studied the activities of microglia, astrocytes, and neurons. We also sought to determine whether an anti-GM-CSF antibody could suppress endogenous microglial activity in the C57BL6 mice and could also suppress microglial activity induced by the recombinant mouse GM-CSF in another group of C57BL6 mice. Using quantitative real-time RT-PCR, we assessed microglial, astrocytic, and neuronal activity by measuring mRNA expression of pro-inflammatory cytokines, GFAP, and the neuronal marker NeuN in the cerebral cortex tissues from C57BL6 mice. We performed immunoblotting and immunohistochemistry of activated microglia in different regions of the brains from control (phosphate-buffered saline-injected C57BL6 mice) and experimental mice (recombinant GM-CSF-injected C57BL6 mice, GM-CSF antibody-injected C57BL6 mice, and recombinant mouse GM-CSF plus anti-GM-CSF antibody-injected C57BL6 mice). We found increased mRNA expression of CD40 (9.75-fold), tumor necrosis factor-alpha (2.1-fold), CD45 (1.73-fold), and CD11c (1.70-fold) in the cerebral cortex of C57BL6 mice that were induced with recombinant GM-CSF, compared with control mice. Further, the anti-GM-CSF antibody suppressed microglia in mice that were induced with recombinant GM-CSF. Our immunoblotting and immunohistochemistry findings of GM-CSF-associated cytokines in C57BL6 mice induced with recombinant GM-CSF, in C57BL6 mice injected with the anti-GM-CSF antibody, and in C57BL6 mice injected with recombinant mouse GM-CSF plus anti-GM-CSF antibody concurred with our real-time RT-PCR findings. These findings suggest that GM-CSF is critical for microglial activation and that anti-GM-CSF antibody suppresses microglial activity in the CNS. The findings from this study may have implications for anti-inflammatory effects of Alzheimer's disease and experimental autoimmune encephalomyelitis mice (a multiple sclerosis mouse model).

Neutralization of granulocyte macrophage colony-stimulating factor decreases amyloid beta 1-42 and suppresses microglial activity in a transgenic mouse model of Alzheimer's disease

The purpose of our study was to investigate microglia and astrocytes that are associated with human mutant amyloid precursor protein and amyloid beta (Abeta). We investigated whether the anti-granulocyte-macrophage-colony stimulating factor (GM-CSF) antibody can suppress microglial activity and decrease Abeta production in Alzheimer's disease transgenic mice (Tg2576 line). An antibody to mouse GM-CSF was introduced by intracerebroventricular (ICV) injections into the brains of 10-month-old Tg2576 male mice. We assessed the effect of several GM-CSF-associated cytokines on microglial activities and their association with Abeta using quantitative real-time RT-PCR, immunoblotting, immunohistochemistry analyses in anti-GM-CSF antibody-injected Tg2576 mice. Using sandwich ELISA technique, we measured intraneuronal Abeta in Tg2576 mice injected with GM-CSF antibody and PBS vehicle-injected control Tg2576 mice. Using double-labeling immunofluorescence analysis of intraneuronal Abeta, Abeta deposits and pro-inflammatory cytokines, we assessed the relationship between Abeta deposits and microglial markers in the Tg2576 mice, and also in the anti-GM-CSF antibody-injected Tg2576 mice. Our real-time RT-PCR analysis showed an increase in the mRNA expression of IL6, CD11c, IL1beta, CD40 and CD11b in the cerebral cortices of the Tg2576 mice compared with their littermate non-transgenic controls. Immunohistochemistry findings of microglial markers agreed with our real-time RT-PCR results. Interestingly, we found significantly decreased levels of activated microglia and Abeta deposits in anti-GM-CSF antibody-injected Tg2576 mice compared with PBS vehicle-injected Tg2576 mice. Findings from our real-time RT-PCR and immunoblotting analysis agreed with immunohistochemistry results. Our double-labeling analyses of intraneuronal Abeta and CD40 revealed that intraneuronal Abeta is associated with neuronal expression of CD40 in Tg2576 mice. Our quantitative sandwich ELISA analysis revealed decreased levels of soluble Abeta1-42 and increased levels of Abeta1-40 in Tg2576 mice injected with the anti-GM-CSF antibody, suggesting that anti-GM-CSF antibody alone decreases soluble Abeta1-42 production and suppresses microglial activity in Tg2576 mice. These findings indicating the ability of the anti-GM-CSF antibody to reduce Abeta1-42 and microglial activity in Tg2576 mice may have therapeutic implications for Alzheimer's disease.

An engineered human antibody fab fragment specific for Pseudomonas aeruginosa PcrV antigen has potent antibacterial activity

Pseudomonas aeruginosa is an opportunistic pathogen that can cause acute lung injury and mortality through the delivery of exotoxins by the type III secretion system (TTSS). PcrV is an important structural protein of the TTSS. An engineered human antibody Fab fragment that binds to the P. aeruginosa PcrV protein with high affinity has been identified and has potent in vitro neutralization activity against the TTSS. The instillation of a single dose of Fab into the lungs of mice provided protection against lethal pulmonary challenge of P. aeruginosa and led to a substantial reduction of viable bacterial counts in the lungs. These results demonstrate that blocking of the TTSS by a Fab lacking antibody Fc-mediated effector functions can be sufficient for the effective clearance of pulmonary P. aeruginosa infection.

Binding to CD20 by anti-B1 antibody or F(ab')(2) is sufficient for induction of apoptosis in B-cell lines

CD20 is a B-cell-specific cell surface protein expressed on mature B lymphocytes and is a target for monoclonal antibody therapy for non-Hodgkin's lymphoma (NHL). Though clear clinical efficacy has been demonstrated with several anti-CD20 antibodies, the mechanisms by which the antibodies activate CD20 and kill cells remain unclear. Proposed mechanisms of action include complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity (ADCC), and induction of apoptosis. In this report we compared the activity of two anti-CD20 antibodies, Anti-B1 Antibody (tositumomab) and rituximab (C2B8), in a variety of cellular assays using a panel of B-cell lines. Anti-B1 Antibody showed a low level of activity in a CDC assay against complement-sensitive B-cell lines, Ramos and Daudi. We found that there is an inverse correlation between the expression of CD55 and CD59 and CDC mediated by either Anti-B1 Antibody or rituximab. Rituximab was more potent at inducing CDC when compared to Anti-B1 Antibody. Using Raji cells as target cells and human peripheral blood leukocytes as effector cells, Anti-B1 Antibody was a potent inducer of ADCC. The activities of Anti-B1 Antibody and rituximab were nearly identical in the ADCC assay. In addition, Anti-B1 Antibody showed direct induction of apoptosis in all B-cell lines tested. In general, crosslinking Anti-B1 Antibody with a goat anti-mouse Ig did not further enhance the percentage of cells undergoing apoptosis. Importantly, a F(ab')(2) fragment of Anti-B1 Antibody induced apoptosis, while the Fab fragment did not, indicating that the Fc region was not required and dimerization of CD20 may be sufficient for induction of apoptosis. In contrast, rituximab, which binds to an overlapping epitope on CD20 with a three-fold lower affinity than Anti-B1 Antibody, did not efficiently induce apoptosis in the cell lines tested in the absence of crosslinking. In conclusion, these two anti-CD20 antibodies have overlapping, but distinct mechanisms of action on B-cell lines.

Comprehensive pharmacokinetics of a humanized antibody and analysis of residual anti-idiotypic responses

A murine antibody to human tumour necrosis factor-alpha (TNF-alpha) (CB0010) was complementarity-determining region (CDR)-grafted using human IgG4 heavy and kappa light chain constant regions. In cynomolgus monkeys, the grafted antibody (CDP571) was eliminated with a half-life of 40-90 hr, two to three times longer than CB0010, and immunogenicity was reduced by > 90%. Responses to the constant regions were almost entirely eliminated and responses to the CDR loop (anti-idiotype) were lowered. CDP571 was given to 24 human volunteers in doses from 0.1 to 10.0 mg/kg. It was well tolerated, with a half-life of approximately 13 days. Anti-CDP571 antibodies were low or undetectable at higher doses. At lower doses, anti-CDP571 peaked at 2 weeks and then declined. The response was primarily IgM (in contrast to the cynomolgus monkey, where by 5 weeks IgG predominated) and was against a conformational epitope comprising heavy and light chain CDR loops. No antibodies were detected against the gamma 4/kappa domains or frameworks. The response had little or no effect on CDP571 binding to TNF-alpha or on plasma clearance.

Human p59fyn(T) regulates OKT3-induced calcium influx by a mechanism distinct from PIP2 hydrolysis in Jurkat T cells

The earliest biochemical event after cross-linking of TCR is the tyrosine phosphorylation of a variety of substrates. At least three nonreceptor tyrosine kinases have been implicated in this signaling cascade: p59fyn(T), p56lck, and ZAP-70. Recently, PLC gamma 1 has been shown to be tyrosine phosphorylated in T cells after receptor activation. This increase in tyrosine phosphorylation correlates with the increased activity of the enzyme. The substrate for PLC gamma 1, phosphatidylinositol 4,5-bisphosphate (PIP2), is hydrolyzed to the protein kinase C activator diacylglycerol and inositol 1,4,5-triphosphate (IP3), which promotes calcium release from the endoplasmic reticulum. These results lend support to the notion that calcium mobilization after TCR cross-linking is mediated by increased levels of IP3. In this study we have cloned and transfected a human p59fyn(T) cDNA in the anti-sense configuration into the human T cell line, Jurkat, resulting in decreased expression of the protein. We find that cell lines expressing significantly reduced levels of p59fyn(T) exhibit significantly lower calcium influx following OKT3 activation. However, the level of IP3 production was unchanged and IP1 and IP2 levels were elevated. These data indicate that p59fyn(T) can regulate calcium influx by a mechanism distinct from PIP2 hydrolysis.

Genetic engineering of hybridoma glutamine metabolism

The murine hybridoma PQXB1/2 cannot be adapted to grow in culture media containing < 0.5 mM glutamine. Transformants selected following electroporation of PQXB1/2 cells with vectors containing a Chinese hamster glutamine synthetase (GS) cDNA under the control of the SV40 early promoter also failed to grow in the absence of glutamine in the culture medium. PQXB1/2 cells have, however, been transformed to glutamine independence following electroporation with a vector containing this glutamine synthetase cDNA under the control of the human cytomegalovirus immediate early promoter. In these cells, sufficient active glutamine synthetase was expressed from one vector per cell to enable growth in glutamine-free media. The specific activity of glutamine synthetase in two transformed cell lines producing parental levels of antibody was increased by 128 and 152%, respectively (0.57 and 0.63 mumol min-1 per 10(6) cells in transformants compared with parental levels of 0.25 mumol min-1 per 10(6) cells). This reprogramming of glutamine synthetase expression and glutamine metabolism is important for developing strategies to deal with ammonia toxicity and the production of cell lines with improved metabolic processes.

Human p59fyn(T) regulates OKT3-induced calcium influx by a mechanism distinct from PIP2 hydrolysis in Jurkat T cells

The earliest biochemical event after cross-linking of TCR is the tyrosine phosphorylation of a variety of substrates. At least three nonreceptor tyrosine kinases have been implicated in this signaling cascade: p59fyn(T), p56lck, and ZAP-70. Recently, PLC gamma 1 has been shown to be tyrosine phosphorylated in T cells after receptor activation. This increase in tyrosine phosphorylation correlates with the increased activity of the enzyme. The substrate for PLC gamma 1, phosphatidylinositol 4,5-bisphosphate (PIP2), is hydrolyzed to the protein kinase C activator diacylglycerol and inositol 1,4,5-triphosphate (IP3), which promotes calcium release from the endoplasmic reticulum. These results lend support to the notion that calcium mobilization after TCR cross-linking is mediated by increased levels of IP3. In this study we have cloned and transfected a human p59fyn(T) cDNA in the anti-sense configuration into the human T cell line, Jurkat, resulting in decreased expression of the protein. We find that cell lines expressing significantly reduced levels of p59fyn(T) exhibit significantly lower calcium influx following OKT3 activation. However, the level of IP3 production was unchanged and IP1 and IP2 levels were elevated. These data indicate that p59fyn(T) can regulate calcium influx by a mechanism distinct from PIP2 hydrolysis.

BCSH-NIBSC anti-D reference reagent for antiglobulin tests: the in-house assessment of red cell washing centrifuges and of operator variability in the detection of weak, macroscopic agglutination. British Committee for Standards in Haematology. National Institute for Biological Standards and Control

A batch of an anti-D preparation, reference 91/608, has been prepared for the preparation of red cells weakly sensitized with IgG that can reveal inhibition of the antiglobulin test by one volume of human serum, diluted 1:1000. The preparation provides an objective assessment of red cell washer efficacy and the confidential, in-house assessment of operator variability in detecting weak but definite macroscopic agglutination by blind, replicate tests. Red cell washer efficacy and poor operator reading procedures causing disruption of weak agglutination are two major causes of false-negative antiglobulin tests; neither are adequately detected by the common quality-control procedure of adding strongly IgG-sensitized red cells ('Coombs control cells') to apparently negative antiglobulin tests. However, weakly IgG-sensitized red cells do offer a valuable control function that can detect some degree of cell washer inefficiency and reading errors although such cells are not a substitute for the more sensitive replicate testing. Test protocols are provided to assess the efficacy of cell washing machines and operator skills in the detection of weak but definite macroscopic agglutination.

The pH, conductivity and osmolality of low ionic strength solutions used within the U.K. for the antiglobulin test

Low ionic strength solutions (LISS) for use in the antiglobulin test were obtained from 356 U.K. laboratories. Of the 324 laboratories using LISS to suspend the test red cells and who returned details of their LISS technique, 15 used unequal proportions of red cell suspension and serum despite the LISS being formulated for use with equal proportions. Of the 22 laboratories mixing LISS with serum and red cells suspended in a normal ionic strength medium, four used a LISS preparation formulated for a LISS-suspension technique and three used a commercially available LISS-addition preparation using proportions of red cells, serum and LISS not recommended by the manufacturer. The mean (standard deviation) pH, conductivity and osmolality of the 334 LISS preparations for LISS-suspension was 6.9 (0.2), 4.1 (0.4) mS/cm and 298 (15) mmole/kg, respectively. It is suggested that attention should be paid to the osmolality and, particularly, conductivity during the preparation of LISS because values were observed that were clearly outside the acceptable range cited in the Guidelines for the Blood Transfusion Services in the United Kingdom, i.e. pH 6.7 +/- 0.2, conductivity 3.7 +/- 0.3 mS/cm and osmolality 295 +/- 5 mmole/kg.