Recurrence rates and clinical outcome for dogs with grade II mast cell tumours with a low AgNOR count and Ki67 index treated with surgery alone

Grade II mast cell tumours (MCT) are tumours with variable biologic behaviour. Multiple factors have been associated with outcome, including proliferation markers. The purpose of this study was to determine if extent of surgical excision affects recurrence rate in dogs with grade II MCT with low proliferation activity, determined by Ki67 and argyrophilic nucleolar organising regions (AgNOR). Eighty-six dogs with cutaneous MCT were evaluated. All dogs had surgical excision of their MCT with a low Ki67 index and combined AgNORxKi67 (Ag67) values. Twenty-three (27%) dogs developed local or distant recurrence during the median follow-up time. Of these dogs, six (7%) had local recurrence, one had complete and five had incomplete histologic margins. This difference in recurrence rates between dogs with complete and incomplete histologic margins was not significant. On the basis of this study, ancillary therapy may not be necessary for patients with incompletely excised grade II MCT with low proliferation activity.

Characterization and screening of IgG binding to the neonatal Fc receptor

The neonatal Fc receptor (FcRn) protects immunoglobulin G (IgG) from degradation and increases the serum half-life of IgG, thereby contributing to a higher concentration of IgG in the serum. Because altered FcRn binding may result in a reduced or prolonged half-life of IgG molecules, it is advisable to characterize Fc receptor binding of therapeutic antibody lead candidates prior to the start of pre-clinical and clinical studies. In this study, we characterized the interactions between FcRn of different species (human, cynomolgus monkey, mouse and rat) and nine IgG molecules from different species and isotypes with common variable heavy (VH) and variable light chain (VL) domains. Binding was analyzed at acidic and neutral pH using surface plasmon resonance (SPR) and biolayer interferometry (BLI). Furthermore, we transferred the well-accepted, but low throughput SPR-based method for FcRn binding characterization to the BLI-based Octet platform to enable a higher sample throughput allowing the characterization of FcRn binding already during early drug discovery phase. We showed that the BLI-based approach is fit-for-purpose and capable of discriminating between IgG molecules with significant differences in FcRn binding affinities. Using this high-throughput approach we investigated FcRn binding of 36 IgG molecules that represented all VH/VL region combinations available in the fully human, recombinant antibody library Ylanthia®. Our results clearly showed normal FcRn binding profiles for all samples. Hence, the variations among the framework parts, complementarity-determining region (CDR) 1 and CDR2 of the fragment antigen binding (Fab) domain did not significantly change FcRn binding.

An automated immunoassay for early specificity profiling of antibodies

Antibody-based therapeutics are of great value for the treatment of human diseases. In addition to functional activity, affinity or physico-chemical properties, antibody specificity is considered to be one of the most crucial attributes for safety and efficacy. Consequently, appropriate studies are required before entering clinical trials. High content protein arrays are widely applied to assess antibody specificity, but this commercial solution can only be applied to final therapeutic antibody candidates because such arrays are expensive and their throughput is limited. A flexible, high-throughput and economical assay that allows specificity testing of IgG or Fab molecules during early discovery is described here. The 384-well microtiter plate assay contains a comprehensive panel of 32 test proteins and uses electrochemiluminescence as readout. The Protein Panel Profiling ( 3P) was used to analyze marketed therapeutic antibodies that all showed highly specific binding profiles. Subsequently, 3P was applied to antibody candidates from early discovery and the results compared well with those obtained with a commercially available high content protein chip. Our results suggest that 3P can be applied as an additional filter for lead selection, allowing the identification of favorable antibody candidates in early discovery and thereby increasing the speed and possibility of success in drug development.

In vitro affinity maturation of human GM-CSF antibodies by targeted CDR-diversification

The mammalian immune system applies somatic hypermutation to select for antibodies with improved dissociation rates in vivo up to an intrinsic limit, previously termed as affinity ceiling. However, for certain therapeutic applications it may be desirable to further improve antibody affinities beyond that limit. In this study the selection of antibodies specific for the pro-inflammatory cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) from the HuCAL GOLD human antibody library is described. In order to increase affinity and also functional activity, in vitro affinity maturation of a pool of lead Fab candidates was carried out. CDR-L3 and parallel CDR-H2 diversification using trinucleotide consensus cassettes were followed by the combination of optimized CDR-L3 and CDR-H2 leading to a 5000-fold improved affinity finally reaching a K(D) of 400 fM. Cytokine neutralizing potential of MOR04357 was evaluated in a TF-1 proliferation assay. Along with affinity optimization a 2000-fold increase in potency was observed compared to the parental antibody. Due to species cross-reactivity MOR04357 also blocks rat GM-CSF induced proliferation of FDCP-1 cells. Receptor inhibition studies showed that MOR04357 prevents the interaction of GM-CSF with the GM-CSF receptor alpha chain. As a consequence this leads to a blockade in signal transduction as measured by abolished STAT5 phosphorylation in the presence of GM-CSF and antibody. Due to its pro-inflammatory role GM-CSF has been implicated in the pathophysiology of inflammatory diseases like rheumatoid arthritis or asthma. Based on the mode of action described herein MOR04357 shows favourable antibody features as a potential drug candidate.

Generation and optimization of human antagonistic antibodies against TIMP-1 as potential therapeutic agents in fibrotic diseases

Impaired matrix metalloproteinase 1 (MMP-1) function, as result of the expression of increased levels of tissue inhibitor of metalloproteinase 1 (TIMP-1), plays an important role in the pathopysiolgical mechanism of fibrosis. In a recently performed clinically relevant rat animal model of established liver fibrosis, it could be shown, that blocking the interaction between the metalloproteinase and its inhibitor has beneficial effects in vivo. The rat TIMP-1 specific antagonistic antibody used in this study was derived from a human combinatorial antibody library (HuCAL) and blocks the interaction between rat TIMP-1 and MMP-13, the rat homologue of human MMP-1. We here describe the utilization of the same antibody source to generate fully human antibodies against human TIMP-1 which could be potential candidates for a therapy of fibrosis in man. In order to develop a highly potent antagonist of TIMP-1 action, antibodies isolated from the library were subjected to a number of different in vitro affinity maturation strategies. By these means, affinity and potency were improved by a factor of 87 and 65 fold, respectively, resulting in a valuable human therapeutic antibody candidate with a monovalent affinity of 150 pM and a potency for in vitro inhibition of TIMP-1/MMP-1 interaction of 200 pM.

Protein microarrays for antibody profiling: Specificity and affinity determination on a chip

Protein microarray technology facilitates the detection and quantification of hundreds of binding reactions in one reaction from a minute amount of sample. Proof-of-concept studies have shown that the set-up of sensitive assay systems based on protein arrays is possible, however, the lack of specific capture reagents limits their use. Therefore, the generation and characterisation of capture molecules is one of the key topics for the development of protein array based systems. Recombinant antibody technologies, such as HuCAL (human combinatorial antibody library; MorphoSys, Munich, Germany), allow the fast generation of highly specific binders to nearly any given target molecule. Although antibody libraries comprise billions of members, it is not the selection process, but the detailed characterisation of the pre-selected monoclonal antibodies that presents the bottleneck for the production of high numbers of specific binders. In order to obtain detailed information on the properties of such antibodies, a microarray-based method has been developed. We show that it is possible to define the specificity of recombinant Fab fragments by protein and peptide microarrays and that antibodies can be classified by binding patterns. Since the assay uses a miniaturised system for the detection of antibody-antigen interactions, the observed binding occurs under ambient analyte conditions as defined by Ekins (J. Pharm. Biomed. Anal. 1989, 7, 155-168). This allows the determination of a relative affinity value for each binding event, and a ranking according to affinity is possible. The new microarray based approach has an extraordinary potential to speed up the screening process for the generation of recombinant antibodies with pre-defined selection criteria, since it is intrinsically a high-throughput technology.

Antifibrotic effects of a tissue inhibitor of metalloproteinase-1 antibody on established liver fibrosis in rats

Liver fibrosis is characterized by increased synthesis, and decreased degradation, of extracellular matrix (ECM) within the injured tissue. Decreased ECM degradation results, in part, from increased expression of tissue inhibitor of metalloproteinase-1 (TIMP-1), which blocks matrix metalloproteinase (MMP) activity. TIMP-1 is also involved in promoting survival of activated hepatic stellate cells (HSCs), a major source of ECM. This study examined the effects of blocking TIMP-1 activity in a clinically relevant model of established liver fibrosis. Rats were treated with carbon tetrachloride (CCl(4)), or olive oil control, for 6 weeks; 24 days into the treatment, the rats were administered a neutralizing anti-TIMP-1 antibody derived from a fully human combinatorial antibody library (HuCAL), PBS, or an isotype control antibody. Livers from CCl(4)-treated rats exhibited substantial damage, including bridging fibrosis, inflammation, and extensive expression of smooth muscle alpha-actin (alpha-SMA). Compared to controls, rats administered anti-TIMP-1 showed a reduction in collagen accumulation by histological examination and hydroxyproline content. Administration of anti-TIMP-1 resulted in a marked decrease in alpha-SMA staining. Zymography analysis showed antibody treatment decreased the activity of MMP-2. In conclusion, administration of a TIMP-1 antibody attenuated CCl(4)-induced liver fibrosis and decreased HSC activation and MMP-2 activity.

From EST to IHC: human antibody pipeline for target research

We have developed a method for the high-level expression of expressed sequence tags (ESTs) as inclusion bodies in Escherichia coli by C-terminal fusion to the N1-domain of g3p of filamentous phage M13. Soluble fusion protein is obtained by an efficient refolding procedure. We have applied such protein preparations to the selection of human antibody fragments from phage-displayed HuCAL libraries. For all fusion proteins tested in this study, HuCAL antibodies could be generated which specifically detect, e.g. in immunohistochemistry, the maternal full-length protein corresponding to the protein fragment. This expression technology, in combination with the automated HuCAL antibody generation (AutoCAL), has proven to be useful for the rapid, high-throughput generation of high-quality human antibodies against EST-encoded protein fragments for target research.

Species-crossreactive scFv against the tumor stroma marker "fibroblast activation protein" selected by phage display from an immunized FAP-/- knock-out mouse

BACKGROUND

Fibroblast activation protein (FAP) is a type II membrane protein expressed on tumor stroma fibroblasts in more than 90% of all carcinomas. FAP serves as a diagnostic marker and is potential therapeutic target for treatment of a wide variety of FAP+ carcinomas. Murine tumor stroma models and FAP-specific antibodies are required to investigate the functional role of FAP in tumor biology and its usefulness for drug targeting. We here describe the development of antibodies with crossreactivity for human (hFAP) and murine FAP (mFAP), which share 89% amino acid identity.

MATERIAL AND METHODS

An FAP-/- mouse was sequentially immunized with recombinant murine and human FAP-CD8 fusion proteins. Immunoglobulin cDNA derived from hyperimmune spleen cells was used for the construction of a combinatorial single chain Fv (scFv) library. Phage display selection of FAP-specific scFv was performed on immobilized hFAP followed by selection on cells expressing murine FAP.

RESULTS

High-affinity, species-crossreactive, FAP-specific scFv were isolated upon sequential phage display selection. A bivalent derivative (minibody M036) constructed thereof was applied for immunohistochemical analyses and allowed detection of FAP expression on stroma cells of different human carcinomas as well as on murine host stroma in a tumor xenograft model.

CONCLUSIONS

MB M036, derived from phage display selected species crossreactive scFv, is suitable for tumor stroma targeting and will be a valuable tool in the analyses of the functional role of FAP in tumor biology as well as in the evaluation of the suitability of FAP for drug targeting.

Human antibody derivatives against the fibroblast activation protein for tumor stroma targeting of carcinomas

The fibroblast activation protein (FAP) is selectively expressed on activated fibroblasts of the tumor stroma on more than 90% of lung, breast and colon carcinomas. The high prevalence and abundance of FAP(+) stroma make it a promising target for in vivo diagnosis and therapy of a variety of carcinomas. We describe the humanization of the murine FAP-specific MAb, F19, which has already been clinically used for in vivo diagnostic purposes. Using phage display technology and human V-repertoires, VL and VH regions of F19 were replaced by analogous human V-regions while retaining the original HCDR3 sequence in order to maintain F19 epitope specificity. The resulting human single-chain fragments of immunoglobulin variable regions (scFv 34, scFv 18) showed affinities of 6 nM on cell membrane-bound FAP. scFv 34 was expressed as a bivalent minibody (Mb 34). The antigen-binding characteristics of Mb 34 were comparable to the parental and a complementarity-determining region (CDR)-grafted version of F19. This was revealed by binding competition studies, FACS analyses and immunohistochemistry on various tumor samples including breast, colon and lung carcinomas. Importantly, compared with the CDR-grafted humanized scFv version of F19, the V-regions of the selected human scFv 34 showed sequence identity with the parental antibody (Ab) only over the short, 15-amino acid long HCDR3. Thus, a largely reduced xenoantigenic potential is expected. These human Ab derivatives are suitable to develop novel therapeutic concepts with broad applicability for a wide variety of histological carcinomas based on tumor stroma targeting.

Human antibody derivatives against the fibroblast activation protein for tumor stroma targeting of carcinomas

The fibroblast activation protein (FAP) is selectively expressed on activated fibroblasts of the tumor stroma on more than 90% of lung, breast and colon carcinomas. The high prevalence and abundance of FAP(+) stroma make it a promising target for in vivo diagnosis and therapy of a variety of carcinomas. We describe the humanization of the murine FAP-specific MAb, F19, which has already been clinically used for in vivo diagnostic purposes. Using phage display technology and human V-repertoires, VL and VH regions of F19 were replaced by analogous human V-regions while retaining the original HCDR3 sequence in order to maintain F19 epitope specificity. The resulting human single-chain fragments of immunoglobulin variable regions (scFv 34, scFv 18) showed affinities of 6 nM on cell membrane-bound FAP. scFv 34 was expressed as a bivalent minibody (Mb 34). The antigen-binding characteristics of Mb 34 were comparable to the parental and a complementarity-determining region (CDR)-grafted version of F19. This was revealed by binding competition studies, FACS analyses and immunohistochemistry on various tumor samples including breast, colon and lung carcinomas. Importantly, compared with the CDR-grafted humanized scFv version of F19, the V-regions of the selected human scFv 34 showed sequence identity with the parental antibody (Ab) only over the short, 15-amino acid long HCDR3. Thus, a largely reduced xenoantigenic potential is expected. These human Ab derivatives are suitable to develop novel therapeutic concepts with broad applicability for a wide variety of histological carcinomas based on tumor stroma targeting.

Procaryotic expression of single-chain variable-fragment (scFv) antibodies: secretion in L-form cells of Proteus mirabilis leads to active product and overcomes the limitations of periplasmic expression in Escherichia coli

Recently it has been demonstrated that L-form cells of Proteus mirabilis (L VI), which lack a periplasmic compartment, can be efficiently used in the production and secretion of heterologous proteins. In search of novel expression systems for recombinant antibodies, we compared levels of single-chain variable-fragment (scFv) production in Escherichia coli JM109 and P. mirabilis L VI, which express four distinct scFvs of potential clinical interest that show differences in levels of expression and in their tendencies to form aggregates upon periplasmic expression. Production of all analyzed scFvs in E. coli was limited by the severe toxic effect of the heterologous product as indicated by inhibition of culture growth and the formation of insoluble aggregates in the periplasmic space, limiting the yield of active product. In contrast, the L-form cells exhibited nearly unlimited growth under the tested production conditions for all scFvs examined. Moreover, expression experiments with P. mirabilis L VI led to scFv concentrations in the range of 40 to 200 mg per liter of culture medium (corresponding to volume yields 33- to 160-fold higher than those with E. coli JM109), depending on the expressed antibody. In a translocation inhibition experiment the secretion of the scFv constructs was shown to be an active transport coupled to the signal cleavage. We suppose that this direct release of the newly synthesized product into a large volume of the growth medium favors folding into the native active structure. The limited aggregation of scFv observed in the P. mirabilis L VI supernatant (occurring in a first-order-kinetics manner) was found to be due to intrinsic features of the scFv and not related to the expression process of the host cells. The P. mirabilis L VI supernatant was found to be advantageous for scFv purification. A two-step chromatography procedure led to homogeneous scFv with high antigen binding activity as revealed from binding experiments with eukaryotic cells.

A TNF receptor antagonistic scFv, which is not secreted in mammalian cells, is expressed as a soluble mono- and bivalent scFv derivative in insect cells

Single chain antibodies (scFv) are usually produced in E. coli, but generation of certain scFv derivatives, such as complex fusion proteins or glycosylated forms of scFv is restricted to eukaryotic expression systems. We investigated the production of soluble mono- and bivalent single chain antibodies (scFv) in eukaryotic cells and describe a cassette vector system for mammalian and baculovirus expression which is compatible with an established vector system for bacterial expression and phage display selection of scFvs. The applied model scFv was derived from a murine antibody (H398) against human tumor necrosis factor receptor 1 (TNFR60), known to be a potent antagonist of TNF action in its monomeric form and a potential therapeutic agent for treatment of TNF-mediated diseases. Surprisingly, the monomeric scFv form of H398 (scFv H398) is expressed but not secreted in different mammalian cells. In contrast, in insect cells using recombinant baculovirus, a monovalent scFv H398 and a bivalent scFv fusion protein with an human IgG1 Fc region were expressed and secreted with correctly processed signal sequence. Concerning the influence of valency of the model Ab and its derivatives on antigen binding affinity and neutralisation of TNF activity, we found that the mono- and bivalent form of scFv H398 possesses the same characteristics as proteolytically produced Fab H398 and original mAb H398, respectively. Furthermore, fusion of the Ig Fc protein to scFv H398 increase the in vitro half-life at 37 degrees C. We conclude that the described cassette vectors readily allow the eukaryotic expression of mono- and bivalent scFv derivatives to analyse the influence of valency of scFv molecules on antigen binding and biological activity.

Characterization of different soluble TNF receptor (TNFR80) derivatives: positive influence of the intracellular domain on receptor/ligand interaction and TNF neutralization capacity

Different soluble human TNFR80 derivatives, a solubilized form of the complete TNFR80, the TNFR80 extracellular domain, a secretory TNFR80 mutant (TR80TM-) with a deleted transmembrane region, and a TNFR80 immunoadhesin were produced in insect cells and characterized side by side with a recombinant human TNFR60 extracellular domain with respect to TNF binding affinity and neutralization of TNF bioactivity. The construct TR80TM- and the solubilized complete TNFR80 revealed a similar TNF binding and neutralization capacity, which was superior to the monovalent TNFR80 extracellular domain and comparable to the bivalent TNFR80 immunoadhesin, already known as a potent TNF antagonist. Determination of ligand off rate constants of the various receptor constructs by surface plasmon resonance revealed a correlation of low off rates with a high TNF neutralization capacity. We propose that the high TNF binding and neutralization capacity of the solubilized complete TNFR80 and TR80TM- in comparison with the monovalent extracellular TNR80 domain is due to a noncovalent self-aggregation of the receptors via their intracellular domain. This finding suggests that efficient soluble TNF antagonists can be derived from TNFR themselves without the need of construction of TNFR Ig Fc fusion proteins.

A bivalent immunoadhesin of the human interferon-gamma receptor is an effective inhibitor of IFN-gamma activity

We describe here the bioengineering of a bivalent IFN-gamma-RFc immunoadhesin consisting of the extracellular domain of the human IFN-gamma receptor alpha chain (IFN-gamma-R) fused to a human IgG1 Fc region (encoding hinge, CH2 and CH3 domain) that was efficiently expressed as a covalently linked homodimer in insect cells and purified in a one-step purification procedure. The IFN-gamma-RFc fusion protein exerted a 3-fold higher ligand binding affinity in binding competition studies in vitro compared with the monovalent extracellular IFN-gamma-R domain. In addition, the in vitro antagonistic activity of IFN-gamma-RFc, as determined by inhibition of IFN-gamma-induced virus protection and HLA-DR expression, was more than 30-fold higher in comparison with the monovalent soluble receptor. The described IFN-gamma-R immunoadhesin is a potential therapeutic reagent to interfere with the disease-promoting activities of IFN-gamma in several autoimmune diseases.

A single-chain TNF receptor antagonist is an effective inhibitor of TNF mediated cytotoxicity

Tumour necrosis factor (TNF) is an important mediator of immune and inflammatory responses and has been recognized as a major pathogenic factor in several autoimmune and inflammatory diseases. TNF receptor TR60 plays a critical role in signalling the pathogenic activities of TNF. We here describe molecular cloning and bacterial production of a single-chain antibody (scFv H398) directed against TR60 which possesses antagonistic activity. VH and VL encoding sequences were isolated by PCR from the murine hybridoma cell line H398, cloned into a scFv expression vector and expressed in Escherichia coli. The recombinant antibody (Ab) fragment was found as an active soluble protein in the periplasm but also formed inclusion bodies. Re-folded scFv H398 purified from inclusion bodies was shown to be functional and stable at 37 degrees C with a half-life of 50 h. Comparison of the antigen binding characteristics of scFv with the parental enzymatically produced Fab H398 revealed that both Ab fragments have the same epitope specificity and an identical antigen binding affinity of 1.5 nM. In an in vitro assay it was demonstrated that scFv H398 is an efficient inhibitor of TNF mediated cytotoxicity with an IC50 of 22 nM, which is comparable to the antagonistic activity of natural Fab H398 with an IC50 of 12 nM. As scFv H398 possesses the high affinity TR60 binding and receptor antagonistic activity of the parental Ab H398 but is expected to be less antigenic in man, it provides a valuable tool for the development of novel therapeutic reagents against TNF mediated diseases.