Christoph Kannicht

Stabilin-1 and -2 constitute a novel family of fasciclin-like hyaluronan receptor homologues

MS-1, a high-molecular-mass protein expressed by non-continuous and angiogenic endothelial cells and by alternatively activated macrophages (Mphi2), and the hepatic sinusoidal endothelial hyaluronan clearance receptor are similar with respect to tissue distribution and biochemical characteristics. In the present study we purified these proteins by immuno- and hyaluronan-affinity chromatography respectively, sequenced tryptic peptides and generated full-length cDNA sequences in both mouse and human. The novel genes, i.e. stabilin-1 and stabilin-2, code for homologous transmembrane proteins featuring seven fasciclin-like adhesion domains, 18-20 epidermal-growth-factor domains, one X-link domain and three to six B-(X(7))-B hyaluronan-binding motifs. Northern-blotting experiments revealed the presence of both stabilins in organs with predominant endothelial sinuses such as liver, spleen and lymph node: stabilin-1 mRNA was also detected in organs with predominant Mphi2 cells, such as placenta, and in interleukin-4/glucocorticoid-stimulated Mphi2 cells in vitro. A polyclonal antibody made against human recombinant stabilin-1 confirmed the expression of stabilin-1 protein in splenic sinus endothelial cells in vivo and in Mphi2 in vitro. On the basis of high similarity at the protein level and the unique domain composition, which differs from that of all other known fasciclin-like proteins and hyaluronan receptors, stabilin-1 and stabilin-2 define a novel family of fasciclin-like hyaluronan receptor homologues that might play a role in cell-cell and cell-matrix interactions in vascular function and inflammatory processes.

Characterisation of the post-translational modifications of a novel, human cell line-derived recombinant human factor VIII

INTRODUCTION Host cell lines used for recombinant protein expression differ in their ability to perform post-translational modifications (PTMs). The currently available recombinant human FVIII (rhFVIII) products are produced in mammalian, non-human cell lines. For rhFVIII, glycosylation and sulfation are vital for functionality and von Willebrand factor (VWF)-binding affinity. Here we present the characterisation of the PTMs of a novel, human cell line-derived recombinant human FVIII (human-cl rhFVIII). rhFVIII expression in a human cell line avoids expression of undesirable mammalian glycoforms like Galα1-3Galβ1-GlcNAc-R (α-Gal) and N-glycolylneuraminic acid (Neu5Gc), which constitute epitopes antigenic to humans. MATERIALS AND METHODS We describe sulfation analysis, glycan profiling and characterisation using liquid chromatography-mass spectrometry and high performance anion exchange chromatography with pulsed amperometric detection. RESULTS AND CONCLUSIONS Human-cl rhFVIII is confirmed to be sulfated and glycosylated comparable to human plasma-derived FVIII. Most importantly, human-cl rhFVIII is devoid of the antigenic Neu5Gc or α-Gal epitopes observed in Chinese Hamster Ovary- and Baby Hamster Kidney-derived rFVIII products. Both the avoidance of non-human glycan structures and the achievement of complete sulfation are proposed to lower the intrinsic immunogenicity of human-cl rhFVIII compared with current rFVIII products.

Functional characteristics of the novel, human-derived recombinant FVIII protein product, human-cl rhFVIII

INTRODUCTION Hemophilia A is routinely treated by administration of exogenous coagulation factor VIII (FVIII). As safety and efficacy of FVIII products have improved over the years, development of FVIII-neutralizing antibodies (FVIII inhibitors) has emerged as the most serious complication. The new human cell line-derived recombinant human FVIII (human-cl rhFVIII) is the first recombinant FVIII product produced in a human cell line without additive animal proteins, with a goal of minimizing the risk of inhibitor development. MATERIALS AND METHODS Biochemical analyzes of purity, molecular and functional attributes of the novel human-cl rhFVIII were undertaken for product characterization. RESULTS AND CONCLUSIONS Human-cl rhFVIII was shown to be highly pure, with host-cell protein and DNA traces comparable to, or lower than, currently marketed recombinant FVIII (rFVIII) products. Human-cl rhFVIII was shown to have high specific FVIII activity and characteristics similar to full-length rFVIII products. Furthermore, no significant discrepancy between one-stage and chromogenic assay results were observed for human-cl rhFVIII, indicating potency ratios of these assays comparable to the full-length rFVIII products. In functional tests, human-cl rhFVIII exhibited physiological thrombin generation and a normal rate of inactivation by activated protein C. Importantly, human-cl rhFVIII displayed higher binding capacity with von Willebrand factor than comparator products, thus minimizing circulating unbound FVIII and further reducing the potential risk of inhibitor development.

Degradation products of factor VIII which can lead to increased immunogenicity.

The biochemical and immunochemical aspects of the development of inhibitors with a plasma–derived, double–virus inactivated factor VIII (FVIII) concentrate (marketed as Octavi SDPlus in Germany and Bisinact in Belgium) are described. A total of 12 cases of inhibitor formation (predominantly type II) were reported in Germany, 8 in Belgium but none in Portugal. Initially, the only difference between the non–pasteurised, SD virus–inactivated product Octavi and the pasteurised product Octavi SDPlus appeared to be pasteurisation, though subsequently, the quality of source material for the product was found to differ in different countries. Separation studies revealed the presence of a 40 kDa peptide fragment in some batches. It was subsequently shown that there was a strong correlation between inhibitor development and batches containing the 40 kDa marker, and a relationship between elevated markers of coagulation activation (FPA in particular) and the occurrence of the 40 kDa marker. Further work revealed that analytical methods commonly used for quality control were not suitable to highlight batch–to–batch differences. It was concluded that inhibitor potential (neoantigenicity) in Octavi SDPlus arose due to two effects; degradation of FVIII already present in source material; and heating of unstable FVIII degradation products. In this case, inhibitors were not caused by the overall production process, nor by GMP failures. The problem of inhibitor potential can be avoided if appropriate preventive measures are taken. Further work is needed to prove non–neoantigenicity and to reinforce the scientific findings, and to characterise pilot batches.

Normal levels of ADAMTS13 and factor H are present in the pharmaceutically licensed plasma for transfusion (Octaplas®) and in the universally applicable plasma (Uniplas) in development

Background and Objectives  The pathomechanism of thrombotic thrombocytopenic purpura (TTP) and atypical haemolytic uraemic syndrome (aHUS) is associated with a severe deficiency of ADAMTS13 and factor H. The aim of this study was to quantify the levels of ADAMTS13 and factor H in the pharmaceutically licensed plasma for transfusion, Octaplas®, and the universally applicable plasma, Uniplas (development product, working title). Furthermore, Octaplas® batches of blood groups A, B, O, AB, and plasmas derived from different sources were compared.

The Cell Adhesion Receptor Carcinoembryonic Antigen-related Cell Adhesion Molecule 1 Regulates Nucleocytoplasmic Trafficking of DNA Polymerase δ-Interacting Protein 38

The homophilic cell-cell adhesion receptor CEACAM1 (carcinoembryonic antigen-related cell adhesion molecule 1, CD66a) acts as a regulator of contact-dependent cell survival, differentiation, and growth. It is involved in the control of proliferation in hematopoietic and epithelial cells and can act as a tumor suppressor. In this study, we identify DNA polymerase δ-interacting protein 38 (PDIP38) as a novel binding partner for CEACAM1-L and CEACAM1-S. We show that PDIP38 can occur in the nucleus, in the cytoplasm and at the plasma membrane in NBT-II, IEC18, RBE, and HeLa cells and that the distribution in NBT-II cells is influenced by the confluency of the cells. We also demonstrate that the interaction of CEACAM1 and PDIP38 is of functional importance in NBT-II cells, which co-express the long and the short CEACAM1 isoform. In subconfluent, proliferating NBT-II cells, perturbation of CEACAM1 by antibody clustering induces increased binding to PDIP38 and results in rapid recruitment of PDIP38 to the plasma membrane. The same treatment of confluent, quiescent NBT-II cells leads to a different response, i.e. translocation of PDIP38 to the nucleus. Together, our data show that PDIP38 can shuttle between the cytoplasmic and the nuclear compartments and that its subcellular localization is regulated by CEACAM1, implicating that PDIP38 may constitute a novel downstream target of CEACAM1 signaling.

Flow-based measurements of von Willebrand factor (VWF) function: Binding to collagen and platelet adhesion under physiological shear rate

INTRODUCTION VWF circulates in plasma as a series of heterogeneous multimers, mediating platelet tethering, translocation and finally adhesion to areas of injured endothelium under physiological high arterial blood flow. VWF-platelet binding requires conformational changes in VWF, which are induced by immobilization and shear. Because of unavailability of a simple flow-based measurement system, VWF activity assays are generally performed under static conditions. We describe an easily reproducible in vitro flow-chamber model using commercially available flow devices to examine VWF-collagen binding and VWF-mediated platelet adhesion under physiological flow conditions. METHODS The collagen surface of the flow-chamber was analyzed by atomic force microscopy. Collagen-bound VWF was characterized by multimer analysis and multi labelling immunofluorescence detection of exposed GPIb binding domains. Platelet adhesion was captured by time-lapse microscopy. RESULTS The described flow-chamber system facilitates multimer analysis of collagen-bound VWF, whereas all VWF multimers bound to collagen under physiological low to high shear rates. Multi labelling immunofluorescence detection exhibited exposed GPIb binding domains co-localized with VWF molecules. VWF-dependent platelet adhesion using time-lapse microscopy showed values comparable to experiments done with whole blood, and platelet adhesion was dependent on the VWF concentration. CONCLUSIONS The established flow-chamber model represents an easy-to-set-up and customized tool for the characterization of VWF-binding to collagen as well as the determination of VWF-dependent platelet adhesion under defined flow conditions in real-time.

N-Glycosylation of the carcinoembryonic antigen related cell adhesion molecule, C-CAM, from rat liver: detection of oversialylated bi- and triantennary structures

Abstract Rat C-CAM is a ubiquitous, transmembrane and carcino-embryonic antigen related cell adhesion molecule. The human counterpart is known as biliary glycoprotein (BGP) or CD66a. It is involved in different cellular functions ranging from intercellular adhesion, microbial receptor activity, signaling and tumor suppression. In the present study N-glyco-sylation of C-CAM immunopurified from rat liver was analyzed in detail. The primary sequence of rat C-CAM contains 15 potential N-glycosylation sites. The N-glycans were enzymatically released from glycopeptides, fluorescently labeled with 2-aminobenzamide, and separated by two-dimensional HPLC. Oligosaccharide structures were characterized by enzymatic sequencing and MALDI-TOF-MS. Mainly bi- and triantennary complex structures were identified. The presence of type I and type II chains in the antennae of these glycans results in heterogeneous glycosylation of C-CAM. Sialylation of the sugars was found to be unusual; bi- and triantennary glycans contained three and four sialic acid residues, respectively, and this linkage seemed to be restricted to the type I chain in the antennae. Approximately 20% of the detected sugars contain these unusual numbers of sialic acids. C-CAM is the first transmembrane protein found to be over-sialylated.

Enzymatic Sequence Analysis of N -Glycans by Exoglycosidase Cleavage and Mass Spectrometry – detection of Lewis X Structures

Enzymatic sequencing of oligosaccharides gives structural information on sequence of monosaccharides and type of linkage within the oligosaccharide chain. This data can be obtained by stepwise enzymatic digestion of a single, isolated oligosaccharide using individual or mixtures of specific exoglycosidases. N-glycans have to be fractionated from mixtures prior to sequence analysis to assign this type of structural information to a specific glycan. Enzymatic sequencing can be applied to oligosaccharide mixtures as well to evaluate the occurrence of distinct oligosac-charide motives of functional and/or structural interest. Here we describe the application of enzymatic sequence analysis to a mixture of N-glycans released from alpha1-acid glycoprotein. The experimental conditions are optimized for detection of possible Lewis X structures after stepwise exoglycosi-dase digestion by MALDI-TOF mass spectrometry. However, the described method is generally applicable to analyze other structural properties of N-glycans by use of the respective specific exoglycosidases.

Development, upscaling and validation of the purification process for human-cl rhFVIII (Nuwiq®), a new generation recombinant factor VIII produced in a human cell-line

INTRODUCTION Human-cl rhFVIII (Nuwiq®), a new generation recombinant factor VIII (rFVIII), is the first rFVIII produced in a human cell-line approved by the European Medicines Agency. AIMS To describe the development, upscaling and process validation for industrial-scale human-cl rhFVIII purification. METHODS AND RESULTS The purification process involves one centrifugation, two filtration, five chromatography columns and two dedicated pathogen clearance steps (solvent/detergent treatment and 20 nm nanofiltration). The key purification step uses an affinity resin (VIIISelect) with high specificity for FVIII, removing essentially all host-cell proteins with >80% product recovery. The production-scale multi-step purification process efficiently removes process- and product-related impurities and results in a high-purity rhFVIII product, with an overall yield of ∼50%. Specific activity of the final product was >9000 IU/mg, and the ratio between active FVIII and total FVIII protein present was >0.9. The entire production process is free of animal-derived products. Leaching of potential harmful compounds from chromatography resins and all pathogens tested were below the limit of quantification in the final product. CONCLUSIONS Human-cl rhFVIII can be produced at 500 L bioreactor scale, maintaining high purity and recoveries. The innovative purification process ensures a high-purity and high-quality human-cl rhFVIII product with a high pathogen safety margin.