Expression of recombinant anti-E-selectin single-chain Fv antibody fragments in stably transfected insect cell lines

Insect cell-based expression and characterization of a single-chain variable antibody fragment directed against blood coagulation factor VIII

A recombinant single-chain variable antibody fragment (scFv) KM33 was previously described as a ligand that can inhibit the function of blood coagulation factor VIII (FVIII). This scFv was previously derived from an individual with anti-FVIII antibodies manifested in FVIII functional deficiency (Hemophilia A) and expressed in bacteria. In the present work, we describe an alternative approach for fast and easy production of KM33 in insect cells (Spodoptera frugiperda). The KM33 gene was codon-optimized and expressed in secreted form using a baculovirus system. The protein was isolated using metal-affinity and size-exclusion chromatography to purity of about 96% and yield of 0.4-1.2 mg per 120 mL of culture, based on several independent expression experiments. In a binding assay using surface plasmon resonance, the insect cell-derived KM33 (iKM33) was qualified as a high-affinity ligand for FVIII. Epitope specificity of iKM33 on FVIII (C1 domain) was confirmed by testing the binding with a relevant mutant of FVIII. In several FVIII functional tests (factor Xa generation, APTT clotting, thrombin generation and video microscopy clot growth assays), iKM33 strongly inhibited FVIII activity in accordance with the clinical effect of the parental antibody. Therefore, the expressed protein was concluded to be fully functional and applicable in various assays with FVIII.

High-level secretion of recombinant monomeric murine and human single-chain Fv antibodies from Drosophila S2 cells

Single-chain variable fragment (scFvs) antibodies are small polypeptides (∼26 kD) containing the heavy (V(H)) and light (V(L)) immunoglobulin domains of a parent antibody connected by a flexible linker. In addition to being frequently used in diagnostics and therapy for an increasing number of human diseases, scFvs are important tools for structural biology as crystallization chaperones. Although scFvs can be expressed in many different organisms, the expression level of an scFv strongly depends on its particular amino acid sequence. We report here a system allowing for easy and efficient cloning of (i) scFvs selected by phage display and (ii) individual heavy and light chain sequences from hybridoma cDNA into expression plasmids engineered for secretion of the recombinant fragment produced in Drosophila S2 cells. We validated the method by producing five scFvs derived from human and murine parent antibodies directed against various antigens. The production yields varied between 5 and 12 mg monomeric scFv per liter of supernatant, indicating a relative independence on the individual sequences. The recombinant scFvs bound their cognate antigen with high affinity, comparable with the parent antibodies. The suitability of the produced recombinant fragments for structural studies was demonstrated by crystallization and structure determination of one of the produced scFvs, derived from a broadly neutralizing antibody against the major glycoprotein E2 of the hepatitis C virus. Structural comparison with the Protein Data Bank revealed the typical spatial organization of V(H) and V(L) domains, further validating the here-reported expression system.

Influence of antigen on the development of MALT lymphoma

Mucosa-associated lymphoid tissue (MALT) B-cell lymphomas develop in the context of autoimmune or chronic inflammations like Helicobacter pylori-induced gastritis. Remission of most gastric MALT lymphomas after eradication of H pylori links tumor cell proliferation to antigen-induced inflammation and the need for antigenic contact. Furthermore, the tumor cells correspond to antigen-activated memory B cells. To investigate the reactivity of the tumor immunoglobulins we employed in vitro-generated antibodies identical to those produced by MALT lymphoma cells. The immunoglobulin rearrangements of 7 MALT lymphomas were amplified, cloned, and expressed as single-chain fragment variable (scFv) antibodies. Antigen specificity of these 7 scFvs was analyzed by immunohistochemical staining of various normal, reactive, and malignant human tissues. Also, an expression library comprising approximately 30,000 proteins from human fetal brains (protein filter) and a peptide library were screened. One scFv stained a subpopulation of tonsillar plasma cells in immunohistochemical studies. On protein filters this scFv recognized the plasma cell-related protein Ufc1. Peptide library screening identified 9 peptides as binding partners of an additional scFv. The majority of MALT lymphoma immunoglobulins studied, however, showed no reactivity against antigens, indicating that the tumor immunoglobulins do not play a significant role in stimulation and proliferation of the MALT lymphoma tumor cells.

The production of antibody fragments and antibody fusion proteins by yeasts and filamentous fungi

In this review we will focus on the current status and views concerning the production of antibody fragments and antibody fusion proteins by yeasts and filamentous fungi. We will focus on single-chain antibody fragment production (scFv and VHH) by these lower eukaryotes and the possible applications of these proteins. Also the coupling of fragments to relevant enzymes or other components will be discussed. As an example of the fusion protein strategy, the 'magic bullet' approach for industrial applications, will be highlighted.

Identification and characterization of an angiogenin-binding DNA sequence that stimulates luciferase reporter gene expression

Angiogenin undergoes nuclear translocation in endothelial and smooth muscle cells where it accumulates in the nucleolus and binds to DNA. Nuclear translocation of angiogenin is necessary for its biological activity and is mediated by an endocytotic pathway that is independent of the microtubule system and lysosomal processing. Because the nucleolus is a subnuclear organelle containing clusters of transcriptionally active ribosomal RNA genes, we studied the binding of angiogenin to the intergenic spacer of the ribosomal RNA gene where many of the transcription regulatory elements are located. Here we report that angiogenin binds to CT repeats that are abundant in the nontranscribed region of the ribosomal RNA gene. An angiogenin-binding DNA sequence (CTCTCTCTCTCTCTCTCCCTC) has been identified and designated angiogenin-binding element (ABE). ABE binds angiogenin specifically and exhibits angiogenin-dependent promoter activity in a luciferase reporter system. CT repeats, or inverted GA box, which are abundantly distributed in the eukaryotic genome and are often located in the 5'-flanking region, have been implicated in regulating gene expression. We have previously shown that angiogenin stimulates rRNA synthesis. The present results suggest that the nuclear function of angiogenin may not only be related to rRNA production but also play a role in regulating expression of genes containing CT repeats.

Amplification of B cell antigen receptor signaling by a Syk/ITAM positive feedback loop

We have established a protocol allowing transient and inducible coexpression of many foreign genes in Drosophila S2 Schneider cells. With this powerful approach of reverse genetics, we studied the interaction of the protein tyrosine kinases Syk and Lyn with the B cell antigen receptor (BCR). We find that Lyn phosphorylates only the first tyrosine whereas Syk phosphorylates both tyrosines of the BCR immunoreceptor tyrosine-based activation motif (ITAM). Furthermore, we show that Syk is a positive allosteric enzyme, which is strongly activated by the binding to the phosphorylated ITAM tyrosines, thus initiating a positive feedback loop at the receptor. The BCR-dependent Syk activation and signal amplification is efficiently counterbalanced by protein tyrosine phosphatases, the activity of which is regulated by H(2)O(2) and the redox equilibrium inside the cell.

Expression of functional recombinant antibody molecules in insect cell expression systems

Recombinant single-chain variable-fragment molecules (scFv) were constructed from a cell line expressing a monoclonal antibody against African cassava mosaic virus (ACMV) and expressed in Escherichia coli. DNA sequences that encoded the scFv were manipulated to allow scFv expression in insect cell lines. A recombinant baculovirus containing the scFv cDNA was constructed and large amounts of scFv were produced in each of three insect cell lines infected with the baculovirus. However, the scFv were not secreted into the medium by any of the cell lines despite the scFv having been linked to a honeybee melittin leader sequence. The same scFv cDNA construct was introduced into Drosophila DS2 cells and a stable recombinant cell line was obtained that produced scFv that was secreted into the medium. Culture medium containing the scFv was used directly in enzyme-linked immunosorbent assay (ELISA) tests to detect ACMV in plant tissues. Another construct that encoded the Ckappa domain of human IgG was fused to the C-terminus of the scFv that was produced and expressed in Drosophila cells. This scFv derivative also accumulated in the medium and was more active in ELISA than scFv lacking the Ckappa domain.

Survey of the 1998 optical biosensor literature

The utilization of optical biosensors to study molecular interactions continues to expand. In 1998, 384 articles relating to the use of commercial biosensors were published in 130 different journals. While significant strides in new applications and methodology were made, a majority of the biosensor literature is of rather poor quality. Basic information about experimental conditions is often not presented and many publications fail to display the experimental data, bringing into question the credibility of the results. This review provides suggestions on how to collect, analyze and report biosensor data.

Analysis of the V genes coding for a monospecific human antibody to myosin and functional expression of single chain Fv fragments

A monospecific human IgM monoclonal antibody (mAb), reactive with myosin from human heart, has been obtained by EBV transformation. This mAb may have a diagnostic potential in the imaging of myocardial necrosis. However, owing to the fact that the molecular mass of an IgM is 900 kDa, a poor diffusion and a slow penetration inside necrotic myocytes could reduce its capacity for scintigraphic detection. In order to alleviate these problems, we constructed the scFv by cloning the VH and VL domains into the pHOG21 vector. Analysis of the V genes proved an unmutated configuration showing that the immortalized B cell issued from the primary IgM repertoire. The expression product in Escherichia coli was a 35 kDa scFv fragment with the antigen-binding specificity of the parental mAb.

Targeting an adenoviral gene vector to cytokine-activated vascular endothelium via E-selectin

We have aimed at selective gene delivery to vascular endothelial cells (EC) at sites of inflammation, by targeting E-selectin, a surface adhesion molecule that is only expressed by activated EC. An anti-E-selectin mAb, 1.2B6, was complexed with the adenovirus vector AdZ.FLAG (expressing the FLAG peptide) by conjugating it to an anti-FLAG mAb. Gene transduction of cultured EC was increased 20-fold compared with AdZ.FLAG complexed with a control bsAb providing EC were activated by cytokines. The anti-E-selectin-complexed vector transduced 29 +/- 9% of intimal EC in segments of pig aorta cultured with cytokines ex vivo, compared with less than 0.1% transduced with the control construct (P < 0.05). This strategy could be developed to target endothelium in inflammation with genes capable of modifying the inflammatory response.

Insect cells as hosts for the expression of recombinant glycoproteins

Baculovirus-mediated expression in insect cells has become well-established for the production of recombinant glycoproteins. Its frequent use arises from the relative ease and speed with which a heterologous protein can be expressed on the laboratory scale and the high chance of obtaining a biologically active protein. In addition to Spodoptera frugiperda Sf9 cells, which are probably the most widely used insect cell line, other mainly lepidopteran cell lines are exploited for protein expression. Recombinant baculovirus is the usual vector for the expression of foreign genes but stable transfection of - especially dipteran - insect cells presents an interesting alternative. Insect cells can be grown on serum free media which is an advantage in terms of costs as well as of biosafety. For large scale culture, conditions have been developed which meet the special requirements of insect cells. With regard to protein folding and post-translational processing, insect cells are second only to mammalian cell lines. Evidence is presented that many processing events known in mammalian systems do also occur in insects. In this review, emphasis is laid, however, on protein glycosylation, particularly N-glycosylation, which in insects differs in many respects from that in mammals. For instance, truncated oligosaccharides containing just three or even only two mannose residues and sometimes fucose have been found on expressed proteins. These small structures can be explained by post-synthetic trimming reactions. Indeed, cell lines having a low level of N-acetyl-beta-glucosaminidase, e.g. Estigmene acrea cells, produce N- glycans with non-reducing terminal N-acetylglucosamine residues. The Trichoplusia ni cell line TN-5B1-4 was even found to produce small amounts of galactose terminated N-glycans. However, there appears to be no significant sialylation of N-glycans in insect cells. Insect cells expressed glycoproteins may, though, be alpha1,3-fucosylated on the reducing-terminal GlcNAc residue. This type of fucosylation renders the N-glycans on one hand resistant to hydrolysis with PNGase F and on the other immunogenic. Even in the absence of alpha1,3-fucosylation, the truncated N-glycans of glycoproteins produced in insect cells constitute a barrier to their use as therapeutics. Attempts and strategies to "mammalianise" the N-glycosylation capacity of insect cells are discussed.

Antibody engineering: comparison of bacterial, yeast, insect and mammalian expression systems

Engineered antibody molecules, and their fragments, are being increasingly exploited as scientific and clinical tools. However, one factor that can limit the applicability of this technology is the ability to express large amounts of active protein. In this review we describe the relative advantages and disadvantages of bacterial, yeast, insect and mammalian expression systems, and discuss some of the problems that can be encountered when using them. There is no 'universal' expression system, that can guarantee high yields of recombinant product, as every antibody-based molecule will pose its own problems in terms of expression. As a result the choice of system will depend on many factors, including the molecular species being expressed, the precise sequence of the individual antibody and the preferences of the individual investigator. However, there are general rules with regards to the design of expression vectors and systems which will help the investigator to make informed choices as to which strategy might be appropriate for their application.