Anti-digoxin scFv fragments expressed in bacteria and in insect cells have different antigen binding properties.

A gene encoding a single-chain antibody fragment directed against digoxin (named 1C10 scFv) was cloned in two expression systems. For this purpose, a new baculovirus transfer cassette fully compatible with the procaryotic pHEN vector was constructed. Baculovirus production led to higher yield than did Escherichia coli expression. The procaryotic fragment showed variations in the fine specificity profile but an affinity constant nearly identical to that of the 1C10 Fab, whereas the eucaryotic scFv fragment had a lower affinity with a specificity profile identical to original mAb. The half-lives of the digoxin:scFv complexes and the global specificity are compatible with therapeutic use of this antibody fragment.

Microheterogeneity of the oligosaccharides carried by the recombinant bovine lactoferrin expressed in Mamestra brassicae cells.

The development of therapeutic glycoprotein production using the baculovirus expression system depends on the ability of insect cell lines to reproduce site specific mammalian-like N-glycans. A combination of 1H-NMR and mass spectrometry techniques (MALD-MS, ES-MS, and CID-MS-MS) allowed us to elucidate the N-linked oligosaccharides microheterogeneity on three different N-glycosylation sites, Asn233, Asn476, and Asn545, of a baculovirus-expressed recombinant bovine lactoferrin produced in Mamestra brassicae. Two families of N-glycan structures have been found: first, oligomannosidic glycans (Man[9-5]GlcNAc2) and secondly, short truncated partially fucosylated glycans (Man(3-2)[Fuc(0-1)]GlcNAc2). These results indicate that Mamestra brassicae cell line is not able to synthesize complex N-glycans, even if an alpha1,6-linked fucose residue is frequently present on the asparagine-bound N-acetylglucosamine residue of short truncated structures. Nevertheless, we have shown that Mamestra brassicae ensures the same N-glycosylation pattern as found on natural bovine lactoferrin showing the same distribution between complex and high-mannose type glycans on the different glycosylation sites. Sites which are naturally occupied by high-mannose glycans (Asn233 and Asn545) are substituted essentially by the same type of N-glycans in the recombinant counterpart, and the site Asn476,which carries sialylated complex type chains in the natural glycoprotein, is substituted by short, truncated, partially fucosylated chains in Mamestra brassicae-expressed bovine lactoferrin. These various results lead us to the conclusion that bovine lactoferrin is an interesting model to determine the potential of glycosylation of the baculovirus/insect cell expression systems.

Obtaining a functional recombinant anti-rhesus (D) antibody using the baculovirus-insect cell expression system.

The cloning and production of a human anti-rhesus (Rh) D monoclonal antibody (mAb) using the baculovirus-insect cell expression system is described. This monoclonal recombinant antibody R.D7C2 derived from a human parental IgM lambda immunoglobulin was obtained after immortalization of lymphocytes by Epstein-Barr virus (EBV). The human heavy (VH) and light (VL) variable regions were cloned from the parental cell line and genetically fused to the human constant IgG1 heavy (H) and light (L) chain genes (gamma 1 and lambda, respectively). A recombinant baculovirus was constructed that directs the co-expression of genes encoding both genetically fused heavy and light chains under the control of two late and strong baculovirus promoters. After infecting the Spodoptera frugiperda (Sf9) insect cell line with this baculovector, a complete IgG1 mAb was secreted in the culture medium indicating that each immunoglobulin chain was correctly processed and assembled with a functional glycosylation into a tetrameric form. In vitro analysis showed that the functional properties of R.D7C2 using agglutination tests were efficient for the specific recognition of Rh-D-positive red blood cells (RBC). In addition, R.D7C2 showed effector functions of the gamma 1 heavy chain resulting in the lysis of Rh+ papain RBC by an antibody-directed cellular cytotoxicity mechanism. These results demonstrate that R.D7C2 can be produced in the baculovirus-insect cell expression system as a source for potential therapeutic application in the treatment of the haemolytic disease of the newborn.

Expression of neuroparsin cDNA in insect cells using baculovirus vectors.

The cDNA encoding neuroparsin A, a polytropic neurohormone of the locust, Locusta migratoria, was inserted into the genome of Autographa californica nuclear polyhedrosis virus such that transcription was under control of the p10 promoter. A polypeptide having the same charge and the same apparent molecular weight as the authentic neuroparsin A and that was reactive against neuroparsin immune serum was produced in recombinant virus-infected lepidopteran cell lines but not in control virus-infected cells. The baculovirus-expressed polypeptide was purified by two steps of liquid chromatography (anion exchange and reversed phase) which were previously used to purify the natural neuroparsin. The purified baculovirus-expressed polypeptide enhanced fluid reabsorption of everted rectum preparations, as did the natural neuroparsin. Thus, this gene expression system produced a polypeptide identical to authentic neuroparsin.

A new vector for efficient generation of p10-single-late-promoter recombinant baculoviruses.

A new baculovirus (BacTen) was constructed in order to generate p10 recombinant expression vectors at high frequency. This virus is an AcMNPV derivative, with the polyhedrin gene deleted and thus exhibiting p10 promoter as a single strong late promoter. The polyhedrin coding sequence was re-inserted subsequently under the control of the p10 promoter, in place of the p10 coding sequence. Two flanking Bsu36I restriction sites were inserted together with the polyhedrin coding region. BacTen can, therefore, be efficiently restricted at the p10 locus and used in co-transfection experiments along with p10 transfer vectors carrying the foreign gene to be expressed. It is shown with three independent transfer vectors, that the proportion of recombinants in the viral progeny can be as high as 80% The BacTen baculovirus represents a new powerful tool for the generation of p10 promoter based expression vectors. in a system without the background of considerable production of very late proteins.

Design of cassette baculovirus vectors for the production of therapeutic antibodies in insect cells.

BACKGROUND: Various systems have been described for the expression of recombinant monoclonal antibodies for therapeutical applications. Insect cells offer great advantages with respect to post-translational modifications, stability, yields and applications. OBJECTIVES: To construct plasmid cassette transfer vectors in order to express chimeric, humanized or human antibodies in insect cells using baculovirus expression system. STUDY DESIGN: Two transfer vectors, pBHuC kappa and pBHuC gamma 1, were designed. They contain a viral promoter (polyhedrin or p10 promoters, respectively), a signal peptide sequence and a human immunoglobulin light chain C kappa gene or heavy chain C gamma 1 sequence, respectively. Restriction sites have been introduced to allow insertion of rearranged variable genes, after amplification by polymerase chain reaction. RESULTS: Recombinant baculoviruses expressing complete immunoglobulins have been generated by a double-recombination event between baculovirus DNA and the loaded cassette transfer vectors. CONCLUSION: Our genetic cassette approach makes this system a very flexible and convenient one for the rapid production of therapeutic monoclonal antibodies with heavy and light chains of any human isotype. Specific variable regions selected by the antibody phage display technology can be easily transferred in these vectors to obtain a complete antibody.

Incorporation of pseudorabies virus gD into human immunodeficiency virus type 1 Gag particles produced in baculovirus-infected cells.

The human immunodeficiency virus type 1 (HIV-1) Pr55gag precursors were previously shown to assemble and bud efficiently as noninfectious virus-like particles (VLPs) when expressed in baculovirus-infected insect cells. In this study, we examined the abilities of foreign antigens to be incorporated on the outer surface of HIV-1 Gag particles. We have used a dual recombinant baculovirus, expressing the HIV-1 Gag gene and gD gene under the control of the P10 and polyhedrin promoters, respectively, to obtain hybrid VLPs. Transmission electron microscopy of insect cells infected with the dual recombinant revealed very large aggregates of particles budding from the cell membrane. The release of VLPs into the culture medium was clearly different for a recombinant baculovirus producing solely HIV-1 Gag, for which particles were uniformly distributed all around the cell surface. Biochemical analysis of hybrid particles indicated that glycoprotein gD was packaged into HIV-1 Gag VLPs. Moreover, the carboxy-terminal p6 region of Gag polyprotein and the glycoprotein gD intracytoplasmic domain were not required for gD incorporation. The experiments described here clearly demonstrate that glycoprotein gD can be packaged with HIV-1 Gag particles and released from insect cells.

Cassette baculovirus vectors for the production of chimeric, humanized, or human antibodies in insect cells.

Plasmid cassette-transfer vectors pBHuC chi and pBHuC gamma l have been designed which enable the construction of recombinant baculoviruses directing the co-expression of complete immunoglobulin in insect cells. We describe the application of these vectors for the expression of a human/mouse chimeric monoclonal antibody of potential immunosuppressive clinical value derived from a mouse anti-human CD29 monoclonal antibody (Mu-K20). The chimeric K20 light and heavy chains produced in sf9 insect cells were correctly processed and assembled into a normal immunoglobulin which is secreted into the culture medium of infected cells. The chimeric mAb Ch-K20-sf9 reproduces in vitro the functional properties of the parental mouse K20, including affinity and inhibition of lymphocyte proliferation. These results demonstrate that the baculovirus/insect cell expression system is suitable for the expression of fully active monoclonal antibodies of therapeutic value. Our generic cassette approach makes this system a very flexible and convenient one for the rapid production of either chimeric, humanized or human mAb with heavy and light chains of any isotype.

Biochemical characterization of Drosophila melanogaster acetylcholinesterase expressed by recombinant baculoviruses.

Recombinant baculoviruses expressing full length and 3' truncated forms of c-DNA encoding the Drosophila melanogaster acetylcholinesterase (AChE) were constructed. Biochemical analyses showed that full length recombinant protein was enzymatically active and anchored to the cell membrane via a glycolipidic residue. DTT treatment dissociated the native form into monomers migrating as did the corresponding form of AChE extracted from drosophila heads. Finally, DFP labelling demonstrated that the specific proteolytic cleavage leading to the formation of 55 and 16 kDa subunits occurred in Sf9 cells. In contrast with the full-length enzyme, C-terminal-truncated forms were highly secreted, confirming the prominent role of the C-terminal hydrophobic peptide for the addition of the glycolipidic residue. Accumulation of inactive precursor was observed when recombinant proteins were overproduced using an improved baculovirus, suggesting a saturation of insect cell machineries.

Competition between baculovirus polyhedrin and p10 gene expression during infection of insect cells.

Polyhedrin and p10 genes are expressed concurrently during the late stage of infection. To determine whether any competition occurs between these two genes at a transcriptional and/or translational level, a series of Autographa californica nuclear polyhedrosis recombinant viruses with deletions of promoter and coding sequences of the p10 or polyhedrin gene was constructed. Two modified baculoviruses with only one of the very late promoters, single late-promoter viruses AcSLP10 and AcSLP33, were made. The polyhedrin gene was used as a reporter gene to allow direct comparison between p10 and polyhedrin-driven expression. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and [35S]methionine labeling experiments showed that polyhedrin synthesis is enhanced in cells infected with baculoviruses carrying only one very late promoter. However, this enhancement is more significant when the polyhedrin gene is located in its natural site. Dot blot hybridization experiments carried out with total cytoplasmic RNA showed that deletion of the p10 promoter resulted in an increase of mRNAs derived from the polyhedrin promoter. In contrast, no increase of p10-promoted mRNA was detected when the polyhedrin gene promoter was deleted.

Gene II product of an aphid-nontransmissible isolate of cauliflower mosaic virus expressed in a baculovirus system possesses aphid transmission factor activity.

A new baculovirus expression system was used to express the gene II which encodes the 18-kDa aphid transmission factor (ATF) protein of two isolates of cauliflower mosaic virus (CaMV), the aphid-transmissible (AT+) Cabb B-JI and the aphid-nontransmissible (AT-) CM1841 isolates. ATF activity was shown to be associated with the baculovirus expression product of CaMV gene II from both the AT+ and the AT- isolates. No differences could be detected in the stability of the P18s from AT+ and AT- isolates expressed in the baculovirus system. These results indicate that the AT- phenotype of CM1841 isolate might not be due to a defective P18 but to an insufficient concentration of it in infected plant tissue.