Modified antigen-binding of human antibodies with glycosylation variations of the light chains produced in sugar-limited human hybridoma cultures

Multiple circulating forms of neprilysin detected with novel epitope-directed monoclonal antibodies

Neprilysin (NEP) is an emerging biomarker for various diseases including heart failure (HF). However, major inter-assay inconsistency in the reported concentrations of circulating NEP and uncertainty with respect to its correlations with type and severity of disease are in part attributed to poorly characterized antibodies supplied in commercial ELISA kits. Validated antibodies with well-defined binding footprints are critical for understanding the biological and clinical context of NEP immunoassay data. To achieve this, we applied in silico epitope prediction and rational peptide selection to generate monoclonal antibodies (mAbs) against spatially distant sites on NEP. One of the selected epitopes contained published N-linked glycosylation sites at N285 and N294. The best antibody pair, mAb 17E11 and 31E1 (glycosylation-sensitive), were characterized by surface plasmon resonance, isotyping, epitope mapping, and western blotting. A validated two-site sandwich NEP ELISA with a limit of detection of 2.15 pg/ml and working range of 13.1-8000 pg/ml was developed with these mAbs. Western analysis using a validated commercial polyclonal antibody (PE pAb) and our mAbs revealed that non-HF and HF plasma NEP circulates as a heterogenous mix of moieties that possibly reflect proteolytic processing, post-translational modifications and homo-dimerization. Both our mAbs detected a ~ 33 kDa NEP fragment which was not apparent with PE pAb, as well as a common ~ 57-60 kDa moiety. These antibodies exhibit different affinities for the various NEP targets. Immunoassay results are dependent on NEP epitopes variably detected by the antibody pairs used, explaining the current discordant NEP measurements derived from different ELISA kits.

Building high affinity human antibodies by altering the glycosylation on the light chain variable region in N-acetylglucosamine-supplemented hybridoma cultures

We attempted to improve antibody affinity by varying glycosylation on the light chain variable region. The human hybridoma line HB4C5 produces an antibody reactive to lung adenocarcinoma, which possess a N-glycosylated carbohydrate chain on the light chain hypervariable region. It has been shown that altering this carbohydrate structure can be accomplished by varying the level of N-acetylglucosamine in glucose free medium, a change in the carbohydrate chain could be induced which resulted in modifying antigen binding. By culturing the cells in media containing more than 20 mM N-acetylglucosamine, cells produced antibody with 10 fold improved affinity as compared with antibody produced in 20 mM glucose-containing medium. A newly induced light chain glycoform produced in the N-acetylglucosamine-containing medium was shown to be responsible for this antigen binding enhancement. Addition of glucose in the N-acetylglucosamine-containing media led to decreased antibody affinity and slightly inhibited production of a new light chain in a dose-dependent manner. Combination of 20 mM N-acetylglucosamine and 0.5 mM glucose gave a higher antibody production without the decrease of the antigen binding. These results indicate that optimization of N-glycosylation on the light chain, which leads to higher antigen binding, can be accomplished by adjusting a ratio of glucose and N-acetylglucosamine in the culture medium.

Effect of culture temperature on a recombinant CHO cell line producing a C-terminal α-amidating enzyme

In order to seek an efficient method for producing a recombinant protein by using animal cell culture, we investigated various effects of the culture temperature on a recombinant CHO cell line (3µ-1S), producing a C-terminal α-amidating enzyme (799BglIIα-AE) originating from Xenopus laevis. The results revealed that a low culture temperature (below 37 °C) led to the following phenomena: [1] inhibited cell growth, [2] enhanced cellular productivity of the recombinant protein, [3] maintained high cell viability, [4] suppressed medium consumption, and [5] suppressed release of impurities from the cells. These findings indicate that a quite simple method, the culture at low temperature, will contribute to the total improvement of the industrial process for the production of the recombinant protein, 799BglIIα-AE.

An Approach to Further Enhance the Cellular Productivity of Exogenous Protein Hyper-producing Chinese Hamster Ovary (CHO) Cells

The cell line D29, which was easily and rapidly established by the promoter-activated production and glutamine synthetase hybrid system, secreted recombinant human interleukin-6 (hIL-6) at a productivity rate of 39.5 mug 10(-6) cells day(-1), one of the highest reported levels worldwide. The productivity rate was about 130-fold higher than that of the cell line A7, which was established without both promoter activation and gene amplification. Although D29 cells had a high copy number and high mRNA level of the hIL-6 gene as well as a high secretion rate of hIL-6, large amounts of intracellular hIL-6 protein accumulated in D29 cells compared to A7 cells. Northern blotting analysis showed no change in the GRP78/BiP expression level in D29 cells. In contrast, an electrophoresis mobility shift assay revealed strong activation of NF-kappaB in D29 cells. These results suggest that large amounts of hIL-6 translated from large amounts of hIL-6 mRNA cause excess accumulation of intact hIL-6 in the endoplasmic reticulum (ER), and that subsequent negative feedback signals via the ER overload response inhibit hIL-6 protein secretion. To enhance the hIL-6 productivity rate of D29 cells by releasing the negative feedback signals, the effect of pyrrolidinedithiocarbamate, an inhibitor of NF-kappaB activation, was examined. Suppression of NF-kappaB activation in D29 cells produced a 25% augmentation of the hIL-6 productivity rate. Therefore, in highly productive cells like D29 cells, the release of negative feedback signals could increase the total amount of recombinant protein secretion.

Impact of temperature reduction and expression of yeast pyruvate carboxylase on hGM-CSF-producing CHO cells

Recently, we demonstrated that a recombinant yeast pyruvate carboxylase expressed in the cytoplasm of BHK-21 cells was shown to partially reconstitute the missing link between glycolysis and TCA, increasing the flux of glucose into the TCA and achieving higher yields of recombinant erythropoietin. In the present study, a CHO cell line producing recombinant human granulocyte macrophage colony stimulating factor was used to evaluate the impact of PYC2 expression and reduced culture temperature. Temperature reduction from 37 to 33 degrees C revealed a reduced growth rate, a prolonged stationary phase and a 2.1-fold increase of the cell specific rhGM-CSF production rate for CHO-K1-hGM-CSF cells. The PYC2-expressing cell clones showed a decreased cell growth and a lower maximum cell concentration compared to the control expressing rhGM-CSF but no PYC2. However, only 65% lactate were produced in PYC2-expressing cells and the product yield was 200% higher compared to the control. The results obtained for CHO cells compared to BHK cells reported previously, indicated that the PYC2 expression dominantly reduced the lactate formation and increased the yield of the recombinant protein to be produced. Finally, the growth and productivity of PYC2-expressing CHO-K1-hGM-CSF cells under both temperature conditions were investigated. The average cell specific rhGM-CSF production increased by 3.2-fold under reduced temperature conditions. The results revealed that the expression of PYC2 and a reduced culture temperature have an additive effect on the cell specific productivity of CHO-K1-hGM-CSF cells.

Cell hybridization, hybridomas, and human hybridomas

Cell hybridization is one of the most basic cytotechnologies. The hemagglutinating virus of Japan was first used to cause cell fusion; however, polyethylene glycol is widely used now because of simplicity of procedure. This chapter first explains the principles of cell hybridization methods and then describes the practical protocols for preparing mouse hybridomas using polyethylene glycol. So far, lack of an excellent human fusion partner cell line that has high fusion efficiencies and does not produce immunoglobulin has hindered the spread of human-human hybridoma preparation methods. In the authors' laboratory NAT-30 and HO-323, human parent cell lines with high fusion efficiencies, have been established to prepare many hybridoma cell lines producing cancer-specific human monoclonal antibodies. Because NAT-30 and HO-323 cell lines are IgM producers, it is difficult to obtain IgG-producing hybridomas because the types of immunoglobulin produced by hybridomas are strongly affected by the characteristics of parent cells. Thus a nonimmunoglobulin-producing human parent cell line, A4H12, derived from human T lymphoma was established that can efficiently obtain IgG-producing human hybridomas. Another problem with preparing human hybridomas is that it is difficult to obtain B lymphocytes immunized with optional antigens for ethical reasons. To overcome this problem, in vitro immunization methods have been developed that allow exposure of a large number of B lymphocytes to cultured cancer cell or soluble antigens. The section on human hybridomas explains human fusion partners, in vitro immunization methods, and the preparation of human-human hybridomas using an electrofusion method. Finally, the application of human monoclonal antibodies to medical uses and the preparation of supranatural monoclonal antibodies are reviewed. These include multifunctional monoclonal antibodies and altered monoclonal antibodies having increased affinity and specificity by exchanging or modifying light chains.