Cell culture processes for monoclonal antibody production

Animal cell culture technology has advanced significantly over the last few decades and is now generally considered a reliable, robust and relatively mature technology. A range of biotherapeutics are currently synthesized using cell culture methods in large scale manufacturing facilities that produce products for both commercial use and clinical studies. The robust implementation of this technology requires optimization of a number of variables, including (1) cell lines capable of synthesizing the required molecules at high productivities that ensure low operating cost; (2) culture media and bioreactor culture conditions that achieve both the requisite productivity and meet product quality specifications; (3) appropriate on-line and off-line sensors capable of providing information that enhances process control; and (4) good understanding of culture performance at different scales to ensure smooth scale-up. Successful implementation also requires appropriate strategies for process development, scale-up and process characterization and validation that enable robust operation and ensure compliance with current regulations. This review provides an overview of the state-of-the art technology in key aspects of cell culture, e.g., generation of highly productive cell lines and optimization of cell culture process conditions. We also summarize the current thinking on appropriate process development strategies and process advances that might affect process development.Key words: monoclonal antibody, expression systems, cell line engineering, cell culture process development, optimization scale-up and technology transfer, process advances     

Cell culture processes for monoclonal antibody production

Animal cell culture technology has advanced significantly over the last few decades and is now generally considered a reliable, robust and relatively mature technology. A range of biotherapeutics are currently synthesized using cell culture methods in large scale manufacturing facilities that produce products for both commercial use and clinical studies. The robust implementation of this technology requires optimization of a number of variables, including 1) cell lines capable of synthesizing the required molecules at high productivities that ensure low operating cost; 2) culture media and bioreactor culture conditions that achieve both the requisite productivity and meet product quality specifications; 3) appropriate on-line and off-line sensors capable of providing information that enhances process knowledge; and 4) good understanding of culture performance at different scales to ensure smooth scale-up. Successful implementation also requires appropriate strategies for process development, scale-up and process characterization and validation that enable robust operation that is compliant with current regulations. This review provides an overview of the state-of-the art technology in key aspects of cell culture, e.g., engineering of highly productive cell lines and optimization of cell culture process conditions. We also summarize the current thinking on appropriate process development strategies and process advances that might affect process development.     

Enhancement of monoclonal antibody production by immobilized hybridoma cell culture with hyperosmolar medium

To determine the effect of hyperosmotic stress on the monoclonal antibody (MAb) production by calcium-alginate-immobilized S3H5/gamma2bA2 hybridoma cells, the osmolalities of medium in the MAb production stage were varied through the addition of NaCI. The specific MAb productivity (q(MAb)) of immobilized cells exposed to abrupt hyperosmotic stress (398 mOsm/kg) was increased by 55% when compared with that of immobilized cells in the control culture (286 mOsm/kg). Furthermore, this enhancement of q(MAb) was not transient. Abrupt increase in osmolality, however, inhibited cell growth, resulting in no increase in volumetric MAb productivity (r(MAb)). On the other hand, gradual increase in osmolality allowed further cell growth while maintaining the enhanced q(MAb) immobilized cells. The q(MAb) immobilized cells at 395 mOsm/kg was 0.661 +/- 0.019 mug/10(6) cells/h, which is almost identical to that of immobilized cells exposed to abrupt osmotic stress. Accordingly, the r(MAb) was increased by ca. 40% when compared with that in the control immobilized cell culture. This enhancement in i(MAb) of immobilized S3H5/gamma2bA2 hybridoma cells by applying gradual osmotic stress suggests the potential of using hyperosmolar medium in other perfusion culture systems for improved MAb production. (c) 1995 John Wiley & Sons, Inc.     

Continuous hybridoma culture in a low-protein serum-free medium supplemented with liposomes

A homemade serum-free medium containing a low protein level under 0.1 g l⁻¹ has been proved to support long-term cultures of VO 208 hybridoma cells successfully up to 50 days. The low protein level was achieved by supplying the lipids through liposomes containing cholesterol, oleic acid, - dipalmitoyl phosphatidylcholine, and bovine serum albumin. The influence of the liposome content in the feeding medium was studied in a continuous culture performed with step variations of the liposomes level, from 7.5 to 30 ml l⁻¹. The cell density decreased at the highest liposomes content while it became higher with 7.5 or 12 ml l⁻¹ of liposomes. For each step variation appeared a transitory activation of the specific rates of nutrient consumption, metabolite production and antibody secretion, as well as a transitory decrease of the specific cell growth rate. The overall structure of the antibodies was not affected during the culture.     

Elucidating the effects of pH shift on IgG1 monoclonal antibody acidic charge variant levels in Chinese hamster ovary cell cultures

Charge variants, especially acidic charge variants, in recombinant monoclonal antibodies are critical quality attributes, which can affect antibodies’ properties in vitro and in vivo. Meanwhile, charge variants are cumulative effects of various post-translational modifications and chemical degradations on antibody. In this work, to investigate the effect of lowering culture pH in the stationary phase on acidic charge variant contents in fed-batch cultures and its mechanism, cell culture experiments in 2-L bioreactors were firstly performed to explore the changes in the charge distribution under the pH downshift condition using weak cation exchange chromatography. It is found that acidic charge variant contents were significantly decreased by pH downshift. Then, to reveal the mechanism by which the content of acidic charge variants is reduced under pH downshift condition, the variation of post-translational modifications and chemical degradations under the pH downshift condition was explored. Meanwhile, the structure of the acidic charge variants was characterized. Several analysis experiments including size exclusion chromatography, capillary electrophoresis-sodium dodecyl sulfate under non-reducing conditions, tryptic peptide map, and reduced antibody mass were applied in this study. The results show that the mechanism by which the content of acidic charge variants is reduced is that the contents of disulfide bond reduction, galactosylation, and asparagine deamination of the HC-N388 in the Fc domain were reduced by pH downshift.     

Evaluation of a simple protein free medium that supports high levels of monoclonal antibody production

A simple protein free medium was formulated and tested in suspension culture using three hybridoma cell lines. The medium, referred to as CDSS (Chemically Defined Serum Substitutes), consisted of the basal medium DMEM:Ham F12, 1:1, with HEPES (D12H), plus pluronic F68, trace elements, ferric citrate, ascorbic acid, and ethanolamine. No protein or lipid components were added. All three cell lines were weaned off serum using CDSS and a commercially available protein free medium PFHM-II. Data shown here indicated that normally cells took 1–7 weeks to wean off serum and an additional 2–7 weeks to adapt to suspension culture. After adaptation the cells were able to grow well in suspension culture using both protein free media and in the main performed better than serum containing controls. The stability of the three hybridoma cells for antibody production following freeze/thaw procedures and long term subculturing was also tested. All three lines were frozen using our protein free CDSS medium (containing 0.75% bovine serum albumin and 10% dimethyl sulfoxide) in liquid nitrogen for up to one year. Cells thawed from these stocks recovered well and were able to maintain good growth and antibody production characteristics. One line was shown to grow using our protein free CDSS medium in suspension culture for 12 weeks without loss of antibody productivity.     

Cell cycle kinetics and monoclonal antibody productivity of hybridoma cells during perfusion culture

The flow-cytometric (FCM) analysis of bivariate DNA/lgG distributions has been conducted to study the cell cycle kinetics and monoclonal antibody (MAb) production during perfusion culture of hybridoma cells. Three different perfusion rates were employed to demonstrate the dependency of MAb synthesis and secretion on cell cycle and growth rate. The results showed that, during the rapid growth period of perfusion culture, the level of intracellular igG contents of hybridoma cells changed significantly at each perfusion rate, while the DNA histograms showing cell cycle phases were almost constant. Meanwhile, during the reduced growth period of perfusion culture, the fraction of cells in the S phase decreased, and the fraction cells in the G1/G0 phase increased with decreasing growth rate. The fraction of cells in the G2/M phase was relatively constant during the whole period of perfusion culture. Positive correlation was found between mean intracellular IgG contents and the specific MAb production rate, suggesting that the deletion of intracellular IgG contents by a flow cytometer could be used as a good indicator for the prediction of changes in specific MAb productivity following manipulation of the culture condition. (c) 1994 John Wiley & Sons, Inc.     

Development of a low-serum medium for the production of monoclonal antibody against congenital adrenal hyperplasia by hybridoma culture

Statistically designed experiments were used in developing a low-serum medium for the production of a diagnostic monoclonal antibody against congenital adrenal hyperplasia using hybridoma 192. A two-level half-fractional factorial design was used for screening six components (Minimum Essential Medium Eagle amino acids, 2-mercaptoethanol, ethanolamine, ferric citrate, zinc sulfate, and sodium selenite). The experimental design was then augmented to central composite design. The basal Dulbecco’s modified Eagle’s medium (DMEM; containing 4?mM L-glutamine, 1% antibiotic–antimycotic agent) supplemented with 0.4% by volume fetal bovine serum (FBS), 311.8?mM ferric citrate, 17.3?nM sodium selenite, and 4.5?mM zinc sulfate (LSD) was found to support the growth of the hybridoma. Specific cell growth rate in the LSD (0.033?±?0.001/h) was slightly lower than in the control medium (i.e., basal DMEM supplemented with 2% FBS; 0.0045?±?0.003/h). Nevertheless, the specific MAb production rate for LSD was higher (0.057?±?0.015 pg/cell?·?h versus 0.004?±?0.002 pg/cell?·?h in LSD and control, respectively). The antibody produced in the LSD showed high specificity and no cross-reactivity with the other structural resemblance’s steroid hormones, revealing no structural changes owing to the new medium formulation developed. The new medium formulation effectively reduced the medium cost by up to 64.6%.     

表达重组抗CD52单克隆抗体CHO细胞灌流培养基的筛选

目的筛选重组抗CD52单克隆抗体CHO细胞株培养和连续灌流表达用培养基,以提高抗体表达量。方法通过调整原有批培养用培养基中谷氨酰胺和植物水解蛋白,获得5种培养基配比。使用模拟灌注方式进行细胞培养,分析细胞密度、活细胞比率和目标蛋白表达,筛选连续灌流细胞培养和表达用培养基。最后在7 L反应器中采用灌注培养方式对筛选获得的培养基进行验证。结果使用50 mL细胞培养管进行模拟灌注培养时,活细胞比率较高,达到90%以上;CHO细胞在添加谷氨酰胺至4.0 mmol/L和植物水解蛋白至5.0 g/L的批培养用培养基中生长速度最快;在基础培养基中抗体表达量比优化前高15%。20 d培养周期内,优化的培养基在7 L反应器中可以维持CHO细胞密度在(2 727±253)万个/mL,活细胞比率在95%以上。结论通过模拟灌注培养,筛选获得了一种在7 L反应器灌流培养中适宜于重组抗CD52单克隆抗体CHO细胞表达的培养基。     

Endothelin in human plasma and culture medium of aortic endothelial cells--detection and characterization with radioimmunoassay using monoclonal antibody

We have developed monoclonal (KY-ET-1-I) and polyclonal (ET-F5) antibodies against endothelin-1 (ET-1) and established sensitive radioimmunoassays (RIAs) with different specificities. The RIA with KY-ET-1-I detected ET-1, ET-2 and ET-3, while the RIA with ET-F5 recognized ET-3 very weakly. Using these RIAs, we have investigated the concentration and molecular forms of ET-1-like immunoreactivity (-LI) in culture medium of bovine aortic endothelial cells and human plasma. Culture medium of endothelial cells contained two major components compatible with big ET and ET-1. ET-1-LI was also detected in human plasma. ET-1-LI in human plasma consisted of apparent two components, the small molecular form emerging at the position of ET-1 and the large form with the peak eluting at the preceding fraction of the elution position of big ET. The concentration of the small form of ET in human plasma was about 5 pg/ml.     

Cell adhesion and metastasis: a monoclonal antibody approach

Cellular adhesion processes are important during the growth of tumors and the generation of metastases. We therefore expect that monoclonal antibodies directed against molecules regulating cell adhesion of tumor cells will be powerful tools for specifically interfering with these processes. In the experimental system of the mouse B16 melanoma, a series of such functional monoclonal antibodies has recently been prepared and their inhibitory effect on the formation of metastatic lesions has been explored.     

Preparation of a monoclonal antibody to a melanoma growth-stimulatory activity released into serum-free culture medium by Hs0294 malignant melanoma cells

Autostimulatory growth factors may contribute to the ability of malignant cells to escape normal growth controls. We have previously shown that Hs0294 human malignant melanoma cells release into culture medium an acid-soluble, heat-stable, trypsin-sensitive, autostimulatory monolayer mitogen which can be purified from acetic acid extracts of conditioned medium by gel filtration, reverse-phase high-performance liquid chromatography, and preparative electrophoresis. The majority of this melanoma growth-stimulatory activity (MGSA) resides in a 16-Kd moiety, though bioactivity is also associated with 24-26 and less than 14-Kd forms of MGSA (Richmond and Thomas: J Cell Physiol 129:375, 1986). In order to further characterize this growth factor, monoclonal antibodies were prepared against a partially purified preparation of the autostimulatory melanoma mitogen. Monoclonal antibody clones were selected based on supernate inhibition of 3H-thymidine incorporation in serum-free Hs0294 melanoma cultures. One of these, termed FB2AH7, slows, but does not completely block, the growth of Hs0294 cells in serum-free medium in a dose-dependent manner. This antibody does not slow the growth of normal rat kidney fibroblasts, which neither produce nor require this mitogen, in either serum-free medium or medium containing 0.8% calf serum. This monoclonal antibody also blocks the mitogenic effects of partially purified preparations of this melanoma growth stimulatory activity (MGSA) on both Hs0294 cells and normal rat kidney fibroblasts. The FB2AH7 antibody has been demonstrated to bind MGSA by Western blot and by immunoprecipitation procedures. Western blot analysis of reverse-phase high-performance liquid chromatography purified growth factor demonstrated that FB2AH7 antibody binds to the 16-Kd and approximately 13-14-Kd forms of MGSA. FB2AH7 antibody can be used in immunoprecipitation experiments to bind the approximately 13-16-Kd forms of MGSA. The specificity of the binding of FB2AH7 antibody for MGSA but not other growth factors has been demonstrated in a modified dot blot assay. These data thus support the hypothesis that MGSA is an autostimulatory melanoma mitogen distinct from other growth factors.     

Effect of bacterial growth in the complexing capacity of a culture medium supplemented with cadmium(II)

The aim of this study was to evaluate complexing capacity (CC) accompanying microbial growth in a metal supplemented culture medium. A combined strategy of square wave anodic stripping voltammetry (SWASV) monitored titration and ion-exchange resins treatment (Chelex 100) has been applied. Culture medium, supplemented with Cd(II) in excess to ligands, was inoculated with an indigenous bacterial culture; total ligand concentration and stability constants were determined at different bacterial growth stages. As far as known, determination of CC in such conditions has not been reported (usually ligands in natural or wastewaters exceed metal concentration). HIDA, (N-(2-hydroxyethyl)iminodiacetic acid), was used as a model ligand to mimic soluble products derived from the resin treatment and bacterial metabolism. Ligand concentration, Lt (1.3 ± 0.1 μM), and the conditional stability constant, K′, (log K′ = 5.7 ± 0.2) were in good agreement with expected values (1.0 ± 0.1 μM and log K′ = 6.1). In the supplemented culture medium, total ligand concentration in the micromolar range (60–80 μM) and conditional stability constants (5.5 < log K′ < 6.5) were determined. Cd(II) complexes detected in the different stages of microbial growth are labile from an electrochemical point of view. Results were compared to the case of Cd(II) non-supplemented broth.     

Beneficial effects of taurine on mouse zygotes developing in protein-free culture medium

The objectives of this study were to determine if mouse zygotes from outbred mice can develop in simple culture medium in the absence of bovine serum albumin (BSA), and if taurine can be used as a medium supplement to improve development. Zygotes from 2 stocks of outbred mice (CD-1 and CF-1) were cultured in simple embryo culture medium (TE medium) lacking BSA and with or without taurine (24 mM), or in regular TE medium with BSA. The presence of BSA had little or no effect on development, but development to post-blastocyst endpoints was enhanced when CD-1 zygotes were cultured in medium containing taurine. In addition, when CD-1 blastocysts were transferred to pseudopregnant animals, embryos cultured in the presence of taurine developed into fetuses more often than those cultured in medium without taurine, and their weights were higher than those of embryos cultured in regular TE medium with BSA. These beneficial effects of taurine do not appear to be the nonspecific effects of a fixed nitrogen source, because the addition of glycine to BSA-free TE medium did not have similar beneficial effects. It was concluded that mouse zygotes from outbred mice do not require BSA for their preimplantation development in culture and that the presence of taurine in preimplantation culture medium is beneficial not only for preimplantation development of the zygotes, but also for their post-blastocyst development.     

Detection and identification of a serine to arginine sequence variant in a therapeutic monoclonal antibody

Sequence variants, also known as unintended amino acid substitutions in the protein primary structure, are one of the critical quality attributes needed to be monitored during process development of monoclonal antibodies (mAbs). Here we report on analytical methods for detection and identification of a sequence variant in an IgG1 mAb expressed in Chinese hamster ovary (CHO) cells. The presence of the sequence variant was detected by an imaged capillary isoelectric focusing (ICIEF) assay, showing a new basic species in mAb charge variant profile. The new basic variant was fractionated and enriched by ion-exchange chromatography, analyzed by reduced light and heavy chain mass determination, and characterized by HPLC-UV/MS/MS of tryptic and endoproteinase Lys-C peptide maps. A Serine to Arginine sequence variant was identified at the heavy chain 441 position (S441R), and confirmed by using synthetic peptides. The relative level of the S441R variant was estimated to be in the range of 0.3-0.6% for several mAb batches analyzed via extracted ion chromatogram (EIC). This work demonstrates the effectiveness of using integrated analytical methods to detect and identify protein heterogeneity and the importance of monitoring product quality during mAb bioprocess development.     

Expression of a human anti-rabies virus monoclonal antibody in tobacco cell culture

A Nicotiana tabacum cv. Xanthi cell culture was initiated from a transgenic plant expressing a human anti-rabies virus monoclonal antibody. Within 3 months, plant cell suspension cultures were established and recombinant protein expression was examined. The antibody was stably produced during culture growth. ELISA, protein G purification, Western blotting, and neutralization assay confirmed that the antibody was fully processed, with association of light and heavy-chains, and that it was able to bind and neutralize rabies virus. Quantification of antibody production in plant cell suspension culture revealed 30 microg/g of cell dry weight for the highest-producing culture (0.5 mg/L), 3 times higher than from the original transgenic plant. The same production level was observed 3 months after cell culture initiation. Plant cell suspension cultures were successfully grown in a new disposable plastic bioreactor, with a growth rate and production level similar to that of cultures in Erlenmeyer flasks.     

Analysis of recombinant monoclonal antibody isoforms by electrospray ionization mass spectrometry as a strategy for streamlining characterization of recombinant monoclonal antibody charge heterogeneity

A therapeutic recombinant monoclonal antibody analyzed by cation-exchange chromatography exhibited a heterogeneous profile composed of approximately 10 isoforms. The peaks were isolated and characterized by electrospray quadrupole time-of-flight mass spectrometry (ESI-q-TOF-MS), N-terminal Edman sequencing, peptide mapping, and other techniques. Acidic (lower pI) peaks were found to represent deamidated and sialyated species. Higher pI peaks were found to contain N- and C-terminal heavy-chain variants. Biological activities of the more abundant isoforms were found to be comparable. An approach streamlining the characterization of antibody charge heterogeneity is proposed.     

Impact of mammalian cell culture conditions on monoclonal antibody charge heterogeneity: an accessory monitoring tool for process development

Recombinant monoclonal antibodies are predominantly produced in mammalian cell culture bioprocesses. Post-translational modifications affect the micro-heterogeneity of the product and thereby influence important quality attributes, such as stability, solubility, pharmacodynamics and pharmacokinetics. The analysis of the surface charge distribution of monoclonal antibodies provides aggregated information about these modifications. In this work, we established a direct injection pH gradient cation exchange chromatography method, which determines charge heterogeneity from cell culture supernatant without any purification steps. This tool was further applied to monitor processes that were performed under certain process conditions. Concretely, we were able to provide insights into charge variant formation during a fed-batch process of a Chinese hamster ovary cell culture, in turn producing a monoclonal antibody under varying temperatures and glucose feed strategies. Glucose concentration impacted the total emergence of acidic variants, whereas the variation of basic species was mainly dependent on process temperature. The formation rates of acidic species were described with a second-order reaction, where a temperature increase favored the conversion. This platform method will aid as a sophisticated optimization tool for mammalian cell culture processes. It provides a quality fingerprint for the produced mAb, which can be tested, compared to the desired target and confirmed early in the process chain.

     

离子交换色谱对抗VEGFR2单抗的电荷异质性分析

目的采用离子交换高效液相色谱(CEX-HPLC)分析抗VEGFR2(抗血管内皮生长因子受体2)单抗制品的电荷异质性。方法应用CEX-HPLC技术,对VEGFR2单抗进行电荷异质性分析,并结合羧肽酶B(CpB)和N-糖酰胺酶F(EndoF2)酶切,初步研究其电荷异质性的成因。结果用CEX-HPLC分析CpB酶切前后单抗,证明其碱性变异体主要由C末端赖氨酸不均一性引起;分析EndoF2酶切前后处理的单抗,证明其酸性变异体部分由N-糖末端上的唾液酸修饰所引起。通过2种酶的顺序酶切可相对准确地分析含C-末端赖氨酸以及含唾液酸单抗的比例。结论采用CEX-HPLC可较好地分析单抗的电荷异质性;并结合合适的酶切处理,可判断单抗主要电荷异质性的来源,为保证单抗制品生产工艺的稳定性及质量控制提供了有效手段。