Comparisons of the glycosylation of a monoclonal antibody produced under nominally identical cell culture conditions in two different bioreactors.

The murine B-lymphocyte hybridoma cell line, CC9C10, was grown in serum-free continuous culture at steady-state dissolved oxygen (DO) concentrations of 10%, 50%, and 100% of air saturation in both LH Series 210 (LH) and New Brunswick Scientific (NBS) CelliGen bioreactors. All culture parameters were monitored and controlled and were nominally identical at steady state in the two bioreactors. The secreted monoclonal antibody (mAb), an immunoglobulin G(1), was purified and subjected to enzymatic deglycosylation using peptide N-glycosidase F (PNGase F). Asparagine-linked (N-linked) oligosaccharide pools released from mAb samples cultured in each bioreactor at each of the three DO setpoints were analyzed by high-pH anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The predominant N-linked structures were core-fucosylated asialo biantennary chains with varying galactosylation. There were also minor amounts of monosialyl oligosaccharides and trace amounts of afucosyl oligosaccharides. The level of DO affects the glycosylation of this mAb. A definite reduction in the level of galactosylation of N-glycan chains was observed at lower DO in both bioreactors, as evidenced by prominent increases in the relative amounts of agalactosyl chains and decreases in the relative amounts of digalactosyl chains-with the relative amounts of monogalactosyl chains being comparatively constant. However, the quantitative results are not precise matches between the two bioreactors. The effect of DO on galactosylation is less pronounced in the NBS bioreactor than in the LH bioreactor, particularly the shift between the relative amounts of agalactosyl and digalactosyl chains in 10% and 50% DO. There are also perceptibly higher levels of sialylation of the mAb glycans in the NBS bioreactor than in the LH bioreactor at all three DO setpoints. The results indicate that the DO effect is not bioreactor specific and that nominally identical steady-state conditions in different chemostat bioreactors may still lead to some incongruities in glycosylation, possibly due to the particular architectures of the bioreactors and the design of their respective monitoring and control systems. The observed differences in N-linked glycosylation of the mAb secreted by the hybridoma grown in the LH and NBS bioreactors may be explained by the differences in oxygen supply and control strategies between the two bioreactors.

Dissolved oxygen concentration in serum-free continuous culture affects N-linked glycosylation of a monoclonal antibody.

The murine B-lymphocyte hybridoma, CC9C10, was grown at steady state in serum-free continuous culture at dissolved oxygen (DO) concentrations of 10, 50, and 100% of air saturation. The secreted mAb, an IgG1, was purified and subjected to both enzymatic deglycosylation using PNGase F and chemical deglycosylation by hydrazinolysis. Both methods resulted in complete removal of N-linked oligosaccharide chains. Isolated N-glycan pools were analyzed by fluorophore-assisted carbohydrate electrophoresis (FACE) and high pH anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The FACE profiles and corresponding HPAEC-PAD chromatograms of N-linked oligosaccharides obtained by PNGase F digestion and hydrazinolysis provided complementary and corroborating information. The predominant N-linked structures were core-fucosylated asialo biantennary chains with varying galactosylation. There were also minor amounts of monosialylated, and trace amounts of afucosyl, oligosaccharides. A definite shift towards decreased galactosylation of glycan chains was observed as DO concentration in continuous culture was reduced. The vast majority of N-linked glycosylation occurred on the heavy chain. There was no evidence for N-linked glycosylation of the light chain or for O-linked glycosylation of the mAb.

The effect of dissolved oxygen on the metabolic profile of a murine hybridoma grown in serum-free medium in continuous culture.

The murine B-lymphocyte hybridoma, CC9C10 was grown at steady state under serum-free conditions in continuous culture at dissolved oxygen (DO) concentrations in the range of 10% to 150% of air saturation. Cells could be maintained with this range at high viability in a steady state at a dilution rate of 1 d(-1), although with lower cell concentrations at higher DO. A higher specific antibody production measured at higher DO was matched by a decrease in the viable cell concentration at steady state, so that the volumetric antibody titre was not changed significantly. An attempt to grow cells at 250% of air saturation was unsuccessful but the cells recovered to normal growth once the DO was decreased.There was a requirement for cellular adaptation at each step-wise increase in dissolved oxygen. Adaptation to a DO of 100% was associated with an increase in the specific activities of glutathione peroxidase (x18), glutathione S-transferase (x11) and superoxide dismutase (x6) which are all known antioxidant enzymes. At DO above 100%, the activities of GPX and GST decreased possibly as a result of inactivation by reactive oxygen radicals.The increase in dissolved oxygen concentration caused changes in energy metabolism. The specific rate of glucose uptake increased at higher dissolved oxygen concentrations with a higher proportion of glucose metabolized anaerobically. Short-term radioactive assays showed that the relative flux of glucose through glycolysis and the pentose phosphate pathway increased whereas the flux through the tricarboxylic acid cycle decreased at high DO. Although the specific glutamine utilization rate increased at higher DO, there was no evidence for a change in the pattern of metabolism. This indicates a possible blockage of glycolytic metabolites into the TCA cycle, and is compatible with a previous suggestion that pyruvate dehydrogenase is inhibited by high oxygen concentrations.Analysis of the oxygen uptake rate of cell suspensions at steady state under all conditions showed a pronounced Crabtree effect which was manifest by a decrease (up to 40%) in oxygen consumption on addition of glucose. This indicates that the degree of aerobic metabolism in these cultures is highly sensitive to the glucose concentration.

Oxygenation of intensive cell-culture system.

The abilities of various methods of oxygenation to meet the demands of high-cell-density culture were investigated using a spin filter perfusion system in a bench-top bioreactor. Oxygen demand at high cell density could not be met by sparging with air inside a spin filter (oxygen transfer values in this condition were comparable with those for surface aeration). Sparging with air outside a spin filter gave adequate oxygen transfer for the support of cell concentrations above 10(7) ml-1 in fully aerobic conditions but the addition of antifoam to control foaming caused blockage of the spinfilter mesh. Bubble-free aeration through immersed silicone tubing with pure oxygen gave similar oxygen transfer rates to that of sparging with air but without the problems of bubble damage and fouling of the spin filter. A supra-optimal level of dissolved oxygen (478% air saturation) inhibited cell growth. However, cells could recover from this stress and reach high density after reduction of the dissolved oxygen level to 50% air saturation.

Peptone, a low-cost growth-promoting nutrient for intensive animal cell culture.

The effect of addition of peptone to serum-free and serum supplemented media for the growth of hybridoma cells in various systems was studied. Supplementation of defined medium with either proteose peptone or meat peptone resulted in significant increases in cell number and specific monoclonal antibody production in batch culture system. Other peptones were either inactive or less effective. In continuous culture, using medium supplemented with new born calf serum, the addition of peptone resulted in 125% and 150% increases in cell and antibody concentrations respectively. Similar increase in cell number (128%) was also obtained in spin-filter perfusion culture when medium was supplemented with peptone. By comparison, the substitution of a defined 1 x MEM amino acids mixture resulted in only a 50% increase. At higher perfusion rates the cell number maintained in steady state using peptone supplement could be increased to 1.3 x 10(7) cells ml-1 while the serum concentration was reduced from 5% to 1% at a perfusion rate of 2.5 volumes per day.

Specific monoclonal antibody productivity and the cell cycle-comparisons of batch, continuous and perfusion cultures.

A selection of mouse hybridoma cell lines showed a variation of approximately two orders of magnitude in intracellular monoclonal antibody contents. The different levels directly influenced apparent specific monoclonal antibody productivity during the death phase but not during the growth phase of a batch culture. The pattern of changes in specific productivity during culture remained basically similar even though at different levels for all cell lines tested. Arresting the cells in the G1 phase using thymidine increased the specific productivity, cell volume and intracellular antibody content but at the same time led to decreased viability. In continuous culture DNA synthesis decreased with decreasing dilution rate though without an accompanying change in cell cycle and cell size distributions. The data shows both the decrease in viability and intracellular antibody content to be important factors which influence the negative association between specific antibody productivity and growth rate. In high cell density perfusion culture, when the cell cycle was prolonged by slow growth, viability was low and dead, but not lysed, cells were retained in the system, the specific antibody productivity was nearly two fold higher than that obtained in either batch or continuous cultures. The results imply that the prolongation of G1 phase and the increase in death rate of cells storing a large amount of antibody together cause an apparent increase in specific antibody productivity.