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From Left: Dr Ng Say Kong, Tang Wen Qin, Dr Eunice Leong, Zheng Zi Ying, Dr Zhang Wei

 

Science

Biologics such as monoclonal antibodies have been approved for treating diseases such as severe, persistent allergic asthma (example, omalizumab) and cancers (example, trastuzumab, pembrolizumab). To make them more accessible, generic monoclonal antibodies products are developed when patents of the original drug expire. These generic products are called “Biosimilars”, and they are recognized by drug regulators to be very similar to the original brand-name counterparts. As development costs of biosimilars are lower, they compete aggressively with brand-name products to, consequently, drive prices down, especially when biosimilars can be produced more efficiently.

One way to reduce the cost of antibody manufacture is by producing them in a continuous manner as opposed to producing them in batches. In the production process, factors that can influence the growth of the animal cells producing the antibodies are important to affecting the overall productivity. In this study, the team explored limiting the amount of nutrients to the cells by feeding according to the cell volume, which increases in the bioreactor ¹.

 

Societal Impact

In this study, the team examined how to produce a biosimilar monoclonal antibody more efficiently using continuous processes. By controlling the nutrient feed rate based on cell volume, antibody productivity was increased by 2.5 to 3-folds. This could lead to considerably lower cost-of-goods, and ultimately less expensive therapeutic antibody drugs.

 

Technical Summary

Biomass specific perfusion rate (BSPR) as opposed to cell specific perfusion rate could be a relevant control parameter for cells that grow in volume during the production phase. Our hypothesis is that growth arrest by overall nutrient limitation leads to earlier high specific productivities. The effects of biomass specific perfusion rate at three levels were examined in mini bioreactors using the Sartorius Ambr250 High Throughput Perfusion system. The three levels of perfusion rates modelled conditions with low, medium, and high concentrations of nutrients.

For cells maintained at the lowest BSPR, nutrients such as glucose and essential amino acids were still present in the media, but cell growth rate was slowed down. Interestingly, these cells grew the largest in size, where compared to the cells maintained at the highest BSPR, there was a 2.2-fold increase in diameter after 14 days in culture. While the specific glucose consumption rate increased as culture time increased, glucose consumption rate relative to the biomass was constant. Finally, the lowest BSPR resulted in the highest volumetric productivity and media efficiency. Across the three BSPRs, the percentage of monomer species analyzed on the size exclusion column were above 97%. There were no significant differences in the percentage of main species in the charge variants analysis. The percentage of non-glycosylated heavy chains were below 2%. In all, this study demonstrated that BSPR can significantly influence cell growth and productivity of cultures with variable cell volumes with little changes in product quality.

Figure 1. (A) Schematic of the comparison between biomass specific perfusion rate (BSPR) and cell specific perfusion rate (CSPR). When a constant BSPR is defined for a process, the media flow rate increases proportionally to the increase in cell diameter or cell volume. In contrast, when a constant CSPR is defined, the media flow rate does not change when the cells grow in size, which could lead to insufficient nutrients and, consequently, negatively affecting growth and productivity. (B) In this study, three levels of BSPRs were used to model conditions of low, medium, and high nutrient availability. The volumetric productivity is a metric to evaluate the mass of antibody produced per bioreactor (represented in a unit volume) in a day.

 

References

¹ Leong, J., Tang, W.Q., Chng, J., Ler, W.X., Manan, N.A., Sim, L.C., Zheng, Z.Y., Zhang, W. Walsh, I., Ziljlstra, G., Pennings, M., & Ng, S. K. (2024). Biomass specific perfusion rate as a control lever for the continuous manufacturing of biosimilar monoclonal antibodies from CHO cell cultures. Biotechnology Journal, 19, e2400092. https://doi.org/10.1002/biot.202400092