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. 2020 Jul 21;20(9-10):412-421.
doi: 10.1002/elsc.202000034. eCollection 2020 Sep.

Investigation of cell line specific responses to pH inhomogeneity and consequences for process design

Katrin Paul  1   2 , Thomas Hartmann  1   2 , Christoph Posch  3 , Dirk Behrens  3 , Christoph Herwig  1   2
Affiliations

Investigation of cell line specific responses to pH inhomogeneity and consequences for process design

Katrin Paul et al. Eng Life Sci. .

Abstract

With increasing bioreactor volumes, the mixing time of the reactor increases as well, which creates an inhomogeneous environment for the cells. This can result in impaired process performance in large-scale production reactors. Particularly the addition of base through the reactor headspace can be problematic, since it creates an area, where cells are repeatedly exposed to an increased pH. The aim of this study is to simulate this large-scale phenomenon at lab-scale and investigate its impact. Two different cell lines were exposed to pH amplitudes of a maximal magnitude of 0.05 units (pH of 6.95). Both cell lines showed similar responses, like decreased viable cell counts, but unaffected lactate levels. However, cell line B showed an initially increased specific productivity in response to the introduced amplitudes, whereas cell line A showed a consistently lower specific productivity. Furthermore, the time point at which base addition is started influences the impact, which pH amplitudes have on process performance. When pH control was started earlier in the process, maximal viable cell counts decreased and the lactate metabolic shift was less pronounced. These results show that the potential negative impact of pH amplitudes can be minimized by strategic process design.

Keywords: 2‐compartment system; CHO; inhomogeneities; large‐scale; pH excursions; scale‐down.

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Conflict of interest statement

The authors have declared no conflict of interest.

Figures

FIGURE 1
FIGURE 1
(A‐B) pH trajectories in the bypass of the 2‐CS for narrow pH control (no amplitudes are introduced), small amplitudes (0.05 pH units) and medium amplitudes (0.1 pH units). (C‐D) Amounts of base which were added throughout the cultivations
FIGURE 2
FIGURE 2
(A‐B) Viable cell concentration (dots) and viability (triangles) trajectories. (C‐D) Absolute lactate levels for the different introduced amplitudes
FIGURE 3
FIGURE 3
(A) Viable cell concentration (dots) and viability (triangles) trajectories. (B) Absolute lactate levels (dots) and percentage of PI positive/Annexin negative cells (triangles) for different time points of the start of pH control
FIGURE 4
FIGURE 4
(A‐B) Percentage of apoptotic cells (dots) and cell size (triangles) over the process time. (C‐D) Percentage of PI positive/Annexin negative particles
FIGURE 5
FIGURE 5
(A‐B) Specific mAb production rate of both cell lines
FIGURE 6
FIGURE 6
(A) Viable cell concentration (dots) and viability (triangles) trajectories. (B) Cell size (dots) and specific antibody production rate (triangles). (C) Absolute lactate levels. (D) Percentage of PI positive/Annexin negative cells for addition of base to the air‐liquid interface and submerse addition
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