Figure 2. Profiles of viable cell density (SUB VCD and 5-L Bio VCD) and viability (SUB Viab and 5-L Bio Viab, in %) of the
seed train bioreactors. The passage of the wave bag into the N-2 bioreactors was performed at working day 20, and the passage
from N-2 to N-1 bioreactor was performed at working day 23. VCD and Viab were determined using the Vi-cell cell counter (Beckman
Coulter). The graphs show mean values with errors bars of two different runs. The variability of the viability is so low that
the error bars are not visible.
The seed trains performed in the 50-L SUB and in the 5-L glass bioreactors resulted in comparable cell density and viability
(Figure 2). For all configurations, viable cell densities at the end of the growth phase ranged from 2.7 to 3.2 × 106 cells/mL, and viability ranged from 95.5 to 98.7%.
Figure 3. Viable cell density bar graph at production day 7 (working day 33) of the production bioreactors. The viable cell
density reached a maximum value at production day 7 (working day 33) and started decreasing on the next day. The values shown
here are means of two or three values with error bars.
The production phase performed in the 50-L SUB and in the 5-L glass bioreactors also gave similar results for the maximum
VCD obtained at production day 7 (working day 33) and integral viable cells (IVC) (Figure 3 and 4). The IVC curves (Figure
4) show comparable cell growth throughout the process between different scales and configurations, whether the seed train
material was coming from the 50-L SUB or the 5-L bioreactor. The metabolites profiles such as glucose, lactate, glutamine,
and glutamate were all comparable between different scales and configurations (data not shown).
Figure 4. Integral viable cell density of the three configurations (SUB/SUB, SUB/5L, and 5L/5L). The graphs are means of two
or three runs with error bars.
The MAb titers obtained at production day 7 (corresponding to the highest point of viable cell concentration) were comparable
for all configurations (Figure 5), again demonstrating the similar performance of the SUB and the 5-L bioreactor in seed train
and production. The titer was plotted against the IVC (slopes: 5L/5L 22.62, SUB/SUB 21.81, SUB/5L 19.23) and the relationship
was found to be linear, as expected.3 The slopes were very close for the three configurations, demonstrating that the same specific productivity is reached in
Figure 5. Product titer bar graph at production day 7 (working day 33). The viable cell density reached a maximum value at
production day 7 (working day 33) and started decreasing on the next day. The values showed here are means with error bars
of two or three values.
The pH in the bioreactor was regulated using CO2 in overlay in the 5-L glass bioreactors and in the 50-L SUB. The pCO2 levels were compared between the SUB and the 5-L runs to assess the CO2 stripping performance of the SUB (Figure 6). As shown in Figure 6, the 50-L SUB cultures or the 5-L bioreactor coming from
the SUB seed train have appropriate pCO2 levels below 60 mmHg. In addition, to assess the impact of pH regulation using CO2 instead of acid, pCO2 data were compared to historical data from a 5-L acid-regulated run and showed that the 50-L SUB production run with the
50-L SUB seed train have even lower pCO2 levels than the acid-regulated runs (40–54 mmHg).
DO Probe Comparison
Figure 6. The pCO2 profiles for the different configurations (SUB/SUB, SUB/5 L, and 5 L/5 L), measured with ABL-5 gas analyzer (Radiometer).
The values showed here are means with error bars of two or three values.
A drawback of single-use bioreactors is the possible impairment of sensors based on electric potential differences because
of the static electricity phenomena.4 However, disposable sensors now are available based on fluorescence, which may not cause the same problems. One of these
probes was tested in the single-use bioreactor to monitor the density of oxygen, in comparison to a reference stainless steel
polarographic probe. The trends of the two probes are identical, even if a small constant difference (<2%) is noted between
the two curves, probably because of calibration (data not shown). Thus, in this specific configuration, no impairment of the
stainless steel DO probe was observed in the environment of the SUB. The disposable fluorescence DO probe showed a comparable
performance, and could probably be used to replace the reference stainless steel probe.