operation in perfusion mode might be the only option for economical production of
vaccines. However, for perfusion systems to be competitive in real-life industrial
applications, robust and efficient retention methods are required to maintain high
densities of viable cells inside the bioreactor. An overview on today’s available cell
retention devices (CRDs) is given below (Figure 6.3).
6.5
CRITICAL FACTORS FOR VIRUS PRODUCTION AT HIGH CELL
DENSITY
Virus production processes differ significantly from those of most cell culture-based
biologicals. Although these processes commonly use animal cells, most biological
products are accumulated in the cell culture broth during the cell-proliferation phase
in batch or fed-batch mode and harvested once peak concentrations are reached. In
contrast, virus production typically requires a biphasic process, which comprises a
TABLE 6.2
Comparison of parameters for available bioreactor operation modes
Batch
Fed-batch
Perfusion
Continuous
Volume
Constant
Increasing
Constant/Increasing
Constant
Cell removal
No
No
No
Yes
Specific cell growth
rate
Decreases
Decreases
Decreases
Constant
Maximum cell
conc. (x1E06
cells/mL)
1–10
2–20
10–160
2–5
Cells
Adherent/
suspension
Adherent/
suspension
Adherent/ suspension Suspension
Qualification staff
Low
Modest
High
Highest
Contamination risk Low
Modest
High
Highest
Foot-print
Large
Smaller
Smallest
Small
Medium
requirement
Medium
Concentrated feed Concentrated feed &
medium
Medium
Equipment
Larger volume,
reduced
auxiliary
equipment
Larger volume,
reduced
auxiliary
equipment
Lower volume,
increased auxiliary
equipment
Lower volume,
increased auxiliary
equipment
Sensors
°C, pH, pO2
°C, pH, pO2
°C, pH, pO2,
°C, pH, pO2
Options for
single-use ∗
Yes
Yes
No, some yes
No, maybe
Note
∗ Options of single-use bioreactors is rather limited by size than by operation mode (single-use bags up
to 3,000 L).
pO2: partial pressure of oxygen.
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Bioprocessing of Viral Vaccines