bottle systems over which process control is limited.
This productivity issue can be overcome by attaching the
cells to a substrate such as a microcarrier. There is now a
great deal of interest in developing vaccines using attachment dependent cells and microcarriers as they allow good
propagation in bioreactors and provider better process
control, often resulting in high-titre vaccine production in
shorter timelines4, 5, 6. Additionally, microcarrier processes
are seen as a candidate for cost-effective vaccine production
at very large scales, to supply the rapidly growing demand
for mass vaccination programmes in densely populated
countries such as China and India.
One technical problem, which is preventing wider adop-
tion of microcarrier culture in bioreactors, is how to accu-
rately mimic bioreactor conditions to optimise cell growth,
adherence and vaccine production with microcarrier
cultures. Spinner flasks and benchtop bioreactors are cur-
rently used to define optimal media, feed and bioprocessing
conditions7. These types of vessels are both resource- and
capital-intensive. Additionally, due to their scale, expense
Cell culture is becoming the route of choice for manufac-
turing many vaccines as it offers distinct advantages over
egg based production which include shorter lead times and
greater process flexibility2.
The most commonly used cell lines for vaccine production are Vero, Madin-Darby canine kidney, (MDCK), PER.
C6 and insect cells. Several of the commonly used cell lines
such as the Vero and MDCK cell lines are attachment dependent and cannot be cultivated well as suspension cultures
■ By Dr. Barney Zoro, Sartorius Stedim Biotech/TAP Biosystems, Royston, UK.
Increasing productivity through the use of microbioreactors and microcarriers
Optimizing Vaccine Process
Scale-Up of Attachment
Dependent Cells
■ 34 SEPTEMBER 2014 | PHARMACEUTICAL PROCESSING
■ PHARMPRO. COM
■BIOPHARM
The ambr microbioreactor system has three com- ponents: the disposable bioreactor ( 10-15 mL
working volume), the workstation and the soft-
ware (Figure 1). Each bioreactor is single-use so
unlike conventional glass vessels do not require
post-run cleaning and sterilisation. To maintain
sterility, the ambr workstation is housed in a biological safety
cabinet and liquid handling automation facilitates aseptic culture set-up,
inoculation, feeding, and pipette tip settling, as well as sampling into
vessels such as 24/96 well plates and ViCell cups. These operating pro-
tocols can be configured for individual control of up to 24 or 48 reactors
operated in parallel. Each bioreactor incorporates individual DO and pH
sensors to enable closed loop control of these parameters. Automated
pH regulation is achieved by CO2 sparging or alkali addition, while O2
is sparged whenever needed to maintain a DO set point. There is also
the option to attach an analysis module to the
workstation for at-line pH calibration, thus
enabling accurate culture control.
The system is supported by software in
which the user sets up a protocol of steps for
the ambr to carry out. The protocol defines
operating parameters such as DO/pH set points,
stirrer speed and temperature. Protocol timings and
details can be edited at any time if steps need to be added, modified
or deleted, including while an experiment is running. Real-time data
such as gas flow rates, volumes, pH/DO values are logged continuously
during a run and external values such as cell counts, metabolites and
vaccine titres can also be imported into the software. Data can be
graphed within the software or exported for production of graphical or
tabular results in spreadsheet software.
