Table 1. AcuSystXCELL Raw Bulk and Net Capacities Extrapolated From Pilot Runs of Three Different Products
The AcuSyst hollow-fiber bioreactor family comprises four bioreactor systems. They support operation of 1, 2, 6, 10, 12, or
20 hollow-fiber cartridges per run and system. The AcuSystXCELL, with a maximum 12 cartridges, was investigated for GMP manufacturing
at the pilot plant (Figure 3). System-specific process development parameters include the media feeding rate, cartridge perfusion
rate, harvest rate, and a pressure cycling regimen. Technical details are described elsewhere.6 Proper process development allows defining parameters for steady state manufacturing over periods of 30 to 90 days. In contrast
to other systems, media perfusion is separated from cell culture space by membranes with a cut off of <10 kD. Proteins are
retained in the cell culture space and can be harvested independently from media perfusion. Harvest rates of 0.5 to 2 cell
culture volumes per day are common and significantly reduce protein residence time in contrast to batch or fed-batch mode.
Thus high titers of up to 1 g/L for low expression cell lines of 5 pg/c-d productivity can be generated in the cell culture
space of a cartridge. This high protein concentration in crude bulk significantly reduces processing time and product losses
downstream.
Figure 3. Biovest AcuSystXCELL – a Pressure-Driven, Hollow Bioreactor Equipped with 12 Cartridges in Operation in a Cleanroom
Setting
These findings are also reported for other types of hollow-fiber bioreactors.7 We observed a reliable correlation of specific cell-line productivity in standard T flasks and yields in a continuous perfusion
bioreactor. Table 1 provides the extrapolated raw bulk and net capacities of the AcuSystXCELL bioreactor for three different
products. The processes were developed at pilot scales. Crude and net product derived from these runs after purification was
extrapolated to the capacity of the 12-cartridge system AcuSystXCELL run by multiplication with the respective scaling factor.
Correlation allows one to roughly calculate the ranges of system capacity on the basis of the specific productivity of customer
cell lines and the batch duration. Short product residence time, high titers, and process economy make the system well suited
for the manufacturing of sensitive, complex, low-volume, high-potency glycoproteins. The importance of short residence times
was addressed several times in the literature.8
Figure 4. Portable WAVE BIOREACTOR System200 of 100-L Working Volume in Operation at a Process Development Lab
The Wave system is a bag-based bioreactor family for batch and repeated batch modes of operation. Seven bioreactor scales
with net culture volume of 1, 5, 10, 25, 100, 250, and 500 L are available. Actually, the largest scale employed at ProBioGen
is the Wave Bioreactor System200, with a nominal culture volume of 100 L (Figure 4). Filling level, rocking rate, and angle
are system-specific process development parameters. The system is especially useful for cell lines secreting significant amounts
at substrate limitations. Products resistant to proteases and glycosidases are preferred to obtain reasonable final titers
in the system.
The use of Acusyst hollow-fiber systems in manufacturing of biopharmaceuticals is still limited. The remaining challenges
for widespread use include:
Sophisticated handling, requires dedicated personnel with long experiences
Consistency of cell harvest over long periods.
As far as we know, the use of Wave bioreactors for biopharmaceutical protein manufacturing is still limited to investigational
medicinal product manufacturing and inoculum production for approved products. The remaining challenges for increasing use
in this area are:
Complexity of linear process scale-up due to different bag geometries
Limited flexibility to develop high performance fed-batch processes (filling level optimum).
