What are the key challenges that face cell-based bioprocess manufacturers today?
Several issues present challenges for manufacturers today, including purification and stabilisation, delivery, yields, contamination,
process development and scaleup.
Purification and stabilisation
Harvest of product cells from adherent cell bioreactors is one of the critical bottlenecks in the cell therapy manufacturing
process. Many processes utilise trypsin or other enzymatic digest methods to remove cells from cultivation surfaces, but the cells
must be neutralised, washed, analysed for purity and formulated within a narrow window of time — as short a timeframe as possible
and typically in less than 1 hour — to produce a reliable product. Many cell production processes are patched together from
singleuse bioprocessing containers designed for supernatant rather than cell harvest. Factors such as particle loads from
singleuse bags, smaller process volumes and lack of terminal sterilisation of the product all impact on process design, as
these factors are not a concern for supernatant processing. There is limited equipment available that has been purpose-designed
for sterile, scalable cell harvest, washing and concentration, although this situation is changing.
Products can currently be formulated and filled into storage or delivery bags or vials for fresh or frozen inventory. Particularly
if products are shipped fresh, the product should be quantified for stability, viability and preferably dose-response.
The factors mentioned above all contribute to delivery concerns with both fresh and frozen product. In addition, the manufacturing
model should be considered — whether the product is allogeneic or autologous, and manufactured in small batches close to the
site of delivery or at scale at a central manufacturing location. Although fixed costs may be lower, operators may be better
trained and have greater process experience, and the product quality and consistency may be easier to control at centralised
sites, none of this matters if the product degrades unacceptably during transport. Each product needs to be assessed separately
due to varying inherent cell lineage characteristics to determine whether fresh or frozen is acceptable and to determine parameters,
that can even possibly be monitored throughout transport, which indicate the cell population viability.
Process development issues
One of the more troubling cell therapy process development issues is trying to develop a consistent, safe and efficacious
autologous stem cell therapy when inherent genetic, and perhaps epigenetic factors, cause cells from different donor/patients
to grow and differentiate at different rates. This means that multiple batches cannot all be maintained by the same protocol
on the same time schedule, which currently precludes automation of that process. Relevant process variables will need to be
defined and measured to take the 'art' out of producing such cultures before this system can become amenable to automation;
therefore being safer and, over time, more efficient and cost effective. The development and integration of additional PAT
into bioreactors will enable automation in the future. At the moment, many assays indicating the culture's growth and differentiation
status are done manually. Development of online, singleuse sensors with feedback loops will permit automation. Additionally,
the FDA guidance on manufacturing autologous somatic cell therapies indicates that acceptable ranges for operating and control
parameters be defined for a cell growth process — typically these would include cell doubling time, cell purity, viability
and culture time. These native differences in the donor cell populations may necessitate the use of alternative parameters
or validation of a wider acceptable range than the manufacturer would prefer.