What are the key challenges that face cell-based bioprocess manufacturers today?
Purification and stabilisationHarvest 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.