The Ever-Important Cell Bank in Biologics Manufacturing
No one in the biologics industry can deny the critical importance of a well characterized, biologic -producing cell line – it is the cornerstone of not only the technical program in that it produces the biologic, but also critical intellectual property for the company’s future. So, what considerations should be taken into account when thinking about laying down the ‘ever-important’ cell bank? Let’s explore!
First off, the cell line must be created or acquired at some point. The key components to a cell line are the parental cell line – also termed the ‘host cell line’ as it is the vehicle to produce the biologic product (or in certain circumstances the host cell becomes the product), and the expression construct which is the internal genetic component that is programmed to produce the biologic product. Now, this is a very basic definition, but the combination of these two elements constitutes the cell line. It is important to note that at the outset of a cell line development program that is aimed at GMP biologic production purposes, it is essential that a parental cell line is chosen which has a proven track record (development, manufacturing, regulatory, and quality) for its intended purpose.
During a cell line development program, a researcher will create a number of cell collections (called clones) through a process of transfection, amplification, and rounds of selection which results in many individual clones that are highly similar to each other but have subtle differences that need to be tested through experimentation aimed to screen for best performance. The selection process may evaluate such parameters as biologic product expression titers, generational stability, product quality, etc., through micro-well, shake flask or other small-scale screening techniques.
Once a couple of specific clones have been selected as ‘interesting’, then these will be introduced to small-scale bioreactor runs to prove out the initial performance characteristics, but then also to begin establishing initial culture conditions that enhance biologic product expression and cell line stability. The aim, as in the initial screening, is to generate enough data from the interesting clones to decide as to which one to progress forward into cell banking and as the foundation for expression of the biologic product.
With the winning clone in hand, it is now time to consider establishing a cell bank that is aimed at preserving a uniform, homogenous stock of the cell line for continued future use that assures a reliable starting point for each batch of biologic production. There are generally five different kinds of cell banks involved in a cell line development program – parental, stock (or reference) culture, research, master and working. By definition, and according to ICH Q5, the parental cell bank is the untransfected cell line, whereas the research, master and working cell lines are all a derived from the transfected clone that was elevated to the top during the selection process due to performance and desirable characteristics. A schematic of how each of these cell banks are related to one another follows:
The stock culture is effectively a small collection preserved from the initial culture that was expanded following the transfection, screening and selection process. This represents the earliest generational (and biologic producing) form of the cell line of interest, and a very important collection to maintain for reference as part of a GMP cell line development program, because with this reference properly preserved and protected, every other forward produced cell bank can be recreated.
From the stock culture a research cell bank can be produced. The importance of establishing a research cell bank is that it can allow for continued biologics process development throughout the product development lifecycle completely independent of the master or working cell banks, thus preserving those precious stocks for GMP manufacturing purposes only. The research cell bank is typically produced under well documented and controlled conditions, but not necessarily GMP as it is for research purposes and should not be used in biologic manufacturing to produce clinical product. That said, it is important that the research cell bank be established under conditions and with raw materials that will be used for GMP cell banking.
As you can see from the figure, our Bioprocess Consultants at BPAI propose that the stock culture be used to create both the research cell bank and the master cell bank – this is with purpose! In doing so, this makes each bank siblings to one another, and therefore of the same approximate generational history, thus establishing a critical link between the two banks – and accordingly establishing one bank that can be used for biologic process development purposes, while the other for GMP biologic production. This is also the reason that keeping the cell banking procedure, conditions and materials as equivalent as possible between the two banks is important. With sibling research and master cell banks, the cell line development program is well established for the future.
Considerations regarding raw materials when establishing any precursor to a master cell bank, or the master cell bank itself, should focus on ensuring an ‘animal origin free’ (AOF) status, along with the highest grade and purity possible. In certain cases, animal origin materials cannot be avoided, in which case it is important that there is traceability to a non-BSE/TSE flagged country that has a track record of supplying these sorts of materials for GMP purposes. Our Bioprocess Consultants at BPAI cannot stress enough the importance in ensuring full traceability of materials in a cell line development program that is intended for future GMP biologics manufacturing – this is critical! From time to time we come across biologics manufacturing programs that are in desperate need of triage due to an animal origin raw material that was inadvertently introduced to the cell line, thus complicating the CMC program and introducing unnecessary risk and questions. Most every manufacturer of GMP-grade raw materials and consumables provide a comprehensive document trail for their products, including certificates of analysis, certificates of origin, sterility assurance, materials of construction, etc. I encourage you to establish a comprehensive documentation trail on any cell line you are considering developing for GMP-related purposes.
With respect to the master cell bank, it is critical that this bank is fully and properly characterized to justify it’s use as a GMP bank to produce GMP biologic products for clinical trials. Characterization testing typically goes above and beyond release testing, with focus on establishing definitive identity, genetic testing, evidence of product expression, etc., as this well characterized cell bank will be used to establish the working cell bank. According to ICH Q5D ‘the extent of characterization…may influence the type or level of routine testing later in manufacturing’. BPAI’s Bioprocess Technology Consultants are often asked by our clients – ‘does a working cell bank have to be established’? Well the answer is – it depends. In BPAI’s experience, for early stage clinical development programs (Phase 1/2), it is usually good enough to rely on an established GMP master cell bank, thereby saving crucial resources until later in the program when production requirements increase. For late Phase 2 programs and beyond, BPAI recommends an expansion of the master cell bank into a working cell bank to preserve the precious master cell bank vials, and in preparation for later stage biologic product development which can be intensive on cell bank vial usage.
Other important considerations with respect to GMP cell banks include:
- Establishing stability of the cell bank on a routine basis if the bank is not consistently used in manufacturing the biologic product.
- Splitting stocks of GMP cell banks (and their precursors) between different storage units and different sites to ensure that the cell banks are protected from catastrophic temperature excursions.
- Maintaining a documented storage history under GMP conditions to positively demonstrate the temperature storage history for the duration of existence of the cell bank.
- Shipping GMP cell banks under validated shipping conditions to ensure a well-documented chain of custody for the shipment, including the use of temperature data loggers that demonstrate temperature requirements have been maintained.
- Creating a new working cell bank from the master cell bank well ahead of exhausting the inventory, and maintaining a few vials of the old working cell bank on file.
Thank you for tuning in to this session on cell banks. If you or your company are being challenged with cell bank related issues, please contact us at BPAI to speak with one of our Bioprocess Consultants.
Bio-Processing Alliance, Inc.