BioPharm International speaks with Robin Ng, senior bioengineer in process development at Shire Pharmaceuticals, about the
factors to consider when setting up the upstream portion of a biomanufacturing process.
BioPharm: What parameters influence the choice of a production system?
Ng: In general, an upstream process in biopharmaceutical production refers to the process of manufacturing the products of interest
using biological entities, such as bacterial or animal cells. Because this process is aimed towards manufacturing, the properties
or attributes of the desired products dictate the selection of a production system. In practice, the production system includes
the selection of host cells, cell lines, and culture media, as well as the bioreactor system and its operating parameters.
It is important to keep in mind that the development of the process is highly tied to the business needs, available resources,
regulatory constraints, and project timeline. In addition, appropriate risk assessments need to be conducted and well documented
throughout the development process to support rational decisions. Therefore, the development of each process is unique because
of the specific constraints encountered during development, as well the advancement of the available technologies. Last but
not least, it is always important to remember that process safety should be a top priority.
BioPharm: Can you briefly describe the process of choosing a cell line for production? What are the criteria for selecting a cell line?
Ng: In the cell-culture process, genetically-engineered cells are used to manufacture the proteins of interest. It is desirable
that the commercial manufacture be initiated from a single Master Cell Bank (MCB). In the initial stage of development, cell
cloning and subcloning are conducted following transfection and amplification. With recent advances in automation, the selection
process is mostly conducted through a high throughput screening (HTS) system where millions of clones are screened and only
a few clones are selected to move forward for further development.
The initial selection criteria for a cell line are typically high titer and robust growth. Obtaining a high-producing cell
line can require additional time and resources. Therefore, it is important for the process developer to understand the needs
and demands for the process. Whenever possible, the target market demand should be revisited to ensure reasonable and balanced
process development efforts.
The secondary criteria in cell-line development include cell stability and product quality attributes. What a process developer
should look for in cell stability is the ability for cells to produce the comparable protein levels (i.e., phenotypic stability)
and maintain genetic integrity as the cells are continuously propagated into the production phase. In most development cases,
many product quality attributes are still unknown during cell-line development. This remains a challenge in cell-culture process
development because clinical data cannot be correlated with various product quality attributes during most of the development
stage. Therefore, appropriate risk assessments based on scientific justification, process understanding, and similar processes
are very important during early development.
It is also important to perform the final selection of candidate cell lines in a representative bioreactor system. The use
of a representative bioreactor system or process is important to help predict process performance in a large-scale bioreactor
system. In most companies, a baseline process will be used to screen the few final candidates cell lines.
It is always helpful to start with a good candidate cell line. Changing cell lines during development is usually undesirable
because it leads to extensive comparability studies between materials generated. Knowing your endpoint is always a good start
for developing your process.