Understanding the process and product goals is just the first step to a holistic approach to process development.
Advances in upstream processing of monoclonal antibodies (mAbs) have resulted in increasing titers, cell densities, and other properties that have challenged existing downstream processing operations. It is essential when developing downstream mAb purification processes to understand the product and process goals and focus on platform solutions that offer the greatest throughput.
Advances in both upstream and downstream technologies are helping to facilitate downstream processing of mAbs, but companies need to use a more holistic approach to process development and pursue various avenues of process intensification if real progress is to be made.
Understand the mAb
Before any process development work is completed, it is imperative, asserts Louise Duffy, senior VP and head of scientific project leaders at Abzena, to first understand exactly how the mAb is constructed and how it will work clinically.
Developers should start by identifying their product quality goals, driven by critical quality attributes, along with process requirements, facility capability, product requirements, and cost of goods, agrees Natraj Ram, vice-president of innovation, bioproduction at Thermo Fisher Scientific.
Considering the product stage (early or late) is also critical to ensure which aspects are prioritized, so that the appropriate level of process understanding and control strategies are achieved during development, according to Ram. Identifying the target scale for the commercial process will also help determine the scale and technology choice and transitions throughout development, he adds.
Leverage platform solutions
The next step, Duffy says, is to develop the downstream process to enhance the purity of the desired mAb while reducing product and process related impurities. That should be done, says Kevin Brower, global head of purification development–mammalian at Sanofi, with a defined platform set of raw materials and a platform approach for performing development.
“Using this approach is the most critical best practice because it provides structure for all process development scientists in their work at the bench as well as structure for interactions across the manufacturing network for tech transfer,” Brower states.
Understanding the tools needed to identify product-related impurities while developing purification is also key, according to Duffy. “These two activities must be done collectively with assay and downstream capability developed collaboratively,” she insists.
Use appropriate resins, filters, chemicals, and single-use components
The ability to achieve high throughput is always an important objective in a production area. For downstream process development, that includes higher flow rate, more rapid turnaround, and more streamlined processes, according to Haiou Yang, director of downstream process development for Avid Bioservices.
For downstream process development, the appropriate choice of resins, filters, chemicals, and single-use components is critical to the success of scale up and manufacturability, adds Ram. Potential requirements for chemicals should be considered depending on the target markets for the mAb product, while resins selection should take into account scalability if a chromatography process will need to be scaled from 1-L to 200-L columns. Assurance of integrity and access to standardized connections are two important factors that should drive the selection of single-use (SU) components.
Determining downstream capacity
The strategy for downstream processing for a particular mAb is dependent on the specifics of the upstream process, the capabilities of the facility, and the available equipment for the various unit operations required for mAb purification and final formulation. In general, each unit operation is sized based on the amount of mAb to be processed, factoring in the recovery of each step as it goes down the sequence.
Overall, the downstream processing capacity is the amount of upstream material that can be processed in a certain amount of time. Sanofi currently uses a mix of in-house Excel calculations and external software to model downstream capacity, identify bottlenecks, and guide its tech transfer activities, according to Brower. He notes that these methods are pretty well-established in the industry.
There are two possible strategies for determining the overall downstream processing capacity, says Ram. The first involves determination of the process throughput for each unit operation, choosing technologies that provide the best throughput considering the operational constraints at scale.
The second option is particularly relevant for batch operations such as mixing and filtration, according to Ram. “In these cases, both throughput and the ease of transitioning from one step to another are both considered and the choice of [single-use] SU technologies thus makes a difference,” he observes.
Having appropriate mixing systems with the right bags, filters, and sensors can help with combining multiple steps in one, Ram explains. For example, he notes that performing the inactivation and neutralization steps with a single mixing system that has a pH sensor built in and is equipped with appropriate tubing to pump in and pump out the material will help with efficient processing.
