We began our discussion with advice Dr. Castan has for companies who want to optimize their fed-batch process. He explained that the most important step is to start with a good medium, then effort should be put into finding a good feed regime. The exact methodology he recommends is found in a recently published application note, “Optimization of fed‑batch culture conditions for a mAb‑producing CHO cell line“.
Factors to consider include keeping product quality in mind before even selecting media and feed. The cell line should be looked at and a clone should be chosen that can provide the appropriate product quality. Next, it is important to select a medium that is good for the cells and supports the product quality profile. Last, process conditions and feeding regime should be tested and selected. Potential roadblocks can be found in delivering the feed itself as high concentrations of amino acids, both basic and acidic, might create solubility issues. This can be mitigated in process development by feeding certain components separately.
Next, I asked about buying pre-formulated media with compatible supplements and what optimization would he recommend. He said that with off the shelf solutions, it is again important to start by selecting the best medium. He recommends investigating several for growth, productivity and product quality before selecting one. After medium is selected move on to an initial feed screen to identify which are beneficial, neutral or detrimental. Then take the good feeds and determine the best ratio for combining the beneficial feeds. This work can be successfully run in scale down models. After the optimal feed ratio has been determined, advanced feeding strategies can be examined. To do this, constant feed volume should be compared to a dynamic feeding approach. A dynamic feeding approach takes into account growth rate and concentration of certain metabolites when deciding on how much and when to feed.
Then we discussed balancing experimental design for media components vs. feed strategy and Andreas recommended focusing efforts on finding good feeds then determining a good ratio of feed components. Static feeds are good enough and advanced feeding strategies should be considered secondary.
I then asked how he recommends incorporating critical quality attributes into an optimization strategy. He says looking very early into product quality and targeting a specific product quality profile is very important. That begins with knowing your clone and what it can deliver. The clone should be selected based on product quality in areas such as glycosylation, aggregate levels, etc. Then, you can see how the product quality is affected by different media selections. It is also important to look at quality with respect to process parameters like pH and physical environment in the process. These three strategies should help dial in the product quality as desired.
I was curious what was new in the way of media formulation and feed strategy design. Dr. Castan said that there is a trend toward mixing and matching of multiple feeds to meet the needs of cell lines. He recommends a toolbox approach where you start with a solid backbone in media development and complementary feeds then top up with certain nutrients and performance boosting components. This toolbox approach permits flexibility and works well compared to other base media and feed strategies.
We then talked about the impact of media and feed on downstream processing. I asked what should be considered in terms of downstream when making optimization changes in upstream. He said that the key to a smooth clarification and downstream process is to maintain high viability at harvest. It is crucial to slow the decrease in viability at the end of the culture. You can do this by building robustness into the culture so that harvest delays don’t dramatically impact viability. Feed regime is also important for maintaining a low decrease in viability in the final days.
Dr. Castan went on to say that this is where dynamic or process dependent feeding can be really important, especially at the end of culture when cells don’t consume as much nutrients and where feeds can change osmolality and actually accelerate decreases in viability. Maintaining good culture for cells is very important in the last phase of the culture for this reason.
I ended the conversation by asking Andreas if he had anything else to add for listeners. He said that when optimizing fed-batch culture, the manufacturing process should be kept in mind at all times. The manufacturability and implementation of feeds and components should be able to scale up to final manufacturing scale. It is important to have an experienced partner who can help to scale up these processes and he believes this is a strength of GE Healthcare. They enjoy partnering with companies who are looking to optimize their processes and scale up to meet commercial manufacturing needs.
To learn more about optimizing fed-batch culture, please see – Optimization of fed‑batch culture conditions for a mAb‑producing CHO cell line