Cancer research is an increasingly complex field and in the area of monoclonal antibody (mAb) production, many hurdles can be presented, starting initially with the analysis of a multitude of clones in small volumes. After the identification of interesting candidates, larger cell culture volumes are needed, and the expression levels of mAbs are assessed and maximized in cell line development. While there are many solutions on the market for growing mammalian cell cultures of 15-1,000 mL to high densities in parallel reactors or as shaker flask cultures, their purification can lead to a production line bottleneck. One time-consuming hurdle is the clarification and sterile filtration of a high-density culture before further processing.
In this on-demand SelectScience webinar, Dr. Noushin Delmdahl, head of product management lab consumables at Sartorius Lab Instruments, presents an innovative new method for tackling the first step into mAb purification – body feed filtration. This method of filtration is facilitated by the addition of diatomaceous earth (DE) as a filter aid, and has been used in the plasma and food/beverage industries for years.
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Q: Can you use this technology to clarify cell cultures expressing proteins other than antibodies?
ND: In principle, any cell culture can be clarified using diatomaceous earth (DE). However, if you want to clarify proteins other than antibodies, we recommend testing a small volume first to make sure that you have full recovery of the protein.
Q: Can cell cultures expressing lentiviruses be clarified using this method?
ND: Yes, but this will require 0.50- or 0.45-micron membrane filters, otherwise you will remove the lentiviruses through the filtration. We don't have a 0.45-micron membrane in the kits we have on the market at the moment. However, we are launching a new kit very soon that will have 0.45-micron membrane filters.
Q: Can other cultures like insects/yeast /bacteria be clarified using DE?
ND: Overall, we have concentrated more on the mammalian cell industry. For insects, we have an application note on Sf9 of insect cells, which we successfully clarified. We have tried clarifying yeast, but so far have not been successful. We have never tried clarifying bacteria.
Q: What's the current volume limits of the method?
ND: The volume limit for one kit is one liter. So, if you use multiple kits in parallel, say four in parallel, you can clarify four liters.
Q: Is DE just like a coarse filter?
ND: Not really, because even a coarse filter will clog at some point. The advantage of using body feed filtration is that DE forms a sponge-like structure with C3 skeletons that don't clog easily.
Q: Do you need to filter more than once to complete clarification?
ND: You only need to filter once. You mix with DE, you clarify, and then you filter. The DE does not pass through the filter, it just facilitates the filtration, allowing everything to pass the 0.2-micron filter in a reasonable time.
Q: Is the amount of DE indicated for a particular volume of cell culture?
ND: Yes, in our kits we specify what amounts of DE are for which densities of cells in a culture. The ready-to-use DE is pre-wetted, which leads to a clean transfer of the DE into your cell culture without dusting and laminar flow and making a mess.
Q: Are there any other commercial plants using this clarification method?
ND: I know of some biopharmaceutical companies that use DE themselves, so they do use DE in their R&D lab, but I don't know of anybody that has introduced DE into the process scale.
Q: Can DE be used in process scale and in monoclonal antibody production?
ND: We used to offer this, but it was unfortunately discontinued due to the difficulty with logistics. In labs, you're working with only a few liters, so you still have volumes of DE that are workable. However, when you get into the thousands of liters, it becomes difficult to efficiently add and mix the DE into the cell culture.
Q: Are there any impurities, or other products released from DE, found in the filtered culture supernatants?
ND: We have a validation guide for the diatomaceous earth, but the diatomaceous earth grade that we are using has been specifically produced for work in the pharmaceutical industry. It has been acid-washed and washed with distilled water, so it is completely clean and there are no impurities that will come out of the DE. We did a lot of tests to show that DE doesn't change anything about the antibody, and it doesn't have any effects on the antibody that are any different to the normal clarification method. So, we would not expect any residual impurities to come out of the DE.
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