During the virtual Bioprocessing Summit in August, Cytiva reported that its new filtration process has advantages compared to traditional centrifuge approaches for removing viruses from suspension cultures.

“People often start with centrifugation, because it’s the easiest way to spin out cells, but that’s difficult at scale because you need larger centrifuges,” according to Cytiva development scientist, Adam McLeod, who spoke as the summit. He added that filtration is easier to scale up, requires fewer pieces of equipment, and is simpler to operate than centrifugation.

Other benefits of filtration, he says, include that the required equipment is inexpensive, and the process produces reproducible results.

In his talk, McLeod presented results from 14 runs with a 0.5–1.1 L bioreactor where, on average, 110% of the lentivirus was recovered. A further 8 runs with 1.5–2.2 L bioreactors produced an average 100.4% recovery rate. He believes the more than 100% recovery rate is due to the removal of debris that prevented the lentivirus freely infecting cells.

McLeod’s team has tested up to a demonstration run on a 27 L bioreactor. He hopes to repeat that experiment because upstream issues caused lower recovery rates due to the filters becoming overloaded and clogged.

Discussing the use of filtration, he says: “Lots of people are using filtration in the field, but there isn’t that much success at the moment. My observation is that people who are used to working on small molecules or mAbs are replicating what they know, and lentivirus is quite different.”

He argues that his team’s success so far is due to pre-soaking the filters with a cell culture media to prevent nonspecific binding of the virus to the filter. “We know lentivirus is quite sticky, so we tried lots of membranes and materials,” he says.

McLeod’s team is also using single-use tubing and filters to keep turnaround times between batches as short as possible. To reduce the risk of contamination, they have closed the process, he says.

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