Simplified Mammalian Cell Harvesting without Centrifuging

insights from industryMichael GraufProcess Development ScientistSartorius Stedim Cellca

An interview with Michael Grauf, conducted by James Ives

Please give me an overview of mammalian cell harvesting and the current gold standard technique currently used in labs.

At the moment, the gold standard in cell harvesting is to first centrifuge the sample to clarify the sample and then filter the remaining sample through a membrane. For large samples, depth filters combined with sterile filters can be used.

These techniques can take time to complete each of the steps, and while centrifuging your cells there is a possibility that some can become damaged.

What cell harvesting technologies does Sartorius offer? What are the advantages of these different methods?

We have a range of cell harvesting technologies which we use at Sartorius Stedim Cellca depending on the volume:

• Minisart High Flow Syringe Filter (0,2 µm, 5,8 cm²) for sterile filtration of supernatant (< 25 mL)
• Sartoclear Dynamics Lab P 15 syringe with diatomaceous earth (DE), sterile filtration of cell suspension (15 mL)
• Sartoclear Dynamics Lab V vacuum filtration with DE (50 mL – 1 L)

Small volumes of < 25 mL will be centrifuged (5 min, 4400 g, 20°C) and the supernatant will be filtered by Sartorius Minisart High Flow Syringe Filters.

For the ambr15 automated microscale bioreactor systems, retention of samples up to a maximum of 15 mL (also from cell suspension generated by the ambr250 or bioreactor) we would use the Sartoclear Dynamics Lab P 15.

The Sartoclear Dynamics Lab P is a syringe with an insoluble, inert, and endotoxin free filter aid inside the syringe. As the cell solution is drawn into the syringe it mixes with the filter aid. Once mixed, a fine sterile filter can be attached to the syringe, which allows for clarification and sterile filtration in a single step, without the need to centrifuge the sample first.

The cell suspension from a bioreactor run (ca. 5 L) will be clarified with two depth and one sterile filter, here we are looking forward to the Sartoclear Dynamics Lab V for the vacuum filtration of 1 L mixed with diatomaceous earth.

The Sartoclear Dynamics Lab V is similar to the Lab P but for larger volumes over 50 mL. Pouches of diatomaceous earth filter aid are added to sample in the beaker and mixed with the sample. This is then added to a flask with a sterile 0.2μm PES filter on top of a receiver flask.

A vacuum pump is applied to quicken the process, while the filter aid stops the filter from becoming clogged. Clarification and sterile filtration can be achieved in 10 minutes without centrifuging the sample.

The advantages of the methods using the clarification method with diatomaceous earth are that:

• there is a reduced handling time of the cell suspension in a non-controlled environment (eg. CO₂ level for pH control in incubator or ambr250, bioreactor)
• lower cost of Sartorius products
• easy handling of diatomaceous earth
• when working with ambr15 bioreactors, the kit components like the plastic syringe tube make simple things like removing the cell culture broth from the tiny reactor opening very easy, even during a run.

What is the advantage of using Sartoclear Dynamics Lab products if Minisart High Flow Syringe filters can filter 25 ml?

Many devices are needed for the Minisart High Flow Syringe filters, they are also easier to block than the Dynamics syringes, which means that the Dynamics range loses less filtrate during the filtering process, reduces hand strain from difficult to filter samples, and makes the process less time consuming.

The Sartoclear Dynamics portfolio does not require a centrifugation step, how does this affect cell harvest yield? Why?

The yield is not affected because of the diatomaceous earth filter aid forms a structure that prevents blockages clogging the filtration layer, which would usually lower the yield.

When compared to a process that includes a centrifugation step, the yield can also be higher as centrifugation can destroy cells and the potentially release proteases which may destroy your protein of interest.

How does conventional filtration compare with the diatomaceous earth body feed filtration method used in Sartoclear Dynamics method? How are blockages stopped?

Until now we have not observed any blockages of sterile filters while using the Sartoclear Dynamics products.

If sample volumes larger than 15 ml need to be harvested, does Sartorius offer a solution?

Sartoclear Dyncamis V can be used for harvest of 50 mL– 1000 mL high density mammalian cell culture samples. These kits simplify the process of filtration considerably.

As they are based on the same DE technology, we assume that the resulting mAb recovery will be very similar to the P15 version. Establishing this new clarification method will be the next task in our lab.

What applications are there for the Sartoclear Dynamics cell harvesting technique?

Sartoclear Dynamics Lab has been developed and optimized for high density mammalian cell harvest, expressing mAb. In our lab we work with CHO cell culture clarification.

These techniques have also been used with insect cells (SF9) (Application note on Sartorius website), which have been harvested successfully using this technology. The harvest of virus from cell cultures is under evaluation.

Monoclonal antibodies (mAbs) are a large area of growth in the pharmaceutical industry, but production costs are high due to production and development costs. How can the Sartoclear help reduce costs in this area?

There are many ways that the Sartoclear Dynamics can help reduce costs, for example, less space is needed for the Sartoclear products compared to conventional filtration devices (pumps and depth filters). This space can be used for other devices.

There is reduced downtime from training as this process is easy to handle, no special training is required. Anyone can handle it.

Also, because the processing time for the initial harvest step is reduced, more samples can be screened in parallel.

What does the future hold for mammalian cell harvest?

We are working at the moment on further applications for the Sartoclear Dynamics range. We are also working to be able to achieve higher titers with a perfusion process (high inoculation and concentrated fed-batches). If the cell suspension is not separated with a TFF or ATF module during the run there is a need to clarify a cell suspension with > 300x10⁵ cells/mL or even higher.

Where can readers find more information?

More information can be found on the Sartorius webpage: https://promotions.sartorius.com/sartoclear-dynamics-lab/

About Michael Grauf

B. Sc. of Biotechnology and M. Sc. of Bioprocess Development from the University of Applied Science Mannheim, during the studies at the University I worked at BioGenerix AG, Mannheim and Steinbeistransferzentrium, Dr. Frey, Mannheim, also dealing with the topics of cell culture cultivation.

I gathered my first two years work experience in the cell line development and analytical department as well as protein A purification at EugeneX Biotechnologies GmbH, Switzerland and since end of 2014 I am working at Sartorius Stedim Cellca GmbH, for two years in the operations department (process development unit) and for the last two years I am in the technology development department in the media and process development group.

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