Frequently Asked Questions
Q: How does C3's hollow fiber technology differ from other perfusion platforms on the market?
A: Many common perfusion platforms utilize hollow fibers as a cell retention mechanism in order to be able to flow media at an acceptable rate. ATF (Alternating Tangential Flow) tank attachments, for example, are a common perfusion system that use hollow fibers like a filter, retaining and circulating the cells back into the tank while passing the cell product through the membrane into a holding tank. However, there are several distinct advantages to C3’s hollow fiber perfusion bioreactor design when comparing to ATF tank systems:
- Homogenous Environment: Cells are grown on the “Cell Side” (extracapillary or EC space) of the hollow fibers, while bulk media flow brings nutrients through the “Media Side” (intracapillary or IC space). This allows for cells to be grown to a high density (~10E9 cells/mL) without exposure to shear stress. In ATF systems, the cells are freely moving through the tank and ATF space with the flow of media and thus exposed to shear. This is important, since cells experiencing too much shear could produce low-quality protein products.
- Save on Media Use: C3’s bioreactors use less media than ATF systems. C3’s bioreactors are designed as high surface area cartridges where cells can grow to high densities in a relatively small space. While media is constantly flowing throughout the bioreactor run, total media usage remains low compared to ATF systems. An ATF-equipped tank is designed to grow cells in a comparatively large tank with very low surface area, where several vessel volumes per day (VVD) of media may be needed. Additionally, to keep the cells alive and producing product, ATF tanks need to be “bled” every day to limit the cell count, which can be up to 30% VVD. C3’s bioreactors do not need to be bled, because the cell mass is embedded in the fiber bundle and takes on the density and consistency of live tissue. Our bioreactors are designed to maintain the cells in a fixed static space with the capillary fibers providing the dynamics to deliver nutrients and remove waste.
- Long-term, Stable Production: C3’s bioreactors can maintain cell health and protein production for up to 100 days (or longer). We have data to show that C3’s bioreactors maintain a consistent environment for the cells as waste is constantly removed and parameters such as pH and lactate are automatically monitored and controlled. This leads to longer periods of protein production, which is especially important for difficult-to-express proteins or low-producing cell lines. ATF systems can support protein production for 30 to 60 days before cell viability (and thus protein production) is dramatically reduced due to membrane fouling and accumulation of dead cells.
- Easy Protein Retention: In C3’s bioreactors, protein product is retained and collected from the Cell Side (EC space). It does not have to cross the hollow fiber membrane to be collected. In contrast, protein produced in ATF systems must cross the hollow fiber membrane, and collection is subject to clogging and fouling.
- Consistency: The homogenous environment in C3’s bioreactors leads to consistent protein product. In an ATF tank system, cells are freely floating in the tank, and cells close to the ATF attachment draws media out may be subjected to more stress than cells in other parts of the tank. This leads to non-homogenous cell growth and protein production, which could affect the quality of product as a run progresses.
Q: Is the quality of the protein produces using C3's hollow fiber platform equivalent to that of fed-batch systems?
A: At C3 we maintain a high level of quality control and batch release testing. Because each product is custom, we can adjust downstream analytical testing to meet the needs of the individual customer. In the past, we have had customers switch from tanks to C3’s bioreactors and from C3’s bioreactors back to tanks without changes to the quality of their protein product.
Q: How are the bioreactors sampled for cell density throughout the cell culture run?
A: C3’s bioreactors are not sampled for cell density throughout the run, as this is not a key process parameter like it is for batch and fed-batch processes. Unlike tank systems, protein production in HFBR is not limited by cell viability. C3 has data showing long-term protein production in an HFBR that can last up to 100 days. Throughout these long-term runs, parameters like pH, glucose, and lactate remain consistent after the initial growth curve and allow us to indirectly assess the health of the cells.
Q: What types of media can be used in C3's bioreactors?
A: C3’s bioreactors have been successfully run with many different commercially available media formulations, including chemically defined, protein free, animal component free, serum-based and serum-free medias. Additionally, C3 has a proprietary basal media that has been optimized for use in HFBR for hybridoma cultures.
Q: Have there been any issues observed with leachables and extractables using C3's hollow fiber systems?
A: C3 has performed a leachable/extractable study on the AutovaxID bioreactor system. The results showed that all levels of extractables and leachables were acceptable for the process supporting a Phase III human therapeutic drug. As with other single-use bioreactor systems, each process requires testing as different media, cells and culture conditions (temperature, pH, lactic acid level, time) will have an impact on the Leachables & Extractables levels.
Q: Can suspension cells be grown in C3's hollow fiber bioreactors?
A: Yes, we have successfully grown suspension cells as well as adherent cells in our hollow fiber bioreactors. The high cell densities achieved on the extracapillary side (EC) and the low EC perfusion rates allow for a tissue-like environment in which there is minimal sloughing for most cell types.