Continuous bleed recycling significantly increases recombinant protein production yield in perfusion cell cultures

Stable operation in mammalian perfusion cell cultures can be achieved using a waste (bleed) stream to remove excess biomass from the reactor. This stream is often considered as a necessary loss sometimes leading to consequent yield drops. In this study, an acoustic settler was used to concentrate the bleed stream in order to harvest concentrated cells and recycle the clarified portion to the bioreactor. The amount of recycled product corresponded to an equivalent increase in harvest flowrate, which led to an increased overall productivity. This equipment was chosen because it can be operated in continuous mode and there are no fouling/clogging risks as it is the case for many other cell retention devices (CRD). Two similar operating conditions (OC) were tested, one with and another without the acoustic settler working. Both conditions were compared with a strong focus on the bleed and harvest streams to evaluate the yield improvement. The separation efficiency (SE), which is the ability of the system to remove cells from the liquid phase, was calculated and was always superior to 99 %. The bleed fraction in this specific example could be decreased from 59.2 % +/- 1.6-3.9 % +/- 1.3 without impacting the process or the product quality and leading up to a 2.25-fold yield improvement.