Influence of Cell Physiological Status on the Intensified Fed-Batch Cultures at Ultra-High Seeding Density

Recent years, intensified fed-batch culture with ultra-high seeding density (uHSD-IFB) is coming to the forefront of manufacturers' choice for its enhanced productivity. However, the effects of seed cell physiological state and aeration strategies on these processes remain underexplored due to the ultra-high seeding density. Currently, the pre-production seeding inoculum (N-1) crucial for the uHSD-IFB cultures relies heavily upon case-by-case empirical experiences. To develop a rational seeding approach as a guideline, we here explored the impact of perfusion rates and cell growth states on the subsequent uHSD-IFB processes. It was found that seed cells in the exponential growth phase with high perfusion rates in the N-1 perfusion stage allowed for higher viable cell density and titer in the production stage. In particular, lower levels of reactive oxygen species, higher proportions of G1 and S phase, and higher specific cell oxygen uptake rates (OURs) were exhibited in these cells, resulting in higher cell specific growth rates and integral of viable cell concentration (IVCC) throughout the production cultures. Further investigation into the effect of aeration strategies was carried out in the benchtop bioreactors. A final yield of 4.5 g/L, an increase of nearly 110%, was achieved by a sophisticated dual sparger system compared to the other two processes with either one l-shaped or micro-sparger. These results provide a direction for the design and establishment of high-titer processes in intensified fed-batch cultures at ultra-high seeding density. Synopsis: In this work, we first explored the impact of perfusion rates and cell growth states on the subsequent uHSD-IFB processes. Further investigation into the effect of aeration strategies of intensified fed-batch process was carried out in the benchtop bioreactors. These results provide a direction for the design and establishment of high-titer processes in intensified fed-batch cultures at ultra-high seeding density.