In the biopharmaceutical industry, Chinese Hamster Ovary (CHO) cells have emerged as the gold-standard expression system for recombinant protein production. The conventional fed-batch culture mode has long dominated industrial applications due to its simple workflow, straightforward operation, and full compliance with regulatory requirements. Nevertheless, driven by the continuous advancement of biotherapeutic R&D, structurally complex proteins such as bispecific antibodies, fusion proteins and enzymes have become mainstream development candidates. This trend has posed unprecedented challenges to traditional CHO cell culture processes.
Taking monoclonal antibodies (mAbs) as an example, the expression titer of an increasing number of mAb molecules has reached 8 g/L or even 10 g/L. In contrast, the yield of most bispecific antibodies and fusion proteins remains far below this level. The core underlying reasons are summarized as follows:
Complex Molecular Structure: Engineered non-native structural designs tend to trigger misfolding, mismatched assembly, aggregation and degradation during protein translation.
Low Secretion Efficiency: Large molecular weight or specific conformational characteristics impair intracellular trafficking and secretion efficiency, leading to intracellular retention of target proteins and insufficient release into culture supernatant.
Metabolic Stress and Cytotoxicity: Excessive metabolic burden is imposed on host cells, while certain target proteins exhibit intrinsic cytotoxicity, resulting in abnormal cell growth and metabolic dysfunction.
Post-Translational Modification Heterogeneity: Poor consistency in glycosylation modification further compromises protein biological functions.
When confronted with the inherent bottlenecks of difficult-to-express molecules, iterative optimization of conventional fed-batch processes typically suffers from diminishing marginal returns and fails to deliver breakthrough improvements. Addressing these technical hurdles necessitates innovative upgrading of cell culture paradigms. If fed-batch is analogized to conventional infantry tactics, emerging culture technologies represent a modern, multi-force coordinated integrated system featuring high flexibility, precision and efficiency.
Intensified Fed-Batch: Win-Win of High Titer and Quality Control
Intensified Fed-Batch (IFB) adopts strategies including high-density inoculation, enhanced feeding regimen and real-time metabolite regulation to elevate volumetric productivity, delivering universal and remarkable titer enhancement effects.
In the cultivation of two bispecific/multispecific antibody candidates with distinct structural designs, the implementation of high-density inoculation and optimized feeding protocols significantly elevated viable cell concentration, with the integral viable cell density (pVCD) increased by 40% and 30% respectively. The production cycle was shortened from 15 days to 12 days. Ultimately, the expression titers of the two candidate molecules were boosted by 109% and 33% compared with conventional fed-batch, validating the outstanding advantages of IFB in substantially improving manufacturing productivity.
Notably, the impact of IFB on product quality varies by cell clone and molecular construct. For Molecule A (Fc fusion protein), elevated enzymatic cleavage reduced the proportion of correctly assembled variants from 80.4% to 71.5%; Molecule B (bispecific antibody) exhibited slight charge profile shift. However, the overall critical quality attributes (CQAs) of both molecules remained within acceptable ranges, indicating that the quality impact of IFB requires case-specific evaluation based on molecular structural characteristics.
Perfusion Culture: Sustained Production and Elevated Product Quality
Perfusion culture maintains a stable physiological microenvironment for cells via continuous medium exchange and real-time product harvesting. It drastically reduces the residence time of target proteins in bioreactors, thereby minimizing protein degradation induced by thermal stress and enzymatic hydrolysis.
For fusion protein production, perfusion culture markedly reduces proteolytic fragmentation, increases the proportion of intact target protein, lowers low-molecular-weight impurities, and substantially improves batch-to-batch consistency of product quality. It also demonstrates superior volumetric productivity and supports ultra-high cell density in bioreactors. The final harvested titer reached 10.1 g/L, far exceeding the performance of conventional fed-batch and standard intensified fed-batch processes, with a notably lower fragmentation level.
Holistic Process Development: Multidimensional Collaborative Optimization to Break Expression Bottlenecks
For a difficult-to-express multispecific antibody candidate, a holistic process development strategy based on interdisciplinary and multi-factor collaborative optimization successfully achieved a titer of 10 g/L.
The full-spectrum optimization strategy covering genetic design to cell culture execution is outlined below:
Signal Peptide and Vector Optimization: Codon optimization, high-efficiency signal peptide screening, and balanced heavy/light chain ratio regulation to enhance protein correct folding and assembly efficiency.
Temperature-Shift Process Development: Reducing culture temperature to prolong cultivation duration, raising specific cellular productivity to 16 pg/cell/day.
Process Intensification: Implementing N-1 perfusion seed culture to elevate inoculation density to 20×10⁶ cells/mL, with peak viable cell density reaching 60×10⁶ cells/mL and final target protein titer up to 11 g/L.
This systematic approach not only achieves a prominent titer elevation but also effectively controls critical quality attributes, with aggregation and fragment levels remaining within specification limits, verifying the technical feasibility and robustness of the integrated process.
Conclusion
Against the backdrop of escalating complexity in biotherapeutic development, conventional fed-batch culture has gradually reached its bottleneck in titer improvement. Emerging culture paradigms including intensified fed-batch, perfusion culture and integrated process development have become pivotal drivers for productivity advancement in biomanufacturing. By systematically optimizing cell culture workflows, these innovative strategies substantially enhance volumetric productivity, enabling a paradigm shift from feasible expression to high-efficiency and stable commercial production. The novel culture modes shorten manufacturing cycles while boosting target protein yields by several folds, providing a reliable and high-efficiency technical solution for the industrialization of challenging biopharmaceuticals.
