Cell-culture growth conditions resulting in the oxidation of a recombinant antigen-binding fragment

Peptide extract from spent yeast improves resistance of Saccharomyces cerevisiae to oxidative stress

Yeast cells face various stress factors during industrial fermentations, since they are exposed to harsh environmental conditions, which may impair biomolecules productivity and yield. In this work, the use of an antioxidant peptide extract obtained from industrial spent yeast was explored as supplement for Saccharomyces cerevisiae fermentation to prevent a common bottleneck: oxidative stress. For that, a recombinant yeast strain, producer of β-farnesene, was firstly incubated with 0.5 and 0.7 g/L peptide extract, in the presence and absence of hydrogen peroxide (an oxidative stress inducer), for 1-5 h, and then assayed for intracellular reactive oxygen species, and growth ability in agar spot assays. Results showed that under 2 mM H₂O_2, the peptide extract could improve cells growth and reduce reactive oxygen species production. Therefore, this antioxidant effect was further evaluated in shake-flasks and 2-L bioreactor batch fermentations. Peptide extract (0.7 g/L) was able to increase yeast resistance to the oxidative stress promoted by 2 mM H₂O₂, by reducing reactive oxygen species levels between 1.2- and 1.7-fold in bioreactor and between 1.2- and 3-fold in shake-flask fermentations. Moreover, improvements on yeast cell density of up to 1.5-fold and 2-fold, and on biomolecule concentration of up to 1.6-fold and 2.8-fold, in bioreactor and shake-flasks, respectively, were obtained. Thus, culture medium supplementation with antioxidant peptide extracted from industrial spent yeast is a promising strategy to improve fermentation performance while valuing biomass waste. This valorization can promote a sustainable and eco-friendly solution for the biotechnology industry by the implementation of a circular economy model. KEY POINTS: • Peptide extract from spent yeast applied for the first time on yeast fermentation. • Antioxidant peptide extract enhanced S. cerevisiae oxidative stress resistance. • Fermentation performance under stress improved by peptide extract supplementation.

Antibody charge variant modulation by in vitro enzymatic treatment in different CHO cell cultures

Charge variants represent a critical quality attribute that must be controlled during the development and manufacturing of monoclonal antibodies (mAb). Previously, we reported the development of a cost-effective enzymatic treatment capable of removing the C-terminal lysine from a mAb produced by a Chinese hamster ovary (CHO) GS cell line. This treatment resulted in a significant decrease in basic charge variants and a corresponding improvement in the main peak, enabling a longer cell culture production duration for titer improvement. Here, we describe this enzymatic treatment protocol in detail and demonstrate its applicability to two additional mAbs produced by distinct industrial cell lines. The simple addition of carboxypeptidase B (CpB) at a ratio of 1:10,000 (w/w) to whole cell cultures significantly improved the main peaks for both mAbs without affecting other critical quality attributes, including size exclusion chromatography impurities and N-glycans. Our results demonstrate that this in vitro CpB treatment protocol can be used as a platform strategy to improve main peak for mAbs that exhibit high levels of basic variants attributable to C-terminal lysines. An in vitro enzymatic treatment in general may be another good addition to existing in vivo CHO cell culture strategies for titer improvement and control of critical quality attributes. This article is protected by copyright. All rights reserved.

Redox as a bioprocess parameter: analytical redox quantification in biological therapeutic production

Engineered Chinese hamster ovary (CHO) cells are the most widely utilized cell line for protein-based therapeutics production at industrial scales. Process development strategies which improve production capacity and quality are often implemented without an understanding of underlying intracellular changes. Intracellular redox conditions drive reactions in pathways critical to biologics production, including bioenergetic and biosynthetic pathways, necessitating methods to quantify redox-related changes. Advances in methods for analytical redox quantification presented here, including bioreactor probes, redox-targeted proteomics, genetically encoded redox-sensitive fluorescent proteins, and biochemical assays, are creating new opportunities to characterize the effects of redox in biologics production. Implementing these methods will lead to enhanced media formulations, improved bioprocess strategies, and new cell line engineering targets and ultimately develop redox into an optimizable bioprocess parameter to improve the yield and quality of these lifesaving medicines.

High shear resistance of insect cells: the basis for substantial improvements in cell culture process design

Multicellular organisms cultivated in continuous stirred tank reactors (CSTRs) are more sensitive to environmental conditions in the suspension culture than microbial cells. The hypothesis, that stirring induced shear stress is the main problem, persists, although it has been shown that these cells are not so sensitive to shear. As these results are largely based on Chinese Hamster Ovary (CHO) cell experiments the question remains if similar behavior is valid for insect cells with a higher specific oxygen demand. The requirement of higher oxygen transfer rates is associated with higher shear forces in the process. Consequently, we focused on the shear resistance of insect cells, using CHO cells as reference system. We applied a microfluidic device that allowed defined variations in shear rates. Both cell lines displayed high resistance to shear rates up to 8.73 × 10⁵ s⁻¹. Based on these results we used microbial CSTRs, operated at high revolution speeds and low aeration rates and found no negative impact on cell viability. Further, this cultivation approach led to substantially reduced gas flow rates, gas bubble and foam formation, while addition of pure oxygen was no longer necessary. Therefore, this study contributes to the development of more robust insect cell culture processes.