'Omics driven discoveries of gene targets for apoptosis attenuation in CHO cells

Overexpression of Tgm2 in Chinese Hamster Ovary Cells Enhances Recombinant Monoclonal Antibody Expression and Promotes Cell Proliferation through Reduction of Apoptosis

Chinese hamster ovary (CHO) cells are the preferred host system for producing protein-based (antibody) therapeutics. However, recombinant CHO cells undergo substantial apoptosis during prolonged cultivation, impairing cell growth and ultimately compromising product yield and quality. Transglutaminase 2 (Tgm2), which mediates post-translational modifications of substrate proteins, regulates critical biological processes including cellular differentiation, apoptosis, cell cycle progression, and extracellular matrix assembly. In this study, we examined the effects of Tgm2 overexpression and knockdown on CHO cell growth and recombinant antibody production. Stable Tgm2 overexpression enhanced CHO cell proliferation while reducing apoptotic rates, resulting in significantly increased recombinant adalimumab expression (2.09 ± 0.08-fold) and specific productivity (1.88 ± 0.08-fold) compared to controls. In contrast, Tgm2 knockdown promoted apoptosis and induced cell cycle arrest. Mechanistically, elevated Tgm2 upregulated antiapoptotic genes (Bcl-2, Bcl-xL, and Mcl-1) while suppressing caspase-3 activity and BAX expression. These effects were associated with PI3K/AKT/mTOR pathway activation. Our findings demonstrate that Tgm2 overexpression enhances proliferation, bolsters antiapoptotic capacity, and improves monoclonal antibody production efficiency in CHO cells, establishing it as a viable strategy for increasing recombinant protein yields.

Unraveling Cytotoxicity in HEK293 Cells During Recombinant AAV Production for Gene Therapy Applications

Transient transfection of HEK293 cells represents the dominant technique for the production of recombinant adeno-associated virus (AAV) vectors. However, recombinant AAV (rAAV) production is cytotoxic, potentially impacting process performance, product yields, and quality, complicating downstream processing. This study characterizes cell death response for rAAV producing HEK293 cells and explores the potential to control cytotoxicity. Initial analysis of triple transfected cells revealed caspase-mediated apoptosis as a likely mechanism of cellular death. Next, the causes of this cytotoxicity were investigated by dissecting transfection steps. Exposing cells to polyethyleneimine (PEI) alone or complexed with a blank plasmid at typical concentrations had a limited impact on cell growth. However, the inclusion of plasmid constructs containing genes to produce rAAVs triggered significant cell death, with the helper plasmid being the most toxic both independently and in combination with packaging and transgene plasmids. Additionally, apoptosis in transfected cultures could be inhibited using the pan-caspase inhibitor, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (Z-VAD.fmk), leading to a 65% increase in peak viable cell density (VCD). Although the rAAV genome titer remained relatively unaltered, capsid levels declined upon cell death inhibition. Consequently, the ratio of full to empty capsids, an important product quality attribute (PQA) for rAAVs increased following caspase inhibition. This study provides insights into apoptosis activation in rAAVs and uncovers avenues for its modulation to alter PQAs.

Enhancing the Antibody Production Efficiency of Chinese Hamster Ovary Cells through Improvement of Disulfide Bond Folding Ability and Apoptosis Resistance

The complex structure of monoclonal antibodies (mAbs) expressed in Chinese hamster ovary (CHO) cells may result in the accumulation of unfolded proteins, triggering endoplasmic reticulum (ER) stress and an unfolded protein response (UPR). If the protein folding ability cannot maintain ER homeostasis, the cell will shut down protein translation and ultimately induce apoptosis. We co-overexpressed HsQSOX1b and survivin proteins in the antibody-producing cell line CHO-PAb to obtain a new cell line, CHO-PAb-QS. Compared with CHO-PAb cells, the survival time of CHO-PAb-QS cells in batch culture was extended by 2 days, and the antibody accumulation and productivity were increased by 52% and 45%, respectively. The proportion of (HC-LC)2 was approximately doubled in the CHO-PAb-QS cells, which adapted to the accelerated disulfide bond folding capacity by upregulating the UPR's strength and increasing the ER content. The results of the apoptosis assays indicated that the CHO-PAb-QS cell line exhibited more excellent resistance to apoptosis induced by ER stress. Finally, CHO-PAb-QS cells exhibited mild oxidative stress but did not significantly alter the redox status. This study demonstrated that strategies based on HsQSOX1b and survivin co-overexpression could facilitate protein disulfide bond folding and anti-apoptosis ability, enhancing antibody production efficiency in CHO cell lines.

Amino acid degradation pathway inhibitory by-products trigger apoptosis in CHO cells

Chinese hamster ovary (CHO) cells are widely used to produce complex biopharmaceuticals. Improving their productivity is necessary to fulfill the growing demand for such products. One way to enhance productivity is by cultivating cells at high densities, but inhibitory by-products, such as metabolite derivatives from amino acid degradation, can hinder achieving high cell densities. This research examines the impact of these inhibitory by-products on high-density cultures. We cultured X1 and X2 CHO cell lines in a small-scale semi-perfusion system and introduced a mix of inhibitory by-products on day 10. The X1 and X2 cell lines were chosen for their varied responses to the by-products; X2 was susceptible, while X1 survived. Proteomics revealed that the X2 cell line presented changes in the proteins linked to apoptosis regulation, cell building block synthesis, cell growth, DNA repair, and energy metabolism. We later used the AB cell line, an apoptosis-resistant cell line, to validate the results. AB behaved similar to X1 under stress. We confirmed the activation of apoptosis in X2 using a caspase assay. This research provides insights into the mechanisms of cell death triggered by inhibitory by-products and can guide the optimization of CHO cell culture for biopharmaceutical manufacturing.

A reflection on the improvement of Chinese Hamster ovary cell-based bioprocesses through advances in proteomic techniques

Chinese hamster ovary (CHO) cells are the preferred mammalian host for the large-scale production of recombinant proteins in the biopharmaceutical industry. Research endeavors have been directed to the optimization of CHO-based bioprocesses to increase protein quantity and quality, often in an empirical manner. To provide a rationale for those achievements, a myriad of CHO proteomic studies has arisen in recent decades. This review gives an overview of significant advances in LC-MS-based proteomics and sheds light on CHO proteomic studies, with a particular focus on CHO cells with superior bioprocessing phenotypes (growth, viability, titer, productivity and cQA), that have exploited novel proteomic or sub-omic techniques. These proteomic findings expand the current knowledge and understanding about the underlying protein clusters, protein regulatory networks and biological pathways governing such phenotypic changes. The proteomic studies, highlighted herein, will help in the targeted modulation of these cell factories to the desired needs.

Insights into the Impact of Rosmarinic Acid on CHO Cell Culture Improvement through Transcriptomics Analysis

The use of antioxidants in Chinese hamster ovary (CHO) cell cultures to improve monoclonal antibody production has been a topic of great interest. Nevertheless, the antioxidants do not have consistent benefits of production improvement, which might be cell line specific and/or process specific. In this work, we investigated how treatment with the antioxidant rosmarinic acid (RA) improved cell growth and titer in CHO cell cultures using transcriptomics. In particular, transcriptomics analysis indicated that RA treatment modified gene expression and strongly affected the MAPK and PI3K/Akt signaling pathways, which regulate cell survival and cell death. Moreover, it was observed that these signaling pathways, which had been identified to be up-regulated on day 2 and day 6 by RA, were also up-regulated over time (from initial growth phase day 2 to slow growth or protein production phase day 6) in both conditions. In summary, this transcriptomics analysis provides insights into the role of the antioxidant RA in industrial cell culture processes. The current study also represents an example in the industry of how omics can be applied to gain an in-depth understanding of CHO cell biology and to identify critical pathways that can contribute to cell culture process improvement and cell line engineering.

Engineering death resistance in CHO cells for improved perfusion culture

The reliable and cost-efficient manufacturing of monoclonal antibodies (mAbs) is essential to fulfil their ever-growing demand. Cell death in bioreactors reduces productivity and product quality, and is largely attributed to apoptosis. In perfusion bioreactors, this leads to the necessity of a bleed stream, which negatively affects the overall process economy. To combat this limitation, death-resistant Chinese hamster ovary cell lines were developed by simultaneously knocking out the apoptosis effector proteins Bak1, Bax, and Bok with CRISPR technology. These cell lines were cultured in fed-batch and perfusion bioreactors and compared to an unmodified control cell line. In fed-batch, the death-resistant cell lines showed higher cell densities and longer culture durations, lasting nearly a month under standard culture conditions. In perfusion, the death-resistant cell lines showed slower drops in viability and displayed an arrest in cell division after which cell size increased instead. Pertinently, the death-resistant cell lines demonstrated the ability to be cultured for several weeks without bleed, and achieved similar volumetric productivities at lower cell densities than that of the control cell line. Perfusion culture reduced fragmentation of the mAb produced, and the death-resistant cell lines showed increased glycosylation in the light chain in both bioreactor modes. These data demonstrate that rationally engineered death-resistant cell lines are ideal for mAb production in perfusion culture, negating the need to bleed the bioreactor whilst maintaining product quantity and quality.