Glycoproteomic Characterization of FUT8 Knock-Out CHO Cells Reveals Roles of FUT8 in the Glycosylation

The α1,6-fucosyltransferase (encoded by FUT8 gene) is the key enzyme transferring fucose to the innermost GlcNAc residue on an N-glycan through an α-1,6 linkage in the mammalian cells. The presence of core fucose on antibody Fc region can inhibit antibody-dependent cellular cytotoxicity (ADCC) and reduce antibody therapeutic efficiency in vivo. Chinese hamster ovary (CHO) cells are the predominant production platform in biopharmaceutical manufacturing. Therefore, the generation of FUT8 knock-out (FUT8KO) CHO cell line is favorable and can be applied to produce completely non-fucosylated antibodies. The characterization of monoclonal antibodies as well as host cell glycoprotein impurities are required for quality control purposes under regulation rules. To understand the role of FUT8 in the glycosylation of CHO cells, we generated a FUT8 knock-out CHO cell line and performed a large-scale glycoproteomics to characterize the FUT8KO and wild-type (WT) CHO cells. The glycopeptides were enriched by hydrophilic chromatography and fractionated 25 fractions by bRPLC followed by analysis using high-resolution liquid chromatography mass spectrometry (LC-MS). A total of 7,127 unique N-linked glycosite-containing intact glycopeptides (IGPs), 928 glycosites, and 442 glycoproteins were identified from FUT8KO and WT CHO cells. Moreover, 28.62% in 442 identified glycoproteins and 26.69% in 928 identified glycosites were significantly changed in the FUT8KO CHO compared to wild-type CHO cells. The relative abundance of all the three N-glycan types (high-mannose, hybrid, and complex) was determined in FUT8KO comparing to wild-type CHO cells. Furthermore, a decrease in fucosylation content was observed in FUT8KO cells, in which core-fucosylated glycans almost disappeared as an effect of FUT8 gene knockout. Meantime, a total of 51 glycosylation-related enzymes were also quantified in these two cell types and 16 of them were significantly altered in the FUT8KO cells, in which sialyltransferases and glucosyltransferases were sharply decreased. These glycoproteomic results revealed that the knock-out of FUT8 not only influenced the core-fucosylation of proteins but also altered other glycosylation synthesis processes and changed the relative abundance of protein glycosylation.

O-109 A first dose-response trial investigating the effects of adding choriogonadotropin beta to follitropin delta in women undergoing ovarian stimulation in a long GnRH agonist protocol

Study question Does addition of choriogonadotropin beta (CG beta) to follitropin delta increase the number of good-quality blastocysts following ovarian stimulation in a long GnRH agonist protocol? Summary answer At the doses investigated, the addition of CG beta reduced the number of intermediate follicles and decreased the number of oocytes and blastocysts. What is known already CG beta is a new recombinant hCG (rhCG) molecule expressed by a human cell line (PER.C6â) with a different glycosylation profile compared to urinary hCG or rhCG derived from a Chinese Hamster Ovary (CHO) cell-line. In the first-in-human trial, the CG beta pharmacokinetics were similar between men and women. In women, the area under the curve (AUC) and the peak serum concentration (Cmax) increased dose proportionally following single and multiple daily doses. In men, a single dose of CG beta provided higher exposure with a longer half-life and proportionately higher testosterone production than rhCG derived from a CHO cell line. Study design, size, duration Placebo-controlled, double-blind, randomised trial (RAINBOW) to explore the efficacy and safety of CG beta as add-on treatment to follitropin delta in women undergoing COS in a long GnRH agonist protocol. The primary endpoint was the number of good-quality blastocysts (grade 3 BB or higher, Gardner and Schoolcraft, 1999). Subjects were randomised to receive either placebo or 1, 2, 4, 8, or 12 µg CG beta added to the daily individualised follitropin delta dose during COS. Participants/materials, setting, methods In total 619 women (30-42 years) with AMH levels between 5 and 35 pmol/L were randomized in equal proportions to the six treatment groups. All subjects were treated with an individualised dose of follitropin delta determined based on AMH (Elecsys AMH Plus Immunoassay) and body weight. Triggering was performed when 3 follicles were ≥17 mm but no more than 25 follicles ≥12 mm were reached Main results and the role of chance The incidence of cycle cancellation (range 0%-2.9%), total follitropin delta dose (mean 112 µg) and duration of stimulation (mean 10 days) were similar across the groups. A reduced number of intermediate follicles (12 to 17 mm) and fewer oocytes (mean range 9.7 to 11.2) were observed for all doses of CG beta compared to the follitropin delta only group (mean 12.5). The mean number of goodquality blastocysts was 3.3 in the follitropin delta group and ranged between 2.1 and 3.0 across the CG beta groups. The incidence of transfer cancellation was higher in the 4, 8 and 12 µg group, mostly as no blastocyst was available for transfer. In the group receiving only follitropin delta, the ongoing pregnancy rate (10-11 weeks after transfer) was high i.e. 43% per started cycle vs 28-39% in CG beta groups and 49% per transfer vs 38-50% in the CG beta groups. In line with the number of collected oocytes, the OHSS incidence was overall lower following follitropin delta with CG beta than following follitropin delta only treatment. Regardless of the dose, CG beta was safe and well-tolerated with low risk of immunogenicity. Limitations, reasons for caution The effect of the unique glycosylation of CG beta and the associated potency implications in women were not known prior to this trial. Further studies will be needed to evaluate potentially lower doses of CG beta for this and/or different indications. Wider implications of the findings The high ongoing pregnancy rate in the follitropin delta group supports the use of individualised follitropin delta dosing in a long GnRH agonist protocol. The differential potency of CG beta may have impaired the growth of intermediate follicles with the investigated doses without affecting the ongoing pregnancy rates per transfer. Trial registration number NCT03564509

Controlling Ratios of Plasmid-Based Double Cut Donor and CRISPR/Cas9 Components to Enhance Targeted Integration of Transgenes in Chinese Hamster Ovary Cells

Chinese hamster ovary (CHO) cells are the most valuable expression host for the commercial production of biotherapeutics. Recent trends in recombinant CHO cell-line development have focused on the site-specific integration of transgenes encoding recombinant proteins over random integration. However, the low efficiency of homology-directed repair upon transfection of Cas9, single-guide RNA (sgRNA), and the donor template has limited its feasibility. Previously, we demonstrated that a double-cut donor (DCD) system enables highly efficient CRISPR/Cas9-mediated targeted integration (TI) in CHO cells. Here, we describe several CRISPR/Cas9 vector systems based on DCD templates using a promoter trap-based TI monitoring cell line. Among them, a multi-component (MC) system consisting of an sgRNA/DCD vector and Cas9 expression vector showed an approximate 1.5-fold increase in knock-in (KI) efficiency compared to the previous DCD system, when a systematically optimized relative ratio of sgRNA/DCD and Cas9 vector was applied. Our optimization efforts revealed that concurrently increasing sgRNA and DCD components relative to Cas9 correlated positively with KI efficiency at a single KI site. Furthermore, we explored component bottlenecks, such as effects of sgRNA components and applicability of the MC system on simultaneous double KI. Taken together, we improved the DCD vector design by tailoring plasmid constructs and relative component ratios, and this system can be widely used in the TI strategy of transgenes, particularly in CHO cell line development and engineering.

Evaluation of the Virus Elimination and Inactivation at Different Stages of the Model Biotechnological Process for the Production of a Drug Based on the Monoclonal Antibody Fab-Fragment

Virus safety insuring is one of the most serious problems in the development of biotechnological drugs produced using animal cell lines. Quantitative assessment of virus removal and inactivation is an integral approach to show the reliability of the target compound production. In this work, the model experiments have been carried out on the purification of the monoclonal antibody recombinant Fab-fragment from viruses of various origins and properties: xenotropic murine leukemia virus (X-MuLV), pseudorabies virus (PRV), Reo-3 virus and encephalomyocarditis virus (EMCV). It was shown that two methods, acidification to pH 3.2 and nanofiltration, made it possible to reduce the virus infectivity to levels undetectable in cell cultures (according to TCID50). The developed multistage purification process of the target protein provided an overall decrease in viral clearance to the following values: X-MuLV≥10.17lg, PRV≥13.98lg, Reo-3≥8.09lg and EMCV≥4.98lg. These results confirm that the developed technology ensures the virus safety during the production of a monoclonal antibody recombinant Fab-fragment by CHO cell line. These results confirm virus safety of production technology of recombinant monoclonal antibody Fab-fragment produced in CHO cell line. virus safety, virus elimination, virus inactivation, nanofiltration, Fab-fragment, monoclonal antibody, CHO cell line

Tracing production instability in a clonally-derived CHO cell line using single cell transcriptomics

A variety of mechanisms including transcriptional silencing, gene copy loss and increased susceptibility to cellular stress have been associated with a sudden or gradual loss of monoclonal antibody (mAb) production in Chinese hamster ovary (CHO) cell lines. In this study, we utilised single cell RNASeq (scRNASeq) to study a clonally-derived CHO cell line that underwent production instability leading to a dramatic reduction of the levels of mAb produced. From the scRNASeq data we identified sub clusters associated with variations in the mAb transgenes and observed that heavy chain gene expression was significantly lower than that of the light chain across the population. Using trajectory inference, the evolution of the cell line was reconstructed and was found to correlate with a reduction in heavy and light chain gene expression. Genes encoding for proteins involved in the response to oxidative stress and apoptosis were found to increase in expression as cells progressed along the trajectory. Future studies of CHO cell lines using this technology have the potential to dramatically enhance our understanding of the characteristics underpinning efficient manufacturing performance as well as product quality.HighlightsA clonally-derived CHO cell line in our laboratory had undergone production instability – in that the amount of intact monoclonal antibody had reduced dramatically to levels at which reliable quantitation was no longer possible. We were, however, able to detect mAb heavy and light chain protein, as well as dimerised light chain species in the cell culture media.Single cell RNASeq was utilised to capture > 3,800 gene expression profiles from the cell line at 72hrs post seeding.Analyses of the scRNASeq data uncovered transcriptional heterogeneity and revealed the presence of multiple intra cell line clusters. The heavy chain transcript was detected at a significantly lower level in comparison light chain transcripts. Light chain gene expression was not only more abundant, but also expressed more uniformly across the cell population.Using unsupervised trajectory analysis, the emergence of heterogeneity in the cell population was traced from those cells most similar to the original isolated clone to those where transcription of the mAb heavy and light chain was undetectable.Subsequent analysis of CHO cell gene expression patterns revealed a correlation between the progression of cells along the trajectory and the upregulation of genes involved in the cellular response to oxidative stress.