Production process reproducibility and product quality consistency of transient gene expression in HEK293 cells with anti-PD1 antibody as the model protein

A high-titer scalable Chinese hamster ovary transient expression platform for production of biotherapeutics

Transient gene expression (TGE) in Chinese hamster ovary (CHO) cells offers a route to accelerate biologics development by delivering material weeks to months earlier than what is possible with conventional cell line development. However, low productivity, inconsistent product quality profiles, and scalability challenges have prevented its broader adoption. In this study, we develop a scalable CHO-based TGE system achieving 1.9 g/L of monoclonal antibody in an unmodified host. We integrated continuous flow-electroporation and alternate tangential flow (ATF) perfusion to enable an end-to-end closed system from N-1 perfusion to fed-batch 50-L bioreactor production. Optimization of both the ATF operation for three-in-one application-cell growth, buffer exchange, and cell mass concentration-and the flow-electroporation process, led to a platform for producing biotherapeutics using transiently transfected cells. We demonstrate scalability up to 50-L bioreactor, maintaining a titer over 1 g/L. We also show comparable quality between both transiently and stably produced material, and consistency across batches. The results confirm that purity, charge variants and N-glycan profiles are similar. Our study demonstrates the potential of CHO-based TGE platforms to accelerate biologics process development timelines and contributes evidence supporting its feasibility for manufacturing early clinical material, aiming to strengthen endorsement for TGE's wider implementation.

Improvement strategies for transient gene expression in mammalian cells

Mammalian cells are suitable hosts for producing recombinant therapeutic proteins, with Chinese hamster ovary (CHO) and human embryonic kidney 293 (HEK293) cells being the most commonly used cell lines. Mammalian cell expression system includes stable and transient gene expression (TGE) system, with the TGE system having the advantages of short cycles and simple operation. By optimizing the TGE system, the expression of recombinant proteins has been significantly improved. Here, the TGE system and the detailed and up-to-date improvement strategies of mammalian cells, including cell line, expression vector, culture media, culture processes, transfection conditions, and co-expression of helper genes, are reviewed. KEY POINTS: • Detailed improvement strategies of transient gene expression system of mammalian cells are reviewed • The composition of transient expression system of mammalian cell are summarized • Proposed optimization prospects for transient gene expression systems.

A novel bispecific antibody drug conjugate targeting HER2 and HER3 with potent therapeutic efficacy against breast cancer

Antibody drug conjugate (ADC) therapy has become one of the most promising approaches in cancer immunotherapy. Bispecific targeting could enhance the efficacy and safety of ADC by improving its specificity, affinity and internalization. In this study we constructed a HER2/HER3-targeting bispecific ADC (BsADC) and characterized its physiochemical properties, target specificity and internalization in vitro, and assessed its anti-tumor activities in breast cancer cell lines and in animal models. The HER2/HER3-targeting BsADC had a drug to antibody ratio (DAR) of 2.89, displayed a high selectivity against the target JIMT-1 breast cancer cells in vitro, as well as a slightly higher level of internalization than HER2- or HER3-monospecific ADCs. More importantly, the bispecific ADC potently inhibited the viability of MCF7, JIMT-1, BT474, BxPC-3 and SKOV-3 cancer cells in vitro. In JIMT-1 breast cancer xenograft mice, a single injection of bispecific ADC (3 mg/kg, i.v.) significantly inhibited the tumor growth with an efficacy comparable to that caused by combined injection of HER2 and HER3-monospecific ADCs (3 mg/kg for each). Our study demonstrates that the bispecific ADC concept can be applied to development of more potent new cancer therapeutics than the monospecific ADCs.

Glyco-signatures in patients with advanced lung cancer during anti-PD-1/PD-L1 immunotherapy

Immune checkpoint inhibitors (ICIs) targeting programmed cell death 1/programmed cell death ligand-1 (PD-1/PD-L1) have significantly prolonged the survival of advanced/metastatic patients with lung cancer. However, only a small proportion of patients can benefit from ICIs, and clinical management of the treatment process remains challenging. Glycosylation has added a new dimension to advance our understanding of tumor immunity and immunotherapy. To systematically characterize anti-PD-1/PD-L1 immunotherapy-related changes in serum glycoproteins, a series of serum samples from 12 patients with metastatic lung squamous cell carcinoma (SCC) and lung adenocarcinoma (ADC), collected before and during ICIs treatment, are firstly analyzed with mass-spectrometry-based label-free quantification method. Second, a stratification analysis is performed among anti-PD-1/PD-L1 responders and non-responders, with serum levels of glycopeptides correlated with treatment response. In addition, in an independent validation cohort, a large-scale site-specific profiling strategy based on chemical labeling is employed to confirm the unusual characteristics of IgG N-glycosylation associated with anti-PD-1/PD-L1 treatment. Unbiased label-free quantitative glycoproteomics reveals serum levels' alterations related to anti-PD-1/PD-L1 treatment in 27 out of 337 quantified glycopeptides. The intact glycopeptide EEQFN 177STYR (H3N4) corresponding to IgG4 is significantly increased during anti-PD-1/PD-L1 treatment (FC=2.65, P=0.0083) and has the highest increase in anti-PD-1/PD-L1 responders (FC=5.84, P=0.0190). Quantitative glycoproteomics based on protein purification and chemical labeling confirms this observation. Furthermore, obvious associations between the two intact glycopeptides (EEQFN 177STYR (H3N4) of IgG4, EEQYN 227STFR (H3N4F1) of IgG3) and response to treatment are observed, which may play a guiding role in cancer immunotherapy. Our findings could benefit future clinical disease management.

Demonstration of a robust high cell density transient CHO platform yielding mAb titers of up to 2 g/L without medium exchange

Biopharmaceuticals like therapeutic monoclonal antibodies (mAbs) and other derived proteins are popular for treating various diseases. Transient gene expression (TGE) is typically used as a fast yet efficient method to generate moderate amounts of material. It has been used to support early stage research and discovery processes. Introduction of a robust high yielding and predictive TGE platform in Chinese hamster ovary (CHO) is crucial. It maintains the consistency in cell lines and processes throughout the early drug discovery and downstream manufacturing processes. This helps researchers to identify the issues at an early stage for timely resolution. In this study, we have demonstrated a simple high-titer platform for TGE in CHO based on a dilution process of seeding cells. We achieved titers ranging from 0.8 to 1.9 g/L for eight model mAbs at three scales (1, 30, 100 mL) in 10 days using our new platform. The ability to seed by dilution significantly streamlined the process and dramatically enhanced platform throughput. We observed a modest reduction in titer ranging from 11% to 28% when cells were seeded using dilution compared to when cells were seeded using medium exchange. Further studies revealed that carry over of spent medium into transfection negatively affected the DNA uptake and transcription processes, while the translation and secretion was minimally impacted. In summary, our transient CHO platform using cells prepared by dilution at high densities can achieve high titers of up to 1.9 g/L, which can be further improved by targeting the bottlenecks of transfection and transcription.

Binding domain on CD22 molecules contributing to the biological activity of T cell-engaging bispecific antibodies

CD22, as the B-cell malignancies antigen, has been targeted for immunotherapies through CAR-T cells, antibody-drug conjugates (ADCs) and immunotoxins via interaction of antibodies with binding domains on the receptor. We hypothesized that avidity and binding domain of antibody to target cells may have significant impact on the biological function in tumor immunotherapy, and T cell-engaging bispecific antibody (TCB) targeting CD22 could be used in the therapy of hematologic malignancies. So, to address the question, we utilized the information of six previously reported CD22 mAbs to generate CD22-TCBs with different avidity to different domains on CD22 protein. We found that the avidity of CD22-TCBs to protein was not consistent with the avidity to target cells, indicating that TCBs had different binding mode to the protein and cells. In vitro results indicated that CD22-TCBs mediated cytotoxicity depended on the avidity of antibodies to target cells rather than to protein. Moreover, distal binding domain of the antigen contributed to the avidity and biological activity of IgG-[L]-scfv-like CD22-TCBs. The T cells' proliferation, activation, cytotoxicity as well as cytokine release were compared, and G5/44 BsAb was selected for further in vivo assessment in anti-tumor activity. In vivo results demonstrated that CD22-TCB (G5/44 BsAb) significantly inhibited the tumors growth in mice. All these data suggested that CD22-TCBs could be developed as a promising candidate for B-cell malignancies therapy through optimizing the design with avidity and binding domain to CD22 target in consideration.

Generating Anti-TIGIT and CD155 Monoclonal Antibodies for Tumor Immunotherapy

Many studies have confirmed that the human poliovirus receptor (PVR; CD155) is related to tumor cell migration, invasion, and thus tumor progression. A PVR receptor binds its ligand T cell Ig and the ITIM domain (TIGIT) to inhibit the function of T and NK cells, thereby allowing tumors to evade immune surveillance. In this study, two IgG1 monoclonal antibodies, anti-CD155 and anti-TIGIT, were expressed by the mammalian transient transfection system, then, antibody-dependent cell-mediated cytotoxicity, antibody-binding affinity, and antitumor efficacy were evaluated subsequently in vitro. In this work, protein A affinity chromatography was used for antibodies' purification. Analysis methods included Western blot, enzyme-linked immunosorbent assay, and flow cytometry. Our data suggested that both the two monoclonal antibodies have a purity of higher than 90%, and bound tightly to the antigen with dissociation constant (K d) and 50% effective concentrations (EC50) below micromolar range. Most notably, these antibodies promote antitumor activity of immune cells in vitro. Therefore, our study laid down the foundation for subsequent in vivo experiments for further evaluation.

The Generation of Dual-Targeting Fusion Protein PD-L1/CD47 for the Inhibition of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a highly aggressive subset of breast cancer with limited therapeutic options. However, its immune evasion mechanisms, characterized by the over-expression of the immune checkpoint molecules PD-L1 and CD47, can be targeted in order to facilitate cancer elimination by cells of innate and adaptive immunity. In this paper, we describe the design, preparation, and evaluation of three novel dual-targeting fusion proteins that were based on the structure frame of prototype IAB (innate and adaptive dependent bispecific fusion protein) and the “Orcutt-type IgG-scFv” molecular model. Three molecules with different spatial conformations were designed to improve antigen–antibody affinity by the addition of Ag–Ab binding sites from the variable region sequences of the anti-PD-L1 monoclonal antibody (mAb) atezolizumab and CV1, a high-affinity receptor of CD47. The results showed that the best-performing among the three proteins designed in this study was protein Pro3; its CV1 N-terminus and Fc domain C-terminus were not sterically hindered. Pro3 was better at boosting T cell proliferation and the engulfment of macrophages than the IAB prototype and, at the same time, retained a level of ADCC activity similar to that of IAB. Through improved design, the novel constructed dual-targeting immunomodulatory protein Pro3 was superior at activating the anti-tumor immune response and has thus shown potential for use in clinical applications.

Generating a Bispecific Antibody Drug Conjugate Targeting PRLR and HER2 with Improving the Internalization

Antibody drug conjugate (ADC) therapy has become one of the most promising approaches in cancer immunotherapy. The bispecific targeting could improve the specificity, affinity, and internalization of the ADC molecules. Prolactin preceptor (PRLR) and HER2 have crosstalk signaling in breast cancer, and PRLR undergoes a rapid internalization compared with HER2. To improve the efficacy of HER2 ADCs with enhancing the target specificity and internalization, we constructed a PRLR/HER2-targeting bispecific ADC (BsADC). We evaluated the characterization of PRLR × HER2 BsADC from the affinity and internalization, and further assessed its in vitro cytotoxicity in human breast-cancer cell lines (BT474, T47D, and MDA-MB-231) using Cell Count Kit-8 analysis. Our data demonstrated that PRLR × HER2 BsADC kept the affinity to two targeting antigens after conjugating drugs and exhibited higher internalization efficiency in comparison to HER2 ADC. Furthermore, PRLR × HER2 BsADC demonstrated to have superior antitumor activity in human breast cancer in vitro. In conclusion, our findings indicate that it is feasible through increasing the internalization of target antibody to enhance the antitumor activity and therapeutic potential that could be further evaluated in in vivo animal model.

IgG-like Bispecific Antibody CD3×EpCAM Generated by Split Intein Against Colorectal Cancer

Background: Colorectal cancer is a commonly diagnosed cancer with high mortality worldwide. Postoperative recidivation and metastasis still are the main challenges in clinical treatments. Thus, it is urgent to develop new therapies against colorectal cancer. Epithelial Cell Adhesion Molecule (EpCAM) is overexpressed in colorectal cancer cells and strongly associated with cancer development. Bispecific antibody (BsAb) is a kind of promising immunotherapy, which could recognize T cells and cancer cells simultaneously to achieve the anti-tumor effects. Methods: A bispecific antibody targeting EpCAM and CD3 with IgG format was genereated by split intein based on the Bispecific Antibody by Protein Splicing" platform. In vitro, the affinity of CD3×EpCAM BsAb was determined by Biolayer interferometry, its cytotoxicity was detected by LDH release assay, T cell recruitment and activation was detected by Flow Cytometry. In vivo, its pharmacokinetic parameters were detected, and anti-tumor effects were evaluated on the tumor cell xenograft mouse model. Results: The results showed that the CD3×EpCAM BsAb could activate and recruit T cells via binding colorectal cells and T cells, which could lead to more potent cytotoxicity to various colorectal cell lines than its parent EpCAM monoclonal antibody (mAb) in vitro. The CD3×EpCAM BsAb had similar pharmacokinetic parameters with EpCAM mAb and inhibits tumor growth on the SW480 tumor cell xenograft mouse model. Conclusion: The CD3×EpCAM BsAb could be a promising candidate for colorectal cancer treatment.

Kinetics study of the natural split Npu DnaE intein in the generation of bispecific IgG antibodies

Rapid and efficient bispecific antibody (BsAb) production for industrial applications is still facing many challenges. We reported a technology platform for generating bispecific IgG antibodies, "Bispecific Antibody by Protein Trans-splicing (BAPTS)." While the "BAPTS" method has shown potential in high-throughput screening of BsAbs, further understanding and optimizing the methodology is desirable. A large number of BsAbs were selected to illustrate the conversion efficiency and kinetics parameters. The temperature of reaction makes no significant influence in conversion efficiency, which can reach more than 70% within 2 h, and CD3 × HER2 BsAb can reach 90%. By fitting trans-splicing reaction to single-component exponential decay curves, the apparent first-order rate constants at a series of temperatures were determined. The rate constant ranges from 0.02 to 0.11 min^-1 at 37 °C, which is a high rate reported for the protein trans-splicing reaction (PTS). The reaction process is activated rapidly with activation energy of 8.9 kcal·mol^-1 (CD3 × HER2) and 5.2 kcal·mol^-1 (CD3 × EGFR). The BsAbs generated by "BAPTS" technology not only had the similar post-translation modifications to the parental antibodies, but also demonstrated excellent in vitro and in vivo bioactivity. The kinetics parameters and activation energy of the reaction illustrate feasible for high-throughput screening and industrial applications using the "BAPTS" approach. KEY POINTS: • The trans-splicing reaction of Npu DnaE intein in "BAPTS" platform is a rapid process with low reaction activation and high rate. • The BsAb generated by "BAPTS" remained effective in tumor cell killing. • The kinetics parameters and activation energy of the reaction illustrate feasible for high-throughput screening and industrial applications using the "BAPTS" approach.

A Novel Bispecific Antibody Targeting CD3 and Lewis Y with Potent Therapeutic Efficacy against Gastric Cancer

Lewis Y antigen, a glycan highly expressed on most epithelial cancers, was targeted for cancer treatment but lacked satisfactory results in some intractable and refractory cancers. Thus, it is highly desirable to develop an effective therapy against these cancers, hopefully based on this target. In this work, we constructed a novel T cell-engaging bispecific antibody targeting Lewis Y and CD3 (m3s193 BsAb) with the IgG-[L]-scfv format. In vitro activity of m3s193 BsAb was evaluated by affinity assay to target cells, cytotoxicity assay, cytokines releasing assay, and T cells proliferation and recruiting assays. Anti-tumor activity against gastric cancer was evaluated in vivo by subcutaneous huPBMCs/tumor cells co-grafting model and huPBMCs intravenous injecting model. In vitro, m3s193 BsAb appeared to have a high binding affinity to Lewis Y positive cells and Jurkat cells. The BsAb showed stronger activity than its parent mAb in T cell recruiting, activation, proliferation, cytokine release, and cytotoxicity. In vivo, m3s193 BsAb not only demonstrated higher therapeutic efficacy in the huPBMCs/tumor co-grafting gastric carcinoma model than the parent mAb but also eliminated tumors in the model of intravenous injection with huPBMCs. Strong anti-tumor activity of m3s193 BsAb revealed that Lewis Y could be targeted in T cell-engaging BsAb for gastric cancer therapy.

A Rational Designed Novel Bispecific Antibody for the Treatment of GBM

Epidermal growth factor receptor variant III (EGFRvIII) is highly and specifically expressed in a subset of lethal glioblastoma (GBM), making the receptor a unique therapeutic target for GBM. Recently, bispecific antibodies (BsAbs) have shown exciting clinical benefits in cancer immunotherapy. Here, we report remarkable results for GBM treatment with a BsAb constructed by the "BAPTS" method. The BsAb was characterized through LC/MS, SEC-HPLC, and SPR. Furthermore, the BsAb was evaluated in vitro for bioactivities through FACS, antigen-dependent T-cell-mediated cytotoxicity, and a cytokine secretion assay, as well as in vivo for antitumor activity and pharmacokinetic (PK) parameters through immunodeficient NOD/SCID and BALB/c mouse models. The results indicated that the EGFRvIII-BsAb eliminated EGFRvIII-positive GBM cells by recruiting and stimulating effector T cells secreting cytotoxic cytokines that killed GBM cells in vitro. The results demonstrated the antitumor potential and long circulation time of EGFRvIII-BsAb in NOD/SCID mice bearing de2-7 subcutaneously heterotopic transplantation tumors and BALB/c mice. In conclusion, our experiments in both in vitro and in vivo have shown the remarkable antitumor activities of EGFRvIII-BsAb, highlighting its potential in clinical applications for the treatment of GBM. Additional merits, including a long circulation time and low immunogenicity, have also made the novel BsAb a promising therapeutic candidate.

A novel bispecific antibody targeting CD3 and prolactin receptor (PRLR) against PRLR-expression breast cancer

BACKGROUND

Prolactin receptor (PRLR) is highly expressed in a subset of human breast cancer and prostate cancer, which makes it a potential target for cancer treatment. In clinical trials, the blockade of PRLR was shown to be safe but with poor efficacy. It is therefore urgent to develop new therapies against PRLR target. Bispecific antibodies (BsAbs) could guide immune cells toward tumor cells, and produced remarkable effects in some cancers.

METHODS

In this study, a bispecific antibody targeting both tumor antigen PRLR and T cell surface CD3 antigen (PRLR-DbsAb) was constructed by split intein mediated protein transsplicing (BAPTS) system for the first time. Its binding activity was determined by Biacore and Flow cytometry, and target-dependent T cell mediated cytotoxicity was detected using LDH release assay. ELISA was utilized to study the secretion of cytokines by immune cells. Subcutaneous tumor mouse models were used to analyze the in vivo anti-tumor effects of PRLR-DbsAb.

RESULTS

PRLR-DbsAb in vitro could recruit and activate T cells to promote the release of Th1 cytokines IFN- γ and TNF- α, which could kill PRLR expressed breast cancer cells. In xenograft models with breast cancer cell line T47D, NOD/SCID mice intraperitoneally injected with PRLR-DbsAb exhibited significant inhibition of tumor growth and a longer survival compared to mice treated with PRLR monoclonal antibody (PRLR mAb).

CONCLUSIONS

Both in vitro and in vivo experiments showed PRLR-DbsAb had a potential therapy of cancer treatment potential therapy for cancer. Immunotherapy may be a promising treatment against the tumor target of PRLR.

Expression of glycosylated human prolactin in HEK293 cells and related N-glycan composition analysis

Prolactin (PRL) is a hormone produced by the pituitary gland with innumerable functions, such as lactation, reproduction, osmotic and immune regulation. The present work describes the synthesis of hPRL in human embryonic kidney (HEK293) cells, transiently transfected with the pcDNA-3.4-TOPO^® vector carrying the hPRL cDNA. A concentration of ~ 20 mg/L, including glycosylated (G-hPRL) and non-glycosylated (NG-hPRL) human prolactin, was obtained, with ~ 19% of G-hPRL, which is higher than that observed in CHO-derived hPRL (~ 10%) and falling within the wide range of 5–30% reported for pituitary-derived hPRL. N-Glycoprofiling analysis of G-hPRL provided: (i) identification of each N-glycan structure and relative intensity; (ii) average N-glycan mass; (iii) molecular mass of the whole glycoprotein and relative carbohydrate mass fraction; (iv) mass fraction of each monosaccharide. The data obtained were compared to pituitary- and CHO-derived G-hPRL. The whole MM of HEK-derived G-hPRL, determined via MALDI–TOF-MS, was 25,123 Da, which is 0.88% higher than pit- and 0.61% higher than CHO-derived G-hPRL. The main difference with the latter was due to sialylation, which was ~ sevenfold lower, but slightly higher than that observed in native G-hPRL. The “in vitro” bioactivity of HEK-G-hPRL was ~ fourfold lower than that of native G-hPRL, with which it had in common also the number of N-glycan structures.

An anti-apoptotic HEK293 cell line provides a robust and high titer platform for transient protein expression in bioreactors

HEK293 transient expression systems are used to quickly generate proteins for research and pre-clinical studies. With the aim of engineering a high-producing host that grows and transfects robustly in bioreactors, we deleted the pro-apoptotic genes Bax and Bak in an HEK293 cell line. The HEK293 Bax Bak double knock-out (HEK293 DKO) cell line exhibited resistance to apoptosis and shear stress. HEK293 DKO cells sourced from 2 L seed train bioreactors were most productive when a pH setpoint of 7.0, a narrow pH deadband of ±0.03, and a DO setpoint of 30% were used. HEK293 DKO seed train cells cultivated for up to 60 days in a 35 L bioreactor showed similar productivities to cells cultivated in shake flasks. To optimize HEK293 DKO transfection cultures, we first evaluated different pH and agitation parameters in ambr15 microbioreactors before scaling up to 10 L wavebag bioreactors. In ambr15 microbioreactors with a pH setpoint of 7.0, a wide pH deadband of ±0.3, and an agitation of 630 rpm, HEK293 DKO transient cultures yielded antibody titers up to 650 mg/L in 7 days. The optimal ambr15 conditions prompted us to operate the 10 L wavebag transfection without direct pH control to mimic the wide pH deadband ranges. The HEK293 DKO transfection process produces high titers at all scales tested. Combined, our optimized HEK293 DKO 35 L bioreactor seed train and 10 L high titer transient processes support efficient, large-scale recombinant protein production for research studies.

Enhanced Production of Anti-PD1 Antibody in CHO Cells through Transient Co-Transfection with Anti-Apoptotic Gene Bcl-xL Combined with Rapamycin

CHO cells are often used to produce monoclonal antibodies in mammalian cell expression systems. In the process of large-scale cell culture, apoptosis is related to cell survival and product quality. Over-expressing an anti-apoptotic gene to delay apoptosis and improve cell growth is one of the strategies for improving productivity of monoclonal antibodies. Autophagy inducer rapamycin can extend the culture duration of CHO cells and affect the yield of antibodies. A method was developed for transient co-transfection of anti-apoptotic genes and genes of interest combined with rapamycin to increase the transient expression of the anti-PD1 antibody. Under the optimal transfection conditions, the combination of Bcl-xL and rapamycin can significantly delay cell apoptosis, inhibit cell proliferation, and prolong cell life-time. As a result, anti-PD1 monoclonal antibody expression levels are increased by more than 2 times.

Bioprocess development of a stable FUT8-/--CHO cell line to produce defucosylated anti-HER2 antibody

In recent years, an increasing number of defucosylated therapeutic antibodies have been applied in clinical practices due to their better efficacy compared to fucosylated counterparts. The establishment of stable and clonal manufacturing cell lines is the basis of therapeutic antibodies production. Bioprocess development of a new cell line is necessary for its future applications in the biopharmaceutical industry. We engineered a stable cell line expressing defucosylated anti-HER2 antibody based on an established α-1,6-fucosyltransferase (FUT8) gene knockout CHO-S cell line. The optimization of medium and feed was evaluated in a small-scale culture system. Then the optimal medium and feed were scaled up in a bioreactor system. After fed-batch culture over 13 days, we evaluated the cell growth, antibody yield, glycan compositions and bioactivities. The production of anti-HER2 antibody from the FUT8 gene knockout CHO-S cells in the bioreactor increased by 37% compared to the shake flask system. The N-glycan profile of the produced antibody was consistent between the bioreactor and shake flask system. The antibody-dependent cellular cytotoxicity activity of the defucosylated antibody increased 14-fold compared to the wild-type antibody, which was the same as our previous results. The results of our bioprocess development demonstrated that the engineered cell line could be developed to a biopharmaceutical industrial cell line.

Development of a recombinant human IL-15·sIL-15Rα/Fc superagonist with improved half-life and its antitumor activity alone or in combination with PD-1 blockade in mouse model

Recombinant human interleukin-15 (IL-15) is a potent cancer immunotherapeutic candidate due to its excellent immune stimulating effects. Previous work demonstrated that IL-15 appeared with short half-life in circulation system, while the complex with its receptor can prolong the half-life as well as benefit its activities in vivo. Therefore, IL-15 complex was more favorably considered for clinical development. Herein we developed IL-15·sIL-15Rα/Fc, a complex comprising of IL-15 and the extracellular region of its receptor alpha subunit which fused to Immunoglobulin G (IgG1) Fc to further prolong the half-life in plasma. Through transient gene expression in HEK293 cells, we expressed the superagonist by co-transfection of plasmids encoding IL-15 and sIL-15Rα/Fc respectively, yielding 36 mg/L of product after purification. Pharmacokinetic study demonstrated that the combination profoundly prolonged the half-life of IL-15 to 13.1 h in mice, about 18 folds longer than that of IL-15 monomer which is around 0.7 h. The bioactivity of the superagonist was characterized by CTLL-2 cells proliferation assay in vitro, showing its capability of stimulating the expansion of memory CD8⁺ T cells (cluster of differentiation) in mouse spleen. Using a HT-29 xenograft NOD-SCID mouse model, we observed tumor growth inhibition in all groups that received the superagonist, indicating its anti-tumor efficacy via stimulating infused human immune cells. In addition, combo cancer treatment by IL-15·sIL-15Rα/Fc and programmed death-1 (PD-1) antibody have shown stronger inhibitory effects as compared with treatment with either single molecule. Therefore, we developed IL-15·sIL-15Rα/Fc to be a long half-life potential cancer immunotherapy candidate that can be applied alone or in synergy with PD-1/PD-L1 blockade.

Production of Therapeutic Enzymes by Lentivirus Transgenesis

Since ERT for several LSDs treatment has emerged at the beginning of the 1980s with Orphan Drug approval, patients' expectancy and life quality have been improved. Most LSDs treatment are based on the replaced of mutated or deficient protein with the natural or recombinant protein.One of the main ERT drawback is the high drug prices. Therefore, different strategies trying to optimize the global ERT biotherapeutic production have been proposed. LVs, a gene delivery tool, can be proposed as an alternative method to generate stable cell lines in manufacturing of recombinant proteins. Since LVs have been used in human gene therapy, clinical trials, safety testing assays and procedures have been developed. Moreover, one of the main advantages of LVs strategy to obtain manufacturing cell line is the short period required as well as the high protein levels achieved.In this chapter, we will focus on LVs as a recombinant protein production platform and we will present a case study that employs LVs to express in a manufacturing cell line, alpha-Galactosidase A (rhαGAL), which is used as ERT for Fabry disease treatment.

Naturally split intein Npu DnaE mediated rapid generation of bispecific IgG antibodies

High product purity, preserving natural IgG architecture, and excellent production efficiency are highly desirable in bispecific antibody manufacturing. We have reported a platform called Bispecific Antibody by Protein Trans-Splicing (BAPTS) to synthesize BsAbs with natural human IgG structure and no chain mispairing. In the method, two antibody fragments carrying different target-specificities are separately expressed in mammalian cells and subsequently fused to form BsAbs by utilizing the trans-splicing property of the split intein Npu DnaE. The hinge region of antibody, a region with less functional impact, is selected for conjugating the two fragments. The method involves the following steps: (i) constructing five plasmids coding antibody components; (ii) separately expressing and purifying two antibody fragments A and B. Fragment A contains one Fab, "Knobs-into-Holes" mutations in the CH3 domain and NPU DnaE^C. Fragment B contains another Fab and NPU DnaE^N; (iii) mixing of fragments A and B under permissive reducing conditions in vitro to enable trans-splicing reaction; (iv) removing the reductant to allow re-oxidation of disulfide bonds; (v) isolating BsAb product from unreacted precursors by affinity chromatography. The method allows correct assembly of two heavy and two light chains to form bispecific IgG antibodies in natural structure with no synthetic linkers. No chain mispairing was observed in the product by UPLC-MASS. In addition, the observed kinetics and low reaction activation energy confirmed that the trans-splicing is thermodynamically favored reaction. The BAPTS technology is feasible for industrial applications.

Rapid development of stable transgene CHO cell lines by CRISPR/Cas9-mediated site-specific integration into C12orf35

Chinese hamster ovary (CHO) cells are the most widely used mammalian hosts for recombinant protein production. However, by conventional random integration strategy, development of a high-expressing and stable recombinant CHO cell line has always been a difficult task due to the heterogenic insertion and its caused requirement of multiple rounds of selection. Site-specific integration of transgenes into CHO hot spots is an ideal strategy to overcome these challenges since it can generate isogenic cell lines with consistent productivity and stability. In this study, we investigated three sites with potential high transcriptional activities: C12orf35, HPRT, and GRIK1, to determine the possible transcriptional hot spots in CHO cells, and further construct a reliable site-specific integration strategy to develop recombinant cell lines efficiently. Genes encoding representative proteins mCherry and anti-PD1 monoclonal antibody were targeted into these three loci respectively through CRISPR/Cas9 technology. Stable cell lines were generated successfully after a single round of selection. In comparison with a random integration control, all the targeted integration cell lines showed higher productivity, among which C12orf35 locus was the most advantageous in both productivity and cell line stability. Binding affinity and N-glycan analysis of the antibody revealed that all batches of product were of similar quality independent on integrated sites. Deep sequencing demonstrated that there was low level of off-target mutations caused by CRISPR/Cas9, but none of them contributed to the development process of transgene cell lines. Our results demonstrated the feasibility of C12orf35 as the target site for exogenous gene integration, and strongly suggested that C12orf35 targeted integration mediated by CRISPR/Cas9 is a reliable strategy for the rapid development of recombinant CHO cell lines.

Enhanced production of anti-PD1 antibody in CHO cells through transient co-transfection with anti-apoptotic genes Bcl-x L and Mcl-1

Apoptosis has a negative impact on the cell survival state during cell cultivation. To optimize mammalian cell culture for production of biopharmaceuticals, one of the important approaches is to extend cell life through over-expression of anti-apoptotic genes. Here, we reported a cost-effective process to enhance cell survival and production of an antibody through transient co-transfection with anti-apoptotic genes Bcl-x _L or Mcl-1 in Chinese hamster ovary (CHO) cells with polyethylenimine (PEI). Under the optimal conditions, it showed reduced levels of apoptosis and improved cell viability after co-transfected with Bcl-x _L or Mcl-1. The overall production yield of the antibody anti-PD1 increased approximately 82% in CHO cells co-transfected with Bcl-x _L , and 34% in CHO cells co-transfected with Mcl-1. This work provides an effective way to increase viability of host cells through delaying apoptosis onset, thus, raise production yield of biopharmaceuticals without the process of generating stable cell lines and subsequent screening.

Human thyroid-stimulating hormone synthesis in human embryonic kidney cells and related N-glycoprofiling analysis for carbohydrate composition determination

A strain of embryonic human kidney cells (HEK293) was transiently co-transfected with the expression vectors coding for the α- and β-subunits of human thyroid-stimulating hormone (hTSH), and, for the first time, a human cell-derived recombinant hTSH was synthesized and extensively characterized. The purification strategy involving two steps provided an overall yield of 55% and a purity level > 90%. The purified material (hTSH-HEK) was analyzed and compared to a CHO-derived recombinant preparation (hTSH-CHO) and to a pituitary-derived (hTSH-Pit) preparation. The three preparations showed an equivalent purity (> 95%) with a hTSH-HEK molecular mass 2.1% lower than that of hTSH-CHO and 2.7% higher than that of hTSH-Pit. Remarkable differences were found in the carbohydrate moiety, the lowest sialic acid content and highest fucose content being observed in hTSH-HEK. In vivo biological activity was confirmed for the three preparations, the hTSH-HEK bioactivity being 39 and 16% lower than those of hTSH-CHO and hTSH-Pit, respectively. The hTSH-HEK circulatory half-life (t _1/2) was also shorter than those of hTSH-CHO (1.5-fold) and hTSH-Pit (1.2-fold). According to these findings, HEK-293-derived hTSH can be considered to be useful for clinical applications, in view as well of its human origin and particular carbohydrate composition.

Efficient generation of bispecific IgG antibodies by split intein mediated protein trans-splicing system

Many methods have been developed to produce bispecific antibodies (BsAbs) for industrial application. However, huge challenges still remain in synthesizing whole length BsAbs, including their assembly, stability, immunogenicity, and pharmacodynamics. Here we present for first time a generic technology platform of generating bispecific IgG antibodies, “Bispecific Antibody by Protein Trans-splicing (BAPTS)”. Different from published methods, we assembled two parental antibody fragments in the hinge region by the protein trans-splicing reaction of a split intein to generate BsAbs without heavy/heavy and light/heavy chain mispairing. Utilizing this simple and efficient approach, there have been several BsAbs (CD3×HER2, CD3×EGFR, EGFR×HER2) synthesized to demonstrate its broad applicability. Correctly paired mAb arms were assembled to form BsAbs that were purified through protein A affinity chromatography to demonstrate industrial applicability at large scale. Further, the products were characterized through physical-biochemistry properties and biological activities to confirm expected quality of the products from “BAPTS”. More importantly, correct pairing was confirmed by mass spectrum. Proof-of-concept studies with CD3×HER2 BsAb (T-cell recruitment) demonstrated superior bioactivity compared with trastuzumab. The results of undetectable mispairing and high biological activity have indicated that this method has the potential to be utilized to manufacture BsAbs with high efficiency at industrial scale.

Producing defucosylated antibodies with enhanced in vitro antibody-dependent cellular cytotoxicity via FUT8 knockout CHO-S cells

To engineer a host cell line that produces defucosylated mAbs with superior antibody-dependent cellular cytotoxicity, we disrupted α-1, 6 fucosyltransferase (FUT8) gene in CHO-S (CHO is Chinese hamster ovary) cells by clustered regularly interspaced short palindromic repeats-CRISPR associated nuclease 9. The gene knockout cell line was evaluated for growth, stability, and product quality. The growth profile of FUT8 gene knockout CHO-S (FUT8 ^-/-) cells was comparable with wild type CHO-S cells. FUT8 catalyzes the transfer of a fucose residue from GDP-fucose to N-glycans residue. Defucosylated IgG1 antibodies produced by FUT8 ^-/- cells showed increased binding affinities to human FcγRIIIa and higher activities in mediating antibody-dependent cellular cytotoxicity, comparing with conventional fucosylated IgG1. Our results demonstrated the potential of using the clustered regularly interspaced short palindromic repeats-CRISPR associated nuclease 9 technology in cell line engineering for biopharmaceutical industrial applications.