PhiC31 integrase can improve the efficiency of different construct designs for monoclonal antibody expression in CHO cells

Study on chromatin regulation patterns of expression vectors in the PhiC31 integration site

The PhiC31 integration system allows for targeted and efficient transgene integration and expression by recognizing pseudo attP sites in mammalian cells and integrating the exogenous genes into the open chromatin regions of active chromatin. In order to investigate the regulatory patterns of efficient gene expression in the open chromatin region of PhiC31 integration, this study utilized Ubiquitous Chromatin Opening Element (UCOE) and activating RNA (saRNA) to modulate the chromatin structure in the promoter region of the PhiC31 integration vector. The study analysed the effects of DNA methylation and nucleosome occupancy changes in the integrated promoter on gene expression levels. The results showed that for the OCT4 promoter with moderate CG density, DNA methylation had a smaller impact on expression compared to changes in nucleosome positioning near the transcription start site, which was crucial for enhancing downstream gene expression. On the other hand, for the SOX2 promoter with high CG density, increased methylation in the CpG island upstream of the transcription start site played a key role in affecting high expression, but the positioning and clustering of nucleosomes also had an important influence. In conclusion, analysing the DNA methylation patterns, nucleosome positioning, and quantity distribution of different promoters can determine whether the PhiC31 integration site possesses the potential to further enhance expression or overcome transgene silencing effects by utilizing chromatin regulatory elements.

Increase recombinant antibody yields through optimizing vector design and production process in CHO cells

Chinese hamster ovary (CHO) cells are the most commonly used host cells for the production of recombinant monoclonal antibodies (mAbs) due to their several advantages. Although the yields of recombinant mAbs can be greatly increased by some strategies, such as medium formulation, culture conditions, and cell engineering, most studies focused on either upstream design or downstream processes. In the present study, we first expressed recombinant adalimumab through combination of the vector design and production process optimization in CHO cells. Bicistronic vector, monocistronic vector, and dual promoter vector were constructed, and the production process was optimized using low-temperature and fed-batch culture. The results showed that the dual promoter vector exhibited the highest yield under the transient and stable transfected cells among three different vector systems in CHO cells. In addition, low-temperature and fed-batch culture could further improve the yields of adalimumab. The purified antibody displayed tumor necrosis factor-α (TNF-α) binding activity. In conclusion, combination of expression vector design and production process optimization can achieve higher expression of recombinant mAbs in CHO cells. KEY POINTS: • The dual promoter vector is more effective for expressing recombinant antibodies. • The yields of antibodies are related to the LC chain expression level. • Low-temperature and feed addition can promote antibody production.

A novel approach for T7 bacteriophage genome integration of exogenous DNA

Background

The comparatively small genome, well elucidated functional genomics and rapid life cycle confer T7 bacteriophage with great advantages for bio-application. Genetic manipulation of T7 genome plays a key role in T7 related applications. As one of the important aspects in T7 phage genetic modification, gene knock-in refers to two main approaches including direct genetic manipulation in vitro and recombineering. Neither of these available methods are efficient enough to support the development of innovative applications capitalizing on T7 bio-system and thus there is room for novel strategies that address this issue. Integration mediated by the ΦC31 integrase is one of the most robust site-specific recombination systems. ΦC31 integrases with enhanced activity and specificity have been developed such that it is ideal to effectuate exogenous DNA knock-in of T7 phage with advanced ΦC31 integrase.

Methods

Plasmid construction was conducted by routine molecular cloning technology. The engineered T7 bacteriophages were constructed through homologous recombination with corresponding plasmids and the functional T7 phage was designated as T7∆G10G11-attB. In the integration reaction, hosts with both executive plasmids (pEXM4) and donor plasmids (pMCBK) were lysed by T7∆G10G11-attB. Progenies of T7 phages that integrated with pMCBK were isolated in restrict hosts and validated by sequencing. T7∆G10G11-attB capacity limit was explored by another integration reactions with donor plasmids that contain exogenous DNA of various lengths.

Results

T7∆G10G11-attB exhibits abortive growth in restrictive hosts, and a bacterial attachment site recognized by ΦC31 integrase (attB) was confirmed to be present in the T7∆G10G11-attB genome via sequencing. The integration reaction demonstrated that plasmids containing the corresponding phage attachment site (attP) could be integrated into the T7∆G10G11-attB genome. The candidate recombinant phage was isolated and validated to have integrated exogenous DNA. The maximum capacity of T7∆G10G11-attB was explored, and it’s found that insertion of exogenous DNA sequences longer than 2 kbp long can be accommodated stably.

Conclusion

We advanced and established a novel approach for gene knock-in into the T7 genome using ΦC31 integrase.

The Epigenetic Regulation of Blinatumomab Gene Expression: Tumor Cell-dependent T cell Response against Lymphoma Cells and Cytotoxic Activity

Conventional treatment for cancer such as surgical resection and chemotherapy can cause damage in cases with advanced cancers. Moreover, the identification of tumor-specific targets has great importance in T-cell therapies. For decades, T cell activity has been stimulated to improve anti-tumor activity. Bispecific antibodies have attracted strong interest from pharmaceutical companies, for their diagnostic and therapeutic use. Blinatumomab is a first-in-class bispecific T engager antibody for the treatment of relapsed or refractory precursor B- cell acute lymphoblastic leukemia. But, it can benefit several cases with CD19⁺ malignancies in the future. PhiC31 integrase-based vectors could selectively integrate therapeutic transgenes into pseudo-attP sites in CHO genome. In this study, production of Blinatumomab in CHO cells using this type of vectors was investigated. We evaluated the effects of histone deacetylases (HDACs) inhibitors such as sodium butyrate and valproic acid, on specific productivity and cell viability of antibody expressing cells. Although sodium butyrate increased specific productivity about 1.7-fold and valproic acid about 1.4-fold, valproic acid was found more efficient because of its less cytotoxic effect on cell growth. We examined the efficacy of expressed Blinatumomab at various effector to target (E/T) ratios. A dose-response analyses of calcein-acetoxymethyl release assay illustrated that the effective dose of expressed mAb required for antibody mediated cytotoxicity was 100 ng/ml and the expressed mAb was more effective at E/T ratios of 10:1 and 5:1. Results of this study indicated that the expressed blinatumomab can be useful for enhancing the cytotoxicity of CD3⁺ T-cells against CD19 ⁺ target cells in vitro.

A comparative study of the bispecific monoclonal antibody, blinatumomab expression in CHO cells and E. coli

The "bispecifics" market improved over the past decade due to the development of many technological platforms including bispecific T cell engagers (BiTEs). The approval of blinatumomab, the most advanced bispecific T-cell engager (BiTE) in clinical trials, can be a significant milestone in the development of bispecific antibodies. Both Chinese hamster ovary (CHO) cells and E. coli strain are considered as the most widely used hosts for the large-scale production of therapeutic monoclonal antibodies. Since both of the economic and qualitative aspects of protein production are important in industry, selection of a suitable protein expression system is very critical. The BsAb gene was cloned into the expression vectors FC550A-1, pcDNA3.1 (+), and PET22b and 6 × His-tagged BsAb then purified on a Ni-NTA chromatography column. Both SDS-PAGE and Western blotting analysis of the purified protein demonstrated that blinatumomab was successfully expressed as a 55 kDa in both expression systems. The antigen-binding properties of blinatumomab were compared in the mammalian system versus Escherichia coli. The results showed that the purified antibody from a mammalian expression system has better binding activity than the one from E. coli host.