The choice of synonymous codons in many species is strongly biased. 2012) effectively improved yield by speeding up translation processing. Optimization of codon usage for CHO (Chung et al. In translation, mRNA produced by transcription is decoded by a ribosome complex to produce a specific amino acid chain, or polypeptide. In addition to strong promoters and a polyA tail on the plasmid, 3′ untranslated regions (UTR) are included at the 3′ end of the codoning sequence to stablize the mRNA (Kuersten and Goodwin 2003). A high mRNA level, obtained by strong promoters and polyA tail, is important for high-yield expression. The pTT5 vector has also included favorable RNA processing signals such as polyA tail, presence of an intron to encourage export from the nucleus, and a splice site to remove this intron (Birch and Racher 2006). To achieve high levels of gene expression, vectors such as pTT5 usually have strong promoters (e.g., the CMV promoter) to drive expression of the antibody genes (Durocher et al. The CHO cell line, due to its good performance in protein folding, secretion, and post-translational modification, is the most commonly used host cell line for both transient and stable expression. Host cell line and expression vector are important for both transient expression and stable expression. For high-yield expression in a stable and high-producing cell line, the most important factors are appropriate host cell line, an efficient vector, and a good selection protocol (Jostock and Knopf 2012). For transient expression, the cell culture media, gene delivery reagents, host cell line, and expression vector are the decisive factors for yield (You et al. The productivity of antibody expression involves multiple factors. Currently, the highest yield for transient expression is around 1 g/L, but 12 g/L can be obtained by stable expression (Frenzel et al. Stable expression process is more widely used in large-scale industrial production (Ho et al. Transient expression allows quick production of small amounts of antibodies for testing during the early stages of drug discovery (Ho et al. MAb production in mammalian cells can be performed through either transient gene expression (TGE) or stable gene expression (SGE). The process of therapeutic drug production must meet productivity, quality, and safety criteria (Gaughan 2016 Li et al. The majority of these antibodies are produced by recombinant DNA technology in mammalian cells (Birch and Racher 2006 Kunert and Reinhart 2016). The unique combination of high affinity, remarkable specificity, and long half-life make monoclonal antibodies (MAbs) successful in the treatment of diseases including bacterial infections, autoimmune disorders, and cancer (Elgundi et al. In conclusion, vector optimization via combination of optimized signal peptide, codon, and UTR is an alternative approach for efficient antibody production with high fidelity N-terminal sequence in CHO cells. The expression level of SGE (stable gene expression) can also be improved effectively with this optimization strategy. The production efficiency and product quality from the identified TGE optimization strategy was further demonstrated through application to two other antibodies. Additionally, the bioactivity of products made from optimized transient gene expression (TGE) was almost identical to the standard sample. Moreover, the main product peak was above 98% as assessed by size-exclusion chromatography (SEC). The combination of UTR with optimal codon and signal peptide to form an expression vector resulted in yield improvement of 150% and correct N-terminal sequences. Further, the yield was doubled by codon optimization and increased by 50% with the presence of untranslated regions (UTR). Mass spectrometry (MS) revealed that signal peptides Esp-K, Bsp-H, and 8Hsp-H were accurately deleted from mature antibodies. First, the heavy chain and light chain were co-expressed in Chinese hamster ovary (CHO) cells with different signal peptides. In order to produce antibodies with a high yield and accurate N-terminal, the expression vector was systematically optimized in this study. It is especially important to maintain the fidelity of N-terminal sequence. For a candidate molecule, optimization of a vector to produce sufficient yield and an accurate primary structure is indispensable in the early stage of the production process development. Producing antibodies with high yield and quality is necessary for clinical applications of antibodies. Antibody drugs have been used to treat a number of diseases successfully.
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