Genetic modification of a chicken expression system for the galactosylation of therapeutic proteins produced in egg white

Genetically modified chickens as bioreactors for protein-based drugs

Protein drug production encompasses various methods, among which animal bioreactors are emerging as a transgenic system. Animal bioreactors have the potential to reduce production costs and increase efficiency, thereby producing recombinant proteins that are crucial for therapeutic applications. Various species, including goats, cattle, rabbits, and poultry, have been genetically engineered to serve as bioreactors. This review delves into the analysis and comparison of different expression systems for protein drug production, highlighting the advantages and limitations of microbial, yeast, plant cell, and mammalian cell expression systems. Additionally, the emerging significance of genetically modified chickens as a potential bioreactor system for producing protein-based drugs is highlighted. The avian bioreactor enables the expression of target genes in ovarian cells, resulting in the production of corresponding gene expression products in egg whites. This production method boasts advantages such as a short cycle, high production efficiency, low research costs, and the expression products being closer to their natural state and easier to purify. It demonstrates immense potential in production applications, scientific research, and sustainable development. The utilization of advanced gene editing technologies, such as CRISPR/Cas9, has revolutionized the precision and efficiency of generating genetically modified chickens. This has paved the way for enhanced production of recombinant therapeutic proteins with desired glycosylation patterns and reduced immunogenic responses.

Glycoblotting-Based Ovo-Sulphoglycomics Reveals Phosphorylated N-Glycans as a Possible Host Factor of AIV Prevalence in Waterfowls

Sulfated N-glycans play a crucial role in the interaction between influenza A virus (IAV) and its host. These glycans have been found to enhance viral replication, highlighting their significance in IAV propagation. This study investigated the expression of acidic N-glycans, specifically sulfated and phosphorylated glycans, in the egg whites of 72 avian species belonging to the Order Anseriformes (waterfowls). We used the glycoblotting-based sulphoglycomics approach to elucidate the diversity of acidic N-glycans and infer their potential role in protecting embryos from infections. Family-specific variations in sulfated and phosphorylated N-glycan profiles were identified in waterfowl egg whites. Different waterfowl species exhibited distinct expressions of sulfated trans-Gal(+) and trans-Gal(-) N-glycan structures. Additionally, species-specific expression of phosphorylated N-glycans was observed. Furthermore, it was found that waterfowl species with high avian influenza virus (AIV) prevalence displayed a higher abundance of phosphorylated hybrid and high-mannose N-glycans on their egg whites. These findings shed light on the importance of phosphorylated and sulfated N-glycans in understanding the role of acidic glycans in IAV propagation.

Regulatory mechanism of chicken lysozyme gene expression in oviducts examined using transgenic technology

The use of promoters that strongly express target genes in the chicken oviduct is beneficial for the production of proteinaceous materials into egg white by transgenic chickens. To examine the regulatory mechanisms of chicken lysozyme gene expression in vivo, genetically manipulated chickens that express human erythropoietin under the control of a lysozyme promoter-enhancer were established. By using several deletion mutants of the promoter-flanking region, we found that a -1.9 kb DNase I hypersensitive site (DHS) was essential for oviduct-specific expression in genetically manipulated chickens. The concentration of human erythropoietin in egg white was 14-75 μg/ml, suggesting that the chicken lysozyme promoter containing -1.9 kb DHS is sufficient for the production of pharmaceuticals using transgenic chickens.

Efficient production of human interferon beta in the white of eggs from ovalbumin gene-targeted hens

Transgenic chickens could potentially serve as bioreactors for commercial production of recombinant proteins in egg white. Many transgenic chickens have been generated by randomly integrating viral vectors into their genomes, but transgene expression has proved insufficient and/or limited to the initial cohort. Herein, we demonstrate the feasibility of integrating human interferon beta (hIFN-β) into the chicken ovalbumin locus and producing hIFN-β in egg white. We knocked in hIFN-β into primordial germ cells using a CRISPR/Cas9 protocol and then generated germline chimeric roosters by cell transplantation into recipient embryos. Two generation-zero founder roosters produced hIFN-β knock-in offspring, and all knock-in female offspring produced abundant egg-white hIFN-β (~3.5 mg/ml). Although female offspring of the first generation were sterile, their male counterparts were fertile and produced a second generation of knock-in hens, for which egg-white hIFN-β production was comparable with that of the first generation. The hIFN-β bioactivity represented only ~5% of total egg-white hIFN-β, but unfolding and refolding of hIFN-β in the egg white fully recovered the bioactivity. These results suggest that transgene insertion at the chicken ovalbumin locus can result in abundant and stable expression of an exogenous protein deposited into egg white and should be amenable to industrial applications.

Analyses of chicken sialyltransferases related to O-glycosylation

The chicken β-galactoside α2,3-sialyltransferase 1, 2, and 5 (ST3Gal1, 2, and 5) genes were cloned, and their enzymes were expressed in 293FT cells. ST3Gal1 and 2 exhibited enzymatic activities toward galactose-β1,3-N-acetylgalactosamine and galactose-β1,3-N-acetylglucosamine. ST3Gal5 only exhibited activity toward lactosylceramide. ST3Gal1 and 2 and previously cloned ST3Gal3 and 6 transferred CMP-sialic acid to asialofetuin. Reverse-transcription-quantitative PCR indicated that ST3Gal1 was expressed at higher levels in the trachea, lung, spleen, and magnum, and the strong expression of ST3Gal5 was observed in the spleen, magnum, and small and large intestines. ST3Gal1, 5, and 6 were also expressed in the tubular gland cells of the magnum, which secretes egg-white proteins. ST3Gal1, 5, and 6 were expressed in the egg chorioallantoic membrane, in which influenza viruses are propagated for the production of vaccines.

Analyses of chicken sialyltransferases related to N-glycosylation

Proteins exogenously expressed and deposited in the egg whites of transgenic chickens did not contain terminal sialic acid in their N-glycan. Since this sugar is important for the biological stability of therapeutic proteins, we examined chicken sialyltransferases (STs). Based on homologies in DNA sequences, we cloned and expressed several chicken STs, which appeared to be involved in N-glycosylation in mammals, in 293FT cells. Enzymatic activity was detected with ST3Gal3, ST3Gal6 and ST6Gal1 using galactose-β1,4-N-acetylglucosamine (Galβ1,4GlcNAc) as an acceptor. Using Golgi fractions from the cell-free extracts of chicken organs, α2,3- and/or α2,6-ST activities were detected in the liver and kidney, but were absent in the oviduct cells in which egg-white proteins were produced. This result suggested that the lack of ST activities in oviduct cells mainly caused the lack of sialic acid in the N-glycan of proteins exogenously expressed and deposited in egg white.