Production of recombinant tumor necrosis factor receptor/Fc fusion protein by genetically manipulated chickens

Genetically engineered birds; pre-CRISPR and CRISPR era

Generating biopharmaceuticals in genetically engineered bioreactors continues to reign supreme. Hence, genetically engineered birds have attracted considerable attention from the biopharmaceutical industry. Fairly recent genome engineering methods have made genome manipulation an easy and affordable task. In this review, we first provide a broad overview of the approaches and main impediments ahead of generating efficient and reliable genetically engineered birds, and various factors that affect the fate of a transgene. This section provides an essential background for the rest of the review, in which we discuss and compare different genome manipulation methods in the pre-CRISPR and CRISPR era in the field of avian genome engineering.

Reproductive management of poultry

Based on data from the UN's Food and Agricultural Organization, about 120 million metric tons of poultry meat were produced globally in 2016. In addition, about 82 million metric tons of eggs were produced. One of the bases for this production is the reproductive efficiency of today's poultry. This, in turn, is due to their inherent reproductive physiology, intensive genetic selection and advances in husbandry/management. The system of reproduction in males in largely similar to that in mammals except that there is no descent of testes. In females, there are marked differences with there being a single ovary and oviduct; the latter being the name of the differentiated entire Müllerian duct. Moreover, females produce eggs with a yolky oocyte surrounded by albumen, membranes and shell. Among the most successful reproductive management techniques are optimizing photoperiod, light intensity and nutrition. Widespread employment of these has allowed maximizing production. Laying hens can be re-cycled toward the end egg production. Other aspects of reproductive management in poultry include the following: artificial insemination (almost exclusively employed in turkeys) and approaches to reduce broodiness together with cage free (colony), conventional, enriched and free-range systems.

Expression of interferon-inducible transmembrane proteins in the chicken and possible role in prevention of viral infections

In mammals, interferon-inducible transmembrane proteins (IFITMs) prevent infections by various enveloped viruses. The expression of IFITMs in chicken was herein examined in the adult and embryonic organs using a quantitative reverse-transcription-polymerase chain reaction. The results obtained revealed that IFITM3 was expressed at a higher level than IFITM1, 2 and 5, in both embryonic and adult organs. However, the expression levels of IFITMs in embryonic organs were less than 5 % of those in adult lungs. Among the embryonic tissues examined, primordial germ cells (PGCs) at day 2.5 expressed relatively higher levels of IFITM3. IFITM3 expression levels were 1.5-fold higher in the chicken cell line DF-1 than in PGCs. The knockdown of IFITM3 in DF-1 cells by siRNA increased the infectivity of a vesicular stomatitis virus G protein-pseudotyped lentiviral vector, suggesting that lower levels of IFITM3 are still sufficient to restrict this viral vector.

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.

Production of transgenic chickens from purified primordial germ cells infected with a lentiviral vector

Replication-defective retroviral or lentiviral vectors have been used for the production of transgenic animals. Chicken primordial germ cells (PGCs) are the precursors for ova and spermatozoa. Here, we describe the production of transgenic chickens via a germline transmission system using PGCs infected with a replication-defective lentiviral vector. PGCs were sorted with a fluorescence-activated cell sorter based on the expression of stage-specific embryonic antigen-1 from 2.5- and 5.5-day embryos. PGCs from both stages of embryo were infected with a lentiviral vector at a similar efficiency in vitro. PGCs were then transferred into the bloodstream of 2.5-day recipient embryos. The efficiency with which the PGCs were delivered and settled in the gonads was lower for PGCs from 5.5-day embryos than those from 2.5-day embryos when a limited number of PGCs was transferred, while the difference was not obvious upon the transfer of increased number of cells. Using a high number of 5.5-day PGCs infected with a lentiviral vector, transgenic chimeras (G(0)) with an acceptable efficiency for germline transmission were obtained. G(0) female chickens produced transgenic progeny (G(1)) with higher efficiency compared to G(0) male chickens. In G(1) transgenic chickens obtained by this method, enhanced green fluorescent protein was effectively expressed under the control of the actin promoter.

Production of recombinant human erythropoietin/Fc fusion protein by genetically manipulated chickens

We previously reported the production of human erythropoietin (hEpo) using genetically manipulated (GM) chickens. The recombinant hEpo was produced in the serum and egg white of the GM chickens, and the oligosaccharide chain structures of the serum-derived hEpo were more favorable than those of the egg white-derived hEpo. In the present study, a retroviral vector encoding an expression cassette for a fusion protein of hEpo and the Fc region of human immunoglobulin G (hEpo/Fc) was injected into developing chicken embryos, with the aim of recovering the serum-derived hEpo from egg yolk through the yolk accumulation mechanism of maternal antibodies. The GM chickens that hatched stably produced the hEpo/Fc fusion protein not only in their serum and egg white, but also in the egg yolk as expected. Lectin blot analyses revealed that significant amounts of the oligosaccharide chains of hEpo/Fc produced in the serum and eggs of GM chickens terminated with galactose, and that the oligosaccharide chains of the serum- and yolk-derived hEpo/Fc incorporated sialic acid residues. Moreover, biological activity assessment using Epo-dependent cells revealed that the yolk-derived hEpo/Fc exhibited a comparable performance to the serum- and CHO-derived hEpo/Fc. These results indicate that transport of Fc fusion proteins from the blood circulation to the yolk in chickens represents an effective strategy for the production of pharmaceutical glycoproteins using transgenic chicken bioreactors.

Production of recombinant human lactoferrin in the allantoic fluid of embryonated chicken eggs and its characteristics

The human iron-binding protein lactoferrin (hLf) has been implicated in a number of important physiological pathways, including those regulating immune function and tumor growth. In an effort to develop an efficient system for production of recombinant hLf (rhLf) that is structurally and functionally equivalent to the natural protein, we generated a recombinant CELO (chicken embryo lethal orphan) avian adenovirus containing an expression cassette for hLf. Embryonated chicken eggs were infected with the generated CELO-Lf virus. rhLf expression was measured in the allantoic fluid of infected eggs by ELISA three days later. The level of recombinant protein was about 0.8mg per embryo. rhLf was efficiently purified (up to 85% yield) from the allantoic fluid of infected eggs using affinity chromatography. rhLf produced in the allantoic fluid was characterized in comparison with natural hLf (nhLf) purified from human breast milk. SDS-PAGE, Western blotting and glycosylation analyzes showed that the recombinant protein had similar physical characteristics to nhLf. In addition, we demonstrated that the antioxidative and antimicrobial activity of rhLf produced in this system is equivalent to that of nhLf. Taken together, these results illustrate the utility of the described "recombinant CELO adenovirus-chicken embryo" system for production of functionally active rhLf. Efficient production of rhLf with accurate structure and function is an important step in furthering investigation of Lf as a potential human drug.