Recombinant protein expression in milk of livestock species

Genetically modified animals for use in biopharmacology: from research to production

Introduction: In this review, the analysis of technologies for obtaining biologically active proteins from various sources is carried out, and the comparative analysis of technologies for creating producers of biologically active proteins is presented. Special attention is paid to genetically modified animals as bioreactors for the pharmaceutical industry of a new type. The necessity of improving the technology of development transgenic rabbit producers and creating a platform solution for the production of biological products is substantiated.

The advantages of using TrB for the production of recombinant proteins: The main advantages of using TrB are the low cost of obtaining valuable complex therapeutic human proteins in readily accessible fluids, their greater safety relative to proteins isolated directly from human blood, and the greater safety of the activity of the native protein.

The advantages of the mammary gland as a system for the expression of recombinant proteins: The mammary gland is the organ of choice for the expression of valuable recombinant proteins because milk is easy to collect in large volumes.

Methods for obtaining transgenic animals: The modern understanding of the regulation of gene expression and the discovery of new tools for gene editing can increase the efficiency of creating bioreactors for animals and help to obtain high concentrations of the target protein.

The advantages of using rabbits as bioreactors producing recombinant proteins in milk: The rabbit is a relatively small animal with a short duration of gestation, puberty and optimal size, capable of producing up to 5 liters of milk per year per female, receiving up to 300 grams of the target protein.

Site-specific integration of rotavirus VP6 gene in rabbit β-casein locus by CRISPR/Cas9 system

Rotavirus (RV) is the leading cause of viral gastroenteritis in neonates and VP6 protein has been discussed as a potential candidate vaccine. CRISPR/Cas9 was the latest generation of gene editing tools that can mediate the site-specific knock-in of exogenous genes, providing strong support for the expression of recombinant proteins. Here, seeking to design a rotavirus vaccine that would be suitable for both mammary-gland-based production and milk-based administration, rabbit β-casein (CSN2) locus was chosen as the target site to integrate the VP6 gene. The efficiency of inducing mutations in different target sites of rabbit CSN2 locus was analyzed and g4 site seems to be the best one to generate mutations (g4 72.76 ± 0.32% vs g1 30.14 ± 1.93%, g2 38.53 ± 0.75%, g3 52.26 ± 1.16%, P < 0.05). We further compared the knock-in efficiency through cytoplasmic injection of two group mixtures (containing 100 ng/μL Cas9 mRNA or Cas9 protein, 20 ng/μL sgRNA4, and 100 ng/μL donor vector) in rabbit zygotes, though the Cas9 mRNA group induced an HDR efficiency as high as 20.0% ± 2.6% than Cas9 protein group (10.3% ± 3.1%), 37.5% of the knock-in events were partial integration in the target site, when Cas9 protein used in the CRISPR/Cas9 system, all of the positive blastocysts showed completely integrated, results showed that the use of Cas9 protein is better than Cas9 mRNA to integrate the correct exogenous gene into the target site. Moreover, the transgenic rabbit that harbored correct integration of VP6 gene was obtained using Cas9 protein group and was used to produce an experimental milk-based rotavirus vaccine. Our research provides a novel strategy to produce rotavirus subunit vaccine and make a foundation for building broader milk-based vaccine protection against other pathogens.

A milk-based self-assemble rotavirus VP6-ferritin nanoparticle vaccine elicited protection against the viral infection

BACKGROUND

Rotavirus is the leading cause of severe dehydrating diarrhea in young children and the inner capsid protein VP6 is a potential vaccine candidate that can induce cross-protective immune responses against different Rotavirus strains. The use of ferritin nanoparticles as the scaffold of the antigen can improve the immunogenicity of the subunit vaccines and provide broader protection. We here present a non-live and self-assemble recombinant rotavirus VP6-ferritin (rVP6-ferritin) nanoparticle vaccine.

RESULTS

The rVP6-ferritin nanoparticles were expressed in E. coli and self-assembled to uniform spherical structure which similar to ferritin, and oral administration of them induced efficient humoral and mucosal immunogenicity in mice. The nanoparticles were further transgenically expressed in the milk of mice, and pup mice breastfed by transgenic rVP6-ferritin mothers had strongly induced immunogenicity and-compared to pups breastfed by wild type mothers-the proportion of rotavirus challenged pups with diarrhea symptoms, the duration and intensity of the diarrhea, and the deleterious effects on overall growth resulting from the diarrhea were all significantly reduced.

CONCLUSIONS

These results suggest that this recombinant VP6-ferritin nanoparticle vaccine can efficiently prevent the death and malnutrition induced by the rotavirus infection in infants and is a promising candidate vaccine for rotavirus.

Expression systems and species used for transgenic animal bioreactors

Transgenic animal bioreactors can produce therapeutic proteins with high value for pharmaceutical use. In this paper, we compared different systems capable of producing therapeutic proteins (bacteria, mammalian cells, transgenic plants, and transgenic animals) and found that transgenic animals were potentially ideal bioreactors for the synthesis of pharmaceutical protein complexes. Compared with other transgenic animal expression systems (egg white, blood, urine, seminal plasma, and silkworm cocoon), the mammary glands of transgenic animals have enormous potential. Compared with other mammalian species (pig, goat, sheep, and cow) that are currently being studied as bioreactors, rabbits offer many advantages: high fertility, easy generation of transgenic founders and offspring, insensitivity to prion diseases, relatively high milk production, and no transmission of severe diseases to humans. Noticeably, for a small- or medium-sized facility, the rabbit system is ideal to produce up to 50 kg of protein per year, considering both economical and hygienic aspects; rabbits are attractive candidates for the mammary-gland-specific expression of recombinant proteins. We also reviewed recombinant proteins that have been produced by targeted expression in the mammary glands of rabbits and discussed the limitations of transgenic animal bioreactors.

Expression of the human granulocyte-macrophage colony stimulating factor (hGM-CSF) gene under control of the 5'-regulatory sequence of the goat alpha-S1-casein gene with and without a MAR element in transgenic mice

Expression of the human granulocyte-macrophage colony-stimulating factor (hGM-CSF) gene under the control of the 5'-regulatory sequence of the goat alpha-S1-casein gene with and without a matrix attachment region (MAR) element from the Drosophila histone 1 gene was studied in four and eight transgenic mouse lines, respectively. Of the four transgenic lines carrying the transgene without MAR, three had correct tissues-specific expression of the hGM-CSF gene in the mammary gland only and no signs of cell mosaicism. The concentration of hGM-CSF in the milk of transgenic females varied from 1.9 to 14 μg/ml. One line presented hGM-CSF in the blood serum, indicating ectopic expression. The values of secretion of hGM-CSF in milk of 6 transgenic lines carrying the transgene with MAR varied from 0.05 to 0.7 μg/ml, and two of these did not express hGM-CSF. Three of the four examined animals from lines of this group showed ectopic expression of the hGM-CSF gene, as determined by RT-PCR and immunofluorescence analyses, as well as the presence of hGM-CSF in the blood serum. Mosaic expression of the hGM-CSF gene in mammary epithelial cells was specific to all examined transgenic mice carrying the transgene with MAR but was never observed in the transgenic mice without MAR. The mosaic expression was not dependent on transgene copy number. Thus, the expected "protective or enhancer effect" from the MAR element on the hGM-CSF gene expression was not observed.

Hybrid expression cassettes consisting of a milk protein promoter and a cytomegalovirus enhancer significantly increase mammary-specific expression of human lactoferrin in transgenic mice

It is very important to develop an effective, specific, and robust expression cassette that ensures a high level of expression in the mammary glands. In this study, we designed and constructed a series of mammary gland-specific vectors containing a complex hybrid promoter/enhancer by utilizing promoter sequences from milk proteins (i.e., goat β-casein, bovine αs1-casein, or goat β-lactoglobulin) and cytomegalovirus enhancer sequences; vectors containing a single milk protein promoter served as controls. Chicken β-globin insulator sequences were also included in some of these vectors. The expression of constructs was analyzed through the generation of transgenic mice. Enzyme-linked immunosorbent assay (ELISA) analysis revealed that the hybrid promoter/enhancer could drive the expression of recombinant human lactoferrin (rhLF) cDNA at high levels (1.17-8.10 mg/ml) in the milk of transgenic mice, whereas control promoters achieved a very low rhLF expression (7-40 ng/ml). Moreover, the expression of rhLF was not detected in the serum or saliva of any transgenic animal. This result shows that all constructs, driven by the hybrid promoter/enhancer, had high mammary gland-specific expression pattern. Together, our results suggest that the use of a hybrid promoter/enhancer is a valuable alternative approach for increasing mammary-specific expression of recombinant hLF in a transgenic mouse model.