Expression of human growth hormone in the milk of transgenic rabbits with transgene mapped to the telomere region of chromosome 7q

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.

Structural and functional characterization of recombinant human growth hormone isolated from transgenic pig milk

This study aimed to establish and reproduce transgenic pigs expressing human growth hormone (hGH) in their milk. We also aimed to purify hGH from the milk, to characterize the purified protein, and to assess the potential of our model for mass production of therapeutic proteins using transgenic techniques. Using ~15.5 L transgenic pig milk, we obtained proteins with ≥ 99% purity after three pre-treatments and five column chromatography steps. To confirm the biosimilarity of our milk-derived purified recombinant hGH (CGH942) with commercially available somatropin (Genotropin), we performed spectroscopy, structural, and biological analyses. We observed no difference between the purified protein and Genotropin samples. Furthermore, rat models were used to assess growth promotion potential. Our results indicate that CGH942 promotes growth, by increasing bone development and body weight. Toxicity assessments revealed no abnormal findings after 4 weeks of continuous administration and 2 weeks of recovery. The no-observed-adverse-effect level for both males and females was determined to be 0.6 mg/kg/day. Thus, no toxicological differences were observed between commercially available somatropin and CGH942 obtained from transgenic pig milk. In conclusion, we describe a transgenic technique using pigs, providing a new platform to produce human therapeutic proteins.

A novel recombinant human plasminogen activator: Efficient expression and hereditary stability in transgenic goats and in vitro thrombolytic bioactivity in the milk of transgenic goats

BACKGROUND

Thromboses is a rapidly growing medical problem worldwide. Low-cost, high-scale production of thrombotic drugs is needed to meet the demand. The production of biomolecules in transgenic animals might help address this issue. To our knowledge, the expression of recombinant human plasminogen activator (rhPA) in goat mammary glands has never been reported before.

METHODS

We constructed a mammary gland-specific expression vector, BLC14/rhPA, which encodes only the essential K2 fibrin-binding and P domains of wild-type tPA (deletion mutant of tPA lacking the F, E, and K1 domains), along with the goat β-lactoglobulin gene signal peptide-coding sequence. The mammary gland-specific expression vector BLC14/rhPA was transfected into goat fetal fibroblast cells by electroporation. After selection for 3 weeks by G418, stably transfected cell colonies were obtained. PCR analysis results indicated that 24 of the resistant clones were transgenic cell lines; of these, 8 lines were selected as the donor cells. The positive cells were starved for 72 h with DMEM/F12 medium containing 0.5% FBS and were then used as do. Finally, 256 reconstructed oocytes were transferred into 26 recipients, and 7 of them became pregnant (pregnancy rate, 26.9%). Two kids were obtained (BP21 and BP22). PCR analysis confirmed that both were transgenic goats. To analyze the heredity of the rhPA expressed in BP21 F0 and F1 transgenic goats, the F0 transgenic goat BP21 was mated with a normal male goat to generate an F1 transgenic goat. Enucleated metaphase II (MII) oocytes and positive donor cells were used to reconstruct embryos, which were transplanted into the oviducts of the recipients.

RESULTS

Western blot results showed a specific 39 kDa band. The rhPA expression level in transgenic goat whey was about 78.32 μg/mL by ELISA. Results of ELISA and the in vitro thrombolysis test (FAPA) showed that specific activity of the rhPA in the milk of F0 and F1 transgenic goats was 13.3 times higher than that of the reteplase reference material.

CONCLUSION

Thus, we demonstrated that BLC14/rhPA was reasonably effective for expression in the mammary glands of transgenic goats, and was stably inherited by the offspring. This study provides the basis for the large-scale production of biological pharmaceuticals in transgenic animals. The expression of biopharmaceuticals by transgenic animals can be used for pharmacological research and bioactive analysis, and transgenic goats were demonstrated to be promising animals for the large-scale production of thrombolytic biopharmaceuticals.

Production of functional human CuZn-SOD and EC-SOD in bitransgenic cloned goat milk

Human copper/zinc superoxide dismutase (CuZn-SOD) and extracellular superoxide dismutase (EC-SOD) are two superoxide dismutases that scavenge reactive oxygen species (ROS). Their biological role of eliminating oxidative stress caused by excessive ROS levels in living organisms has been utilized in medical treatment, preventing skin photoaging and food preservation. In this study, we employed two sequences that encode human CuZn-SOD and EC-SOD, along with goat beta-casein 5' and 3' regulatory elements, to construct mammary gland-specific expression vectors. Bitransgenic goats were generated using somatic cell nuclear transfer (SCNT), which employed co-transfection to generate bitransgenic goat fetal fibroblast cells as donor cells, and the expression of human CuZn-SOD and EC-SOD and their biological activities were assayed in the milk. PCR and Southern blot analysis confirmed that the cloned goat harbors both hCuZn-SOD and hEC-SOD transgenes. rhCuZn-SOD and rhEC-SOD were expressed in the mammary glands of bitransgenic goat, as determined by western blotting. The expression levels were 100.14 ± 5.09 mg/L for rhCuZn-SOD and 279.10 ± 5.38 mg/L for rhEC-SOD, as determined using ELISA. A total superoxide dismutase assay with WST-8 indicates that the biological activity of rhCuZn-SOD and rhEC-SOD in goat milk is 1451 ± 136 U/mL. The results indicate that two expression vectors can simultaneously transfect goat fetal fibroblast cells as donor cells to produce transgenic goats by SCNT, and the CuZn-SOD and EC-SOD proteins secreted in the mammary glands showed biological activity. The present study thus describes an initial step in the production of recombinant human SODs that may potentially be used for therapeutic purposes.

Biology and Diseases of Rabbits

Beginning in 1931, an inbred rabbit colony was developed at the Phipps Institute for the Study, Treatment and Prevention of Tuberculosis at the University of Pennsylvania. This colony was used to study natural resistance to infection with tuberculosis (Robertson et al., 1966). Other inbred colonies or well-defined breeding colonies were also developed at the University of Illinois College of Medicine Center for Genetics, the Laboratories of the International Health Division of The Rockefeller Foundation, the University of Utrecht in the Netherlands, and Jackson Laboratories. These colonies were moved or closed in the years to follow. Since 1973, the U.S. Department of Agriculture has reported the total number of certain species of animals used by registered research facilities (1997). In 1973, 447,570 rabbits were used in research. There has been an overall decrease in numbers of rabbits used. This decreasing trend started in the mid-1990s. In 2010, 210,172 rabbits were used in research. Despite the overall drop in the number used in research, the rabbit is still a valuable model and tool for many disciplines.

Construction and in vivo evaluation of a mammary gland-specific expression vector for human lysozyme

A mammary gland-specific expression vector p205C3 was constructed with the 5'- and 3'-flanking regions of β-lactoglobulin gene and the first intron of β-casein gene of Chinese dairy goat as regulatory sequences. Human lysozyme (hLYZ) cDNA from mammary gland was cloned into p205C3 and the recombinant vector was used to generate transgenic mice by microinjection. Based on the lysoplate assay, four female offspring of one male founder were detected expressing recombinant hLYZ in their milk at the levels of 5-200 mg/l, and the expressed protein had the same molecular weight as that of normal hLYZ. Besides mammary glands, ectopic expressions were also found in the spleens and the small intestines of the transgenic mice. Among the offspring, the female transgenic mice maintained and expressed the transgene stably with a highest expression level of 750 mg/l. Therefore, p205C3 could be used to develop animal mammary gland bioreactors expressing hLYZ.

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.