Production of pharmaceutical proteins from transgenic animals

Detection of recombinant human lactoferrin and lysozyme produced in a bitransgenic cow

Lactoferrin and lysozyme are 2 glycoproteins with great antimicrobial activity, being part of the nonspecific defensive system of human milk, though their use in commercial products is difficult because human milk is a limited source. Therefore, many investigations have been carried out to produce those proteins in biological systems, such as bacteria, yeasts, or plants. Mammals seem to be more suitable as expression systems for human proteins, however, especially for those that are glycosylated. In the present study, we developed a bicistronic commercial vector containing a goat β-casein promoter and an internal ribosome entry site fragment between the human lactoferrin and human lysozyme genes to allow the introduction of both genes into bovine adult fibroblasts in a single transfection. Embryos were obtained by somatic cell nuclear transfer, and, after 6 transferences to recipients, 3 pregnancies and 1 viable bitransgenic calf were obtained. The presence of the vector was confirmed by fluorescent in situ hybridization of skin cells. At 13 mo of life and after artificial induction of lactation, both recombinant proteins were found in the colostrum and milk of the bitransgenic calf. Human lactoferrin concentration in the colostrum was 0.0098 mg/mL and that in milk was 0.011 mg/mL; human lysozyme concentration in the colostrum was 0.0022 mg/mL and that in milk was 0.0024 mg/mL. The molar concentration of both human proteins revealed no differences in protein production of the internal ribosome entry site upstream and downstream protein. The enzymatic activity of lysozyme in the transgenic milk was comparable to that of human milk, being 6 and 10 times higher than that of bovine lysozyme present in milk. This work represents an important step to obtain multiple proteins or enhance single protein production by using animal pharming and fewer regulatory and antibiotic-resistant foreign sequences, allowing the design of humanized milk with added biological value for newborn nutrition and development. Transgenic animals can offer a unique opportunity to the dairy industry, providing starting materials suitable to develop specific products with high added value.

The transgenic animal platform for biopharmaceutical production

The recombinant production of therapeutic proteins for human diseases is currently the largest source of innovation in the pharmaceutical industry. The market growth has been the driving force on efforts for the development of new therapeutic proteins, in which transgenesis emerges as key component. The use of the transgenic animal platform offers attractive possibilities, residing on the low production costs allied to high productivity and quality of the recombinant proteins. Although many strategies have evolved over the past decades for the generation of transgenic founders, transgenesis in livestock animals generally faces some challenges, mainly due to random transgene integration and control over transgene copy number. But new developments in gene editing with CRISPR/Cas system promises to revolutionize the field for its simplicity and high efficiency. In addition, for the final approval of any given recombinant protein for animal or human use, the production and characterization of bioreactor founders and expression patterns and functionality of the proteins are technical part of the process, which also requires regulatory and administrative decisions, with a large emphasis on biosafety. The approval of two mammary gland-derived recombinant proteins for commercial and clinical use has boosted the interest for more efficient, safer and economic ways to generate transgenic founders to meet the increasing demand for biomedical proteins worldwide.

Methodological strategies for transgene copy number quantification in goats (Capra hircus) using real-time PCR

Taking into account the importance of goats as transgenic models, as well as the rarity of copy number (CN) studies in farm animals, the present work aimed to evaluate methodological strategies for accurate and precise transgene CN quantification in goats using quantitative polymerase chain reaction (qPCR). Mouse and goat lines transgenic for human granulocyte-colony stimulating factor were used. After selecting the best genomic DNA extraction method to be applied in mouse and goat samples, intra-assay variations, accuracy and precision of CN quantifications were assessed. The optimized conditions were submitted to mathematical strategies and used to quantify CN in goat lines. The findings were as follows: validation of qPCR conditions is required, and amplification efficiency is the most important. Absolute and relative quantifications are able to produce similar results. For normalized absolute quantification, the same plasmid fragment used to generate goat lines must be mixed with wild-type goat genomic DNA, allowing the choice of an endogenous reference gene for data normalization. For relative quantifications, a resin-based genomic DNA extraction method is strongly recommended when using mouse tail tips as calibrators to avoid tissue-specific inhibitors. Efficient qPCR amplifications (≥95%) allow reliable CN measurements with SYBR technology. TaqMan must be used with caution in goats if the nucleotide sequence of the endogenous reference gene is not yet well understood. Adhering to these general guidelines can result in more exact CN determination in goats. Even when working under nonoptimal circumstances, if assays are performed that respect the minimum qPCR requirements, good estimations of transgene CN can be achieved.

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

The advent of transgenic technology has provided methods for the production of pharmaceuticals by the isolation of these proteins from transgenic animals. The mammary gland has been focused on as a bioreactor, since milk is easily collected from lactating animals and protein production can be expressed at very high levels, including hormones and enzymes. We demonstrate here the expression pattern of recombinant human growth hormone (rhGH) in transgenic rabbits carrying hGH genomic sequences driven by the rat whey acidic protein (WAP) promoter. The transgene was mapped to the q26-27 telomere region of chromosome 7q by fluorescence in situ hybridization (FISH). Nearly 30 % of the F1 generation demonstrated the presence of transgene. The recombinant growth hormone was detected in the milk of the transgenic rabbit females, but not in serum, up to the level of 10 μg/ml. Ectopic expression of the transgene in the brain, heart, kidney, liver, and salivary gland was not observed, indicating that a short sequence of rat WAP promoter (969 bp) contained essential sequences directing expression exclusively to the mammary gland. The biological activity of recombinant growth hormone was measured by immunoreactivity and the capability to stimulate growth of the hormone-dependent Nb211 cell line.

Laparoscopy vs. laparotomy for embryo transfer to produce transgenic goats (Capra hircus)

This study was performed to produce transgenic Korean native goat (Capra hircus) by laparoscopic embryo transfer (ET) to overcome the limitations of ET performed by laparotomy. Transgenic embryos were produced by DNA pronuclear microinjection of in vivo zygotes. The recipient goats were synchronized for estrus by using an introvaginal progesterone devices as a controlled internal drug-releasing insert (CIDR) for 13 days and injection of 400 IU PMSG 48 h before removal of the insert. Embryos were transferred on day 3 and 4 after removal of the insert. Recipient goats were deprived of feed for 48 h, then suspended in a laparotomy cradle at an angle of 45°. After obtaining a sufficient pneumoperitoneum, the laparoscope and forceps were inserted abdominally through 5 mm trocar sleeves. Examination of the ovaries and uterus was performed and then 213 embryos were transferred into the oviducts via the infundibula of 76 recipient goats. To compare pregnancy rates, ET was also performed by laparotomy in 82 recipient goats. The pregnancies in the recipient goats were diagnosed by ultrasound on day 30 after embryo transfer. The pregnancy rate with laparoscopic ET was significantly higher than with ET performed by laparotomy (46.1% vs. 28.6%, p < 0.05). In addition, the pregnancy rates were compared between ovulated and non-ovulated ovaries of the recipient goats in the laparoscopic ET group. No significant difference was observed between the pregnancy rates of ovulated and non-ovulated ovaries (41.3% vs. 33.3%, p < 0.05) suggesting that ET may also be possible in non-ovulated recipients through artificial rupture of Graafian follicles. These results suggest that laparoscopic ET is a highly efficient method for the transfer of goat embryos.

Characterization of maleuric acid derivatives on transgenic human monoclonal antibody due to post-secretional modifications in goat milk

A fully human antibody to tumor necrosis factor-alpha was expressed in the mammary glands of transgenic goats. The goat expressed antibody (gAb) is heterogeneous and has several isoforms due to typical cellular post-translational modifications. In addition, one post-secretional modification on gAb was discovered by high-resolution cation exchange chromatography (CIEX). The presence of these variants in the final product was shown to be dependent upon the initial milk storage and traditional purification methodologies used. These observations allow for the development of new sample recovery and purification processes to eliminate these variants. Various enzymatic treatments were used to characterize different gAb heavy chain C-terminal lysine and sialic acid variants. In addition, an unknown derivative with the additional mass of 140 Da was found in transgenic gAb using mass spectrometry (MS). The modification sites were identified as the N-termini of gAb light chains and heavy chains using Q-TOF MS. Characterization of transgenic gAb isoforms was facilitated by utilizing different enzymes, CIEX and MS techniques. A maleuric acid modification on the N-terminal portion of gAb was shown to be consistent with the available data characterizing this new derivative of transgenic gAb isoforms in goat milk.

Ectopic expression of tethered human follicle-stimulating hormone (hFSH) gene in transgenic mice

To determine whether the mammary gland can be used to secrete large quantities of a bioactive heterodimeric protein into milk, we used a bovine beta-casein promoter to target and express human follicle-stimulating hormone (hFSH) in the mammary gland into the milk of transgenic mice. We also identified the effects of hFSH leaked into the bloodstream. Transgenic mice produced a high level (up to 300 mIU/ml) of recombinant hFSH in the mammary gland. Human FSH was expressed in the mammary gland and brain, as determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. In vitro bioactivity was also identified by cyclic AMP (cAMP) assay. The highest activity was showed in the transgenic mice line 11. However, hFSH leaked into the bloodstream was a powerful factor in the generation of breast and ovarian tumors from the transgenic mice line 11. These results suggest that change of endogenous hormones (FSH and progesterone) may affect the morphology and blood cell counts of peripheral blood and, especially, provoke breast and ovarian tumors.

Transgene expression of biological active recombinant human granulocyte-colony stimulating factor (hG-CSF) into mouse urine

We have generated transgenic mice that expressed human granulocyte-colony stimulating factor (hG-CSF) in their urine. In particular, the expression plasmid DNA containing mouse uroplakin II promoter was used to direct the uroepithelium-specific transcription of the transgene. In this study, the hG-CSF transcript was detected only in bladder, as was determined by RT-PCR analysis. Furthermore, hG-CSF protein was detected in the suprabasal layer of the uroepithelium and ureter, as was demonstrated by immunohistochemistry. The hG-CSF was secreted into urine at a high level (approx. 500 pg/ml), and it was able to enhance the proliferation of DMSO treated HL-60 cells, suggesting that the transgenic urine-derived hG-CSF was bioactive. However, the recombinant hG-CSF was leaked to peripheral circulation system. To examine the relationship between hG-CSF in the blood stream and the proliferation of hematopoietic cells, we tested the transgenic mouse blood with hematocrit analysis. An increase of the total number of neutrophils in the transgenic mice peripheral blood was not observed; therefore, the leakage of human G-CSF can probably be expected to do no harm to the transgenic mouse. Our results demonstrate that bladder can be safely used as a bioreactor to produce biologically important substances such as recombinant G-CSF.

Cloning and characterization of 5' upstream promoter region of rat WAP gene

Regulatory regions of genes encoding milk proteins are frequently used to produce in the mammary gland of transgenic animals a variety of pharmaceutically and medically important human proteins. One such example is the whey acidic protein (WAP) promoter region, identified so far in the genome of mouse, rat, rabbit, camel, pig, brushtail possum and Tammar wallaby. The aim of the present study was cloning and characterization of the 5' upstream promoter region of rat WAP gene. Using Genome Walking procedure, we cloned the region extending from -849 to -3671 bp. We have shown that there are two conserved regions highly similar to hypersensitive sites present in mouse and rabbit upstream region of WAP gene with binding sites for STAT5 transcription factor, essential for expression of WAP gene in mammary glands during lactation. We characterized dispersed and tandem repeats in the upstream region of rat WAP gen localized not far away from the translation initiation site.

Renal tubule-specific expression and urinary secretion of human growth hormone: a kidney-based transgenic bioreactor growth

Tissue-specific expression of human genes and secretion of human proteins into the body fluids in transgenic animals provides an important means of manufacturing large-quantity and high-quality pharmaceuticals. The present study demonstrates using transgenic mice that a 3.0 kb promoter of the mouse Tamm-Horsfall protein (THP, or uromodulin) gene directs the specific expression of human growth hormone (hGH) gene in the kidney followed by the secretion of hGH protein into the urine. hGH expression was detected in renal tubules that actively produce the THP, that is, the ascending limb of Henle's loop and distal convoluted tubules. Up to 500 ng/ml of hGH was detected in the urine, and this level remained constant throughout the 10-month observation period. hGH was also detectable in the stomach epithelium and serum in two of the transgenic lines, suggesting position-dependent effects of the transgene and leakage of hGH from the site of synthesis into the bloodstream, respectively. These results indicate that the 3.0 kb mouse THP promoter is primarily kidney-specific and can be used to convert kidney into a bioreactor in transgenic animals to produce recombinant proteins. Given the capacity of urine production independent of age, sex and lactation, the ease of urinary protein purification, and the potentially distinct machinery for post-translational modifications in the kidney epithelial cells, the kidney-based transgenic bioreactor may offer unique opportunities for producing certain complex pharmaceuticals.

Analysis of the flanking regions of the human alpha-lactalbumin gene responsible for position-effect independent expression

Transgenic rats with the 130 kb bacterial artificial chromosome construct bLA, including the alpha-lactalbumin gene, had position-independent and copy number-dependent expression, which confirmed previous experiments using the 210 kb yeast artificial construct, yLALBA. To identify elements that confer a position effect, we compared the yLALBA and bLA sequences. yLALBA was chimeric. A common 32 kb region was identified and the total nucleotide sequence was determined. We previously analyzed transgenic rats using polymerase chain reaction to compare the integrity and expression of the transgenes. The -6 to +9 kb region is considered to be necessary for position-independent expression. Transgenic rats lacking the -3.4 to -0.85 kb region had a severe position effect. This 2.5 kb region contains two DNaseI hypersensitive sites at -1.0 and -2.8 kb. The 2.5 kb region is proposed to be a locus control region of the human alpha-lactalbumin gene.

Gene transfer strategies in animal transgenesis

Position effects in animal transgenesis have prevented the reproducible success and limited the initial expectations of this technique in many biotechnological projects. Historically, several strategies have been devised to overcome such position effects, including the progressive addition of regulatory elements belonging to the same or to a heterologous expression domain. An expression domain is thought to contain all regulatory elements that are needed to specifically control the expression of a given gene in time and space. The lack of profound knowledge on the chromatin structure of expression domains of biotechnological interest, such as mammary gland-specific genes, explains why most standard expression vectors have failed to drive high-level, position-independent, and copy-number-dependent expression of transgenes in a reproducible manner. In contrast, the application of artificial chromosome-type constructs to animal transgenesis usually ensures optimal expression levels. YACs, BACs, and PACs have become crucial tools in animal transgenesis, allowing the inclusion of distant key regulatory sequences, previously unknown, that are characteristic for each expression domain. These elements contribute to insulating the artificial chromosome-type constructs from chromosomal position effects and are fundamental in order to guarantee the correct expression of transgenes.

New strategies to prevent mastitis

Bovine mastitis remains as the disease causing the biggest economic losses to the dairy industry, despite the intensive research and prevention measures at herd level carried out for decades. Antibiotics are widely used to combat mastitis, but focus should be shifted from treatment to more economical and efficient prevention. The bacteriological aetiology of mastitis has changed from contagious to environmental pathogens, which has reduced the efficacy of the traditional mastitis control strategies. Considerable progress in the understanding of epidemiology, immunology, diagnostics and pathogenesis of mastitis has been made. The modern molecular biological methods offer good possibilities for the research of the epidemiological and virulence aspects of bacteria, which may help in building-up specific mastitis control strategies for dairy herds. Studies on the host response and relationship between somatic cell count and susceptibility to mastitis offer tools for genetic improvement of dairy cows. Biotechnological approaches for mastitis prevention are in the developmental stage, but many problems are associated, e.g. with vaccination of dairy cows against mastitis. Different methods of immunomodulation for the prevention of mastitis have shown promise in experimental trials, but the evidence is not yet enough to support commercial applications. Improving nutrition, housing and environment of dairy cattle are still crucial in the prevention of mastitis, especially during the most susceptible period after parturition. New milking techniques including robotic milking may provide better possibility for proper milking and improved udder health. Mastitis control should be part of the herd health programme in the dairy herds. In this paper, results from recent research and proposals for new prevention strategies in the field of mastitis are reviewed.

Expression of recombinant human granulocyte macrophage-colony stimulating factor (hGM-CSF) in mouse urine

We have generated transgenic mice expressing human granulocyte macrophage-colony stimulating factor (hGM-CSF) in urine. In particular, the expression plasmid DNA containing mouse uroplakin II promoter was used to direct uroepithelium-specific transcription of transgene. In this study, hGM-CSF transcript was detected only in bladder uroepithelium as determined by northern blot analysis. Furthermore, hGM-CSF protein was detected in the suprabasal layer of the uroepithelium and ureter by immunohistochemistry. The hGM-CSF was secreted into urine at high level (up to 180 ng/ml), and enhanced proliferation of hGM-CSF-dependent human acute monocyte leukemic cells, suggesting that transgenic urine-derived hGM-CSF was bioactive. This is the first case of demonstrating biological activity of a cytokine produced in the urine of a transgenic animal. Our results demonstrate that bladder can be used as a bioreactor to produce biologically important substances. In addition, it suggests a potential application of bladder expression system to livestock for high-yield production of pharmaceuticals.

Transgenic farm animals: applications in agriculture and biomedicine

During the last decade, tremendous progress has been made in the area of transgenic farm animals. While there are many important transgenic farm animal applications in agriculture, funding has been very limited and progress has been rather slow in this area. Encouragingly, the potential applications of transgenic farm animals as bioreactors for producing human therapeutic proteins and as organ donors for transplantations in humans have attracted vast funding from the private sectors. Several transgenic animal products are already in various phases of clinical trials. Estimates are, that in the near future, the worlds demands on human pharmaceutical proteins may largely be met by transgenic farm animals. While there are still major challenges ahead in the area of xenotransplantation using transgenic animal organs, transgenic tissues or cells have demonstrated promising results as a potential tool for gene therapy. Recent development on cloning, embryonic stem cells and alternative transgenic methods may further expand the transgenic applications in both agriculture and biomedicine.

Transgenic livestock: premises and promises

Microinjection of DNA constructs into pronuclei of zygotes has been the method of choice for the generation of transgenic livestock. However, this procedure is characterized by low efficiency (1-4% transgenic offspring), random integration and variable expression of the transgene as well as a considerable proportion of mosaicism. Furthermore, it is extremely time consuming and costly. As a consequence, commercial application has focused on the production of recombinant proteins in the mammary gland of transgenic animals and xenotransplantation, e.g. the use of porcine organs in human organ transplantation. In addition, transgenic pigs carrying a modified porcine growth hormone (hMt-pGH) construct show significant improvements in economically important traits without adverse side effects of a GH overproduction. Improvements of transgenic technology will likely come from the generation of appropriate cell lines suitable for transfection or even homologous recombination and their subsequent use in nuclear transfer. Additionally, in the mouse a number of sophisticated molecular tools have been developed that allow precise modifications of the genome. These include the application of artificial chromosomes from yeast (YAC) or bacteria (BAC) for position-independent and copy-number-dependent expression of a transgene, the Tet-system (tetracycline inducible) for a tight temporal control of transgene expression, as well as conditional mutagenesis by applying site-specific DNA recombinases (e.g. Cre, FLP). The successful adaptation of these molecular tools to livestock will enable the fulfillment of many of the promises originally thought to be achievable when transgenic livestock were first reported.

Production of recombinant human type I procollagen homotrimer in the mammary gland of transgenic mice

The large scale production of recombinant collagen for use in biomaterials requires an efficient expression system capable of processing a large (> 400 Kd) multisubunit protein requiring post-translational modifications. To investigate whether the mammary gland of transgenic animals fulfills these requirements, transgenic mice were generated containing the alpha S1-casein mammary gland-specific promoter operatively linked to 37 Kb of the human alpha 1(I) procollagen structural gene and 3' flanking region. The frequency of transgenic lines established was 12%. High levels of soluble triple helical homotrimeric [(alpha 1)3] type I procollagen were detected (up to 8 mg/ml) exclusively in the milk of six out of 9 lines of lactating transgenic mice. The transgene-derived human procollagen chains underwent efficient assembly into a triple helical structure. Although proline or lysine hydroxylation has never been described for any milk protein, procollagen was detected with these post-translational modifications. The procollagen was stable in milk; minimal degradation was observed. These results show that the mammary gland is capable of expressing a large procollagen gene construct, efficiently assembling the individual polypeptide chains into a stable triple helix, and secreting the intact molecule into the milk.

Transgenic animal bioreactors

The production of recombinant proteins is one of the major successes of biotechnology. Animal cells are required to synthesize proteins with the appropriate post-translational modifications. Transgenic animals are being used for this purpose. Milk, egg white, blood, urine, seminal plasma and silk worm cocoon from transgenic animals are candidates to be the source of recombinant proteins at an industrial scale. Although the first recombinant protein produced by transgenic animals is expected to be in the market in 2000, a certain number of technical problems remain to be solved before the various systems are optimized. Although the generation of transgenic farm animals has become recently easier mainly with the technique of animal cloning using transfected somatic cells as nuclear donor, this point remains a limitation as far as cost is concerned. Numerous experiments carried out for the last 15 years have shown that the expression of the transgene is predictable only to a limited extent. This is clearly due to the fact that the expression vectors are not constructed in an appropriate manner. This undoubtedly comes from the fact that all the signals contained in genes have not yet been identified. Gene constructions thus result sometime in poorly functional expression vectors. One possibility consists in using long genomic DNA fragments contained in YAC or BAC vectors. The other relies on the identification of the major important elements required to obtain a satisfactory transgene expression. These elements include essentially gene insulators, chromatin openers, matrix attached regions, enhancers and introns. A certain number of proteins having complex structures (formed by several subunits, being glycosylated, cleaved, carboxylated...) have been obtained at levels sufficient for an industrial exploitation. In other cases, the mammary cellular machinery seems insufficient to promote all the post-translational modifications. The addition of genes coding for enzymes involved in protein maturation has been envisaged and successfully performed in one case. Furin gene expressed specifically in the mammary gland proved to able to cleave native human protein C with good efficiency. In a certain number of cases, the recombinant proteins produced in milk have deleterious effects on the mammary gland function or in the animals themselves. This comes independently from ectopic expression of the transgenes and from the transfer of the recombinant proteins from milk to blood. One possibility to eliminate or reduce these side-effects may be to use systems inducible by an exogenous molecule such as tetracycline allowing the transgene to be expressed only during lactation and strictly in the mammary gland. The purification of recombinant proteins from milk is generally not particularly difficult. This may not be the case, however, when the endogenous proteins such as serum albumin or antibodies are abundantly present in milk. This problem may be still more crucial if proteins are produced in blood. Among the biological contaminants potentially present in the recombinant proteins prepared from transgenic animals, prions are certainly those raising the major concern. The selection of animals chosen to generate transgenics on one hand and the elimination of the potentially contaminated animals, thanks to recently defined quite sensitive tests may reduce the risk to an extremely low level. The available techniques to produce pharmaceutical proteins in milk can be used as well to optimize milk composition of farm animals, to add nutriceuticals in milk and potentially to reduce or even eliminate some mammary infectious diseases.

Transgenic milk as a method for the production of recombinant antibodies

Recombinant antibodies and their derivatives are increasingly being used as therapeutic agents. Clinical applications of antibodies often require large amounts of highly purified molecules, sometimes for multiple treatments. The development of very efficient expression systems is essential to the full exploitation of the antibody technology. Production of recombinant protein in the milk of transgenic dairy animals is currently being tested as an alternative to plasma fractionation for the manufacture of a number of blood factors (human antithrombin, human alpha-1-antitrypsin, human serum albumin, factor IX). The ability to routinely yield mg/ml levels of antibodies and the scale-up flexibility make transgenic production an attractive alternative to mammalian cell culture as a source of large quantities of biotherapeutics. The following review examines the potential of transgenic expression for the production of recombinant therapeutic antibodies.

Transgenic rabbits for the production of biologically-active recombinant proteins in the milk

The use of live bioreactors for the expression of human genes in the mammary gland of transgenic animals is one of the most cost-effective ways for the production of valuable recombinant therapeutic proteins. Among the transgenic species used so far, rabbits are good candidates for the expression of tens to hundreds of grams of complex proteins in the milk during lactation. The lactating mammary gland of rabbits has proven to be effective in the processing of complex proteins. In this work. the potential use of rabbits as bioreactors is discussed based on our results and the published data.

Zona pellucida glycoprotein mZP3 produced in milk of transgenic mice is active as a sperm receptor, but can be lethal to newborns

Mouse egg zona pellucida glycoprotein mZP3 (approximately 83 kDa M(r)) serves as a species-specific sperm receptor and acrosome reaction-inducer during fertilization in mice. These biological activities are dependent on certain mZP3 serine/threonine- (O-) linked oligosaccharides present at the combining-site for sperm. In an attempt to produce large amounts of biologically active mZP3, we generated several transgenic mouse lines carrying the full-length mZP3 gene fused to the beta-casein gene promoter and transcription termination sequence. We found that different transgenic mouse lines have different amounts of recombinant mZP3 (approximately 63 kDa M(r)) in milk of lactating females, from approximately 0.3 to 3.5 micrograms/microliter of milk. In all cases, purified milk-mZP3 is active as a sperm receptor and acrosome reaction-inducer in vitro. Unexpectedly, we also found that development of litters from these transgenic mice is related to the amount of mZP3 in the mother's milk. In the most extreme case, litters from the highest expressers fail to live beyond about day-7 post partum unless placed immediately after birth with surrogate wild-type mothers. Litters from lower expressers initially display a complex phenotype that includes effects on hair and body growth, but some of the mice survive and, in time, are restored to a wild-type phenotype. These results demonstrate that relatively large amounts of biologically active mZP3 can be produced in transgenic mouse milk for structural and other studies, but that the presence of mZP3 in milk has dramatic developmental effects on litters, ranging from retarded hair and body growth to death of newborn pups.

Analysis of control elements for position-independent expression of human alpha-lactalbumin YAC

A major problem in the production of transgenic animal bioreactors using microinjections is the low production rate of high-expressing transgenic animals due to the position effect. We previously reported that transgenic rats carrying the 210 kb yeast artificial chromosome (YAC) including the human alpha-lactalbumin gene express the transgene in a position-independent manner. The 210 kb YAC was thought to have all the elements necessary for position-independent expression. In this paper, we constructed fragmented YAC clones and a cosmid clone, and produced transgenic rats to analyze these elements. Transgenic rats with both the 50 kb upstream and downstream regions of the alpha-lactalbumin gene had position-independent expression. Transgenic rats with the 20 kb upstream and downstream regions, however, had position-dependent expression. Therefore, all the elements necessary for position-independent expression are thought to be located in the 50 kb upstream to 50 kb downstream region of the alpha-lactalbumin gene. Furthermore, we replaced the human alpha-lactalbumin promoter with the bovine alphaS1-casein promoter in the 210 kb YAC and produced transgenic rats. Position-dependent expression was observed. The elements required for position-independent expression of the bovine alphaS1-casein gene are different from those required for the human alpha-lactalbumin gene, despite the fact that the two genes have the same tissue and developmental specificity.

High-level expressing YAC vector for transgenic animal bioreactors

The position effect is one major problem in the production of transgenic animals as mammary gland bioreactors. In the present study, we introduced the human growth hormone (hGH) gene into 210-kb human alpha-lactalbumin position-independent YAC vectors using homologous recombination and produced transgenic rats via microinjection of YAC DNA into rat embryos. The efficiency of producing transgenic rats with the YAC vector DNA was the same as that using plasmid constructs. All analyzed transgenic rats had one copy of the transgene and produced milk containing a high level of hGH (0.25-8.9 mg/ml). In transgenic rats with the YAC vector in which the human alpha-lactalbumin gene was replaced with the hGH gene, tissue specificity of hGH mRNA was the same as that of the endogenous rat alpha-lactalbumin gene. Thus, the 210-kb human alpha-lactalbumin YAC is a useful vector for high-level expression of foreign genes in the milk of transgenic animals.

Transgenic bioreactors

Since the generation of the first transgenic mice in 1980, transgene technology has also been successfully applied to large farm animals. Although this technology can be employed to improve certain production traits of livestock, this approach has not been very successful so far owing to unwanted effects encountered in the production animals. However, by using tissue-specific targeting of the transgene expression, it is possible to produce heterologous proteins in the extracellular space of large transgenic farm animals. Even though some recombinant proteins, such as human hemoglobin, have been produced in the blood of transgenic pigs, in the majority of the cases mammary gland targeted expression of the transgene has been employed. Using production genes driven by regulatory sequences of milk protein genes a number of valuable therapeutic proteins have been produced in the milk of transgenic bioreactors, ranging from rabbits to dairy cattle. Unlike bacterial fermentors, the mammary gland of transgenic bioreactors appear to carry out proper postsynthetic modifications of human proteins required for full biological activity. In comparison with mammalian cell bioreactors, transgenic livestock with mammary gland targeted expression seems to be able to produce valuable human therapeutic proteins at very low cost. Although not one transgenically produced therapeutic protein is yet on the market, the first such proteins have recently entered or even completed clinical trials required for their approval.

Transgenic animal bioreactors in biotechnology and production of blood proteins

The regulatory elements of genes used to target the tissue-specific expression of heterologous human proteins have been studied in vitro and in transgenic mice. Hybrid genes exhibiting the desired performance have been introduced into large animals. Complex proteins like protein C, factor IX, factor VIII, fibrinogen and hemoglobin, in addition to simpler proteins like alpha 1-antitrypsin, antithrombin III, albumin and tissue plasminogen activator have been produced in transgenic livestock. The amount of functional protein secreted when the transgene is expressed at high levels may be limited by the required posttranslational modifications in host tissues. This can be overcome by engineering the transgenic bioreactor to express the appropriate modifying enzymes. Genetically engineered livestock are thus rapidly becoming a choice for the production of recombinant human blood proteins.

Utilization of genetically altered animals in the pharmaceutical industry

The study of transgenic and gene-deleted (knockout) mice provides important insights into the in vivo function and interaction of specific gene products. Within the pharmaceutical industry, genetically altered mice are used predominantly in discovery research to characterize the diverse functions of one or multiple gene products or to establish animal models of human disease for proof-of-concept studies. We recently used genetically altered animals in drug discovery to examine the NF-kappaB family of transcriptional regulatory genes and to elucidate their essential role in the early onset of immune and inflammatory responses. Transgenic and knockout mice are also useful in drug development, because questions regarding risk assessment and carcinogenesis, xenobiotic metabolism, receptor- and ligand-mediated toxicity, and immunotoxicity can be evaluated using these genetically altered mice. For example, the p53 knockout mouse is one of several genetically altered mice whose use may increase the sensitivity and decrease the time and cost of rodent carcinogenicity bioassays. As with any experimental model system, data obtained from genetically altered mice must be interpreted carefully. The complete inactivation of a gene may result in altered expression of related genes or physiologic compensation for the loss of the gene product. Consideration must also be given to the genetic background of the mouse strain and the impact of strain variability on disease or toxicity models. Despite these potential limitations, knockout mice provide a powerful tool for the advancement of drugs in the pharmaceutical industry.

Stable production of human insulin-like growth factor 1 (IGF-1) in the milk of hemi- and homozygous transgenic rabbits over several generations

One transgenic rabbit line was generated carrying a fusion gene consisting of the cDNA for human IGF-1 fused to a mammary gland specific expression cassette derived from bovine alpha-S1-casein sequences. Transgene expression was shown to be strictly tissue and lactation period specific. The transgenic rabbit line was bred for six generations. All transgenic animals showed stable production of biologically active IGF-1 over the generations and no apparent effect on the physiological or reproductive performance was observed. The absence of adverse effects on homozygous transgenic rabbits suggested the absence of insertional mutagenesis. Eight hemizygous transgenic offspring analysed produced on average 363 +/- 12 micrograms/ml (ranging from 223 +/- 61 to 484 +/- 39 micrograms/ml) mature human IGF-1 in their milk, whereas three homozygous animals produced on average 543 +/- 41 micrograms/ml (ranging from 360 +/- 15 to 678 +/- 80 micrograms/ml). Homozygous hulGF-1 females clearly showed a significantly increased production performance of the recombinant protein.

Recombinant human acid alpha-glucosidase: high level production in mouse milk, biochemical characteristics, correction of enzyme deficiency in GSDII KO mice

Glycogen storage disease type II (GSDII) is caused by lysosomal acid alpha-glucosidase deficiency. Patients have a rapidly fatal or slowly progressive impairment of muscle function. Enzyme replacement therapy is under investigation. For large-scale, cost-effective production of recombinant human acid alpha-glucosidase in the milk of transgenic animals, we have fused the human acid alpha-glucosidase gene to 6.3 kb of the bovine alphaS1-casein gene promoter and have tested the performance of this transgene in mice. The highest production level reached was 2 mg/ml. The major fraction of the purified recombinant enzyme has a molecular mass of 110 kDa and resembles the natural acid alpha-glucosidase precursor from human urine and the recombinant precursor secreted by CHO cells, with respect to pH optimum, Km, Vmax, N-terminal amino acid sequence and glycosylation pattern. The therapeutic potential of the recombinant enzyme produced in milk is demonstrated in vitro and in vivo. The precursor is taken up in a mannose 6-phosphate receptor-dependent manner by cultured fibroblasts, is converted to mature enzyme of 76 kDa and depletes the glycogen deposit in fibroblasts of patients. When injected intravenously, the milk enzyme corrects the acid alpha-glucosidase deficiency in heart and skeletal muscle of GSDII knockout mice.

High-level expression of bovine beta-lactoglobulin gene in transgenic mice

To study the expression of the bovine beta-lactoglobulin (BLG) gene we isolated the BLG gene from a genomic library and introduced it into murine germline. Bovine BLG gene including 2.8 kbp of 5' and 1.9 kbp of 3' flanking region was expressed efficiently and mammary gland-specifically in transgenic mice. Expression levels of BLG in milk exceeded 1 mg ml-1 in all four mouse lines analyzed. However, in two mouse lines originating from female founders BLG expression levels varied from less than 0.02 mg ml-1 up to 1 mg ml-1. In both lines originating from male founders all analyzed female mice excreted bovine BLG into their milk at a high and constant level of 1-2 mg ml-1. BLG expression was stable within individual mice in two successive lactations and the amount of BLG in the milk of mice correlated with the level of BLG mRNA in the mammary tissue. Methylation analyses of HpaII sites revealed that transgene copies were on average more methylated in mice which excreted low levels of BLG into their milk. Each mouse line had its own methylation pattern and, in addition, each mouse had more or less identical methylation patterns in mammary gland, brain and kidney DNA. Genomic sequencing of the BLG gene indicated that the promoter region (bases -162 to +391 with respect to the transcription start site) was heavily methylated except for distinct CpG sites that were only partially methylated both in transgenic mice and lactating cattle.

Establishment and initial characterization of the ovine mammary epithelial cell line NISH

Analysis of the molecular mechanisms involved in the differentiation and formation of the characteristic three-dimensional structures of the developing mammary gland of the major milk-producing livestock (ducts, end buds, and alveoli) requires in vitro model cell cultures. The few cell lines that have been established from dairy animals do not fully reproduce the entire program of mammary differentiation. Here we present the initial characterization of a unique mammary epithelial cell line derived spontaneously from midpregnant sheep (NISH). These cells form in vitro functional structures resembling ducts, lateral buds, and alveoli that secrete beta-lactoglobulin (BLG) in an ECM (extracellular matrix)-dependent manner. Interestingly, the presence of growth hormone dramatically increased BLG secretion from NISH cells cultured on ECM. It appears that GH is required not only to establish the structural organization but also is continuously needed to maintain BLG expression. Stable transfection of NISH cells with BLG/Human Serum Albumin (HSA) hybrid gene constructs revealed that the relative level of expression was comparable to the in vivo secretion of HSA in transgenic mice carrying these gene sequences. No expression could be detected in cells transfected with hybrid genes carrying either HSA cDNA or the entire HSA gene, and HSA expression was dependent on the presence of intronic sequences. These results demonstrate that NISH cells may prove a useful tool for studying the differentiation and organogenesis of mammary epithelial cells under defined culture conditions. Furthermore, transfected NISH cells may be an alternative for the transgenic mouse model in evaluating the potential of gene constructs to be efficiently expressed in the mammary gland of transgenic farm animals.

The bladder as a bioreactor: urothelium production and secretion of growth hormone into urine

Uroplakin genes are expressed in a bladder-specific and differentiation-dependent fashion. Using a 3.6-kb promoter of mouse uroplakin II gene, we have generated transgenic mice that express human growth hormone (hGH) in their bladder epithelium, resulting in its secretion into the urine at 100-500 ng/ml. The levels of urine hGH concentration remain constant for longer than 8 months. hGH is present as aggregates mostly in the uroplakin-delivering cytoplasmic vesicles that are targeted to fuse with the apical surface. Using the bladder as a bioreactor offers unique advantages, including the utility of all animals throughout their lives. Using urine, which contains little protein and lipid, as a starting material facilitates recombinant protein purification.

Characterization and partial purification of bovine alpha-lactalbumin and beta-casein produced in milk of transgenic mice

Bovine alpha-lactalbumin (alpha-LA) and bovine beta-casein (beta-CN), from milk from transgenic mice were characterized and partially purified using electrophoretic, immunoblotting, and chromatographic methods. The transgenically expressed bovine milk proteins were identified using PAGE or by a combination of preparative isoelectrofocusing followed by Western immunoblotting. The heterologous bovine alpha-IA and bovine beta-CN had molecular masses that were identical to those of those of the native proteins. The estimated expression of the proteins was 1.0 mg/ml of milk for alpha-LA and 3.0 mg/ml for beta-CN. The calcium binding of bovine alpha-LA suggested that the protein produced in murine milk has the same electrophoretic shift as native bovine alpha-LA after the removal of calcium. Nitrogen-linked glycosylation of native and murine synthesized bovine alpha-LA was identified by peptide-N-glycosidase F treatment, and the N-terminal amino acid sequence of HPLC-purified bovine alpha-LA from mouse milk was confirmed to be identical to native bovine alpha-LA. In addition, the phosphorylation of the bovine beta-CN expressed in the milk of transgenic mice was the same as that of native bovine beta-CN, as determined by phosphatase digestion.

Cre-mediated recombination at the murine whey acidic protein (mWAP) locus

The mouse whey acidic protein (WAP) gene in mouse embryonic stem (ES) cells has been targeted with a loxP-flanked neomycin phosphotransferase-thymidine kinase (neo-TK) cassette inserted into exon 4. Southern blot revealed that 51 of 199 colonies were correctly targeted (1:4). Next, a Cre-encoding plasmid was electroporated into a targeted cell line to cause the deletion of the neo-TK cassette. Modified ES cell colonies were identified by polymerase chain reaction (PCR); 44 out of 50 colonies (88%) had undergone Cre-mediated deletion. Finally, a loxP-tagged cell line was co-electroporated with a Cre-encoding plasmid and a loxP-containing neo plasmid for site-specific insertion into the WAP locus. The frequency of this event was 23% (11 of 48) of that obtained with random integration. This demonstrates the feasibility of using the Cre-loxP system for site-specific integration in ES cells. Moreover, this is the first report of targeting a loxP-containing transgene into a predetermined location in ES cells. Ultimately, a mouse model derived from these modified ES cells will usher in a second generation of animal "bioreactor" models where the inserted transgene is controlled exclusively by the endogenous locus regulatory elements. In addition, oncogenesis can be explored from single copy oncogene/tumor suppressor gene inserts, which are regulated in a temporal and tissue-specific manner. It is hoped that regulation of transgene expression in this fashion will help elucidate the underlying mechanisms of normal development in the mammary gland.

Transgenic dairy cattle: genetic engineering on a large scale

Amid the explosion of fundamental knowledge generated from transgenic animal models, a small group of scientists has been producing transgenic livestock with goals of improving animal production efficiency and generating new products. The ability to modify mammary-specific genes provides an opportunity to pursue several distinctly different avenues of research. The objective of the emerging gene "pharming" industry is to produce pharmaceuticals for treating human diseases. It is argued that mammary glands are an ideal site for producing complex bioactive proteins that can be cost effectively harvested and purified. Consequently, during the past decade, approximately a dozen companies have been created to capture the US market for pharmaceuticals produced from transgenic bioreactors estimated at $3 billion annually. Several products produced in this way are now in human clinical trials. Another research direction, which has been widely discussed but has received less attention in the laboratory, is genetic engineering of the bovine mammary gland to alter the composition of milk destined for human consumption. Proposals include increasing or altering endogenous proteins, decreasing fat, and altering milk composition to resemble that of human milk. Initial studies using transgenic mice to investigate the feasibility of enhancing manufacturing properties of milk have been encouraging. The potential profitability of gene "pharming" seems clear, as do the benefits of transgenic cows producing milk that has been optimized for food products. To take full advantage of enhanced milk, it may be desirable to restructure the method by which dairy producers are compensated. However, the cost of producing functional transgenic cattle will remain a severe limitation to realizing the potential of transgenic cattle until inefficiencies of transgenic technology are overcome. These inefficiencies include low rates of gene integration, poor embryo survival, and unpredictable transgene behavior.

Recombinant expression and secretion of a natural splicing variant containing the ectodomain of porcine LH receptor in HC11 mammary epithelial cells

Large-scale synthesis of active recombinant porcine luteinizing hormone/chorionic gonadotropin receptor (pLHR) is required for biophysical and structural studies. This study was undertaken to improve expression of the corresponding cDNA already obtained with a number of other systems, (i) by turning to cells from mammalian origin able to perform adequate glycosylation, (ii) by using an expression vector containing the acknowledged high-performance rabbit WAP gene upstream region together with transcription and translation stimulating sequences, and (iii) by expressing natural splicing variants. Selection of the transfected HC11 cells was performed in terms of pLHR expression using specific radioligand binding and immunoradiometric assays. Secretion of pLHR ectodomain into the culture medium of the HC11 clones was quantified, and reached 70 ng/ml, which represents the highest active amount ever produced. However, this level of expression was relatively low in comparison to that currently observed with bGH cDNA used as reporter gene. Additional investigations were performed in order to gain further insight into the limitation of the production of pLHR relative to bovine or human growth hormone using the same expression system. A high number of copies of cDNA in the genome of HC11 cells was found, provided that an antibiotic selection pressure was maintained to avoid drifting. The low mRNA levels detected for pLHR relative to hGH mRNAs correlate well with the relative protein production levels. They could arise from poor stability of mRNAs, a fact already observed for the natural receptor in gonadal cells. These results thus constitute a promising indicator for possible expression of pLHR in the milk of transgenic animals.

Position-independent and high-level expression of human alpha-lactalbumin in the milk of transgenic rats carrying a 210-kb YAC DNA

The level of expression of transgenes in transgenic animals varies among lines, and is often much lower than that of endogenous genes (position effects). In order to surmount position effects and establish a more efficient production system of transgenic animals producing pharmaceutical proteins in their milk, transgenic rats carrying 210-kb YAC DNA containing the human alpha-lactalbumin gene were produced. Three transgenic lines transmitted the transgene to the next generation. They had one copy of the alpha-lactalbumin gene and secreted human alpha-lactalbumin in their milk at concentrations of 2.0-4.3 mg/ml. No position effect was seen. The transgene was expressed specifically in the mammary gland of the transgenic rats. The 210-kb region is thought to contain all the DNA elements required for proper expression of the human alpha-lactalbumin gene. The YAC carrying the human alpha-lactalbumin gene is a potential vector for the expression of foreign genes in the mammary gland.

Co-integration of beta-lactoglobulin/human serum albumin hybrid genes with the entire beta-lactoglobulin gene or the matrix attachment region element: repression of human serum albumin and beta-lactoglobulin expression in the mammary gland and dual regulation of the transgenes

The effect of co-integration of the entire beta-lactoglobulin (BLG) gene or matrix attachment region (MAR) sequences on the expression of various BLG/ human serum albumin (HSA) gene constructs was tested in transgenic mice. These former sequences were chosen because of their reported ability to insulate transgenes from the neighboring host genomic DNA sequences and/or to provide a more permissive transcriptional environment. When introduced alone, a cDNA-based BLG/HSA construct was expressed in 60% of transgenic strains and HSA was secreted at levels up to 0.3 mg/ml into the milk. Upon co-integration with either the entire BLG gene or MAR element, HSA RNA and protein expression were completely abrogated. While the co-integrated BLG gene suppressed the proportion of expresser strains carrying cDNA as well as genomic BLG/HSA constructs, the MAR element only exerted its negative effect on the cDNA-based BLG/HSA construct. In transgenics expressing both HSA and BLG, the tissue specificity and developmental patterns of BLG expression were altered and resembled the less stringent pattern of the BLG/HSA expression. These results demonstrate that rescue of transgene expression through co-integration with BLG or MAR sequences do not apply universally.