Characterization of recombinant human factor IX expressed in transgenic mice and in derived trans-immortalized hepatic cell lines

Effect of propeptide amino acid substitution in γ-carboxylation, activity and expression of recombinant human coagulation factor IX

The production of recombinant vitamin K dependent (VKD) proteins for therapeutic purposes is an important challenge in the pharmaceutical industry. These proteins are primarily synthesized as precursor molecules and contain pre-propeptide sequences. The propeptide is connected to γ-carboxylase enzyme through the γ-carboxylase recognition site for the direct γ-carboxylation of VKD proteins that has a significant impact on their biological activity. Propeptides have different attitudes toward γ-carboxylase and certain amino acids in propeptide sequences are responsible for the differences in γ-carboxylase affinity. By aiming to replace amino acids in hFIX propeptide domain based on the prothrombin propeptide, pMT-hFIX-M14 expression cassette, containing cDNA of hFIX with substituted -14 residues (Asp to Ala) was made. After transfection of Drosophila S2 cells, expression of the active hFIX was analyzed by performing ELISA and coagulation test. A 1.4-fold increase in the mutant recombinant hFIX expression level was observed in comparison with that of a native recombinant hFIX. The enhanced hFIX activity and specific activity of the hFIXD-14A (2.2 and 1.6 times, respectively) were further confirmed by comparing coagulation activity levels of substituted and native hFIX. Enrichment for functional, fully γ-carboxylated hFIX species via barium citrate adsorption demonstrated 2-fold enhanced recovery in the S2-expressing hFIXD-14A relative to that expressed native hFIX. These results show that changing -14 residues leads to a decrease in the binding affinity to substrate, increase in γ-carboxylation and activity of recombinant hFIX. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:515-520, 2018.

Low-Dose Gene Therapy for Murine PKU Using Episomal Naked DNA Vectors Expressing PAH from Its Endogenous Liver Promoter

Limited duration of transgene expression, insertional mutagenesis, and size limitations for transgene cassettes pose challenges and risk factors for many gene therapy vectors. Here, we report on physiological expression of liver phenylalanine hydroxylase (PAH) by delivery of naked DNA/minicircle (MC)-based vectors for correction of homozygous enu2 mice, a model of human phenylketonuria (PKU). Because MC vectors lack a defined size limit, we constructed a MC vector expressing a codon-optimized murine Pah cDNA that includes a truncated intron and is under the transcriptional control of a 3.6-kb native Pah promoter/enhancer sequence. This vector, delivered via hydrodynamic injection, yielded therapeutic liver PAH activity and sustained correction of blood phenylalanine comparable to viral or synthetic liver promoters. Therapeutic efficacy was seen with vector copy numbers of <1 vector genome per diploid hepatocyte genome and was achieved at a vector dose that was significantly lowered. Partial hepatectomy and subsequent liver regeneration was associated with >95% loss of vector genomes and PAH activity in liver, demonstrating that MC vectors had not integrated into the liver genome. In conclusion, MC vectors, which do not have a defined size-limitation, offer a favorable safety profile for hepatic gene therapy due to their non-integration in combination with native promoters.

DNA aptamer affinity ligands for highly selective purification of human plasma-related proteins from multiple sources

Nucleic acid aptamers are promising ligands for analytical and preparative-scale affinity chromatography applications. However, a full industrial exploitation requires that aptamer-grafted chromatography media provide a number of high technical standards that remained largely untested. Ideally, they should exhibit relatively high binding capacity associated to a very high degree of specificity. In addition, they must be highly resistant to harsh cleaning/sanitization conditions, as well as to prolonged and repeated exposure to biological environment. Here, we present practical examples of aptamer affinity chromatography for the purification of three human therapeutic proteins from various sources: Factor VII, Factor H and Factor IX. In a single chromatographic step, three DNA aptamer ligands enabled the efficient purification of their target protein, with an unprecedented degree of selectivity (from 0.5% to 98% of purity in one step). Furthermore, these aptamers demonstrated a high stability under harsh sanitization conditions (100h soaking in 1M NaOH). These results pave the way toward a wider adoption of aptamer-based affinity ligands in the industrial-scale purification of not only plasma-derived proteins but also of any other protein in general.

Functional expression of the human coagulation factor IX using heterologous signal peptide and propeptide sequences in mammalian cell line

OBJECTIVE

To study the functions of pre-pro leader peptides of the human and porcine prothrombins on the human FIX (hFIX) expression.

RESULTS

In silico analysis predicted higher secretion efficiencies for the prothrombins-derived signal peptides, in comparison with the native hFIX signal peptide. Replacements of the hFIX pre-pro sequence with those of the two prothrombins, led to increased levels of transcription of the chimeric transgenes, as compared to the native clone. This was in consistent with the lower minimum free energies, calculated for the recombinant transcripts, based on their secondary structures. Evaluation of secretion efficiency revealed that the highest and lowest FIX secretions belong to signal peptides derived from porcine' prothrombin and hFIX, respectively. Coagulation activities of the FIX expressed from chimeric variants could be increased up to tenfold, relative to the native clone.

CONCLUSION

The feasibility of a leader-peptide replacement for the improvement of both transcription and post-transcriptional processes is described that can be relevant for production the vitamin-K dependent proteins.

Development of a transgenic mouse model with immune tolerance for human coagulation factor VIIa

PURPOSE

Human factor VIIa (FVIIa) is commonly used as bypassing therapy to treat bleeding episodes in hemophilia patients with neutralizing antibodies to factors VIII (FVIII) or IX (FIX). There is a need for a suitable animal model to assess the immunogenicity of new FVIIa products during preclinical development. The aim of this study was the design of a novel transgenic mouse model with immune tolerance to human FVIIa.

METHODS

The model was generated by transgenic expression of human F7 cDNA. FVIIa-specific immune responses after treatment with human FVIIa were assessed by analyzing circulating antibodies, antibody producing plasma cells and CD4(+) T cells.

RESULTS

In contrast to wild-type mice, human FVII transgenic mice did not develop antibodies when treated with human FVIIa. The immune tolerance was specific and could be broken by application of human FVIIa together with a strong stimulus of the innate immune system. Break of tolerance was associated with increased numbers of pro-inflammatory FVIIa-specific CD4(+) T cells.

CONCLUSIONS

The new mouse model is suitable to study the influence of the innate immune system on maintenance and break of immune tolerance against FVIIa and could be used to assess the immunogenicity of new FVIIa products during pre-clinical development.

Pilot production of recombinant human clotting factor IX from transgenic sow milk

Valuable pharmaceutical proteins produced from the mammary glands of transgenic livestock have potential use in the biomedical industry. In this study, recombinant human clotting factor IX (rhFIX) produced from transgenic sow milk for preclinical animal studies have been established. The transgenic sow milk was skimmed and treated with sodium phosphate buffer to remove abundant casein protein. Then, the γ-carboxylated rhFIX fraction was segregated through the Q Sepharose chromatography from uncarboxylated one. For safety issue, the process included virus inactivation by solvent/detergent (S/D) treatment. Subsequently, the S/D treated sample was loaded into the Heparin Sepharose column to recover the rhFIX fraction, which was then reapplied to the Heparin Sepharose column to enhance rhFIX purity and lower the ratio of activated form rhFIX (rhFIXa) easily. This was possible due to the higher affinity of the Heparin affinity sorbent for rhFIXa than for the rhFIX zymogen. Furthermore, an IgA removal column was used to eliminate porcine IgA in purified rhFIX. Finally, nanofiltration was performed for viral clearance. Consequently, a high-quality rhFIX product was produced (approximately 700 mg per batch). Other values for final rhFIX preparation were as follows: purity, >99%; average specific activity, 415.6±57.7 IU/mL and total milk impurity, <0.5 ng/mg. This is the first report that described the whole process and stable production of bioactive rhFIX from transgenic sow milk. The overall manufacturing process presented here has the potential for industrial production of rhFIX for treatment of hemophilia B patients.

Expression of biologically active human clotting factor IX in Drosophila S2 cells: γ-carboxylation of a human vitamin K-dependent protein by the insect enzyme

The Drosophila γ-glutamyl carboxylase (dγC) has substrate recognition properties similar to that of the vertebrate γ-carboxylase (γC), and its carboxylated product yield, in vitro, was shown to be more than that obtained with the human enzyme. However, whether the Drosophila enzyme is able to γ-carboxylate the human vitamin K-dependent (VKD) proteins, such as the human coagulation factor IX (hFIX), as synthesized in cultured Drosophila cells was not known. To examine this possibility, the Drosophila Schnider (S2) cell line was transfected with a metallothionein promoter-regulated hFIX-expressing plasmid. After induction with copper ion, expression efficiency of the active hFIX was analyzed by performing enzyme-linked immunosorbent assey (ELISA) and coagulation test on the culture supernatant of the transfected S2 cells during 72 h of postinduction. In comparison with Chinese hamster ovary cell line, S2 cells showed higher (≈ 12-fold) expression level of the hFIX. The γ-carboxylation of the Drosophila-derived hFIX was confirmed by evaluation of the expressed protein, after being precipitated with barium citrate. The biological activity of the S2 cell-derived hFIX indicated the capability of S2 cells to fulfill the required γ-carboxylation of the expressed hFIX. Coexpression of the human γ-glutamyl carboxylases (hγC) was also shown to improve both expression and γ-carboxylation of the hFIX. This is the first in vivo data to describe the ability of the dγC to recognize the human-based propeptide as substrate, which is an essential step for production of biologically active γ-carboxylated VKD proteins.

Accumulation of functional recombinant human coagulation factor IX in transgenic soybean seeds

The seed-based production of recombinant proteins is an efficient strategy to achieve the accumulation, correct folding, and increased stability of these recombinant proteins. Among potential plant molecular farming systems, soybean [Glycine max (L.) Merrill] is a viable option for the production of recombinant proteins due to its high protein content, known regulatory sequences, efficient gene transfer protocols, and a scalable production system under greenhouse conditions. We report here the expression and stable accumulation of human coagulation factor IX (hFIX) in transgenic soybean seeds. A biolistic process was utilised to co-introduce a plasmid carrying the hFIX gene under the transcriptional control of the α' subunit of a β-conglycinin seed-specific promoter and an α-Coixin signal peptide in soybean embryonic axes from mature seeds. The 56-kDa hFIX protein was expressed in the transgenic seeds at levels of up to 0.23% (0.8 g kg(-1) seed) of the total soluble seed protein as determined by an enzyme-linked immunosorbent assay (ELISA) and western blot. Ultrastructural immunocytochemistry assays indicated that the recombinant hFIX in seed cotyledonary cells was efficiently directed to protein storage vacuoles. Mass spectrometry characterisation confirmed the presence of the hFIX recombinant protein sequence. Protein extracts from transgenic seeds showed a blood-clotting activity of up to 1.4% of normal plasma. Our results demonstrate the correct processing and stable accumulation of functional hFIX in soybean seeds stored for 6 years under room temperature conditions (22 ± 2°C).

A systematic study of the function of the human beta-globin introns on the expression of the human coagulation factor IX in cultured Chinese hamster ovary cells

BACKGROUND

Intronic sequences have the potential to improve gene expression in eukaryotes by a variety of mechanisms. In this context, human beta-globin (hBG) introns were inserted into the human factor IX (hFIX) cDNA in cytomegalovirus (CMV)-regulated plasmids. The resulting construct was then used for further expression analysis in vitro.

METHODS

Seven hFIX-expressing plasmids with different combinations of the two hBG introns and the Kozak element were constructed and used for a systematic expression analysis in cultured Chinese hamster ovary (CHO) cells. In parallel, the hBG intronic sequences were analysed for the presence of possible regulatory elements.

RESULTS

All the constructed plasmids resulted in transient expression of the hFIX. However, the coagulation activities varied according to the particular constructs used. Based on the hFIX antigenic assay, a wide range of variation was observed during persistent expression. The second hBG intron appears to be more effective than the first one. The expression level was further increased upon the inclusion of the Kozak element. Sequence analysis has detected several transcription factor binding (TFB) motifs in both of the introns, but with a higher frequency in the second one.

CONCLUSIONS

Potentials of hBG introns as enhancer-like elements for the expression of the hFIX in cultured CHO cells and a higher activity with respect to the second hBG intron compared to the first one were demonstrated. The larger number of TFBs in the second hBG intron reflects its stronger effect. The results obtained suggest possible synergistic functions of the hBG introns and Kozak on the expression level of hFIX in vitro.

Sustained liver-specific transgene expression from the albumin promoter in mice following hydrodynamic plasmid DNA delivery

BACKGROUND

To properly study gene expression in vivo, often long-term expression is desired. Previous studies using plasmid DNA (pDNA) vectors have typically resulted in short-term expression. Here, we evaluated combinations of the albumin promoter with different enhancers and untranslated regions for liver-specific expression in mice.

METHODS

A series of pDNA secreted alkaline phosphatase (SEAP) reporter gene expression vectors was constructed using the albumin promoter and various other expression cassette elements. Each was evaluated for level and duration of SEAP expression in mice following hydrodynamic tail vein delivery.

RESULTS

Sustained liver expression was obtained from vectors combining the albumin promoter with an albumin 3' untranslated region (3'UTR). The level of expression was increased by inclusion of enhancers and a 5' intron. The optimal expression vector consisted of the albumin promoter combined with an alpha-fetoprotein MERII enhancer, 5' intron from the factor IX gene, and the 3'UTR from the albumin gene including intron 14. With this vector, SEAP reporter gene expression levels remained high for 1 year, at levels comparable to those obtained from the cytomegalovirus (CMV) promoter on day 1. Expression of human apolipoprotein E3 (hApoE) in ApoE knockout mice provided a dose-dependent correction of their hypercholesterolemia.

CONCLUSIONS

Liver-specific sustained transgene expression can be obtained at very high levels from optimized pDNA vectors, without the use of integration systems. Such vectors will further facilitate biological studies of genes in vivo and may find application in gene therapy.

Direct comparison of hepatocyte-specific expression cassettes following adenoviral and nonviral hydrodynamic gene transfer

Hepatocytes are a key target for treatment of inborn errors of metabolism, dyslipidemia and coagulation disorders. The development of potent expression cassettes is a critical target to improve the therapeutic index of gene transfer vectors. Here we evaluated 22 hepatocyte-specific expression cassettes containing a human apo A-I transgene following hydrodynamic transfer of plasmids or adenoviral transfer with E1E3E4-deleted vectors in C57BL/6 mice. The DC172 promoter consisting of a 890 bp human alpha(1)-antitrypsin promoter and two copies of the 160 bp alpha(1)-microglobulin enhancer results in superior expression levels compared to constructs containing the 1.5 kb human alpha(1)-antitrypsin promoter, the 790 bp synthetic liver-specific promoter or the DC190 promoter containing a 520 bp human albumin promoter and two copies of the 99 bp prothrombin enhancer. The most potent expression cassette consists of the DC172 promoter upstream of the transgene and two copies of the hepatic control region-1. Minicircles containing this expression cassette induce persistent physiological human apo A-I or human factor IX levels after hydrodynamic transfer. In conclusion, in this comparative study of 22 hepatocyte-specific expression cassettes, the DC172 promoter in combination with two copies of the hepatic control region-1 induces the highest expression levels following hydrodynamic and adenoviral transfer.

Biosynthesis of FVIII in megakaryocytic cells: improved production and biochemical characterization

Haemophilia A is an attractive target for gene therapy. We designed a haemophilia A gene therapy strategy involving the genetic modification of haematopoietic stem cells to achieve tissue-specific expression of a factor VIII (FVIII) transgene in the megakaryocytic lineage. Platelets would then serve as vehicles to store the expressed FVIII and deliver the coagulation factor at the site of vascular injury. A local correction of the haemostasis defect could, therefore, be expected following platelet activation and secretion. In this study, we demonstrated that a model of haematopoietic cell lines (Dami cells) could produce a correctly processed FVIII. FVIII transgenes were placed under the control of the human platelet glycoprotein IIb (GPIIb) promoter and used for stable transfection of the Dami megakaryocytic cell line. The highest FVIII production was obtained when the FVIII transgene contained a factor IX intron 1 gene sequence inserted in the FVIII intron 1 and 13 sites. Reverse transcription polymerase chain reaction demonstrated that the splicing of these introns was complete. Recombinant FVIII (rFVIII) produced in Dami cells was a biologically active molecule (specific activity: 5664 IU/mg) that was correctly glycosylated and sulphated. This recombinant FVIII protein exhibited biochemical characteristics after deglycosylation or thrombin activation that were comparable to a commercially available B-domainless rFVIII. These results demonstrate the advantages of a modified FVIII transgene and represent the first biochemical characterization of megakaryocyte-produced FVIII.

A novel gene expression system: non-viral gene transfer for hemophilia as model systems

It is highly desirable to generate tissue-specific and persistently high-level transgene expression per genomic copy from gene therapy vectors. Such vectors can reduce the cost and preparation of the vectors and reduce possible host immune responses to the vector and potential toxicity. Many gene therapy vectors have failed to produce therapeutic levels of transgene because of inefficient promoters, loss of vector or gene expression from episomal vectors, or a silencing effect of integration sites on integrating vectors. Using in vivo screening of vectors incorporating many different combinations of gene regulatory sequences, liver-specific, high-expressing vectors to accommodate factor IX, factor VIII, and other genes for effective gene transfer have been established. Persistent and high levels of factor IX and factor VIII gene expression for treating hemophilia B and A, respectively, were achieved in mouse livers using hydrodynamics-based gene transfer of naked plasmid DNA incorporating these novel gene expression systems. Some other systems to prolong or stabilize the gene expression following gene transfer are also discussed.

Novel hemophilia B mouse models exhibiting a range of mutations in the Factor IX gene

Animal models have been critical to the development of novel therapeutics in hemophilia. A deficiency of current murine models of hemophilia B is that they are all due to gene deletions, a type of mutation that is relatively rare in the human hemophilia population. We generated mice with a range of mutations in the Factor IX (F.IX) gene; these more faithfully reflect the types of mutations that cause disease in the human population. Transgenic mice expressing either wild-type human F.IX (hF.IX), or F.IX variants with premature translation termination codons, or missense mutations, under the control of the murine transthyretin promoter, were generated and crossed with mice carrying a large deletion of the murine F.IX gene. Gene copy number, F.IX transcript levels in the liver, intrahepatocyte protein expression, and circulating levels of F.IX protein in the mice were determined and compared with data generated by transient transfection assays using the same F.IX variants. Mice were injected with a viral vector expressing hF.IX and displayed a range of immune responses to the transgene product, depending on the underlying mutation. These new mouse models faithfully mimic the mutations causing human disease, and will prove useful for testing novel therapies for hemophilia. (Blood. 2004;104:2767-2774)

Limitation in use of heterologous reporter genes for gene promoter analysis. Silencer activity associated with the cloramphenicol acetyltransferase reporter gene

Various heterologous reporter genes have been widely used for the functional characterization of gene promoters. Many such studies often found weak to very strong silencer activities to be associated with specific parts of the basal promoter or further upstream regions. In this study, we carried out a systematic study on human blood coagulation factor IX (hFIX) and anti-coagulant protein C (hPC) genes, previously shown to have silencer activities associated with their 5'-flanking regions containing promoter sequences. With newly constructed chloramphenicol acetyltransferase (CAT) reporter vectors carrying hFIX or hPC gene promoter sequences, we confirmed the strong silencer activities associated with the regions nt -1895 through nt -416 of the hFIX gene or with the region nt -802 through nt -82 of the hPC gene. However, no such silencer activities associated with the specific regions were found when autologous hFIX cDNA, hFIX minigenes, or hPC minigenes were used as reporters in the expression vector system. Relative levels of CAT, hFIX, and hPC proteins produced in the transient assays correlated well with their mRNA levels. Human FIX minigene constructs containing a simian virus 40 (SV40) 3'-untranslated region (UTR) taken from the CAT reporter gene showed no silencer activity, indicating that SV40 3'-UTR sequence of the CAT reporter gene does not contribute to the silencer activity. Expression vectors constructed with the beta-galactosidase gene under the control of hFIX gene promoter sequences also showed no silencer activity associated with the region nt -1895 through nt -416. These findings indicate that silencer activities associated with specific regions of promoter sequences as analyzed with CAT reporter genes may represent artifacts specific to the CAT reporter genes. Our findings strongly suggest a need for re-examination of promoter characterizations of many eukaryotic genes, which have been studied to date with CAT reporter genes.

Complete and sustained phenotypic correction of hemophilia B in mice following hepatic gene transfer of a high-expressing human factor IX plasmid

Therapeutic correction of hemophilia B was achieved by rapid infusion of a large-volume solution containing a high-expressing human factor IX (hFIX) plasmid into the tail vein of hemophilia B mice. hFIX circulated at therapeutic levels (1-5 micro g mL-1) in all animals for more than 1 year as determined by both species-specific antigen assay and an activated partial thromboplastin time (APTT)-based clotting assay. There was acute, transient hepatic tissue damage by the infusion procedure and no significant inhibitory anti-hFIX antibodies developed. No bleeding episode was observed during or after treatment. Immunohistochemical studies indicated that the hFIX gene was exclusively expressed in hepatocytes, and that transduced cells had readily detectable hFIX protein at 4 h postinfusion, and stainable protein persisted for up to 1 year. Repeated infusions of hFIX plasmids boosted the hFIX expression to higher levels. These results demonstrate that hemophilia B can be treated by gene transfer of naked hFIX plasmids.

Expression of factor VIII in recombinant and transgenic systems

Deficiency in a coagulation factor VIII (FVIII) causes a genetic disorder hemophilia A, which is treated by repeated infusions of expensive FVIII products. Recombinant FVIII (rFVIII), the culmination of years of extensive international research, is an important alternative to plasma-derived FVIII (pdFVIII) and is considered to have a higher margin of safety. Advances in biotechnology allowed production of rFVIII at industrial scale, which significantly improved treatment of hemophilia A patients. We review the contemporary methods used for FVIII expression in mammalian cell culture systems and discuss the factors responsible for insufficient recoveries of rFVIII, such as inefficient accumulation of FVIII mRNA in the cell, complexity of the mechanisms of FVIII secretion, and instability of secreted FVIII. The approaches to improve the yield of rFVIII in cell culture systems include genetic engineering of B-domain-deleted FVIII, introduction of introns into FVIII cDNA constructs for more efficient processing and accumulation of FVIII mRNA, and introduction of mutations into chaperone-binding sites of FVIII to improve its secretion. Design of FVIII with prolonged half-life in vivo is considered as another promising direction in improving rFVIII protein and efficiency of hemophilia A therapy. As an alternative to expression of rFVIII in cell culture systems, we discuss production of rFVIII in transgenic animals, where high levels of rFVIII have been successfully secreted into milk. We also pay attention to the major limitations of this approach, such as safety issues associated with potential transmission of animal pathogens. Finally, we present a brief characterization of commercial recombinant FVIII products currently available on the market for hemophilia A treatment.

Factors influencing in vivo transduction by recombinant adeno-associated viral vectors expressing the human factor IX cDNA

Long-term expression of coagulation factor IX (FIX) has been observed in murine and canine models following administration of recombinant adeno-associated viral (rAAV) vectors into either the portal vein or muscle. These studies were designed to evaluate factors that influence rAAV-mediated FIX expression. Stable and persistent human FIX (hFIX) expression (> 22 weeks) was observed from 4 vectors after injection into the portal circulation of immunodeficient mice. The level of expression was dependent on promoter with the highest expression, 10% of physiologic levels, observed with a vector containing the cytomegalovirus (CMV) enhancer/beta-actin promoter complex (CAGG). The kinetics of expression after injection of vector particles into muscle, tail vein, or portal vein were similar with hFIX detectable at 2 weeks and reaching a plateau by 8 weeks. For a given dose, intraportal administration of rAAV CAGG-FIX resulted in a 1.5-fold or 4-fold higher level of hFIX compared to tail vein or intramuscular injections, respectively. Polymerase chain reaction analysis demonstrated predominant localization of the rAAV FIX genome in liver and spleen after tail vein injection with a higher proportion in liver after portal vein injection. Therapeutic levels of hFIX were detected in the majority of immunocompetent mice (21 of 22) following intravenous administration of rAAV vector without the development of anti-hFIX antibodies, but hFIX was not detected in 14 immunocompetent mice following intramuscular administration, irrespective of strain. Instead, neutralizing anti-hFIX antibodies were detected in all the mice. These observations may have important implications for hemophilia B gene therapy with rAAV vectors.

Inclusion of the hepatic locus control region, an intron, and untranslated region increases and stabilizes hepatic factor IX gene expression in vivo but not in vitro

We systematically compared human factor IX gene expression from a variety of plasmids containing different cis-regulatory sequences after transfection into different hepatocyte cell lines, or in vivo, after their injection into the livers of mice. Although there was a 1.5- to 2.0-fold variation in gene expression from cultured cells, a 65-fold variation was observed in the in vivo studies. We found that a plasmid containing the apolipoprotein E locus control region (HCR), human alpha1-antitrypsin (hAAT) promoter, hFIX minigene (hFIXmg) sequence including a portion of the first intron (intron A), 3'-untranslated region (3'-UTR), and a bovine growth hormone polyadenylation signal (bpA) produced the highest serum level of human factor IX, reaching 18 microg/ml (normal = 5 microg/ml) 1 day after injection. Although most of the plasmid DNAs resulted in transient gene expression, inclusion of an intron, a polyadenylation signal from either the 1.7-kb 3'-UTR or the 0.3-kb bpA, and the HCR resulted in persistent and therapeutic levels of hFIX gene expression, ranging from 0.5 to 2 microg/ml (10 to 40% of normal) for 225 days (length of experiment). These data underscore the importance of cis sequences for enhancing in vivo hepatic gene expression and reemphasize the lack of correlation of gene expression in tissue culture and in vivo studies.

Persistent delivery of factor IX in mice: gene therapy for hemophilia using implantable microcapsules

Severe hemophilia B is a life-threatening, life long condition caused by absence of or defective coagulation factor IX. Gene therapy could provide an alternative treatment to repeated injection of plasma-derived concentrate or recombinant factor IX. We have previously described the use of implantable microcapsules containing recombinant myoblasts to deliver human factor IX in mice. This study reports the generation of improved myoblast-specific expression vectors. Mouse myoblast clones transfected with the various vectors secreted factor IX in vitro, at rates between 70 and 1000 ng/10(6) cells/day. The recombinant myoblast clones were then encapsulated and implanted into mice. Immunocompetent mice implanted with encapsulated myoblasts had up to 65 ng of factor IX per milliliter in their plasma for up to 14 days, after which antibodies to human factor IX became detectable, and this coincided with decreased factor IX in mouse plasma. In immunodeficient mice, however, factor IX delivery was maintained at a constant level for at least 6 weeks (end of experiment). Interestingly, the highest-secreting myoblast clone in vitro did not deliver the highest level of hFIX in vivo. This discrepancy observed between performance in vitro and in vivo may have important implications for the development of gene therapy protocols based on recombinant cells.

Production of minigene-containing retroviral vectors using an alphavirus/retrovirus hybrid vector system

In an attempt to increase the synthesis of human clotting factors VIII and IX in transduced cells, optimized expression cassettes containing genomic genelike elements (minigenes) were assembled. Plasmid DNA containing factor VIII or factor IX minigenes and driven by three human cellular promoters (albumin, factor IX, PGK) or the strong viral promoter RSV-LTR were electroporated into TE671 and HepG2 cell lines, and clotting factor levels were determined by ELISA. In comparison with a parallel transfection of MLV-LTR-promoted retroviral vector plasmid DNAs, the PGK- and RSV-LTR-promoted minigene constructs produced equal or greater amounts of clotting factor proteins. A factor IX minigene cassette was cloned into the retrovirus-based gene transfer vector LN (in both forward and reverse orientations) and the minigene vector was introduced into the Phoenix retroviral packaging cell line. Analysis of neo(r) cells demonstrated that insertion of a factor IX minigene into the retroviral vector LN resulted in rearrangement of the factor IX sequence and loss of factor IX expression in the Phoenix packaging cell line. The same factor IX minigene was then inserted into an alphavirus/retrovirus hybrid vector that facilitates the synthesis of retroviral vector RNA in the cytoplasm of cells. Alphavirus/retrovirus virions were produced and used to transduce the Phoenix retroviral vector packaging cell line. The cytoplasmically produced factor IX minigene-containing retroviral vectors were collected and used to transduce TE671 cells. Analysis of transduced cells demonstrated stable transfer of the minigene and expression of factor IX.

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.

Human factor IX transgenic sheep produced by transfer of nuclei from transfected fetal fibroblasts

Ovine primary fetal fibroblasts were cotransfected with a neomycin resistance marker gene (neo) and a human coagulation factor IX genomic construct designed for expression of the encoded protein in sheep milk. Two cloned transfectants and a population of neomycin (G418)-resistant cells were used as donors for nuclear transfer to enucleated oocytes. Six transgenic lambs were liveborn: Three produced from cloned cells contained factor IX and neo transgenes, whereas three produced from the uncloned population contained the marker gene only. Somatic cells can therefore be subjected to genetic manipulation in vitro and produce viable animals by nuclear transfer. Production of transgenic sheep by nuclear transfer requires fewer than half the animals needed for pronuclear microinjection.

Increment of hFIX expression with endogenous intron 1 in vitro

This paper probes into the feasibility of increasing expression level of hFIX gene with endogenous intron 1 sequence. hFIX minigene was obtained with middle sequence truncated intron 1 inserted into the relative site of hFIX cDNA, and plasmid vector pKG5i'IX, retroviral vector GINaCi'IX were constructed. These vectors were transduced into target cells of PA317, C2C12, primary rabbit skin fibroblasts (RSF) and primary human skin fibroblasts (HSF). The expression level of mixed colonies are PA317/pKGoi'IX, 151 ng/10(6) cells/24h; PA317/G1NaCi'IX, 308 ng/10(6) cells/24 h; C2C12/G1 NaCi'IX, 188 ng/10(5) cells/24 h; RSF/G1NaCi'IX, 1929 ng/10(5) cells/24 h; HSF/G1NaCi'IX, 1646 ng/10(6) cells/24 h. These results indicated that hFIX minigene with intron 1 is able to increase the expression level to about 3 times of that of hFIX cDNA. Meanwhile, in order to study the application of hFIX minigene in the retroviral-mediated gene transfer system and refrain from intron splicing during viral production, a retroviral vector G1NaCi'IXR with reversely inserted hFIX minigene expression cassette was constructed. The expression level of reverse constructor in PA317 cells was 390 ng/10(6) cells/24 h with 79% of bioactivity. PCR detection of HT/G1NaCi'IXR cells infected with PA317/G1NaCi'IXR supernatant confirmed the existence of intron 1 sequence. These results suggested that expression vector with forward-inserted intron1-carrying hFIX expression cassette can be used in directed gene transfer, but when using the retroviral-mediated gene transfer system, reversely-inserted intronl-carrying hFIX expression cassette should be considered.

Regulation of human renin secretion and gene transcription in Calu-6 cells

Calu-6 cells were characterized for studying the transcriptional regulation of the human renin gene. Analysis of cis-acting elements of the renin promoter showed the highest activity within the first 582 bp in serum-free conditions and of the 892 bp in the presence of serum. cAMP activates renin mRNA synthesis parallel to renin production (20-fold increase) as well renin promoter activity (2-fold). cAMP response element and the (-77 to -67) element are both necessary for activation of the renin promoter but do not act independently. Functional analysis of Intron A revealed the presence of a silencer specific to renin-producing cells.

Gene structure of the rat kainate receptor subunit KA2 and characterization of an intronic negative regulatory region

We have isolated and analyzed the structure of the gene grik5 (glutamate receptor ionotropic kainate 5), encoding the rat kainate receptor subunit KA2. Six overlapping DNA fragments containing the entire grik5 gene were identified in a rat genomic library. grik5 is a unique gene composed of 20 exons that together span over 54 kilobases (kb). Reporter gene analysis demonstrated that 2 kb of grik5 5'-flanking sequence confers tissue-specific expression on a chloramphenicol acetyltransferase gene in vitro. We show that (i) the first intron of grik5 (3.4 kb) inhibited transcription of the chloramphenicol acetyltransferase gene driven by the 2-kb grik5 5'-flanking region; (ii) the negative regulatory element was located within 500 bp of the 3'-end of intron 1, and this 500-bp fragment selectively bound nuclear proteins isolated from neural and nonneural cells; (iii) the effect of the negative regulatory element on grik5 transcription was orientation- and distance-independent; and (iv) a 24-nucleotide sequence (CTTTCTGTGGCCTCTGACCTTTCC) was identified as the binding site for nuclear proteins within the 500-bp fragment, as determined by footprinting and gel shift assays. We conclude that an intronic element that displays features of a silencer modulates grik5 transcription.

Role of intron I in expression of the human factor IX gene

The first intron (intron I) of the human factor IX gene, which has been previously suggested of having an expression-augmenting activity, was systematically studied for its potential enhancer activity. When tested with the chloramphenicol acetyltransferase expression vector with a minimal factor IX promoter, subregions of intron I showed only marginal enhancing activities (1.7-1.9-fold enhancement at the highest). Smaller subregions encompassing nucleotides 5660-6350 of the intron sequence even showed some weak negative regulatory activities (approximately 50% suppression at the highest), while a cytomegalovirus enhancer sequence, which was used as the positive control, had a 7-fold enhancement. A set of three factor IX minigene expression vectors with the same factor IX promoter were then constructed: p-416FIXc which contained the factor IX cDNA, p-416FIXm1 which contained the factor IX cDNA with a largely truncated intron I, and p-416FIXm2 which contained the factor IX cDNA with the intron I sequence further truncated. The p-416FIXm1 and p-416FIXm2 constructs showed 7-9-fold higher expression activities than p-416FIXc. The elevated factor IX antigen levels agreed well with the grossly elevated factor IX clotting activity and mRNA levels. These results indicate that the expression enhancing activity of intron I is not due to specific enhancer elements present in the intron subsequences, but is due to functional splicing sequences present in the precursor mRNAs produced from the minigene constructs containing intron I. By being efficiently assembled into spliceosome complexes, transcripts with splicing sequences may be better protected in the nucleus from random degradations than those without such sequences.

T helper cell unresponsiveness: rapid induction in antigen-transgenic and reversion in non-transgenic mice

T cell tolerance is usually established by clonal deletion of self-specific T cells in the thymus, or some times, in the periphery. Alternatively, tolerance may also be achieved by induction of clonal T cell unresponsiveness by a poorly understood mechanism called "anergy". We found that transgenic mice expressing a soluble form of vesicular stomatitis virus (VSV) glycoprotein (G) predominantly in liver and kidney exhibited normal B cell responses. VSV-G-specific T help-independent neutralizing IgM responses were within normal ranges, but no T help-dependent neutralizing IgG antibodies were generated upon immunization with recombinant VSV-G protein and recombinant vaccinia virus expressing VSV-G. This demonstrated absence of B cell tolerance but presence of T helper cell unresponsiveness. After adoptive transfer of transgenic spleen cells into thymectomized immuno-incompetent hosts, the unresponsive T helper cells regained function and switched the neutralizing IgM response to IgG, comparably to control T helper cells, within 7 days. Conversely, when naive non-transgenic spleen cells were transferred into transgenic mice, VSV-G-specific T helper cells became unresponsive within 3-4 days. These results suggest that VSV-G-specific T helper cells are rendered unresponsive within a few days in the VSV-G transgenic host also outside of the thymus and that this unresponsiveness was reversed by transfer into antigen-free recipients.

From in vitro to in vivo. Progress in the use of cultured cells for human therapy

The use of cultured cells with the ultimate goal of using the cells or their products for human therapy has experienced an exponential growth during the last decade. Stable cell cultures have been established and genetically modified to obtain high quality products for protein replacement therapy or vaccines. Cells have also been directly isolated from the human organism and, after their expansion in vitro, been retransferred as skin grafts for treatment of burns or for cancer therapy by activated lymphocytes. With the explosive development of molecular biology techniques, it is now possible to genetically modify ex vivo, cells derived from the human body. These modifications should allow targeted expression of therapeutic genes into specific cells which will, upon retransfer to the body, exert their therapeutic action in a diseased organism.

Adenovirus mediated expression of therapeutic plasma levels of human factor IX in mice

Gene therapy strategies designed to combat haemophilia B, caused by defects in clotting factor IX, have so far concentrated on ex vivo approaches. We have now evaluated adenoviral vector-mediated expression of human factor IX in vivo. Injection of the vector Av1H9B, which encodes human factor IX cDNA, into the tail veins of mice resulted in efficient liver transduction and plasma levels of human factor IX that would be therapeutic for haemophilia B patients. However, levels slowly declined to baseline by nine weeks and were not re-established by a second vector injection. These results address both the advantages and obstacles to the use of adenoviral vectors for treatment of haemophilia B.

Novel cell lines derived from transgenic mice expressing recombinant human proteins. Transgenic hepatoma-derived cell lines

We have used transgenic mouse technology to establish immortalized hepatoma cell lines stably secreting heterologous proteins, such as human alpha 1-antitrypsin and human factor IX. Hepatocyte-specific regulatory DNA sequences were used to target both the expression of an onc gene and the gene coding for the human protein to the liver of transgenic mice which eventually developed hepatocellular carcinomas. Tumour cells were subsequently established as permanent cell lines, which maintained a differentiated phenotype under specific culture conditions, being capable of producing biologically active and correctly processed human alpha 1-antitrypsin and factor IX. Moreover, a preliminary analysis has shown that certain cell lines express elevated total cytochrome P450 activity. These cells could therefore represent a useful alternative to the use of animals or primary cultures in drug safety testing.

Characterization of trans-immortalized hepatic cell lines established from transgenic mice

Hepato-specific regulatory (promoter/enhancer) DNA sequences were used for targeting the expression of onc genes, such as murine c-myc and Simian Virus 40 T Antigen, to hepatocytes of transgenic mice which subsequently developed hepatocellular carcinomas after a variable period of time (depending on the type of onc gene employed). Several trans-immortalized cell lines were established and compared with respect to the expression of adult hepatic markers and response to growth factors. Despite the morphological differences observed between trans-hepatomas, owing to the expression of the two different onc genes, all tumor-derived cell lines behaved in a comparable fashion during long-term culture displaying an adult hepatic phenotype for at least 40 passages. They differed, however, in response to epidermal growth factor. When the gene coding for human alpha 1-antitrypsin was placed under the control of the same hepato-specific promoter/enhancer, high levels of the human recombinant protein could be harvested from the supernatants of trans-hepatoma-derived cell lines.