Hemophilia gene therapy comes of age

Concurrent with the development of recombinant factor replacement products, the characterization of the F9 and F8 genes over 3 decades ago allowed for the development of recombinant factor products and made the hemophilias a target disease for gene transfer. The progress of hemophilia gene therapy has been announced in 3 American Society of Hematology scientific plenary sessions, including the first "cure" in a large animal model of hemophilia B in 1998, first in human sustained vector-derived factor IX activity in 2011, and our clinical trial results reporting sustained vector-derived factor IX activity well into the mild or normal range in 2016. This progression to clinically meaningful success combined with numerous ongoing recombinant adeno-associated virus (rAAV)-mediated hemophilia gene transfer clinical trials suggest that the goal of gene therapy to alter the paradigm of hemophilia care may soon be realized. Although several novel therapeutics have recently emerged for hemophilia, gene therapy is unique in its potential for a one-time disease-altering, or even curative, treatment. This review will focus on the prior progress and current clinical trial investigation of rAAV-mediated gene transfer for hemophilia A and B.

Gene therapy in an era of emerging treatment options for hemophilia B

Factor IX deficiency (hemophilia B) is less common than factor VIII deficiency (hemophilia A), and innovations in therapy for hemophilia B have generally lagged behind those for hemophilia A. Recently, the first sustained correction of the hemophilia bleeding phenotype by clotting factor gene therapy has been described using recombinant adeno-associated virus (AAV) to deliver factor IX. Despite this success, many individuals with hemophilia B, including children, men with active hepatitis, and individuals who have pre-existing natural immunity to AAV, are not eligible for the current iteration of hemophilia B gene therapy. In addition, recent advances in recombinant factor IX protein engineering have led some hemophilia treaters to reconsider the urgency of genetic cure. Current clinical and preclinical approaches to advancing AAV-based and alternative approaches to factor IX gene therapy are considered in the context of current demographics and treatment of the hemophilia B population.

Mesenchymal stem cell treatment for hemophilia: a review of current knowledge

Hemophilia remains a non-curative disease, and patients are constrained to undergo repeated injections of clotting factors. In contrast, the sustained production of endogenous factors VIII (FVIII) or IX (FIX) by the patient's own cells could represent a curative treatment. Gene therapy has thus provided new hope for these patients. However, the issues surrounding the durability of expression and immune responses against gene transfer vectors remain. Cell therapy, involving stem cells expanded in vitro, can provide de novo protein synthesis and, if implanted successfully, could induce a steady-state production of low quantities of factors, which may keep the patient above the level required to prevent spontaneous bleeding. Liver-derived stem cells are already being assessed in clinical trials for inborn errors of metabolism and, in view of their capacity to produce FVIII and FIX in cell culture, they are now also being considered for clinical application in hemophilia patients.

Next generation FIX muteins with FVIII-independent activity for alternative treatment of hemophilia A

BACKGROUND

FVIII neutralizing antibodies are the main complication of substitution therapy in hemophilia A (HA); auto-antibodies against FVIII causing acquired HA can also occur. Treatment of inhibitor patients remains challenging because prophylactic treatment with existing FVIII bypassing agents, all based on constitutively active coagulation factors, is difficult due to their short half-life.

OBJECTIVES

To generate zymogenic FIX variants with FVIII-independent activity for gene- and protein-based therapy for HA.

METHODS

Modifications were introduced into FIX based on current knowledge of FIX structure and FVIII-independent function followed by random screening. Activity, thrombin generation and FX activation by FIX mutants were characterized in the presence and absence of FVIII. Phenotype correction of promising candidates was assessed by the tail-clip assay in FVIII-knockout mice.

RESULTS

About 1600 clones were screened and three mutations (L6F, S102N and E185D) identified, which improved FVIII-independent activity in combination with our previously described variant FIX-ITV. By systematic combination of all mutations, six FIX mutants with the desired bypassing activity were designed. Candidate mutants FIX-IDAV and FIX-FIAV demonstrated the most efficient thrombin generation in FVIII-deficient plasma and had considerably increased activities towards FX in the absence of FVIII, in that they showed an up to 5-fold increase in catalytic efficiency. Expression of FIX-IDAV in FVIII knockout mice reduced blood loss after the tail-clip assay, even in the presence of neutralizing FVIII antibodies.

CONCLUSION

Activatable bioengineered FIX molecules (as opposed to pre-activated coagulation factors) with FVIII-independent activity might be a promising tool for improving HA treatment, especially for patients with inhibitors.

Comparison of two laboratory assays in monitoring the efficacy of different prophylaxis regimens for severe haemophilia

BACKGROUND

The goal of this study was to compare the validity of two laboratory assays, rotation thromboelastometry (ROTEM) and endogenous thrombin potential (ETP), in monitoring and evaluating different prophylactic treatment regimens in patients with severe haemophilia.

METHODS

Twenty adult patients with severe haemophilia were divided into three groups according to treatment regimen with concentrate of factor (F) VIII/IX: full-dose prophylaxis (5 patients), intermediate-dose prophylaxis (5 patients), and on demand treatment (10 patients).

RESULTS

The ROTEM for the group treated with full-dose prophylaxis was significantly lower than ROTEM for the group treated with intermediate-dose prophylaxis (p = 0.025). Among the patients given full-dose prophylaxis, 40% (2 patients) had prolonged ROTEM after 3 months of treatment, while among those given intermediate-dose prophylaxis all patients (100%, 5 patients) had prolonged ROTEM (p = 0.038). The ETP was significantly improved after 3 months of full-dose in comparison with intermediate-dose prophylaxis (p = 0.042).

CONCLUSIONS

ROTEM and ETP are useful laboratory assays for monitoring efficacy of different prophylaxis regimens with concentrate of FVIII/IX in patients with severe haemophilia, helping in making decisions regarding optimal dose-regimen prophylaxis.

Oral gene therapy for hemophilia B using chitosan-formulated FIX mutants

BACKGROUND

Oral gene delivery of non-viral vectors is an attractive strategy to achieve transgene expression. Although expected efficacy from non-viral delivery systems is relatively low, repeated vector administration is possible and may help to obtain durable transgene expression in a therapeutic range.

OBJECTIVES

To test the principle feasibility of using factor (F) IX variants with improved function combined with an optimized oral delivery system in hemophilia B (HB) mice.

METHODS

FIX modifications were introduced by site-directed mutagenesis into plasmid- or minicircle-based expression cassettes. Vectors were formulated as chitosan nanoparticles for oral delivery to HB mice. Protection of vector DNA in nanoparticle constructs and transfection efficiency were characterized. HB mice received eGFP-formulated chitosan nanoparticles to confirm gene transfer in vivo. FIX expression, phenotype correction and the potential of nanoparticles to induce immunotolerance (ITI) against exogenous FIX were evaluated after repeated oral administration.

RESULTS

Transfection of HEK 293T cells or livers of FIX-knockout mice with nanoparticles resulted in GFP or functional FIX expression. Oral administration of FIX mutants resulted in exclusive FIX expression in the small intestine, as confirmed by RT-PCR and fluorescence staining. HB mice demonstrated transient FIX expression reaching > 14% of normal activity and partial phenotype correction after oral delivery of FIX mutants with high specific activity and improved tissue release.

CONCLUSION

The feasibility of oral, non-viral delivery of FIX was established and improved by bioengineered FIX proteins and optimized vectors. Thus, these data might point the way for development of a clinically applicable oral gene transfer strategy for hemophilia B.

[Isolation and gene modification of amniotic fluid derived progenitor cells]

We established methods to isolate human amniotic fluid-derived progenitor cells (hAFPCs), and analyze the ability of hAFPCs to secrete human coagulation factor IX (hFIX) after gene modification. The hAFPCs were manually isolated by selection for attachment to gelatin coated culture dish. hFIX cDNA was transfected into hAPFCs by using a lentiviral vector. The hFIX protein concentration and activity produced from hAFPCs were determined by enzyme-linked immunosorbent assay (ELISA) and clotting assay. The isolated spindle-shaped cells showed fibroblastoid morphology after three culture passages. The doubling time in culture was 39.05 hours. Immunocytochemistry staining of the fibroblast-like cells from amniotic fluid detected expression of stem cell markers such as SSEA4 and TRA1-60. Quantitative PCR analysis demonstrated the expression of NANOG, OCT4 and SOX2 mRNAs. Transfected hAFPCs could produce and secrete hFIX into the culture medium. The observed concentration of secreted hFIX was 20.37% +/- 2.77% two days after passage, with clotting activity of 16.42% +/- 1.78%. The amount of hFIX:Ag reached a plateau of 50.35% +/- 5.42%, with clotting activity 45.34% +/- 4.67%. In conclusion, this study established method to isolate and culture amniotic fluid progenitor cells. Transfected hAFPCs can produce hFIX at stable levels in vitro, and clotting activity increases with higher hFIX concentration. Genetically engineered hAFPC are a potential method for prenatal treatment of hemophilia B.

Genetically modified adipose tissue-derived stem/stromal cells, using simian immunodeficiency virus-based lentiviral vectors, in the treatment of hemophilia B

Hemophilia is an X-linked bleeding disorder, and patients with hemophilia are deficient in a biologically active coagulation factor. This study was designed to combine the efficiency of lentiviral vector transduction techniques with murine adipose tissue-derived stem/stromal cells (mADSCs) as a new method to produce secreted human coagulation factor IX (hFIX) and to treat hemophilia B. mADSCs were transduced with simian immunodeficiency virus (SIV)-hFIX lentiviral vector at multiplicities of infection (MOIs) from 1 to 60, and the most effective dose was at an MOI of 10, as determined by hFIX production. hFIX protein secretion persisted over the 28-day experimental period. Cell sheets composed of lentiviral vector-transduced mADSCs were engineered to further enhance the usefulness of these cells for future therapeutic applications in transplantation modalities. These experiments demonstrated that genetically transduced ADSCs may become a valuable cell source for establishing cell-based gene therapies for plasma protein deficiencies, such as hemophilia.

Topical gene electrotransfer to the epidermis of hairless guinea pig by non-invasive multielectrode array

Topical gene delivery to the epidermis has the potential to be an effective therapy for skin disorders, cutaneous cancers, vaccinations and systemic metabolic diseases. Previously, we reported on a non-invasive multielectrode array (MEA) that efficiently delivered plasmid DNA and enhanced expression to the skin of several animal models by in vivo gene electrotransfer. Here, we characterized plasmid DNA delivery with the MEA in a hairless guinea pig model, which has a similar histology and structure to human skin. Significant elevation of gene expression up to 4 logs was achieved with intradermal DNA administration followed by topical non-invasive skin gene electrotransfer. This delivery produced gene expression in the skin of hairless guinea pig up to 12 to 15 days. Gene expression was observed exclusively in the epidermis. Skin gene electrotransfer with the MEA resulted in only minimal and mild skin changes. A low level of human Factor IX was detected in the plasma of hairless guinea pig after gene electrotransfer with the MEA, although a significant increase of Factor IX was obtained in the skin of animals. These results suggest gene electrotransfer with the MEA can be a safe, efficient, non-invasive skin delivery method for skin disorders, vaccinations and potential systemic diseases where low levels of gene products are sufficient.

Platelet and endothelial expression of clotting factors for the treatment of hemophilia

Hemostasis is achieved by the coordinate interaction of plasma, platelets, and vascular endothelium. Coagulation factors circulate in plasma with synthesis in liver and in endothelium. Interaction between Factor VIII (FVIII) and von Willebrand factor (VWF) in plasma is critically important, but there remains some question about whether this relationship is first established within the endothelial cell or in plasma. When FVIII is expressed with VWF in a cell that stores VWF, FVIII will also be stored and released. The manuscript will summarize some studies in which gene therapy exploits this relationship between VWF and FVIII to achieve hemostasis even in the presence of circulating inhibitory antibodies to FVIII. VWF is critical to this efficacy in the presence of inhibitors. Since FIX expression in platelets is effective for hemophilia B, efficacy in the presence of inhibitory antibodies to FIX was not achieved and emphasized the importance of VWF to the efficacy of platelet FVIII expression. These approaches have been studied in murine models but will need further study before this approach can be attempted clinically.

Detection and characterization of hepatic engraftment of embryonic stem derived cells by fluorescent stereomicroscopy

BACKGROUND

Embryonic stem (ES) cells have been investigated as a potential replacement therapy for failed organs, such as the liver. However, detection of hepatic engraftment from candidate stem cells has been difficult due to low engraftment efficiency. Previous detection methods required that the graft be processed by molecular and/or immunohistochemical techniques, limiting further functional studies. This study evaluated the use of three-dimensional fluorescent stereomicroscopy for gross detection of ES cell derived hepatic engraftment.

MATERIAL AND METHODS

Murine ES cells expressing the enhanced green fluorescence protein (EGFP) underwent directed endodermal lineage differentiation. Three days after two thirds partial hepatectomy, cells were injected into the liver parenchyma, and livers were harvested at 10 to 20 d and examined by fluorescence stereomicroscopy with a GFP2 long pass filter (100447084; Leica Microsystems AG, Wetzlar, Germany). The sensitivity and reliability of the test was evaluated using quantitative polymerase chain reaction (q-PCR) to assay for the presence of EGFP mRNA in the tissue.

RESULTS

Fluorescent microscopy detected EGFP-positive cells engrafted with normal histology in 5 of 11 specimens. EGFP mRNA was confirmed in all five specimens by q-PCR. Only one of the 11 specimens was negative by fluorescence stereomicroscopy and positive by q-PCR, P < 0.02, Fisher's exact test.

CONCLUSION

Utilization of three-dimensional stereomicroscopy with a GFP2 long pass filter is a powerful and fast screening tool for GFP-ES derived hepatic engraftment.

Quality Assurance in Hemostasis: The Perspective from the College of American Pathologists Proficiency Testing Program

External quality assurance (EQA) is an important component of the total quality assurance program of a clinical hemostasis laboratory. The College of American Pathologists (CAP) helps meet this requirement by providing a proficiency testing program that evaluates a broad range of hemostasis methods and analytes. This article reviews the published experience of the CAP proficiency testing program in hemostasis. The purpose is to formulate general conclusions about the benefits of EQA. Between 1963 and 2006, the performance characteristics of a variety of tests have been evaluated, including the prothrombin time, activated partial thromboplastin time, coagulation factor activity assays (e.g., fibrinogen, factor [F] VIII, FIX, FXI), von Willebrand factor assays, unfractionated heparin monitoring, lupus anticoagulant testing, and platelet function. Based on the results of these evaluations, the major benefits of EQA are to (1) enhance patient care and safety through improved laboratory testing; (2) characterize test accuracy and precision across multiple methods; (3) correlate specific method variables with accuracy and precision; (4) identify interfering substances and quantify their effects across multiple methods; (5) identify clinical laboratories that are at risk for poor performance so that their performance can improve; and (6) satisfy accreditation and regulatory requirements.

Cell lineage and differentiation in taste buds

Mammalian taste buds are maintained through continuous cell renewal so that taste bud cells are constantly generated from progenitor cells throughout life. Taste bud cells are composed of basal cells and elongated cells. Elongated cells are derived from basal cells and contain taste receptor cells (TRC). Morphologically, elongated cells consist of three distinct types of cells: Types I, II and III. In contrast to the remarkable progress in understanding of the molecular basis for taste reception, the mechanisms of taste bud maintenance have remained a major area of inquiry. In this article, we review the expression of regulatory genes in taste buds and their involvement in taste bud cell differentiation. Three major topics include: 1) the Sonic hedgehog (Shh)-expressing cell in the basal cell in taste buds as a transient precursor of elongated cells and as a signal center for the proliferation of progenitor cells; 2) the Mash1-expressing cell as an immature cell state of both Type II and Type III cells and as a mature cell state of Type III cell; and 3) the nerve dependency of gene expression in taste buds. Problems in the application of NCAM for the type III cell marker are also discussed.

Expression of human factor IX gene in murine plasma through lentiviral vector-infected haematopoietic stem cells

1. Haematopoietic stem cells (HSC) are an attractive target for gene therapy. Gene transfer to HSC can provide a potential cure for many inherited diseases. Moreover, recombinant lentiviral vectors can transfer genes efficiently to HSC. In the present study, we used the recombinant lentiviruses FUGW (Flip, ubiquitin promoter, GFP and WRE vector) and FUXW (Flip, ubiquitin promoter, F IX and WRE vector), which carry the enhanced green fluorescent protein (EGFP) and human factor IX (hFIX) gene, respectively, to infect HSC. 2. High titres of recombinant lentivirus were prepared from 293T cells by calcium phosphate-mediated transient cotransfection. Murine mononuclear cells (MNC) separated from murine bone marrow and HSC separated by magnetic cell sorting were cultured in vitro. Cells they were infected by the recombinant lentiviruses FUGW and FUXW. The expression of EGFP was observed under a fluorescent microscope and was analysed by fluorescence-activated cell sorting, whereas the expression of hFIX was detected by ELISA. 3. The results show that the lentiviral vectors can efficiently infect murine HSC in vitro and that transduction was more efficient following cytokine treatment with interleukin (IL)-3, IL-6 and stem cell factor. 4. Haematopoietic stem cells infected with lentivirus FUXW were transplanted into [(60)Co]-irradiated non-obese diabetic/severe combined immunodeficiency (NOD-SCID) mice. The expression of hFIX in the blood plasma of the transplanted mice reached a peak of 44.9 +/- 7.6 ng/mL on Day 7. An assay of transaminase levels and a histological study of the liver showed that there was no significant damage following HSC transplantation to mice. 5. The results of the present study suggest that transplantation of HSC results in the persistant expression of hFIX in mice, which may be useful in haemophilia B gene therapy.

Efficacy and safety of adeno-associated viral vectors based on serotype 8 and 9 vs. lentiviral vectors for hemophilia B gene therapy

BACKGROUND

Adeno-associated viral (AAV) and lentiviral vectors are promising vectors for gene therapy for hemophilia because they are devoid of viral genes and have the potential for long-term gene expression.

OBJECTIVES

To compare the performance of different AAV serotypes (AAV8 and AAV9) vs. lentiviral vectors expressing factor (F) IX.

METHODS AND RESULTS

AAV-based and lentiviral vectors were generated that express FIX from the same hepatocyte-specific expression cassette. AAV9 transduced the liver as efficiently as AAV8 and resulted in supra-physiological FIX levels (3000-6000% of normal) stably correcting the bleeding diathesis. Surprisingly, AAV9 resulted in unprecedented and widespread cardiac gene transfer, which was more efficient than with AAV8. AAV8 and AAV9 were not associated with any proinflammatory cytokine induction, in accordance with their minimal interactions with innate immune effectors. In contrast, lentiviral transduction resulted in modest and stable FIX levels near the therapeutic threshold (1%) and triggered a rapid self-limiting proinflammatory response (interleukin-6), which probably reflected their ability to efficiently interact with the innate immune system.

CONCLUSIONS

AAV8 and 9 result in significantly higher FIX expression levels and have a reduced proinflammatory risk in comparison with lentiviral vectors. The unexpected cardiotropic properties of AAV9 have implications for gene therapy for heart disease.

Efficient AAV1-AAV2 hybrid vector for gene therapy of hemophilia

Adeno-associated virus (AAV) serotype 1 (AAV1) has been shown to be more effective than the well-studied AAV serotype 2 (AAV2) in muscle gene transfer. Replacement of amino acids 350 to 430 of AAV2 VP1 with the corresponding amino acids from VP1 of AAV1 resulted in a hybrid vector, termed AAV-221-IV, which behaved similarly to AAV1 in vitro and in vivo in muscle. Intramuscular injection of 1x10(11) vector particles per mouse of hybrid vector carrying a human FIX transgene in CD4 knockout mice resulted in an average level of human FIX in the plasma of 450 ng/ml, 4- to 10-fold higher than in mice injected with an AAV2 vector carrying the same transgene, and 80% of the transgene levels in animals treated with the same dose of AAV1. DNA analysis of injected muscle showed a 10-fold higher copy number after gene delivery by the hybrid vector compared with AAV2. A comparison of total DNA versus DNA from intact virus particles suggests a higher stability of hybrid virus particles. These results suggest that changes in the AAV capsid have an effect on virus-cell receptor interaction, and also influence trafficking and processing of the virus particle in the cell. This "hybrid vector" retains the heparin-binding sites of AAV2 and, therefore, can be purified by passage through a heparin-Sepharose column with the same efficiency as AAV2. When tested in vivo, either in CD4 knockout mice or in a hemophilic mouse model, the heparin-purified hybrid vector showed >10-fold higher activity than similarly purified AAV2. This demonstrates the utility of this hybrid vector in the performance of large-scale heparin column purification to generate a vector with a high expression profile for muscle-directed gene delivery. Initiation of clinical studies with this hybrid vector may be facilitated because it differs from AAV2 by only nine amino acids.

siRNA silencing of calumenin enhances functional factor IX production

To improve production of functional fully gamma-carboxylated recombinant human clotting factor IX (r-hFIX), cell lines stably overexpressing r-hFIX have been engineered to also overexpress proteins of the gamma-carboxylation system. Here we demonstrate that siRNA silencing of calumenin, an inhibitor of the gamma-carboxylation system, enhances production of functional r-hFIX produced by engineered BHK21 cells. The production yield of functional r-hFIX was 80% in engineered cells where calumenin had been silenced 78%. We propose that this high-yield expression system can easily be adapted to overproduce functional forms of all members of the vitamin K-dependent protein family.

Stem cell-derived erythroid cells mediate long-term systemic protein delivery

We demonstrate here the capacity of erythroid cells to mediate long-term, systemic and therapeutic protein delivery in vivo. By targeting human factor IX (hFIX) expression to late-stage erythropoiesis, we achieve long-term hFIX secretion at levels significantly higher (>tenfold) than those obtained with an archetypal ubiquitous promoter in a mouse model of hemophilia B. Erythroid cell-derived hFIX is biologically active, resulting in phenotypic correction of the bleeding disorder. In addition to achieving high expression levels and resistance to transcriptional silencing, red cell-mediated protein delivery offers multiple advantages including immune tolerance induction, reduction of the risk of insertional oncogenesis and relative ease of application by either engrafting transduced hematopoietic stem cells or transfusing ex vivo-generated, stem cell-derived erythroid cells.

Heterochromatin protein 1 deleted chromo domain decreases gene silencing of transgene in mouse

The heterochromatin protein 1 (HP1) regulates epigenetic gene silencing by promoting and maintaining chromatin condensation. To decrease gene silencing, the chromo domain (CD) in the M31 (the main HP1 in mouse) was deleted by site-directed mutagenesis. Vector pcDNA3.1(+)/M31-DeltaCD, in which the M31-DeltaCD is driven by the CMV promoter, and vector pcDNA3.1(+)/P1A3-M31-DeltaCD, in which the M31-DeltaCD is driven by a goat ss-casein promoter were constructed. The former vector was transfected into a murine fibroblast cell line, which can express enhanced green fluorescent protein (EGFP). EGFP expression, which was determined by flow cytometric analysis, increased approximately 80% in the transfected cells. After injection of the latter vector into transgenic mouse mammary glands, which can express human clotting factor IX (hFIX), the hFIX expression level in the mouse milk increased approximately 40-60% and hFIX in one mouse milk was maintained at a high concentration for over 10 days.

Increased production of functional recombinant human clotting factor IX by baby hamster kidney cells engineered to overexpress VKORC1, the vitamin K 2,3-epoxide-reducing enzyme of the vitamin K cycle

Some recombinant vitamin K-dependent blood coagulation factors (factors VII, IX, and protein C) have become valuable pharmaceuticals in the treatment of bleeding complications and sepsis. Because of their vitamin K-dependent post-translational modification, their synthesis by eukaryotic cells is essential. The eukaryotic cell harbors a vitamin K-dependent gamma-carboxylation system that converts the proteins to gamma-carboxyglutamic acid-containing proteins. However, the system in eukaryotic cells has limited capacity, and cell lines overexpressing vitamin K-dependent clotting factors produce only a fraction of the recombinant proteins as fully gamma-carboxylated, physiologically competent proteins. In this work we have used recombinant human factor IX (r-hFIX)-producing baby hamster kidney (BHK) cells, engineered to stably overexpress various components of the gamma-carboxylation system of the cell, to determine whether increased production of functional r-hFIX can be accomplished. All BHK cell lines secreted r-hFIX into serum-free medium. Overexpression of gamma-carboxylase is shown to inhibit production of functional r-hFIX. On the other hand, cells overexpressing VKORC1, the reduced vitamin K cofactor-producing enzyme of the vitamin K-dependent gamma-carboxylation system, produced 2.9-fold more functional r-hFIX than control BHK cells. The data are consistent with the notion that VKORC1 is the rate-limiting step in the system and is a key regulatory protein in synthesis of active vitamin K-dependent proteins. The data suggest that overexpression of VKORC1 can be utilized for increased cellular production of recombinant vitamin K-dependent proteins.

Haemophilic factors produced by transgenic livestock: abundance that can enable alternative therapies worldwide

Haemophilia replacement factors, both plasma-derived and recombinant, are in relatively short supply and are high-cost products. This has stymied the study and development of alternative methods of administration of haemophilia therapy even in the most economically advanced countries, owing to the large amounts of material needed because bioabsorption and bioavailability of haemophilic factors can be less than 10% when using non-intravenous routes of delivery. There is therefore a need to increase access to therapy worldwide by decreasing the cost and increasing the abundance so that therapy can be achieved through simplified, alternative delivery methods. Transgenic livestock have been used to produce haemophilic factors in milk. Only the pig mammary gland has been shown to carry out the post-translational processing necessary to enable both the biological activity and long circulation half-life needed for therapeutic glycoproteins. Furthermore, the large amounts of recombinant protein that can be produced from pig milk make feasible the use of alternative delivery methods such as oral, intratracheal, subcutaneous, and intramuscular administration.

A new potent hFIX plasmid for hemophilia B gene therapy

PURPOSE

The purpose of this work was to construct and characterize a new potent hFIX plasmid, p2SV-hFIX, which has two hFIX expression units containing the SV40 promoter/enhancer for hemophilia B gene therapy.

METHODS

p1SV-hFIX was constructed by insertion of amplified hFIX cDNA at the ECORI and Xbal sites of pSI expression vector containing simian virus 40 (SV40) promoter/enhancer. To construct p2SV-hFIX, the hFIX expression cassette was isolated from p1SV-hFIX by digestion with restriction enzymes, and the purified expression cassette was inserted at the BglII site of another plSV-hFIX. The gene expression of p1SV-hFIX, p2SV-hFIX, and a plasmid containing a liver-specific apoE enhancer and alpha antitrypsin promoter, pAAV-hAAT-hFIX. were evaluated in various cell lines using polyethylenimine (PEI) as a gene carrier in vitro.

RESULTS

The construction of p1SV-hFIX and p2SV-hFIX were confirmed by restriction enzyme studies. The transfection efficiency of p2SV-hFIX was 3.83-fold and 7.16-fold higher than that of pAAV-hAAT-hFIX in C2C12 and NIH3T3 cells, respectively. p2SV-hFIX also showed higher transfection efficiency than p1SV-hFIX in both cells.

CONCLUSIONS

In accordance with these results, p2SV-hFIX is a new potent hFIX plasmid that can be transfected in various cells. Systemic delivery of p2SV-hFIX via intravenous or intramuscular injection is feasible for treatment of hemophilia B.

Coagulation factors with improved properties for hemophilia gene therapy

Hemophilias A and B are X-linked bleeding disorders that result in a qualitative or quantitative deficiency in coagulation factors VIII (FVIII) and IX (FIX), respectively. Affected patients experience significant morbidity as a result of repeated joint hemorrhages and subsequent arthropathy, and there is increased mortality related to life-threatening bleeding events. The mainstay of therapy is episodic or prophylactic infusions of plasma-derived or recombinant FVIII or FIX. However, gene transfer holds the promise of maintaining plasma levels of FVIII or FIX high enough to prevent the development of joint disease and reduce the risk of life-threatening bleeds or possibly even achieving normal plasma levels. Human gene therapy trials thus far have fallen short of this goal. This review summarizes the inherent limitations in expression of recombinant FVIII and the bioengineering strategies that are currently being explored for constructing novel recombinant FVIII molecules that have improved function. Current strategies for FVIII include increasing mRNA levels, improving secretion efficiency, increasing the rate of thrombin activation, stabilization of the activated form of FVIII, and strategies to prolong FVIII half-life in plasma by disrupting FVIII interaction with its clearance receptors. Strategies to improve the function of FIX include increasing the mRNA levels, reducing interaction with collagen IV, and increasing the specific activity. These novel molecules partnered with advances in gene transfer vector design and delivery may ultimately achieve persistent expression of FVIII and FIX, leading to an effective long-term treatment strategy for the hemophilias.

Increased incidence of neoplasia of the digestive tract in men with persistent activation of the coagulant pathway

BACKGROUND

Thrombin promotes angiogenesis and cell proliferation in cancer. Whether thrombin turnover influences cancer incidence is unknown.

OBJECTIVES

To explore the relation between the status of the coagulant pathway and cancer incidence by population survey.

METHODS

Of 4,009 middle-aged men clinically free of malignancy, 3052 (76.1%) were recruited. Measurements of hemostatic status were made annually for 4 years, and follow-up for morbidity and mortality was maintained thereafter. Persistent activation of the coagulant pathway was diagnosed when prothrombin fragment 1+2 and fibrinopeptide A concentrations exceeded the upper quartiles of the population distribution in two consecutive annual examinations. Cancer incidence rates in men developing persistent activation (taking the time of onset of activation as baseline) were compared with those in men remaining free of this condition.

RESULTS

Persistent activation of the hemostatic pathway was a distinct entity found in 111 men [43 expected by chance alone (P <0.001)], and associated with activation throughout the coagulation pathway. Total mortality (/1000 person-years) was higher in those with persistent activation than in others (17.1 and 9.7, respectively, P=0.015), owing to a higher mortality from all cancers (11.3 and 5.1, respectively, P=0.01), due in turn largely to a higher mortality from cancers of the digestive tract (6.3 and 1.9, respectively, P=0.004). Trends were similar for non-fatal cancers.

CONCLUSIONS

Persistent activation of the coagulant pathway plays a role in the preclinical phase of cancer and is associated with an increased incidence of clinical malignancy, especially of the digestive tract.

Two novel mutations in EGF-like domains of human factor IX dramatically impair intracellular processing and secretion

We investigated the mechanisms responsible for severe factor IX (FIX) deficiency in two cross-reacting material (CRM)-negative hemophilia B patients with a mutation in the first and second epidermal growth factor (EGF) domains of FIX (C71Y and C109Y, respectively). We have determined the kinetics of mutant FIX biosynthesis and secretion in comparison with wild-type FIX (FIXwt). In transfected cells, FIXwt was retrieved as two intracellular molecular forms, rapidly secreted into the culture medium. One appeared to be correctly N-glycosylated, and corresponded to a form trafficking between the endoplasmic reticulum (ER) and Golgi apparatus. The other corresponded to the mature form, ready to be secreted, exhibiting correct N-glycosylation and sialylation. In contrast, the two mutants, FIXC71Y and FIXC109Y, were not secreted from the cells and did not accumulate intracellularly. Relative to FIXwt, they were retained longer in the ER and were only N-glycosylated. In addition, the intracellular concentration of the FIX mutants increased when ALLN, an inhibitor of cysteine proteases and of the proteasome degradation pathway, was added to the culture medium. Both the FIX mutants and FIXwt were associated in the ER with the 78-kDa glucose-regulated protein (GRP78/BiP) and calreticulin (CRT), though the amount of CRT associated with the two mutants was twice as strong as with FIXwt. These results strongly suggest that chaperone and lectin molecules act in concert to ensure both proper folding of FIXwt and the retention of mutant molecules.

Efficient delivery of human clotting factor IX after injection of lentiviral vectors in utero

AIM

To explore gene transfer feasibility for human clotting factor IX (hFIX) mediated by recombinant lentivirus in utero.

METHODS

ICR mice fetus at 17-19 d gestation were received lentiviral vectors carrying hFIX cDNA under the control of liver specific promoter by intrahepatic injection. The expression and distribution of hFIX cDNA and possible immune responses against the hFIX were assessed by ELISA, PCR, RT-PCR, and immunohistochemistry, respectively.

RESULTS

The serum hFIX protein were detected at different time points in all newborn mice, the highest level of hFIX was 50 microg/L and lasted for more than 30 d. Anti-hFIX antibody was not detected. hFIX cDNA was detected in liver, spleen, and heart. The expression of hFIX cDNA was only detected in liver. Besides, no germ line transmission was found at DNA and RNA levels, and no side effect associated with gene transfer was detected.

CONCLUSION

The efficient delivery of hFIX can be achieved by prenatal gene transfer. It thus shows the feasibility of gene therapy for hemophilia in utero.

Thrombophilic families with inheritably associated high levels of coagulation factors VIII, IX and XI

We describe six families in which associated high levels of coagulation factors (F) XI, FIX and FVIII (each with a plasma concentration higher than the 95th percentile found in a control group of 500 asymptomatic individuals: respectively, 135, 145 and 155 IU dL-1) were inherited as a dominant autosomic genetic traits. In these six families, this syndrome is associated with venous thromboembolic events (Odds ratio 41 [4.9-353], P = 0.0006). It seems to predispose to idiopathic events and, as age increases, is often associated with recurrence. First thrombotic episodes occur in young patients (50% of the carriers are symptomatic at the age of 32 years) and in women, can be unmasked by hormonal treatments, mainly oral contraceptives. The association of high levels of coagulation FXI, FIX and FVIII is thus a new rare high-risk inherited thrombophilia syndrome.

[Quality control of recombinant adeno-associated virus type 2/human blood coagulation factor IX]

AIM

To establish quality control requirements and methods for recombinant adeno-associated virus(rAAV) type 2/human blood coagulation factor IX (rAAV-2/hFIX).

METHODS

Identification of rAAV genome fragments, potential contaminants including wild type AAV(wtAAV) and helper virus, were detected by PCR. Purity of rAAV-2/hFIX was analyzed by cation-exchange HPLC and SDS-PAGE. Virus partical numbers were performed by dot blot assay. hFIX expression was demonstrated by ELISA and potency of hFIX was verified by APTT.

RESULTS

Identity of rAAV-2/hFIX was proved. Residues of wtAAV and helper virus were conformed to requirements. Purity of rAAV-2/hFIX were more than 98%. Partical numbers of rAAV-2/hFIX were more than 1.0 x 10(15) VG.L-1. hFIX expression was more than 20.0 micrograms.L-1. hFIX potency was verified by APTT following rAAV-2/hFIX injected to FIX gene knockout mice, potency results conformed to requirements.

CONCLUSION

The methods and requirements had been established for quality control of rAAV-2/hFIX.

Regulation of human factor IX expression using doxycycline-inducible gene expression system

Following substitution therapy with human factor IX (hFIX) concentrate, therapy of haemophilia B by viral gene transfer has become an attractive alternative therapy in recent years. However, high doses of expressed hFIX, which can already be achieved in animal studies, may cause thrombosis in humans (van Hylckama Vlieg et al., 2000). Thus, it should be possible to maintain transgene expression within the therapeutic range. Therefore, we inserted elements of the tetracycline (Tet)-dependent Tet-On gene regulatory system into replication deficient adenovectors. The new system consists of two adenovectors: a response vector expressing hFIX (Ad5.TRE.hFIX), and a regulator vector expressing a second generation reverse tetracycline transactivator controlled by a CMV- (Ad5.CMV.rtTA) or human alpha1-antitrypsin-promoter (Ad5.hAAT.rtTA). Expression studies in four human cell lines showed high expression of hFIX from Ad5.TRE.hFIX in all cell lines in combination with Ad5.CMV.rtTA regulator vector, but only high specific expression in HepG2-cells in combination with Ad5.hAAT.rtTA regulator vector. Additionally, up- and down-regulation of hFIX expression could be demonstrated in vitro with the Ad5.TRE.hFIX/Ad5.CMV.rtTA combination and modulating doxycycline concentrations. When SCID-mice were infected with the Ad5.TRE.hFIX/Ad5.CMV.rtTA combination, up- and down-regulation of hFIX expression was achieved by oral doses of doxycycline for a period of at least two months. Replacement of the Ad5.CMV.rtTA vector by the Ad5.hAAT.rtTA vector showed minimal expression of hFIX in vivo. Although hFIX expression showed a slow and gradual decrease over time in vivo with the Ad5.CMV.rtTA vector, it remained within the therapeutic range. To date, regulation of hFIX has not been described in this way.

The promise of third-generation recombinant therapy and gene therapy

Recombinant factor VIII and IX products have well-established efficacy and safety records. However, concerns about the possibility of viral transmission have prompted efforts to develop recombinant products that are free of added human and animal proteins. The currently licensed second-generation recombinant factor VIII concentrates were introduced in 2000. Two new third-generation products, manufactured without any human- or animal-derived materials, are currently in development and clinical testing. As an alternative to exogenous factor replacement, gene therapy is under investigation for use in the treatment of hemophilia. Gene therapy involves the stable insertion of a functional gene for long-term expression and secretion of endogenous factor VIII or IX protein. Methods used to date have been based on retroviral, adenoviral, and adeno-associated viral vectors, as well as nonviral electroporation. Three phase I trials using these approaches have been completed as of 2002, and one more is ongoing. This article reviews the results of recent clinical studies investigating third-generation recombinant products and gene-based approaches to hemophilia treatment.

Myocardial fibrosis in mice with overexpression of human blood coagulation factor IX

Elevated circulatory levels of many blood coagulation factors are known to be a risk factor for deep vein thrombosis in humans. Here we report the first direct demonstration of a close association between elevated circulatory factor IX levels in mice with thrombosis as well as myocardial fibrosis. Transgenic mice overexpressing human factor IX at persistently high levels died at much younger ages than their cohorts expressing lower levels, or nontransgenic control animals. The median survival age of animals was inversely related to the circulatory levels of human factor IX. Prematurely dying animals had focal fibrotic lesions predominantly present in the left ventricular myocardium, and vasculatures in these lesions showed fibrin deposition. Thromboemboli were also present in other organs, including lung and brain. These observations support the hypothesis that persistently high circulatory levels of factor IX are a risk factor not only for thrombosis and/or thromboembolism, but also for myocardial fibrosis mimicking human myocardial infarction.

Gene transfer as an approach to treating hemophilia

Gene therapy is a novel area of therapeutics in which the active agent is a nucleic acid sequence rather than a protein or small molecule. Successful clinical applications of gene transfer have been limited to date because of shortcomings in the available gene delivery vehicles. The goal of gene transfer for hemophilia is to achieve sustained expression of factor (F) VIII or FIX at levels high enough to improve the symptoms of the disease. Hemophilia has proved to be an attractive model for those interested in gene transfer, and multiple gene transfer strategies are currently being investigated. So far, five different trials, three for hemophilia A and two for hemophilia B, have enrolled approximately 40 patients with severe hemophilia. This article summarizes the gene transfer strategies being investigated, the available preclinical data, and the early clinical results. In the past year, several groups have demonstrated sustained expression of clotting factors at levels of 5 to 10% of normal in large animal models of hemophilia. The goal of the ongoing clinical studies is to determine whether these results can safely be extended to humans.

Negative-strand RNA viral vectors: intravenous application of Sendai virus vectors for the systemic delivery of therapeutic genes

Treatment by gene replacement is critical in the field of gene therapy. Suitable vectors for the delivery of therapeutic genes have to be generated and tested in preclinical settings. Recently, extraordinary features for a local gene delivery by Sendai virus vectors (SeVV) have been reported for different tissues. Here we show that direct intravenous application of SeVV in mice is not only feasible and safe, but it results in the secretion of therapeutic proteins to the circulation, for example, human clotting Factor IX (hFIX). In vitro characterization of first-generation SeVV demonstrated that secreted amounts of hFIX were at least comparable to published results for retroviral or adeno-associated viral vectors. Furthermore, as a consideration for application in humans, SeVV transduction led to efficient hFIX synthesis in primary human hepatocytes, and SeVV-encoded hFIX proteins could be shown to be functionally active in the human clotting cascade. In conclusion, our investigations demonstrate for the first time that intravenous administration of negative-strand RNA viral vectors may become a useful tool for the wide area of gene replacement requirements.

Epstein-Barr virus vectors provide prolonged robust factor IX expression in mice

We demonstrate that vectors incorporating components from Epstein-Barr virus (EBV) for retention and from human genomic DNA for replication greatly enhance the level and duration of marker gene expression in dividing cultured cells. The same types of vectors were tested in vivo by high-pressure tail vein injection of naked DNA in mice, resulting in liver delivery and expression. The therapeutic gene was a human factor IX (hFIX) minigene comprising genomically derived 5', 3', and intronic sequences that provided relatively good gene expression in vivo. We demonstrated that addition of the EBV EBNA1 gene and its family of repeats binding sites provided a 10- to 100-fold increase in prolonged hFIX expression in mouse liver. A single 25-microg dose of vector DNA generated normal (>5 microg/mL) levels of hFIX throughout the 8 month duration of the experiment. Vector DNA with or without the EBV sequences was retained in liver cells, and vector replication was not a factor in these nondividing liver cells. Instead, it appears that enhancement of stable hFIX expression by the EBV components was responsible for the increased level and duration of therapeutic gene expression. The EBV sequences also significantly enhanced stable expression of a vector carrying the full genomic hFIX gene delivered to mouse liver. These results underline the crucial importance of appropriate gene expression signals on gene therapy vectors and the utility of EBV sequences in particular for increasing stable gene expression.

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.

[The study on the stable inheritance and expression of foreign gene in transgenic mice]

Two transgenic mouse strains, in which the expression of human factor IX (hFIX) in the milk were different significantly, were bred, and the foreign gene integration as well as the content of hFIX in the milk were detected by PCR, Southern blot, FISH and ELISA, respectively. The results showed that approximately 50% offsprings were transgenic positive. Foreign gene integrated in mouse chromosomes was intact. The hFIX expression of each mouse in the same strain was different, the content of hFIX in the milk was (43.32 +/- 5.41) microgram/mL in FIX-33 transgenic strain and (1.16 +/- 0.45) microgram/mL in FIX-124 transgenic strain. Meanwhile, the hFIX gene expression between the two strains was different remarkably (P < 0.01). We conclude that the characteristics of inheritance and expression in the founder were able to be transferred to their offsprings stably.

Site-specific genomic integration produces therapeutic Factor IX levels in mice

We used the integrase from phage phiC31 to integrate the human Factor IX (hFIX) gene permanently into specific sites in the mouse genome. A plasmid containing attB and an expression cassette for hFIX was delivered to the livers of mice by using high-pressure tail vein injection. When an integrase expression plasmid was co-injected, hFIX serum levels increased more than tenfold to approximately 4 microg/ml, similar to normal FIX levels, and remained stable throughout the more than eight months of the experiment. hFIX levels persisted after partial hepatectomy, suggesting genomic integration of the vector. Site-specific integration was proven by characterizing and quantifying genomic integration in the liver at the DNA level. Integration was documented at two pseudo-attP sites, native sequences with partial identity to attP, with one site highly predominant. This study demonstrates in vivo gene transfer in an animal by site-specific genomic integration.

Sustained high-level expression of human factor IX (hFIX) after liver-targeted delivery of recombinant adeno-associated virus encoding the hFIX gene in rhesus macaques

The feasibility, safety, and efficacy of liver-directed gene transfer was evaluated in 5 male macaques (aged 2.5 to 6.5 years) by using a recombinant adeno-associated viral (rAAV) vector (rAAV-2 CAGG-hFIX) that had previously mediated persistent therapeutic expression of human factor IX (hFIX; 6%-10% of physiologic levels) in murine models. A dose of 4 x 10(12) vector genomes (vgs)/kg of body weight was administered through the hepatic artery or portal vein. Persistence of the rAAV vgs as circular monomers and dimers and high-molecular-weight concatamers was documented in liver tissue by Southern blot analysis for periods of up to 1 year. Vector particles were present in plasma, urine, or saliva for several days after infusion (as shown by polymerase chain reaction analysis), and the vgs were detected in spleen tissue at low copy numbers. An enzyme-linked immunosorption assay capable of detecting between 1% and 25% of normal levels of hFIX in rhesus plasma was developed by using hyperimmune serum from a rhesus monkey that had received an adenoviral vector encoding hFIX. Two macaques having 3 and 40 rAAV genome equivalents/cell, respectively, in liver tissue had 4% and 8% of normal physiologic plasma levels of hFIX, respectively. A level of hFIX that was 3% of normal levels was transiently detected in one other macaque, which had a genome copy number of 25 before abrogation by a neutralizing antibody (inhibitor) to hFIX. This nonhuman-primate model will be useful in further evaluation and development of rAAV vectors for gene therapy of hemophilia B.

Expression of coagulation factor IX in a haematopoietic cell line

We have developed a gene therapy project for haemophilia B which aims to express factor IX (FIX) in haematopoietic lineage. Haematopoietic stem cells and subsequent megakaryocyte-derived cells represent the target cells of this approach. Our speculation is that platelets can deliver the coagulation factor at the site of injury, and subsequently correct the haemostasis defect. In order to direct FIX expression in cells from the megakaryocytic lineage, we designed a FIX cassette where the FIX cDNA was placed under the control of the tissue-specific glycoprotein IIb (GPIIb) promoter. In stably transfected HEL cells, FIX production was higher when driven by the GPIIb promoter compared to the CMV promoter. Using a cassette containing both the GPIIb promoter and a truncated FIX intron 1, FIX synthesis was dramatically increased in HEL cells. Northern blot analysis demonstrated an increase in FIX mRNA amounts, which paralleled with an increase of FIX antigen in the culture supernatants. Using a one-stage clotting assay and an activation by FXIa and FVIIa/TF, the HEL-derived recombinant FIX was shown to be a biologically active protein. This recombinant protein exhibited a 60-kDa molecular mass and was more heterogeneous than plasma immunopurified FIX (Mononine). The molecular mass difference could be partly explained by a different glycosylation pattern. The GPIIb promoter appears therefore to be a very attractive sequence to specifically direct FIX production in the megakaryocytic compartment of hematopoietic cells. These data also demonstrate that hematopoietic cells may represent potential target cells in an approach to gene therapy of haemophilia B.

Retroviral vectors produced in the cytoplasmic vaccinia virus system transduce intron-containing genes

Introns and polyadenylation (pA) sites are known to improve transcript stability and nuclear-cytoplasmic transport and are normally present in efficient gene expression vectors. Standard retroviral vectors, however, do not allow the inclusion of such sequence elements, as mRNA processing at internal splice and pA sites interferes with the production of functional full-length vector genomes. In this report we examined the capability of hybrid vaccinia/retroviral vectors to transduce complex gene cassettes with nuclear RNA processing signals within the retroviral genome. A retroviral vector was constructed that contains a gene of interest (the human coagulation factor IX [FIX] cDNA), including an intron and an internal pA site. The modified proviral vector genome was cloned downstream of a vaccinia virus promoter and was inserted into the vaccinia virus genome. Infection of a packaging cell line with the recombinant vaccinia virus vector resulted in secretion of retroviral particles at average titers of 10(5) CFU per ml of cell culture supernatant. Due to the cytoplasmic transcription and the nonrecognition of nuclear transcription signals in the vaccinia virus system, full-length transcripts were obtained that still contained the intron. In the retrovirally transduced cell lines the FIX transcripts were terminated at the internal pA site. The transcripts were quantitatively spliced, and FIX was secreted. Recombinant cell lines with stable single-copy inserts containing sequence elements necessary for efficient gene function could be generated. Thus, a relatively simple cytoplasmic system for the generation of complex retroviral vectors is described. Retroviral vectors transducing intron-containing gene cassettes may play a further role in gene therapy applications.

Production of human clotting Factor IX without toxicity in mice after vascular delivery of a lentiviral vector

Replication-deficient lentiviral vectors (LV) have been shown to enable the stable genetic modification of multiple cell types in vivo. We demonstrate here that vascular and hepatic delivery of a third-generation HIV-derived lentiviral vector encoding human Factor IX (LV-hFIX) produced potentially therapeutic serum levels of hFIX protein with no vector-mediated local or systemic toxicity of adult mice. Portal vein administration produced the highest serum levels of hFIX and demonstrated proportionally higher levels of gene transfer to the liver with up to 4% of hepatocytes expressing hFIX. Vascular delivery of a lentiviral vector encoding GFP resulted in genetic modification of up to 12% of liver cells. Cell proliferation was not required for hepatocyte transduction with either vector. Serum hFIX levels reached 4% of normal levels following vascular LV-mediated hFIX gene transfer and remained stable for months following vector administration.

Selection of in vitro produced, transgenic embryos by nested PCR for efficient production of transgenic goats

The production of valuable pharmaceutical proteins using transgenic animals as bioreactors has become one of the goals of biotechnology. However, the efficiency of producing transgenic animals by means of pronuclear microinjection is low. This may be attributed in part to the low integration rate of foreign DNA. Therefore, a large number of recipients are required to produce transgenic animals. We recently developed a transgenic procedure that combined the techniques of goat oocyte in vitro maturation (IVM), in vitro fertilization (IVF), microinjection, preimplantation selection of the transgenic embryos with nested PCR and transferring the transgenic embryos into the recipient goat uterus to produce transgenic goats. Thirty-seven transgenic embryos determined by nested PCR were transferred to thirty-two recipient goats. In the end, four live-born kids were produced. As predicted, all the live kids were transgenic as identified by PCR as well as Southern blot hybridization, The integration rate was 100% (4/4) which was completely in accordance with the results of embryo preimplantation detection. The results showed a significant decrease in the number of recipients required as only 8 recipients (32/4) were needed to obtain one live transgenic goat. We suggest that the transgenic system described herein may provide an improved way to efficiently produce transgenic goats on a large scale.

Posttranslational modifications of recombinant myotube-synthesized human factor IX

Recent data demonstrate that the introduction into skeletal muscle of an adeno-associated viral (AAV) vector expressing blood coagulation factor IX (F.IX) can result in long-term expression of the transgene product and amelioration of the bleeding diathesis in animals with hemophilia B. These data suggest that biologically active F.IX can be synthesized in skeletal muscle. Factor IX undergoes extensive posttranslational modifications in the liver, the normal site of synthesis. In addition to affecting specific activity, these posttranslational modifications can also affect recovery, half-life in the circulation, and the immunogenicity of the protein. Before initiating a human trial of an AAV-mediated, muscle-directed approach for treating hemophilia B, a detailed biochemical analysis of F.IX synthesized in skeletal muscle was carried out. As a model system, human myotubes transduced with an AAV vector expressing F.IX was used. F.IX was purified from conditioned medium using a novel strategy designed to purify material representative of all species of rF.IX in the medium. Purified F.IX was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), N-terminal sequence analysis, chemical gamma-carboxyglutamyl analysis, carbohydrate analysis, assays for tyrosine sulfation, and serine phosphorylation, and for specific activity. Results show that myotube-synthesized F.IX has specific activity similar to that of liver-synthesized F.IX. Posttranslational modifications critical for specific activity, including removal of the signal sequence and propeptide, and gamma-carboxylation of the N-terminal glutamic acid residues, are also similar, but carbohydrate analysis and assessment of tyrosine sulfation and serine phosphorylation disclose differences. In vivo experiments in mice showed that these differences affect recovery but not half-life of muscle-synthesized F.IX.

Acetaminophen causes an increased International Normalized Ratio by reducing functional factor VII

Acetaminophen may increase International Normalized Ratio (INR) in patients taking anticoagulation medication, and in patients with acetaminophen poisoning without hepatic injury. The objective of this study was to describe and investigate the effect of acetaminophen on INR. The authors studied patients admitted to a regional toxicology treatment center with acetaminophen poisoning with INR and without potentially confounding coingestion or hepatic injury. Exposed and nonexposed (control) cohorts were recruited from admissions with acetaminophen poisoning and psychotropic drug poisoning, respectively. From 1,437 acetaminophen poisonings, after exclusions, there were 143 admissions with 205 estimations of INR. INR showed a time-dependent increase. Fifty percent of all patients and 66% of those with an extrapolated 4-hour acetaminophen concentration > or = 150 mg/L had an abnormal INR at some time. Dose ingested (p = 0.01) and nomogram-based risk (p for trend = 0.005) were correlated with the effect. N-acetylcysteine had a protective effect. Functional factor VII was lower (p = 0.005) in exposed patients (n = 30) than controls (n = 8), and less than antigenic factor VII in exposed patients (p = 0.03). Factor IX was lower (p = 0.02). Factor VIIIc was not significantly different. The authors concluded that an isolated, small rise in INR is common after acetaminophen poisoning without hepatic injury. It appears to be caused by inhibition of Vitamin K-dependent activation of coagulation factors. This effect suggests a possible mechanism for the observed interaction between acetaminophen and warfarin.