Liver-directed gene therapy: a retroviral vector with a complete LTR and the ApoE enhancer-alpha 1-antitrypsin promoter dramatically increases expression of human alpha 1-antitrypsin in vivo

Safety and feasibility of the gene transfer of hemopexin for conditions with increased free heme

Heme is a fundamental molecule for several biological processes, but when released in the extracellular space such as in hemolytic diseases, it can be toxic to cells and tissues. Hemopexin (HPX) is a circulating protein responsible for removing free heme from the circulation, whose levels can be severely depleted in conditions such as sickle cell diseases. Accordingly, increasing HPX levels represents an attractive strategy to mitigate the deleterious effects of heme in these conditions. Gene transfer of liver-produced proteins with adeno-associated virus (AAV) has been shown to be an effective and safety strategy in animal and human studies mainly in hemophilia. Here, we report the feasibility of increasing HPX levels using an AAV8 vector expressing human HPX (hHPX). C57Bl mice were injected with escalating doses of our vector, and expression was assessed by enzyme immunoassay (ELISA), Western blot, and quantitative polymerase chain reaction (qPCR). In addition, the biological activity of transgenic hHPX was confirmed using two different models of heme challenge consisting of serial heme injections or phenylhydrazine-induced hemolysis. Sustained expression of hHPX was confirmed for up to 26 weeks in plasma. Expression was dose-dependent and not associated with clinical signs of toxicity. hHPX levels were significantly reduced by heme infusions and phenylhydrazine-induced hemolysis. No clinical toxicity or laboratory signs of liver damage were observed in preliminary short-term heme challenge studies. Our results confirm that long-term expression of hHPX is feasible and safe in mice, even in the presence of heme overload. Additional studies are needed to explore the effect of transgenic HPX protein in animal models of chronic hemolysis.

Adeno-Associated Virus Gene Therapy for Hemophilia

In vivo gene therapy is rapidly emerging as a new therapeutic paradigm for monogenic disorders. For almost three decades, hemophilia A (HA) and hemophilia B (HB) have served as model disorders for the development of gene therapy. This effort is soon to bear fruit with completed pivotal adeno-associated viral (AAV) vector gene addition trials reporting encouraging results and regulatory approval widely anticipated in the near future for the current generation of HA and HB AAV vectors. Here we review the clinical development of AAV gene therapy for HA and HB and examine outstanding questions that have recently emerged from AAV clinical trials for hemophilia and other monogenic disorders.

Characteristics of BAY 2599023 in the Current Treatment Landscape of Hemophilia A Gene Therapy

Hemophilia A, a single gene disorder leading to deficient Factor VIII (FVIII), is a suitable candidate for gene therapy. The aspiration is for single administration of a genetic therapy that would allow the production of endogenous FVIII sufficient to restore hemostasis and other biological processes. This would potentially result in reliable protection from bleeding and its associated physical and emotional impacts. Gene therapy offers the possibility of a clinically relevant improvement in disease phenotype and transformational improvement in quality of life, including an opportunity to engage in physical activities more confidently. Gene therapy products for hemophilia A in advanced clinical development use adeno-associated viral (AAV) vectors and a codon-optimized B-domain deleted FVIII transgene. However, the different AAV-based gene therapies have distinct design features, such as choice of vector capsid, enhancer and promoter regions, FVIII transgene sequence and manufacturing processes. These, in turn, impact patient eligibility, safety and efficacy. Ideally, gene therapy technology for hemophilia A should offer bleed protection, durable FVIII expression, broad eligibility and limited response variability between patients, and long-term safety. However, several limitations and challenges must be overcome. Here, we introduce the characteristics of the BAY 2599023 (AAVhu37.hFVIIIco, DTX 201) gene therapy product, including the low prevalence in the general population of anti-AAV-hu37 antibodies, as well as other gene therapy AAV products and approaches. We will examine how these can potentially meet the challenges of gene therapy, with the ultimate aim of improving the lives of patients with hemophilia A.

Long-term correction of hemorrhagic diathesis in hemophilia A mice by an AAV-delivered hybrid FVIII composed of the human heavy chain and the rat light chain

Conventional therapies for hemophilia A (HA) are prophylactic or on-demand intravenous FVIII infusions. However, they are expensive and inconvenient to perform. Thus, better strategies for HA treatment must be developed. In this study, a recombinant FVIII cDNA encoding a human/rat hybrid FVIII with an enhanced procoagulant potential for adeno-associated virus (AAV)-delivered gene therapy was developed. Plasmids containing human FVIII heavy chain (hHC), human light chain (hLC), and rat light chain (rLC) were transfected into cells and hydrodynamically injected into HA mice. Purified AAV viruses were intravenously injected into HA mice at two doses. Results showed that the hHC + rLC protein had a higher activity than the hHC + hLC protein at comparable expression levels. The specific activity of hHC + rLC was about 4- to 8-fold higher than that of their counterparts. Hydrodynamic injection experiments obtained consistent results. Notably, the HA mice undergoing the AAV-delivered hHC + rLC treatment exhibited a visibly higher activity than those treated with hHC + hLC, and the therapeutic effects lasted for up to 40 weeks. In conclusion, the application of the hybrid FVIII (hHC + rLC) via an AAV-delivered gene therapy substantially improved the hemorrhagic diathesis of the HA mice. These data might be of help to the development of optimized FVIII expression cassette for HA gene therapy.

Translational Potential of Immune Tolerance Induction by AAV Liver-Directed Factor VIII Gene Therapy for Hemophilia A

Hemophilia A (HA) is an X-linked bleeding disorder due to deficiencies in coagulation factor VIII (FVIII). The major complication of current protein-based therapies is the development of neutralizing anti-FVIII antibodies, termed inhibitors, that block the hemostatic effect of therapeutic FVIII. Inhibitors develop in about 20-30% of people with severe HA, but the risk is dependent on the interaction between environmental and genetic factors, including the underlying F8 gene mutation. Recently, multiple clinical trials evaluating adeno-associated viral (AAV) vector liver-directed gene therapy for HA have reported promising results of therapeutically relevant to curative FVIII levels. The inclusion criteria for most trials prevented enrollment of subjects with a history of inhibitors. However, preclinical data from small and large animal models of HA with inhibitors suggests that liver-directed gene therapy can in fact eradicate pre-existing anti-FVIII antibodies, induce immune tolerance, and provide long-term therapeutic FVIII expression to prevent bleeding. Herein, we review the accumulating evidence that continuous uninterrupted expression of FVIII and other transgenes after liver-directed AAV gene therapy can bias the immune system toward immune tolerance induction, discuss the current understanding of the immunological mechanisms of this process, and outline questions that will need to be addressed to translate this strategy to clinical trials.

Protein-Engineered Coagulation Factors for Hemophilia Gene Therapy

Hemophilia A (HA) and hemophilia B (HB) are X-linked bleeding disorders due to inheritable deficiencies in either coagulation factor VIII (FVIII) or factor IX (FIX), respectively. Recently, gene therapy clinical trials with adeno-associated virus (AAV) vectors and protein-engineered transgenes, B-domain deleted (BDD) FVIII and FIX-Padua, have reported near-phenotypic cures in subjects with HA and HB, respectively. Here, we review the biology and the clinical development of FVIII-BDD and FIX-Padua as transgenes. We also examine alternative bioengineering strategies for FVIII and FIX, as well as the immunological challenges of these approaches. Other engineered proteins and their potential use in gene therapy for hemophilia with inhibitors are also discussed. Continued advancement of gene therapy for HA and HB using protein-engineered transgenes has the potential to alleviate the substantial medical and psychosocial burdens of the disease.

Engineering cell-based therapies to interface robustly with host physiology

Engineered cell-based therapies comprise a rapidly growing clinical technology for treating disease by leveraging the natural capabilities of cells, including migration, information transduction, and biosynthesis and secretion. There now exists a substantial portfolio of intracellular and extracellular sensors that enable bioengineers to program cells to execute defined responses to specific changes in state or environmental cues. As our capability to construct more sophisticated cellular programs increases, assessing and improving the degree to which cell-based therapies perform as desired in vivo will become an increasingly important consideration and opportunity for technological advancement. In this review, we seek to describe both current capabilities and potential needs for building cell-based therapies that interface with host physiology in a manner that is robust - a phrase we use in this context to describe the achievement of therapeutic efficacy across a range of patients and implementations. We first review the portfolio of sensors and outputs currently available for use in cell-based therapies by highlighting key advancements and current gaps. Then, we propose a conceptual framework for evaluating and pursuing robust clinical performance of engineered cell-based therapies.

Genome-wide RNAi screening identifies host restriction factors critical for in vivo AAV transduction

Viral vectors based on the adeno-associated virus (AAV) hold great promise for in vivo gene transfer; several unknowns, however, still limit the vectors' broader and more efficient application. Here, we report the results of a high-throughput, whole-genome siRNA screening aimed at identifying cellular factors regulating AAV transduction. We identified 1,483 genes affecting vector efficiency more than 4-fold and up to 50-fold, either negatively or positively. Most of these factors have not previously been associated to AAV infection. The most effective siRNAs were independent from the virus serotype or analyzed cell type and were equally evident for single-stranded and self-complementary AAV vectors. A common characteristic of the most effective siRNAs was the induction of cellular DNA damage and activation of a cell cycle checkpoint. This information can be exploited for the development of more efficient AAV-based gene delivery procedures. Administration of the most effective siRNAs identified by the screening to the liver significantly improved in vivo AAV transduction efficiency.

An engineered U1 small nuclear RNA rescues splicing defective coagulation F7 gene expression in mice

BACKGROUND

The ability of the spliceosomal small nuclear RNA U1 (U1snRNA) to rescue pre-mRNA splicing impaired by mutations makes it an attractive therapeutic molecule. Coagulation factor deficiencies due to splicing mutations are relatively frequent and could therefore benefit from this strategy. However, the effects of U1snRNAs in vivo remain unknown.

OBJECTIVES

To assess the rescue of the F7 c.859+5G>A splicing mutation (FVII+5A), causing severe human factor VII (hFVII) deficiency, by the modified U1snRNA+5a (U1+5a) in a murine model.

METHODS

Mice expressing the human F7 c.859+5G>A mutant were generated following liver-directed expression by plasmid or recombinant adeno-associated viral (AAV) vector administration. The rescue of the splice-site defective pre-mRNA by U1+5a was monitored in liver and plasma through hFVII-specific assays.

RESULTS

Injection of plasmids encoding the U1+5a rescued plasma hFVII levels, which increased from undetectable to ~8.5% of those obtained with the wild-type hFVII plasmid control. To assess long-term effects, mice were injected with low and high doses of two AAV vectors encoding the FVII+5A splice site mutant as template to be corrected by U1+5a. This strategy resulted in hFVII plasma levels of 3.9 ± 0.8 or 23.3 ± 5.1 ng mL⁻¹ in a dose-dependent manner, corresponding in patients to circulating FVII levels of ~1-4.5% of normal. Moreover, in both experimental models, we also detected correctly spliced hFVII transcripts and hFVII-positive cells in liver cells.

CONCLUSIONS

Here we provide the first in vivo proof of-principle of the rescue of the expression of a splicing-defective F7 mutant by U1snRNAs, thus highlighting their therapeutic potential in coagulation disorders.

Quantitative analysis of α-L-iduronidase expression in immunocompetent mice treated with the Sleeping Beauty transposon system

The Sleeping Beauty transposon system, a non-viral, integrating vector that can deliver the alpha-L-iduronidase-encoding gene, is efficient in correcting mucopolysaccharidosis type I in NOD/SCID mice. However, in previous studies we failed to attain reliable long-term alpha-L-iduronidase expression in immunocompetent mice. Here, we focused on achieving sustained high-level expression in immunocompetent C57BL/6 mice. In our standard liver-directed treatment we hydrodynamically infuse mice with plasmids containing a SB transposon-encoding human alpha-L-iduronidase, along with a source of SB transposase. We sought to 1) minimize expression of the therapeutic enzyme in antigen-presenting cells, while avoiding promoter shutdown and gender bias, 2) increase transposition efficiency and 3) improve immunosuppression. By using a liver-specific promoter to drive IDUA expression, the SB100X hyperactive transposase and transient cyclophosphamide immunosuppression we achieved therapeutic-level (>100 wild-type) stabilized expression for 1 year in 50% of C57BL/6 mice. To gain insights into the causes of variability in transgene expression, we quantified the rates of alpha-L-iduronidase activity decay vis-a-vis transposition and transgene maintenance using the data obtained in this and previous studies. Our analyses showed that immune responses are the most important variable to control in order to prevent loss of transgene expression. Cumulatively, our results allow transition to pre-clinical studies of SB-mediated alpha-L-iduronidase expression and correction of mucopolysaccharidosis type I in animal models.

Terminal differentiation of cardiac and skeletal myocytes induces permissivity to AAV transduction by relieving inhibition imposed by DNA damage response proteins

Gene therapy vectors based on the adeno-associated virus (AAV) are extremely efficient for gene transfer into post-mitotic cells of heart, muscle, brain, and retina. The reason for their exquisite tropism for these cells has long remained elusive. Here, we show that upon terminal differentiation, cardiac and skeletal myocytes downregulate proteins of the DNA damage response (DDR) and that this markedly induces permissivity to AAV transduction. We observed that expression of members of the MRN complex (Mre11, Rad50, Nbs1), which bind the incoming AAV genomes, faded in cardiomyocytes at ~2 weeks after birth, as well as upon myoblast differentiation in vitro; in both cases, withdrawal of the cells from the cell cycle coincided with increased AAV permissivity. Treatment of proliferating cells with short-interfering RNAs (siRNAs) against the MRN proteins, or with microRNA-24, which is normally upregulated upon terminal differentiation and negatively controls the Nbs1 levels, significantly increased permissivity to AAV transduction. Consistently, delivery of these small RNAs to the juvenile liver concomitant with AAV markedly improved in vivo hepatocyte transduction. Collectively, these findings support the conclusion that cellular DDR proteins inhibit AAV transduction and that terminal cell differentiation relieves this restriction.

Site-specific integration and tailoring of cassette design for sustainable gene transfer

Integrative gene transfer methods are limited by variable transgene expression and by the consequences of random insertional mutagenesis that confound interpretation in gene-function studies and may cause adverse events in gene therapy. Site-specific integration may overcome these hurdles. Toward this goal, we studied the transcriptional and epigenetic impact of different transgene expression cassettes, targeted by engineered zinc-finger nucleases to the CCR5 and AAVS1 genomic loci of human cells. Analyses performed before and after integration defined features of the locus and cassette design that together allow robust transgene expression without detectable transcriptional perturbation of the targeted locus and its flanking genes in many cell types, including primary human lymphocytes. We thus provide a framework for sustainable gene transfer in AAVS1 that can be used for dependable genetic manipulation, neutral marking of the cell and improved safety of therapeutic applications, and demonstrate its feasibility by rapidly generating human lymphocytes and stem cells carrying targeted and benign transgene insertions.

The Sleeping Beauty transposon system: a non-viral vector for gene therapy

Over the past decade, the Sleeping Beauty (SB) transposon system has been developed as the leading non-viral vector for gene therapy. This vector combines the advantages of viruses and naked DNA. Here we review progress over the last 2 years in vector design, methods of delivery and safety that have supported its use in the clinic. Currently, the SB vector has been validated for ex vivo gene delivery to stem cells, including T-cells for the treatment of lymphoma. Progress in delivery of SB transposons to liver for treatment of various systemic diseases, such as hemophilia and mucopolysaccharidoses types I and VII, has encountered some problems, but even here progress is being made.

Delivery of an EBV episome by a self-circularizing helper-dependent adenovirus: long-term transgene expression in immunocompetent mice

Epstein-Barr virus (EBV) evolved an episomal system for maintaining life-long, latent infection of human B lymphocytes. Circular episomes engineered from EBV components required for this latent form of infection have the capacity to persist in most types of replicating mammalian cells without DNA integration and the pitfalls of insertional mutagenesis. EBV episomes are typically transduced using low-efficiency methods. Here we present a method for efficient delivery of EBV episomes to nuclei of hepatocytes in living mice using a helper-dependent adenoviral vector and Cre-mediated recombination in vivo to generate circular EBV episomes following infection. Cre is transiently expressed from a hepatocyte-specific promoter so that vector generation and transgene expression are tissue specific. We show long-term persistence of the circularized vector DNA and expression of a reporter gene in hepatocytes of immunocompetent mice.

A study of the expression of functional human coagulation factor IX in keratinocytes using a nonviral vector regulated by K14 promoter

Ex vivo gene therapy requires a suitable bioreactor for production and delivery of the gene products into a target tissue, and keratinocyte is suitable model in this regard because of its potential for systemic release of proteins. To establish a keratinocyte-specific expression system, a mammalian-based expression plasmid equipped with a 2,240-bp fragment from the human keratin 14 (k14) gene enhancer/promoter region was constructed and used for the insertion of the human coagulation factor IX (hFIX)-cDNA downstream the K14-derived regulatory elements. The human epidermal keratinocytes isolated from neonatal foreskin were cultivated in keratinocyte serum-free media and transfected with the recombinant plasmid. The K14-promoter-driven expression of recombinant hFIX (rhFIX) was evaluated by performing coagulation test as well as enzyme-linked immunosorbent assay on the cultured media collected from the transfected cells at various stages. The rhFIX corresponding transcript and protein were confirmed by performing reverse transcription PCR as well as immunoblotting experiments, respectively. Based on the coagulation activities obtained from the conditioned media of nine isolated clones, the hFIX expression levels vary from 5% to 39% of normal human plasma. Expression levels of the hFIX obtained in this study are comparable to those reported for viral systems. The obtained data supported the potential of keratinocyte for the expression and secretion of biologically active rhFIX and underscore the importance of the examined cis sequences for enhancing gene expression in a mammalian expression system. Besides, it has provided means for further bioengineering strategies to improve the expression efficiency of the hFIX in keratinocytes and other mammalian host cells.

AAV2/8-mediated correction of OTC deficiency is robust in adult but not neonatal Spf(ash) mice

Ornithine transcarbamylase (OTC) deficiency, the most common urea cycle disorder, is associated with severe hyperammonemia accompanied by a high risk of neurological damage and death in patients presenting with the neonatal-onset form. Contemporary therapies, including liver transplantation, remain inadequate with considerable morbidity, justifying vigorous investigation of alternate therapies. Clinical evidence suggests that as little as 3% normal enzyme activity is sufficient to ameliorate the severe neonatal phenotype, making OTC deficiency an ideal model for the development of liver-targeted gene therapy. In this study, we investigated metabolic correction in neonatal and adult male OTC-deficient Spf(ash) mice following adeno-associated virus (AAV)2/8-mediated delivery of the murine OTC complementary DNA under the transcriptional control of a liver-specific promoter. Substantially supraphysiological levels of OTC enzymatic activity were readily achieved in both adult and neonatal mice following a single intraperitoneal (i.p.) injection, with metabolic correction in adults being robust and life-long. In the neonates, however, full metabolic correction was transient, although modest levels of OTC expression persisted into adulthood. Although not directly testable in Spf(ash) mice, these levels were theoretically sufficient to prevent hyperammonemia in a null phenotype. This loss of expression in the neonatal liver is the consequence of hepatocellular proliferation and presents an added challenge to human therapy.

Long-term hepatitis C internal ribosome entry site-dependent gene expression mediated by phage φC31 integrase in mouse model

Background

The lack of a robust small animal model for hepatitis C virus (HCV) has hindered the development of novel drugs, including internal ribosome entry site (IRES) inhibitors. Phage φC31 integrase has emerged as a potent tool for achieving long-term gene expression in vivo. This study utilized φC31 integrase to develop a stable, reproducible and easily accessible HCV IRES mouse model.

Methods

φC31 integrase plasmid and the reporter vector, HCV-IRES–luciferase expression cassette (containing an attB site), was codelivered to murine livers using high pressure tail vein injection. HCV IRES-dependent translation refected by luciferase expression was accurately monitored in vivo by bioluminescence imaging. Genomic integration of the transgene was confirmed by partial hepatectomy and nested PCR. An HCV IRES-targeted short hairpin RNA (shRNA) expression plasmid, sh184, was hydrodynamically transfected into mouse liver to study its inhibition efficacy in vivo.

Results

φC31 integrase mediated intramolecular recombination between wild-type attB and attP sites in mice. The expression of luciferase was stable after 30 days post-transfection and remained so for 300 days only in the livers of mice that were coinjected with the integrase-encoding plasmid. Luciferase levels reduced dramatically after hydrodynamic transfection of sh184.

Conclusions

These results indicate that this mouse model provides a powerful tool for accurate and long-term evaluation of potential anti-IRES compounds in vivo.

Robust in vivo transduction of a genetically stable Epstein-Barr virus episome to hepatocytes in mice by a hybrid viral vector

To make a safe, long-lasting gene delivery vehicle, we developed a hybrid vector that leverages the relative strengths of adenovirus and Epstein-Barr virus (EBV). A fully gene-deleted helper-dependent adenovirus (HDAd) is used as the delivery vehicle for its scalability and high transduction efficiency. Upon delivery, a portion of the HDAd vector is recombined to form a circular plasmid. This episome includes two elements from EBV: an EBV nuclear antigen 1 (EBNA1) expression cassette and an EBNA1 binding region. Along with a human replication origin, these elements provide considerable genetic stability to the episome in replicating cells while avoiding insertional mutagenesis. Here, we demonstrate that this hybrid approach is highly efficient at delivering EBV episomes to target cells in vivo. We achieved nearly 100% transduction of hepatocytes after a single intravenous injection in mice. This is a substantial improvement over the transduction efficiency of previously available physical and viral methods. Bioluminescent imaging of vector-transduced mice demonstrated that luciferase transgene expression from the hybrid was robust and compared well to a traditional HDAd vector. Quantitative PCR analysis confirmed that the EBV episome was stable at approximately 30 copies per cell for up to 50 weeks and that it remained circular and extrachromosomal. Approaches for adapting the HDAd-EBV hybrid to a variety of disease targets and the potential benefits of this approach are discussed.

Recombinant expression of coagulation factor VIII in hepatic and non-hepatic cell lines stably transduced with third generation lentiviral vectors comprising the minimal factor VIII promoter

BACKGROUND

Lentiviral vectors have the capacity to transduce stably non-dividing, differentiated and undifferentiated cells of various tissues, including liver. To obtain high-level expression of transgenes, vectors often rely on viral promoters. However, recent data suggest that the supraphysiologic expression from ubiquitous viral promoters may not be beneficial and harbor the risk of oncogene activation. Therefore this study explored the lentiviral-mediated expression of human coagulation factor VIII (FVIII) driven by the physiologic FVIII gene promoter (FVIII-p), the liver-specific human alpha-1-antitrypsin gene promoter (hAAT-p), the ubiquitous but non-viral EF1alpha promoter (EF1alpha-p) and the viral CMV promoter.

METHODS

Hepatic and non-hepatic cell lines were stably transduced with lentiviral vectors encoding FVIIIdelB and EGFP. To compare the different promoters, lentiviral vectors were cloned to drive FVIII expression from FVIII-p, EF1alpha-p, hAAT-p and CMV-p.

RESULTS

As expected, the strong viral CMV-p and the ubiquitous EF1alpha-p resulted in the highest FVIII expression in all cell lines tested (CMV-p 1.85 IU/mL/10(6) cells for 293T, 3.15 for HepG2, 5.03 for SK-Hep, 0.91 for Hepa1-6; EF1-alpha promoter 0.30 IU/mL/10(6) cells for 293T, 0.04 for HepG2, 2.75 for SK-Hep, 0.46 for Hepa1-6). While the hAAT-p resulted in low FVIII levels (0.10 IU/mL/10(6)cells in HepG2 and 0.04 in Hepa1-6), the FVIII promoter gave reasonable expression levels in hepatic cells (0.47 IU/mL/10(6)cells in Hepa1-6 and 0.44 in SK-Hep).

DISCUSSION

These results indicate the potential usefulness of the FVIII-p for hemophilia A gene therapy.

The prospects of hepatic drug delivery and gene therapy

Liver targeted therapy is designed to deliver a substance preferentially to the organ in order to increase the accumulation, improve the therapeutic effect and reduce toxicity to other organs. The aim of selective targeting is to deliver a substance to a specific cell type in the liver. A variety of vehicles have been designed and further modified for selective targeting of therapeutics to the liver. The targeting properties and strategies of commonly used agents, such as liposomes, microspheres and recombinant chylomicrons, are discussed. Viral and non-viral vectors, such as cationic liposomes, reconstituted chylomicron remnants, adenoviruses, adeno-associated viruses, retroviruses, and SV-40, are currently being evaluated for the delivery of DNA to the liver. New developments in improving the targeting efficiency of the available vectors while avoiding their disadvantages have made their use in clinical trials of various genetic disorders possible. For viral hepatitis, antisense and ribozyme techniques are being employed with selective targeting approaches. A commonly employed current strategy for targeting hepatocellular carcinoma cells is to make the tumour cells convert non-toxic 'prodrugs' to toxic metabolites in situ, achieving a high concentration of the toxic product in the local milieu, while avoiding systemic toxicity. Although gene therapy itself is in its infancy, some encouraging results have been developed in studies of familial hypercholesterolaemia, haemophilia, alpha1-antitrypsin deficiency and Crigler-Najjar syndrome. The potential strengths as well as the problems with these studies are discussed.

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.

The size of sinusoidal fenestrae is a critical determinant of hepatocyte transduction after adenoviral gene transfer

The hepatotropism and intrahepatic distribution of adenoviral vectors may be species dependent. Hepatocyte transduction was evaluated in three rabbit strains after transfer with E1E3E4-deleted adenoviral vectors containing a hepatocyte specific alpha1-antitrypsin promoter-driven expression cassette (AdAT4). Intravenous administration of 4 x 10(12) particles/kg of AdAT4 induced human apo A-I levels above 40 mg/dl in Dutch Belt, but below 1 mg/dl in New Zealand White and Fauve de Bourgogne rabbits. Diameters of sinusoidal fenestrae were significantly (P=0.0014) larger in Dutch Belt (124+/-3.4 nm) than in New Zealand White (108+/-1.3 nm) and Fauve de Bourgogne (105+/-2.6 nm) rabbits, suggesting that a smaller size constitutes a barrier for hepatocyte transduction. Indeed, intraportal transfer preceded by intraportal injection of sodium decanoate, which increases the diameter of sinusoidal fenestrae to 123+/-3.4 nm (P<0.01) in New Zealand White rabbits, increased human apo A-I levels 32- and 120-fold in New Zealand White and Fauve de Bourgogne rabbits, respectively, but did not affect expression in Dutch Belt rabbits. In conclusion, size of sinusoidal fenestrae appears to be a critical determinant of hepatocyte transduction after adenoviral transfer.

Novel therapeutic approach for hemophilia using gene delivery of an engineered secreted activated Factor VII

Hemophilia is a bleeding disorder caused by mutations in the genes encoding coagulation Factor VIII (FVIII) or FIX. Current treatment is through intravenous infusion of the missing protein. The major complication of treatment is the development of neutralizing Ab's to the clotting factor. Infusion of recombinant activated human Factor VII (rhFVIIa), driving procoagulant reactions independently of human FVIII (hFVIII) or hFIX, has been successful in such patients and could in theory provide hemostasis in all hemophilia patients. However, its high cost and short half-life have limited its use. Here, we report a novel treatment strategy with a recombinant adeno-associated virus vector delivering a modified FVII transgene that can be intracellularly processed and secreted as activated FVII (FVIIa). We show long-term expression, as well as phenotypic correction of hemophilia B mice following gene transfer of the murine FVIIa homolog, with no evidence of thrombotic complications at these doses. These data hold promise for a potential treatment for hemophilia and other bleeding disorders.

Engineered long terminal repeats of retroviral vectors enhance transgene expression in hepatocytes in vitro and in vivo

To analyze the important elements for retroviral expression in hepatocytes, cis-acting elements in the U3 region of the long terminal repeat (LTR) of the polycythemic strain of spleen focus-forming virus (SFFVp) were analyzed in a hepatocellular carcinoma cell line. Two cis-acting elements located within the upstream region of the direct repeat, which positively regulated retroviral expression, were identified. Transcription factors NFAT5 and Sp1, which are ubiquitously expressed in a variety of tissues, bound to these elements. To increase specificity without lowering the potency of retroviral expression in hepatocytes, these elements were replaced by a sequence derived from the hepatitis B virus enhancer II region. Novel vectors, SF-Hep3 and SF-Hep5 (SFFVp-based vector for hepatocytes 3 and 5), were developed with these engineered LTRs. The engineered LTRs of these vectors enhanced the retroviral expression only in hepatocellular carcinoma cell lines in vitro. These vectors also increased transgene expression 4- to 9-fold or 3.5- to 5-fold in comparison with a Moloney murine leukemia virus-based vector or a vector containing the wild-type LTR of SFFVp, respectively, in murine hepatocytes in vivo.

The effect of age on hepatic gene transfer with self-inactivating lentiviral vectors in vivo

It is known that cellular proliferation, by either compensatory regeneration or direct hyperplasia, can augment lentiviral vector transduction into hepatocytes in vivo. For this reason, the present study was designed to determine if adolescent mice (312 weeks of age), which still have relatively proliferating livers, would have differential transduction compared to older (7 weeks of age) mice. Self-inactivating lentiviral vectors containing the human alpha(1)-antitrypsin (hAAT) promoter driving the expression of either the bacterial lacZ gene or the hAAT cDNA were generated for these studies. We found that adolescent mice given lentiviral vectors expressing lacZ (50 micro g p24/mouse) via intravenous administration had a significantly higher level of hepatocyte transduction as measured by X-gal staining of liver sections compared to the 7-week-old mice. In addition, serum hAAT levels were nearly 40-fold higher in 312-week-old mice administered lentiviral vectors expressing hAAT (50 micro g p24/mouse) compared to the 7-week-old mice. Moreover, the incorporation of a matrix attachment region from immunoglobulin kappa significantly increased transduction of hepatocytes in vivo. Although there was a small reduction in the circulating levels of hAAT, likely due to an immune response against the transgene product, gene expression was sustained for the duration of the study (30 weeks in total). In conclusion, the present study strongly demonstrates that lentiviral vector transduction efficiency and transgene expression were significantly enhanced in adolescent compared to older mice.

Neonatal or hepatocyte growth factor-potentiated adult gene therapy with a retroviral vector results in therapeutic levels of canine factor IX for hemophilia B

Hemophilia B is a bleeding disorder resulting from factor IX (FIX) deficiency that might be treated with gene therapy. Neonatal delivery would correct the disease sooner than would transfer into adults, and could reduce immunological responses. Neonatal mice were injected intravenously with a Moloney murine leukemia virus-based retroviral vector (RV) expressing canine FIX (cFIX). They achieved 150% to 280% of normal cFIX antigen levels in plasma (100% is 5 microg/mL), which was functional in vitro and in vivo. Three newborn hemophilia B dogs that were injected intravenously with RV achieved 12% to 36% of normal cFIX antigen levels, which improved coagulation tests. Only one mild bleed has occurred during 14 total months of evaluation. This is the first demonstration of prolonged expression after neonatal gene therapy for hemophilia B in mice or dogs. Most animals failed to make antibodies to cFIX, demonstrating that neonatal gene transfer may induce tolerance. Although hepatocytes from newborns replicate, those from adults do not. Adult mice therefore received hepatocyte growth factor to induce hepatocyte replication prior to intravenous injection of RV. This resulted in expression of 35% of normal cFIX antigen levels for 11 months, although all mice produced anti-cFIX antibodies. This is the first demonstration that high levels of FIX activity can be achieved with an RV in adults without a partial hepatectomy to induce hepatocyte replication. We conclude that RV-mediated hepatic gene therapy is effective for treating hemophilia B in mice and dogs, although the immune system may complicate gene transfer in adults.

AAV-mediated gene transfer for hemophilia

The goal of our work has been to establish an experimental basis for gene transfer as a method of treating hemophilia, an inherited bleeding disorder that results from the absence of functional factor VIII or factor IX. Using an adeno-associated viral vector derived from AAV serotype 2, we have shown in mice and in hemophilic dogs that we can achieve long-term expression (>3 years) of clotting factor at levels that would result in an improvement of clinical symptoms of the disease. A phase I trial of intramuscular injection of AAV-F.IX showed no evidence of local or systemic toxicity in any of the subjects. Muscle biopsies showed evidence for gene transfer and expression by polymerase chain reaction, Southern blot, and immunohistochemistry. We have also shown that AAV-F.IX can be delivered into the portal veins of hemophilic dogs and that this results in high circulating levels of factor IX, on the order of 5% to 14%, whereas delivery of similar doses to skeletal muscle results in factor levels of only 1% to 2%. Based on these results, a trial of AAV-mediated liver-directed gene transfer for hemophilia B has been proposed and is reviewed here.

Adeno-associated virus-mediated gene transfer for hemophilia B

Hemophilia is the bleeding diathesis caused by mutations in the gene encoding factor VIII (hemophilia A) or factor IX (hemophilia B). Currently, the disease is treated by intravenous infusion of the missing purified clotting factor. The goal of gene transfer for treating hemophilia is to achieve sustained expression of factor VIII or factor IX at levels high enough to improve the symptoms of the disease. Hemophilia has proven to be an attractive model for those interested in gene transfer, and multiple gene-transfer strategies are currently being investigated for the hemophilias. The most promising preclinical studies have been with adeno-associated viral vectors (AAV); introduction of AAV vectors expressing factor IX into skeletal muscle or liver in hemophilic dogs has resulted in the long-term expression of factor IX at levels that are adequate to improve disease symptoms. Efforts to translate these findings into the clinical arena have proceeded slowly because of the lack of prior clinical experience with parenteral administration of AAV. In a staged approach, AAV-factor IX (AAV-F.IX) was first administered at doses of up to 1.8 x 10(12) vector genomes/kg (vg/kg) into the skeletal muscles of men with hemophilia B. This trial established the safety of parenteral administration and also showed that general characteristics of AAV transduction were similar in mice, dogs, and humans. In an ongoing trial, AAV-F.IX is being administered into the hepatic circulation of men with severe hemophilia B. The goal of these studies is to identify a safe dose that reliably yields circulating levels of factor IX >2% of normal levels in all subjects. This goal has already been achieved in the hemophilia B dog model; the ongoing study will determine whether a similar result can be achieved in humans with hemophilia B.

An adenoviral expression system for AAV rep78 using homologous recombination

The construction and amplification of adenoviral (Ad) vectors expressing biologically active transgenes that are cytotoxic or inhibit Ad replication can be extremely difficult, if not impossible. In this study, we harnessed the ability of Ad genomes to undergo efficient homologous recombination to reconstitute the adeno-associated virus (AAV) rep78 gene, a cytotoxic gene that strongly inhibits Ad replication, which was divided between two parental, first-generation Ad vectors. A functional open reading frame was generated by recombination only upon co-infection of both parental vectors and after the onset of viral DNA replication. We were able to amplify both parental rep78 vectors to normal titers without any signs of inhibition or toxicity and could use them to generate progeny vectors containing a functional rep78 gene without any Ad genes. Using this vector recombination system in AAV rescue assays demonstrated that no Ad protein was essential for Rep78 mediated rescue of AAV ITR flanked DNA from plasmid or Ad backbones; the amount of rescue product generated was substantially greater in the presence of Ad infection; neither cellular nor viral DNA replication was necessary for rescue to occur; and progeny vector genomes were efficiently co-replicated along with conventional, first-generation Ad vectors.

Effect of promoters and enhancers on expression, transgene DNA persistence, and hepatotoxicity after adenoviral gene transfer of human apolipoprotein A-I

Liver-directed gene transfer offers new perspectives for the treatment of inherited metabolic diseases and disorders of lipoprotein metabolism. Potent expression cassettes for transgenes in the liver may optimize gene transfer efficiency and improve the therapeutic index of gene transfer vectors. An E(1)-deleted adenovirus comprising the hepatocyte specific 256-base pair (bp) human apolipoprotein A-I (apo A-I) promoter, the genomic human apo A-I DNA, and four human apo E enhancers (AdA-I.gA-I.4xapoE) was associated with low hepatotoxicity, high transgene DNA persistence and absence of promoter shut-off, resulting in human apo A-I plasma levels above 100 mg/dl for 35 days in C57BL/6 mice. In the present investigation, the human apo A-I promoter was compared to the murine small nuclear RNA U1b, the human apolipoprotein C-II (apo C-II), and the human alpha(1) antitrypsin (hAAT) promoters and the effect of copy number and position of liver-specific human apo E enhancers in 16 adenoviral constructs was evaluated. The vector containing the 1.5-kb hAAT instead of the apo A-I promoter (AdhAAT.gA-I.4xapoE) induced 3.7-fold (p < 0.01) more human apo A-I reaching plasma levels above 300 mg/dl for 35 days. The composition of the expression cassette was a major determinant of human apo A-I transgene DNA copy number at day 35. Hepatotoxicity after adenoviral gene transfer was dependent on the promoter and the number of enhancers, and was higher with the enhancers in a 5' position. The combination of the hAAT promoter and four copies of the human apo E enhancer appears to be the expression cassette of choice for hepatocyte-specific overexpression of transgenes after gene transfer.

Cytotoxic immune response blunts long-term transgene expression after efficient retroviral-mediated hepatic gene transfer in rat

Vectors derived from oncoretroviruses can transduce a small proportion of hepatocytes when injected in the regenerating liver. Transgene expression may be sustained for months without immune response. In striking contrast, we observed a rapid extinction when the intravenous injection of a high input of nuclear beta-galactosidase (beta-gal) expression vector, one day after partial hepatectomy, led to a significant proportion of transduced cells in the liver. Extinction was associated with liver inflammation on tissue sections and appearance of antibodies against the transgene product, while vector genomes became undetectable in liver tissue by PCR. These observations suggested the elimination of transduced cells by an immune response. Transgenic rats tolerant for cytoplasmic beta-gal, or normal rats depleted in CD8 T lymphocytes, steadily expressed the beta-gal vector. In the spleen of normal rats, we detected cytotoxic cells directed against cells expressing beta-gal after the injection of the beta-gal vector. In jaundiced Gunn rats deficient in bilirubin glucuronosyl transferase (BGT1) and treated with a human BGT1 cDNA expression vector, we observed the same kinetics of extinction as well as the appearance of anti-BGT1 antibodies. This study demonstrates that retrovirus-mediated gene transfer may induce cytotoxic T lymphocytes specifically directed against transgene-expressing cells.

Panniculitis. Part II. Mostly lobular panniculitis

The second part of our review of panniculitis summarizes the clinicopathologic features of the mostly lobular panniculitides. Erythema induratum of Bazin (nodular vasculitis) represents the most common variant of lobular panniculitis with vasculitis, although controversy persists about the nature of the involved vessels. Mostly lobular panniculitides without vasculitis comprise a series of disparate disorders. These include sclerosing panniculitis that results from chronic venous insufficiency of the lower extremities; panniculitis with calcification of the vessel walls such as calciphylaxis and oxalosis; and inflammatory diseases with crystals within the adipocytes such as sclerema neonatorum, subcutaneous fat necrosis of the newborn, and poststeroid panniculitis. Connective tissue diseases, such as systemic lupus erythematosus and dermatomyositis, pancreatic diseases, and alpha(1)-antitrypsin deficiency may also show a mostly lobular panniculitis with characteristic histopathologic features. Lobular panniculitis may also be an expression of infections, trauma, or factitial causes involving the subcutaneous fat. Lipoatrophy refers to a loss of subcutaneous fat due to a previous inflammatory process involving the subcutis, and it may be the late-stage lesion of several types of panniculitis. In contrast, lipodystrophy means an absence of subcutaneous fat with no evidence of inflammation and often the process is associated with endocrinologic, metabolic, or autoimmune diseases. Finally, cytophagic histiocytic panniculitis is the term that has been used to describe two different processes: one is inflammatory, a lobular panniculitis, and the other one is neoplastic, a subcutaneous T-cell lymphoma. The only common feature of these two different processes is the presence of cytophagocytosis in the lesions. (J Am Acad Dermatol 2001;45:325-61.)

LEARNING OBJECTIVE

At the completion of this learning activity, participants should be familiar with the pathogenesis, clinical manifestations, histopathologic findings, and treatment options for the most frequent variants of the lobular panniculitides.

In vivo treatment of hemophilia A and mucopolysaccharidosis type VII using nonprimate lentiviral vectors

Gene therapy holds great promise for the treatment of a variety of inherited diseases, including hemophilia A and mucopolysaccharidosis type VII (MPS VII). In both these disorders, subnormal levels of replacement protein have therapeutic effects. Thus we hypothesized that transduction of a small proportion of cells by feline immunodeficiency virus (FIV)-based lentiviral vectors might provide sufficient levels of transgene expression for phenotypic correction. We intravenously injected replication-deficient FIV-based vectors encoding either human factor VIII or human beta-glucuronidase into factor VIII-deficient or beta-glucuronidase-deficient mice, respectively. This route of delivery targeted multiple organs, with the liver as the primary transduction site. In the hemophilia A mice, factor VIII expression persisted for the duration of the experiments (approximately 5 months), and recipient mice survived an otherwise lethal bleeding episode (tail-clipping). In mucopolysaccharidosis type VII mice, substantial beta-glucuronidase activity was detected in several tissues and corresponded with marked reduction of lysosomal storage in liver and spleen. These findings indicate that gene transfer with FIV-based lentiviral vectors can permanently introduce transgenes into a sufficient number of hepatocytes for long-term therapeutic effect and suggest potential clinical value of FIV-based lentiviral vectors for treatment of hemophilia A and MPS VII.

Strong, long-term transgene expression in rat liver using chicken beta-actin promoter associated with cytomegalovirus immediate-early enhancer (CAG promoter)

For successful gene therapy in hepatic enzyme deficiencies, it is essential to use promoters that can maintain strong transcriptional activity for the long term in the liver. Using Gunn rats, a model animal for Crigler-Najjar syndrome type I, the long-term transcriptional function of the CAG promoter (a combination of chicken beta-actin promoter and cytomegalovirus immediate-early enhancer) was evaluated in the rat liver. We constructed a plasmid pCAGGHUGT, containing expression cassettes of human bilirubin UDP-glucuronosyltransferase (BUGT) and hygromycin phosphotransferase, under the control of the CAG promoter and murine phosphoglycerate kinase promoter, respectively. Conditionally immortalized Gunn rat hepatocytes (IGRH), which had been established using mutant SV40 large T antigen ((TS)T), were transfected with pCAG-GHUGT. A stably transfected clone IGRHUGT, expressing a high level of BUGT, was obtained after selection with hygromycin. At 33 degrees C, the cells doubled in number in approximately 72 h; however, at 37 degrees C, cell proliferation stopped, indicating that the characteristic of temperature-dependent proliferation was retained in this clone. Ten million cells were injected into the spleen of syngeneic Gunn rats five times at 10-day intervals. Serum bilirubin levels were reduced by 45-50% at 70 days after the first transplantation and remained so throughout the duration of the study (120 days). These results suggested that the CAG promoter was able to maintain strong transcriptional activity in rat liver for at least 120 days.

Delivery of a retroviral vector expressing human beta-glucuronidase to the liver and spleen decreases lysosomal storage in mucopolysaccharidosis VII mice

Mucopolysaccharidosis VII (MPS VII) is caused by beta-glucuronidase (beta-gluc) deficiency and results in lysosomal storage due to the inability to degrade glycosaminoglycans. Transfer of a beta-gluc gene into the liver reduces hepatic pathology as well as storage in other organs via uptake of secreted protein. A Moloney murine leukemia-based retroviral vector expressing the human beta-gluc cDNA was injected intravascularly into MPS VII mice during hepatocyte replication, which was induced with im injection of an adenoviral vector that transiently expressed hepatocyte growth factor (Ad.CMV. HGF). This procedure resulted in transduction of approximately 1% of hepatocytes, 1% of normal liver enzyme activity, and a reduction in lysosomal storage in the liver at 3.5 months. Surprisingly, controls that received retroviral vector without HGF had transduction of nonparenchymal cells in the liver, significant levels of enzyme and RNA in the liver at 2 but not 3.5 months, and reduced lysosomal storage at 3.5 months. Transduction was also achieved in the replicating cells of the spleen, where lysosomal storage was reduced. An approach using a retroviral vector without a growth factor might temporarily reduce lysosomal storage in the liver and spleen in humans. Addition of HGF might be used to augment and prolong gene transfer.

Priming of hepatitis C virus-specific cytotoxic T lymphocytes in mice following portal vein injection of a liver-specific plasmid DNA

The immunology of hepatitis C virus (HCV) infection should be studied in the context of HCV antigen expression in the liver, because HCV primarily infects this organ. Indeed, the nature, function, and fate of T cells primed after antigen expression in the liver might differ from those primed when antigens are expressed systemically or in other organs, because the nature of the antigen-presenting cells (APCs) involved may be different. In addition, the normal liver contains a resident population of lymphocytes that differ from those present at other sites. Thus, we investigated whether HCV-specific CD8(+) cytotoxic T cells (CTLs) could be elicited following portal vein (PV) injection of plasmid DNA in mice whose hepatic veins were transiently occluded. We show that PV injection of mice with "naked" DNA expressing the HCV-NS5a protein, under the control of a liver-specific enhancer/promoter, resulted in NS5a expression in the liver and the priming of HCV-specific CTLs. These results suggested that such a model might be relevant to the study of HCV-specific immune responses primed during natural infection.

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.

[Effect of portal branch ligation on liver regeneration in the rat]

GOAL

The aim of this study was to assess liver regeneration after partial portal ligation.

METHODS

70% partial portal occlusion was obtained by ligation of the left portal vein branch. Total liver weight ratio were measured 96 hours after partial portal occlusion and in sham operated animals. The kinetics of hepatocytes division was evaluated by measuring the incorporation of 5-bromo-21-deoxyuridine into replicating cells at various time points by immunohistochemistry.

RESULTS

Partial portal occlusion did not alter the total liver weight 96 hours after surgery. It resulted in atrophy of the ligated lobes and hypertrophy of the lobes with preserved portal flow. Hypertrophy was associated to an increase of the percentage of replicating hepatocytes. The replication rate was maximum at 28 hours with a peak at 12.5% and was prolonged beyond the 48th hour.

CONCLUSIONS

Partial portal occlusion results in major and prolonged regeneration process in the liver lobes with preserved portal flow.

In vivo retrovirus-mediated gene transfer to the liver of dogs results in transient expression and induction of a cytotoxic immune response

Gene transfer in regenerating dog liver using high-titer recombinant retroviral vectors carrying the E. coli beta-galactosidase gene was studied. Supernatants containing amphotropic or gibbon ape pseudotyped recombinant retroviruses were infused into a peripheral vein in beagle dogs after partial hepatectomy. The kinetics of liver regeneration were determined in the animals and daily infusions were carried out for 4 or 5 days during the regeneration period. Up to 2.8% of hepatocytes were beta-galactosidase positive at the end of the procedure. However, the number of positive cells declined rapidly and few positive hepatocytes were detected after 3 weeks. PCR demonstrated the disappearance of the provirus. Histologically, inflammatory lesions were observed in the transduced livers. Finally, we demonstrated the presence of a cytotoxic T lymphocyte immune response directed against beta-galactosidase-expressing cells, which could explain the disappearance of the transgene. This work suggests that the efficiency of in vivo gene delivery using high-titer retroviral vectors directly infused into the circulation may be hampered by a cytotoxic immune response against the infected cells.

Gene therapy expression vectors based on the clotting Factor IX promoter

The liver is one of the prime targets for gene therapy, and the correction of defects in a variety of clotting factor genes is one of the main goals of liver-directed therapies. The use of transcriptional regulatory elements derived from these genes may provide for the optimal expression of transduced genes. We have applied our knowledge of the promoter structure of the clotting Factor IX gene to design optimized expression vectors for use in gene therapy. The activity of the proximal promoter has been augmented by the introduction of a multimerized upstream site which we have previously shown to be a prime regulator of the pro- moter. Introduction of this element increases promoter activity at least 20-fold over the proximal promoter alone when assayed in the human liver cell line Hep G2. This optimized promoter is significantly more active than the SV40 enhancer/early promoter. The expression of the optimized Factor IX promoter is also more persistent in the short term. The inclusion of a liver-specific locus control region, derived from the apolipoprotein E/C locus, did not further augment expression levels. These Factor IX vectors also exhibit a high degree of tissue specificity, as measured by transfection into breast and muscle cell lines.

Overexpression of Bcl-2 protects human hepatoma cells from Fas-antibody-mediated apoptosis

BACKGROUND/AIMS

Fas is a cell surface antigen, that triggers apoptosis upon specific ligand or antibody binding. The proto-oncogene bcl-2 prevents apoptosis induced by various treatments. The aim of our study was to evaluate whether Bcl-2 protects hepatoma cells from Fas-mediated apoptosis.

METHODS

Two human cell lines, HCC-T and HepG2 were used. Expression of Fas antigen and Bcl-2 was detected by flow cytometry and Western blotting. Cell viability and apoptotic change were examined after anti-Fas- and antisense oligodeoxynucleotide treatments. Apoptotic cells were detected by nick-end labelling and the TUNEL method. To test if Bcl-2 expression can protect HepG2 cells from Fas-mediated apoptosis, the cells were transduced using retroviral vector, LZBC, designed to coexpress E. coli beta-galactosidase and human Bcl-2. To further confirm the protective effect of Bcl-2 expression against Fas-mediated apoptosis in HepG2, Bcl-2 expressing plasmid vector was produced and a cell line stably expressing Bcl-2 was cloned.

RESULTS

Western blot analysis showed constitutive Bcl-2 expression in HCC-T cells, but not in HepG2 cells. HCC-T was resistant to apoptosis after treatment with an agonist anti-Fas antibody (1 microg/ml for 3 days), whereas 33% of the HepG2 cells were killed by this treatment. Inhibition of Bcl-2 expression by transfection of antisense oligodeoxynucleotides caused spontaneous apoptosis in HCC-T, but not in HepG2 cells, suggesting that Bcl-2 is essential for survival of HCC-T cells, whereas other proteins may substitute for it in HepG2 cells. Following LZBC infection, 10% HepG2 cells were beta-galactosidase-positive by X-gal staining and Bcl-2-positive. In cells surviving after anti-Fas treatment, the proportion of beta-galactosidase-positive cells increased to 50% and the beta-galactosidase activity increased 6-fold, indicating that Bcl-2 expression protected the cells from Fas-mediated apoptosis. In the cloned HepG2 cells stably expressing Bcl-2, the extent of Fas-mediated apoptosis was inversely related to the level of Bcl-2 expression.

CONCLUSION

Bcl-2 confers protection to human hepatoma cells against Fas-mediated apoptosis, and is essential for survival of some, but not all, hepatoma cells.

Hydrodynamics-based transfection in animals by systemic administration of plasmid DNA

Development of methods that allow an efficient expression of exogenous genes in animals would provide tools for gene function studies, treatment of diseases and for obtaining gene products. Therefore, we have developed a hydrodynamics-based procedure for expressing transgenes in mice by systemic administration of plasmid DNA. Using cDNA of luciferase and beta-galactosidase as a reporter gene, we demonstrated that an efficient gene transfer and expression can be achieved by a rapid injection of a large volume of DNA solution into animals via the tail vein. Among the organs expressing the transgene, the liver showed the highest level of gene expression. As high as 45 microg of luciferase protein per gram of liver can be achi- eved by a single tail vein injection of 5 microg of plasmid DNA into a mouse. Histochemical analysis using beta-galactosidase gene as a reporter reveals that approximately 40percent of hepatocytes express the transgene. The time-response curve shows that the level of transgene expression in the liver reaches the peak level in approximately 8 h after injection and decreases thereafter. The peak level of gene expression can be regained by repeated injection of plasmid DNA. These results suggest that a simple, convenient and efficient method has been developed and which can be used as an effective means for studying gene function, gene regulation and molecular pathophysiology through gene transfer, as well as for expressing proteins in animals.

Regulation of N-acetylgalactosamine 4-sulfatase expression in retrovirus-transduced feline mucopolysaccharidosis type VI muscle cells

As a preliminary step toward muscle-mediated gene therapy in the mucopolysaccharidosis (MPS) type VI cat, we have analyzed the transcriptional regulation of feline N-acetylgalactosamine 4-sulfatase (f4S) gene expression from various retroviral constructs in primary cultures of muscle cells. Two retroviral constructs were made containing the f4S cDNA under the transcriptional control of the human polypeptide chain-elongation factor 1alpha (EF1alpha) gene promoter or the cytomegalovirus (CMV) immediate-early promoter. Two further retroviral constructs were made with the murine muscle creatine kinase (mck) enhancer sequence upstream of the internal promoter. Virus made from each construct was used to transduce feline MPS VI myoblasts. The mck enhancer significantly upregulated f4S gene expression from both the EF1alpha promoter and the CMV promoter in transduced myoblasts and in differentiated myofibers. The highest level of 4S activity was observed in myoblasts and myofibers transduced with the retroviral construct Lmckcmv4S, in which the f4S gene is under the transcriptional regulation of the mck enhancer and CMV immediate-early promoter. Lmckcmv4S-transduced myofibers demonstrated correction of glycosaminoglycan storage and contained a 58-fold elevated level of 4S activity compared with normal myofibers. Recombinant f4S secreted from Lmckcmv4S-transduced myofibers was endocytosed by feline MPS VI myofibers, leading to correction of the biochemical storage phenotype.

Embolization of portal vein branches induces hepatocyte replication in swine: a potential step in hepatic gene therapy

PURPOSE

To determine whether embolization of portal vein branches would stimulate hepatocyte replication in pigs.

MATERIALS AND METHODS

The portal vein branches supplying 50%-70% of the liver were embolized in eight pigs by using a combination of coils and polyvinyl alcohol particles. The extent of embolization was assessed at portography in all animals and at computed tomography in one animal. Hepatocyte replication was determined by calculating the percentage of cells that incorporated bromodeoxyuridine into their nuclei. Animals survived up to 35 days after the procedure.

RESULTS

Embolization of the portal vein branches supplying the left and median lobes caused transient increases of less than 70% in portal vein pressures and of less than 100% in liver enzyme levels. Indocyanine green clearance was measured in two animals and decreased less than 50%. The percentage of replicating hepatocytes in the nonembolized lobe was 0% on day 0, 7% on day 2, 14% on day 7, and 2% on day 12.

CONCLUSION

Substantial hepatocyte replication occurred 2-7 days after embolization of portal vein branches. Further research will help determine if this procedure can facilitate retroviral transduction in large animals. If successful, the low morbidity of this method may allow its use in humans for gene therapy.

Fas-mediated apoptosis is involved in the elimination of gene-transduced hepatocytes with E1/E3-deleted adenoviral vectors

Gene-transduced hepatocytes with E1/E3-deleted adenoviral vectors are eliminated immediately and the expression of transduced genes disappears rapidly following the vector administration. In this report, we analysed the involvement of apoptotic cell death in the elimination of hepatocytes infected with adenoviral vectors. An E1/E3-deleted adenoviral vector expressing Escherichia coli β-galactosidase (LacZ) was injected via the portal vein into congenitally Fas-deficient mice (lpr), Fas ligand-deficient mice (gld) and their control mice, MRL and C3H. 5-Bromo-4-chloro-3-indolyl-β-D-galactoside (X-gal) staining of the liver specimens showed that 80-100% of hepatocytes were LacZ positive at 7 days after virus administration, suggesting that most of the hepatocytes received the injected adenoviral vectors. In normal mice, the number of LacZ-positive cells decreased dramatically at 14 and 21 days after transduction and few positive cells were observed at day 28. β-Galactosidase activity, quantified by the O-nitrophenyl-beta-D-galactopyranoside assay, gave comparable results to X-gal staining. At days 14 or 21, many apoptotic hepatocytes and apoptotic infiltrating cells were detected with the terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling (TUNEL) in situ apoptosis detection method. This observation suggested that the apoptotic process was associated with the elimination of adenovirus-infected hepatocytes. To test the involvement of the Fas-Fas ligand interaction in this apoptotic process, the period of transgene expression was measured in 1pr and gld mice, which had received the same amount of AxCALacZ. X-Gal histochemical analysis detected many LacZ-positive cells in 1pr or gld mice liver even at 21 or 28 days after AxCALacZ injection. There were significant differences in the reduction rates of β-galactosidase activity of liver homogenates between lpr and MRL, or gld and C3H mice. Based on these observations, we conclude that the Fas-mediated apoptotic process is involved in the elimination of hepatocytes infected with E1/E3-deleted adenoviral vectors.

Therapeutic levels of human protein C in rats after retroviral vector-mediated hepatic gene therapy

Protein C deficiency results in a thrombotic disorder that might be treated by expressing a normal human protein C (hPC) gene in patients. An amphotropic retroviral vector with a liver-specific promoter and the hPC cDNA was delivered to rat hepatocytes in vivo during liver regeneration. Expression of hPC varied from 55 to 203 ng/ml (1.3-5.0% of normal) for 2 wk after transduction. Expression increased to an average of 900 ng/ml (22% of normal) in some rats and was maintained at stable levels for 1 yr. All of these rats developed anti-hPC antibodies and exhibited a prolonged hPC half-life in vivo. The hPC was functional as determined by a chromogenic substrate assay after immunoprecipitation. We conclude that most rats achieved hPC levels that would prevent purpura fulminans, and that hepatic gene therapy might become a viable treatment for patients with severe homozygous hPC deficiency. Anti-hPC antibodies increased the hPC half-life and plasma levels in some rats, but did not interfere with its functional activity. Thus, the development of antibodies against a plasma protein does not necessarily abrogate its biological effect in gene therapy experiments.

Ex vivo hepatic gene therapy of a mouse model of Hereditary Tyrosinemia Type I

Previously, this lab has reported the use of hepatocyte transplantation and in vivo gene therapy for the correction of a mouse model of Hereditary Tyrosinemia Type I (HT1). Here, we demonstrate repopulation of fumarylacetoacetate hydrolase (FAH)-deficient livers with cultured hepatocytes. Correction of the disease phenotype was achieved by retrovirally transducing cultured FAH- hepatocytes ex vivo, followed by transplantation and selective repopulation. Treated mice were phenotypically normal and had corrected plasma amino acid levels and liver function tests. Our results demonstrate that efficient hepatic repopulation using ex vivo genetically manipulated hepatocytes is feasible.

In vivo gene delivery to the liver using reconstituted chylomicron remnants as a novel nonviral vector

Lipoproteins are emulsion particles that consist of lipids and apolipoproteins. Their natural function is to transport lipids and/or cholesterol to different tissues. We have taken advantage of the hydrophobic interior of these natural emulsions to solubilize DNA. Negatively charged DNA was first complexed with cationic lipids containing a quaternary amine head group. The resulting hydrophobic complex was extracted by chloroform and then incorporated into reconstituted chylomicron remnant particles ( approximately 100 nm in diameter) with an efficiency approximately 65%. When injected into the portal vein of mice, there were approximately 5 ng of a transgene product (luciferase) produced per mg of liver protein per 100 microg injected DNA. This level of transgene expression was approximately 100-fold higher than that of mice injected with naked DNA. However, such a high expression was not found after tail vein injection. Histochemical examination revealed that a large number of parenchymal cells and other types of cells in the liver expressed the transgene. Gene expression in the liver increased with increasing injected dose, and was nearly saturated with 50 microg DNA. At this dose, the expression was kept at high level in the liver for 2 days and then gradually reduced and almost disappeared by 7 days. However, by additional injection at day 7, gene expression in the liver was completely restored. By injection of plasmid DNA encoding human alpha1-antitrypsin, significant concentrations of hAAT were detected in the serum of injected animals. This is the first nonviral vector that resembles a natural lipoprotein carrier.

Highly efficient retrovirus-mediated gene transfer into rat hepatocytes in vivo

We have used high-titer (10(8) ffu/ml) recombinant retroviral vectors to transfer the beta-galactosidase (beta-Gal) gene to rat hepatocytes in vivo. In animals injected twice in the portal blood stream the next day after partial hepatectomy, half of the hepatocytes (46 +/- 17%) expressed the marker at the end of liver regeneration. The number of positive cells closely correlated with the viral titer as well as with beta-Gal enzymatic activity present in the whole liver. Because genes transferred via retroviral vectors in the liver are known to be expressed permanently, our present results open new possibilities for the development of gene therapy protocols for hereditary liver diseases using recombinant retroviral vectors.