A non-immunogenic adenoviral vector, coexpressing CTLA4Ig and bilirubin-uridine-diphosphoglucuronateglucuronosyltransferase permits long-term, repeatable transgene expression in the Gunn rat model of Crigler-Najjar syndrome

Drug- and Drug Abuse-Associated Hyperbilirubinemia: Experience With Atazanavir

Hyperbilirubinemia is a common finding in individuals with a history of substance abuse. Although this may indicate a serious disorder of liver function, this is not always the case. An understanding of bilirubin formation, metabolism, and transport can provide a helpful approach to dealing with these patients. This is typified by studies of patients treated with the antiretroviral drug atazanavir. Atazanavir has been associated with hyperbilirubinemia in as many as one-third of individuals for whom it has been prescribed, evoking concerns of hepatotoxicity. The studies in this report were designed to determine mechanisms by which this occurs. The data show that this drug inhibits the enzyme UDP-glucuronosyl transferase-1A1, responsible for conjugating bilirubin with glucuronic acid. This conjugation step is required for bilirubin excretion into bile, and when it is inhibited, bilirubin refluxes from the liver into the circulation, causing unconjugated hyperbilirubinemia. Other parameters of bilirubin formation, binding to albumin in the circulation, uptake into hepatocytes, and intracellular protein binding in hepatocytes were unaffected by atazanavir. The effect of atazanavir on serum bilirubin levels is reversible, consistent with lack of structural damage to the liver.

Self in vivo production of a synthetic biological drug CTLA4Ig using a minicircle vector

Cytotoxic T lymphocyte-associated antigen 4 immunoglobulin fusion protein (CTLA4Ig, abatacept) is a B7/CD28 costimulation inhibitor that can ward off the immune response by preventing the activation of naïve T cells. This therapeutic agent is administered to patients with autoimmune diseases such as rheumatoid arthritis. Its antiarthritic efficacy is satisfactory, but the limitations are the necessity for frequent injection and high cost. Minicircles can robustly express the target molecule and excrete it outside the cell as an indirect method to produce the protein of interest in vivo. We inserted the sequence of abatacept into the minicircle vector, and by successful in vivo injection the host was able to produce the synthetic protein drug. Intravenous infusion of the minicircle induced spontaneous production of CTLA4Ig in mice with collagen-induced arthritis. Self-produced CTLA4Ig significantly decreased the symptoms of arthritis. Injection of minicircle CTLA4Ig regulated Foxp3(+) T cells and Th17 cells. Parental and mock vectors did not ameliorate arthritis or modify the T cell population. We have developed a new concept of spontaneous protein drug delivery using a minicircle vector. Self in vivo production of a synthetic protein drug may be useful when biological drugs cannot be injected because of manufacturing or practical problems.

Lentiviral vectors that express UGT1A1 in liver and contain miR-142 target sequences normalize hyperbilirubinemia in Gunn rats

BACKGROUND & AIMS

Crigler-Najjar type 1 (CN-I) is an inherited liver disease caused by an absence of bilirubin-uridine 5'-diphosphate-glucuronosyltransferase (UGT1A1) activity. It results in life-threatening levels of unconjugated bilirubin, and therapeutic options are limited. We used adult Gunn rats (an animal model of the disease) to evaluate the efficiency of lentiviral-based gene therapy to express UGT1A1 in liver.

METHODS

Gunn rats were given intraportal injections of VSVG-pseudotyped lentiviral vectors that encode UGT1A1 under the control of a liver-specific transthyretin promoter (mTTR.hUGT1A1); this vector does not contain target sequences for miR-142, a microRNA that is expressed specifically in hematopoietic cells. Rats were also injected with the vector mTTR.hUGT1A1.142T, which contains 4 copies of the miR-142 target sequences; its messenger RNA should be degraded in antigen-presenting cells. Bilirubinemia was monitored, and the presence of transduced hepatocytes was analyzed by quantitative polymerase chain reaction. Vector expression was tested in vitro in rat hematopoietic cells.

RESULTS

In Gunn rats, bilirubin levels normalized 2 weeks after administration of mTTR.hUGT1A1. However, hyperbilirubinemia resumed 8 weeks after vector administration, concomitant with the induction of an immune response. In contrast, in rats injected with mTTR-UGT1A1.142T, bilirubin levels normalized for up to 6 months and transduced cells were not eliminated.

CONCLUSIONS

Lentiviral vectors that express UGT1A1 reduce hyperbilirubinemia in immunocompetent Gunn rats for at least 6 months. The immune response against virally expressed UGT1A1 can be circumvented by inclusion of miR-142 target sequences, which reduce vector expression in antigen-presenting cells. This lentiviral-based gene therapy approach might be developed to treat patients with CN-I.

Advances with the use of bio-inspired vectors towards creation of artificial viruses

IMPORTANCE OF THE FIELD

In recent years, there has been a great deal of interest in the development of recombinant vectors based on biological motifs with potential applications in gene therapy. Several such vectors have been genetically engineered, resulting in biomacromolecules with new properties that are not present in nature.

AREAS COVERED IN THIS REVIEW

This review briefly discusses the advantages and disadvantages of the current state-of-the-art gene delivery systems (viral and non-viral) and then provides an overview on the application of various biological motifs in vector development for gene delivery. Finally, it highlights some of the most advanced bio-inspired vectors that are designed to perform several self-guided functions.

WHAT THE READER WILL GAIN

This review helps the readers get a better understanding about the history and evolution of bio-inspired fusion vectors with the potential to merge the strengths of both viral and non-viral vectors in order to create efficient, safe and cost-effective gene delivery systems.

TAKE HOME MESSAGE

With the emergence of new technologies such as recombinant bio-inspired vectors, it may not take long before non-viral vectors are observed that are not just safe and tissue-specific, but even more efficient than viral vectors.

The expression of exogenous genes in macrophages: obstacles and opportunities

Over the past three decades many techniques for expressing exogenous genes in a variety of cells and cell lines have been developed. Exogenous gene expression in macrophages has lagged behind that of other nonhematopioetic cells. There are many reasons for this, but most are due to technical difficulties associated with transfecting macrophages. As professional phagocytes, macrophages are endowed with many potent degradative enzymes that can disrupt nucleic acid integrity and make gene transfer into these cells an inefficient process. This is especially true of activated macrophages which undergo a dramatic change in their physiology following exposure to immune or inflammatory stimuli. Viral transduction of these cells has been hampered because macrophages are end-stage cells that generally do not divide; therefore, some of the vectors that depend on integration into a replicative genome have met with limited success. Furthermore, macrophages are quite responsive to "danger signals," and therefore several of the original viral vectors that were used for gene transfer induced potent anti-viral responses in these cells making these vectors inappropriate for gene delivery. Many of these difficulties have been largely overcome, and relatively high efficiency gene expression in primary human or murine macrophages is becoming more routine. In the present chapter we discuss some of the gene expression techniques that have met with success and review the advantages and disadvantages of each.

Crigler-Najjar syndrome: therapeutic options and consequences of mutations in the UGT1A1 complex

Crigler-Najjar syndrome (CN), a rare inherited disorder characterized by failure of bilirubin glucuronidation, can lead to severe disability and death from kernicterus. Gilbert syndrome is a more common, benign familial unconjugated hyperbilirubinemia. The underlying problem in both conditions is impaired bilirubin conjugation and elimination due to a mutation in uridine 5'-diphosphate glucuronyltransferase. The mainstay of current management of CN is phototherapy, followed by liver transplantation. Here, we review other therapies, including hepatocyte transplantation, that have been successfully used to lessen the phenotype, although long-term engraftment of cells remains elusive. Gene therapy holds hope for the future whereby the patient's hepatocytes are transduced with the wild-type gene. Outstanding issues include safety of the gene vector and establishing immunotolerance to both vector and the new protein. The significant advances in understanding the relevance of mutations in UGT not only in glucuronidation of bilirubin, but other drugs and substances, are also reviewed.

Gene therapy for liver enzyme deficiencies: what have we learned from models for Crigler-Najjar and tyrosinemia?

The liver is the site of numerous metabolic inherited diseases. It has unique features that make it compliant to various gene therapy approaches. Many vector types and gene delivery strategies have been evaluated during the past 20 years in a number of animal models of metabolic liver diseases. However, the complete cure of inherited liver deficiencies by gene therapy in relevant animal models were only reported recently. These successes were achieved thanks to major advances in vector technology. In this review, we will focus on Crigler-Najjar disease and hereditary tyrosinemia, two paradigmatic examples of the two categories of enzymatic liver deficiencies: type I, in which the genetic defect does not affect liver histology; and type II, in which liver lesions are present.

Lack of repeat transduction by recombinant adeno-associated virus type 5/5 vectors in the mouse airway

While recombinant adeno-associated virus (rAAV) vectors promote long-term transgene expression in the lungs and other organs, the goal of correcting chronic inherited lung diseases such as cystic fibrosis with this type of viral gene transfer vector is limited by the requirement of achieving stable potent transgene expression, potentially requiring vector readministration. Here we evaluated the abilities of rAAV type 5/5 (rAAV5/5) vectors based on the genome and capsid of AAV5 to efficiently transduce the lungs and nasal epithelium of mice after repeated administration. Transduction efficiency as judged by reporter gene expression was markedly reduced on a second rAAV5/5 administration and effectively abolished on a third. Varying the period between administrations from 8 to 36 weeks did not allow efficient repeated administration. A rapid rise in anti-AAV5 antibodies was noted after rAAV5/5 vector administration that was sustained for the entire period of investigation (in some cases exceeding 9 months). Furthermore, this antibody response and subsequent failure to repeatedly administer the vector were not rescued by the in vivo expression of CTLA4Ig from an rAAV5/5 vector. These results suggest that without the development of an effective and clinically acceptable immunosuppression strategy, treatments for chronic diseases that require repeated administration of rAAV5/5 vectors will be unsuccessful.

Ex vivo lentivirus transduction and immediate transplantation of uncultured hepatocytes for treating hyperbilirubinemic Gunn rat

BACKGROUND

Ex vivo liver gene therapy provides an attractive alternative to orthotopic liver transplantation for the treatment of liver diseases. We previously reported a protocol in which human primary hepatocytes are highly transduced in Suspension with Lentiviral vectors and Immediately Transplanted (SLIT). Here, we evaluated the SLIT approach in Gunn rats, the animal model for Crigler-Najjar syndrome type 1, a defect in bilirubin UDP-glucuronosyltransferase (BUGT).

METHODS

We constructed lentiviral vectors coding for BUGT under control of an ubiquitous promoter. Control vectors contained Green Fluorescent Protein (GFP) under control of the same promoter. Hepatocytes were isolated from jaundiced Gunn rats and transduced in suspension for four hr. After washing, 2x10 hepatocytes were immediately transplanted into syngeneic rats. Bilirubinemia and bile pigments were regularly assessed after cell transplantation. The percentage and presence of transduced hepatocytes was analyzed by immunohistochemistry in GFP-transplanted animals.

RESULTS

In rats receiving BUGT-transduced hepatocytes, bilirubinemia decreased by about 30%. The level of correction remained stable for up to 240 days. Bilirubin glucuronides were present in the bile of treated animals, indicating the metabolic activity of engrafted hepatocytes. In contrast, bilirubinemia in GFP-transplanted rats did not decline but rather increased. GFP-positive hepatocytes amounted to 0.5-1% of the liver, which is in agreement with the number of transplanted and genetically-modified hepatocytes (6x10).

CONCLUSIONS

This work reports the first demonstration of long-term metabolic benefit after rapid transplantation of ex vivo lentivirally tranduced hepatocytes. Therefore, this study demonstrates the therapeutic proof-of-principle and potential of the SLIT approach for treating inherited metabolic liver diseases.

In vivo analysis of adenovirus-specific cytotoxic T lymphocyte response in mice deficient in CD28, fas ligand, and perforin

Adenoviruses (Ad) have been extensively studied as gene delivery vectors in gene therapy and as vaccine carriers. The cell-mediated cytotoxicity induced by Ad is of great interest in both applications. However, the mechanism underlying Ad-specific cytotoxic T lymphocyte (CTL) generation and effector function remains unclear. In this study, we used a novel MHC class I tetramer and an in vivo CTL assay to examine the role of CD28, perforin, Fas ligand (FasL), and TNF-alpha in the generation and function of Ad-specific CTLs in vivo. During the primary response, there was a significant defect in both the generation and in vivo effector function of Ad-specific CTLs in CD28-/- mice, but not in CD4+ T cell-depleted mice or CD4-/- mice. The relative role of CTL effector molecules was assayed by in vivo CTL assay in perforin- or FasL-mutant mice, using donor cells from Fas-deficient or TNFR1/TNFR2-deficient mice. The results indicated that the in vivo CTL activity is mediated mainly by perforin. In the absence of perforin, production of FasL, but not TNF-alpha, by the CTLs results in lower level Ad-specific killing of target cells. These results provide important implications concerning the development of safe and effective Ad vectors for gene therapy and vaccines.

High expression level of recombinant human erythropoietin in the milk of non-transgenic goats

The high degree of structural conservation of erythropoietin between species, make it, especially, difficult to produce this protein growth factor in the milk of transgenic animals. Here, we show that through the direct transduction of the mammary epithelium, it is possible to produce high levels of recombinant human erythropoietin in the milk of non-transgenic goats without causing harm to the animals. The efficiency of viral transduction was improved through a temporal disruption of tight-junctions with EGTA allowing for the expression of human erythropoietin at levels of up to 2g/L in milk. The human erythropoietin was purified from the milk using a multi-step protocol involving milk clarification, two precipitation steps and two affinity chromatographies, with a yield of about 70% and purity over 98%. However, the human erythropoietin expressed in milk was underglycosylated, which seems to be the main cause for its low in vivo hematopoietic activity. Nonetheless, these results demonstrate that through the direct transduction of the mammary epithelium it is possible to produce potentially toxic proteins in milk, at levels high enough for their purification and biological characterization.

Successful Treatment of UGT1A1 Deficiency in a Rat Model of Crigler–Najjar Disease by Intravenous Administration of a Liver-Specific Lentiviral Vector

Treatment of congenital and acquired liver disease is one of the main issues in the field of gene therapy. Self-inactivating lentiviral vectors have several potential advantages over alternative systems. We have constructed a self-inactivating lentiviral vector (LV-ALBUGT) that expresses the human bilirubin UDP-glucuronosyltransferase (UGT1A1) from a liver-specific promoter. UGT1A1 is involved in the clearance of heme metabolites in the liver. This enzyme is deficient in Crigler-Najjar disease, a recessive inherited disorder in humans characterized by chronic severe jaundice, i.e., high plasma bilirubin levels. Gunn rats suffer from the same defect and are used as an animal model of this disease. We have treated juvenile Gunn rats by single intravenous injection with the LV-ALBUGT vector. Over 1 year after treatment with the highest dose (5 x 10(8) transducing units), we observed a stable reduction of bilirubin levels to near normal levels and normal secretion of bilirubin conjugates in the bile, in contrast to untreated animals. In situ hybridization showed expression of the therapeutic gene in more than 30% of liver parenchymal cells. Thus, we demonstrate stable and complete clinical remission of a congenital metabolic liver disease in an animal model, after systemic administration of a therapeutic lentiviral vector.

Different Osteogenic Potentials of Recombinant Human BMP-6 Adeno-Associated Virus and Adenovirus in Two Rat Strains

The osteogenic potential of AAV5hBMP6 was compared with that of ADhBMP6 in immunodeficient and immunocompetent rats. AAV5hBMP6 (2.3 x 10(12) particles) and ADhBMP6 (5 x 10(7) PFU) elicited viral antibody production in immunocompetent rats. Among rats that received AAV5hBMP6, the earliest time points at which the bone was visible under CT scanner were 30 days in 2-month-old Sprague-Dawley (SD) rats and 60 days in 18-month-old SD rats. The mean volumes of ectopic bone 90 days after viral injection were 0.31 +/- 0.14 cm(3) in athymic nude rats, 0.64 +/- 0.12 cm(3) in 2-month-old SD rats, and 0.21 +/- 0.10 cm(3) in 18-month-old SD rats. In contrast, among rats that received ADhBMP6, the earliest time points to observe the bone formation by CT scan were 15 days in 2-month-old rats and no bone formation in 18-month-old SD rats. The mean volumes of ectopic bone were 4.17 +/- 0.05 cm(3) in athymic nude rats and 0.06 +/- 0.03 cm(3) in 2-month-old SD rats. Although both types of viruses induced an immune response in immunocompetent animals, this response played different roles in the process of bone formation induced by the BMP6 vectors.

Mixed hematopoietic molecular chimerism results in permanent transgene expression from retrovirally transduced hepatocytes in mice

BACKGROUND

Cytotoxic immune elimination of transduced hepatocytes may limit gene therapy for inherited liver diseases. Using beta-galactosidase as a marker gene, we studied whether creation of mixed beta-galactosidase molecular hematopoietic chimerism could induce tolerance to beta-galactosidase-transduced hepatocytes.

METHODS

Molecular hematopoietic chimerism was established in irradiated recipient mice by transplantation of either a mixture of wild-type and beta-galactosidase-transgenic bone marrow or autologous bone marrow stem cells that were transduced with beta-galactosidase lentiviral vectors. After transplantation, mice were hepatectomized and injected with beta-galactosidase recombinant retroviruses to transduce regenerating hepatocytes. We monitored the presence of beta-galactosidase-expressing hepatocytes as well as the appearance of anti-beta-galactosidase antibodies during the time.

RESULTS

In control animals, anti-beta-galactosidase antibodies and cytotoxic T-lymphocyte (CTL) response developed as early as 3 weeks after gene transfer. Transduced hepatocytes disappeared concomitantly. In bone marrow transplanted mice, tolerance could be observed in a significant proportion of animals. Tolerance resulted in permanent liver transgene expression and was absent unless a chimerism above 1% was achieved, demonstrating a threshold effect.

CONCLUSIONS

Creation of a molecular hematopoietic chimerism can result in transgene tolerance and evade immune rejection of retrovirally transduced hepatocytes. This strategy may be useful for hepatic inherited diseases in which the transgene product behaves as a non-self protein.

Therapeutic lentivirus-mediated neonatal in vivo gene therapy in hyperbilirubinemic Gunn rats

Crigler-Najjar type 1 disease (CN-1) is a genetic disorder characterized by high levels of unconjugated bilirubin due to the absence of hepatic UDPglucuronosyltransferase (UGT1) activity. Here we show that in vivo neonatal hepatocyte transduction with a lentiviral vector expressing the defective enzyme resulted in long-term correction in Gunn rats, a model of CN-1. Lentiviral vectors harboring the human UGT1 cDNA (approved symbol UGT1A1) under the control of a liver-specific transthyretin promoter were produced. Two-day-old Gunn rats were injected with 50 microl of vector. Bilirubinemia was monitored at 6 weeks and monthly thereafter. At 6 weeks, bilirubinemia was completely normalized in treated animals, whereas it remained around 100 microM in control rats. The level of correction remained stable for up to 42 weeks. Large amounts of bilirubin conjugates were present in the bile of corrected animals. PCR and Western blots confirmed the presence and expression of UGT1 in liver. The estimated proportion of transduced hepatocytes was 40% and transduced cells were not detected in extrahepatic tissues except bone marrow in some animals. This work represents the first demonstration of a complete and permanent correction of hyperbilirubinemia in Gunn rats using lentiviral vectors.

Long-term tracing of adenoviral expression in rat and rabbit using luciferase imaging

BACKGROUND

Luciferase optical imaging provides a novel method to monitor transgene expression in small living animals. As the genetic and immunological heritages of particular animals significantly affect the expression of adenovirus-delivered transgenes, it is essential to know the expression patterns specific to athymic nude and Sprague-Dawley rats, two strains commonly used in rodent models. In this study we set out to determine these patterns. At the same time, we tested luciferase optical imaging in a larger animal, the rabbit.

METHODS

A recombinant luciferase adenoviral vector was injected subcutaneously or intramuscularly into athymic nude rats, Sprague-Dawley rats, and Dutch Belted rabbits. The luciferase expression was assessed using a cooled charge-coupled device.

RESULTS

The luminescent signal was capable of passing through at least 1.3 cm of muscle tissue and proved to be much stronger when luciferin was delivered via a local injection than by an intraperitoneal injection. Although the types of immune cells differed between immunodeficient and immunocompetent rats, similar amounts and patterns of luciferase expression were observed in the musculature in two rat strains during the 1st month after a viral intramuscular injection. The duration of luciferase expression was longer than 15 months in athymic nude rats, 9 months in Sprague-Dawley rats, and 6 months in rabbits following a direct viral injection.

CONCLUSIONS

Luciferase expression after adenoviral gene delivery can persist for longer than 6 months, even in immunocompetent animals. Live imaging of luciferase expression can be performed not only in small animals, but also in larger animals such as rabbits.

Single Hepatic Venous Injection of Liver-Specific Naked Plasmid Vector Expressing Human UGT1A1 Leads to Long-Term Correction of Hyperbilirubinemia and Prevention of Chronic Bilirubin Toxicity in Gunn Rats

Previously, we have demonstrated that hepatic venous injection of pcDNA3hUGT1A1 expressing human bilirubin glucuronosyl transferase 1A1 (hUGT1A1) under the control of the cytomegalovirus promoter results in excretion of bilirubin glucuronides in bile and significant decrease in serum bilirubin for at least 2 weeks in the Gunn rat, an animal model of Crigler-Najjar syndrome type I. In this study we compared repeat delivery of pcDNA3hUGT1A1 with single injection of pBShUGT1A1 expressing hUGT1A1 under liver-specific regulatory control, for treatment of hyperbilirubinemia in the Gunn rat. Although repeat injections of pcDNA3hUGT1A1 consistently reduced serum bilirubin levels, the effect did not exceed 2 weeks; hUGT1A1 was detectable in livers only for 2 weeks, despite the presence of vector and transcript for at least 1 month. In contrast, injection of pBShUGT1A1 resulted in persistence of vector, transcript, and recombinant protein and sustained correction of hyperbilirubinemia for at least 8 months; furthermore, renal tubular damage, the principal manifestation of chronic bilirubin toxicity in the Gunn rat, was prevented. Sera from animals treated with pBShUGT1A1 consistently contained anti-hUGT1A1 antibodies, but a significant increase in the number of hepatic CD4(+) and CD8(+) cells was seen only in the pcDNA3hUGT1A1 group; thus liver-specific expression of hUGT1A1 may attenuate immune response. Our results provide further evidence of the feasibility of long-term correction of hepatic enzyme deficiencies with plasmid vectors optimized for expression in the liver.

Successful gene therapy of the Gunn rat by in vivo neonatal hepatic gene transfer using murine oncoretroviral vectors

Crigler-Najjar type 1 disease (CN1) is a rare inherited metabolic disease characterized by complete absence of hepatic UDP-glucuronosyl transferase (UGT1), resulting in high levels of unconjugated bilirubin. CN1 is an attractive candidate disease for gene therapy. Here we show that in vivo neonatal hepatocyte transduction using recombinant oncoretroviral vectors results in long-term and complete phenotype correction in Gunn rats, a model for CN1. Two-day-old newborn Gunn rats were injected via the temporal vein with 200 microL UGT1 or control beta-galactosidase retroviral vectors. In UGT1-injected animals, bilirubinemia was normal at 6 weeks (3 micromol/L) and remained in the normal range (i.e., <10 micromol/L) for more than 34 weeks. In contrast, in beta-galactosidase-injected animals as well as in noninjected controls, bilirubinemia remained at a high level (i.e., >100 micromol/L) during the whole experimental follow-up. Large amounts of bilirubin monoglucuronides and diglucuronides were present in the bile of treated animals. Finally, polymerase chain reaction and reverse transcription polymerase chain reaction analysis as well as Western blot confirmed the presence and expression of UGT1 almost exclusively in the liver. The estimated proportion of transduced hepatocytes was in the range of 5% to 10%. In conclusion, complete and permanent correction of hyperbilirubinemia in newborn Gunn rats using retroviral vectors can be obtained, paving the way for future gene therapy for CN1.

Long-term correction of hyperbilirubinemia in the Gunn rat by repeated intravenous delivery of naked plasmid DNA into muscle

We evaluated nonviral gene delivery into skeletal muscle via femoral artery and great saphenous vein for correction of hyperbilirubinemia in the Gunn rat, the animal model of Crigler-Najjar syndrome type I. A single injection of pDNA expressing hUGT1A1 under the CMV promoter resulted in excretion of bilirubin glucuronides in bile and a significant decrease in serum bilirubin for at least 2 or 4 weeks, respectively. Loss of metabolic effect was associated with a decrease in recombinant protein in muscle, while pDNA and transcript were detectable 4 weeks after gene delivery. Monthly intravenous gene delivery maintained metabolic correction for at least 5 months. Fibrosis around vessels in the arterial group limited the number of successful repeat gene transfer sessions to 3. Animals expressing hUGT1A1 developed anti-hUGT1A1 antibodies and lymphocytic infiltrate in muscle. Immunosuppression abrogated antibody response, ameliorated lymphocytic inflammation, and enhanced metabolic correction but did not prevent a decrease in the amount of recombinant protein. In conclusion, repeated intravenous delivery of pDNA into muscle enables long-term correction of hyperbilirubinemia in the Gunn rat. The procedure is safe and simple, with great clinical potential. Further studies are needed to explain the mechanisms of loss and improve the stability of recombinant hUGT1A1 in muscle.

Gene therapy of liver diseases

Many liver diseases lack satisfactory treatment and alternative therapeutic options are urgently needed. Gene therapy is a new mode of treatment for both inherited and acquired diseases, based on the transfer of genetic material to the tissues. Genes are incorporated into appropriate vectors in order to facilitate their entrance and function inside the target cells. Gene therapy vectors can be constructed on the basis of viral or non-viral molecular structures. Viral vectors are frequently used, due to their higher transduction efficiency. Both the type of vector and the expression cassette determine the duration, specificity and inducibility of gene expression. A considerable number of preclinical studies indicate that a great variety of liver diseases, including inherited metabolic defects, chronic viral hepatitis, liver cirrhosis and primary and metastatic liver cancer, are amenable to gene therapy. Gene transfer to the liver can also be used to convert this organ into a factory of secreted proteins needed to treat conditions that do not affect the liver itself. Clinical trials of gene therapy for the treatment of inherited diseases and liver cancer have been initiated but human gene therapy is still in its infancy. Recent progress in vector technology and imaging techniques, allowing in vivo assessment of gene expression, will facilitate the development of clinical applications of gene therapy.

Nonviral gene transfer into liver and muscle for treatment of hyperbilirubinemia in the gunn rat

We evaluated naked plasmid DNA (pDNA)-mediated expression of human hepatic bilirubin UDP-glucuronosyltransferase (hUGT1A1) in skeletal muscle to correct hyperbilirubinemia in the UGT1A1-deficient Gunn rat, an animal model of Crigler-Najjar syndrome type I (CN-I). After delivery of pDNA encoding hUGT1A1 via hepatic vein or femoral artery, in vitro bilirubin glucuronidation activity was detectable in Gunn rat liver and muscle extracts. Expression of hUGT1A1 in Gunn rat liver or muscle resulted in excretion of bilirubin glucuronides in bile. Total biliary bilirubin concentrations increased from a pretreatment average of 10.5 +/- 2.1 microM to 29.2 +/- 4.2 microM after gene transfer into the liver, and to 28.6 +/- 3.8 microM after gene transfer into muscle. Total serum bilirubin decreased by up to 31.2 +/- 6.9 and 29.2 +/- 3.7% and remained significantly lower for at least 1 and 2 weeks, respectively. Tissue damage associated with the procedure was minimal and reversible. Our results demonstrate that muscle can be genetically modified to glucuronidate bilirubin, leading to elimination in bile. A 30% decrease in serum bilirubin, if sustained, would provide meaningful clinical benefit for CN-I patients. However, to be clinically useful, this method needs further optimization and stable gene expression must be achieved.

Lifelong elimination of hyperbilirubinemia in the Gunn rat with a single injection of helper-dependent adenoviral vector

Crigler-Najjar syndrome is a recessively inherited disorder characterized by severe unconjugated hyperbilirubinemia caused by a deficiency of uridine diphospho-glucuronosyl transferase 1A1. Current therapy relies on phototherapy to prevent kernicterus, but liver transplantation presently is the only permanent cure. Gene therapy is a potential alternative, and recent work has shown that helper-dependent adenoviral (HD-Ad) vectors, devoid of all viral coding sequences, induce prolonged transgene expression and exhibit significantly less chronic toxicity than early-generation Ad vectors. We used a HD-Ad vector to achieve liver-restricted expression of human uridine diphospho-glucuronosyl transferase 1A1 in the Gunn rat, a model of the human disorder. Total plasma bilirubin levels were reduced from >5.0 mg/dl to <<1.4 mg/dl for >2 yr after a single i.v. administration of vector expressing the therapeutic transgene at a dose of 3 x 10(12) viral particles per kg. HPLC analysis of bile from treated rats showed the presence of bilirubin glucuronides at normal WT levels >2 yr after one injection of vector, and i.v. injection of bilirubins IIIalpha and XIIIalpha in the same animals revealed excess bilirubin-conjugating capacity. There was no significant elevation of liver enzymes (alanine aminotransferase) and only transient, moderate thrombocytopenia after injection of the vector. A clinically significant reduction in serum bilirubin was observed with a dose as low as 6 x 10(11) viral particles per kg. We conclude that complete, long-term correction of hyperbilirubinemia in the Gunn rat model of Crigler-Najjar syndrome can be achieved with one injection of HD-Ad vector and negligible chronic toxicity.

Challenges and strategies: the immune responses in gene therapy

The host immune responses, including T lymphocytes mediated immune response and humoral immune responses are the important parts of the challenges in gene therapy. There are some potential immunostimulants in gene delivery systems, such as viral and non-viral vectors. Viral gene products, transgene products, viral proteins derived from viral particles required by dead-end infection, and CpG DNA in plasmid may play important roles in inducing the host immune responses when foreign genes are transferred into the targeted tissues. The immune responses should lead to many problems in gene therapy: transient expression of therapeutic gene, non-efficient re-administration of the same vectors, and severe side-effects in clinical trials. Although RNAi may act as gene therapeutic agent for suppression of specific gene expression, little attention has been given to the potential non-specific effects that might be induced. It was reported that small interfering RNAs (siRNAs) can induce the host interferon response following transfected to mammalian cells. Facing these challenges, a number of studies have been focused on taking measures to solve them, such as immunosuppression, selection of different administration routes and dose of the vectors, using the tissue-specific promoters and modifying the vectors.

Prolonged local expression of anti-CD4 antibody by adenovirally transduced allografts can promote long-term graft survival

BACKGROUND

Currently, successful transplantation of allografts requires the systemic use of immunosuppressive drugs. These can cause serious morbidity due to toxicity and increased susceptibility to cancer and infections. Local production of immunosuppressive molecules limited to the graft site would reduce the need for conventional, generalized immunosuppressive therapies and thus educe fewer side effects. This is particularly salient in a disease like type 1 diabetes, which is not immediately life-threatening yet islet allografts can effect a cure.

METHODS

We studied the efficacy of locally produced anti-CD4 antibody, mediated by adenovirus (Adv-anti-CD4) transduction of islets, to enhance allograft survival. Adenovirus-transduced islets were transplanted under the kidney capsule of diabetic recipients and graft rejection determined by monitoring blood glucose levels.

RESULTS

Adv-anti-CD4 transduction of mouse islets afforded protection against allogeneic rejection after transplantation into fully mismatched recipients. In some recipients, the islet allograft survival was prolonged (persisting for at least 15 weeks), corresponding to the prolonged expression of the anti-CD4 antibody. The effect was local, as absence of CD4+ T lymphocytes was observed primarily at the graft site.

CONCLUSIONS

Immunosuppressive effects can be restricted locally by our strategy. Local production of a single antibody against one subset of T lymphocytes can protect mouse islets from allograft rejection during transplantation to treat diabetes. Our findings foreshadow that this strategy may be even more effective when a combination of antibodies are used and that similar strategies may prevent xenograft rejection.

Sustained Muscle Expression of Dystrophin from a High-Capacity Adenoviral Vector with Systemic Gene Transfer of T Cell Costimulatory Blockade

Adenoviral vector (Ad)-mediated gene delivery of normal, full-length dystrophin to skeletal muscle provides a promising strategy for the treatment of Duchenne muscular dystrophy (DMD). However, cellular and humoral immune responses induced by vector gene transfer limit the application of this approach. Blockade of the costimulatory interaction between naïve T cells and antigen-presenting cells has proven to be a successful means to diminish immunity induced by gene transfer. In this study we explore the potential of supplementing dystrophin gene delivery to dystrophin-deficient Dmd mouse skeletal muscle with systemic gene delivery of CTLA4Ig and CD40Ig molecules to effect costimulatory blockade. We found that systemic administration of a high-capacity Ad (HC-Ad) vector carrying murine CTLA4Ig (AdmCTLA4Ig) either alone or codelivered with an HC-Ad vector carrying murine CD40Ig (AdmCD40Ig) provided sustained expression of recombinant full-length murine dystrophin from an HC-Ad vector carrying the dystrophin cDNA (AdmDys). The level of AdmDys vector genomes remained stable in animals cotreated with systemic delivery of vectors carrying molecules to block costimulation. In addition, muscle CD4(+) and CD8(+) T cell infiltrates and Th1 cytokine production by splenocytes were reduced. The production of neutralizing antibody against Ad vector was significantly inhibited in mice receiving systemic codelivery of both AdmCTLA4Ig and AdmCD40Ig, but not in the mice treated with AdmCTLA4Ig alone. The results suggested that coblockade of both CD28/B7 and CD40L/CD40 costimulatory pathways is required for effective inhibition of the Ad vector-induced humoral immune response in Dmd mice, whereas blockade of CD28/B7 alone by murine CTLA4Ig would be sufficient for prolonged dystrophin expression in treated muscle.

Glucuronidation and the UDP-glucuronosyltransferases in health and disease

This article is an updated report of a symposium held at the June 2000 annual meeting of the American Society for Pharmacology and Experimental Therapeutics in Boston. The symposium was sponsored by the ASPET Divisions for Drug Metabolism and Molecular Pharmacology. The report covers research from the authors' laboratories on the structure and regulation of UDP-glucuronosyltransferase (UGT) genes, glucuronidation of xenobiotics and endobiotics, the toxicological relevance of UGTs, the role of UGT polymorphisms in cancer susceptibility, and gene therapy for UGT deficiencies.

Long term transgene expression by hepatocytes transduced with retroviral vectors requires induction of immune tolerance to the transgene

BACKGROUND/AIMS

Gene therapy for inherited liver diseases requires permanent expression of the therapeutic gene. However, in vivo liver transduction with retroviral vectors triggers an immune elimination of transduced hepatocytes. Here we investigated whether immune response could be prevented by treatment with compounds known to induce tolerance in organ transplantation: CTLA4Ig and LF-15-0195.

METHODS

CTLA4Ig was administered either via i.p. injection of the drug or by i.m. injection of recombinant adenoviruses encoding CTLA4Ig. LF-15-0195 was administered i.p. All animals were subjected to partial hepatectomy and received beta-galactosidase retroviral vectors intravenously. Appearance of anti-beta-galactosidase antibodies was monitored and the number of positive hepatocytes was assessed at day 7 and at sacrifice.

RESULTS

No beta-galactosidase antibodies were detected as long as CTLA4Ig was detectable in serum. Short-term treatment with CTLA4Ig induced tolerance in a significant proportion of animals only at high dose (1 mg/kg). Administration of CTLA4Ig adenovectors resulted in prolonged secretion of CTLA4Ig and permanent absence of anti-beta-galactosidase antibodies. LF-15-0915 administration achieved tolerance in some animals.

CONCLUSIONS

In conclusion, manipulation of the immune system at the time of virus delivery using clinically relevant tolerance-inducing protocols is a promising approach to achieve long term expression after retrovirus-mediated gene transfer to the liver.

CTLA4Ig delivered by high-capacity adenoviral vector induces stable expression of dystrophin in mdx mouse muscle

Adenoviral (Ad) vector-mediated gene delivery of normal, full-length dystrophin to skeletal muscle provides a promising strategy for the treatment of Duchenne muscular dystrophy (DMD), an X-linked recessive, dystrophin-deficient muscle disease. Studies in animal models suggest that successful DMD gene therapy by Ad vector-mediated gene transfer would be precluded by cellular and humoral immune responses induced by vector capsid and transgene proteins. To address the immunity induced by Ad vector-mediated dystrophin gene delivery to dystrophic muscle, we developed high-capacity adenoviral (HC-Ad) vectors expressing mouse dystrophin driven by the muscle creatine kinase promoter (AdmDys) and mCTLA4Ig (AdmCTLA4Ig) individually, or together from one vector (AdmCTLA4Ig/mDys). We found stable expression of dystrophin protein in the tibialis anterior muscles of mdx mice, coinjected with AdmCTLA4Ig and AdmDys, or injected alone with AdmCTLA4Ig/mDys, whereas the expression of dystrophin protein in the control group coinjected with AdmDys and an empty vector decreased by at least 50% between 2 and 8 weeks after administration. Additionally, we observed reductions in Ad vector-induced Th1 and Th2 cytokines, Ad vector-specific cytotoxic T lymphocyte activation and neutralizing anti-Ad antibodies in both experimental groups that received a mCTLA4Ig-expressing vector as compared to the control group. This study demonstrates that the coexpression of mCTLA4Ig and dystrophin in skeletal muscle provided by HC-Ad vector-mediated gene transfer can provide stable expression of dystrophin in immunocompetent, adult mdx mouse muscle and applies a potentially powerful strategy to overcome adaptive immunity induced by Ad vector-mediated dystrophin gene delivery toward the ultimate goal of treatment for DMD.

Modifying Adenoviral Vectors for Use as Gene-Based Cancer Vaccines

The past decade has produced significant advances in our understanding of antigen-presenting cells, tumor antigens, and other components of the immune response to cancer. Gene-based vaccination is emerging as one of the more promising approaches for loading dendritic cells (DC) with tumor-associated antigens. In this respect, it is proposed that adenoviral (AdV) vectors can deliver high antigen concentrations, promote effective processing and MHC expression, and stimulate potent cell-mediated immunity. While AdV vectors have performed well in pre-clinical vaccine models, their application to patient care has limitations. The in vivo administration of AdV vectors is associated with both innate and adaptive host responses that result in tissue inflammation and injury, viral neutralization, and premature clearance of AdV-transduced cells. A variety of strategies have been developed to address these limitations. The ideal vaccine would avoid vector-related immune responses, have relative specificity for transducing DC, and induce high levels of transgene expression. This review describes the range of host responses to AdV vaccines, identifies strategies to reduce viral recognition and enhance transgene antigen expression, and suggests future approaches to vector development and administration. There is every reason to believe that safer and more effective forms of AdV-based vaccines can be developed and applied to patient therapy.

AAV gene transfer to the retina does not protect retrovirally transduced hepatocytes from the immune response

Gene therapy of inherited hepatic disease relies on sustained expression of the therapeutic transgene. In many instances, such expression will require immune tolerization to the non-self therapeutic transgene product. We previously demonstrated that a cytotoxic immune response eliminated hepatocytes after in vivo transduction using recombinant retroviral vectors. In the present study we investigated whether prior gene transfer to the retina, which is suspected to induce immune tolerance, could alleviate the immune response occurring after retrovirus mediated gene transfer to the liver. Retinal cells were transduced using adeno-associated viral vectors harbouring a beta-galactosidase transgene. Sixty days later, regenerating hepatocytes were transduced after partial hepatectomy using a recombinant retrovirus carrying the transgene. Three weeks later, anti beta-galactosidase antibodies were present in all animals. Elimination of the transduced hepatocytes eventually occurred in all animals by 2 months after liver gene transfer, although sustained beta-galactosidase expression was still present in the retina in 66% of the animals. We conclude that although the retina behaves as an immunoprivileged site, gene expression in the subretinal space is not sufficient to induce immune tolerance to a transgene product expressed in the liver.

Molecular therapies for viral hepatitis

Current treatment modalities available for hepatitis B virus (HBV) or hepatitis C virus (HCV) infections are not efficient. The enormous disease burden caused by these two infections makes the development of novel therapies critical. For HCV, the development of an effective vaccine is urgent in view of the escalating number of infected individuals. Molecular therapies for HBV and HCV infection can be directed at reducing viral load by interfering with the life cycle of the viruses or at generating immune response against viral epitopes. The antiviral approaches consist of the delivery or expression of antisense RNAs, ribozymes or dominant negative proteins. Viral biology can be interrupted by attacking various potential targets within the two viruses. DNA-based vaccination strategies are being explored for both prevention and treatment of these diseases. Both non-viral and recombinant viral vectors are being developed for safe, effective and long-term gene transfer to the liver. Although no "ideal" vector is available at this time, the ingenuity of numerous investigators is leading to the improvement of the vector systems, promising successful application of gene therapy to the prevention and treatment of viral hepatitis in the foreseeable future.

Gene therapy progress and prospects: adenoviral vectors

In September 1999, the perceptions of the use of adenoviral (Ad) vectors for gene therapy were altered when a patient exposed via the hepatic artery to a high dose of adenoviral vector succumbed to the toxicity related to vector administration. Appropriately, concerns were raised about continued use of the Ad vector system and, importantly, there were increased efforts to more fully understand the toxicity. Today it is recognized that there is no ideal vector system, and that while Ad vectors are not suitable for all applications, the significant advantages over other vector systems including efficient transduction of a variety of cell types, both quiescent and dividing, make it optimal for certain applications. These include protocols where high levels of short-term expression are sufficient to provide a therapeutic benefit. Potential target applications include therapeutic angiogenesis, administration into immune-privileged sites such as the CNS, or treatments where the adjuvant effect of adenovirus can be of benefit such as cancer vaccines. Broader applicability of Ad vectors will require resolution of toxicity issues. This review will therefore focus on studies conducted over the last 2 years that have advanced our understanding of the toxicity associated with Ad vectors, studies that have employed methods to reduce toxicity and improvements in Ad vectors themselves that will reduce toxicity by one of several mechanisms. These mechanisms include retargeting vector to the tissue of interest, minimizing or eliminating viral gene expression that is thought to result in loss of transduced cells, or by methods that seek to reduce the vector dose required for therapeutic benefit. An area where there remains significant room for improvement is when readministration of vector is required because transgene expression has decreased to background levels.

Immunological hurdles to lung gene therapy

Gene delivery has the potential to offer effective treatment to patients with life-threatening lung diseases such as cystic fibrosis, alpha1-antitrypsin deficiency and lung cancer. Phase I/II clinical trials have shown that, in principle, gene transfer to the lung is feasible and safe. However, gene expression from both viral and non-viral gene delivery systems has been inefficient. In addition to extra- and intracellular barriers, the host innate and acquired immune system represents a major barrier to successful gene transfer to the lung. Results from studies in experimental animals and clinical trials have shown that inflammatory, antibody and T cell responses can limit transgene expression duration and readministration of the gene transfer vector. We will review here how the development of pharmacological and/or immunological agents can modulate the host immune system and the limitations of these strategies. A better understanding of the immunological barriers which exist in the lung might allow for a more sustained expression of the transgene and importantly help overcome the problem of readministration of viral vectors.

Gene therapy for inherited hyperbilirubinemias

Crigler-Najjar syndrome type 1 (CN-1) is a potentially lethal condition, and is the only inherited disorder of bilirubin metabolism that needs treatment beyond the neonatal period. Currently, orthotopic liver transplantation is the only available cure for CN-1. Because the liver architecture is not disturbed in CN-1 and partial correction of bilirubin-UDP-glucuronosyltransferase (UGT1A1) activity is expected to be sufficient for protection against kernicterus, cell and gene therapies are being developed using the Gunn rat as an animal model of the disease. Ex vivo gene therapy based on the transplantation of genetically manipulated hepatocytes and in vivo gene transfer using recombinant adenovirus and Simian virus 40 (SV40)-based vectors have yielded significant success. The novel strategy of in vivo site-directed mutagenesis has also resulted in modest, but significant, correction of the genetic abnormality. Newer viral and nonviral gene delivery methods are being explored and have been discussed in brief. In summary, effective gene therapy methods have been validated in Gunn rats. Despite considerable remaining hurdles, gene therapy for CN-1 could become a clinical reality by the turn of this decade.