Gene therapy for human alpha1-antitrypsin deficiency in an animal model using SV40-derived vectors

Migration of bone marrow progenitor cells in the adult brain of rats and rabbits

Neurogenesis takes place in the adult mammalian brain in three areas: Subgranular zone of the dentate gyrus (DG); subventricular zone of the lateral ventricle; olfactory bulb. Different molecular markers can be used to characterize the cells involved in adult neurogenesis. It has been recently suggested that a population of bone marrow (BM) progenitor cells may migrate to the brain and differentiate into neuronal lineage. To explore this hypothesis, we injected recombinant SV40-derived vectors into the BM and followed the potential migration of the transduced cells. Long-term BM-directed gene transfer using recombinant SV40-derived vectors leads to expression of the genes delivered to the BM firstly in circulating cells, then after several months in mature neurons and microglial cells, and thus without central nervous system (CNS) lesion. Most of transgene-expressing cells expressed NeuN, a marker of mature neurons. Thus, BM-derived cells may function as progenitors of CNS cells in adult animals. The mechanism by which the cells from the BM come to be neurons remains to be determined. Although the observed gradual increase in transgene-expressing neurons over 16 mo suggests that the pathway involved differentiation of BM-resident cells into neurons, cell fusion as the principal route cannot be totally ruled out. Additional studies using similar viral vectors showed that BM-derived progenitor cells migrating in the CNS express markers of neuronal precursors or immature neurons. Transgene-positive cells were found in the subgranular zone of the DG of the hippocampus 16 mo after intramarrow injection of the vector. In addition to cells expressing markers of mature neurons, transgene-positive cells were also positive for nestin and doublecortin, molecules expressed by developing neuronal cells. These cells were actively proliferating, as shown by short term BrdU incorporation studies. Inducing seizures by using kainic acid increased the number of BM progenitor cells transduced by SV40 vectors migrating to the hippocampus, and these cells were seen at earlier time points in the DG. We show that the cell membrane chemokine receptor, CCR5, and its ligands, enhance CNS inflammation and seizure activity in a model of neuronal excitotoxicity. SV40-based gene delivery of RNAi targeting CCR5 to the BM results in downregulating CCR5 in circulating cells, suggesting that CCR5 plays an important role in regulating traffic of BM-derived cells into the CNS, both in the basal state and in response to injury. Furthermore, reduction in CCR5 expression in circulating cells provides profound neuroprotection from excitotoxic neuronal injury, reduces neuroinflammation, and increases neuronal regeneration following this type of insult. These results suggest that BM-derived, transgene-expressing, cells can migrate to the brain and that they become neurons, at least in part, by differentiating into neuron precursors and subsequently developing into mature neurons.

Challenges and Prospects for Alpha-1 Antitrypsin Deficiency Gene Therapy

Alpha-1 antitrypsin (AAT) is a protease inhibitor belonging to the serpin family. A number of identified mutations in the SERPINA1 gene encoding this protein result in alpha-1 antitrypsin deficiency (AATD). A decrease in AAT serum concentration or reduced biological activity causes considerable risk of chronic respiratory and liver disorders. As a monogenic disease, AATD appears to be an attractive target for gene therapy, particularly for patients with pulmonary dysfunction, where augmentation of functional AAT levels in plasma might slow down respiratory disease development. The short AAT coding sequence and its activity in the extracellular matrix would enable an increase in systemic serum AAT production by cellular secretion. In vitro and in vivo experimental AAT gene transfer with gamma-retroviral, lentiviral, adenoviral, and adeno-associated viral (AAV) vectors has resulted in enhanced AAT serum levels and a promising safety profile. Human clinical trials using intramuscular viral transfer with AAV1 and AAV2 vectors of the AAT gene demonstrated its safety, but did not achieve a protective level of AAT >11 μM in serum. This review provides an in-depth critical analysis of current progress in AATD gene therapy based on viral gene transfer. The factors affecting transgene expression levels, such as site of administration, dose and type of vector, and activity of the immune system, are discussed further as crucial variables for optimizing the clinical effectiveness of gene therapy in AATD subjects.

Gene transfer of master autophagy regulator TFEB results in clearance of toxic protein and correction of hepatic disease in alpha-1-anti-trypsin deficiency

Alpha-1-anti-trypsin deficiency is the most common genetic cause of liver disease in children and liver transplantation is currently the only available treatment. Enhancement of liver autophagy increases degradation of mutant, hepatotoxic alpha-1-anti-trypsin (ATZ). We investigated the therapeutic potential of liver-directed gene transfer of transcription factor EB (TFEB), a master gene that regulates lysosomal function and autophagy, in PiZ transgenic mice, recapitulating the human hepatic disease. Hepatocyte TFEB gene transfer resulted in dramatic reduction of hepatic ATZ, liver apoptosis and fibrosis, which are key features of alpha-1-anti-trypsin deficiency. Correction of the liver phenotype resulted from increased ATZ polymer degradation mediated by enhancement of autophagy flux and reduced ATZ monomer by decreased hepatic NFκB activation and IL-6 that drives ATZ gene expression. In conclusion, TFEB gene transfer is a novel strategy for treatment of liver disease of alpha-1-anti-trypsin deficiency. This study may pave the way towards applications of TFEB gene transfer for treatment of a wide spectrum of human disorders due to intracellular accumulation of toxic proteins.

Combination therapy utilizing shRNA knockdown and an optimized resistant transgene for rescue of diseases caused by misfolded proteins

Molecular knockdown of disease proteins and restoration of wild-type activity represent a promising but challenging strategy for the treatment of diseases that result from the accumulation of misfolded proteins (i.e., Huntington disease, amyotrophic lateral sclerosis, and α-1 antitrypsin deficiency). In this study we used alpha-1 antitrypsin (AAT) deficiency with the piZZ mutant phenotype as a model system to evaluate the efficiency of gene-delivery approaches that both silence the piZZ transcript (e.g., shRNA) and restore circulating wild-type AAT expression from resistant codon-optimized AAT (AAT-opt) transgene cassette using adeno-associated virus (AAV) vector delivery. After systemic injection of a self-complimentary AAV serotype 8 (scAAV8) vector encoding shRNA in piZZ transgenic mice, both mutant AAT mRNA in the liver and defected serum protein level were inhibited by 95%, whereas liver pathology, as monitored by dPAS and fibrosis staining, reversed. To restore blood AAT levels in AAV8/shRNA-treated mice, several strategies to restore functional AAT levels were tested, including using AAV AAT-opt transgene cassettes targeted to muscle and liver, or combination vectors carrying piZZ shRNA and AAT-opt transgenes separately, or a single bicistronic AAV vector. With these molecular approaches, we observed over 90% knockdown of mutant AAT with a 13- to 30-fold increase of circulating wild-type AAT protein from the shRNA-resistant AAT-opt cassette. The molecular approaches applied in this study can simultaneously prevent liver pathology and restore blood AAT concentration in AAT deficiencies. Based on these observations, similar gene-therapy strategies could be considered for any diseases caused by accumulation of misfolded proteins.

Gene therapy for alpha-1 antitrypsin deficiency

Alpha-1 antitrypsin (AAT) deficiency is a common single-gene disorder among Northern Europeans and North Americans. The carrier frequency for the common missense mutation (Z-AAT) ranges from 4% in the US to nearly 25% in the Republic of Ireland. Severe AAT deficiency (plasma levels below 11 μm) is most commonly associated with an adult-onset lung disease, with pan-acinar emphysema and airway inflammation, which is thought to be primarily owing to the loss of function of AAT in neutralizing neutrophil elastase and other pro-inflammatory enzymes. In 5-10% of patients, severe liver disease may develop. This may occur at any time from infancy to adulthood, and is thought to be owing to toxicity from the Z-AAT mutant protein that folds poorly and forms insoluble polymers within the hepatocyte, which is the primary site for AAT production. Thus, gene therapy for AAT lung disease is conceived of as augmentation of serum levels (a prolonged form of protein replacement, which is currently in use), while gene therapy for liver disease presents the problem of also having to downregulate the production of Z-AAT protein. Over the years, numerous strategies have been employed for the gene therapy of both AAT-deficient lung disease and liver disease. These will be reviewed with an emphasis on modalities that have reached clinical trials recently.

Gene transfer to the cerebellum

There are several diseases for which gene transfer therapy to the cerebellum might be practicable. In these studies, we used recombinant Tag-deleted SV40-derived vectors (rSV40s) to study gene delivery targeting the cerebellum. These vectors transduce neurons and microglia very effectively in vitro and in vivo, and so we tested them to evaluate gene transfer to the cerebellum in vivo. Using a rSV40 vector carrying human immunodeficiency virus (HIV)-Nef with a C-terminal FLAG epitope, we characterized the distribution, duration, and cell types transduced. Rats received test and control vectors by stereotaxic injection into the cerebellum. Transgene expression was assessed 1, 2, and 4 weeks later by immunostaining of serial brain sections. FLAG epitope-expressing cells were seen, at all times after vector administration, principally detected in the Purkinje cells of the cerebellum, identified as immunopositive for calbindin. Occasional microglial cells were tranduced; transgene expression was not detected in astrocytes or oligodendrocytes. No inflammatory or other reaction was detected at any time. Thus, SV40-derived vectors can deliver effective, safe, and durable transgene expression to the cerebellum.

Differentiation and characterization of metabolically functioning hepatocytes from human embryonic stem cells

Human embryonic stem cells (hESCs) may provide a cell source for functional hepatocytes for clinical applications and drug development. Initially, the hESC population was enriched to be more than 85% definitive endoderm (DE) as assessed by the expression of CXCR4, SOX17, and FOXA2. We then successfully converted DE into hepatic progenitors with 93% of the cells being positive for alpha-feto protein within 9 days. The percentage of albumin positive cells gradually increased to 90% at days 20-22 after differentiation. Moreover, our hESC-derived hepatocytes (hEH) developed a complete biotransformation system including phase I and II metabolizing enyzmes and phase III transporters. Nuclear receptors, which are critical in regulating the expression of metabolizing enzymes, were also expressed by our hEH. Using ultraperformance liquid chromatography-tandem mass spectrometry technology, we identified seven metabolic pathways of the drug bufuralol including four newly-reported ones in our hEH, which are the same as those in freshly isolated human primary hepatocytes (hPH). In addition, the results of the metabolism of four drugs indicate that our hEH have the capacity to metabolize these drugs at levels that are comparable to hPH. In conclusion, we have generated a relatively homogenous population of hepatocytes from hESCs, which appear to have complete metabolic function that is comparable to primary liver cells. These results represent a significant step towards the efficient differentiation of mature hepatocytes for cell-based therapeutics as well as for pharmacology and toxicology studies.

HIV-1 gp120 neurotoxicity proximally and at a distance from the point of exposure: protection by rSV40 delivery of antioxidant enzymes

Toxicity of HIV-1 envelope glycoprotein (gp120) for substantia nigra (SN) neurons may contribute to the Parkinsonian manifestations often seen in HIV-1-associated dementia (HAD). We studied the neurotoxicity of gp120 for dopaminergic neurons and potential neuroprotection by antioxidant gene delivery. Rats were injected stereotaxically into their caudate-putamen (CP); CP and (substantia nigra) SN neuron loss was quantified. The area of neuron loss extended several millimeters from the injection site, approximately 35% of the CP area. SN neurons, outside of this area of direct neurotoxicity, were also severely affected. Dopaminergic SN neurons (expressing tyrosine hydroxylase, TH, in the SN and dopamine transporter, DAT, in the CP) were mostly affected: intra-CP gp120 caused approximately 50% DAT+ SN neuron loss. Prior intra-CP gene delivery of Cu/Zn superoxide dismutase (SOD1) or glutathione peroxidase (GPx1) protected SN neurons from intra-CP gp120. Thus, SN dopaminergic neurons are highly sensitive to HIV-1 gp120-induced neurotoxicity, and antioxidant gene delivery, even at a distance, is protective.

Pancreatic acinar and islet cell infection by low-dose SV40 administration

OBJECTIVES

Viral vector uptake into the pancreas is rare. The few viral vectors reported to transduce in vivo pancreatic islets after systemic injection required additional physical measures, such as direct pancreatic injection or hepatic vessel clamping. Because pancreatic islet uptake of the human polyomavirus family member BK virus was previously reported in hamsters after systemic administration, we hypothesized that SV40, a polyomavirus member remarkably similar to BK virus, may also infect the pancreas.

METHODS

We injected intravenously a low dose of SV40, unaided by any other physical or chemical means, and evaluated viral uptake by pancreatic islets and pancreatic exocrine tissue via polymerase chain reaction, Western blot, electron microscopy, immunofluorescent microscopy, and protein A-gold immunocytochemistry.

RESULTS

Pancreatic uptake of SV40 was comparable to other major organs (ie, liver and spleen). SV40 viral particles were detected in both pancreatic islets and acini. In pancreatic islets, all islet cell types were infected by SV40, albeit the infection rate of glucagon-producing alpha cells surpassed beta- and delta-islet cells. Low-dose SV40 administration was not sufficient to induce heterologous gene expression in the pancreas.

CONCLUSIONS

Our study shows that pancreatic islet and acinar cell uptake of SV40 is feasible with a single, low-dose intravenous injection. However, this dose did not result in gene delivery into the murine pancreas.

The promise of gene therapy for the treatment of alpha-1 antitrypsin deficiency

In the last 13 years, three gene therapy trials for the treatment of alpha-1 antitrypsin deficiency have been conducted. The first trial delivered plasmid encoding the alpha-1 antitrypsin cDNA to the nasal epithelium using cationic liposomes. The last two trials delivered recombinant adeno-associated vectors encoding the alpha-1 antitrypsin cDNA by intramuscular injection. In this review, the progress of ongoing clinical trials and new gene therapy technologies is discussed.

Sustained expression of alpha1-antitrypsin after transplantation of manipulated hematopoietic stem cells

Inherited mutations in the human alpha(1)-antitrypsin (AAT) gene lead to deficient circulating levels of AAT protein and a predisposition to developing emphysema. Gene therapy for individuals deficient in AAT is an attractive goal, because transfer of a normal AAT gene into any cell type able to secrete AAT should reverse deficient AAT levels and attenuate progression of lung disease. Here we present an approach for AAT gene transfer based on the transplantation of lentivirally transduced hematopoietic stem cells (HSCs). We develop a novel dual-promoter lentiviral system to transfer normal human AAT cDNA as well as a fluorescent tracking "reporter gene" into murine HSCs. After transplantation of 3,000 transduced HSCs into irradiated mouse recipients, we demonstrate simultaneous and sustained systemic expression of both genes in vivo for at least 31 weeks. The stem cells transduced with this protocol maintain multipotency, self-renewal potential, and the ability to reconstitute the hematopoietic systems of both primary and secondary recipients. This lentiviral-based system may be useful for investigations requiring the systemic secretion of anti-proteases or cytokines relevant to the pathogenesis of a variety of lung diseases.

Protecting neurons from HIV-1 gp120-induced oxidant stress using both localized intracerebral and generalized intraventricular administration of antioxidant enzymes delivered by SV40-derived vectors

Human immunodeficiency virus-1 (HIV-1) is the most frequent cause of dementia in adults under 40. We sought to use gene delivery to protect from HIV-1-related neuron loss. Because HIV-1 envelope (Env) gp120 elicits oxidant stress and apoptosis in cultured neurons, we established reproducible parameters of Env-mediated neurotoxicity in vivo, then tested neuroprotection using gene delivery of antioxidant enzymes. We injected 100-500 ng mul(-1)gp120 stereotaxically into rat caudate-putamens (CP) and assayed brains for apoptosis by terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) 6-h to 14-day post-injection. Peak apoptosis occurred 1 day after injection of 250 and 500 ng microl(-1)gp120. TUNEL-positive cells mostly expressed neuronal markers (NeuroTrace), although some expressed CD68 and so were most likely microglial cells. Finally, we compared neuroprotection from gp120-induced apoptosis provided by localized and generalized intra-central nervous system (CNS) gene delivery. Recombinant SV40 vectors carrying Cu/Zn superoxide dismutase (SOD1) or glutathione peroxidase (GPx1) were injected into the CP, where gp120 was administered 4-24 weeks later. Alternatively, we inoculated the vector into the lateral ventricle (LV), with or without prior intraperitoneal (i.p.) administration of mannitol. Intracerebral injection of SV(SOD1) or SV(GPx1) significantly protected neurons from gp120-induced apoptosis throughout the 24-week study. Intraventricular vector administration protected from gp120 neurotoxicity comparably, particularly if preceded by mannitol i.p. Thus, HIV-1 gp120 is neurotoxic in vivo, and intracerebral or intra-ventricular administration of rSV40 vectors carrying antioxidant enzymes is neuroprotective. These findings suggest the potential utility of both localized and widespread gene delivery in treating neuroAIDS and other CNS diseases characterized by excessive oxidative stress.

Differentiation and enrichment of hepatocyte-like cells from human embryonic stem cells in vitro and in vivo

Human embryonic stem cells (hESC) may provide a cell source for functional hepatocytes. The aim of this study is to establish a viable human hepatocyte-like cell line from hESC that can be used for cell-based therapies. The differentiated hESC were enriched by transducing with a lentivirus vector containing the green fluorescent protein (GFP) gene driven by the alpha1-antitrypsin promoter; the GFP gene is expressed in committed hepatocyte progenitors and hepatocytes. GFP+ hESC were purified by laser microdissection and pressure catapulting. In addition, differentiated hESC that were transduced with a lentivirus triple-fusion vector were transplanted into NOD-SCID mice, and the luciferase-induced bioluminescence in the livers was evaluated by a charge-coupled device camera. GFP+ hESC expressed a large series of liver-specific genes, and expression levels of these genes were significantly improved by purifying GFP+ hESC; our results demonstrated that purified differentiated hESC express nearly physiological levels of liver-specific genes and have liver-specific functions that are comparable to those of primary human hepatocytes. The differentiated hESC survived and engrafted in mouse livers, and human liver-specific mRNA and protein species were detected in the transplanted mouse liver and serum at 3 weeks after transplantation. This is the first time that human albumin generated by hESC-derived hepatocytes was detected in the serum of an animal model. This also represents the first successful transplantation of differentiated hESC in an animal liver and the first bioluminescence imaging of hESC in the liver. This study is an initial step in establishing a viable hepatocyte-like cell line from hESC. Disclosure of potential conflicts of interest is found at the end of this article.

Strategies for CNS-directed gene delivery: in vivo gene transfer to the brain using SV40-derived vectors

Gene transfer to the central nervous system (CNS) has been approached using various vectors. Recombinant SV40-derived vectors (rSV40s) transduce neurons and microglia effectively in vitro, so we tested rSV40s gene transfer to the CNS in vivo, and characterized the distribution, duration and cell types transduced. We used rSV40s carrying Human Immunodeficiency Virus Type 1 Net protein (HIV-1 Nef) with a C-terminal FLAG epitope tag as a marker, and another with Cu/Zn superoxide dismutase (SOD1). Rats were given vectors stereotaxically, either intraparenchymally into the caudate-putamen (CP) or into the lateral ventricle (LV). FLAG expression was studied for 3 months by immunostaining serial brain sections. After intraparenchymal administration, numerous transgene-expressing cells were seen, many as far as 4 mm from the injection site. Transgene expression remained strong throughout the 3-month study period. Coimmunostaining for lineage markers showed that neurons and, more rarely, microglial cells were tranduced, except astrocytes and oligodendroglia. After injection into the LV, high levels of transgene expression were detected throughout the frontal cortex by Western analysis. Systemic mannitol-induced hyperosmolarity further augmented LV transgene delivery. SV40-derived vectors may, thus, be useful for long-term gene expression in the brain, whether locally by intraparenchymal administration or diffusely by intraventricular injection, with or without mannitol.

Liver transduction with a simian virus 40 vector encoding insulin-like growth factor I reduces hepatic damage and the development of liver cirrhosis

Liver transplantation is the only treatment for advanced liver cirrhosis. Therapies halting the progression of the disease are urgently needed. Administration of recombinant insulin-like growth factor-I (rIGF-I) induces hepatoprotective effects in experimental cirrhosis. Therefore, we analyzed the efficacy of a recombinant simian virus 40 vector (rSV40) encoding IGF-I (rSVIGF-I) to prevent cirrhosis progression. First, transgene expression was evaluated in mice injected with rSV40 encoding luciferase, which showed long-term hepatic expression of the transgene. Interestingly, luciferase expression increased significantly in CCl(4)-damaged livers and upon IGF-I administration, thus liver injury and IGF-I expression from rSVIGF-I should favor transgene expression. rSVIGF-I therapeutic efficacy was studied in rats where liver cirrhosis was induced by CCl(4) inhalation during 36 weeks. At the end of the study, the hepatic levels of IGF-I and IGF-binding protein 3 were higher in rSVIGF-I-treated rats than in control cirrhotic animals. Cirrhotic rats treated with rSVIGF-I had reduced serum bilirubin, transaminases and liver fibrosis scores and increased hepatic expression of hepatocyte growth factor and STAT3alpha as compared to cirrhotic animals. Furthermore, cirrhotic animals showed testis atrophy and altered spermatogenesis, whereas testicular size and histology were normal in cirrhotic rats that received rSVIGF-I. Therefore, rSV40-mediated sustained expression of IGF-I in the liver slowed cirrhosis progression.

Replication-deficient rSV40 mediate pancreatic gene transfer and long-term inhibition of tumor growth

Pancreatic cancer is one of the most aggressive and devastating human malignancies. There is an urgent need for more effective therapy for patients with advanced disease. In this context, genetic therapy potentially represents a rational new approach to treating pancreatic cancer, which could provide an adjunct to conventional options. Because of the promise of recombinant SV40 vectors, we tested their ability to deliver a transgene, and to target a transcript, so as to inhibit pancreatic tumors growth in vivo. BxPC3 and Capan-1 cells were efficiently transduced using SV40 vectors without selection, as compared to synthetic vectors PEI. SV40 vectors were as efficient as adenoviral vectors, and provided long-term transgene expression. Next, we devised a SV40-derived, targeted gene therapy approach of pancreatic cancer, by combining hTR tumor-specific promoter with sst2 somatostatin receptor tumor-suppressor gene. In vitro cell proliferation was strongly impaired following administration of SV(hTR-sst2). SV40-derived sst2-mediated antiproliferative effect was dependent on the local production of somatostatin. In vivo, intratumoral gene transfer of sst2 using rSV40 vectors resulted in a marked inhibition of Capan-1 tumor progression, and proliferation. These results represent the initial steps toward a novel approach to the gene therapy of pancreatic cancer using SV40 as a vector.

Rat bone marrow progenitor cells transduced in situ by rSV40 vectors differentiate into multiple central nervous system cell lineages

Using bone marrow-directed gene transfer, we tested whether bone marrow-derived cells may function as progenitors of central nervous system (CNS) cells in adult animals. SV40-derived gene delivery vectors were injected directly into femoral bone marrow, and we examined transgene expression in blood and brain for 0-16 months thereafter by immunostaining for FLAG epitope marker. An average of 5% of peripheral blood cells and 25% of femoral marrow cells were FLAG(+) throughout the study. CNS FLAG-expressing cells were mainly detected in the dentate gyrus (DG) and periventricular subependymal zone (PSZ). Although absent before 1 month and rare at 4 months, DG and PSZ FLAG(+) cells were abundant 16 months after bone marrow injection. Approximately 5% of DG cells expressed FLAG, including neurons (48.6%) and microglia (49.7%), and occasional astrocytes (1.6%), as determined by double immunostaining for FLAG and lineage markers. These data suggest that one or more populations of cells resident within adult bone marrow can migrate to the brain and differentiate into CNS-specific cells.

Alpha-1-antitrypsin deficiency: diagnosis, pathophysiology, and management

Alpha-1-antitrypsin deficiency is a relatively common but under-recognized genetic disease in which individuals homozygous for the mutant Z disease-associated allele are at risk for the development of liver disease and emphysema. The protein product of the mutant Z gene is synthesized in hepatocytes but accumulates intracellularly rather than being appropriately secreted. The downstream effects of the intracellular accumulation of the mutant Z protein include the formation of unique protein polymers, activation of autophagy, mitochondrial injury, endoplasmic reticulum stress, and caspase activation, which subsequently progress in a cascade, causing chronic hepatocellular injury. The variable clinical presentations among affected individuals suggest an important contribution of genetic and environmental disease modifiers, which are only now being identified. The heterozygous carrier state for the mutant Z gene, found in 1.5% to 3% of the population, is not itself a common cause of liver injury but may be a modifier gene for other liver diseases.

In vivo gene transfer into rat bone marrow progenitor cells using rSV40 viral vectors

Hematopoietic stem cell (HSC) gene transfer has been attempted almost entirely ex vivo and has been limited by cytokine-induced loss of self-renewal capacity and transplantation-related defects in homing and engraftment. Here, we attempted to circumvent such limitations by injecting vectors directly into the bone marrow (BM) to transduce HSCs in their native environment. Simian virus 40 (SV40)-derived gene delivery vectors were used because they transduce resting CD34+ cells very efficiently. Rats received SV-(Nef-FLAG), carrying FLAG marker epitope--or a control recombinant SV40 (rSV40)--directly into both femoral marrow cavities. Intracellular transgene expression by peripheral blood (PB) or BM cells was detected by cytofluorimetry. An average of 5.3% PB leukocytes expressed FLAG for the entire study--56 weeks. Transgene expression was sustained in multiple cell lineages, including granulocytes (average, 3.3% of leukocytes, 20.4% of granulocytes), CD3+ T lymphocytes (average, 0.53% of leukocytes, 1% of total T cells), and CD45R+ B lymphocytes, indicating gene transfer to long-lived progenitor cells with multilineage capacity. An average of 15% of femoral marrow cells expressed FLAG up to 16.5 months after transduction. Thus, direct intramarrow administration of rSV40s yields efficient gene transfer to rat BM progenitor cells and may be worthy of further investigation.

Inherited metabolic liver disease

PURPOSE OF REVIEW

The purpose of this review is to identify and discuss recent findings related to inherited metabolic disorders of the liver that increase our understanding of the pathophysiology and treatment for hemochromatosis and other iron overload disorders, Wilson disease and alpha one antitrypsin deficiency.

RECENT FINDINGS

The main theme in the recent discoveries for both iron overload disorders and Wilson disease is our increasing understanding that the phenotypic expression of these disorders are greatly influenced by genes involved in the metabolic pathways for these metals, or influence the progression of liver disease independent of metal metabolism. For example, the role of hepcidin dysregulation in hemochromatosis has been a surprising discovery that provides some mechanistic understanding for the increased iron absorption that is present in this disorder.

SUMMARY

Given the recent explosion of information on iron and copper metabolism and the cellular processing of alpha one antitrypsin, the highlights reviewed in this article will help the reader keep up to date with the current understanding of these diseases and potential future approaches to their treatment.