Production of glycosylated physiologically "normal" human alpha 1-antitrypsin by mouse fibroblasts modified by insertion of a human alpha 1-antitrypsin cDNA using a retroviral vector

Gene therapy for alpha-1 antitrypsin deficiency: an update

INTRODUCTION

Altering the human genetic code has been explored since the early 1990s as a definitive answer for the treatment of monogenic and acquired diseases which do not respond to conventional therapies. In Alpha-1 antitrypsin deficiency (AATD) the proper synthesis and secretion of alpha-1 antitrypsin (AAT) protein is impaired, leading to its toxic hepatic accumulation along with its pulmonary insufficiency, which is associated with parenchymal proteolytic destruction. Because AATD is caused by mutations in a single gene whose correction alone would normalize the mutant phenotype, it has become a popular target for both augmentation gene therapy and gene editing. Although gene therapy products are already a reality for the treatment of some pathologies, such as inherited retinal dystrophy and spinal muscular atrophy, AATD-related pulmonary and, especially, liver diseases still lack effective therapeutic options.

AREAS COVERED

Here, we review the course, challenges, and achievements of AATD gene therapy as well as update on new strategies being developed.

EXPERT OPINION

Reaching safe and clinically effective expression of the AAT is currently the greatest challenge for AATD gene therapy. The improvement and emergence of technologies that use gene introduction, silencing and correction hold promise for the treatment of AATD.

Oncostatin M and TNF-α Induce Alpha-1 Antitrypsin Production in Undifferentiated Adipose Stromal Cells

Alpha-1 antitrypsin (A1AT), a circulating acute-phase reactant antiprotease, is produced and secreted by cells of endodermal epithelial origin, primarily hepatocytes, and by immune cells. Deficiency of A1AT is associated with increased risk of excessive lung inflammation and injury, especially following chronic cigarette smoke (CS) exposure. Exogenous administration of mesenchymal progenitor cells, including adipose tissue-derived stromal/stem cells (ASC), alleviates CS-induced lung injury through paracrine effectors such as growth factors. It is unknown, however, if mesodermal ASC can secrete functional A1AT and if CS exposure affects their A1AT production. Human ASC collected via liposuction from nonsmoking or smoking donors were stimulated by inflammatory cytokines tumor necrosis alpha (TNFα), oncostatin M (OSM), and/or dexamethasone (DEX) or were exposed to sublethal concentrations of ambient air control or CS extract (0.5%-2%). We detected minimal expression and secretion of A1AT by cultured ASC during unstimulated conditions, which significantly increased following stimulation with TNFα or OSM. Furthermore, TNFα and OSM synergistically enhanced A1AT expression and secretion, which were further increased by DEX. The A1AT transcript variant produced by stimulated ASC resembled that produced by bronchial epithelial cells rather than the variant produced by monocytes/macrophages. While the cigarette smoking status of the ASC donor had no measurable effect on the ability of ASC to induce A1AT expression, active exposure to CS extract markedly reduced A1AT expression and secretion by cultured ASC, as well as human tracheobronchial epithelial cells. ASC-secreted A1AT covalently complexed with neutrophil elastase in control ASC, but not in cells transfected with A1AT siRNA. Undifferentiated ASC may require priming to secrete functional A1AT, a potent antiprotease that may be relevant to stem cell therapeutic effects.

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.

Proteolytic and N-glycan processing of human α1-antitrypsin expressed in Nicotiana benthamiana

Plants are increasingly being used as an expression system for complex recombinant proteins. However, our limited knowledge of the intrinsic factors that act along the secretory pathway, which may compromise product integrity, renders process design difficult in some cases. Here, we pursued the recombinant expression of the human protease inhibitor α1-antitrypsin (A1AT) in Nicotiana benthamiana. This serum protein undergoes intensive posttranslational modifications. Unusually high levels of recombinant A1AT were expressed in leaves (up to 6 mg g(-1) of leaf material) in two forms: full-length A1AT located in the endoplasmic reticulum displaying inhibitory activity, and secreted A1AT processed in the reactive center loop, thus rendering it unable to interact with target proteinases. We found that the terminal protein processing is most likely a consequence of the intrinsic function of A1AT (i.e. its interaction with proteases [most likely serine proteases] along the secretory pathway). Secreted A1AT carried vacuolar-type paucimannosidic N-glycans generated by the activity of hexosaminidases located in the apoplast/plasma membrane. Notwithstanding, an intensive glycoengineering approach led to secreted A1AT carrying sialylated N-glycan structures largely resembling its serum-derived counterpart. In summary, we elucidate unique insights in plant glycosylation processes and show important aspects of postendoplasmic reticulum protein processing in plants.

Production and characterization of a novel human recombinant alpha-1-antitrypsin in PER.C6 cells

Alpha-1-antitrypsin (A1PI) is a proteinase inhibitor of the serpin superfamily and circulates in plasma at about 1-2 g/L. A1PI deficiency in humans often results in organ damage, particularly to the lungs and liver. Current augmentation therapies rely entirely on A1PI isolated from human plasma, thus prompting an evaluation of alternate sources. We have co-expressed recombinant A1PI and α-2,3-sialyltransferase in the human cell line, PER.C6. The requirement for sialyltransferase overexpression in PER.C6 and the essential contribution of sialic acid glycan capping on pdA1PI and recA1PI to prevent rapid A1PI plasma elimination is shown. Using assays to predict high levels of A1PI production and sialylation, stably transfected PER.C6 cells were screened through two rounds of cell cloning to ensure monoclonality. Fed-batch culturing was used to evaluate recA1PI production and cell line characteristics, identifying subclones expressing over 2.5 g/L recA1PI. Cell stability was assessed over 50 generations, verifying subclone stability during continuous culture. Finally, data are presented showing that recA1PI and pdA1PI are equivalent in their ability to block elastase activity in functional cell-based assays and their pharmacokinetic properties. These data show that recombinant human A1PI recovered from PER.C6 cells offers a reliable source of functionally active A1PI for augmentation therapies and, potentially, other diseases.

Site-specific enzymatic polysialylation of therapeutic proteins using bacterial enzymes

The posttranslational modification of therapeutic proteins with terminal sialic acids is one means of improving their circulating half-life, thereby improving their efficiency. We have developed a two-step in vitro enzymatic modification of glycoproteins, which has previously only been achieved by chemical means [Gregoriadis G, Jain S, Papaioannou I, Laing P (2005) Int J Pharm 300:125-130). This two-step procedure uses the Campylobacter jejuni Cst-II α2,8-sialyltransferase to provide a primer on N-linked glycans, followed by polysialylation using the Neisseria meningitidis α2,8-polysialyltransferase. Here, we have demonstrated the ability of this system to modify three glycoproteins with varying N-linked glycan compositions: the human therapeutic proteins alpha-1-antitrypsin (A1AT) and factor IX, as well as bovine fetuin. The chain length of the polysialic acid addition was optimized by controlling reaction conditions. After demonstrating the ability of this system to modify a variety of proteins, the effect of polysialylation on the activity and serum half-life of A1AT was examined. The polysialylation of A1AT did not adversely affect its in vitro inhibition activity against human neutrophil elastase. The polysialylation of A1AT resulted in a significantly improved pharmacokinetic profile when the modified proteins were injected into CD-1 mice. Together, these results suggest that polysialylated A1AT may be useful for improved augmentation therapy for patients with a deficiency in this protein and that this modification may be applied to other therapeutic proteins.

Gene therapy approaches for stem cell protection

Cytotoxic exposure of bone marrow and other non-hematopoietic organs containing self-renewing stem cell populations is associated with damage to the supportive microenvironment. Recent evidence indicates that radical oxygen species resulting from the initial oxidative stress persist for months after ionizing irradiation exposure of tissues including oral cavity, esophagus, lung and bone marrow. Antioxidant gene therapy using manganese superoxide dismutase plasmid liposomes has provided organ-specific radiation protection associated with delay or prevention of acute and late toxicity. Recent evidence has suggested that manganese superoxide dismutase transgene expression in cells of the organ microenvironment contributes significantly to the mechanism of protection. Incorporating this knowledge into designs of novel approaches for stem cell protection is addressed in the present review.

Recombinant human alpha-1 proteinase inhibitor: towards therapeutic use

Human alpha-1-proteinase inhibitor is a well-characterized protease inhibitor with a wide spectrum of anti-protease activity. Its major physiological role is inhibition of neutrophil elastase in the lungs, and its deficiency is associated with progressive ultimately fatal emphysema. Currently in the US, only plasma-derived human alpha-1-proteinase inhibitor is available for augmentation therapy, which appears to be insufficient to meet the anticipated clinical demand. Moreover, despite effective viral clearance steps in the manufacturing process, the potential risk of contamination with new and unknown pathogens still exists. In response, multiple efforts to develop recombinant versions of human alpha-1-proteinase inhibitor, as an alternative to the plasma-derived protein, have been reported. Over the last two decades, various systems have been used to express the human gene for alpha-1-proteinase inhibitor. This paper reviews the recombinant versions of human alpha-1-proteinase inhibitor produced in various hosts, considers current major safety and efficacy issues regarding recombinant glycoproteins as potential therapeutics, and the factors that are impeding progress in this area(1).

Intrapleural administration of a serotype 5 adeno-associated virus coding for α1-antitrypsin mediates persistent, high lung and serum levels of α1-antitrypsin

alpha1-Antitrypsin (alpha1AT) is a serine proteinase inhibitor that protects the lung from degradation by neutrophil proteases. In alpha1AT deficiency, an autosomal recessive disorder resulting from mutations in the alpha1AT (approved symbol SERPINA1) gene, serum alpha1AT levels of < 570 microg/ml are associated with development of emphysema. Adeno-associated virus (AAV) serotype 2 (AAV2) vectors expressing alpha1AT administered intramuscularly or intravenously mediate sustained serum levels of alpha1AT in experimental animals. Since the lung is only 2% of the body weight, AAV vector delivery to the muscle or liver is inefficient, as most of the alpha1AT does not reach the lung. The present study evaluates AAV2- and AAV5-mediated delivery of human alpha1AT (halpha1AT) to C57BL/6 mice using the intrapleural space as a platform for local production of alpha1AT. Intrapleural administration of either an AAV5-halpha1AT or an AAV2-halpha1AT vector achieves higher lung and serum levels of alpha1AT than intramuscular delivery. AAV5-mediated serum and lung alpha1AT levels were 10-fold higher than those achieved by AAV2 delivery via either route. The diaphragm, lung, and heart are the major sites of transgene expression following intrapleural administration of an AAV5 reporter vector. At 40 weeks postadministration, intrapleural administration of the AAV5-halpha1AT vector mediated serum alpha1AT levels of 900 +/- 50 microg/ml, 1.6-fold higher than the accepted therapeutic level of 570 microg/ml. In the context that the pleura is a safe site for administration, intrapleural administration using AAV5 vectors may represent an attractive gene therapy strategy for alpha1AT deficiency in humans.

Long-term expression of human alpha1-antitrypsin gene in mouse liver achieved by intravenous administration of plasmid DNA using a hydrodynamics-based procedure

The liver is an important target organ for gene transfer due to its large capacity for synthesizing serum proteins and its involvement in numerous genetic and acquired diseases. Previously, we and others have shown that an efficient gene transfer to liver cells in vivo can be achieved by an intravenous injection of plasmid DNA using a hydrodynamics-based procedure. In this study, we systematically characterized the expression of transgene encoding a secretory protein in mouse. Using human alpha1-antitrypsin (hAAT) gene as a reporter, we demonstrate that the serum level of hAAT can reach as high as 0.5 mg/ml by a simple tail vein injection of 10-50 microg plasmid DNA into a mouse. The serum hAAT reaches the peak level 1 day after DNA injection and then declines during the following 2 to 4 weeks to 2-5 microg/ml, a level which persists for at least 6 months. Southern analysis of extracted DNA and RT-PCR analysis of RNA from the liver reveal that hAAT gene is active and present as episomal form after 6 months. These results suggest that the hydrodynamics-based transfection procedure provides a valuable tool for screening genes for therapeutic purposes in whole animals.

Use of nonautologous microencapsulated fibroblasts in growth hormone gene therapy to improve growth of midget swine

The aim of the present study was to investigate the expression activity, both in vitro and in vivo, of the porcine growth hormone complementary DNA (pGH cDNA) in porcine fetal fibroblast (PFF) cells. The pGH gene had been constructed inside the bicistronic retroviral vector PSN and subsequently transfected into PFF cells further encapsulated with immunoprotective microcapsules. This would provide a way to evaluate the improvement in growth performance of Tao-Yuan swine by the use of nonautologous microencapsulated fibroblasts carrying the pGH cDNA via the technique of somatic gene therapy. Results from Southern blot analysis confirmed that the full length of the pGH cDNA was completely integrated into the genome of the PFF cells after they had been infected one to four times using a PSN retroviral vector. Moreover, Northern blot analysis showed that high transcription activity was present in clones infected twice, and exogenous pGH secretion was found when the pGH-infected PFF had been further cultured for 48 hr in vitro and subjected to immunoblot assay. Encapsulation of the pGH-PFF with an alginate-poly-L-lysine-alginate membrane did not show any deterioration in their proliferation and survival both in vitro and in vivo. The pGH gene in encapsulated recombinant fibroblasts was fully expressed after it had been transplanted into the peritoneal cavity of the Tao-Yuan swine, and reverse transcription-polymerase chain reaction (RT-PCR) analysis was performed on the microcapsules retrieved 1 month later. The feasibility of pGH gene therapy to improve midget Tao-Yuan swine growth enhancement is further supported by the fact that transplantation of the encapsulated recombinant fibroblast cells resulted in a much more significant increase in weight gain than in those swine in either the age-matched untreated control group or in those that had been transplanted with uncapsulated recombinant PFF cells (10.56 +/- 1.01 kg versus 6.95 +/- 0.94 and 5.27 +/- 1.30 kg; p < 0.05). These experimental data suggest that growth hormone gene therapy did provide an alternative approach for growth improvement in midget Tao-Yuan swine.

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.

Glycosylation of human alpha 1-antitrypsin in Saccharomyces cerevisiae and methylotrophic yeasts

Human alpha 1-antitrypsin (alpha 1-AT) is a major serine protease inhibitor in plasma, secreted as a glycoprotein with a complex type of carbohydrate at three asparagine residues. To study glycosylation of heterologous proteins in yeast, we investigated the glycosylation pattern of the human alpha 1-AT secreted in the baker's yeast Saccharomyces cerevisiae and in the methylotrophic yeasts, Hansenula polymorpha and Pichia pastoris. The partial digestion of the recombinant alpha 1-AT with endoglycosidase H and the expression in the mnn9 deletion mutant of S. cerevisiae showed that the recombinant alpha 1-AT secreted in S. cerevisiae was heterogeneous, consisting of molecules containing core carbohydrates on either two or all three asparagine residues. Besides the core carbohydrates, variable numbers of mannose outer chains were also added to some of the secreted alpha 1-AT. The human alpha 1-AT secreted in both methylotrophic yeasts was also heterogeneous and hypermannosylated as observed in S. cerevisiae, although the overall length of mannose outer chains of alpha 1-AT in the methylotrophic yeasts appeared to be relatively shorter than those of alpha 1-AT in S. cerevisiae. The alpha 1-AT secreted from both methylotrophic yeasts retained its biological activity as an elastase inhibitor comparable to that of alpha 1-AT from S. cerevisiae, suggesting that the different glycosylation profile does not affect the in vitro activity of the protein.

Bioengineering: alpha 1-proteinase inhibitor site-specific mutagenesis. The prospect for improving the inhibitor

alpha 1-Proteinase inhibitor (alpha 1-PI) augmentation therapy has been licensed for treatment of alpha 1-PI-deficient individuals with pulmonary emphysema. The currently available product is purified from pooled human plasma. To obtain larger amounts of protein free from possible unknown plasma contaminants, human alpha 1-PI has been produced by recombinant DNA. Since wild-type alpha 1-PI is susceptible to oxidative impairment, several alpha 1-PI variants in which the active site oxidation-sensitive residue is replaced by inert residues have been constructed. This article is aimed at reviewing the history, biological efficacy, advantages, disadvantages, and concerns linked to alpha 1-PI recombinant DNA and site-specific mutagenesis technology.

Human alpha 1-antitrypsin gene transfer to in vivo mouse hepatocytes

The in vivo gene transfer to mouse hepatocytes of pTG 7101, a plasmid containing the full-length gene encoding human alpha 1-antitrypsin (alpha 1-AT) DNA, has been studied by iv administration of recombinant DNA (100 ng/mouse) encapsulated in large and small liposomes. Our results from immunohistochemical liver sections and cytophotometric analysis of hepatocyte chromophore absorbance indicate that human alpha 1-AT was expressed in liver parenchymal cells from mice treated (48 hr before) with DNA encapsulated in small liposomes, and this effect remained for at least 2 weeks. In contrast, the efficiency was greatly limited when large liposomes were used as a vehicle for gene transfer. Additional experiments were performed to study using an ELISA procedure the presence in mouse plasma of human alpha 1-AT from mice treated with encapsulated plasmid in small liposomes or small empty liposomes plus free DNA. According to the immunohistochemical data, the results indicate that detectable alpha 1-AT can only be observed in plasma from mice treated with encapsulated plasmid in small liposomes.

Approaches to maximizing stable expression of alpha 1-antitrypsin in transformed CHO cells

A variety of approaches to maximizing the production of recombinant human alpha 1-antitrypsin (AAT) in Chinese hamster ovary (CHO) cells have been investigated. The highly active and inducible human cytomegalovirus immediate early (IE) promoter/enhancer was used to drive transcription of a recombinant AAT gene in transiently transfected and stably transformed CHO cells. The AAT gene was modified to incorporate highly efficient 3'RNA processing signals from the herpes simplex virus type 2 IE gene 5, and optimal translational initiation signals were created by site-directed mutagenesis. The effect of flanking the recombinant gene with matrix attachment regions was investigated. Combinations of these modifications allowed secretion of up to 44 micrograms AAT/ml per day by cell lines growing in serum-rich medium. This could be increased to up to 100 micrograms AAT/ml per day upon chemical induction of expression by propionate, butyrate or hexamethylene bisacetamide. Cell lines adapted to grow in protein-free medium produced less AAT but still responded to chemical induction to secrete up to 14 micrograms/ml per day of readily purified AAT.

Long-term expression of a retrovirally introduced beta-galactosidase gene in rodent cells implanted in vivo using biodegradable polymer meshes

Grafts of various types of cells have been performed using bioresorbable polymer matrices. These synthetic fibers are degraded by hydrolysis into normal metabolic intermediates and induce a number of events that are conductive to healing and/or repair, the most important of which may be angiogenesis. The use of biodegradable meshes to deliver genetically altered cells was studied. A beta-galactosidase gene was inserted into Long-Evans rat bone marrow stromal (BMS) cells or fibroblasts derived from C57BL/6J mouse embryos using the retroviral vector LNL-SLX beta gal. Expression was monitored using X-gal staining. X-gal+ cells from monolayer cultures were seeded onto either polyglycolic acid (PGA) or polyglactin (PGL) biodegradable meshes and grown to confluence. Two types of grafts were performed: (1) embryonic C57BL/6J mouse fibroblasts (EMF) into either nude mice or adult C57BL/6J mice, and (2) Long-Evans rat BMS into Long-Evans rats. Beta-Galactosidase activity was found for up to 152 days for EMF in nude mice, 123 days for EMF in adult C57BL/6J mice, and 90 days for grafts of syngeneic BMS cells into Long-Evans rats. Noninfected cells grafted using the same methods did not stain with X-gal.

Expression of human α1 antitrypsin in transgenic sheep

We have recently described the production of large amounts (< or = 65 grams per litre) of enzymatically active human alpha 1 antitrypsin in the milk of transgenic sheep (Wright et al., 1991). Here, we describe in more detail the expression of the human protein in the milk of these animals throughout the lactation period. Human alpha 1 antitrypsin is also found at much lower levels in the plasma of transgenic ewes before, during and after lactation. It is also detected in male plasma at very low levels. We have previously shown human alpha 1 antitrypsin purified from transgenic sheep milk to be indistinguishable from commercially available human plasma derived alpha 1 antitrypsin in terms of gross sugar content and in vitro activity. Here we extend this comparison to more detailed analyses of glycosylation state, amino-terminal sequence, pI value, and molecular weight determination by mass spectrometry.

High Level Expression of Active Human Alpha-1-Antitrypsin in the Milk of Transgenic Sheep

We describe the generation of five sheep transgenic for a fusion of the ovine beta-lactoglobulin gene promotor to the human alpha 1-antitrypsin (h alpha 1AT) genomic sequences. Four of these animals are female and one male. Analysis of the expression of h alpha 1AT in the milk of three of these females shows that all express the human protein at levels greater than 1 gram per liter. In one case initial levels exceeded 60 grams per liter and stabilized at approximately 35 grams per liter as lactation progressed. Human alpha 1AT purified from the milk of these animals appears to be fully N-glycosylated and has a biological activity indistinguishable from human plasma-derived material.

Prospects for homologous recombination in human gene therapy

The ideal approach to gene therapy of hereditary diseases or gene correction therapy is considered. The advantages, disadvantages and limits of gene targeting by homologous recombination are discussed with regard to its possible application in gene correction therapy and in comparison with retroviral-mediated gene complementation therapy.

Improvement of avian leukosis virus (ALV)-based retrovirus vectors by using different cis-acting sequences from ALVs

Production and expression of double-expression vectors which transduce both Neo(r) and lacZ genes and are based on the structure of avian leukosis virus were enhanced by using cis-acting sequences (long terminal repeats and noncoding sequences) from Rous-associated virus-1 and Rous-associated virus-2 rather than those of avian erythroblastosis virus previously used in our constructs. Polyclonal producer cells obtained after transfection of these vectors into the Isolde packaging cell line gave rise to titers as high as 3 x 10(5) lacZ CFU/ml, whereas it was possible to isolate clones of producer cells giving rise to titers of more than 10(6) resistance focus-forming units per ml.

Retroviral vector-mediated in vivo expression of low-density-lipoprotein receptors in the Watanabe heritable hyperlipidemic rabbit

We have achieved in vivo expression of recombinant low-density-lipoprotein (LDL) receptors in the Watanabe heritable hyperlipidemic (WHHL) rabbit, an animal model for the human disease familial hypercholesterolemia. A retroviral vector was constructed containing the human LDL receptor cDNA and was used to stably transduce primary skin fibroblasts from WHHL rabbits. The integrity and function of the introduced LDL receptor was established by immunoprecipitation, by a fluorescent LDL binding assay, and by the ability of the transduced cells to suppress 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase activity in response to exogenous cholesterol. Autologous transduced fibroblasts were reimplanted into donor rabbits; in vivo LDL receptor expression and the survival of the transduced cells were analyzed by immunohistochemistry and by LDL binding assays performed on cells recovered from the implants. LDL receptor-bearing cells could be identified on tissue sections and recovered from implants for up to four weeks. Total and LDL cholesterol levels decreased significantly after implantation of the transduced cells; however, control experiments indicated that the decreases were not mediated through the recombinant LDL receptor. While in vivo stable expression of recombinant LDL receptors in Watanabe rabbits is possible, consequent changes in lipid levels must be interpreted with caution. This system of site-specific in vivo expression of recombinant LDL receptors permits further evaluation of the role of LDL receptor-gene replacement in the therapy of hypercholesterolemia.

High-level expression of biologically active human alpha 1-antitrypsin in the milk of transgenic mice

Reduced circulating levels of alpha 1-antitrypsin (alpha 1 AT) are associated with certain alpha 1 AT genotypes and increased susceptibility to emphysema. Unfortunately, the amounts of alpha 1 AT that would be required for replacement therapy are beyond the capacity of plasma fractionation and mammalian cell culture systems. Thus, we have examined the potential of transgenic animals as an alternative means of producing human alpha 1 AT. A hybrid gene constructed by using sequences from the ovine milk protein gene beta-lactoglobulin fused to an alpha 1 AT "minigene" was used to generate transgenic mice. Of 13 independent transgenic mice and mouse lines, 5 expressed the hybrid gene in the mammary gland, 5 in the salivary glands, and 2 in both these tissues. Human alpha 1 AT was secreted into the milk of each of the 7 mice and mouse lines that expressed the hybrid gene in the mammary gland. Four of these mammary-expressing transgenic mice and mouse lines produced concentrations of at least 0.5 mg of alpha 1 AT per ml in their milk; one line (AATB 35) produced 7 mg of this protein per ml. alpha 1 AT from transgenic mouse milk was similar in size to human plasma-derived alpha 1 AT and showed a similar capacity to inhibit trypsin. Expression at equivalent levels in transgenic sheep or cattle would yield sufficient alpha 1 AT for therapeutic purposes.

Molecular basis of alpha 1-antitrypsin deficiency and emphysema associated with the alpha 1-antitrypsin Mmineral springs allele

The Mmineral springs alpha 1-antitrypsin (alpha 1AT) allele, causing alpha 1AT deficiency and emphysema, is unique among the alpha 1AT-deficiency alleles in that it was observed in a black family, whereas most mutations causing alpha 1AT deficiency are confined to Caucasian populations of European descent. Immobilized pH gradient analysis of serum demonstrated that alpha 1AT Mmineral springs migrated cathodal to the normal M2 allele. Evaluation of Mmineral springs alpha 1AT as an inhibitor of neutrophil elastase, its natural substrate, demonstrated markedly lower than normal function. Characterization of the alpha 1AT Mmineral springs gene demonstrated that it differed from the common normal M1(Ala213) allele by a single-base substitution causing the amino acid substitution Gly-67 (GGG)----Glu-67 (GAG). Capitalizing on the fact that this mutation creates a polymorphism for the restriction endonuclease AvaII, family analysis demonstrated that the Mmineral springs alpha 1AT allele was transmitted in an autosomal-codominant fashion. Evaluation of genomic DNA showed that the index case was homozygous for the alpha 1AT Mmineral springs allele. Cytoplasmic blot analysis of blood monocytes of the Mmineral springs homozygote demonstrated levels of alpha 1AT mRNA transcripts comparable to those in cells of a normal M1 (Val213) homozygote control. Evaluation of in vitro translation of Mmineral springs alpha 1AT mRNA transcripts demonstrated a normal capacity to direct the translation of alpha 1AT. Evaluation of secretion of alpha 1AT by the blood monocytes by pulse-chase labeling with [35S]methionine, however, demonstrated less secretion by the Mmineral springs cells than normal cells. To characterize the posttranslational events causing the alpha 1AT-secretory defect associated with the alpha 1AT Mmineral springs gene, retroviral gene transfer was used to establish polyclonal populations of murine fibroblasts containing either a normal human M1 alpha 1AT cDNA or an Mmineral springs alpha 1AT cDNA and expressing comparable levels of human alpha 1AT mRNA transcripts. Pulse-chase labeling of these cells with [35S]methionine demonstrated less secretion of human alpha 1AT from the Mmineral springs cells than from the M1 cells, and evaluation of cell lysates also demonstrated lower amounts of intracellular human alpha 1AT in the Mmineral springs cells than in the normal M1 control cells. Thus, the Gly-67 --> Glu mutation that characterizes Mmineral springs causes reduced alpha 1AT secretion on the basis of aberrant posttranslational alpha 1AT biosynthesis by a mechanism distinct from that associated with the alpha 1AT Z allele, whereby intracellular aggregation of the mutant protein is etiologic of the alpha 1AT-secretory defect. Furthermore, for the alpha 1AT protein that does reach the circulation, this mutation markedly affects the ability of the molecule to inhibit neutrophil elastase; i.e., the alpha 1AT Mmineral springs allele predisposes to emphysema on the basis of serum apha 1AT deficiency coupled with alpha AT dysfunction.

Molecular basis of alpha 1-antitrypsin deficiency and emphysema associated with the alpha 1-antitrypsin Mmineral springs allele

The Mmineral springs alpha 1-antitrypsin (alpha 1AT) allele, causing alpha 1AT deficiency and emphysema, is unique among the alpha 1AT-deficiency alleles in that it was observed in a black family, whereas most mutations causing alpha 1AT deficiency are confined to Caucasian populations of European descent. Immobilized pH gradient analysis of serum demonstrated that alpha 1AT Mmineral springs migrated cathodal to the normal M2 allele. Evaluation of Mmineral springs alpha 1AT as an inhibitor of neutrophil elastase, its natural substrate, demonstrated markedly lower than normal function. Characterization of the alpha 1AT Mmineral springs gene demonstrated that it differed from the common normal M1(Ala213) allele by a single-base substitution causing the amino acid substitution Gly-67 (GGG)----Glu-67 (GAG). Capitalizing on the fact that this mutation creates a polymorphism for the restriction endonuclease AvaII, family analysis demonstrated that the Mmineral springs alpha 1AT allele was transmitted in an autosomal-codominant fashion. Evaluation of genomic DNA showed that the index case was homozygous for the alpha 1AT Mmineral springs allele. Cytoplasmic blot analysis of blood monocytes of the Mmineral springs homozygote demonstrated levels of alpha 1AT mRNA transcripts comparable to those in cells of a normal M1 (Val213) homozygote control. Evaluation of in vitro translation of Mmineral springs alpha 1AT mRNA transcripts demonstrated a normal capacity to direct the translation of alpha 1AT. Evaluation of secretion of alpha 1AT by the blood monocytes by pulse-chase labeling with [35S]methionine, however, demonstrated less secretion by the Mmineral springs cells than normal cells. To characterize the posttranslational events causing the alpha 1AT-secretory defect associated with the alpha 1AT Mmineral springs gene, retroviral gene transfer was used to establish polyclonal populations of murine fibroblasts containing either a normal human M1 alpha 1AT cDNA or an Mmineral springs alpha 1AT cDNA and expressing comparable levels of human alpha 1AT mRNA transcripts. Pulse-chase labeling of these cells with [35S]methionine demonstrated less secretion of human alpha 1AT from the Mmineral springs cells than from the M1 cells, and evaluation of cell lysates also demonstrated lower amounts of intracellular human alpha 1AT in the Mmineral springs cells than in the normal M1 control cells. Thus, the Gly-67 --> Glu mutation that characterizes Mmineral springs causes reduced alpha 1AT secretion on the basis of aberrant posttranslational alpha 1AT biosynthesis by a mechanism distinct from that associated with the alpha 1AT Z allele, whereby intracellular aggregation of the mutant protein is etiologic of the alpha 1AT-secretory defect. Furthermore, for the alpha 1AT protein that does reach the circulation, this mutation markedly affects the ability of the molecule to inhibit neutrophil elastase; i.e., the alpha 1AT Mmineral springs allele predisposes to emphysema on the basis of serum apha 1AT deficiency coupled with alpha AT dysfunction.

Improved gene expression upon transfer of the adenosine deaminase minigene outside the transcriptional unit of a retroviral vector

This study describes a type of retroviral vector called double-copy (DC) vector that was designed to improve the expression of transduced genes. The unique feature of DC vectors is that the transduced gene is inserted within the U3 region of the 3' long terminal repeat (LTR). Consequently, in the infected cell the gene is duplicated and transferred to the 5' LTR. The important result is that in its new position the gene is placed outside the retroviral transcriptional unit, eliminating or at least reducing the negative effects of the retroviral transcriptional unit. The utility of the DC vector design was tested by using a 2.1-kilobase-pair (kbp)-long adenosine deaminase (ADA; EC 3.5.4.4) minigene that was inserted into the 3' LTR of the N2 retroviral vector, generating a 2.7-kbp-long chimeric LTR. DNA blot analysis was used to show that the chimeric LTR was faithfully duplicated in cells infected with the corresponding virus, generating two copies of the ADA minigene, one copy in each LTR. Insertion of the ADA minigene into the 3' LTR of the N2 vector led to a 10- to 20-fold increase in ADA transcripts and human ADA isozyme synthesized in NIH 3T3 cells as compared to cells harboring the same vector in which the ADA minigene was inserted between the two LTRs. A similar increase in ADA expression was observed in two human lymphoid cell lines tested, HUT 78 and Raji. These results are consistent with previous observations that upstream promoters exert an inhibitory effect on promoters placed downstream and bear out the predictions used in the design of DC vectors. The use of DC vectors may contribute to the solution of the problems encountered in expressing retrovirally transduced genes in cultured cells and, in particular, when introduced into the live animal.

Alpha 1-antitrypsin deficiency caused by the alpha 1-antitrypsin Nullmattawa gene. An insertion mutation rendering the alpha 1-antitrypsin gene incapable of producing alpha 1-antitrypsin

alpha 1-Antitrypsin (alpha 1AT) deficiency is a hereditary disorder associated with reduced serum alpha 1AT levels and the development of pulmonary emphysema. An alpha 1AT gene is defined as "Null" when no alpha 1AT in serum is attributed to that alpha 1AT gene. Although all alpha 1AT Null genes have identical phenotypic consequences (i.e. no detectable alpha 1AT in the serum), different genotypic mechanisms can cause the Null state. This study defines the molecular basis for the alpha 1AT gene Nullmattawa, identified and cloned from genomic DNA of an individual with the Null-Null phenotype and emphysema resulting from the heterozygous inheritance of the Nullmattawa and Nullbellingham genes. Sequencing of exons Ic-V and all exon-intron junctions of the Nullmattawa gene demonstrated it was identical to the common normal M1(Val213) alpha 1AT gene except for the insertion of a single nucleotide within the coding region of exon V, causing a 3' frameshift with generation of a premature stop signal. Family analysis using oligonucleotide probes specific for the Nullmattawa sequence demonstrated the gene was inherited in an autosomal fashion. Examination of blood monocytes demonstrated that a normal-sized, 1.8-kb alpha 1AT mRNA transcript is associated with the Nullmattawa gene and in vitro translation of mRNA with the Nullmattawa mutation showed it translated at a normal rate but produced a truncated alpha 1AT protein. Additionally, retroviral transfer of the alpha 1AT Nullmattawa cDNA to murine fibroblasts demonstrated no detectable intracellular or secreted alpha 1AT, despite the presence of alpha 1AT Nullmattawa mRNA transcripts. These findings are consistent with the concept that the molecular pathophysiology of Nullmattawa is likely manifested at a posttranslational level. The identification of the Nullmattawa gene supports the concept that Null alpha 1AT alleles represent a heterogenous group in which very different mechanisms cause the identical phenotypic state.

High-level recombinant gene expression in rabbit endothelial cells transduced by retroviral vectors

By virtue of its immediate contact with the circulating blood, the endothelium provides an attractive target for retroviral vector transduction for the purpose of gene therapy. To see whether efficient gene transfer and expression was feasible, rabbit aortic endothelial cells were infected with three Moloney murine leukemia virus-derived retroviral vectors. Two of these vectors carry genes encoding products that are not secreted: N2, containing only the selectable marker gene neoR, and SAX, containing both neoR gene and an SV40-promoted adenosine deaminase (ADA) gene. The third vector, G2N, contains a secretory rat growth hormone (rGH) gene and an SV40-promoted neoR gene. Infection with all three vectors resulted in expression of the respective genes. A high level of human ADA expression was observed in infected endothelial cell populations both before and after selection in G418. G2N-infected rabbit aortic endothelial cells that were grown on a synthetic vascular graft continued to secrete rGH into the culture medium. These studies suggest that endothelial cells may serve as vehicles for the introduction in vivo of functioning recombinant genes.

An alternative approach to somatic cell gene therapy

Mouse primary skin fibroblasts were infected with a recombinant retrovirus containing human factor IX cDNA. Bulk infected cells capable of synthesizing and secreting biologically active human factor IX protein were embedded in collagen, and the implant was grafted under the epidermis. Sera from the transplanted mice contain human factor IX protein for at least 10-12 days. Loss of immunoreactive human factor IX protein in the mouse serum is not due to graft rejection. Instead, the mouse serum contains anti-human factor IX antibodies, which react with the protein. We suggest that retroviral-infected primary skin fibroblasts offer an alternative approach to somatic cell gene therapy.

Clonal gene therapy: transplanted mouse fibroblast clones express human alpha 1-antitrypsin gene in vivo

A retroviral vector was used to insert human alpha 1-antitrypsin (alpha 1AT) complementary DNA into the genome of mouse fibroblasts to create a clonal population of mouse fibroblasts secreting human alpha 1AT. After demonstrating that this clone of fibroblasts produced alpha 1AT after more than 100 population doublings in the absence of selection pressure, the clone was transplanted into the peritoneal cavities of nude mice. When the animals were evaluated 4 weeks later, human alpha 1AT was detected in both sera and the epithelial surface of the lungs. The transplanted clone of fibroblasts could be recovered from the peritoneal cavities of those mice and demonstrated to still be producing human alpha 1AT. Thus, even after removal of selective pressure, a single clone of retroviral vector-infected cells that expressed an exogenous gene in vitro, continued to do so in vivo, and when recovered, continued to produce the product of the exogenous gene.