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

Increased Remnant Lipoproteins in Apo E Deficient Mice Induce Coronary Atherosclerosis following Transverse Aortic Constriction and Aggravate the Development of Pressure Overload-Induced Cardiac Hypertrophy and Heart Failure

Murine coronary arteries are very resistant to the development of atherosclerosis, which may be related to their intramyocardial course. Blood pressure promotes atherosclerotic plaque formation by acting as a physical force that potentiates the migration of pro-atherogenic lipoproteins across the endothelium. C57BL/6N apolipoprotein (apo) E deficient mice have increased remnant lipoproteins that are a risk factor for coronary atherosclerosis. In this study, our aim was to quantify coronary atherosclerosis and artery remodeling following transverse aortic constriction (TAC) in C57BL/6N apo E−/− mice and to evaluate the impact of increased remnant lipoproteins on the development of pressure overload-induced cardiac hypertrophy and heart failure. Advanced atherosclerotic lesions were observed in the left coronary artery of C57BL/6N apo E−/− TAC mice but not in C57BL/6N TAC mice. Pressure overload resulted in markedly increased cardiac hypertrophy and more pronounced heart failure in C57BL/6N apo E−/− TAC mice in comparison to C57BL/6N TAC mice. Pathological hypertrophy, as evidenced by increased myocardial fibrosis and capillary rarefaction, was more prominent in C57BL/6N TAC apo E−/− than in C57BL/6N TAC mice and led to more marked cardiac dysfunction. In conclusion, TAC in apo E deficient mice induces coronary atherosclerosis and aggravates the development of pathological cardiac hypertrophy and heart failure.

Low-Dose Gene Therapy for Murine PKU Using Episomal Naked DNA Vectors Expressing PAH from Its Endogenous Liver Promoter

Limited duration of transgene expression, insertional mutagenesis, and size limitations for transgene cassettes pose challenges and risk factors for many gene therapy vectors. Here, we report on physiological expression of liver phenylalanine hydroxylase (PAH) by delivery of naked DNA/minicircle (MC)-based vectors for correction of homozygous enu2 mice, a model of human phenylketonuria (PKU). Because MC vectors lack a defined size limit, we constructed a MC vector expressing a codon-optimized murine Pah cDNA that includes a truncated intron and is under the transcriptional control of a 3.6-kb native Pah promoter/enhancer sequence. This vector, delivered via hydrodynamic injection, yielded therapeutic liver PAH activity and sustained correction of blood phenylalanine comparable to viral or synthetic liver promoters. Therapeutic efficacy was seen with vector copy numbers of <1 vector genome per diploid hepatocyte genome and was achieved at a vector dose that was significantly lowered. Partial hepatectomy and subsequent liver regeneration was associated with >95% loss of vector genomes and PAH activity in liver, demonstrating that MC vectors had not integrated into the liver genome. In conclusion, MC vectors, which do not have a defined size-limitation, offer a favorable safety profile for hepatic gene therapy due to their non-integration in combination with native promoters.

Impaired cholesterol efflux capacity and vasculoprotective function of high-density lipoprotein in heart transplant recipients

BACKGROUND

High-density lipoprotein (HDL) metabolism is significantly altered in heart transplant recipients. We hypothesized that HDL function may be impaired in these patients.

METHODS

Fifty-two patients undergoing coronary angiography between 5 and 15 years after heart transplantation were recruited in this cross-sectional study. Cholesterol efflux capacity of apolipoprotein B-depleted plasma was analyzed using a validated assay. The vasculoprotective function of HDL was studied by means of an endothelial progenitor cell migration assay.

RESULTS

HDL cholesterol levels were similar in heart transplant patients compared with healthy controls. However, normalized cholesterol efflux and vasculoprotective function were reduced by 24.1% (p < 0.001) and 27.0% (p < 0.01), respectively, in heart transplant recipients compared with healthy controls. HDL function was similar in patients with and without cardiac allograft vasculopathy (CAV) and was not related to C-reactive protein (CRP) levels. An interaction effect (p = 0.0584) was observed between etiology of heart failure before transplantation and steroid use as factors of HDL cholesterol levels. Lower HDL cholesterol levels occurred in patients with prior ischemic cardiomyopathy who were not taking steroids. However, HDL function was independent of the etiology of heart failure before transplantation and steroid use. The percentage of patients with a CRP level ≥6 mg/liter was 3.92-fold (p < 0.01) higher in patients with CAV than in patients without CAV.

CONCLUSIONS

HDL function is impaired in heart transplant recipients, but it is unrelated to CAV status. The proportion of patients with a CRP level ≥6 mg/liter is prominently higher in CAV-positive patients.

All human EF1α promoters are not equal: markedly affect gene expression in constructs from different sources

The promoter is a major element in the expression cassette of gene therapy vectors. Optimal promoter selection can enhance target specificity and gene expression. Recently, we evaluated three different human elongation factor 1 alpha (EF1α) promoters. The three promoters were put into the same expression vector, pAC-luc, driving expression of the luciferase cDNA. The activity from one EF1α promoter (termed EF1α -3), obtained in a commercial vector, was markedly lower when tested in vitro (from 50 - 500 x) in four cell lines and in vivo in rat submandibular glands (~250 x). Sequence differences in the EF1α -3 promoter likely account for the activity differences seen. Investigators need to recognize that all promoters of the same name may not be equivalent in driving transgene expression.

Beneficial effects of selective HDL-raising gene transfer on survival, cardiac remodelling and cardiac function after myocardial infarction in mice

Post-myocardial infarction (MI) ejection fraction is decreased in patients with low high-density lipoprotein (HDL) cholesterol levels, independent of the degree of coronary atherosclerosis. The objective of this study is to evaluate whether selective HDL-raising gene transfer exerts cardioprotective effects post MI. Gene transfer in C57BL/6 low-density lipoprotein receptor (LDLr)^−/− mice was performed with the E1E3E4-deleted adenoviral vector AdA-I, inducing hepatocyte-specific expression of human apo A-I, or with the control vector Adnull. A ligation of the left anterior descending coronary artery was performed 2 weeks after transfer or saline injection. HDL cholesterol levels were persistently 1.5-times (P<0.0001) higher in AdA-I mice compared with controls. Survival was increased (P<0.01) in AdA-I MI mice compared with control MI mice during the 28-day follow-up period (hazard ratio for mortality 0.42; 95% confidence interval 0.24–0.76). Longitudinal morphometric analysis demonstrated attenuated infarct expansion and inhibition of left ventricular (LV) dilatation in AdA-I MI mice compared with controls. AdA-I transfer exerted immunomodulatory effects and increased neovascularisation in the infarct zone. Increased HDL after AdA-I transfer significantly improved systolic and diastolic cardiac function post MI, and led to a preservation of peripheral blood pressure. In conclusion, selective HDL-raising gene transfer may impede the development of heart failure.

Including the p53 ELAV-like protein-binding site in vector cassettes enhances transgene expression in rat submandibular gland

OBJECTIVE

ELAV-like proteins regulate mRNA stability and/or translation. We evaluated whether inclusion of binding sites for ELAV-like HuR proteins in vector cassettes could improve transgene expression in the salivary gland.

METHODS

Western blots and immunofluorescence staining were used to determine whether HuR protein was expressed in salivary cells and tissue. HuR binding sites were inserted into the pACEF1α-luc-BGH expression plasmid. Cell lines were transfected with plasmids in vitro and luciferase expression measured. Rat submandibular glands were transfected in vivo with plasmids containing ELAV-like HuR protein-binding sites. An adenoviral vector with p53 ELAV-like HuR protein-binding site was generated and also tested in vivo. Four unique 29mer HuR shRNA constructs were used in A5 cells to evaluate whether there was a specific interaction between HuR protein and the p53 HuR protein-binding site.

RESULTS

Salivary cells express HuR protein. Inclusion of the p53 ELAV-like HuR protein-binding site resulted in high luciferase activity in salivary cells in vitro, with similar results in vivo. In vitro shRNA data demonstrated that the high luciferase activity was mediated by the interaction between HuR protein and the p53 HuR protein-binding site. The AdEF1α-luc-p53BGH, including this binding site, mediated very high luciferase activity, ~4-fold that seen with the CMV promoter, in rat submandibular glands.

CONCLUSIONS

Including the p53 ELAV-like protein-binding site in transgene cassettes may enhance therapeutic vectors intended for use with salivary glands.

Construction of an oncolytic herpes simplex virus that precisely targets hepatocellular carcinoma cells

Selective replication in tumor cells is a highly desirable feature for oncolytic viruses. Recent studies have shown that microRNAs (miRNAs) play important roles in controlling gene expression, and that certain tissue-specific miRNAs are frequently downregulated in malignant cells. miR-122 is a liver-specific microRNA. It is abundantly expressed in normal hepatocytes but is absent in many hepatocellular carcinoma (HCC) cells. We hypothesized that expression of an essential viral gene by a liver-specific promoter would initially restrict virus replication to cells of hepatic origin and that adding miR-122 complementary sequences to the viral gene would make the transcripts degradable by miR-122 in normal hepatocytes, thus further confining its replication to HCC. We have constructed such an oncolytic herpes simplex virus by linking the essential viral glycoprotein H gene with the liver-specific apolipoprotein E (apoE)-AAT promoter and by adding the miR-122a complimentary sequence to the 3' untranslated region (3'UTR). To further increase the safety of this virus, complementary sequences from miR-124a and let-7 were also engineered into the same 3'UTR. Designated liver-cancer specific oncolytic virus (LCSOV), it was highly selective in killing HCC cells and in shrinking HCC xenografts. We conclude that LCSOV is a highly specific oncolytic virus that can precisely target HCC.

Regression and stabilization of advanced murine atherosclerotic lesions: a comparison of LDL lowering and HDL raising gene transfer strategies

Both reductions in atherogenic lipoproteins and increases in high-density lipoprotein (HDL) levels may affect atherosclerosis regression. Here, the relative potential of low-density lipoprotein (LDL) lowering and HDL raising gene transfer strategies to induce regression of complex murine atherosclerotic lesions was directly compared. Male C57BL/6 LDL receptor (LDLr)^−/− mice were fed an atherogenic diet (1.25% cholesterol and 10% coconut oil) to induce advanced atherosclerotic lesions. A baseline group was killed after 6 months and remaining mice were randomized into a control progression (Adnull or saline), an apolipoprotein (apo) A-I (AdA-I), an LDLr (AdLDLr), or a combined apo A-I/LDLr (AdA-I/AdLDLr) adenoviral gene transfer group and followed-up for another 12 weeks with continuation of the atherogenic diet. Gene transfer with AdLDLr decreased non-HDL cholesterol levels persistently by 95% (p < 0.001) compared with baseline. This drastic reduction of non-HDL cholesterol levels induced lesion regression by 28% (p < 0.001) in the aortic root and by 25% (p < 0.05) in the brachiocephalic artery at 12 weeks after transfer. Change in lesion size was accompanied by enhanced plaque stability, as evidenced by increased collagen content, reduced lesional macrophage content, a drastic reduction of necrotic core area, and decreased expression of inflammatory genes. Elevated HDL cholesterol following AdA-I transfer increased collagen content in lesions, but did not induce regression. Apo A-I gene transfer on top of AdLDLr transfer resulted in additive effects, particularly on inflammatory gene expression. In conclusion, drastic lipid lowering induced by a powerful gene transfer strategy leads to pronounced regression and stabilization of advanced murine atherosclerosis.

Gene therapy for liver regeneration: experimental studies and prospects for clinical trials

The liver is an exceptional organ, not only because of its unique anatomical and physiological characteristics, but also because of its unlimited regenerative capacity. Unfolding of the molecular mechanisms that govern liver regeneration has allowed researchers to exploit them to augment liver regeneration. Dramatic progress in the field, however, was made by the introduction of the powerful tool of gene therapy. Transfer of genetic materials, such as hepatocyte growth factor, using both viral and non-viral vectors has proved to be successful in augmenting liver regeneration in various animal models. For future clinical studies, ongoing research aims at eliminating toxicity of viral vectors and increasing transduction efficiency of non-viral vectors, which are the main drawbacks of these systems. Another goal of current research is to develop gene therapy that targets specific liver cells using receptors that are unique to and highly expressed by different liver cell types. The outcome of such investigations will, undoubtedly, pave the way for future successful clinical trials.

Hepatocyte-specific ABCA1 transfer increases HDL cholesterol but impairs HDL function and accelerates atherosclerosis

AIMS

The ATP-binding cassette transporter A1 (ABCA1) lipidates apolipoprotein (apo) A-I. The hypothesis that hepatocyte-specific ABCA1 overexpression results in high-density lipoprotein (HDL) dysfunction was evaluated by comparing the effects of murine ABCA1 (AdABCA1) and human apo A-I (AdA-I) transfer on lipoprotein profile, HDL function, and progression of atherosclerosis.

METHODS AND RESULTS

Gene transfer in male and female C57BL/6 apo E(-/-) mice was performed at the age of 3 months with E1E3E4-deleted adenoviral vectors containing hepatocyte-specific expression cassettes. Atherosclerosis was quantified at baseline and 56 days later in AdABCA1, AdA-I, and control mice. HDL cholesterol after AdA-I transfer was 1.7-fold (P < 0.001) and 1.8-fold (P < 0.001) higher in male and female mice, respectively, and potently inhibited atherosclerosis progression compared with respective controls. Notwithstanding a 1.4-fold (P < 0.01) and a 1.7-fold (P < 0.01) increase of HDL cholesterol in male and female mice, respectively, after AdABCA1 transfer, the intima was 2.2-fold (P < 0.001) larger in male and 1.3-fold (P = NS) larger in female mice compared with respective controls. HDL isolated from control and AdA-I mice but not from AdABCA1 mice enhanced endothelial progenitor cell (EPC) migration in vitro and reduced endothelial cell death in vitro after serum and growth factor withdrawal. Scavenger receptor class B type I (SR-BI) protein level in the liver was significantly lower in AdABCA1 mice than in control and AdA-I mice.

CONCLUSION

Hepatocyte-specific ABCA1 transfer decreases SR-BI protein level in the liver and abrogates beneficial effects of HDL on EPCs and endothelial cells. Decreased HDL function may underlie accelerated atherosclerosis in AdABCA1 apo E(-/-)mice.

Impact of HDL on adipose tissue metabolism and adiponectin expression

OBJECTIVE

The objective of the current study was to investigate the hypothesis that high-density lipoprotein (HDL) influences adipocyte metabolism and adiponectin expression. Therefore, HDL was increased in vivo via apolipoprotein (apo) A-I gene transfer and in vitro via supplementation of HDL to partly differentiated adipocytes, in the presence or absence of lipopolysaccharide (LPS), known to decrease HDL cholesterol and adiponectin levels in vivo.

METHODS AND RESULTS

Apo A-I transfer resulted in a significant increase of HDL cholesterol in control and LPS-injected C57BL/6 mice, which was paralleled by an increase in plasma adiponectin levels and adiponectin expression in abdominal fat. Triglyceride and free fatty acids levels after LPS administration were 2.2-fold (p<0.05) and 1.3-fold (p<0.05) lower, respectively, in Ad.hapoA-I-LPS than in Ad.Null-LPS mice. In parallel, the LPS-induced mRNA expression of hormone sensitive lipase was 3.5-fold (p=0.05) decreased in the Ad.hapoA-I-LPS group. On the other hand, apo A-I transfer abrogated the LPS-mediated reduction in lipin-1 and CD36 mRNA expression by 8.2-fold (p<0.05) and 18-fold (p<0.05), respectively. Concomitantly, the phosphorylation state of Akt was 2.0-fold (p<0.05) increased in the Ad.hapoA-I-LPS compared to the Ad.Null-LPS group. Pre-incubation of partly differentiated adipocytes with HDL (50 microg protein/ml) increased adiponectin expression by 1.5-fold under basal conditions (p<0.05) and could abrogate LPS-induced down-regulation of adiponectin, both in a phosphatidylinositol-3-kinase-dependent manner.

CONCLUSIONS

HDL affects adipocyte metabolism and adiponectin expression.

Apolipoprotein A-I and lecithin:cholesterol acyltransferase transfer induce cholesterol unloading in complex atherosclerotic lesions

Plasma levels of high-density lipoprotein (HDL) cholesterol and its major apolipoprotein (apo), apo A-I, are inversely correlated with the incidence of ischemic cardiovascular diseases. Reverse cholesterol transport is likely the main mechanism underlying the atheroprotective effects of HDL. Here, we investigated whether increased HDL cholesterol following hepatocyte-directed adenoviral rabbit apo A-I (AdrA-I) or rabbit lecithin-cholesterol acyltransferase (LCAT) (AdrLCAT) transfer may induce cholesterol unloading in complex atherosclerotic lesions in heterozygous low-density lipoprotein receptor-deficient rabbits fed a 0.15% cholesterol diet for 420 days before and for 120 days after transfer. HDL cholesterol levels increased 2.0-fold (P<0.001) and 1.9-fold (P<0.001) in the 120 days after transfer with AdrA-I and AdrLCAT, respectively, compared to levels just before transfer whereas non-HDL cholesterol remained unchanged. Increased HDL cholesterol following AdrA-I and AdrLCAT transfer resulted in a 31% (P<0.05) reduction of the intima/media ratio in comparison with the control progression group. Compared to the baseline group killed after 420 days of cholesterol diet, AdrA-I and AdrLCAT transfer reduced the percentage of Oil Red O area 1.6-fold (P<0.001) and 1.4-fold (P<0.001), respectively. In conclusion, increased HDL cholesterol after AdrA-I and AdrLCAT transfer inhibits progression of atherosclerosis and induces cholesterol unloading in complex lesions in rabbits.

Critical role of scavenger receptor-BI–expressing bone marrow–derived endothelial progenitor cells in the attenuation of allograft vasculopathy after human apo A-I transfer

Allograft vasculopathy is the leading cause of death in patients with heart transplantation. Accelerated endothelial regeneration mediated by enhanced endothelial progenitor cell (EPC) incorporation may attenuate the development of allograft vasculopathy. We investigated the hypothesis that modulation of EPC biology and attenuation of allograft vasculopathy by increased high-density lipoprotein cholesterol after human apo A-I (AdA-I) transfer requires scavenger receptor (SR)–BI expression in bone marrow–derived EPCs. After AdA-I transfer, the number of circulating EPCs increased 2.0-fold (P < .001) at different time points in C57BL/6 mice transplanted with SR-BI+/+ bone marrow but remained unaltered in mice with SR-BI−/− bone marrow. The effect of high-density lipoprotein on EPC migration in vitro requires signaling via SR-BI and extracellular signal-regulated kinases and is dependent on increased nitric oxide (NO) production in EPCs. Human apo A-I transfer 2 weeks before paratopic artery transplantation reduced intimal area at day 21 3.7-fold (P < .001) in mice with SR-BI+/+ bone marrow but had no effect in mice with SR-BI−/− bone marrow. AdA-I transfer potently stimulated EPC incorporation and accelerated endothelial regeneration in chimeric SR-BI+/+ mice but not in chimeric SR-BI−/− mice. In conclusion, human apo A-I transfer accelerates endothelial regeneration mediated via SR-BI expressing bone marrow–derived EPCs, thereby preventing allograft vasculopathy.

Wild-type apo A-I and apo A-I(Milano) gene transfer reduce native and transplant arteriosclerosis to a similar extent

Apolipoprotein (apo) A-I(Milano) is an apo A-I mutant characterized by a cysteine for arginine substitution at position 173. Apo A-I(Milano) carriers have much less atherosclerosis than expected from their low plasma high-density lipoprotein cholesterol levels, suggesting that this mutant may have superior atheroprotective properties. Here, we compare the effect of hepatocyte-directed gene transfer of wild-type human apo A-I and human apo A-I(Milano) on endothelial progenitor cell (EPC) biology and on the progression of native atherosclerosis and allograft vasculopathy in C57BL/6 apo E(-/-) mice. Human apo A-I and apo A-I(Milano) transfer resulted in an equivalent increase of EPC number and function as well as EPC incorporation and endothelial regeneration in allografts and inhibited the progression of native atherosclerosis and allograft vasculopathy to a similar extent. In conclusion, the current head-to-head comparison indicates that human apo A-I(Milano) transfer is not superior compared to wild-type human apo A-I transfer.

Direct comparison of hepatocyte-specific expression cassettes following adenoviral and nonviral hydrodynamic gene transfer

Hepatocytes are a key target for treatment of inborn errors of metabolism, dyslipidemia and coagulation disorders. The development of potent expression cassettes is a critical target to improve the therapeutic index of gene transfer vectors. Here we evaluated 22 hepatocyte-specific expression cassettes containing a human apo A-I transgene following hydrodynamic transfer of plasmids or adenoviral transfer with E1E3E4-deleted vectors in C57BL/6 mice. The DC172 promoter consisting of a 890 bp human alpha(1)-antitrypsin promoter and two copies of the 160 bp alpha(1)-microglobulin enhancer results in superior expression levels compared to constructs containing the 1.5 kb human alpha(1)-antitrypsin promoter, the 790 bp synthetic liver-specific promoter or the DC190 promoter containing a 520 bp human albumin promoter and two copies of the 99 bp prothrombin enhancer. The most potent expression cassette consists of the DC172 promoter upstream of the transgene and two copies of the hepatic control region-1. Minicircles containing this expression cassette induce persistent physiological human apo A-I or human factor IX levels after hydrodynamic transfer. In conclusion, in this comparative study of 22 hepatocyte-specific expression cassettes, the DC172 promoter in combination with two copies of the hepatic control region-1 induces the highest expression levels following hydrodynamic and adenoviral transfer.

An efficient and safe herpes simplex virus type 1 amplicon vector for transcriptionally targeted therapy of human hepatocellular carcinomas

Our previous studies have shown that transgene expression could be targeted to proliferating cells when cell cycle transcriptional regulatory elements were incorporated into herpes simplex virus type 1 (HSV-1) amplicon backbone vectors. In the study reported here, we further demonstrated the transcriptional activation of transgene expression in association with the onset of cellular proliferation using the mouse partial hepatectomy model. Moreover, transcriptional regulation could be rendered specific to human hepatocellular carcinoma (HCC) cells by inserting the chimeric gene Gal4/NF-YA under the regulation of the HCC-specific hybrid promoter. The hybrid promoter, which consists of four copies of the apolipoprotein E (ApoE) enhancer element inserted upstream of the human alpha1-antitrypsin(hAAT) promoter, induced an higher level of transcription than other liver-specific promoters such as alpha-fetoprotein (AFP) and albumin (Alb) promoter. As a consequence, the enhancement of tissue-specific expression in the context of Gal4/NF-YA fusion proteins enabled the monitoring of transgene expression using a bioluminescence imaging system. Furthermore, these vectors have been shown to be non-toxic and exhibited potent infectivity for proliferating primary HCC cells and HCC cell lines. Together, these results demonstrated that the new hybrid vectors could provide options for the design of safe and efficient systemic gene therapeutic strategies for human HCC.

Persistent liver expression of murine apoA-l using vectors based on adeno-associated viral vectors serotypes 5 and 1

Plasma levels of high-density lipoprotein-cholesterol (HDL-C) and apolipoprotein A-l (apoA-l) are inversely related to risk for coronary heart disease. Overexpression of apoA-l inhibits atherosclerosis in animal models. A method of stably expressing apoA-l using somatic gene transfer would be of interest. Pseudotyped adeno-associated virus (AAV) vectors comprised of inverted terminal repeats from AAV serotype 2 have been used for liver-directed gene transfers. We hypothesized that liver-directed gene transfer of apoA-l using vectors based on AAV serotypes 1 and 5 would result in higher-level, prolonged expression of apoA-l and increased HDL-C. To test this hypothesis we injected apoA-l-/- mice via the tail vein with either AAV2, AAV1 or AAV5 vectors encoding the murine apoA-l cDNA driven by the liver-specific thyroxine binding globulin promoter. Plasma levels of murine apoA-l and HDL-C were highest in mice injected with the AAV1-based vector and lowest in mice injected with the AAV2-based vector. Expression of apoA-l was stable up to 1 year after vector injection. These results indicate that AAV5 and AAV1 are more effective vectors for achieving higher levels of stable transgene expression of apoA-l after liver-directed gene transfer than AAV2. Furthermore, AAV1-based vectors generate higher apoA-l levels than AAV5-based vectors. It is possible that the levels of expression achieved using these vectors will be therapeutic in preventing atherosclerosis.

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.

Elimination of innate immune responses and liver inflammation by PEGylation of adenoviral vectors and methylprednisolone

Improvement of the therapeutic index of adenoviral gene transfer requires the development of strategies to abrogate adenoviral capsid-induced inflammation and cytokine production. The effect of monomethoxypolyethylene glycol (MPEG) conjugation to adenoviral vectors and of methylprednisolone (MP) on innate immunity, liver inflammation, and thrombocyte counts was evaluated after transfer of 1011 particles of E1/E3/E4- deleted adenoviral vector expressing human apolipoprotein A-I (apoA-I). Gene transfer with unPEGylated vectors induced peak interleukin-6 (IL-6) plasma levels that were 66-fold above baseline levels in C57BL/6 mice. PEGylation combined with 4 mg of MP 6 hr before and at the time of gene transfer suppressed IL-6 plasma levels to baseline values at all time points. This combination resulted in 24-, 28-, 5.9-, 42-, 26-, and 2.5- fold reduced mRNA expression in the liver of monocyte chemoattractant protein-1, macrophage inflammatory protein-2, interferon-inducible protein-10, macrophage inflammatory protein-1 beta, lipopolysaccharide-induced CXC chemokine, and keratinocyte-derived chemokine, respectively; abrogated neutrophil infiltration in the liver; and reduced alanine aminotransferase levels. PEGylation reduced vector uptake in the spleen and in nonparenchymal liver cells. PEGylation also inhibited the development of thrombocytopenia. In conclusion, PEGylation of adenoviral vectors combined with MP administration improves the therapeutic index of adenoviral gene transfer.

Evaluation of viral and mammalian promoters for use in gene delivery to salivary glands

To optimize vectors for salivary gland gene transfer, we screened viral [cytomegalovirus (CMV; human immediate early), Rous sarcoma virus (RSV), simian virus 40, and Moloney murine leukemia virus long terminal repeat] and mammalian [elongation factor 1alpha (EF1alpha), cytokeratin 18 (K18), cytokeratin 19 (K19), kallikrein (Kall), and amylase (AMY), all human, and rat aquaporin-5 (rAQP5), and derivative elements] promoters driving luciferase activity in vitro and in vivo. In adenoviral vectors, the CMV promoter showed highest activity, with the EF1alpha and RSV promoters slightly less powerful, in rat submandibular glands (SMGs). The K18 2.5-kb, K19 3.0-kb, and rAQP5 0.4-kb and Kall promoters had intermediate activity, while the AMY promoter exhibited lowest activity. To localize transgene expression, enhanced green fluorescence protein was used. The CMV, RSV, EF1alpha, K18 2.5-kb, K19 3.0-kb, rAQP5 0.4-kb, and AMY promoters were not cell-type specific in SMGs; however, the Kall promoter was primarily active in ductal cells. These data will facilitate optimal expression cassette design for salivary gland gene transfer.

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

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

Adenoviral vector mediates high expression levels of human growth hormone in the milk of mice and goats

The production of large quantities of complex proteins with biopharmaceutical purposes is the main drawback for their more extensive use. Here we demonstrated that a direct instillation of a recombinant adenoviral vector containing an expression cassette for the human growth hormone gene into the mammary gland of mice and goats allowed for the efficient secretion of human growth hormone in the milk. Through this approach we were able to express human growth hormone at maximal levels of 2.8 mg/ml in the milk of mice and up to 0.3 mg/ml in goat milk. We found that the expression levels were closely dependent on both the degree of differentiation of the secretory epithelium and on the adenoviral dose used. Here we demonstrated that the direct transduction of mammary epithelial cells by means of a recombinant adenovirus could be a suitable alternative to transgenic technology for the production of recombinant proteins of biopharmaceutical interest.

Long-Term Correction of Ornithine Transcarbamylase Deficiency by WPRE-Mediated Overexpression Using a Helper-Dependent Adenovirus

The urea cycle disorders (UCDs) are important models for developing gene replacement therapy for liver diseases. Long-term correction of the most common UCD, ornithine transcarbamylase (OTC) deficiency, has yet to be achieved in clinical or preclinical settings. The single human clinical trial using early-generation adenovirus (Ad) failed to show any biochemical correction. In adult OTC-deficient mice, an E1/E2-deleted Ad vector expressing the mouse OTC gene, but not the human, was only transiently therapeutic. By using post-transcriptional overexpression in the context of the less immunogenic helper-dependent adenoviral vector, we achieved metabolic correction of adult OTC-deficient mice for >6 months. Demonstrating this result were normalized orotic aciduria, normal hepatic enzyme activity, and elevated OTC RNA and protein levels in the absence of chronic hepatotoxicity. Overexpressing the human protein may have overcome two potential mechanisms accounting for poor cross-species complementation: a kinetic block at the level of mitochondrial import or a dominant negative effect by the mutant polypeptide. These data represent an important approach for treating human inborn errors of hepatocyte metabolism like the UCDs that require high-level transduction and gene expression for clinical correction.

Helper-dependent adenovirus vectors elicit intact innate but attenuated adaptive host immune responses in vivo

Helper-dependent adenovirus (HD-Ad) vectors with all adenoviral genes deleted mediate very long-term expression of therapeutic transgenes in a variety of animal models of disease. These vectors are associated with reduced toxicity and improved safety relative to traditional early region 1 deletion first-generation Ad (FG-Ad) vectors. Many studies have clearly demonstrated that FG-Ad vectors induce innate and adaptive immune responses in vivo; however, a comprehensive analysis of host immune responses to HD-Ad vectors has not yet been performed. In DBA/2 mice, intravenous injection of HD-Ad vectors encoding LacZ (HD-AdLacZ) or a murine secreted alkaline phosphatase (HD-AdSEAP) induced an early expression of inflammatory cytokine and chemokine genes in the liver, including interferon-inducible protein 10, macrophage inflammatory protein 2, and tumor necrosis factor alpha, and were expressed in a pattern similar to that induced by FG-Ad vectors encoding AdSEAP. Like AdSEAP, and consistent with the pattern of cellular gene expression, HD-AdLacZ and HD-AdSEAP induced the recruitment of CD11b-positive leukocytes to the transduced liver within hours of administration. AdSEAP also induced a second phase of liver inflammation, consisting of inflammatory gene expression and CD3-positive lymphocytic infiltrates 7 days posttransduction. In contrast, beyond 24 h no infiltrates or expression of inflammatory genes was detected in the livers of mice receiving HD-AdSEAP. Despite the lack of liver inflammation at 7 days, Ad-specific cytotoxic T lymphocytes could be detected in mice receiving HD-AdSEAP. This lack of liver inflammation was not due to reduced transduction since levels of transgene expression and the amounts of vector DNA in the liver were equivalent in mice receiving HD-AdSEAP and AdSEAP. These results demonstrate that HD-Ad vectors induce intact innate but attenuated adaptive immune responses in vivo.

Advances in vector-mediated gene transfer

Clinical applications of gene transfer technology initially targeted the treatment of inherited monogenetic disorders and cancers refractory to conventional therapies. Today, gene transfer approaches are being developed for most tissues and for multiple disorders including those affecting quality of life. The focus herein is eventual application of gene transfer technology for the management of organ-directed autoimmunity. A specific example is presented: Sjögren's syndrome and localized salivary gland gene transfer. The status of relevant pre-clinical gene transfer studies is reviewed, with an emphasis on use of adenoviral and adeno-associated viral vectors. Current limitations of effective organ-directed gene transfer are also discussed.

Distribution and toxicity resulting from adenoviral vector administration to a single salivary gland in adult rats

BACKGROUND

We examined the distribution and toxicity associated with a single salivary gland administration of a recombinant adenoviral vector, AdCMVH3, encoding human histatin 3.

METHODS

Adult rats received different doses of AdCMVH3 (0, 106, 3 x 107, and 109 pfu; 50 microl) via the right submandibular gland and were followed for 15 days. Food consumption, weight gain, clinical appearance, and serum chemistry were monitored, and a necropsy was performed. Vector distribution was examined by polymerase chain reaction, and selected saliva samples were tested for replication-competent adenovirus (RCA).

RESULTS

All animals survived to sacrifice (days 2, 8, and 15), and appeared normal clinically. There were no differences in food consumption, weight gain, and serum chemistry. The only consistent necropsy findings were lymphoid infiltrates and necrosis in the target submandibular glands of high-dosage animals. AdCMVH3 detection was virus dose dependent, decreased with time, and at low dose preferentially observed in the targeted gland. No RCA was detected.

CONCLUSIONS

Salivary gland administration of 109 pfu AdCMVH3 elicits an initial focal pathologic response and wide tissue distribution. There is no associated systemic toxicity up to 15 days, and lower doses are primarily found in glands.

Episomal persistence of recombinant adenoviral vector genomes during the cell cycle in vivo

Previously we showed that recombinant adenoviral helper-dependent (HD) vectors result in long-term transgene expression levels in vivo which slowly declined by 95% over a period of 1 year. In this study, we further establish that this was not predominantly immune mediated. To determine if cell turnover was responsible for the loss of transgene expression, we induced rapid hepatocyte cell cycling in mouse liver, by performing a surgical two-thirds partial hepatectomy. We observed a 55 and 65% reduction in transgene expression levels and a 50 and 71% loss of vector genomes for the HD vector and the first-generation adenoviral vector. In sharp contrast, in nonviral, episomal plasmid DNA-injected mice, transgene expression levels and DNA copy numbers decreased by 95 and 99%, respectively. These findings suggest that cell division alone was not the primary reason for the slow decrease in transgene expression levels and that recombinant adenoviral vectors have a more robust mechanism for maintaining persistence during cell cycling. Several potential mechanisms are proposed.

Humoral immune response in mice against a circulating antigen induced by adenoviral transfer is strictly dependent on expression in antigen-presenting cells

Adenoviral transfer of human apo A-I in Balb/c mice induces a strong humoral immune response against the transgene product when expression is driven from the ubiquitously active CMV promoter but induces no immune response when driven by the hepatocyte-specific 256-base pair apo A-I promoter. Here the hypothesis was tested, which is that the humoral immune response against the circulating transgene product correlates with its expression in antigen-presenting cells. No humoral immune response was observed after adenoviral transfer of vectors with human apo A-I expression driven by the hepatocyte-specific apo C-II or 1.5-kilobase (kb) human alpha(1)-antitrypsin promoter, but antibodies were induced after transfer with vectors driven by the ubiquitously active U1b promoter and the murine MHCII E beta promoter. A strict correlation was observed between antigen expression in the spleen and the occurrence of an immune response. Coinjection of the 1.5-kb human alpha(1)-antitrypsin and the murine MHCII E beta promoter-driven vectors resulted in a very short-lived humoral immune response against human apo A-I, suggesting that the time course of human apo A-I expression is a critical determinant of the development of tolerance for human apo A-I. High titers of antibodies against human apo A-I after subcutaneous gene transfer with the MHCII E beta promoter-driven vector underscore the potential of this promoter for vaccination purposes. In conclusion, humoral immune response in mice against a circulating antigen induced by adenoviral transfer is strictly dependent on expression in antigen-presenting cells.

Therapeutic factor VIII levels and negligible toxicity in mouse and dog models of hemophilia A following gene therapy with high-capacity adenoviral vectors

High-capacity adenoviral (HC-Ad) vectors expressing B-domain-deleted human or canine factor VIII from different liver-specific promoters were evaluated for gene therapy of hemophilia A. Intravenous administration of these vectors into hemophilic FVIII-deficient immunodeficient SCID mice (FVIIIKO-SCID) at a dose of 5 x 10(9) infectious units (IU) resulted in efficient hepatic gene delivery and long-term expression of supraphysiologic FVIII levels (exceeding 15 000 mU/mL), correcting the bleeding diathesis. Injection of only 5 x 10(7) IU still resulted in therapeutic FVIII levels. In immunocompetent hemophilic FVIII-deficient mice (FVIIIKO), FVIII expression levels peaked at 75 000 mU/mL but declined thereafter because of neutralizing anti-FVIII antibodies and a cellular immune response. Vector administration did not result in thrombocytopenia, anemia, or elevation of the proinflammatory cytokine interleukin-6 (IL-6) and caused no or only transient elevations in serum transaminases. Following transient in vivo depletion of macrophages before gene transfer, significantly higher and stable FVIII expression levels were observed. Injection of only 5 x 10(6) HC-Ad vectors after macrophage depletion resulted in long-term therapeutic FVIII levels in the FVIIIKO and FVIIIKO-SCID mice. Intravenous injection of an HC-Ad vector into a hemophilia A dog at a dose of 4.3 x 10(9) IU/kg led to transient therapeutic canine FVIII levels that partially corrected whole-blood clotting time. Inhibitory antibodies to canine FVIII could not be detected, and there were no signs of hepatotoxicity or of hematologic abnormalities. These results contribute to a better understanding of the safety and efficacy of HC-Ad vectors and suggest that the therapeutic window of HC-Ad vectors could be improved by minimizing the interaction between HC-Ad vectors and the innate immune system.

HDL therapy for the acute treatment of atherosclerosis

Although pharmacologic intervention to treat atherosclerosis originally focused on lowering LDL-cholesterol levels as a therapeutic target, a number of intervention trials have also highlighted the powerful effect of elevating HDL-cholesterol levels to reduce cardiovascular morbidity and mortality. Although the mechanism(s) by which HDL beneficially alters the atherosclerotic disease process is (are) still unknown, it is presumed that high levels of HDL facilitate the efflux of cholesterol from the arterial wall, thereby enhancing the transport of cholesterol and other lipids from arteries back to the liver for biliary excretion as fecal sterols and bile acids. It has therefore been hypothesized that through a rapid facilitation of HDL mediated cholesterol efflux from arteries by infusion of synthetic apolipoprotein A-I (apoA-I)/phospholipid (A-I/PL) complexes, HDL therapy could have an acute therapeutic application to treat cardiovascular disease at the site of action, namely the vulnerable, unstable atherosclerotic plaque. Single high dose infusions and repeated injections of lower doses of apoA-I variants or mimetics complexed to phospholipids have produced remarkable effects on the progression and regression of atherosclerosis in animal models. The positive results of these preclinical experiments have compelled researchers to perform exploratory studies in human subjects in which reconstituted HDL and synthetic A-I/PL complexes are infused through a peripheral vein. These clinical studies are testing the hypothesis and the potential use of synthetic HDL as a new treatment modality for acute coronary syndromes. Given that there is an unmet medical need for new and more effective therapies to elevate HDL-cholesterol levels and improve HDL function, a historical review, update and discussion of the preclinical and clinical studies which support the use of HDL therapy for reducing cardiovascular morbidity and mortality is warranted.

Persistent hepatic expression of human apo A-I after transfer with a helper-virus independent adenoviral vector

Gene transfer with 'gutted' vectors is associated with persistent transgene expression and absence of hepatotoxicity, but the requirement of helper viruses hampers efficient production and leads to contamination of viral batches with these helper-viruses. In the present study, gene transfer with a helper-virus independent E(1)/E(3)/E(4)-deleted adenoviral vector induced persistent expression of human apo A-I (200 +/- 16 mg/dl at day 35, 190 +/- 15 mg/dl at 4 months, 170 +/- 16 mg/dl at 6 months) and stable transgene DNA levels (3.5 +/- 0.60 at day 35, 3.3 +/- 0.39 at 4 months, 3.1 +/- 0.47 mg/dl at 6 months) in C57BL/6 mice in the absence of significant toxicity. The vector contained the 1.5 kb human alpha(1)-antitrypsin promoter in front of the genomic human apo A-I sequence and four copies of the human apo E enhancer (hAAT.gA-I.4xapoE) and was deleted in E(1), E(3) and E(4). Reintroduction of E(4) ORF 3 and E(4) ORF 4 in the viral backbone caused a more than four-fold decline of transgene DNA between day 35 and 4 months after transfer both in wild-type and in C57BL/6 SCID and C57BL/6 Rag-1(-/-) mice, indicating that the effect of E(4) ORF 3 and E(4) ORF 4 is independent of a cellular immune response against viral epitopes. Co-injection of an E(1)-deleted vector containing no expression cassette and the E(1)/E(3)/E(4)-deleted vector containing the hAAT.gA-I.4xapoE expression cassette indicated that E(4) gene products destabilize transgene DNA in trans. Gene transfer with an E(1)/E(3)/E(4)-deleted vector containing only E(4) ORF 3 and the hAAT.gA-I.4xapoE expression cassette was associated with transgene DNA decline, but not with hepatotoxicity, indicating that transgene DNA persistence and hepatotoxicity are dissociated processes. After transfer with E(1)/E(3)/E(4)-deleted vectors containing expression cassettes with a different promoter or a different position of the apo E enhancers, transgene DNA levels were less stable than after transfer with the vector containing hAAT.gA-I.4xapoE, indicating that the expression cassette is an important determinant of episomal stability. In conclusion, gene transfer with an E(1)/E(3)/E(4)-deleted vector containing the hAAT.gA-I.4xapoE expression cassette induces persistent expression of human apo A-I in the absence of hepatotoxicity. Transgene DNA turnover is independent of an adaptive cellular immune response against viral epitopes and of hepatotoxicity. E(1)/E(3)/E(4)-deleted vectors containing transgenes under control of the hAAT promoter in combination with four copies of the human apo E enhancer may be suitable for hepatocyte-specific overexpression of transgenes after gene transfer. doi:10.1038/sj.gt.3301824