Impact of transgenic oilseed rape expressing oryzacystatin-1 (OC-1) and of insecticidal proteins on longevity and digestive enzymes of the solitary bee Osmia bicornis

The risk that insect-resistant transgenic plants may pose for solitary bees was assessed by determining longevity of adult Osmia bicornis (O. rufa) chronically exposed to transgenic oilseed rape expressing oryzacystatin-1 (OC-1) or to the purified insecticidal proteins recombinant rOC-1, Kunitz soybean trypsin inhibitor (SBTI), Galanthus nivalis agglutinin (GNA), or Bacillus thuringiensis toxin Cry1Ab dissolved in sugar solution (at 0.01 and 0.1%, w:v, Cry1Ab only at 0.01%). Compared to control bees, longevity was significantly reduced by SBTI and GNA at both concentrations and by rOC-1 at 0.1%, but not by Cry1Ab or rOC-1 at 0.01%. Longevity on the OC-1 oilseed rape was not significantly different from the control plants. The effects of SBTI and rOC-1 on longevity were investigated through characterization of the digestive proteinases of O. bicornis and analysis of the response in proteinase profiles to ingestion of these proteinase inhibitors. A relatively complex profile of at least four types of soluble proteolytic enzymes was identified. Serine proteinases were found to be predominant, with metallo and especially cysteine proteinases making a smaller albeit significant contribution. The compensatory response to in vivo enzyme inhibition was similar for SBTI and rOC-1 although less pronounced for rOC-1. It consisted of a non-specific overproduction of native proteinases, both sensitive and insensitive, and the induction of a novel aspartic proteinase.

Characterisation of midgut digestive proteases from the maize stem borer Busseola fusca

BACKGROUND

Insect damage is a major constraint on maize production. Control of Busseola fusca (Fuller) in sub-Saharan Africa is relatively ineffective; the major larval digestive enzymes were characterised with a view to developing future control strategies.

RESULTS

Using BODIPY-FL Casein, maximal activity was at pH 9.5, with six protease forms visualised by gelatin-PAGE. Synthetic substrates and diagnostic inhibitors demonstrated the presence of serine proteases. Chymostatin was a potent inhibitor of general proteolysis (90%), providing strong evidence for the presence of chymotrypsin; it also caused significant inhibition (>95%) with SA(2)PFpNA as substrate. The I(50) values for chymostatin with casein and SA(2)PFpNA were 0.0075 microM and 0.06 microM respectively. Z-Phe-Arg-pNA activity was inhibited by chymostatin and TLCK (50 and 30% respectively), suggesting the presence of trypsin-like activity. BApNA hydrolysis was also strongly inhibited by chymostatin and TLCK (92 and 75%), suggesting trypsin activity, while SBBI, PMSF, pepstatin and E-64 had no significant effect. Interestingly, SBBI (I(50) = 0.39 microM) and SBTI both inhibited general proteolysis by approximately 70%, suggesting that SBBI's dual inhibitory role makes this inhibitor a potentially useful candidate for expression in maize for control of B. fusca.

CONCLUSION

These results provide a basis for the rational design of insect-resistant transgenic maize expressing protease inhibitors.

Potential effects of oilseed rape expressing oryzacystatin-1 (OC-1) and of purified insecticidal proteins on larvae of the solitary bee Osmia bicornis

Despite their importance as pollinators in crops and wild plants, solitary bees have not previously been included in non-target testing of insect-resistant transgenic crop plants. Larvae of many solitary bees feed almost exclusively on pollen and thus could be highly exposed to transgene products expressed in the pollen. The potential effects of pollen from oilseed rape expressing the cysteine protease inhibitor oryzacystatin-1 (OC-1) were investigated on larvae of the solitary bee Osmia bicornis ( = O. rufa). Furthermore, recombinant OC-1 (rOC-1), the Bt toxin Cry1Ab and the snowdrop lectin Galanthus nivalis agglutinin (GNA) were evaluated for effects on the life history parameters of this important pollinator. Pollen provisions from transgenic OC-1 oilseed rape did not affect overall development. Similarly, high doses of rOC-1 and Cry1Ab as well as a low dose of GNA failed to cause any significant effects. However, a high dose of GNA (0.1%) in the larval diet resulted in significantly increased development time and reduced efficiency in conversion of pollen food into larval body weight. Our results suggest that OC-1 and Cry1Ab expressing transgenic crops would pose a negligible risk for O. bicornis larvae, whereas GNA expressing plants could cause detrimental effects, but only if bees were exposed to high levels of the protein. The described bioassay with bee brood is not only suitable for early tier non-target tests of transgenic plants, but also has broader applicability to other crop protection products.

Critical assessment of lifelong phenotype correction in hyperbilirubinemic Gunn rats after retroviral mediated gene transfer

Among inherited diseases of the liver, Crigler-Najjar type 1 disease (CN-1), which results from complete deficiency in bilirubin UDP-glucuronosyltransferase activity (B-UGT1), is an attractive target for gene therapy studies. Hyperbilirubinemic Gunn rats, a model of CN-1, were injected at 2 days of age with lentiviral or oncoretroviral vectors encoding the human B-UGT1. After injection, bilirubinemia was normalized for up to 95 weeks. Bilirubin conjugates were present in the bile, demonstrating liver transduction. PCR and enzyme activity analysis confirmed gene and phenotype correction in liver. We observed that when using a strong viral promoter, a complete correction was achieved with less than 5% of B-UGT1 copy per haploid genome and after a reconstitution of 12% B-UGT1 normal activity. Liver histology remained normal throughout the experiment and tissue distribution analysis revealed preferential hepatocyte transduction after systemic delivery. Finally, no adverse immune response occurred even after induction of nonspecific liver inflammation, suggesting immune ignorance to the therapeutic protein. Our present results document the lifelong safety of gene therapy for CN-1 with retroviral vectors. They offer a better delineation of liver gene correction level required to achieve complete correction of bilirubinemia and pave the way for future clinical application of gene therapy for inherited liver disorders.

Bitrophic and tritrophic effects of Bt Cry3A transgenic potato on beneficial, non-target, beetles

Insect-resistant transgenic plants have been suggested to have unpredictable effects on the biodiversity of the agro-ecosystem, including potential effects on insect natural enemies, beneficial in control of crop pests. Whilst carnivorous as adults, many of these predators may also consume plant tissues, in particular plant pollen and nectar. Coleoptera are important in terms of agro-ecological research not only because of the large number of species in this order, but also because of their role as biological control agents. Thus any detrimental impact on this group of insects would be highly undesirable. The effects of potato expressing the coleopteran-specific Bacillus thuringiensis delta-endotoxin Cry3A (Bt Cry3A) on the ladybird beetle Harmonia axyridis and the carabid beetle Nebria brevicollis were investigated via the bitrophic interaction of the adult ladybird with potato flowers and the tritrophic interaction of the carabid consuming a non-target potato pest. Immunoassays confirmed accumulation of the transgene product in potato leaves and floral tissues (at levels of up to 0.01% (pollen) and 0.0285% (anthers) of total soluble protein). Despite H. axyridis and N. brevicollis belonging to the targeted insect order, no significant effects upon survival or overall body mass change of either beetle were observed. Furthermore, Bt Cry3A had no detrimental effects on reproductive fitness of either beetle species, either in terms of fecundity or subsequent egg viability. Behavioural analysis revealed no significant impact of Bt Cry3A on beetle activity or locomoter behaviour. Ligand blots indicate that this is due to either the absence of Bt-binding sites in brush border membrane vesicles (BBMV) isolated from Nebria brevicollis, or in the case of Harmonia axyridis, the binding did not functionally lead to behavioural or physical effects.

Prey-mediated effects of transgenic canola on a beneficial, non-target, carabid beetle

Transgenic plants producing insecticidal proteins from Bacillus thuringiensis (Bt) can control some major insect pests and reduce reliance on sprayed insecticides. However, large scale adoption of this technology has raised concerns about potential negative effects, including evolution of pest resistance to Bt toxins, transgene flow from Bt crops to other plants, and harm to non-target beneficial organisms. Furthermore, concern has also been expressed over the effects this technology may have on biodiversity in general. Ecologically relevant risk assessment is therefore required (Risk = Hazard x Exposure). Transgenic plants that produce Bt toxins to kill insect pests could harm beneficial predators. This might occur directly by transmission of toxin via prey, or indirectly by toxin-induced reduction in prey quality (Hazard). To test these hypotheses, we determined the effects of Bt-producing canola on a predatory ground beetle (Pterostichus madidus) fed larvae of diamondback moth (Plutella xylostella) that were either susceptible or resistant to the Bt toxin. Survival, weight gain, and adult reproductive fitness did not differ between beetles fed prey reared on Bt-producing plants and those fed prey from control plants. Furthermore, while Bt-resistant prey was shown to deliver high levels of toxin to the beetle when they were consumed, no significant impact upon the beetle was observed. Subsequent investigation showed that in choice tests (Exposure), starved and partially satiated female beetles avoided Bt-fed susceptible prey, but not Bt-fed resistant prey. However, in the rare cases when starved females initially selected Bt-fed susceptible prey, they rapidly rejected them after beginning to feed. This prey type was shown to provide sufficient nutrition to support reproduction in the bioassay suggesting that Bt-fed susceptible prey is acceptable in the absence of alternative prey, however adults possess a discrimination ability based on prey quality. These results suggest that the direct effects of Bt-producing canola on predator life history was minimal, and that predators' behavioural preferences may mitigate negative indirect effects of reduced quality of prey caused by consumption of Bt-producing plants. The results presented here therefore suggest that cultivation of Bt canola may lead to conservation of non-target predatory and scavenging organisms beneficial in pest control, such as carabids, and may therefore provide more sustainable agricultural systems than current practices. In addition, minimal impacts on beneficial carabids in agro-ecosystems suggest that Bt canola crops are likely to be compatible with integrated pest management (IPM) systems.

Comparing the impact of conventional pesticide and use of a transgenic pest-resistant crop on the beneficial carabid beetle Pterostichus melanarius

The potential impact of a chemical pesticide control method has been compared with that of transgenic plants expressing a protease inhibitor conferring insect resistance by utilising a tritrophic system comprising the crop plant Brassica napus (L.) (Oilseed rape), the pest mollusc Deroceras reticulatum (Müller) and the predatory carabid beetle Pterostichus melanarius (Illiger). Cypermethrin, as the most widely used pesticide in UK oilseed rape (OSR) cultivation, was selected as the conventional treatment. OSR expressing a cysteine protease inhibitor, oryzacystatin-1 (OC-1), was the transgenic comparator. In feeding trials, D. reticulatum showed no significant long-term effects on measured life history parameters (survival, weight gain, food consumption) as a result of exposure to either the cypermethrin or OC-1 treatment. However, D. reticulatum was able to respond to the presence of the dietary inhibitor by producing two novel proteases following exposure to OC-1-expressing OSR. Similarly, P. melanarius showed no detectable alterations in mortality, weight gain or food consumption when feeding on D. reticulatum previously fed either pesticide-contaminated or GM plant material. Furthermore, as with the slug, a novel form of protease, approximately M(r) 27 kDa, was induced in the carabid in response to feeding on slugs fed OC-1-expressing OSR.

Direct effects of snowdrop lectin (GNA) on larvae of three aphid predators and fate of GNA after ingestion

Plants genetically modified to express Galanthus nivalis agglutinin (GNA) have been found to confer partial resistance to homopteran pests. Laboratory experiments were conducted to investigate direct effects of GNA on larvae of three species of aphid predators that differ in their feeding and digestive physiology, i.e. Chrysoperla carnea, Adalia bipunctata and Coccinella septempunctata. Longevity of all three predator species was directly affected by GNA, when they were fed a sucrose solution containing 1% GNA. However, a difference in sensitivity towards GNA was observed when comparing the first and last larval stage of the three species. In vitro studies revealed that gut enzymes from none of the three species were able to break down GNA. In vivo feed-chase studies demonstrated accumulation of GNA in the larvae. After the larvae had been transferred to a diet devoid of GNA, the protein stayed present in the body of C. carnea, but decreased over time in both ladybirds. Binding studies showed that GNA binds to glycoproteins that can be found in the guts of larvae of all three predator species. Immunoassay by Western blotting of haemolymph samples only occasionally showed the presence of GNA. Fluorescence microscopy confirmed GNA accumulation in the midgut of C. carnea larvae. Implications of these findings for non-target risk assessment of GNA-transgenic crops are discussed.

Transgenic plants for insect pest control: a forward looking scientific perspective

One of the first successes of plant biotechnology has been the creation and commercialisation of transgenic crops exhibiting resistance to major insect pests. First generation products encompassed plants with single insecticidal Bt genes with resistance against major pests of corn and cotton. Modelling studies predicted that usefulness of these resistant plants would be short-lived, as a result of the ability of insects to develop resistance against single insecticidal gene products. However, despite such dire predictions no such collapse has taken place and the acreage of transgenic insect resistance crops has been increasing at a steady rate over the 9 years since the deployment of the first transgenic insect resistant plant. However, in order to assure durability and sustainability of resistance, novel strategies have been contemplated and are being developed. This perspective addresses a number of potentially useful strategies to assure the longevity of second and third generation insect resistant plants.

How Family 26 Glycoside Hydrolases Orchestrate Catalysis on Different Polysaccharides

One of the most intriguing features of the 90 glycoside hydrolase families (GHs) is the range of specificities displayed by different members of the same family, whereas the catalytic apparatus and mechanism are often invariant. Family GH26 predominantly comprises beta-1,4 mannanases; however, a bifunctional Clostridium thermocellum GH26 member (hereafter CtLic26A) displays a markedly different specificity. We show that CtLic26A is a lichenase, specific for mixed (Glcbeta1,4Glcbeta1,4Glcbeta1,3)n oligo- and polysaccharides, and displays no activity on manno-configured substrates or beta-1,4-linked homopolymers of glucose or xylose. The three-dimensional structure of the native form of CtLic26A has been solved at 1.50-A resolution, revealing a characteristic (beta/alpha)8 barrel with Glu-109 and Glu-222 acting as the catalytic acid/base and nucleophile in a double-displacement mechanism. The complex with the competitive inhibitor, Glc-beta-1,3-isofagomine (Ki 1 microm), at 1.60 A sheds light on substrate recognition in the -2 and -1 subsites and illuminates why the enzyme is specific for lichenan-based substrates. Hydrolysis of beta-mannosides by GH26 members is thought to proceed through transition states in the B2,5 (boat) conformation in which structural distinction of glucosides versus mannosides reflects not the configuration at C2 but the recognition of the pseudoaxial O3 of the B2,5 conformation. We suggest a different conformational itinerary for the GH26 enzymes active on gluco-configured substrates.

Liver gene therapy: advances and hurdles

Liver gene therapy is being developed as an alternative to orthotopic liver transplantation, which is the only effective therapy for many liver diseases. The liver has unique features that make it attractive for in vivo and ex vivo gene transfer. In vivo approach is far less invasive than ex vivo approach, although in most cases, host immune response directed against the transgene product and/or vector particles severely impairs the efficiency of gene transfer, and precludes long-term transgene expression after in vivo gene delivery. Ex vivo approach allows for an elective targeting of the hepatocytes, avoiding that the transgene be expressed in professional antigen-presenting, but is faced with the low in vitro proliferative ability of hepatocytes, and to the low in vivo liver repopulating ability of transplanted cells. In some specific situations where immune response was controlled or transplanted cells had a strong growth advantage over host hepatocytes, gene transfer resulted in long-term and complete correction of a liver genetic defect. In this review, we will outline the liver diseases that may benefit from gene therapy, the vector technology under investigation, the advances and the problems to be overcome.

Impact of oilseed rape expressing the insecticidal serine protease inhibitor, mustard trypsin inhibitor-2 on the beneficial predator Pterostichus madidus

Abstract Insect-resistant transgenic plants have been suggested to have deleterious effects on beneficial predators feeding on crop pests, through transmission of the transgene product by the pest to the predator. To test this hypothesis, effects of oilseed rape expressing the serine protease inhibitor, mustard trypsin inhibitor -2 (MTI-2), on the predatory ground beetle Pterostichus madidus were investigated, using diamondback moth, Plutella xylostella as the intermediary pest species. As expected, oilseed rape expressing MTI-2 had a deleterious effect on the development and survival of the pest. However, incomplete pest mortality resulted in survivors being available to predators at the next trophic level, and inhibition studies confirmed the presence of biologically active transgene product in pest larvae. Characterization of proteolytic digestive enzymes of P. madidus demonstrated that adults utilize serine proteases with trypsin-like and chymotrypsin-like specificities; the former activity was completely inhibited by MTI-2 in vitro. When P. madidus consumed prey reared on MTI-2 expressing plants over the reproductive period in their life cycle, no significant effects upon survival were observed as a result of exposure to the inhibitor. However, there was a short-term significant inhibition of weight gain in female beetles fed unlimited prey containing MTI-2, with a concomitant reduction of prey consumption. Biochemical analyses showed that the inhibitory effects of MTI-2 delivered via prey on gut proteolysis in the carabid decreased with time of exposure, possibly resulting from up-regulation of inhibitor-insensitive proteases. Of ecological significance, consumption of MTI-2 dosed prey had no detrimental effects on reproductive fitness of adult P. madidus.

Plant–insect interactions: molecular approaches to insect resistance

Recent advances in our understanding of induced responses in plants and their regulation, brought about by a revolution in molecular biology, have re-focused attention on the potential exploitation of endogenous resistance mechanisms for crop protection. The future goal of crop biotechnology is thus to engineer a durable, multimechanistic resistance to insect pests through an understanding of the diversity of plant responses to insect attack.

Impact of oilseed rape expressing the insecticidal cysteine protease inhibitor oryzacystatin on the beneficial predator Harmonia axyridis (multicoloured Asian ladybeetle)

Insect-resistant transgenic plants have been suggested to have deleterious effects on beneficial predators through transmission of the transgene product by the pest to the predator. To test this hypothesis, effects of oilseed rape expressing the cysteine protease inhibitor oryzacystatin-1 (OC-1) on the predatory ladybird Harmonia axyridis were investigated using diamondback moth Plutella xylostella as the pest species. As expected, oilseed rape expressing OC-1 had no effects on either development or survival of the pest, which utilizes serine digestive proteases. Immunoassays confirmed accumulation of the transgene product in pest larval tissues at levels of up to 3 ng per gut. Characterization of proteolytic digestive enzymes of H. axyridis demonstrated that larvae and adults utilize cysteine and aspartic proteases; the former activity was completely inhibited by oryzacystatin in vitro. However, when H. axyridis larvae consumed prey reared on OC-1 expressing plants over their entire life cycle, no significant effects upon survival or overall development were observed. The inhibitor initially stimulated development, with a shortening of the developmental period of the second instar by 27% (P < 0.0001) accompanied by a 36% increase in weight of second instar larvae (P = 0.007). OC-1 had no detrimental effects on reproductive fitness of adult H. axyridis. Interestingly there was a significant increase in consumption of OC-1 dosed prey. The results show that prey reared on transgenic plants expressing a protein which inhibited ladybird digestive enzymes in vitro had no effects in vivo; the ladybird was able to up-regulate digestive proteases in response to the inhibitor.

The case of the monarch butterfly: a verdict is returned

A publication reporting the harmful effects on the monarch butterfly of maize genetically modified to express insecticidal delta-endotoxins from the soil bacterium Bacillus thuringiensis (Bt) caused much public interest. A series of ecologically based studies were subsequently carried out to evaluate rigorously the impact of pollen from such crops and to quantify the risks. The results demonstrated that the commercial large-scale cultivation of current Bt-maize hybrids did not pose a significant risk to the monarch population. Further studies also demonstrated that Bt-expressing crops posed little risk to other nontarget insects, including beneficial insects such as pollinators and natural enemies.

Efficient retroviral gene transfer to the liver in vivo using nonpolypeptidic mitogens

Recombinant retroviral vectors are attractive tools for achieving sustained expression of a therapeutic gene in the liver. However, cell division is required for efficient transduction with these vectors. Here we report that two widely used liver mitogens, triiodothyronin (T3) and cyproterone acetate (CPA), enable hepatocyte transduction with recombinant retroviral vectors delivered in vivo into the bloodstream. Treatment with T3 as well as CPA, alone or in combination, resulted in an increase in hepatocyte replication predominantly around the portal tract. The mitogenic activity made it possible to transduce hepatocytes in the same location. Moreover, when administered together, the two drugs synergized and the transduction level reached 5% of hepatocytes. This transduction level is compatible with clinical applications for a number of inherited liver diseases. Since these two compounds have a long history of safe clinical use, we propose that these liver mitogens may have potential for clinical application in liver-directed gene therapy.

Immune-dependent distant bystander effect after adenovirus-mediated suicide gene transfer in a rat model of liver colorectal metastasis

Gene transfer of the herpes simplex virus thymidine kinase (HSV-tk) gene sensitizes tumor cells to the toxic effect of ganciclovir (GCV). The toxic effect of GCV extends to nontransduced surrounding cells by a metabolic process known as the bystander effect. A distant bystander effect, which involves anatomically separated tumors, has been reported in vivo. Our aim was to evaluate and characterize such distant effect in a rat model of colorectal tumors implanted in the liver using adenovirus to carry the HSV-tk gene. Two colorectal tumors were implanted in two distinct liver lobes of the liver. One of the tumor was transduced with an adenoviral vector containing HSV-tk gene. The volumes of the tumors were monitored after GCV treatment. Implication of the immune system was studied histologically and after in vivo manipulations. After GCV administration, the nontransduced distant tumor regressed partially or completely in the experimental group. Immunohistochemical analysis revealed the presence of CD8+ lymphocytes in the distant lesion. HSV-tk/GCV-induced immune response against tumors was evidenced by an adoptive transfer assay (Winn assay) and the distant bystander effect was blunted after CD8+ lymphocytes depletion. However, the survival rates for treated animals were not improved. These findings demonstrate that an immune-mediated effective distant bystander effect can be obtained after limited adenoviral-mediated transfer of the HSV-tk gene.

Critical aspects of viral vectors for gene transfer into the kidney

Viral vectors have been used in vitro and in vivo for more than a decade, with some significant results in specific situations, e.g., when recombinant adeno-associated virus is used for the long-term transduction of skeletal muscle in coagulation factor IX-deficient patients. However, the kidney has been quite difficult to transduce with any viral vector currently available. When viral transduction occurs, it is often heterogeneous, transient, and eventually associated with immune and toxic side effects. However, recombinant adeno-associated virus and lentiviral vectors remain to be fully evaluated in the kidney; the former is small enough to be filtered through the glomerular basement membrane. This may be critical, because glomerular filtration is required for DNA complex-mediated transduction of tubular cells. An alternative to in situ renal gene transfer is secretion of a therapeutic protein from a distant site, such as skeletal muscle. Several examples provide evidence that this could be a clinically relevant approach. It also may allow accurate determination of the pathophysiologic mechanisms involved in the establishment and maintenance of experimental glomerulonephritis.

Hyaluronidase enhances recombinant adeno-associated virus (rAAV)-mediated gene transfer in the rat skeletal muscle

Skeletal muscle is a privileged target for long-term rAAV-mediated gene transfer in mouse, rat, dog and non-human primates. Intramuscular injections of rAAV encoding human factor IX in hemophilia B patients have been initiated, based on promising results gathered in affected dogs. We found that intramuscular rAAV administration in rats resulted in restricted transduction essentially along the myofibers axis with poor lateral diffusion. This suggested that the transduction rate might be limited by the ability of the virus to reach sites distant from the injection point. We tested whether hyaluronidase, an enzyme which dissociates the extracellular matrix, could enhance vector diffusion when injected in the rat muscle before administration of rAAV encoding either nuclear-localized beta-galactosidase (rAAVCMVnlsLacZ) or the human alpha-1-antitrypsin (rAAVCMVhAAT) under the control of the cytomegalovirus immediate--early promoter (CMV). The results showed that pretreatment of the rat anterior tibialis muscle with hyaluronidase resulted in: (1) a larger diffusion of the virus indicated by an increase in the area containing LacZ-transduced fibers, and (2) a two- to three-fold increase of transduction efficiency measured by the number of LacZ-positive fibers or by the hAAT serum concentration. We also provide evidence that hyaluronidase was well tolerated and was not associated with short- or long-term toxicity evaluated by morphological studies. Finally, in our experimental conditions, hyaluronidase did not promote rAAV dissemination to other organs as assessed by PCR to detect vector sequences. We conclude that pretreatment of skeletal muscle by hyaluronidase, a clinically available reagent, was harmless and resulted in a consistent and significant increase in rAAV diffusion and transduction levels.

In vivo retrovirus-mediated gene transfer into lamb liver

TOPIC

Highly efficient retrovirus-mediated gene transfer into hepatocytes in vivo has been previously reported in the rat. Before considering human applications of these techniques in the treatment of inherited liver diseases, it was necessary to document its efficiency in a large animal model. Lamb was choosen because the liver was similar to human liver regarding size and anatomy.

MATERIALS AND METHODS

To induce hepatocyte division which is necessary for infection with retroviral particles, animals were subjected to a left hepatectomy. Kinetics of liver regeneration were assessed on sequential liver biopsies after partial hepatectomy in order to provide an evaluation of the peak of maximal liver regeneration in a first animal group. Recombinant retroviruses encoding a reporter gene (E. coli beta galactosidase) were then perfused through the portal vein of the regenerating liver in a second animal group.

RESULTS

The more intense liver regeneration occurred from one to 6 days after partial hepatectomy, with the highest thymidine kinase rate and MIB-1 antibody staining on the second day. The proportion of genetically modified lamb hepatocytes expressing the reporter gene was less than 1%, despite the use of higher titers of retroviral particles than those described in previous reports.

CONCLUSION

The results obtained in rodent livers with this in vivo gene transfer methodology cannot currently be scaled up in a large ruminant model. The efficacy of vectors has to be tested in other large mammals before planning gene therapy trials for the treatment of inherited liver diseases.

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

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

[Evaluation of recombinant retrovirus and adenovirus for gene transfer to normal and pathologic intestinal tissue]

Intestinal tract is an attractive target for gene therapy. A number of diseases could benefit from gene transfer into this organ and in particular inflammatory diseases such as Crohn's disease. In the present report, we have evaluated the efficiency of retroviral and adenoviral recombinant vectors for transferring a marker gene (beta galactosidase from E. Coli) in two parts of the intestinal tract: the small bowel and the left part of the colon. Retroviruses were inefficient for the transfer of the marker gene in these two sites either in normal conditions or after induction of inflammation by treatment with acetic acid or trinitrobenzene. Conversely, beta galactosidase positive cells were found in small bowel as well as colon following gene transfer with adenoviral vectors. Moreover the location of the positive cells in the intestinal wall was dependent upon the route of injection of the adenoviral vectors (transparietal, endoluminal or intramural).

Mature hepatocytes actively divide and express gamma-glutamyl transpeptidase after D-galactosamine liver injury

AIMS/BACKGROUND

We studied the fate of hepatocytes in the rat liver after D-galactosamine injury by genetic labeling using recombinant retroviruses carrying the Escherichia coli lacZ gene coupled to a nuclear localization signal.

METHODS

Hepatocytes were either labeled by direct injection of 2.5 ml high-titer retrovirus-containing medium in the regenerating liver parenchyma after administration of a single dose of D-galactosamine. Alternatively hepatocytes were pre-labeled, 24 h after a two-thirds hepatectomy, by injecting the same volume of retroviral solution in the portal vein and D-galactosamine was administered 15 days later. Gamma-glutamyl transpeptidase and beta-galactosidase activities were assessed on cryostat sections, along with localization of the hepatocyte-specific HES6 antigen.

RESULTS

Morphological observations, as well as beta-galactosidase activity detection, showed that hepatocytes actively divide as early as 1 day after D-galactosamine injection. Gamma-glutamyl transpeptidase activity was detected in biliary cells, but also in mature hepatocytes, pre-labeled with beta-galactosidase before D-galactosamine administration.

CONCLUSIONS

These experiments demonstrate that hepatocytes can divide to restore the liver mass after D-galactosamine liver injury. Furthermore, we also show that gamma-glutamyl transpeptidase, which has been reported to be expressed only by fetal or preneoplastic hepatocytes, can be re-expressed by mature hepatocytes during the recovery process.