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

Polyploidization without mitosis improves in vivo liver transduction with lentiviral vectors

Lentiviral vectors are efficient gene delivery vehicles for therapeutic and research applications. In contrast to oncoretroviral vectors, they are able to infect most nonproliferating cells. In the liver, induction of cell proliferation dramatically improved hepatocyte transduction using all types of retroviral vectors. However, the precise relationship between hepatocyte division and transduction efficiency has not been determined yet. Here we compared gene transfer efficiency in the liver after in vivo injection of recombinant lentiviral or Moloney murine leukemia viral (MoMuLV) vectors in hepatectomized rats treated or not with retrorsine, an alkaloid that blocks hepatocyte division and induces megalocytosis. Partial hepatectomy alone resulted in a similar increase in hepatocyte transduction using either vector. In retrorsine-treated and partially hepatectomized rats, transduction with MoMuLV vectors dropped dramatically. In contrast, we observed that retrorsine treatment combined with partial hepatectomy increased lentiviral transduction to higher levels than hepatectomy alone. Analysis of nuclear ploidy in single cells showed that a high level of transduction was associated with polyploidization. In conclusion, endoreplication could be exploited to improve the efficiency of liver-directed lentiviral gene therapy.

AFP-specific immunotherapy impairs growth of autochthonous hepatocellular carcinoma in mice

BACKGROUND AND AIMS

In this study, we have assessed the potential of antigen-specific immunotherapy against hepatocellular carcinoma (HCC) in conditions of low tumour burden, in an autochthonous HCC model.

METHODS

Diethylnitrosamine (DEN) injected into infant mice results in the development of multi-nodular HCC in which alpha-fetoprotein (AFP) is re-expressed. DEN-injected animals received an antigen-specific immunization with a synthetic vector consisting of a low dose of AFP-encoding plasmid formulated with the amphiphilic block copolymer 704 (DNAmAFP/704). Animals were treated at 4 and 5 months, before macroscopic nodules were detected, and were sacrificed at 8 months. The tumour burden, as well as liver histology, was assessed. AFP and MHC class I molecule expression in the nodules were monitored by qRT-PCR.

RESULTS

The AFP-specific immunotherapy led to a significant (65%) reduction in tumour size. The reduced expression of AFP and MHC class I molecules was measured in the remaining nodules taken from the DNAmAFP/704-treated group.

CONCLUSIONS

This is the first study demonstrating the relevance of antigen-specific immunotherapy in an autochthonous HCC model. In this context, we validated the use of an anti-tumour immunotherapy based on vaccination with nanoparticles consisting of low dose antigen-encoding DNA formulated with a block copolymer. Our results demonstrate the potential of this strategy as adjuvant immunotherapy to reduce the recurrence risk after local treatment of HCC patients.

Direct in vivo cell lineage analysis in the retrorsine and 2AAF models of liver injury after genetic labeling in adult and newborn rats

Backgrounds and Aims

When hepatocyte proliferation is impaired, liver regeneration proceeds from the division of non parenchymal hepatocyte progenitors. Oval cells and Small Hepatocyte-like Progenitor Cells (SHPCs) represent the two most studied examples of such epithelial cells with putative stem cell capacity. In the present study we wished to compare the origin of SHPCs proliferating after retrorsine administration to the one of oval cells observed after 2-Acetyl-Amino fluorene (2-AAF) treatment.

Methodology/Principal Findings

We used retroviral-mediated nlslacZ genetic labeling of dividing cells to study the fate of cells in the liver. Labeling was performed either in adult rats before treatment or in newborn animals. Labeled cells were identified and characterised by immunohistochemistry. In adult-labeled animals, labeling was restricted to mature hepatocytes. Retrorsine treatment did not modify the overall number of labeled cells in the liver whereas after 2-AAF administration unlabeled oval cells were recorded and the total number of labeled cells decreased significantly. When labeling was performed in newborn rats, results after retrorsine administration were identical to those obtained in adult-labeled rats. In contrast, in the 2-AAF regimen numerous labeled oval cells were present and were able to generate new labeled hepatocytes. Furthermore, we also observed labeled biliary tracts in 2-AAF treated rats.

Conclusions

Our results srongly suggest that SHPCs are derived from hepatocytes and we confirm that SHPCs and oval cells do not share the same origin. We also show that hepatic progenitors are labeled in newborn rats suggesting future directions for in vivo lineage studies.

EfficientIn VivoXenogeneic Retroviral Vector-Mediated Gene Transduction into Human Hepatocytes

We developed a method for efficient retroviral vector-mediated gene transfer into human hepatocytes, using a human hepatocyte-bearing mouse model. Normal human hepatocytes were transplanted into the livers of immunodeficient and liver-damaged mice. Donor hepatocytes multiplied and replaced the host hepatocytes, which yielded human hepatocyte-bearing mice (human hepatocyte-chimeric mice). As control cells, rat hepatocytes were similarly transplanted. The replacement level reached 86% at 8 weeks and 100% at 5 weeks posttransplantation of human and rat hepatocytes, respectively. Human and rat hepatocytes in the host liver showed a high bromodeoxyuridine-labeling index during the first 2 weeks posttransplantation. Human- and rat-chimeric mice were injected 7 and 10 days posttransplantation, respectively, with retroviral vectors carrying the beta-galactosidase gene and were thereafter injected daily for 20 and 10 days, respectively. The level of beta-galactosidase-positive hepatocytes in the human- and rat-chimeric mice reached 7.1 +/- 1.8% at 8 weeks and 5.3 +/- 0.9% at 5 weeks after transplantation, respectively. The human hepatocyte-chimeric mouse will be useful for testing the ability of vectors to transduce human cells.

Tolerance induction via a B-cell delivered gene therapy-based protocol: optimization and role of the Ig scaffold

Our previous studies indicated that antigen-specific tolerance could be achieved by the injection of LPS-activated B-cell blasts that were retrovirally gene-transferred with an IgG-antigen fusion construct. This system was shown to be effective for tolerance induction with a variety of inserted antigens ranging in size from a single peptide to a large multi-epitope protein in a variety of mouse strains. Moreover, it was shown to be effective in four animal models for human disease. To optimize the existing protocol, establish the role of the IgG H chain scaffold, and provide baseline for potential clinical applications, we examined the effects of different B-cell activators, including lipopolysaccharide (LPS), anti-CD40, CpG oligodeoxynucleotide (CpG-ODN), and anti-IgM plus IL-4, on B-cell proliferation, GFP transduction efficiency, and tolerance induction in vivo. The results show that all activators except CpG-ODN have similar effects on retroviral gene transfer and peptide-IgG-induced tolerance. Furthermore, dose-response analyses showed that T-cell tolerance could be induced with 10(5) peptide-IgG LPS B-cell blasts, but that 10(6) transduced B-cells were needed for humoral unresponsiveness. Transduced anti-IgM-induced blasts were tolerogenic at 10(6) cells, but no dose of transduced CpG blasts was tolerogenic. Finally, to examine the role of IgG scaffold, a retroviral construct encoding lambda repressor p1-102 and signal peptide of murine IgG heavy chain was engineered to allow secretion of the p1-102 domain in the same manner as that of p1-102-IgG fusion protein. The results demonstrate that not only is IgG scaffold important in tolerance induction and maintenance of the long-lasting immune hyporesponsiveness, but assembly of the IgG heterodimer may be required for the efficacy of this system.

Long term phenobarbital administration does not promote the multiplication of hepatocytes replicating after single cyproterone acetate administration

Cyproterone acetate (CPA) is a synthetic antiandrogenic compound which is widely used in clinic but suspected to be hepatocarcinogenic. CPA is also mitogenic in rat liver. Using genetic labeling of dividing cells, we examined whether hepatocytes dividing in response to acute CPA administration could give rise to preneoplastic foci after administration of a tumor promoter: phenobarbital. CPA was administered orally to rats and dividing hepatocytes were genetically labeled using retroviral vectors carrying the beta-galactosidase gene. After labeling rats were given phenobarbital for 10 months and sacrificed. The presence of beta-galactosidase labeled hepatocytes as well as preneoplastic hepatocytes was assessed by immunohistochemistry. Genetic labeling of hepatocytes was obtained in all animals. At the end of phenobarbital administration, no hepatic tumors were observed. Preneoplastic foci were not increased in treated animals as compared to control rats. Moreover beta-galactosidase positive hepatocytes were never detected in preneoplastic foci. Finally, the size of the beta-galactosidase positive clusters was smaller in treated animals as compared to control rats. We conclude that acute CPA administration is not carcinogenic in rat liver and does not initiate preneoplastic hepatocytes capable to give rise to foci after phenobarbital promotion. Therefore the mitogenic property of CPA is distinct from its putative carcinogenic activity. Finally, analysis of the size of beta-galactosidase positive cells clusters demonstrate that phenobarbital does not induce hepatocyte proliferation in rats.

Follistatin allows efficient retroviral-mediated gene transfer into rat liver

Retroviral vectors are widely used tools for gene therapy. However, in vivo gene transfer is only effective in dividing cells, which, in liver, requires a regenerative stimulus. Follistatin is effective in promoting liver regeneration after 90% and 70% hepatectomy in rats. We studied its efficacy on liver regeneration and retroviral-mediated gene delivery in 50% hepatectomized rats. When human recombinant follistatin was infused into the portal vein immediately after 50% hepatectomy, hepatocyte proliferation was significantly higher than in control 50% hepatectomized rats. A single injection of virus particles administered 23 h after follistatin infusion resulted in more than 20% gene transduction efficiency in hepatocytes compared to 3% in control rats. It is concluded that a single injection of follistatin induces onset of proliferation in 50% hepatectomized rats and allows efficient retroviral-mediated gene transfer to the liver.

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.

Mature hepatocytes are the source of small hepatocyte-like progenitor cells in the retrorsine model of liver injury

BACKGROUND/AIMS

Mature hepatocytes divide to restore liver mass after injury. However, when hepatocyte division is impaired by retrorsine poisoning, regeneration proceeds from another cell type: the small hepatocyte-like progenitor cells (SHPCs). Our aim was to test whether SHPCs could originate from mature hepatocytes.

METHODS

Mature hepatocytes were genetically labeled using retroviral vectors harboring the beta-galactosidase gene. After labeling, retrorsine was administered to rats followed by a partial hepatectomy to trigger regeneration. A liver biopsy was performed one month after surgery and rats were sacrificed one month later.

RESULTS

We observed the proliferation of small hepatocytes arranged in clusters in liver biopsies. These cells expressed Ki67 antigen and displayed a high mitotic index. At sacrifice, regeneration was completed and clusters had merged. A significant proportion of clusters also expressed beta-galactosidase demonstrating their origin from labeled mature hepatocytes. Finally, the overall proportion of beta-galactosidase positive cells was identical at the time of hepatectomy as well as in liver biopsy and at sacrifice.

CONCLUSIONS

The constant proportion of beta-galactosidase positive cells during the regeneration process demonstrates that mature hepatocytes are randomly recruited to proliferate and compensate parenchyma loss in this model. Furthermore, mature hepatocytes are the source of SHPC after retrorsine injury.

Specific targeted binding of herpes simplex virus type 1 to hepatocytes via the human hepatitis B virus preS1 peptide

To improve the utility of herpes simplex virus type 1 (HSV-1) vectors for gene therapy, the viral envelope needs to be manipulated to achieve cell-specific gene delivery. In this report, we have engineered an HSV-1 mutant virus, KgBpK(-) gC(-), deleted for the glycoprotein C (gC) and the heparan sulfate-binding domain (pK) of gB, in order to express gC:preS1 and gC:preS1 active peptide (preS1ap) fusion molecules. PreS1, and a 27 amino acid active peptide inside preS1 (preS1ap), are supposed to be the molecules that the human hepatitis B virus (HBV) needs to bind specifically to hepatocytes. Biochemical analysis demonstrated that the gC:preS1ap fusion molecule was expressed and incorporated into the envelope of the recombinant HSV-1 virus KgBpK(-)gC:preS1ap. Moreover, KgBpK(-)gC:preS1ap recombinant virus gained a specific binding activity to an hepatoblastoma cell line (HepG2) with a consequent productive infection. In addition, anti-preS1-specific antibodies were shown to neutralize recombinant virus infectivity, and a synthetic preS1ap peptide was able to elute KgBpK(-)gC:preS1ap virus bound on HpeG2 cells. These data provide further evidence that HSV-1 can productively infect cells through a specific binding to a non-HSV-1 receptor. Furthermore, these data strongly support the hypothesis that the HBV preS1ap molecule is an HBV ligand to hepatocytes.