Transduction of primary human hepatocytes with amphotropic and xenotropic retroviral vectors

Effective Cryopreservation and Long-Term Storage of Primary Human Hepatocytes with Recovery of Viability, Differentiation, and Replicative Potential

Despite reports of successful cryopreservation of primary human hepatocytes, existing methods do not produce sufficient recovery of viable cells to meet the needs of basic research or clinical trials of hepatocellular transplantation. We now describe a protocol for efficient cryopreservation of primary human hepatocytes using University of Wisconsin (UW) solution, fetal bovine serum, and dimethyl sulfoxide (DMSO). This method provides >90% viability of differentiated, primary human hepatocytes 8 mo after cryopreservation as measured by trypan blue exclusion, preserves hepatocyte morphology, liver-specific gene expression α1 antitrypsin), and replication. The effectiveness of UW solution as a cryopreservative agent suggests that metabolic as well as ultrastructural factors may be important in the effective cryopreservation of primary human hepatocytes. The present method represents an effective protocol for cryopreserving differentiated primary human hepatocytes for research. This method may allow characterization and banking of human hepatocytes for clinical applications, including hepatocellular transplantation and hepatic assist devices.

Porcine hepatocyte isolation and reversible immortalization mediated by retroviral transfer and site-specific recombination

AIM: To develop a hepatocyte cell line, we immortalized primary porcine hepatocytes with a retroviral vector SSR#69 containing the Simian Virus 40 T antigen (SV40Tag).

METHODS: We first established a method of porcine hepatocyte isolation with a modified four-step retrograde perfusion technique. Then the porcine hepatocytes were immortalized with retroviral vector SSR#69 expressing SV40T and hygromycin-resistance genes flanked by paired loxP recombination targets. SV40T cDNA in the expanded cells was subsequently excised by Cre/LoxP site-specific recombination.

RESULTS: The resultant hepatocytes with high viability (97%) were successfully immortalized with retroviral vector SSR#69. One of the immortalized clones showed the typical morphological appearance, TJPH-1, and was selected by clone rings and expanded in culture. After excision of the SV40T gene with Cre-recombinase, cells stopped growing. The population of reverted cells exhibited the characteristics of differentiated hepatocytes.

CONCLUSION: In conclusion, we herein describe a modified method of hepatocyte isolation and subsequently established a porcine hepatocyte cell line mediated by retroviral transfer and site-specific recombination.

In vivo expression of human ATP:cob(I)alamin adenosyltransferase (ATR) using recombinant adeno-associated virus (rAAV) serotypes 2 and 8

BACKGROUND

Methylmalonic aciduria (MMA) is an autosomal recessive disease with symptoms that include ketoacidosis, lethargy, recurrent vomiting, dehydration, respiratory distress, muscular hypotonia and death due to methylmalonic acid levels that are up to 1000-fold greater than normal. CblB MMA, a subset of the mutations leading to MMA, is caused by a deficiency in the enzyme cob(I)alamin adenosyltransferase (ATR). No animal model currently exists for this disease. ATR functions within the mitochondria matrix in the final conversion of cobalamin into coenzyme B(12), adenosylcobalamin (AdoCbl). AdoCbl is a required coenzyme for the mitochondrial enzyme methylmalonyl-CoA mutase (MCM).

METHODS

The human ATR cDNA was cloned into a recombinant adeno-associated virus (rAAV) vector and packaged into AAV 2 or 8 capsids and delivered by portal vein injection to C57/Bl6 mice at a dose of 1 x 10(10) and 1 x 10(11) particles. Eight weeks post-injection RNA, genomic DNA and protein were then extracted and analyzed.

RESULTS

Using primer pairs specific to the cytomegalovirus (CMV) enhancer/chicken beta-actin (CBAT) promoter within the rAAV vectors, genome copy numbers were found to be 0.03, 2.03 and 0.10 per cell in liver for the rAAV8 low dose, rAAV8 high dose and rAAV2 high dose, respectively. Western blotting performed on mitochondrial protein extracts demonstrated protein levels were comparable to control levels in the rAAV8 low dose and rAAV2 high dose animals and 3- to 5-fold higher than control levels were observed in high dose animals. Immunostaining demonstrated enhanced transduction efficiency of hepatocytes to over 40% in the rAAV8 high dose animals, compared to 9% and 5% transduction in rAAV2 high dose and rAAV8 low dose animals, respectively.

CONCLUSIONS

These data demonstrate the feasibility of efficient ATR gene transfer to the liver as a prelude to future gene therapy experiments.

Enhanced gene delivery in vitro and in vivo by improved transferrin-lipoplexes

Cationic liposomes and the complexes they form with DNA (lipoplexes) constitute the most promising alternative to the use of viral vectors for gene therapy. One of the limitations to their application in vivo, however, is the inhibition of gene delivery by serum. In a previous study, we demonstrated that transferrin (Tf)-lipoplexes were superior to plain lipoplexes in transfecting HeLa cells in the presence of high concentrations of serum. With the goal of obtaining efficient gene expression in vivo, we evaluated the efficacy of Tf-lipoplexes (containing DOTAP and cholesterol) in transfecting primary hepatocytes and adipocytes in the presence of high serum concentrations. The association of transferrin with cationic liposomes increased luciferase expression compared to plain lipoplexes in primary cells as well as in HepG2 and 3T3-L1 differentiated adipocytes. The complexes were not cytotoxic and were highly effective in protecting DNA from attack by DNase I. An efficient and reliable method was developed to prepare lipoplexes containing both Tf and protamine sulfate, where the latter was mixed with transferrin, followed by the addition of cationic liposomes and DNA. The resulting protamine-Tf-lipoplexes increased significantly the levels of gene expression in cultured cells and in various tissues in mice following i.v. administration.

Induction of three-dimensional assembly of human liver cells by simulated microgravity

The establishment of long-term cultures of functional primary human liver cells (PHLC) is formidable. Developed at NASA, the Rotary Cell Culture System (RCCS) allows the creation of the unique microgravity environment of low shear force, high-mass transfer, and 3-dimensional cell culture of dissimilar cell types. The aim of our study was to establish long-term hepatocyte cultures in simulated microgravity. PHLC were harvested from human livers by collagenase perfusion and were cultured in RCCS. PHLC aggregates were readily formed and increased up to 1 cm long. The expansion of PHLC in bioreactors was further evaluated with microcarriers and biodegradable scaffolds. While microcarriers were not conducive to formation of spheroids, PHLC cultured with biodegradable scaffolds formed aggregates up to 3 cm long. Analyses of PHLC spheroids revealed tissue-like structures composed of hepatocytes, biliary epithelial cells, and/or progenitor liver cells that were arranged as bile duct-like structures along nascent vascular sprouts. Electron microscopy revealed groups of cohesive hepatocytes surrounded by complex stromal structures and reticulin fibers, bile canaliculi with multiple microvilli, and tight cellular junctions. Albumin mRNA was expressed throughout the 60-d culture. A simulated microgravity environment is conducive to maintaining long-term cultures of functional hepatocytes. This model system will assist in developing improved protocols for autologous hepatocyte transplantation, gene therapy, and liver assist devices, and facilitate studies of liver regeneration and cell-to-cell interactions that occur in vivo.

Receptors for polytropic and xenotropic mouse leukaemia viruses encoded by a single gene at Rmc1

The onset of leukaemia caused by type C retroviruses (MLV) in mice is accelerated by the emergence of recombinant polytropic or mink cell focus-forming (MCF) viruses. Susceptibility to infection by polytropic/MCF and also by closely related xenotropic MLV has been mapped to Rmc1 on mouse chromosome 1 (refs 5-7). To identify this gene, we introduced an expression cDNA library prepared from mouse NIH3T3 fibroblasts into nonpermissive hamster cells and screened these cells for acquired susceptibility to MCF viruses encoding beta-galactosidase and G418 resistance. From hamster cell clones identified in the screen, we recovered a mouse cDNA that maps to Rmc1 and confers MCF MLV infection when expressed in nonpermissive cell lines. It encodes a membrane protein related to Syg1p (suppressor of yeast G alpha deletion; ref. 8). The receptor-binding domain of the MCF MLV envelope protein binds specifically to Xenopus laevis oocytes that express mouse Syg1, suggesting it functions as a receptor that mediates virus entry. We also obtained the cDNA encoding human SYG1. When expressed in hamster cells, it establishes infectivity by MCF MLV as well as xenotropic MLV, which do not infect laboratory mice.

Efficient pseudotyping of murine leukemia virus particles with chimeric human foamy virus envelope proteins

Incorporation of human foamy virus (HFV) envelope proteins into murine leukemia virus (MuLV) particles was studied in a transient transfection packaging cell system. We report here that wild-type HFV envelope protein can pseudotype MuLV particles, albeit at low efficiency. Complete or partial removal of the HFV cytoplasmic tail resulted in an abolishment or reduction of HFV-mediated infectivity, implicating a role of the HFV envelope cytoplasmic tail in the pseudotyping of MuLV particles. Mutation of the endoplasmic reticulum retention signal present in the HFV envelope cytoplasmic tail did not result in a higher relative infectivity of pseudotyped retroviral vectors. However, a chimeric envelope protein, containing an unprocessed MuLV envelope cytoplasmic domain fused to a truncated HFV envelope protein, showed an enhanced HFV specific infectivity as a result of an increased incorporation of chimeric envelope proteins into MuLV particles.

Myoblast gene therapy in canine mucopolysaccharidosis. I: Abrogation by an immune response to alpha-L-iduronidase

Three dogs with deficiency of the lysosomal enzyme alpha-L-iduronidase were treated by gene replacement therapy targeted at muscle. Direct intramuscular injections of plasmid encoding the alpha-L-iduronidase gene cDNA resulted in no detectable enzyme production, but may have resulted in immunologic sensitization to iduronidase protein, which the dogs lack totally. Myoblasts were grown from skeletal muscle biopsies and transduced with a retroviral vector containing the canine gene under control of the muscle creatine kinase enhancer. Several hundred-fold overexpression of enzyme production occurred in cultured cells; however, following reintroduction of the cultured cells into dogs, enzyme production declined rapidly. Concurrent with the falling enzyme levels, there was production of specific immunoglobulin G (IgG) antibody against iduronidase that was further associated with cellular infiltration of the myoblast injection sites. Most inflammatory cells were lymphocytes and plasma cells, suggesting local humoral and cellular immune responses to the enzyme-producing muscle cells. PCR analysis of tissues collected 2-22 weeks after the final treatment showed the persistence of Neo and canine alpha-L-iduronidase sequences in a progressively decreasing percentage of myoblasts. Results from this study in a canine model of mucopolysaccharidosis I underscore the fact that immunologic reactions to cells producing desirable, normal, but foreign, proteins may be as much an impediment to gene therapy as reactions to the viral vectors used to introduce the foreign gene.

Human gene therapy in gastrointestinal diseases: in vivo and in vitro approaches

The first clinical trial in human gene therapy began in 1989 with the successful introduction of marker genes into peripheral blood cells as tumor-infiltrating lymphocytes (TIL) in order to investigate the biological behavior of manipulated cells in humans. In further studies, it was possible to ameliorate clinical genetic diseases based on only one single genetic defect such as adenosine deaminase deficiency (ADA) by repeated infusion of manipulated peripheral blood cells. Meanwhile, a multitude of clinical gene transfer studies were initiated. Three main strategies have thus far been applied in human cancer gene therapy: (1) Reinforcement of the body's immune response by gene transfer into immunological cells; (2) reinforcement of the immune response by manipulating tumor cells; and (3) transfer of drug-sensitive genes into tumor cells with subsequent drug treatment. The first clinical trial in gene therapy for gastrointestinal diseases was performed in 1992 with the introduction of the low-density protein receptor gene (LDL) into liver tissue. Human cancer gene therapy of gastrointestinal diseases is still only in the initial phase of research.

A pilot study of ex vivo gene therapy for homozygous familial hypercholesterolaemia

The outcome of the first pilot study of liver-directed gene therapy is reported here. Five patients with homozygous familial hypercholesterolaemia (FH) ranging in age from 7 to 41 years were enrolled; each patient tolerated the procedure well without significant complications. Transgene expression was detected in a limited number of hepatocytes of liver tissue harvested four months after gene transfer from all five patients. Significant and prolonged reductions in low density lipoprotein (LDL) cholesterol were demonstrated in three of five patients; in vivo LDL catabolism was increased 53% following gene therapy in a receptor negative patient, who realized a reduction in serum LDL equal to approximately 150 mg dl-1. This study demonstrates the feasibility of engrafting limited numbers of retrovirus-transduced hepatocytes without morbidity and achieving persistent gene expression lasting at least four months after gene therapy. The variable metabolic responses observed following low-level genetic reconstitution in the five patients studied precludes a broader application of liver-directed gene therapy without modifications that consistently effect substantially greater gene transfer.

Infection by retroviral vectors outside of their host range in the presence of replication-defective adenovirus

Retrovirus infection is normally limited to cells within a specific host range which express a cognate receptor that is recognized by the product of the env gene. We describe retrovirus infection of cells outside of their normal host range when the infection is performed in the presence of a replication-defective adenovirus (dl312). In the presence of adenovirus, several different ecotropic vectors are shown to infect human cell lines (HeLa and PLC/PRF), and a xenotropic vector is shown to infect murine cells (NIH 3T3). Infectivity is demonstrated by 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal) staining, selection with G418 for neomycin resistance, and PCR identification of the provirus in infected cells. Infectivity is quantitatively dependent upon both the concentration of adenovirus (10(6) to 10(8) PFU/ml) and the concentration of retrovirus. Infection requires the simultaneous presence of adenovirus in the retrovirus infection medium and is not stimulated by preincubation and removal of adenovirus from the cells before retrovirus infection. The presence of adenovirus is shown to enhance the uptake of fluorescently labeled retrovirus particles into cells outside of their normal host range, demonstrating that the adenovirus enhances viral entry into cells in the absence of the recognized cognate receptor. This observation suggests new opportunities for developing safe retroviral vectors for gene therapy and new mechanisms for the pathogenesis of retroviral disease.

Efficient retroviral-mediated gene transfer into primary culture of murine and human hepatocytes: expression of the LDL receptor

The ex vivo approach to hepatic gene therapy involves several steps, which include the isolation and culture of hepatocytes, followed by their transduction with a retrovirus. Subsequently, autologous hepatocytes are transplanted. The number of hepatocytes that can be transduced by retroviruses bearing the therapeutic gene is one of the limiting steps that can impair the success of this strategy. We presently describe an experimental approach that leads to improved transduction efficiency in mouse and human hepatocytes in vitro. By using a recombinant retrovirus bearing the Escherichia coli beta-galactosidase gene, we show that addition of growth factors to the cells, namely human hepatocyte growth factor (HGF), allows marked increase in the transduction efficiency in mouse (up to 80%) and human (40%) hepatocytes. Familial hypercholesterolemia (FH) is due to mutation in the low-density lipoprotein (LDL) receptor gene and results in a deficiency in LDL receptors. Transduction of the human LDL receptor cDNA under the transcriptional control of the L-type pyruvate kinase promoter-activator into mouse hepatocytes led to an elevated tissue-specific expression of the human protein. These results suggest that the ex vivo approach remains a promising alternative for hepatic gene therapy.

A general method for the generation of high-titer, pantropic retroviral vectors: highly efficient infection of primary hepatocytes

Retroviral vectors have been central components in many studies leading to human gene therapy. However, the generally low titers and inefficient infectivity of retroviral vectors in human cells have limited their use. We previously reported that the G protein of vesicular stomatitis virus can serve as the exclusive envelope protein component for one specific retroviral vector, LGRNL, that expresses vesicular stomatitis virus G. We now report a more useful general transient transfection scheme for producing very high-titer vesicular stomatitis virus G-enveloped pseudotypes from any Moloney murine leukemia-based retroviral vector without having to rely on the expression of the cytotoxic G protein from the retroviral vector itself. We also demonstrate very high efficiency of infection with a pseudotyped lacZ vector in primary mouse hepatocytes. We suggest that pseudotyped retroviral vectors carrying reporter genes will permit genetic studies in many previously inaccessible vertebrate and invertebrate systems. Furthermore, because these vectors represent retroviral vectors of sufficiently high titer to allow efficient direct retroviral-mediated in vivo gene transfer, we also suggest that pseudotyped vectors carrying potentially therapeutic genes will become useful to test the potential for in vivo gene therapy.

Retroviral delivery of DNA into the livers of transgenic mice bearing premalignant and malignant hepatocellular carcinomas

To develop gene therapy for hepatocellular carcinoma (HCC), we infused mice through the portal vein with retrovirus carrying the Escherichia coli beta-galactosidase reporter gene under the transcriptional control of the viral long terminal repeat (LTR) and the promoter from the mouse multidrug resistance gene mdr1b. Two transgenic mouse HCC models were used, one bearing the human hepatitis B viral envelope protein and the other SV40 T antigen. These animals develop HCC with predictable pathological manifestations. The viral transduction efficiency appeared to depend upon the stage of the disease in the animals. The most efficient transduction occurred when the livers had developed microscopic nodular hyperplasia; in some cases as many as 0.01-0.1 copies/cell were transduced. The transduction efficiency was lower in the late stage of the disease when livers had a heavy tumor burden and in the early stage when no lesion was evident. Low viral transduction efficacy was also seen in nontransgenic animals but was significantly increased by partial hepatectomy. The expression of the reporter gene in these animals was very low, as determined by histological staining. These results suggest that hepatocarcinogenesis can enhance retroviral delivery of foreign genes into the liver. Further development by increasing the viral transducing efficiency and the level of expression of transduced gene is required.

Factors influencing retroviral-mediated gene transfer into hepatocytes in vivo

Direct gene transfer into hepatocytes represents an attractive alternative to organ transplantation for the treatment of genetic liver diseases. This approach is hampered either by the difficulty to obtain, cultivate, and reimplant hepatocytes or by the poor stability of the expression of the transgene. In the present report, we show that direct in vivo infection of hepatocytes with a retroviral vector following partial hepatectomy results in a life-long expression of the transgene in adult rats and mice. We demonstrate that the kinetics of hepatocyte susceptibility to infection is closely associated with the kinetics of cell division. We also present evidence that a complete vascular exclusion of the organ allows better gene transfer as compared to simple portal infusion of the viral particles, presumably through a higher volume of retrovirus-containing medium delivered to the liver.

Generation of high-titer pseudotyped retroviral vectors with very broad host range

Encapsidation of the VSV G protein into the virions of MoMLV-derived retroviral vectors in the absence of other VSV-encoded proteins is shown to be an efficient process, although the exact mechanism for this process is currently unclear. Unlike the conventional retroviral vectors bearing the amphotropic envelope protein, the pseudotyped virus has the ability to withstand the shearing forces encountered during ultracentrifugation. This property of the pseudotyped virus enables the generation of high-titer retroviral vector stocks and has potential application for in vivo gene therapy studies. We have found as many as four copies of a pseudotyped vector to integrate into the genome of a single cell when a high multiplicity of infection was used to infect the cells. Multiple integration events were not observed with amphotropic retroviral vectors, probably because of their low virus titers. In addition, when retroviral vectors are pseudotyped with the VSV G protein, they acquire the host range of VSV and are able to infect nonmammalian cells derived from fish, Xenopus, mosquito, and Lepidoptera. Since techniques for efficient gene transfer in some of these nonmammalian systems are not currently available, retrovirus-mediated gene transfer described here should be useful for transgenic and other genetic studies in lower vertebrate species. The inability to establish a stable cell line expressing the VSV G protein, however, limits large-scale production of the pseudotyped retroviral vectors. Generation of stable packaging cell lines for the pseudotyped retroviral vectors is a major challenge for the future.

Circumvention of chemotherapy-induced myelosuppression by transfer of the mdr1 gene

Drug-induced myelosuppression is a frequent reason for curtailing chemotherapy in cancer patients. 'Rescue' of myelosuppressed patients with autologous marrow transplants is reasonably advanced and permits an increase in the dose of anticancer drugs. Despite this improvement, patients often relapse with drug resistance disease. The human multidrug resistance (mdr1) gene might make it possible to render hemopoietic stem cells resistant to anticancer drugs after transfer of this gene. By introducing resistant stem cells into patients it might be possible to treat these patients repeatedly with otherwise ablative therapy. This review explores the feasibility of mdr1 gene therapy.

Retrovirus-mediated gene transfer into canine thyroid using an ex vivo strategy

We describe studies in a canine model aimed at establishing methods for ex vivo gene delivery to thyroid follicular cells. Canine follicular cells were harvested from tissue obtained by unilateral lobectomy, grown in thyrotropin-containing media, and transduced with amphotropic retroviral vectors carrying Escherichia coli beta-galactosidase or Tn7 neomycin-resistance genes. Up to 30% of cells were transduced with retroviral vectors containing the neomycin resistance gene, and transduced cells could be selected with G418. Significantly, transduced and selected cells exhibited the morphology of thyroid follicular cells and continued to express thyroglobulin. To assess the viability of cultivated and transduced cells for transplantation, cells were stained with the vital fluorescent dye DiI, recovered by trypsinization, and transplanted into the contralateral thyroid lobe of autologous animals. Engraftment was demonstrated by fluorescence microscopy and identification of proviral sequences 7-10 days after transplantation. Proviral transcripts were evident using coupled reverse transcription and the polymerase chain reaction using total RNA from transplanted glands. Thyroid follicular cells may represent an attractive target for gene therapy due to their proliferative potential, their large protein synthetic and secretory capacity, and their susceptibility to regulation. The thyroid might be a target for therapy of congenital or acquired thyroid diseases as well as disorders requiring regulated expression of proteins in the circulation. This work demonstrates the feasibility of ex vivo gene delivery to thyroid follicular cells that may be used in future investigations.

Correction of methylmalonyl-CoA mutase deficiency inMut o fibroblasts and constitution of gene expression in primary human hepatocytes by retroviral-mediated gene transfer

Methylmalonic acidemia is an often fatal inborn error of organic acid metabolism due to deficiency of methylmalonyl-CoA mutase. The cloning of genes encoding this enzyme and the advent of technologies for gene transfer have introduced the possibility of somatic gene therapy for this disorder. Gene therapy may require replacement of the defective enzyme in hepatocytes, which have a greater capacity for propionate metabolism than other somatic cells and represent the principle physiological site of propionate metabolism. We describe construction of an amphotropic retroviral vector containing the human methylmalonyl-CoA mutase cDNA. This vector is shown to transduce primary MCM-deficient fibroblasts and restore levels of [14C]propionate metabolism by cultures of nonselected cells to normal. This vector will transduce primary human hepatocytes and direct transcription of recombinant human MCM from the integrated provirus. This work demonstrates the feasibility of retroviral-mediated gene transfer of methylmalonyl-CoA mutase into primary human cells, including hepatocytes which represent a difficult, but potentially necessary, target for gene therapy of methylmalonic acidemia.