Therapeutic serum concentrations of human alpha-1-antitrypsin after adenoviral-mediated gene transfer into mouse hepatocytes

Alpha-1-antitrypsin is a relatively common genetic deficiency that results in early emphysema. The liver as the natural source of most alpha-1-antitrypsin synthesis was the target organ selected for gene replacement therapy studies. Previous work used recombinant retroviral vectors that encode the human alpha-1-antitrypsin cDNA for ex vivo and direct in vivo transduction of hepatocytes in dogs and rodents. This approach led to low levels of human protein in the serum of recipients. In this study, recombinant adenoviral vectors that express the human alpha-1-antitrypsin cDNA under the transcriptional control of the phosphoglycerate kinase (PGK) or RSV-LTR promoters have been constructed and used for the direct transduction of mouse hepatocytes in vivo. The animals transduced with the recombinant adenoviral vectors had therapeutic serum levels of human alpha-1-antitrypsin of up to 700 micrograms/mL. Thus, adenovirus-mediated gene transfer of the hAAT cDNA into the liver was able to produce therapeutic serum concentrations of protein.

In vivo hepatic gene therapy: complete albeit transient correction of factor IX deficiency in hemophilia B dogs

Hemophilia B is a bleeding disorder caused by mutations in the factor IX gene. The disorder is X-linked recessive with a prevalence of about 1 in 30,000 Caucasian males. Factor IX is naturally synthesized in the liver and secreted into blood. Here we report the construction of recombinant adenoviral vectors containing the canine factor IX cDNA that are capable of transducing hepatocytes in mice at high efficiencies in vivo without partial hepatectomy. The recombinant viral vector was used to treat hemophilia B dogs by direct vector infusion into the portal vasculature of deficient animals. Plasma factor IX concentrations in the treated hemophilia B dogs increased from 0 to 300% of the level present in normal dogs, resulting in complete amelioration of the disease as demonstrated by normal blood coagulation and hemostatic measurements. Although plasma factor IX concentration started to decline after a few days, therapeutic levels of factor IX persisted for 1-2 months in the treated animals. The results validate the principle of in vivo hepatic gene delivery to reconstitute the genetic deficiency in a large animal model and suggest that gene therapy is achievable when long-acting vectors are developed.

In vivo gene therapy of hemophilia B: sustained partial correction in factor IX-deficient dogs

The liver represents a model organ for gene therapy. A method has been developed for hepatic gene transfer in vivo by the direct infusion of recombinant retroviral vectors into the portal vasculature, which results in the persistent expression of exogenous genes. To determine if these technologies are applicable for the treatment of hemophilia B patients, preclinical efficacy studies were done in a hemophilia B dog model. When the canine factor IX complementary DNA was transduced directly into the hepatocytes of affected dogs in vivo, the animals constitutively expressed low levels of canine factor IX for more than 5 months. Persistent expression of the clotting factor resulted in reductions of whole blood clotting and partial thromboplastin times of the treated animals. Thus, long-term treatment of hemophilia B patients may be feasible by direct hepatic gene therapy in vivo.

Hepatic gene therapy: persistent expression of human alpha 1-antitrypsin in mice after direct gene delivery in vivo

The liver represents an excellent target organ for gene therapy. The current strategy for hepatic gene therapy involves the isolation of primary hepatocytes from a resected liver lobe, transduction of therapeutic genes in vitro followed by autologous hepatocellular transplantation. This ex vivo approach is a rather complex procedure in its entirety; thus, a simple method for direct gene delivery into hepatocytes in vivo has been developed. The procedure involves partial hepatectomy followed by the portal vein infusion of recombinant retroviral vectors. Histological analysis of hepatocytes after in vivo delivery of a recombinant retrovirus bearing the E. coli beta-galactosidase gene showed that 1-2% of the parenchymal cells were transduced. Direct hepatic transfer of human alpha 1-antitrypsin cDNA under the transcriptional direction of the albumin promoter-enhancer led to constitutive expression of the human protein in the sera of recipients at concentrations of 30-1,400 ng/ml for at least 6 months. The experimental animals showed no signs of illness and histologic analysis of the liver revealed no evidence of pathologic abnormalities. The results suggest that the in vivo approach is an attractive alternative for hepatic gene therapy.

Expression of human alpha 1-antitrypsin in dogs after autologous transplantation of retroviral transduced hepatocytes

The liver represents an excellent organ for gene therapy since many genetic disorders result from the deficiency of liver-specific gene products. We have previously demonstrated that transgenic mouse hepatocytes can be heterologously transplanted into congenic recipients where they survived indefinitely and continued to function as hepatocytes. Here we demonstrate the autologous transplantation of retrovirally transduced canine hepatocytes. At least 1 x 10(9) hepatocytes or 5% of the liver mass can be transplanted by the portal vasculature. In two animals we have transplanted hepatocytes transduced with a retroviral vector containing the human alpha 1-antitrypsin cDNA under transcriptional control of the cytomegalovirus promoter. Both animals had significant human alpha 1-antitrypsin in the serum for 1 month. Although the serum levels of human alpha 1-antitrypsin eventually fell due to inactivation of the cytomegalovirus promoter, PCR analysis demonstrated that a significant fraction of transduced hepatocytes migrated to the liver and continued to survive in vivo. The results suggest that gene therapy of hepatic deficiencies may be achieved by hepatocellular transplantation after genetic reconstitution with the use of promoters of cellular genes that are active in the normal liver.

Mouse hepatocytes migrate to liver parenchyma and function indefinitely after intrasplenic transplantation

One approach to gene therapy for hepatic diseases is to remove hepatocytes from an affected individual, genetically alter them in vitro, and reimplant them into a receptive locus. Although returning hepatocytes to the liver itself would be advantageous, the feasibility of this approach has never been evaluated due to the inability to distinguish donor from host hepatocytes. To unambiguously identify transplanted hepatocytes after transplantation, and to better quantitate their number and degree of liver function, two transgenic mouse lines were generated in a C57BL/6 background. The first expresses the Escherichia coli beta-galactosidase gene from the relatively liver-specific human alpha 1-antitrypsin (hAAT) promoter and allows transgenic hepatocytes to be readily identified after 5-bromo-4-chloro-3-indolyl beta-D-galactoside staining; the second produces the hAAT protein under control of the same promoter, which enables hepatocyte survival and maintenance of liver function to be quantitated by measuring the serum levels of hAAT. Hepatocytes isolated from transgenic donors were transplanted into nontransgenic C57BL/6 recipients by intrasplenic injection. Surprisingly, a large fraction of these cells were identified within the liver parenchyma but not the spleen at 2 months after transplantation. The high levels of serum hAAT detected in transplant recipients were stable for greater than 6 months, suggesting that established cells will survive indefinitely. These results have important implications for liver organogenesis and hepatic gene therapy.

Inhibition of experimental metastasis and extracellular matrix degradation by butanol extracts from B16-F1 murine melanoma

We previously demonstrated that noncytolytic butanol extraction of B16 melanoma cells can increase the number of experimental lung metastases, and that brief incubation of the extracted cells with the extracted moieties reduces metastatic phenotype. This study examined the possibility that the extracted components are endogenous inhibitors of tumor cell surface-associated, degradative enzymes. The activity was found to be tumor associated, since only tumor extracts could reduce the number of experimental lung metastases of a variety of solid tumors. The activity in crude butanol extracts of B16-F1 that modulated the metastatic phenotype of extracted B16-F10 was partially purified by preparative isoelectric focusing and high-performance gel permeation chromatography. Incubation of extracted B16-F10 cells with low (Mr 2,000-10,000) molecular weight materials focusing in the pH 5.6 to 5.8 region of the preparative isoelectric focusing gradient significantly reduced the number of experimental lung foci. Ampholines alone had no effect. Evidence that the extracted moiety might be an endogenous enzyme inhibitor was obtained with the use of the subendothelial matrix degradation assay, wherein B16-F10 cells digest 35S-labeled heparan sulfate proteoglycan. The same materials that reduced the metastatic potential of butanol-extracted B16-F10 cells also inhibited extracellular matrix degradation by 30 to 85%, as well as the activity of partially purified heparanase (endo-beta-glucuronidase). The metalloproteinase inhibitor 1,10-phenanthroline and the heparanase inhibitor heparin partially (30 to 50%) blocked extracellular matrix degradation. Conversely, inhibitors of serine, thiol, acid, and other proteases had little or no effect on extracellular matrix degradation. These data provide evidence that an endogenous, heat-stable inhibitor of cell surface degradative enzymes such as heparanase may play a role in hematogenous metastasis, and support the hypothesis that butanol extraction activates some of these surface enzymes by removing the endogenous inhibitors.