Factors influencing immune response after in vivo retrovirus-mediated gene transfer to the liver

Application of Flow Cytometry in the Evaluation of Primary Immunodeficiencies

Primary immunodeficiency disorders (PIDDs) are a heterogeneous group of inherited disorders of the immune system. Currently more than 250 different PIDDs with a known genetic defect have been recognized. The diagnosis of many of these disorders is supported strongly by a wide variety of flow cytometry applications. Flow cytometry offers a rapid and sensitive tool for diagnosis and classification of PIDDs. It is applicable in the initial workup and subsequent management of several primary immunodeficiency diseases. As our understanding of the pathogenesis and management of these diseases increases, the majority of these tests can be easily established in the diagnostic laboratory. Thus, the focus of this article is on the application of flow cytometry in the diagnosis and/or evaluation of PIDDs.

Lentiviral vectors that express UGT1A1 in liver and contain miR-142 target sequences normalize hyperbilirubinemia in Gunn rats

BACKGROUND & AIMS

Crigler-Najjar type 1 (CN-I) is an inherited liver disease caused by an absence of bilirubin-uridine 5'-diphosphate-glucuronosyltransferase (UGT1A1) activity. It results in life-threatening levels of unconjugated bilirubin, and therapeutic options are limited. We used adult Gunn rats (an animal model of the disease) to evaluate the efficiency of lentiviral-based gene therapy to express UGT1A1 in liver.

METHODS

Gunn rats were given intraportal injections of VSVG-pseudotyped lentiviral vectors that encode UGT1A1 under the control of a liver-specific transthyretin promoter (mTTR.hUGT1A1); this vector does not contain target sequences for miR-142, a microRNA that is expressed specifically in hematopoietic cells. Rats were also injected with the vector mTTR.hUGT1A1.142T, which contains 4 copies of the miR-142 target sequences; its messenger RNA should be degraded in antigen-presenting cells. Bilirubinemia was monitored, and the presence of transduced hepatocytes was analyzed by quantitative polymerase chain reaction. Vector expression was tested in vitro in rat hematopoietic cells.

RESULTS

In Gunn rats, bilirubin levels normalized 2 weeks after administration of mTTR.hUGT1A1. However, hyperbilirubinemia resumed 8 weeks after vector administration, concomitant with the induction of an immune response. In contrast, in rats injected with mTTR-UGT1A1.142T, bilirubin levels normalized for up to 6 months and transduced cells were not eliminated.

CONCLUSIONS

Lentiviral vectors that express UGT1A1 reduce hyperbilirubinemia in immunocompetent Gunn rats for at least 6 months. The immune response against virally expressed UGT1A1 can be circumvented by inclusion of miR-142 target sequences, which reduce vector expression in antigen-presenting cells. This lentiviral-based gene therapy approach might be developed to treat patients with CN-I.

Long-term correction of diabetes in rats after lentiviral hepatic insulin gene therapy

AIMS/HYPOTHESIS

Type 1 diabetes results from the autoimmune destruction of pancreatic beta cells. Exogenous insulin therapy cannot achieve precise physiological control of blood glucose concentrations, and debilitating complications develop. Lentiviral vectors are promising tools for liver-directed gene therapy. However, to date, transduction rates in vivo remain low in hepatocytes, without the induction of cell cycling. We investigated long-term transgene expression in quiescent hepatocytes in vitro and determined whether the lentiviral delivery of furin-cleavable insulin to the liver could reverse diabetes in rats.

MATERIALS AND METHODS

To improve transduction efficiency in vitro, we optimised hepatocyte isolation and maintenance protocols and, using an improved surgical delivery method, delivered furin-cleavable insulin alone or empty vector to the livers of streptozotocin-induced diabetic rats by means of a lentiviral vector. Rats were monitored for changes in body weight and blood glucose, and intravenous glucose tolerance tests were performed. Expression of insulin was determined by RT-PCR, immunohistochemistry and electron microscopy.

RESULTS

We achieved long-term transgene expression in quiescent hepatocytes in vitro (87 +/- 1.2% transduction efficiency), with up to 60 +/- 3.2% transduction in vivo. We normalised blood glucose for 500 days-a significantly longer period than previously reported-making this the first successful study using a lentiviral vector. This procedure resulted in the expression of genes encoding several beta cell transcription factors, some pancreatic endocrine transdifferentiation, hepatic insulin storage in granules, and restoration of glucose tolerance. Liver function tests remained normal. Importantly, pancreatic exocrine transdifferentiation did not occur.

CONCLUSIONS/INTERPRETATION

Our data suggest that this regimen may ultimately be employed for the treatment of type 1 diabetes.

Entecavir: a new nucleoside analog for the treatment of chronic hepatitis B infection

BACKGROUND

Chronic hepatitis B infection carries considerable risk for the development of cirrhosis and hepatocellular carcinoma. Treatment options are increasing but are limited to interferon alfa-2b, pegylated interferon alfa-2a, lamivudine, adefovir dipivoxil, and entecavir. Entecavir, a nucleoside analog, is the newest oral antiviral approved in the United States for treatment of chronic hepatitis B.

OBJECTIVE

To review the available data for entecavir regarding its pharmacology, pharmacokinetics, safety, efficacy, and clinical use.

METHODS

A MEDLINE, EMBASE, and Cochrane search of the English-language literature from January 1997-May 2006 was performed. Preapproval studies provided by the manufacturer and abstracts from recent scientific meetings on infectious disease and hepatology were also reviewed.

RESULTS

Three phase III clinical trials representing more than 1600 subjects established the superior efficacy and equivalent safety of entecavir compared with lamivudine for treating patients who are hepatitis B early antigen (HBeAg) positive, HBeAg negative, or refractory to lamivudine. Entecavir resistance has not occurred in nucleoside-naïve patients but may develop in those who already possess lamivudine resistance mutations.

CONCLUSION

Trial results, along with previously published response rates for adefovir dipivoxil and interferon monotherapy, make entecavir the preferred first-line treatment option for patients with chronic hepatitis B who are nucleoside naïve, HBeAg positive or negative, and have compensated liver disease. Both entecavir and adefovir dipivoxil maintain activity against hepatitis B virus in patients with chronic hepatitis B who are refractory to lamivudine, and both agents are reasonable first-line treatment options. Longer trials involving nucleoside-naïve, lamivudine-refractory patients are needed to determine entecavir's optimal treatment duration, long-term safety, and durability of response, including rate of resistance.

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.

AAV gene transfer to the retina does not protect retrovirally transduced hepatocytes from the immune response

Gene therapy of inherited hepatic disease relies on sustained expression of the therapeutic transgene. In many instances, such expression will require immune tolerization to the non-self therapeutic transgene product. We previously demonstrated that a cytotoxic immune response eliminated hepatocytes after in vivo transduction using recombinant retroviral vectors. In the present study we investigated whether prior gene transfer to the retina, which is suspected to induce immune tolerance, could alleviate the immune response occurring after retrovirus mediated gene transfer to the liver. Retinal cells were transduced using adeno-associated viral vectors harbouring a beta-galactosidase transgene. Sixty days later, regenerating hepatocytes were transduced after partial hepatectomy using a recombinant retrovirus carrying the transgene. Three weeks later, anti beta-galactosidase antibodies were present in all animals. Elimination of the transduced hepatocytes eventually occurred in all animals by 2 months after liver gene transfer, although sustained beta-galactosidase expression was still present in the retina in 66% of the animals. We conclude that although the retina behaves as an immunoprivileged site, gene expression in the subretinal space is not sufficient to induce immune tolerance to a transgene product expressed in the liver.