Effective Gene Therapy in a Mouse Model of Prion Diseases

Karine Toupet,Valérie Compan,Françoise Ibos,Chantal Mourton-Gilles,Nadine Mestre-Francés,Pierre Corbeau,Jean-Michel Verdier,Carole Crozet,Véronique Perrier

doi:10.1371/journal.pone.0002773

Abstract

Classical drug therapies against prion diseases have encountered serious difficulties. It has become urgent to develop radically different therapeutic strategies. Previously, we showed that VSV-G pseudotyped FIV derived vectors carrying dominant negative mutants of the PrP gene are efficient to inhibit prion replication in chronically prion-infected cells. Besides, they can transduce neurons and cells of the lymphoreticular system, highlighting their potential use in gene therapy approaches. Here, we used lentiviral gene transfer to deliver PrPQ167R virions possessing anti-prion properties to analyse their efficiency in vivo. Since treatment for prion diseases is initiated belatedly in human patients, we focused on the development of a curative therapeutic protocol targeting the late stage of the disease, either at 35 or 105 days post-infection (d.p.i.) with prions. We observed a prolongation in the lifespan of the treated mice that prompted us to develop a system of cannula implantation into the brain of prion-infected mice. Chronic injections of PrPQ167R virions were done at 80 and 95 d.p.i. After only two injections, survival of the treated mice was extended by 30 days (20%), accompanied by substantial improvement in behaviour. This delay was correlated with: (i) a strong reduction of spongiosis in the ipsilateral side of the brain by comparison with the contralateral side; and (ii) a remarkable decrease in astrocytic gliosis in the whole brain. These results suggest that chronic injections of dominant negative lentiviral vectors into the brain, may be a promising approach for a curative treatment of prion diseases.

Highlights

Transmissible spongiform encephalopathies (TSEs), or prion diseases, are fatal neurodegenerative disorders in humans and animals for which no effective therapy exists
C57Bl/6 mice inoculated with the Me7 prion strain are an effective model of prion diseases that have been well described for their incubation time, vacuolization profiles, and immunohistology [34,35]
As previous injections performed in healthy mice showed the potential use of lentiviral vectors in gene therapy [28], our objectives was to administer dominant negative virions to evaluate their efficiency in the curative treatment of prion diseases (Figure 1B)

Summary

Introduction

Transmissible spongiform encephalopathies (TSEs), or prion diseases, are fatal neurodegenerative disorders in humans and animals for which no effective therapy exists. The pathogenesis of prion diseases is based on the presence of PrPSc, a proteaseresistant isoform of the normal cellular prion protein called PrPC [1,2]. The progressive accumulation of PrPSc in the brains of affected individuals, which can occur for up to 20 years, is associated with the neurodegeneration. The emergence of acquired forms of human TSEs in younger people, such as variant CJD (vCJD) and iatrogenic CJD (iCJD) resulting from contaminated cadaveric growth hormone mostly in France [4] or dura grafts in Japan [4], have highlighted the urgent need for effective treatments. Two recent studies have reported vCJD cases likely resulting from the transfusion of prion-contaminated blood [5,6], raising concerns about the safety of blood products as well as the possibility of a second epidemic of vCJD

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