Development of lentiviral vectors as a tool for gene therapy in the eye
(Corinne Kostic)
Most retina degeneration disorders are due to photoreceptor or RPE dysfunction, which prompted us to define appropriate tools to specifically target these cells. One basis of gene therapy approach is to target the appropriate tissue or cells, allowing specific expression of the therapeutic gene where it is supposed to act as well as avoiding damaging secondary effects. This specificity may be determined at different levels: the vector may have a limited tropism, the transgene may have a specific function restricted to a defined cell type, or the promoter may lead to cell- or tissue-specific expression. We chose to work on the latter possibility and to examine expression of different promoters in mouse retina using lentiviral vector delivery (Kostic et al 2003). We also show that limited diffusion of the vectors is due to a physical barrier present between photoreceptors and RPE (Grüter et al 2005). We are pursuing studies to enhance lentiviral diffusion and transduction in mouse retina to optimize gene transfer in different animal models.
10.08.10

Preclinical trials for gene therapy in LCA mouse models
(Corinne Kostic & Yvan Arsenijevic)
Leber congenital amaurosis (LCA) is an autosomal recessive childhood-onset retinal dystrophy where RPE65 mutation account for 10-15% of the cases (Gu et al., 1997; Marlhens et al., 1997). We are pursuing a preclinical study for treatment of LCA by lentiviral-mediated gene transfer of RPE65 in different mice model for LCA. We would like to define a precise therapeutic window and the effect of gene transfer on cone photoreceptors. We are able to obtain a good ERG response in RPE65 -/- mice treated at postnatal day 5 with a lentiviral vector expressing RPE65 (Bemelmans et al., 2006). We also demonstrated preservation of cone function and survival up to 4 months after treatment. However cone were not protected when the treatment was applied in young adults (1 month of age) revealing the limited therapeutic window for cone rescue (Bemelmans et al., 2006). Considering that half of RPE65 patients have a misense mutation which may lead to only partial loss of function, we would like to evaluate the therapeutic window in the knock-in mouse model bearing the R91W mutation found in patients.  We are currently characterizing the rescue using histological analysis, behavioural tests and measurement of the PLR.

Parallely, our unit has identified 3 families from Northern Tunisia suffering from LCA with all affected patients (n=12) bearing a homozygous R91W RPE65 mutation. Until now, the clinical evolution of LCA has been poorly studied. We are currently investigating these families in order to precisely describe the evolution of this disease and to reveal which therapeutical window could be applicable. It is important to reveal at which ages cone and rod vision begin to decline and, subsequently, disappear. The rate of degeneration must be clearly identified to determine the percentage of cells that can still be saved by a potential gene therapy.
29.09.09