395. Developing Bone Marrow Transplant and Lentiviral Vectors for Friedreich Ataxia

Abstract

Friedreich ataxia (FRDA) is a debilitating neurodegenerative disorder with disease onset at around 10-15 years of age. It affects 1 in 29 000 individuals of Caucasian descent and is characterised by progressive gait and limb ataxia. This leads to an ongoing loss of motor coordination which results in affected individuals becoming wheelchair-dependent within 15 years after disease onset - decreasing their quality of life. FRDA patients also experience other disease symptoms such as cardiomyopathy, with heart complications being the leading cause of death with life expectancy decrease to 30-40 years. There is currently no treatment which can cure or slow the neurodegeneration inherent to FRDA and patients undergo various symptomatic treatments to manage disease symptoms. It is thus essential to develop new treatments effective at slowing disease progression to improve the quality of life of FRDA patients. FRDA is caused in most cases by a homozygous GAA trinucleotide repeat expansion within intron 1 of FXN which encodes the frataxin, a mitochondrial protein. As the expansion only reduces the level and does not alter the frataxin protein structure, it is predicted that increasing frataxin will be therapeutically beneficial to FRDA patients. This research aims to introduce frataxin into cells via cell and gene therapy as a potential treatment for FRDA. This introduction of frataxin will not illicit an immune response as patients do produce frataxin at very low levels. We are investigating if transplanting wild-type bone marrow into an irradiated FRDA mouse model increases frataxin and alleviates the neurological phenotype of slight coordination impairment and locomotor defects which develop around six months of age. Reconstitution of the haematopoietic system with GFP-positive donor bone marrow cells in corrected recipient mice indicated successful engraftment following transplant. GFP-positive cells also successfully engrafted into the dorsal root ganglia (DRG) and spinal cord, both major sites of neuropathology in FRDA, of corrected mice - demonstrating low-level chimerism. Immunofluorescence studies showed increased neuronal marking in the DRG of corrected mice, particularly proprioceptive neurons which are highly affected in FRDA patients. Increased frataxin protein is observed in some tissues of corrected mice. Corrected mice also exhibited significant improvement in motor coordination post-transplant. For autologous gene therapy via bone marrow transplant, we are currently developing a lentiviral vector that over-expresses frataxin. These data together illustrate the potential of bone marrow transplant in correcting FRDA in vivo and provide an avenue for the delivery of therapeutic viral vectors for gene therapy.