A Human Cellular Model Of Choroideremia Generated Via Patient Ips Cells

Abstract

Purpose: : The first clinical trials of retinal gene therapy were carried out in 2008 with positive results. Consequently, the requirements for future preclinical studies of other diseases will be less stringent, notably concerning the need for large animal disease models. However, a growing number of diseases lack even an appropriate small model, compromising their chances of one day reaching a clinical trial. In such cases, a viable alternative would be to perform preclinical studies on human cellular models of the pathogenic retina.

Methods: : As a pilot project, we generated a human cellular model of the X-linked disease choroideremia (CHM). CHM represents 2% of retinal dystrophies and is characterised by night blindness in childhood leading to blindness by 50 y of age. It is due to mutations in the CHM gene encoding Rab escort protein 1 (REP1). Mouse and zebrafish REP1-deficient models are lethal. As it is impossible to obtain retinal cells from a CHM patient, we generated these cells from skin fibroblasts via the intermediate use of induced pluripotent stem (iPS) cells.

Results: : We obtained the first bona fide iPS clone of a CHM patient carrying a deletion of exon 8. We differentiated this iPS clone into a retinal pigment epithelium (RPE) monolayer that expresses RPE-specific markers, is polarised, has tight junctions and is capable of active transport. Ultra-structural studies demonstrate the presence of microvilli on the surface and a characteristic RPE subcellular organisation. We are currently studying the differences in phagocytosis, melanosome trafficking and visual cycle differences between wild type and patient RPE. This work will allow disease modelling in a human system as well as provide the readouts for evaluating phenotype restoration following viral-mediated CHM gene transfer.

Conclusions: : The use of such innovative human disease systems are more economical and less time-consuming alternatives to animal models, as well as more biologically relevant for further understanding disease pathogenesis and for preclinical therapeutic studies. Moreover, considering the current climate of retinal gene therapy, preclinical trials on human cells will allow a more rapid transition to phase I trials for diseases lacking an appropriate animal model.

Keywords: gene transfer/gene therapy • retinal pigment epithelium • degenerations/dystrophies