Table 1: A summary of cell replacement therapies currently in development for retinal repair, including the main challenges and clinical trial information (adapted from

Cell Therapy

Main Challenges

Clinical Trial Examples

Embryonic stem cells (ESCs)

>  Obtaining safe, stable and effective cell    sources

>  Finding a realistic up-scaling strategy

>  Chance of immunorejection

 >  Advanced Dry Macular Degeneration treatment (California, US) [52]

 >  Age related Macular Degeneration treatment (Israel) [53]

 >  Stargardt Macular Dystrophy treatment (US) [54]

 >  Advanced Dry Age related Macular Degeneration treatment (US)  [55] + long term follow up study [56]

 >  Advanced Dry Age related Macular Degeneration treatment (Korea) [57]

Induced pluripotent stem cells (iPSCs)

>  Potential time + cost of autologous cell therapy

>  May require gene correction before autologous transplantation

 >  Investigation of genetic retinal diseases (Minnesota, US) [58]

 >  Investigation of retinal degenerative diseases (Maryland, US) [59]

 >  iPSCs derived from retinoblastoma patients (Tennessee, US) [60]

 >  Age related Macular Degeneration treatment (UK) [61]

Mesenchymal stem cells (MSCs)

>  Large scale differentiation of MSCs into functional cells makes cell replacement therapy problematic

 >  Stem cell ophthalmology treatment study (Florida, US) [62]

Adipose stem cells (ASCs)

>  Risk of transplanted cells migrating towards non-targeted regions

>  Potential costs of autologous cell therapy

 >  Glaucomatous neurodegeneration treatment (Russia) [63]

Retinal progenitor cells (RPCs)

> Ability to integrate into retinal circuitry

> Chance of immunorejection

 >  Retinitis pigmentosa treatment (UK + US) [46,47]

 >  Retinitis pigmentosa treatment (California, US) [64]

Retinal pigmented epithelium (RPE) transplantation

>  High chance of immunorejection

>  Survival + function of transplanted RPE difficult on aged and deteriorated Bruch's membrane

 >  Acute Wet Macular Degeneration treatment (London, UK) [65]

 >  Age related Macular Degeneration treatment (Austria) [66]