Safe and immune-tolerant 'designer' RPE cells towards the treatment of age-related macular degeneration

Abstract

Purpose : Frequent anti-VEGF injections and use of immunosuppressive drugs during RPE cell therapy can cause severe side effects. Also, the fear of tumorigenicity of grafted cells remains an issue. We test the hypothesis that cells, grafted into a diseased eye, expressing our local acting anti-VEGF biologics, ‘VEGF Sticky-trap’, with FailSafe^TM and immune cloaking technologies, is safe and controllable as a long-term treatment option for AMD. This approach combines the cells’ positive therapeutic effect with that of local acting biologics, avoiding potentially harmful side effects.

Methods : In a mouse model of AMD, we have grafted engineered human RPE to replace the lost cells in the recipient’s eye that a) produce a drug-inducible, local acting anti-VEGF biologic (VEGF Sticky-trap, PMID: 24705878) and b) control cell growth by introducing a suicide switch to the cell’s genome (FailSafe^TM, PMID: 30429614). The RPE cells generated in vitro from hES cells were further modified to make them “invisible” (iACT Stealth^TM, PMID: 31417198) to the immune system (cloaked cells), or not (uncloaked cells). To assess the efficacy, safety and toxicology of all genetic modifications, cells (cloaked and uncloaked) were injected in the subretinal space (40,000 cells per eye) and subcutaneously (either 1 million cells per flank or 100,000 cells intradermal in ear pinnae) in albino BL6 mice. Immune-compromised NSG mice served as a control and cell survival and efficacy was followed through life eye imaging or BLI imaging.

Results : We have demonstrated the function of all three genome altering systems (FailSafe^TM, iACT Stealth and VEGF Sticky-trap) separately, in pilot studies and are moving forward to a pre-clinical phase with small (mouse) and large animal models (rabbit, pig) to test in cell therapy settings. Thus far we have demonstrated, in vitro and in vivo (in mice), that cells survive up to 10 months in subretinal spaces and that each genetic modification continues to function in tandem.

Conclusions : Immuno-cloaking is essential to avoid graft rejection and/or immunosuppressive drugs, while tight regulation of cell proliferation (FailSafe^TM system) and drug-induced VEGF Sticky-trap expression was demonstrated. No adverse events were reported in mice receiving genetically modified cells. We expect our genome edited therapeutic cells to advance the development of novel and improved therapies for AMD and beyond.

This is a 2021 ARVO Annual Meeting abstract.