Developing safe and immune-tolerated cells for treatment of neurological diseases

Background & Aim Cell therapy-based regenerative medicine provides a powerful tool against diseases that have been intractable to treat with conventional medicine. Employing genome-editing strategies, we addressed the safety concerns associated with cell-based regenerative medicine through the development of the FailSafe (FS) Cell System. This proprietary technology inserts a suicide gene into a cell division essential locus, allowing selective elimination of proliferative cells through the administration of a pro-drug, whilst also protecting the suicide gene from inactivation. When incorporated into mouse embryonic stem cells (mESCs) and injected subcutaneously, the Fail-Safe system allows the proliferating component of a teratoma to be eliminated by brief treatment with the pro-drug for the suicide gene. The remaining non-proliferating component is induced into a stable and dormant ectopic tissue. To enable the development of economically feasible “off-the-shelf” cell products, we identified a set of eight immune-modulating genes involved in allograft tolerance and rejection. When expressed in FailSafe mESCs, the immune-cloaking system is sufficient to prevent rejection of ectopic tissues in immune-competent major histocompatibility complex-mismatched recipient mice. In the current study we sought to demonstrate the application of our technology for treatment of neurological diseases. Methods, Results & Conclusion By incorporating expression of enhanced firefly luciferase, we used bioluminescence imaging (BLI) to monitor the survival and proliferation of gene-edited mESCs after stereotaxic injection into the mouse brain. Small numbers (1 × 104) of mESCs injected into the lateral ventricles were detectable by BLI. Weekly monitoring of live animals revealed that the BL signal increased over time, indicative of the proliferation of injected cells. Histological examination of brain tissue confirmed that mESCs formed teratomas containing structures derived from the three primary germ layers. In mice that received gene-edited mESCs, teratoma development could be prevented by intraperitoneal administration of the pro-drug. Moreover, proliferating cells could be eliminated from developing teratomas, as shown by a decreased BL signal over time and Ki67 staining in tissue sections. Importantly, grafted cells that had undergone terminal differentiation remained intact. These technologies will therefore facilitate the advancement of cell-based regenerative therapies for neurological diseases.