Human iPSC-derived Microglia Cells Integrated into Mouse Retina and Recapitulated Features of Endogenous Microglia Cells

Abstract Microglia exhibit both maladaptive and adaptive roles in the pathogenesis of neurodegenerative diseases and have emerged as a therapeutic target for central nervous system (CNS) disorders, including those affecting the retina. Replacing maladaptive microglia, such as those impacted by aging or over-activation, with exogenous microglia that enable adaptive functions has been proposed as a potential therapeutic strategy for neurodegenerative diseases. To investigate the potential of microglial cell replacement as a strategy for retinal diseases, we first employed an efficient protocol to generate a significant quantity of human-induced pluripotent stem cells (hiPSC)-derived microglia. These cells demonstrated expression of microglia-enriched genes and showed typical microglial functions such as a robust response to LPS and phagocytosis. We then evaluated the xenotransplantation of these hiPSC-derived microglia into the subretinal space of adult mice that have been pharmacologically depleted of endogenous retinal microglia. Long-term post-transplantation analysis demonstrated that transplanted hiPSC-derived microglia successfully integrated into the mouse retina as ramified cells, occupying the retinal loci previously filled by the endogenous microglia and expresse microglia homeostatic markers such as P2ry12 and Tmem119. Further, these integrated human microglia were found juxtaposed alongside endogenous murine microglia for up to eight months in the retina, indicating their ability to establish a stable homeostatic state in vivo. Following retinal pigment epithelial (RPE) cell injury, transplanted microglia demonstrated responses typical of endogenous microglia, including migration, proliferation, and phagocytosis. Our findings indicate the feasibility of microglial transplantation and integration in the retina and suggest that modulating microglia through depletion and replacement may be a therapeutic strategy for treating neurodegenerative retinal diseases.