Chimeric human organoid and mouse brain slice co-cultures to study microglial function

Studying the dynamic role of microglia in brain development and neurodegenerative diseases requires models that closely resemble the human brain environment. While human induced pluripotent stem cell (iPSC)-derived organoids (hORGs) effectively reproduce key neuronal and certain glial cell types, modeling human microglia in vitro remains challenging. Inspired by recent approaches demonstrating enhanced microglial maturation in hORGs transplanted into mouse brains, we develop a chimeric model by co-culturing hORGs with mouse brain slice cultures (mBSCs). This system reveals cross-species interactions associated with an earlier onset of cortical neuronal differentiation markers in the hORGs. Human iPSC-derived microglia, pre-differentiated in mBSCs, migrate into the hORGs and adopt ramified morphology. They remain viable for several months and respond to laser-induced injury, demonstrating long-term functionality. This in vitro model supports long-term study of human microglia in a brain-like environment, providing a platform for mechanistic studies and screening compounds that target microglial function.