Xenotransplantation of Human PSC-derived Microglia Creates a Chimeric Mouse Brain Model that Recapitulates Features of Adult Human Microglia

Microglia, the brain-resident macrophages, exhibit highly dynamic functions in neurodevelopment and neurodegeneration. Human microglia possess unique features as compared to mouse microglia, but our understanding of human microglial functions is largely limited by an inability to obtain human microglia under resting, homeostatic states. We developed a human pluripotent stem cell (hPSC)-based microglial chimeric mouse brain model by transplanting hPSC-derived primitive macrophage precursors into neonatal mouse brains. The engrafted human microglia widely disperse in the brain and replace mouse microglia in corpus callosum at 6 months post-transplantation. Single-cell RNA-sequencing of the hPSC microglial chimeric mouse brains reveals that xenografted hPSC-derived microglia largely retain human microglial identity, as they exhibit signature gene expression patterns consistent with physiological human microglia and recapitulate heterogeneity of adult human microglia. Importantly, the chimeric mouse brain also models species-specific transcriptomic differences in the expression of neurological disease-risk genes in microglia. This model will serve as a novel tool to study the role of human microglia in brain development and degeneration. Single-cell RNA sequencing was performed using 10X Genomics Chromium equipment and kits to assess human iPSC-derived microglia transplanted into postnatal day 0 immunocompromised mice. Forebrain samples were collected from four different transplanted animals at 6 months after transplant. Cells were dissociated and processed for sequencing.