Deterministic programming of human pluripotent stem cells into microglia facilitates studying their role in health and disease

Microglia, the resident immune cells of the central nervous system (CNS), are derived from yolk sac macrophages that populate the developing CNS during early embryonic development. Once established, the microglia population is self-maintained throughout life by local proliferation. As a scalable source of microglia-like cells (MGLs), we here present a forward programming protocol for their generation from human pluripotent stem cells (hPSCs). The transient overexpression of PU.1 and C/EBPb in hPSCs led to a homogenous population of mature microglia within 16 days. MGLs met microglia characteristics on a morphological, transcriptional, and functional level. MGLs facilitated the investigation of a human tauopathy model in cortical neuron-microglia cocultures, revealing a secondary dystrophic microglia phenotype. Single cell RNA-sequencing of microglia integrated into hPSC-derived cortical brain organoids, demonstrated a shift of microglia signatures towards a more developmental in vivo-like phenotype inducing intercellular interactions promoting neurogenesis and arborisation. Taken together, our microglia forward programming platform represents a novel tool for both reductionist studies in monocultures and complex coculture systems including 3D brain organoids for the study of cellular interactions in healthy or diseased environments.