Topoisomerase I inhibition yields a CD74^high/MHC^high human microglial subtype with enhanced Aβ uptake

While efforts to identify microglial subtypes have recently accelerated, the relation of transcriptomically defined states to cellular function has been largely limited to in silico annotations. Here, we characterize two topoisomerase I inhibitors that polarize human microglia toward a distinct state characterized by increased antigen presentation gene expression. Using HMC3 cells, iPSC-derived microglia, and cerebral organoids, we show that Camptothecin induces a CD74^high/MHC^high microglia-like cell subtype specialized in amyloid beta phagocytosis and reduced IL-6, IL-8, and MCP-1 secretion in response to TNF-α stimulation. Moreover, Camptothecin suppresses amyloid toxicity and restores microglia to their homeostatic morphology in a zebrafish amyloid proteinopathy model. We also identify Topotecan, a Food and Drug Administration (FDA)-approved Camptothecin analog, as a driver of the CD74^high/MHC^high signature. This report provides a reproducible approach to recapitulate a human microglial state in vitro, enabling its functional characterization and providing a foundation for rational modulation of human microglia in vivo.