UNCOVERING SEXUAL DIMORPHISM IN HUMAN MICROGLIA USING ORGANOID-BASED PLATFORMS

Microglia are the brain’s resident immune cells, with critical roles in neurodevelopment and neuroprotection. Sex differences in neurodevelopmental and psychiatric disorders suggest underlying immune dimorphism, yet the mechanisms and functional consequences of sex-specific microglial states in the human developing brain remain poorly understood. To address this, we generated sex‑specific ImmunoBrain organoids from human induced pluripotent stem cells, enabling the study of microglial heterogeneity in a human-relevant context. Single‑cell RNA sequencing revealed a female‑enriched microglial subpopulation that displayed heightened responsiveness to environmental stimuli. Functional immune challenges further demonstrated that male and female microglia mount distinct transcriptional and phenotypic responses, with certain female‑specific reactions confined to this subpopulation. To disentangle intrinsic versus niche‑driven effects, we engineered sex‑mismatched organoids by combining male microglia with female organoids and vice versa. These experiments revealed that the observed sexual dimorphism is primarily instructed by the brain organoid environment, rather than by cell‑autonomous sex differences. Our findings demonstrate that the brain’s niche profoundly shapes microglial phenotype and function during development, providing a mechanistic framework for understanding how female microglia may modulate the brain’s susceptibility to environmental perturbations and contribute to sex‑biased risk in neurodevelopmental disorders.