Rationale and emerging evidence for microglial replacement in Alzheimer's disease.

Microglial biology in Alzheimer's disease (AD) has become a major focus of investigation, aiming to define how these cells contribute to neurodegeneration and to develop new therapeutic strategies. Once regarded as passive responders, microglia are now recognized as active regulators of brain homeostasis, immune signaling, and synaptic remodeling. Their interactions with genetic risk variants and age-related changes are increasingly understood to play central roles in AD pathogenesis. In this mini-review, we summarize recent progress in identifying microglial contributions to AD through genetic and transcriptomic studies. We discuss how microglia respond to amyloid-β and tau pathology by shifting into diverse functional disease-associated states, which may either protect or harm the brain depending on context and disease stage. We also outline the rationale for targeting microglia through replacement strategies and review emerging approaches using circulation-derived myeloid cells (CDMCs), and human pluripotent stem cell-derived microglia-like cells. These replacement methods have shown potential to rectify microglial functions and modify AD-related pathology in preclinical models, offering a novel therapeutic direction for neurodegenerative diseases.