A myeloid trisomy 21-associated gene variant is protective from Alzheimer's disease.

Alzheimer's disease causes progressive cognitive decline, yet some individuals remain resilient despite developing hallmark pathology. A subset of people with Down syndrome (DS), the most common genetic cause of Alzheimer's disease, demonstrates such resilience. Given the elevated risk of hematopoietic mutations in DS, we hypothesize that certain variants may confer microglial resilience. Here, we introduce a myeloid DS-linked CSF2RB A455D mutation into human pluripotent stem cell-derived microglia from both donors with DS and healthy donors and study their function in 4-10-month-old chimeric mice. We find that this mutation suppresses type I interferon signaling in response to tau pathology, reducing inflammation while enhancing phagocytosis, thereby ameliorating microglial senescence. CSF2RB A455D-expressing microglia form a unique protective subpopulation and preserve neuronal functions. Importantly, they replace diseased wild-type microglia after tau exposure. These findings provide proof of concept that engineered human microglia can enhance resilience against tauopathy, opening avenues for microglial replacement therapies.