Peripheral Blood-Derived Microglia-Like Cells Decrease Amyloid-β Burden and Ameliorate Cognitive Impairment in a Mouse Model of Alzheimer's Disease.

Amyloid-β (Aβ) accumulation in the brain triggers the onset of Alzheimer's disease (AD), and its prevention and elimination are high priorities for anti-AD therapeutic strategies. Microglia, the resident immune cells in the brain, promote Aβ clearance by phagocytosis. Previously, we demonstrated that injection of primary cultured rat microglia and mouse bone marrow-derived microglia-like cells into the brain decreases the level of Aβ and that intrahippocampal injection of these cells ameliorates cognitive impairment in a mouse model of AD. To advance this cell therapeutic strategy to the clinical stage, less invasive ways of preparing autologous microglia-like cells from elderly patients are required. In this study, we demonstrated that hematopoietic stem cells mobilized from the bone marrow to peripheral blood by administering granulocyte colony-stimulating factor and a CXCR4 antagonist to mice differentiated into microglia-like cells upon stimulation with colony-stimulating factor 1 and interleukin-34. The peripheral blood-derived microglia-like (PBDML) cells expressed microglial markers and engaged in Aβ phagocytosis. Although PBDML cells were in an anti-inflammatory state under nonstimulated conditions, they expressed mRNAs encoding proinflammatory cytokines following lipopolysaccharide treatment. PBDML cells injected into the hippocampi of a mouse AD model survived for at least 36 days while phagocytosing Aβ, contributed to a reduction in brain Aβ burden, and ameliorated cognitive impairment in the mice. These results strongly suggest that PBDML cells are a promising source for the development of a novel cell therapy against AD.