.....METHODS: In this study, we used tricyclodecan-9-yl-xanthogenate (D609) to induce human mesenchymal stem cells isolated from Wharton jelly of the umbilical cord (HUMSCs) to differentiate into neuron-like cells (HUMSC-NCs), and transplanted the HUMSC-NCs into an AβPP/PS1 transgenic AD mouse model. The effects of HUMSC-NC transplantation on the cognitive function, synapsin I level, amyloid β-peptides (Aβ) deposition, and microglial function of the mice were investigated.....RESULTS: We found that transplantation of HUMSC-NCs into AβPP/PS1 mice improved the cognitive function, increased synapsin I level, and significantly reduced Aβ deposition in the mice. The beneficial effects were associated with "alternatively activated" microglia (M2-like microglia). In the mice transplanted with HUMSC-NCs, M2-like microglial activation was significantly increased, and the expression of antiinflammatory cytokine associated with M2-like microglia, interleukin-4 (IL-4), was also increased, whereas the expression of proinflammatory cytokines associated with classic microglia (M1-like microglia), including interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), was significantly reduced. Moreover, the expression of Aβ-degrading factors, insulin-degrading enzyme (IDE) and neprilysin (NEP), was increased substantially in the mice treated with HUMSC-NCs.