Stem cell therapies for Alzheimer's disease: is it time?

Purpose of review Stem cell therapy has the potential to modify the disease of Alzheimer's disease. This article aims to describe the mechanisms of action, preclinical animal studies, human clinical trials, and challenges for the future direction of stem cell therapy for Alzheimer's disease. Recent findings Stem cells of diverse origins (embryonic, placental or umbilical cord blood, and induced pluripotent stem cells) and cell types (neural and mesenchymal stem cells) are widely studied in both animals and humans. Summary In terms of mechanism of actions, recent research focused on the interplay between amyloid-beta Ab (and tau), neurons, and glia. Stem cells can induce direct regeneration of neurons and synapses. They can also prevent activation of pro-inflammatory microglia, promote activation of anti-inflammatory microglia, inhibit astrogliosis, and promote nonreactive astrocytes. These effects in return may increase amyloid-beta (Ab) degradation, decrease the risk of the Ab cascade, repair injured neurons, and enhance synaptogenesis. Two completed and nine ongoing clinical trials using diverse stem cells and administration methods (intravenous, subcutaneous, and intra-cranial) were found for the treatment of Alzheimer's disease. Although stem cell therapy shows great potential to become a prospective treatment for Alzheimer's disease in the future, these studies are still in their early stages and more studies showing safety and efficacy are needed.