A method treating a subject with Alzheimer's disease wherein Aβ-reactive immune cells, splenocytes and lymphocytes, are generated in vitro or in vivo, re-stimulated in vitro, and then adoptively transferred into the cognitively-impaired subject. The population of immune cells can be derived from a donor with a natural or adaptive immune response to Aβ, stimulated by exposure to Aβ in vivo. The donor cells are then collected and re-stimulated by subsequent exposure to Aβ in vitro prior to administration to the subject. Alternatively, the population of immune cells can be derived from the subject and then stimulated by exposure to Aβ in vitro.