An object of the invention is to provide a peptide based on a sequence of an amyloid ² peptide that may allow for induction of enhanced immune response and is safe and efficacious for prophylaxis and treatment of Alzheimer disease. An amyloid ² peptide or a portion thereof with addition or insertion of cysteine or a cysteine analogue, and a method for enhancing immune response to amyloid ² using said peptide, a medicament for prophylaxis and treatment of Alzheimer disease using said amyloid peptide that induces an enhanced immune response, amd a DNA vaccine comprising a gene coding for an amyloid ² peptide or a sequence derived from an amyloid ² peptide with addition or insertion of cysteine or a cysteine analogue, as expected to be similarly efficacious.
