Provided are methods and compositions for treating cancer in humans, the cancer being characterized by expression of Her-2/neu. The methods involve vaccinating a patient with an Ii-Key/MHC class II hybrid construct and thereby stimulating an immune response to the native Her-2/neu protein. The construct may be in the form of an Ii-Key hybrid peptide or a nucleic acid encoding an Ii-Key hybrid peptide. Methods are described wherein the cancer being treated is breast cancer. Also claimed is a pharmaceutical composition comprising an Ii-Key/MHC class II hybrid construct with and without an adjuvant. The adjuvant can include GM-CSF. The Ii-Key hybrid construct includes the LRMK (SEQ ID NO: 2) residues of Ii-Key protein and an MHC Class II epitope of a protein or portion thereof which is used in the vaccine or a DNA encoding the same hybrid peptide.