Abstract: Disclosed is an antigen presentation enhancing hybrid polypeptide which includes three elements. The first element is an N-terminal element consisting essentially of 4-16 residues of the mammalian li-Key peptide LRMKLPKPPKPVSKMR (SEQ ID NO: 1) and non-N-terminal deletion modifications thereof that retain antigen presentation enhancing activity. The second element is a chemical structure covalently linking the N-terminal element described above to the MHC Class II-presented epitope described below. The chemical structure is a covalently joined group of atoms which when arranged in a linear fashion forms a flexible chain which extends up to the length of 20 amino acids likewise arranged in a linear fashion, the chemical structure being selected from the group consisting of: i) immunologically neutral chemical structures, ii) a MHC Class I epitope or a portion thereof, and/or iii) an antibody-recognized determinant or a portion thereof.