Engineering DNA vaccine design for maximizing epitope-specific immunity has allowed epitope enhancement by sequence modification. The recent molecular understanding of the immune response is leading to new strategies to induce more effective immune responses. Self-tolerance might lead to deletion of T cells specific for the most effective epitopes, leaving only low-avidity T cells [77, 78] . Therefore, not all sequences are optimal antigenic epitopes. A process termed epitope enhancement is expected to make the sequences of many epitopes of cancer more immunogenic [79] . Epitope sequences can be modified to increase the affinity of the epitope peptide for the MHC molecule. The knowledge of sequence motifs for peptide binding is the key to improve the primary and/or secondary "anchor residues" that provide much of the specificity of binding to the MHC molecule [80, 81] . This strategy can greatly increase the potency of a vaccine and can convert a subdominant epitope into a dominant one by making it more competitive for available MHC molecules, thereby increasing the level of specific peptide-MHC complexes on the antigen presenting cell surface [82] . Epitope enhancement has been used to increase the affinity for both MHC class I and class II molecules (reviewed in [83] ).