The invention provides for the synthesis of more effective generators of a T-cell immune response by providing peptide derivatives that are MHC class I-restricted antigens. The peptide derivatives of the present invention are prepared or derived from a parent peptide of 8 to 11 amino acid residues in length, wherein the peptide derivative contains a non-natural amino acid substituted in place of a naturally-occurring amino acid residue at one or more primary anchor positions in the parent peptide or at position 6, position 7, or the C-terminus. The exemplary polypeptides are derived from the survivin, hTERT, CYP1B1 and MART-1 antigens.