Abstract: The invention concerns a method for identifying sub-dominant/cryptic epitopes exhibited by a class I HLA molecule, said method comprising at least the following steps: a) selecting, from the sequence of a protein with respect to which it is desired to induce a cytotoxic T lymphocyte response, at least a peptide sequence of 8 to 11 amino acids capable of constituting an epitope of said protein exhibited by a class I HLA molecule, and corresponding to a peptide with low affinity for said class I HLA molecule and non-immunogenic; b) preparing, for each selected sequence, a variant peptide derived from said sequence, by substituting the N-terminal amino acid with a tyrosine residue; c) determining the immunogenicity of each variant peptide obtained at step b) by selecting, among the latter, each immunogenic peptide, generating a CTL response specific to the target cells expressing the protein wherefrom it is derived and identifying the peptide sequence wherefrom said immunogenic peptide is derived.