There is disclosed a T-cell preparation comprising T-cells specific for a peptide when presented on an MHC molecule. The peptide corresponds to a fragment of the RAS protein and comprises a region of at least 8 amino acids which include position 12, 13 or 61 of the RAS protein. This region has at least 6 amino acid residues, other than at said position 12, 13 or 61, which are identical to the corresponding region of the RAS protein. The peptide has an amino acid substitution at the amino acid corresponding to position 12, 13 or 61 of the RAS protein.
