The invention concerns the optimisation of the wild R9M peptide and the use of the resulting peptides for therapeutic vaccination and/or preventive vaccination against leukemia in humans. More particularly, the invention concerns mutated immunogenic peptides derived from the human TEL/AML1 fusion protein comprising the wild R9M peptide sequence Arg-Ile-Ala-Glu-Czs-Ile-Leu-Gly-Met. The invention also concerns polynucleotides coding for the mutated R9M immunogenic peptides, cellular expression vectors comprising nucleic acid sequences expressing the mutated R9M immunogenic peptides and polyclonal or monoclonal antibodies capable of being fixed on at least one of said peptides/polynucleotides. The invention further concerns the use of said peptides, polynucleotides and/or antibodies for preparing vaccines, anti-tumoral medicines and compositions and for in vitro and in vivo stimulation of the immune response in humans.