 The 12;21 chromosomal translocation occurs in leukemic cells from 20(30% of patients with B-lineage childhood acute lymphoblastic leukemia, the result being the TEL/AML1 fusion gene carrying a sequence different from TEL or AML1.     ///    "Furthermore, these T-cell clones proliferated in response to several altered peptide ligands carrying a single residue substitution in the TEL/AML1 peptide, and some induced augmentation of proliferation and production of Th1-type cytokines. "    ///    "We established two human CD4+ alphabeta T-cell clones (T31.1 and Y41.2) reacting to the TEL/AML1 fusion region, from two unrelated healthy donors. "    ///    "In order to do this, we stimulated peripheral blood mononuclear cells with synthetic peptides corresponding to the TEL/ AML1 fusion region. "    ///    "Both T31.1 and Y41.2 proliferated in response to TEL/ AML1 fusion protein as well as to a peptide IGRIAECILGMNPSR, in the context of HLA-DP5 and DP17, respectively, and killed B lymphoblastoid cells pulsed with the peptide. "    ///    "Because the protein newly formed by TEL/ AML1 fusion is probably not tolerated by human immune system, the fusion region is a good candidate for tumor antigen expressed only in TEL/ AML1-positive leukemic cells. "    ///    Augmentation of immune response by altered peptide ligands of the antigenic peptide in a human CD4+ T-cell clone reacting to TEL/AML1 fusion protein.. 