Quantification of TEL-AML1 transcript for minimal residual disease assessment in childhood acute lymphoblastic leukaemia

Strategies currently used for residual disease detection in acute lymphobla stic leukaemia (ALL) rely on polymerase chain reaction (PCR) detection of i mmunoglobulin and T-cell receptor rearrangements. The TEL-AML1 fusion trans cript, which is associated with t(12;21) (p13;q22), is found in 25% of chil dhood B-cell precursor ALL, and represents an interesting alternative targe t. We compared two methods for quantitating TEL-AML1 fusion transcripts: co mpetitive PCR and real-time PCR. These techniques showed similar sensitivit y (5 x 10(-5)) and reproducibility. Giving highly correlated results, both techniques can be conveniently used for TEL-AML1 transcript quantification. The constancy of TEL-AML1 expression was evaluated by measuring TEL-AML1 t ranscripts at different steps of the cell cycle, and in 21 cases of ALL at diagnosis. No major variation in TEL-AML1 expression was observed during th e cell cycle or in 20/21 of the ALL patients. Residual disease was then det ermined after completion of induction therapy in 20 patients with a TEL-AML 1-positive ALL. Seven patients out of 20 (35%) were still positive, includi ng two patients with high level of residual blasts (close to or beyond 10(- 2)). When comparison was possible, results obtained using TEL-AML1 quantifi cation were in accordance with those obtained using T-cell receptor rearran gements analysis.