PRECLINICAL EVALUATION OF PROBES TO DETECT T(8-21) AML MINIMAL RESIDUAL DISEASE BY FLUORESCENCE IN-SITU HYBRIDIZATION

The 8;21 translocation in acute myeloid leukemia (AML) results in a co nsistent fusion transcript, AML1/ETO. Long-term clinical remission occ urs in some patients despite incomplete eradication of AML1/ETO as dem onstrated by RT-PCR, thus limiting the usefulness of this assay. An im portant future goal will be to determine if there is a level of minima l residual disease (MRD) in patients below which relapse is unlikely. For the detection of MRD, we have developed reagents for fluorescence in situ hybridization (FISH) that identify both derivative 8 and 21 ch romosomes with a high analytical sensitivity. In t(8;21) AML cells, tw o fused signals were detected in addition to the normal 8 and 21 allel es. The sensitivity and specificity of this probe mixture were analyze d in cell lines and patient bone marrows, One and two randomly juxtapo sed signals were observed in 2.4 and 0.04% of normal cells, respective ly. However, these were easily differentiated from t(8;21) cells by th e absence of signals from the normal alleles. Using as criteria the pr esence of two fused signals plus the normal alleles, we observed no fa lse positives among 5,000 normal cells. The probe correctly identified 20/20 patients with t(8;21) AML and 10/10 non-t(8;21) patients. In ce ll dilution experiments, the analytical sensitivity of this reagent wa s equal to that of the X chromosome and Y chromosome alpha-satellite p robes. These optimized probes should facilitate the quantitative asses sment-and study of MRD in t(8;21) AML. (C) 1998 Wiley-Liss, Inc.