Preleukemic TEL-AML1-positive clones at cell level of 10-3 to 10-4 do not persist into adulthood

The TEL-AML1 translocation, t(12;21)(p13;q22), is one of the most frequent genetic aberrations in childhood B-cell precursor acute lymphoblastic leukemia (ALL), where it occurs in 25% of all cases. In contrast, the translocation is seen in only 3% of adult ALL cases. Evidence suggests that the TEL-AML1 translocation occurs in utero in 1 % of all newborn children at cell levels of 10(-3) to 10(-4). In this study, we explore the prevalence of TEL-AML1-positive cells in 2 cohorts of healthy blood donors by real-time and nested reverse transcription-polymerase chain reaction. Overall, TEL-AML1-positive cells were demonstrated in 10 of 2005 healthy donors, that is, a prevalence of 0.5% (95% confidence interval, 0.2-0.3%). The level of TEL-AML1-positive cells was estimated to 10(-5) to 10(-6). The observed prevalence of TEL-AML1-positive cells in healthy adults is of the same order of magnitude as the prevalence reported in healthy newborns, but the observed cell level of 10(-5) to 10(-6) is much lower. These data indicates that prenatal TEL-AML1 subclones does not persist throughout adult life at cell levels of 10-3 to 10-4. The findings are compatible with the risk of t(12;21)(p13;q22) ALL correlating with the total number of TEL-AML1-positive cells in peripheral blood in both childhood and adulthood.