Terminal transferase surveillance of remission bone marrows in childhood acute lymphoblastic leukemia: improved sensitivity with countercurrent centrifugal elutriation.

In an attempt to better define hematologic remission and relapse in children with TdT positive acute lymphoblastic leukemia (ALL), 101 bone marrow (BM) aspirates were obtained from 74 pediatric patients. The mononuclear cell population of these specimens was isolated using countercurrent centrifugal elutriation (CCE) and characterized by an immunofluorescent terminal deoxynucleotidyl transferase (IF-TdT) assay. Twenty-two children with non-leukemic disorders had a median of 8% (range 0-34%) TdT positive mononuclear bone marrow cells. This was similar to values obtained for 25 children with ALL off therapy and in remission (median 10%, range 1-22%) and 16 children with ALL on continuous anti-leukemic therapy and in remission (median 7%, range 1-26%). Twenty-three BM samples were obtained from 11 children in early or high risk to relapse because of increased immature cells on a routine marrow examination or previous relapse(s). Samples from the early and high risk to relapse groups contained a median of 56% (range 25-80%) and 39% (range 25-72%) TdT positive cells. In contrast, the median percent marrow lymphoblasts identified using standard morphologic criteria for these 2 groups was 12.5% (range 9-23%) and 3% (range 0-5%), respectively. All high risk patients relapsed in their BM 1-4 1/2 months after these TdT determinations. Longitudinal studies in 4 patients at increased risk to relapse consistently demonstrated elevated percentages of TdT positive cells while morphologic surveillance was inadequate in establishing a clinical diagnosis of leukemic relapse. CCE in combination with an IF-TdT assay may enhance detection of recurrent and/or residual leukemia in BM samples from children with TdT positive ALL.