Detection of minimal residual disease in patients with childhood common acute lymphoblastic leukemia after autologous bone marrow transplantation with ex vivo purging and systemic IL-2 infusion: Unsuccessful prediction of subsequent relapse

We sequentially analyzed minimal residual disease (MRD) in 7 children with common acute lymphoblastic leukemia (cALL) after autologous bone marrow transplantation (ABMT) with ex vivo purging followed by systemic interleukin-2 infusion. After ABMT, 3 of the 7 patients remained in complete remission (CR) for more than 1 year, and 4 subsequently relapsed. MRD was estimated by polymerase chain reaction amplification to detect the leukemia clone-specific immunoglobulin heavy chain third complementarity determining region (IgH CDR-III). The IgH CDR-III sequences from the relapsed patients were identical with those determined at each respective initial diagnosis. In 2 patients, the levels of MRD were 10^-2 and 10^-5 in the harvested bone marrow (BM) cells, and even after purging the levels were 10^-4 and 10^-5 cells, respectively. One of the 2 patients relapsed 3 months after ABMT, while the other remained in CR for 33 months after ABMT. Among the 4 patients who subsequently relapsed after ABMT, MRD was not detected in the BM samples even 1 month before relapse. Our results suggest that PCR-negativity does not necessarily indicate a lower risk of subsequent relapse. Detection of MRD tends to favor the assessment of the therapeutic effects rather than prediction of relapse.