Relapse of pediatric acute lymphoblastic leukemia (ALL) remains the main cause of treatment failure after allogeneic stem cell transplantation (alloSCT). A high level of minimal residual disease (MRD) before alloSCT has been shown to predict these relapses. Patients at risk might benefit from a preemptive alloimmune intervention. In this first prospective, MRD-guided intervention study, 48 patients were stratified according to pre-SCT MRD level. Eighteen children with MRD level 1 × 10 4 were eligible for intervention, consisting of early cyclosporine A tapering followed by consecutive, incremental donor lymphocyte infusions (n1-4). The intervention was associated with graft versus host disease grade II in only 23% of patients. Event-free survival in the intervention group was 19%. However, in contrast with the usual early recurrence of leukemia, relapses were delayed up to 3 years after SCT. In addition, several relapses presented at unusual extramedullary sites suggesting that the immune intervention may have altered the pattern of leukemia recurrence. In 8 out of 11 evaluable patients, relapse was preceded by MRD recurrence (median 9 weeks, range 0-30). We conclude that in children with high-risk ALL, immunotherapy-based regimens after SCT are feasible and may need to be further intensified to achieve total eradication of residual leukemic cells.

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Erasmus MC: University Medical Center Rotterdam

Lankester, A.C, Bierings, M, van Wering, E.R, Wijkhuijs, J.M, de Weger, R.A, Wijnen, J.T, … Schilham, M.W. (2010). Preemptive alloimmune intervention in high-risk pediatric acute lymphoblastic leukemia patients guided by minimal residual disease level before stem cell transplantation. Leukemia, 24(8), 1462–1469. doi:10.1038/leu.2010.133