Intensive minimal residual disease monitoring to drive early intervention after allogeneic hematopoietic stem cell transplant for pediatric acute leukemia.

Abstract

e18531 Background: Relapse of acute leukemia (AL) remains the main cause of death after allogeneic stem cell transplantation (HSCT) in children. Minimal residual disease (MRD) allows to detect leukemia cells in the bone marrow at low level. The impact of post-HSCT MRD monitoring to detect early leukemia recurrence, to guide therapeutic intervention, and to prevent overt relapse is unknown. We report our experience of systematic MRD monitoring after pediatric HSCT. Methods: All patients who underwent HSCT from January 2012 to December 2017 for an AL had bone marrow MRD performed for 2 years (months 1, 2, 3, 5, 7, 9, 12, 15, 18, 21 and 24). MRD was assessed by flow-cytometry (FC) and, when a molecular alteration was present, by nested RT-PCR. Results: Seventy-one HSCT were performed for AL of myeloid (n=38), lymphoid (n=31) or mixed (n=2) lineage in 59 patients at a median (range) age of 6.5 (0.7-18.4) years. Nine cases did not engraft or had a refractory disease at month+1 evaluation. In all other cases (n=62) MRD was monitored using FC (n=58) and/or RT-PCR (n=34). Thirty-three cases had a MRD detection and/or an overt relapse (≥5% blasts). In 23/33 cases (70%), MRD was detected without simultaneous overt relapse. In the 10 others, an overt relapse occurred without prior MRD detection. Among the cases monitored with RT-PCR, only one relapse occurred without a prior MRD detection. The follow-up protocol was not respected in this particular case. On early MRD detection, 20/23 cases underwent therapeutic intervention, the most frequent being the discontinuation of immunosuppressive drugs (n=13), with subsequent undetectable MRD in 6. Other interventions included chemotherapy (n=8), donor lymphocyte infusion (n=6) and/or interferon ± interleukine 2 (n=3), leading to an undetectable MRD in 3 cases. Overall after first MRD detection, 9/23 (39%) cases never experienced a subsequent overt relapse. Conclusions: Intensified MRD monitoring detected 70% of leukemia recurrences before overt relapse. Therapeutic intervention were taken in most of the cases and 39% never experienced overt leukemia relapse. More efficient immunotherapies may improve the impact of preemptive interventions.