DS-ALL patients have a higher rate of relapse and treatment-related mortality. We describe a DS-ALL patient with late bone marrow relapse who was treated per British ALL R3 reinduction chemotherapy. The patient remained in remission for approximately two years after therapy was discontinued due to severe systemic infections.

1 Division of Pediatric Hematology and Oncology, Department of Pediatrics, Rainbow Babies and Children’s Hospital, Case Western Reserve University, Cleveland, OH.* CorrespondenceJignesh Dalal, Pediatric Hematology Oncology, Rainbow Babies and Children’s Hospital, Case Western Reserve University, 11100 Euclid Avenue, Cleveland OH 44106, Tel: 216 844 3345, Email: Jignesh.dalal@uhhospitals.orgText word count: 951Brief running title: Challenges in HLH transplantKey words: primary hemophagocytic lymphohistiocytosis, hematopoietic stem cell transplant, mixed chimerismTables: 1

Relapsed acute lymphoblastic leukemia (ALL) with high minimal residual disease (MRD) after reinduction has poor prognosis. ALL patients with Down syndrome (DS) have a higher rate of relapse and treatment related mortality. We describe a DS and ALL patient with late bone marrow relapse who was treated per British ALL R3 reinduction chemotherapy. His therapy was discontinued due to severe systemic infections. The patient remained in remission for approximately two years without further treatment. We hypothesize that the sustained remission is attributed to chemotherapy combined with increased cortisol production and cytokine release as a result of systemic stress from infections.