Outcome of Hematopoietic Stem Cell Transplantation for Pediatric Acute Lymphoblastic Leukemia in Third Complete Remission (CR3): A Vital Role for Graft-Versus-Host-Disease/Graft-Versus-Leukemia Effect in Survival.

Children with acute lymphoblastic leukemia (ALL) who suffer 2 relapses could be salvaged by hematopoietic stem cell transplantation (HSCT) when a suitable stem cell source is available provided they respond to the pre HSCT chemotherapy and at least enter morphological remission. However, these patients are at very high risk for post HSCT relapse and also at a high risk for transplant related mortality (TRM). Our objective, herein, was to review the outcome of children (0–18years) with ALL who received allogeneic HSCT in third complete remission (CR3) at our institution. Between January 1994 – August 2005, twenty-two consecutive children in CR3 received HSCT in the Hospital for Sick Children, Toronto, Canada. Conditioning regimens included single dose of VP16 (60mg/kg infused over 4 hours) and fractionated total body irradiation (TBI; 1200cGy) in six fractions over 3 days (VP16/TBI) in 10 patients (1994–1998) and cyclophosphamide 50mg/kg infused over 1 hour daily for 4 days followed by the same dose of fractionated TBI (CY/TBI) in 12 patients (1999–2005). Graft-versus-host disease (GVHD) prophylaxis included cyclosporine A and a short course of methotrexate for the majority of patients, and all patients were in complete morphological remission prior to HSCT. Median age was 8.4 years (range 3–15.4). Donor source was as follows: matched sibling donor (MSD), 8; matched unrelated donor (MUD) 6; one antigen mismatch related donor (MMRD) 4; one antigen mismatched unrelated donor (MMUD) 3; and one patient received 1 antigen mismatched cord progenitor stem cells. White cell engraftment was successful in all patients at a median of 18 days (range 9–29). Ten patients died of TRM, seven relapsed, one died from other causes and four patients are long term survivors at a median follow up of 3.7 years (range 1–10.2). All patients who did not develop clinical acute or chronic GVHD relapsed and died. Event free survival was (EFS 19% ± 4%). Three out of the 4 survivors received MMUD and all 4 survivors had moderate to severe acute GVHD and three had chronic GVHD, limited in two and extensive in one.

Conclusion: Children with ALL in CR3 receiving HSCT are extremely high risk for relapse and transplant related mortality. These children have already relapsed twice and demonstrated chemotherapy resistance and GVL/GVHD plays a key role in leukemia eradication. Although, TRM is high in such patients and GVHD could potentially increase TRM, there are no survivors without GVHD and exploring means of inducing GVHD by reduction of immunosuppressive medications or other means of immunotherapy should seriously be considered in these patients.