Serial assessment of regulatory T cells (Tregs) in pediatric AML: A prospective study

9549 Background: Data of Tregs in pediatric AML is lacking. The study objectives were determining Tregs in pediatric AML at diagnosis and follow up; and correlating with outcome. Methods: From Nov 2010-May 2011, 30 consecutive AML patients ≤ 18 years were prospectively enrolled with 6 healthy controls. All patients received daunorubicin / cytarabine induction and 3 courses of cytarabine. Tregs (CD4+CD25+FoxP3+) were assessed at diagnosis, post-induction, post-consolidation, 3 and 6 months follow up and relapse. Results: 30 cases with median age 9.5 years; male/female ratio 14:16 had significantly higher baseline Tregs than healthy controls (12.36±4.65% vs 3.16±1.49%; p=0.0001). Patients with high Tregs frequency were females (p=0.044), WBC>50,000/mm3 (p=0.023), hypoalbuminemia (p=0.002), absence of lymphadenopathy (p=0.04) and linear correlation with peripheral blood blast% (r=0.55, p=0.0014). CR rate was 83.3% (25/30); EFS 38% and OS 73% at 14 months follow up. When Tregs were categorized as high and low based on median value, CR rate (86.6% vs 80%, p=NS), EFS [17% vs 60%, HR 1.46 (0.51-4.14) p=0.46] and OS (66% vs 80%, HR 0.58 (0.13-2.44) p=0.45) were not different. Amongst those who achieved CR, there were 7/13 relapses in those with high Tregs versus 3/12 in those with low Tregs (p=0.226).Tregs reduced post-induction (12.1±4.6 vs 6.32±2.8, p