CD52 Is Expressed in Childhood Acute Myeloid Leukemia and May Be a Target for Alemtuzumab.

Abstract

Event free survival in children with Acute Myeloid Leukemia (AML) remains low at approximately 50%, and more effective therapy is urgently needed. Alemtuzumab is an anti-CD52 humanized antibody with activity in Chronic Lymphocytic Leukemia. In adults with AML, CD52 was expressed in 36% of patients. Alemtuzumab treatment in relapsed adult AML patients resulted in complete response without platelet recovery (CRp) in 2/9 (22%), reduction of marrow blasts in 1/9 (11%) and reduction of peripheral blasts in 5/9 (56%) (Cancer , 2006; 106:2645–51). The expression of CD52 has not been reported in childhood AML. AML (excluding M3) was diagnosed in 48 children at our institution from February 2002 to February 2007. The flow cytometric expression of CD52 antigens was studied in 41 pediatric patients at diagnosis: 20 girls and 21 boys and median age 5.1 years (range 0–18). CD52 expression ≥ 20% of leukemic blasts was considered positive. Of the 41 AML patients, 19 (46%) were positive and 22 (54%) were negative for CD52. In the CD52 positive patients the median expression was 72% (range 22%–99%), and intensity was moderate to dim. Expression by cytogenetic risk groups is demonstrated in Table 1:Cytogenetic Risk GroupLow Risk: t(8;21) or Inv(16)/t(16;16)Intermediate RiskHigh Risk: −7 or -5/5q-Down SyndromeCD52 positive7921CD52 negative21334More low-risk patients were CD52 positive than negative, but the reverse was true for patients with Down syndrome. Age, gender, FAB subtype or presenting white blood cell count did not correlate with CD52 expression. Event free survival and overall survival were similar in CD52 positive and negative patients. In summary, CD52 is expressed in almost half of children with AML. The activity of single agent Alemtuzumab in adults with AML suggests that this agent should be evaluated to treat CD52-positive pediatric AML patients in combination with chemotherapy.