CD117 CD34 EXPRESSION IN LEUKEMIC BLASTS

CD117 is a transmembrane protein receptor encoded by the c-kit protoon cogene. The CD117 ligand is stem cell factor, an important hematopoiet ic regulator. CD117 is present on approximately 4% of normal bone marr ow mononuclear cells and in acute myelogenous leukemia (AML) and chron ic myelogenous leukemia in myeloid blast crisis, but rarely in acute l ymphoblastic leukemia (ALL). Initially viewed as a primitive myeloid m arker, CD117 has been identified in all FAB subtypes of AML and may pr edict poor outcome. CD34, a primitive stem cell marker, may also predi ct poor outcome. The aim of this study was to examine the relationship between CD117 and CD34 expression on leukemic blasts and to determine whether CD117 is related to lymphoid-associated antigen (LAA) express ion in AML. Consecutive bone marrow samples were studied from cases of ANL (30 cases), myelodysplastic syndromes (MDS) (4 cases), myeloproli ferative disorders in blast crisis (MPD-BC) (6 cases), and ALL (5 case s). Cases were diagnosed according to FAB criteria and included M0 (3 cases), M1 (2 cases), M2 (13 cases), M3 (1 case), M4 (6 cases), M5 (3 cases), M6 (1 case), AML NOS (1 case), RAEB (3 cases), and RAEB-T (1 c ase). CD117 and CD34 were analyzed by multiparameter flow cytometry. B lasts in 10 de novo AML samples were CD117+/CD34+ in 4 cases, CD117+/C D34- in 3 cases, CD117-/CD34+ in 1 case, and CD117-/CD34- in 2 cases. Blasts in 20 cases of relapsed AML were CD117+/CD34+ in 13 cases, CD11 7+/CD34- in 6 cases, and CD117-/CD34+ in 1 case. Blasts in MDS were CD 117+/CD34+ in 3 cases, CD117-/CD34+ in 1 case. Blasts in MPD-BC were C D117+/CD34+ in 4 cases, CD117-/CD34+ in 2 cases. Blasts in ALL were CD 117+/CD34+ in 1 case, CD117-/CD34+ in 1 case, CD117-/CD34- in 3 cases. Of 26 cases of CD117+ AML, CD4 was expressed in 15 (58%) cases, CD7 i n 7 (27%) cases, and CD2 in 2 (8%) cases. CD117/CD34 expression did no t correlate with FAB subtype of AML. CD117 is borne on most leukemic b lasts of myeloid origin (in this study, 87% of AML, 80% of MPD-myeloid BC, and 75% of MDS) and does not exclude expression of LAA. Although CD117 is a receptor for stem cell factor, its expression does not appe ar to correlate with CD34 positivity.