Abstract: BACKGROUND＆AIM：To investigate the effect of an anti-CD44 antibody,HI44a,in inducing differentiation and apoptosis of freshly isolated acute myeloid leukemic cells. MATERIAL AND METHODS：The effect of HI44a on the differentiation and apoptosis of fresh leukemia cell from 31 acute myeloid leukemia patients were studied in vitro. Cell morphology, nitroblue tetrazolium(NBT) reduction and expression of CD11b, CD14 and CD15 were measured. Early apoptotic cells were detected by annexin-Ⅴassay. Expressions of G-CSF, M-CSF and c-myc transcript were investigated by RT-PCR. RESULTS：In the presence of HI44a, the primary leukemia cells became more mature in morphology, the percentage of NBT-positive cells increased to 31％ (control 9％), 55％ (control 10％), 25％ (control 12％) and 32％(control 11％) in all the four subtypes, there was a significant difference between the groups (P<0.01). The expression of CD11b, CD14 and CD15 also increased to 19.29％,40.60％and 66.82％, respectively, whereas that in untreated control cells was 9.65％，27.40％ and 57.38％. In addition, HI44a could efficiently induce leukemia cell to undergo apoptosis, the mean percentage of early apoptotic cells was significantly increased compared to the untreated control AML cells (41.18％ vs 26.21％). This effect was associated with enhanced M-CSF transcript expression and decreased c-myc transcript expression. CONCLUSION： HI44a could effectively induce differentiation and apoptosis of leukemia cells and thus warrants further studies as a therapy for acute myeloid leukemia.

Key words: anti-CD44 antibody, acute myeloid leukemia cell, differentiation, apoptosis