153-159 Quantification of all-

CXCR4 is the receptor of CXC chemokine SDF-1 and may play a role in the homing of hematopoietic stem cells. We have investigated the CXCR4 gene expression during ATRA treatment in acute promyelocytic leukaemia (APL) patients. APL is a characteristic disorder with a specific translocation between PML and RAR alpha genes on chromosome 15 and 17. ATRA-induced differentiation of APL cells is strictly dependent on the presence of PML-RAR alpha. In our study, five APL patiens were involved. Two samples from each patient were compared to each other: Primary diagnostic sample and a sample taken at remission. Quantitative real-time PCR (LightCycler) has been used for quantification, which is a recently developed method for rapid and sensitive detection of gene expression. CXCR4 gene ratios were found under-expressed in cases 1 and 6 with blast counts at diagnosis 18%, and 20% but only moderately under-expressed in cases two and four where the blast count was at diagnosis 50%, and 80%. It was over-expressed only in case three where the blast count was 95%. These findings indicate that ATRA treatment might be effective in CXCR4 gene expression related to amount of the blast population in APL. Further gene expression studies would be helpful to understand how ATRA works on CXCR4 related molecular pathways in APL pathogenesis.