Acute Myeloid Leukemia Cells Fuse with Vascular Endothelium

Abstract 504 The hematopoietic niche supports both normal and malignant hematopoiesis. We have evaluated the functional interactions between leukemic cells and the endothelial cell component of the hematopoietic niche. Highly enriched populations of circulating human acute myeloid leukemia (AML) cells were obtained by therapeutic leukapheresis. These primary AML cells rapidly homed to and associated with pre-existing vascular tubes in vitro. Co-culture of human lung microvascular endothelial cells (HLMVEC) with AML cells both inhibited AML apoptosis by ∼50% (p 50% human AML cells in the bone marrow) we observed leukemic infiltration into the perivascular region of both large and small vessels of the mouse liver, and AML cells were frequently integrated into the vascular endothelium. Confocal microscopy surprisingly revealed the co-expression of human CD45 and the mouse endothelial cell marker CD31. To evaluate these apparently fused leukemia/endothelial cells further, single cell suspensions from the livers of mice engrafted with AML cells were FACS sorted based on the co-expression of human CD33 and mouse CD31. Multiplex PCR analysis of single hCD33+/mCD31+ cells verified the presence of both mouse genes ( fah and tspy or D2Mit206 ) and human genes ( flt3 and tty-15 ). The presence of the patient specific, leukemia-associated Flt3-ITD mutation confirmed that fusion occurs between malignant cells and vascular endothelium. AML and endothelial cell fusion was also confirmed by interphase fluorescent in situ hybridization (FISH) with species specific centromeric probes. In conclusion, the results from this study indicate that the functionally important cross-talk between normal hematopoietic stem/progenitor cells and vascular endothelium extends to malignant hematopoiesis. The fusion of primary AML cells with normal endothelial cells raises the possibility that vascular endothelium may serve as a reservoir for occult leukemia. Disclosures: No relevant conflicts of interest to declare.