Abstract 1030: Are endothelial cells essential for the development of leukemia

Background The most pronounced micro-environmental changes observed in the bone marrow of leukemia patients are endothelial proliferation and angiogenesis. The molecular basis underlying how blood vessels sustain/initiate leukemia remains poorly understood. However, this may explain why anti-angiogenic agents are effective treatments for leukemia. Aim To define whether modification of the endothelium initiates and/ or perpetuates leukemia and determine the genes responsible. Methods Sleeping Beauty (SB) is a system of insertional mutagenesis that randomly integrates transposons into genomic DNA. Endothelial-specific SB activation was achieved by driving CRE-recombinase expression via the Tie-2 promoter/enhancer. Tissues were analyzed for histology, immune profiles and genes with insertional mutations. Colony forming unit (CFU) assays were performed on magnetically selected CD45-/CD31+ endothelial cells and CD45-/CD31-/Sca1+ hematopoietic stem cells isolated from bone marrow of CRE+ and CRE- mice and the resulting colonies analyzed by flow cytometry for CD3 (lymphoid) and CD14 (myeloid) populations. Results Over 50 weeks all CRE+ mice (n=106), but none of the WT mice (n=35), became moribund and were sacrificed. At necropsy, CRE+ mice displayed peripheral leukocytosis and gross anatomical/histological modifications in spleens, livers and thymus. Molecular analyses showed amplifications of either T cell (CD3; 49%) or macrophage (CD14; 28%) populations or both (23%) in the spleen and bone marrow of CRE+ mice. These leukocytes were SB positive indicating they originated from endothelial cells, and not hematopoietic stem cells. This was confirmed by CFU assays in which elevated CD3+ and CD14+ populations were found arising from the CD45-/CD31+ cells but not CD45-/CD31-/Sca1+ cells from CRE+ mice relative to WT mice. Targeted deep sequencing identified genes related to cytokine mediated signaling and transcriptional control. Many of the identified genes are already implicated in human leukemia. Conclusions Targeting SB insertional mutagenesis to the endothelium resulted in hematological malignancy in mice indicating direct control over both myeloid and lymphoid differentiation by endothelial cells. Targeted deep sequencing identified changes to known mediators in hematological lineage specification, validating our model. Also identified were novel candidates that may contribute to the development of leukemia and offer new therapeutic targets to treat this maligna