Hemangioblastic Activity of Infant Leukemia with t(4;11).

Background: Infant leukemia patients with t(4;11) have an extremely high risk for treatment failure. Hemangioblasts are cells that were initially described in the embryonic yolk sac, where they make both blood and blood vessels when these two systems are forming. It was demonstrated that hemangioblasts are present in the adult bone marrow and CML patients. Recently, subgroups of infant ALL patients with t(4;11) were found to have gene expression profiles similar to hemangioblasts by microarray. However, whether infant leukemia cells behave like hemangioblasts and produce their own blood vessels remains unknown.

Objective: We sought to determine whether infant leukemia cells with t(4;11) are derived from malignant hemangioblasts and can produce their own blood vessels.

Design/Methods: Three childhood leukemia cell lines with t(4;11): MV4-11, SEM-K2 and RS4-11, were used to analyze the expression pattern of key angiogenic receptors by flow cytometry and angiogenesis related proteins by protein array in comparison with benign endothelial cells. These cell lines were also cultured in vitro using Matrilgel, an in vitro angiogenesis assay system, in order to test their ability to produce vascular tubes. These cell lines were injected into the immune deficient NOD/SCID mice after sublethal irradiation to establish leukemia in vivo. Some of primary cells from MLL patients were obtained and subcutaneously injected into NOD/SCID mice mixed with BD Matrigel to observe their vessel development in vivo together with these three cell lines. The bone marrow, liver, spleen and tumor tissues together with Matrigel were collected to look for the evidence of t(4;11) in endothelial cells by immunohistochemical staining and fluorescent in situ hybridization (FISH).

Results: The leukemia cell lines expressed many angiogenetic cytokines, such as VEGF, VEGF-D, RANTES, PIGF, PDGF-BB, MCP-1, IGF-1, ENA-78, and angiogenin, at the same levels as HUVEC cells, a human umbilical vessel endothelial cell line. Different cell lines expressed some angiogenesis-related receptors, such as CD31, Tie-2, PDGFRalpha, CD141, CD146, and KDR. None of the cell lines formed tubes in Matrigel. When these three cell lines generated leukemia in NOD/SCID mice, the microvessel density level increased in the tumor areas. However, immunostaining for human and murine endothelial markers demonstrated that all the vessels came from the mouse, not from the human leukemia cells.

Conclusions: We conclude that infant leukemia cell lines with t(4;11) have proangiogenesic activity. However, these cells do not function as hemangioblasts, as they do not produce blood vessels in culture or in vivo in NOD/SCID mice. We plan to look further by examing bone marrow biopsies from patients with t(4;11) leukemia to determine whether the translocation is present in their blood vessels.