Identification of tumorigenic cells and implication of their aberrant differentiation in human hemangioblastomas.

The cytological origin of hemangioblastomas (HBs) is controversial possibly owing to limitation in the framework of normal vascular development. Our previous study reported that SSEA1 (stage-specific embryonic antigen-1) cells had the potential of HB-like structure formation in vitro cellular models. Here, we characterized primary proliferating tumor-initiating cells (TICs) and their neoplasmtic transformation. Neural stem cell marker SSEA1 and its lineage-related genes were demonstrated; no embryonic and mesenchymal stem cell markers were detected whereas their lineage-related genes in part were activated. Immunohistochemistry showed that the proliferating marker was preferentially expressed in SSEA1 cells. There was significant difference in the percentage of SSEA1 cells (SSEA1+/Ki67+ cells) between inherited and sporadic HBs although the tumor proliferative index (Ki67+ cells/ all cells) did not reach statistical significance between the two groups. Further, corresponding to the morphological changes of nucleolus in number and size, these highly proliferating SSEA1 cells demonstrated coexpression of either D2-40 or the mesodermal marker Scl (stem cell leukemia), brachyury, and Flk-1 (vascular endothelial growth factor-2), respectively, indicative of the neoplasmtic transformation into the stromal or vascular cells. The present data suggest that HBs might derive from neoplastic transformation of neural stem cells/progenitors. Such findings also provide new insights into the biology of HBs and the definition of TICs in situ, as well as the mechanisms of tumor neovascularization.