Establishment of an in vivo model for pediatric Ewing tumors by transplantation into NOD/scid mice

Ewing tumors are a clinically heterogeneous group of childhood sarcomas tha t represent a paradigm for understanding solid tumor biology, as they are t he first group of sarcomas for which a chromosome translocation has been ch aracterized at the molecular level. However. the biologic organization of t he tumor, especially the processes that govern proliferation, differentiati on, and metastasis of primitive tumor stem cells is poorly understood. Ther efore, to develop a biologically relevant in vivo model, five different Ewi ng tumor cell lines and primary tumor cells from three patients were transp lanted into immune-deficient mice via intravenous injection. NOD/scid mice that carry a complex immune deficiency and thus nearly completely lack the ability to reject human cells were used as recipients. Overall. 26 of 52 mi ce (50%) transplanted with VH-64, WE-68, CADO-ES1, TC-71, and RM-82 cells a nd 4 of 10 mice (40%) transplanted with primary tumor cells engrafted. More over, primary cells that did not grow in vitro proliferated in mice. The pa ttern of metastasis was similar to that in patients with frequent metastase s in lungs (62%), bone marrow (30%), and bone (23%). Using limiting dilutio n experiments, the frequency of the engraftment unit was estimated at 1 Ewi ng tumor-initiating cell in 3 x 10(5) VH-64 cells. These data demonstrate t hat we have been able to establish an in vivo model that recapitulates many aspects of growth and progression of human Ewing tumors. For the first tim e, this model provides the opportunity to identify and characterize primiti ve in vivo clonogenic solid tumor stem cells. This model will, therefore, b e instrumental in studying many aspects of tumor cell biology, including or gan-selective metastasis and tumor angiogenesis.