To determine whether Tie2-mediated changes in glioma phenotype modulates the neoplastic characteristics of these tumors in vivo, we injected U251.vector or U251.Tie2 cells into the brains of immunodeficient mice, and then we sacrificed the animals approximately 20 days after cell implantation, and analyzed their brains for the presence of tumors. The gene discussed is TEK; the disease is central nervous system cancer.