A side population of glioma stem-like cells was isolated from the C6 lacZ7 glioma cell line (transfected with �-galactosidase) and engrafted into rat spinal cord. After 7 days tissue was collected and immunostained for �-galactosidase (red) to detect tumor cells and nestin (green), which stains both C6 tumor cells and progenitor cells. Tumor cells (�-galactosidase, red) that also express nestin are seen as yellow. Many nestin-positive cells were �-galactosidase negative, indicating they were not tumor cells but probably were neural or endothelial progenitor cells recruited to the tumor site. Nuclei arelabeled with Hoechst dye (blue). For further details, please see Gilg and colleagues on page 1804 in this issue.

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