GFAP and glioblastoma: Furthermore, immunohistochemical analysis of the tumor xenograft generated from 5-ALA/FACS-positive cells revealed a mitotically active (Ki67 positive) tumor, negative for the smooth muscle marker reticulin, but positive for glial fibrillary acidic protein (astrocytic marker) and vimentin (mesenchymal marker), collectively confirming glial and tumor origin of the xenograft from 5-ALA-positive GBM cells (Figure 6D–F).