PVR and glioblastoma: Compared with normal astrocytes (CC-2565), significantly higher expression of CD44 and CD155 in GBM cell lines was demonstrated by flow cytometry (p<0.0001 for both CD44 and CD155 expression in terms of positive cell population and fluorescence fold with the exception of UPMC which showed a similar fluorescence fold to CC-2565 (p>0.05; Fig. 1d).