We examined whether the loss of cell viability that we observed in E6- and E7- shRNA-infected SiHa and CaSki cells was caused via apoptosis by using flow cytometry to assess annexin V binding and PI permeability of nonpermeabilized SiHa and CaSki cells 72 h after infection with lentivirus expressing the E6, E7 and control shRNA (Fig. 6). This evidence concerns the gene ANXA5 and infection.