In retinoblastoma cell lines Y79 (Figure 5C), WERI-Rb-1 (Figure 5D) transfected with EGP2-TK, EGP2-TK-2T, EGP2-TK-4T, EGP2-TK-2C and EGP2-TK-4C constructs, followed by GCV treatment showed no significant difference in cell death. Here, TKT is linked to retinoblastoma.