Fig. 4 Transduction of C 6 glioma cells with ADV-tk in vitro. A, expression of HSV-tk gene in 
C 6 glioma cells after transduction by ADV-tk. 5 x 10 6 cells were plated on 1.5cm diameter 
wells and transduced with the viral vector using different M.O.I. as indicated. Cells were 
harvested two days later and protein extract was prepared by freeze thawing. The 
thymidine kinase activity was determined by phosphorylation of 3 H-acyclovir as described 
previously (8). B, GCV susceptibility of ADV-tk transduced C 6 glioma cells. Duplicate plates 
of C 6 glioma cells were incubated for 6 hr with ADV-tk at M.O.I.s of 0 to 1000. After 
transduction the cells were treated with either PBS or GCV at a concentration of lOmg/ml, 
and the surviving cells were counted 68 hr later. 
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