mice. Mice were treated with GCV (150 mg/kg I.P, b.i.d., x 5 doses) five days post 
tumor inoculation. Survival studies were then performed. Groups of mice receiving 
either 50% or 100% STK transduced tumor cells contained mice which exhibited long 
term survival (> 70 days), Groups 5 and 4 respectively (figure 19). Control mice, 
receiving kbalb-LNL cells +/- GCV or kbalb-STK without GCV did not exhibit long term 
survival (Groups 1, 2, and 3). Groups receiving 1% or 10% STK transduced cells 
contained no long term survivors but had a trend towards surviving longer than the 
controls (data not shown). Therefore, the ability of TK positive tumor cells to affect TK 
negative tumor cells can be demonstrated in a large enclosed body cavity. 
We next analyzed whether TK positive tumor cells could affect a preexisting tumor. 
The kbalb tumor model was used to address this question. Mice were inoculated I.P. 
with 2 x 10 5 kbalb-LNL (except Group 1 which received kbalb-STK) tumor cells on day 
0. Group 1 and 2 received no further treatment. Group 3 received GCV therapy 
beginning on day 5. Group 4 received 1x1 0 6 kbalb-STK cells and Group 5 received 
1 x 10 7 kbalb-STK cells on day 5 and GCV beginning on day 9. Group 6 mice 
received 1 x 10 6 kbalb-STK cells on day 1 and GCV therapy beginning on day 5. As 
shown in figures 20 and 21, mice in Groups 4, 5, and 6 had prolonged survival as 
compared to control groups (Groups 1,2, and 3). Group 6 mice had a mean survival of 
approximately 31 days as compared to 18 days for Group 3 ( p < 0.05). 
The above experiment which demonstrated the effect of kbalb-STK transduced 
tumor cells on preexisting tumor was repeated using other tumor lines. On day 0 mice 
were inoculated with EMT 6.8 tumor cells (murine mammary tumor) alone (Group 1) or 
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Recombinant DNA Research, Volume 15 
