20 
15 
% STK 
16 
% Rejection 
100 
E 
E 
L 
m 
•» 
E 
o 
L 
e 
E 
3 
h 
100 
0* STK 
50* STK 
50 
10 
1 
0 
* Mice 
5 
5 
4 
4 
5 
100 
75 
0 
0 
The ability of immunodeficient mice to reject STK transduced cells was also studied. 
Nude and non-lethally irradiated mice were inoculated subcutaneously with 205-STK 
or 207- STK tumor cells at varying ratios as described above and treated with GCV. 
The immunodeficient mice did not reject tumor even when 100% of the tumor cells 
contained the HSV-TK gene (figure 17 and 18). Therefore, there appears to be 
possibly two mechanisms involved in the killing effect of TK positive cells on TK 
negative cells. 
17 18 
Non-lethally Irradiated Nude 
% STK 
* Mice 
% Rejection 
% STK 
* Mice 
% Reiect 
100 
4 
25 
100 
4 
25 
50 
4 
0 
50 
3 
0 
0 
3 
0 
0 
3 
0 
The effect of kbalb TK positive tumor cells on TK negative cells was analyzed using 
an intraperitoneal tumor model. Previous experiments demonstrated that in a 
relatively confined space, subcutaneously, as few as 50% TK positive cells within a 
tumor could cause regression of the tumor. Varying ratios of kbalb tumor cells (2x1 0 5 ) 
transduced with either the STK or LNL retroviral vector were injected I.P. into Balb/c 
Recombinant DNA Research, Volume 15 
[583] 
