Vims Production from Vector-Infected 
PA 1 2 Cells' 
A. 
DHFR-virus- 
DHFR-virus 
Helper 
infected PA 12 
titer 
titer 
cell done 
(CFU/ml) 
(FFU/ml) 
1 
2 x 10* 
<1 
2 
2 x 10* 
<1 
3 
2x10* 
N.D.* 
4 
1 x 10* 
N.D.* 
3 
4 x 10* 
N.D.* 
6 
4 x 10* 
<1 
B 
Neo-virus (N2) 
Neo- virus 
Helper 
•infected PA 12 
titer 
tiler 
cell clone 
(CFU/ml) 
(FFU/ml) 
1 
3 x 10* 
20 
2 
4 x 10* 
<1 
3 
2 x 10’ 
40 
4 
1 x 10’ 
190 
3 
3 x 10* 
200 
C. 
Neo-virus (LNL2) 
Neo- virus 
Helper 
-infected PA 1 2 
titer 
titer 
cell clone 
(CFU/ml) 
(FFU/ml) 
10 
5 x I0 3 
<1 
11 
<10 1 
<1 
12 
10* 
<1 
13 
I0 3 
<1 
14 
10 3 
<1 
13 
<10* 
<1 
16 
2 x 10 3 
<1 
*Virus titer was measured in medium exposed to cells for 
24 h. 
*N.D., not determined. 
Table 2. (Miller et al. f 1986) 
Recombinant DNA Research, Volume 12 
[1831 
