I have been trying to transfact NK92MI with a regulatory construct ptTs-Neo, (Clontech, cat # 630925) over the last one month. I am using the Lonza kit (VCA-1001). When I transfer the cells in G418 containing media (0.25mg./ml), they are dying. I am not getting any substantial amount of cells so that I can proceed further. I am kind of surprised because the drug concntration is fairly low to kill a trasfected cell. My maxiprep worked well. Also, I did a control transfection with the construct provided by Lonza. It showed about 30-35% transfection efficiency. Does anybody have any idea on this?