When suicide gene TK was been injected to local tumor, as a result of the bystander effect, even if only a few normal or tumor cells been infected by TK, the encircling uninfected tumor cells can also be killed thus the therapeutic effect on tumor should be independent of transfection efficiency on the initial injection, the reason is because tumor cells metabolize actively and can motivationally devour TK and immune-mediated destruction effect mechanism releasing by dying cells through gap junction and Connexin intercellular channel.