Then if the vector is successfully introduced into cells, the cells can become G418-resistant cells. After treating with G418, these vector(-) cells will die, while vector(+) cells will survive.
In this context, successful introduction of a vector into cells enables them to develop resistance to G418. Subsequently, cells that have not undergone exposure to G418 (vector(-)) will meet their demise, whereas cells that have been exposed (vector(+)) will persist.