Abstract: This invention encompasses a composition for killing target cells, such as tumor cells. The composition comprises a first and a second adenoviral vector that have complementary function and are mutually dependent on each other for replication in a target cell. One of said adenoviral vectors has a target cell-activated promoter or a functional deletion that controls and limits propagation of the adenoviral vectors in the target cells which directly or indirectly kills the target cells. One of the adenoviral vectors comprises a gene encoding a protein which is expressed in the target cells and can induce anticancer immune responses. The target cells may be hepatoma, breast cancer, melanoma, colon cancer, or prostate cancer cells, for example. The vectors of this invention may also be utilized to treat other diseases such as restenosis, in which case the target cell may be a vascular smooth muscle cell, for example.