The present invention provides a vector system in which a MuLV-Gag gene, a MuLV-Pol gene, and a GaLV-Env gene are expressed in two separate vectors. The vector system is capable of inserting a therapeutic gene to these two separate vectors, and in this raged, the size of an inserted gene is not limited and a variety of foreign therapeutic genes may be inserted to the vectors. Accordingly, the foreign therapeutic gene may be delivered in a safe and efficient manner to desired tissue of cells of aberrant proliferation. Therefore, the vector system is applicable in a composition for delivering a gene targeting the aberrantly dividing cells of aberrant proliferation, wherein the composition includes a retrovirus produced by cell line transfection. The vector system is also applicable in a composition for preventing or treating a disease caused by cells of aberrant proliferation of, such as cancer cells.