A novel non-viral vector consisting of a plasmid DNA encoding the human gene for interleukin 12 (IL-12) and a biocompatible, biodegradable delivery polymer with potential antineoplastic activity. EGEN-001 is designed to increase the local concentration of IL-12 in the tumor microenvironment. IL-12 stimulates T-cell-independent production of IFN-gamma by peripheral blood mononuclear cells (PBMCs); enhances natural killer (NK) cell lytic activity; acts as a growth factor for T- and NK-cells; and is important for T-cell differentiation. IL-12 may potentiate antitumoral functions of the host immune system, resulting in immune-mediated tumor regression.