Novel means have been discovered for increasing the resistance of an animal host (including humans) to diseases caused by intracellular bacteria, protozoa, and viruses. The infection treated may, for example, be equine infectious anemia, or infection by the human immunodeficiency virus. Novel means have also been found for treating tumors. Augmentation of the host's defenses against infectious diseases or tumors is achieved by "arming" the host's cells with an exogenous gene encoding a natural or synthetic lytic peptide. For example, the transfection of hematopoietic stem cells and embryonic cells will produce animals with enhanced disease resistance; and transfection of TIL (tumor infiltrating lymphocytes) cells or other cells can be used in the treatment of tumors. Genes coding for a cecropin or other native or synthetic lytic peptide can be transferred and stably expressed in mammalian, bony fish, other vertebrate, and other animal cells. The transformed cells have the ability to produce and secrete a broad spectrum chemotherapeutic agent that has a systemic effect on certain pathogens, particularly pathogens that might otherwise evade or overcome host defenses. Novel means have also been discovered for transforming a eukaryotic cell with a gene under the control of an exogenous promoter that is responsive to an inducer of an acute-phase peptide or protein. For example, a moth promoter for the cecropin B gene has been found to function appropriately in a mammalian cell.