We transfected host cells with an antimicrobial peptide/protein-encoding gene as a way to enhance host defense mechanisms against infection. The human beta-defensin 2 (HBD-2) gene was chosen as a model because its protein does not require cell type-specific processing. Using a retroviral vector carrying HBD-2 cDNA, we treated several mouse or human cell lines and primary cell cultures including fibroblasts, salivary gland cells, endothelial cells, and T cells. All transduced cells produced detectable HBD-2. In Escherichia coli gel overlay experiments, secreted HBD-2 from selected cell lines showed potent antimicrobial activity electrophoretically identical to that of purified HBD-2. We then used a mouse model (nonobese diabetic/severely compromised immunodeficient [NOD/SCID]) to test HBD-2 antimicrobial activities in vivo. HT-1080 cells carrying HBD-2 or control vector were implanted subcutaneously into NOD/SCID mice to allow tumor formation. Escherichia coli was then injected into each tumor mass. Tumors were resected after 16 hr and homogenized for bacterial colony-forming unit analysis. Compared with control tumors, HBD-2-bearing tumors contained only 7.8 +/- 3.3% viable bacteria. On the basis of this demonstration of HBD-2 in vivo antimicrobial activity, enhancement of antibacterial host defense by HBD-2 gene therapy may be feasible.