In vivo correction of genetic defects of monocyte/macrophages using attenuated Salmonella as oral vectors for targeted gene delivery

Macrophages are normal targets for Salmonella during natural infections, an d it has been demonstrated that attenuated bacteria can deliver nucleic aci d vaccine constructs. Therefore, we assessed if attenuated Salmonella can b e used for the in vivo delivery of transgenes to their natural cellular tar get, in an attempt to correct genetic defects associated with monocytes/mac rophages. This system would offer the distinct advantage of achieving a spe cific targeting of defective cells in a non-invasive form. Using a reporter gene, we demonstrated that attenuated Salmonella could be used as an effec tive in vitro delivery system to transfer genetic material into nondividing cells like murine macrophages. In vivo, the oral administration of attenua ted Salmonella allows targeted delivery of transgenes to macrophages and su bsequently expression of transgenes at a systemic level. IFN gamma -deficie nt mice (GKO) were thus selected as a model for the in vivo validation of t he Salmonella-based delivery approach. Attenuated Salmonella, used as the c arrier for a eukaryotic expression vector encoding the murine IFN gamma gen e, was able to restore the production of this cytokine in GKO macrophages. Their oral administration to IFN gamma -deficient mice also re-established, in these immunocompromised animals, the natural resistance to bacterial in fections. These results demonstrate, for the first time, that attenuated Sa lmonella can be successfully used in vivo as a DNA delivery system for the correction of a genetic defect associated with monocyte/macrophages.