Oral transgene vaccination mediated by attenuated Salmonellae is an effective method to prevent Herpes simplex virus-2 induced disease in mice.

An attenuated strain of Salmonella typhimurium has been used as a carrier for oral genetic immunization. The eukaryotic expression vector pCMV containing the gene of the glycoprotein D (gD) of the herpes simplex virus 2 was used to transform Salmonellae. The oral immunization with the transformed salmonellae elicited a strong cellular immune response in both, the mucosal and systemic compartments (spleen, ileal lymph nodes and Peyer patches). The immune response mainly consisted in a dramatic activation of IFN-gamma-secreting cells. Twenty hours following the challenge with five lethal doses of virus, mRNA for IFN-gamma was observed in vaginal tissues from mice immunized with salmonella harboring the plasmid pgD but not in tissues from mice immunized by the intramuscular route with pgD. After an intravaginal challenge all immunized mice survived without developing symptoms. Furthermore, the immunization with Salmonella resulted in a more effective control of viral shedding than intramuscular immunization. We have unequivocally demonstrated by the introduction of an intron in the green fluorescent protein that the expression of the plasmid was due to the transcription of the protein by an eukaryotic nuclear process and not as a result of expression of the protein by the bacteria. Macrophages and dendritic cells were found expressing the protein in systemic and mucosal compartments of the immune system.