Oral Vaccination with Attenuated Salmonella Expressing Viral M25 Protein Effectively Protects Mice Against Murine Cytomegalovirus Infection

Attenuated <i>Salmonella</i> strains are promising oral vectors for vaccination against human infectious diseases. Human cytomegalovirus (CMV) is among the most common causes of disability in children, including intellectual disability and sensorineural hearing loss. Developing an anti-CMV vaccine is a major public health priority. We report in this study the construction of a new attenuated <i>Salmonella</i> strain to express murine cytomegalovirus (MCMV) M25 protein and its use for vaccination in mice against MCMV infection. In mice orally vaccinated with the constructed <i>Salmonella</i> vector carrying the M25 expression cassette, we revealed a substantial induction of anti-MCMV serum IgG and mucosal IgA humoral responses and a considerable elicitation of anti-MCMV T cell responses. When the vaccinated mice were challenged intraperitoneally and intranasally with MCMV, we observed a significant inhibition of virus infection and growth in various organs including spleens, livers, lungs, and salivary glands, compared to the non-vaccinated animals or those receiving a control vaccine without M25 protein expression. Moreover, we showed effective protection of these vaccinated mice from MCMV challenge. Our study provides the first direct evidence that an attenuated <i>Salmonella</i>-based vector with the MCMV M25 expression cassette can induce strong humoral and T cell responses and provide effective protection against MCMV infection. These results illustrate the feasibility of engineering <i>Salmonella</i>-based vectors expressing the M25 antigen for anti-CMV oral vaccine development.