Final Report Summary - OMVAC (Outer Membrane Vesicles (OMVs) from “Vaccinobacter”: A Synthetic Biology approach for effective vaccines against infectious diseases and cancer) OMVs are closed spheroid particles released by Gram-negative bacteria in the extracellular milieu. OMVs are particularly attractive as vaccine platform for three main features:1) they carry potent stimulators of the immune system, 2) they can be efficiently decorated with foreign antigens, and 3) they can be easily purified from bacterial culture supernatant . The unique properties of OMVs have already been exploited to develop vaccines for human use and OMVs represent a key component of the recently approved anti-Meningococcus B vaccine (Bexero) currently available in Europe and the USA. However, for their full-blown exploitation as vaccine platform, OMVs need be optimized. Scope of the OMVAC project was to apply Synthetic Biology to achieve four main objectives: 1) identification of the best strategy for decorating OMVs with foreign antigens, 2) removal of a large fraction of OMV endogenous proteins to enhanced the immune responses toward engineered antigens, 3) reduction of OMVs intrinsic reactogenicity, and 4) demonstration the effectiveness of the optimized OMV platform for the development of vaccines against infectious diseases and cancer.As far as the selection of novel strategies for OMV engineering is concerned, the project activities has led to the definition of different engineering protocols, one of which turns out to be particularly efficient, allowing the accumulation of foreign antigens in quantities often exceeding the 20% of total OMV proteins. Moreover, taking advantage of optimized gene editing approaches, the project has generated novel E. coli derivatives releasing OMVs deprived of tens of endogenous proteins and featuring reduced adjuvanticity properties as judged by the analyses of TLR agonistic activities and cytokine release. The effectiveness of the engineering strategies and the utility of the proteome minimized, OMV-releasing strains have been demonstrated by showing that OMVs decorated with five selected Staphylococcus aureus antigens elicit potent protective immune responses against S. aureus challenge in different mouse models. Finally, and particularly important, the project has demonstrated for the first time that OMVs engineered with cancer neo-epitopes are capable of eliciting CD4+/CD8+ T cell responses that protect immune competent mice in different cancer models.
