Targeted-pig trial on safety and immunogenicity of serum-derived exosomes obtained from Porcine Respiratory and Reproductive virus infections

Background: The porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important diseases of veterinary interest. Available vaccines have serious limitations such as little protective immunity, possible reversion to virulence, inability to induce long lasting and heterologous protection. As previously reported by us, exosomes from PRRSV convalescent swine sera contain immunogenic viral proteins. The aim of this study was to perform a targeted-pig trial to test the safety and immunogenicity of such exosomes. Methods: PRRSV convalescent sera were obtained from pigs that overcome PRRSV acute infection. Exosomes were obtained by a combination of ultracentrifugation and size exclusion chromatography and characterized by BCA, Flow cytometry, nanosight, Cryo-TEM and proteomic analyses. Animals were vaccinated with exosomes and/or viral peptides identified by proteomics in combination with Montanide. Immune responses were measured by a commercial ELISA (IDEXX X3 PRRSV), by an indirect in-house ELISA and by IFN-y ELISPOT. Results: No clinical symptoms or adverse effects were observed in animals infected with up-to 2 mg of exosomes, unequivocally demonstrating that this vaccine formulation is free of virus and safe. ELISA analysis demonstrated that immunizations elicited specific humoral IgG immune responses, albeit variably. Yet, sera from these same vaccinated animals was diagnosed free of virus using a commercial test; thus, indicating that this vaccine approach is able to differentiate vaccinated from infected animals. Last, priming the animals with exosomes from convalescence animals and boosting them with synthetic peptides identified by MS associated with them, elicited distinctive and high IFN-y immune response when stimulated with viral peptides (around 400 SFCx106 PBMCS). Summary/Conclusion: Altogether, our data support further development of plasma-derived exosomes from convalescence animals as a novel antigen discovery and vaccine strategy against PRRSV.