Montanide Gel01 ST Adjuvant Enhances PRRS Modified Live Vaccine Efficacy by Regulating Porcine Humoral and Cellular Immune Responses

Porcine reproductive and respiratory syndrome (PRRS) is a devastating disease caused by the PRRS virus. The Montanide class of flexible polymeric adjuvants has recently been shown to enhance protective immunity against PRRSV infection in piglets when used in combination with PRRS modified live vaccines (MLV). In this study, we explored the efficacy and immunological mechanisms of protection of Montanide Gel01 ST (Gel01) adjuvanted modified live PRRSV vaccine in pigs challenged with two genetically distinct strains of PRRSV. Gel01-MLV reduced lymph node pathology scores in pigs challenged with VR-2332 (parental strain of MLV vaccine) but not that in pigs challenged with MN184A (heterologous strain), when compared to that in pigs vaccinated with un-adjuvanted MLV. Pigs vaccinated with Gel01-MLV had higher levels of PRRS-specific antibodies, as measured by IDEXX ELISA and virus neutralizing antibodies, after vaccination and VR-2332 challenge. In addition, pigs vaccinated with Gel01-MLV had decreased levels of IFN-γ, IL-10, and T-regulatory lymphocytes in the blood as compared to that in pigs vaccinated with MLV alone. Interestingly, we found that addition of Gel01 did not change the profile of other T lymphocyte populations after PRRSV challenge. These results demonstrate that the MLV adjuvanted with Gel01 provides enhanced protection against homologous PRRSV infection, possibly by regulating the production of PRRSV-specific antibodies and cytokines involved in the development of T-regulatory cells. Thus, Gel01 ST is a promising adjuvant that can be formulated with PRRSV MLV vaccines to reduce disease severity and tissue damage caused by PRRSV infection in pigs.