MIL-53(Al)–oil/water emulsion composite as an adjuvant promotes immune responses to an inactivated pseudorabies virus vaccine in mice and pigs

Although vaccination with inactivated vaccines is a popular preventive method against pseudorabies virus (PRV) infection, inactivated vaccines have poor protection efficiency because of their weak immunogenicity. The development of an effective adjuvant is urgently needed to improve the efficacy of inactivated PRV vaccines. In this study, a promising nanocomposite adjuvant named as MIL@A–SW01–C was developed by combining polyacrylic acid-coated metal–organic framework MIL-53(Al) (MIL@A) and squalene (oil)-in-water emulsion (SW01) and then mixing it with a carbomer solution. One part of the MIL@A was loaded onto the oil/water interface of SW01 emulsion via hydrophobic interaction and coordination, while another part was dispersed in the continuous water phase using carbomer. MIL@A–SW01–C showed good biocompatibility, high PRV (antigen)-loading capability, and sustained antigen release. Furthermore, the MIL@A–SW01–C adjuvanted PRV vaccine induced high specific serum antibody titers, increased splenocyte proliferation and cytokine secretion, and a more balanced Th1/Th2 immune response compared with commercial adjuvants, such as alum and biphasic 201. In the mouse challenge experiment, two- and one-shot vaccinations resulted in survival rates of 73.3% and 86.7%, respectively. After one-shot vaccination, the host animal pigs were also challenged with wild PRV. A protection rate of 100% was achieved, which was much higher than that observed with commercial adjuvants. This study not only establishes the superiority of MIL@A–SW01–C composite nanoadjuvant for inactivated PRV vaccine in mice and pigs but also presents an effective method for developing promising nanoadjuvants. We have developed a nanocomposite of MIL-53(Al) and oil-in-water emulsion (MIL@A-SW01-C) as a promising adjuvant for the inactivated PRV vaccines. MIL@A-SW01-C has good biocompatibility, high PRV (antigen) loading capability, and a good property of sustained antigen release. The developed nanoadjuvant induced much higher specific IgG antibody titers, increased splenocyte proliferation and cytokine secretion, and a more balanced Th1/Th2 immune response than commercial adjuvants alum and biphasic 201. In challenge experiments with mice, survival rates of 73.3% and 86.7% were achieved from two-shot vaccination and one-shot vaccination, respectively. At the same time, a protection rate of 100% was achieved with the host animal pigs challenged with wild PRV.