A Bacterium-like Particle Vaccine Displaying Envelope Proteins of Canine Distemper Virus Can Induce Immune Responses in Mice and Dogs.

Canine distemper virus (CDV) can cause fatal infections in giant pandas. Vaccination is crucial to prevent CDV infection in giant pandas. In this study, two bacterium-like particle vaccines F-GEM and H-GEM displaying the trimeric F protein or tetrameric H protein of CDV were constructed based on the Gram-positive enhanced-matrix protein anchor (GEM-PA) surface display system. Electron microscopy and Western blot results revealed that the F or H protein was successfully anchored on the surface of GEM particles. Furthermore, one more bacterium-like particle vaccine F and H-GEM was also designed, a mixture consisting of F-GEM and H-GEM at a ratio of 1:1. To evaluate the effect of the three vaccines, mice were immunized with F-GEM, H-GEM or F and H-GEM. It was found that the level of IgG-specific antibodies and neutralizing antibodies in the F and H-GEM group was higher than the other two groups. Additionally, F and H-GEM also increased the secretion of Th1-related and Th2-related cytokines. Moreover, F and H-GEM induce IgG and neutralizing antibodies' response in dogs. Conclusions: In summary, F and H-GEM can provoke better immune responses to CDV in mice and dogs. The bacterium-like particle vaccine F and H-GEM might be a potential vaccine candidate for giant pandas against CDV infection.