Preparation of poloxamer-based CPV virus-like particle vaccine and its immunological evaluation in mice

Poloxamers are thermosensitive triblock copolymers valued for their safety and sustained-release properties. Using China's prevalent CPV-2c strain (JSLYG-18) of canine parvovirus (CPV), we produced virus-like particles (VLPs) via prokaryotic expression and formulated a thermosensitive poloxamer gel vaccine. The results showed that the optimal formulation of the poloxamer thermosensitive gel consisted of 17% poloxamer 407 (P407), 3.2% poloxamer 188 (P188), and 0.3% hydroxypropyl methylcellulose (HPMC), with a gelation temperature (T_m) of 35.8 °C, demonstrating excellent stability and ease of preparation. In vitro drug release studies revealed that BSA was released from the poloxamer gel over 48 h, with a cumulative release rate of 98.2%, following the Weibull kinetic model, indicating a synergistic mechanism of drug diffusion and gel erosion. The poloxamer-based VLPs vaccine exhibited minimal tissue irritation and enhanced immune responses in mice, including activation of splenic lymphocytes. Post-immunization, serum IgG levels reached 1:3 × 10⁵, and neutralizing antibody titers reached 1:300. Both were significantly higher than those in the naked VLPs protein group, with prolonged antibody persistence. These findings demonstrate that the poloxamer thermosensitive gel-based CPV VLPs vaccine not only possesses excellent immunogenicity but also serves as a promising vaccine delivery platform for further application.