Vaccine Potency and Structure of Yeast-Produced Polio Type 2 Stabilized Virus-like Particles

Poliovirus (PV) is on the brink of eradication due to global vaccination programs utilizing live-attenuated oral and inactivated polio vaccines. Recombinant PV virus-like particles (VLPs) are emerging as a safe next-generation vaccine candidate for the impending polio-free era. In this study, we investigate the production, antigenicity, thermostability, immunogenicity, and structures of VLPs derived from PV serotype 2 (PV2) wildtype strain and thermally stabilized mutant (wtVLP and sVLP, respectively). Both PV2 wtVLP and sVLP are efficiently produced in Pichia pastoris yeast. The PV2 sVLP displays higher levels of D-antigen and significantly enhanced thermostability than the wtVLP. Unlike the wtVLP, the sVLP elicits neutralizing antibodies in mice at levels comparable to those induced by inactivated polio vaccine. The addition of an aluminum hydroxide adjuvant to sVLP results in faster induction and a higher magnitude of neutralizing antibodies. Furthermore, our cryo-EM structural study of both sVLP and wtVLP reveals a native conformation for the sVLP and a non-native expanded conformation for the wtVLP. Our work not only validates the yeast-produced PV2 sVLP as a promising vaccine candidate with high production potential but also sheds light on the structural mechanisms that underpin the assembly and immunogenicity of the PV2 sVLP. These findings may expedite the development of sVLP-based PV vaccines.