Lyophilized monkeypox mRNA lipid nanoparticle vaccines with long-term stability and robust immune responses in mice

The World Health Organization (WHO) has recently declared another global health emergency due to the rapidly spreading monkeypox (Mpox) outbreak in numerous African countries. To address the unmet need to contain the outbreak using the existing vaccines, this study developed a lyophilization process for an effective, scalable and affordable Mpox mRNA-LNP vaccine candidate to address the global health crisis. A comprehensive evaluation and optimization of the vaccine formulation (the type/concentration of cryoprotectants, the type/concentration of buffer system, as well as the mRNA concentration and reconstitution solvent) and the freeze-drying process parameters (freezing method, temperature, cooling rate and primary/secondary drying conditions) were conducted. The freeze-dried product exhibits a uniform appearance and a moisture content of less than 1%. Reconstitution of the lyophilized mRNA-LNP resulted in equivalent particle size/polydispersity index, encapsulation efficiency and mRNA integrity compared to that of freshly prepared mRNA-LNP. Furthermore, the lyophilization process can be scaled up 100-fold to 2000 vials/batch. Notably, the lyophilized mRNA-LNP demonstrated a storage stability of at least 12 months at 4°C, and at ambient temperature for a minimum of 8 h post-reconstitution, exhibiting minimal deterioration in product quality. The in vitro biological activity and in vivo immunogenicity of the lyophilized mRNA-LNP was comparable to that of the freshly prepared mRNA-LNP. These results provide a compelling rationale for the utilization of lyophilization technology in enhancing the accessibility of the Mpox mRNA vaccine in developing countries, a strategy that is crucial for containing the global epidemic of Mpox infection.