Abstract
Conventional mRNA vaccines played a crucial role in mitigating the COVID-19 pandemic but remain hampered by inherent instability, transient expression, limited payload capacity, and complex manufacturing, including their reliance on lipid nanoparticle (LNP) encapsulation. To address these challenges, this study describes the Gemini platform, an expression system with a bifunctional eukaryotic-prokaryotic promoter that can be deployed as either a self-amplifying RNA (saRNA) or as a self-amplifying DNA (saDNA) replicon, enabling robust amplification and expression of genetic cargo. Gemini eliminates the requirement for LNPs, exhibits enhanced stability during freeze-thaw cycles and lyophilization, and is compatible with ambient-temperature storage, thereby simplifying production and distribution. It maintains a strong safety profile, supports larger and more complex payloads than conventional mRNA vaccines, and induces prolonged protein expression, as demonstrated by a potent single-dose SARS-CoV-2 Gemini-based vaccine. With rapid, scalable manufacturing and flexibility across saRNA and saDNA formats, Gemini represents a versatile next-generation platform with potential for broad applications in molecular medicine and pandemic preparedness.