Engineered VPg saRNA achieves cap-independent, low-immunogenic and precise encoding of therapeutic proteins in vivo.

Self-amplifying mRNA (saRNA) vectors hold promise for the sustained expression of mRNA vaccines in vivo. However, their inherently high immunogenicity and low-fidelity replication-stemming from the RNA viral genome's replication mechanisms-limit their efficacy as replacements or adjuncts to protein therapies. Here we report an engineered viral protein genome-linked (VPg) saRNA vector derived from a Norovirus replicon, designed for rapid loading of therapeutic protein mRNAs in vitro. The engineered VPg saRNA is adapted for a range of therapeutic scenarios, including treatment of tumor-associated cachexia under conditions of translational restriction in cap-dependent metabolism, precise encoding of oncolytic mRNAs in vivo to achieve complex functionality, and therapy for graft-versus-host disease in highly auto-immune environments. VPg saRNA addresses key limitations of linear mRNA and conventional saRNA therapies, broadening the potential applications of mRNA-based treatments.