Tethering designer short double-stranded RNA to mRNA for co-delivery of molecularly-targeted adjuvants and antigens towards cancer vaccination

Abstract

Immunostimulatory adjuvants play pivotal roles in mRNA cancer vaccines. Herein, mRNA architectonics-based approach was employed to enhance immunostimulatory properties of mRNA, by tethering immunostimulatory short 24-base-pair double-stranded RNA (dsRNA) to mRNA via hybridization, for specific stimulation of retinoic acid-inducible gene-I (RIG-I), an innate immune receptor triggering effective cellular immunity. This approach ensures the co-delivery of mRNA and adjuvants to obtain antigen expression and immune activation in the same antigen presenting cells for effective vaccination, and allows the tuning of immunostimulatory effects by controlling dsRNA number to avoid safety concerns associated with excessive immunostimulation. Thorough in vitro screening provided optimal mRNA structure that induces the secretion of a broad spectrum of proinflammatory molecules and effectively activated mouse and human dendritic cells, with minimal effect on antigen translation efficiency of mRNA. The optimal mRNA formulation improved the potency of mRNA vaccine to induce cytotoxic immune responses after encapsulation into mRNA lipoplex, and exhibited high therapeutic efficiency in lung metastatic model of melanoma using mRNA encoding tumor associated antigen. Furthermore, this system is versatile to potentiate vaccination effect with the use of mRNA polyplex micelle.