Improving cellular immunity for cancer treatment by tethering mRNA vaccine with short-double-stranded adjuvants | Poster Board #3602

The performance of mRNA cancer vaccines can be potentially improved by incorporating immunostimulatory adjuvant into antigen-encoding mRNA. Instead of locating the adjuvancy at the packaging components, we applied RNA engineering to directly confer it at the antigen-encoding mRNA by tethering short double-stranded RNA (dsRNA), a substrate recognizable by the RIG-I innate immune receptor, onto the mRNA strand via hybridization with the dsRNA positioned so as to not hamper the mRNA’s ability to express antigen proteins. We determined the optimized structure of dsRNA that most efficiently stimulates RIG-I by screening several candidates of different length and sequences. Ultimately, the optimized structure effectively activated dendritic cells (murine and human origin) and stimulated those cells to secrete a wide range of proinflammatory cytokines without increasing the levels of anti-inflammatory cytokines. Notably, the design offered the tuning of immunostimulation intensity through the modulation of the number of dsRNA along the mRNA strand as a means to prevent excessive immunostimulation. As a proof of concept for its application as a vaccine, we demonstrated that dsRNA-tethered mRNA encoding ovalbumin (OVA) in anionic lipoplex formulation used in clinical trials provided appreciable cellular immunity in the mice model and a more potent therapeutic effect in mouse lymphoma (E.G7-OVA) model. Finally, we show that the platform is versatile by offering it in two other formulations, ionizable lipid-based lipid nanoparticles and polyplex micelles. To conclude, the platform developed here offers a simple and versatile approach to provide a variety of mRNA cancer vaccine formulations with the desired degree of immunostimulation.