Adjuvanted RNA Origami-A Tunable Peptide Assembly Platform for Constructing Cancer Nanovaccines

Cancer peptide vaccines represent a promising strategy to develop targeted and personalized treatments for cancer patients. While tumor peptides alone are insufficient in mounting effective immune responses, the addition of adjuvants can enhance their immunogenicity. Nanoparticle delivery systems have been explored as vaccine carriers to incorporate both adjuvants and peptides. One such nanoparticle is RNA origami (RNA-OG), a nucleic acid nanostructure that is programmed to form different sizes and shapes. Our designed RNA-OG can incorporate various biomolecules and has intrinsic adjuvant activity by acting as a toll-like receptor 3 agonist. We previously showed that the RNA-OG functions as an adjuvanted, carrier-free vaccine platform to assemble peptides. Although effective, only a fixed number of peptides (13) could be covalently linked to each RNA-OG.

Here, we developed a simple physical assembly strategy to attach polylysine-linked neopeptides onto RNA-OG so that the number of peptides per RNA-OG could be readily tuned and tested for their immunogenicity.

Although the vaccines with a high number of peptides, i.e., 100-200 peptides/RNA-OG, led to greater peptide presentation by bone marrow-derived dendritic cells, they failed to mount effective CD8⁺ T cell responses against engrafted tumor cells, probably owing to an induction of early T cell exhaustion. Interestingly, the same vaccine format with a low number of peptides, i.e., 10-15 peptides/RNA-OG, enhanced CD8⁺ T cell responses without provoking T cell exhaustion in tumor-bearing mice, leading to strong protective anti-tumor immunity. In comparison, the covalently assembled RNA-OG-peptide vaccine, having a similarly low peptide dosage, offered the highest therapeutic efficacy. Thus, our RNA-OG nanostructure provides a simple and tunable platform for peptide loading to optimize vaccine efficacy.

Our findings have significant implications for peptide vaccine design regarding peptide dosages and structural stability of RNA-OG complexed with peptides, which could guide the development of more effective peptide vaccines for cancer immunotherapy.