Rational Design and Immunological Mechanisms of Circular RNA-Based Vaccines: Emerging Frontiers in Combating Pathogen Infection

Abstract

Vaccines remain one of the most effective tools in combating infectious diseases, though traditional platforms are constrained by limitations including suboptimal immunogenicity, safety concerns, and manufacturing complexity. Circular RNA (circRNA) vaccines have recently emerged as a novel vaccine modality, demonstrating unique advantages including high stability, low innate immunogenicity, and sustained antigen expression. Although early research has predominantly focused on viral targets, accumulating evidence now supports the application potential of circRNA vaccines against diverse pathogens, particularly antibiotic-resistant bacteria. Through encoding critical antigens or virulence factors, these circRNA vaccines demonstrate capability to induce protective immune responses, presenting a viable alternative to conventional antimicrobial strategies. This review highlights recent advances in circRNA vaccine development, spanning synthetic circularization techniques, delivery approaches, and immunological mechanisms. We emphasize their potential against viral, bacterial, fungal, and parasitic infections, while addressing current challenges and future research directions of this emerging platform. Collectively, these insights underscore circRNA's multifaceted versatility and its expanding relevance in next-generation vaccine innovation.

Keywords: RNA delivery; circRNA vaccine; circular RNA; pathogens infection.

Figure 1

Key development timeline of circRNA vaccines. Timeline of key milestones in circRNA discovery, functional characterization, and vaccine development. Timeline illustrating major advances in circRNA biology, from early discoveries of circular RNAs to their functional characterization and recent application in vaccine development.

Figure 2

Molecular mechanism of circRNA vaccine activity in vivo. CircRNA vaccines delivered via LNPs are taken up by antigen-presenting cells (APCs) and translated into antigens by ribosomes. Antigens are processed by the proteasome and presented via MHC I to activate CD8⁺ T cells, which secrete cytokines and cytolytic molecules to initiate cellular immunity. Antigens can also be presented via MHC II, activating CD4⁺ T cells that assist B cells in producing neutralizing antibodies, thereby promoting humoral responses.

Figure 3

Different delivery system of circRNA. Schematic illustration of various delivery strategies for circRNA-based vaccines. Multiple approaches have been explored to enhance the delivery efficiency and immunogenicity of circular RNA (circRNA) vaccines, including (1) naked circRNAs, (2) dendritic cells (DCs) loaded with circRNAs, (3) virus-like particles (VLPs), (4) adeno-associated virus (AAV)-mediated delivery, (5) exosomes, and (6) lipid nanoparticles (LNPs).

Figure 4

Immune activation by circRNA vaccines in antiviral applications. CircRNA vaccines activate antiviral immune responses against a range of viruses, including SARS-CoV-2, influenza, HBV, monkeypox, and Zika virus. Through circRNA–miRNA–mRNA regulatory networks, they modulate immune-related gene expression, thereby initiating both humoral and cellular immunity. This immune activation is characterized by increased cytokine production, CD4⁺/CD8⁺ T cell responses, and the generation of neutralizing antibodies, collectively contributing to effective antiviral defense.

Figure 5

circRNA vaccine in anti-bacterial infection. CircRNAs contribute to antibacterial and antifungal immunity by regulating immune-related signaling pathways. Through miRNA sponging, they modulate key effectors, including Syk, TNKS2, ATG16L1, CTLA4, MAP3K8, and PTPN11, thereby promoting or suppressing autophagy, cytokine production, and cellular immune activity.