COVID-19 has significantly accelerated advancements in mRNA vaccine and therapeutic technologies. However, there are several downsides of the current mRNA vaccine technology such as hypersensitivity reactions and anaphylaxis in some individuals and poor thermal stability, which complicates storage and transportation. This urges the need for the advancement of this technology. Additionally, mouse models used in vaccine efficacy studies may not fully reflect human physiology and immune responses due to genetic differences and variations in immune system function. This project seeks to combine traditional mouse studies with an innovative human airway organoid platform to evaluate the efficacy of in-house developed mRNA vaccine candidates.
Human airway organoid cultures and air–liquid interface (ALI) models were generated from primary human nasopharyngeal samples. We assessed vaccine uptake, reactogenicity, and immunogenicity of an in-house designed circular RNA vaccine encoding the CVB3 A62G mutation and formulated with mannose-modified lipid nanoparticles (LNPs), in comparison with a commercially available linear mRNA vaccine formulated with ALC-0315 LNPs. Both vaccines were designed to target the SARS-CoV-2 Delta strain. Both formulations did not induce IL-6 production in ALI cultures. However, uptake of the circular RNA vaccine was significantly higher than that of the linear mRNA vaccine after 24 and 72 hours post-incubation. SARS-CoV-2 spike receptor-binding domain (RBD) protein was detected in cell lysates as well as apical and basolateral supernatants of ALI cultures treated with the circular RNA vaccine, whereas RBD protein was detected only in apical supernatants following treatment with the linear formulation. To assess immunogenicity in vivo, mice were immunized with two doses of vaccine (1 µg per dose), and serum samples were collected one-month post-immunization. Both linear and circular vaccines elicited comparable neutralizing antibody responses. Sera from mice immunized with the circular RNA vaccine significantly reduced viral load in Delta-infected airway organoids but not observed with sera from mice immunized with the linear vaccine.
In conclusion, the circular RNA vaccine demonstrates superior cellular uptake and enhanced protective efficacy against SARS-CoV-2 Delta infection in human airway organoids compared to the linear mRNA vaccine. The integration of human organoid and animal models establishes a robust preclinical platform for evaluating mRNA vaccine efficacy.