Nicole Hernandez

Background: Zika virus (ZIKV) is a mosquito-borne flavivirus associated with severe congenital abnormalities, including microcephaly, intracranial calcifications, developmental delay, and neurologic complications.⁸ Despite its global health impact, there is currently no approved vaccine for ZIKV prevention.⁹ One of the major barriers to vaccine development is antibody-dependent enhancement (ADE), in which cross-reactive, non-neutralizing antibodies facilitate viral entry into Fc gamma receptor-bearing immune cells, potentially increasing disease severity during subsequent dengue flavivirus infection.⁷ Therefore, novel vaccine strategies are needed that generate durable, highly specific neutralizing antibodies while minimizing cross-reactivity and reduce vaccine side effects.

Objective: The purpose of this literature review was to evaluate whether circular RNA (circRNA) vaccine platforms may overcome limitations of previous ZIKV vaccine approaches by improving RNA stability, antigen expression, immune specificity, and vaccine safety.

Search Methods: A literature search was conducted in PubMed to identify primary research articles published between 2021 and 2024 using the following keywords: “congenital ZIKV”, “ADE and dengue- cross reactivity”, “LNP immunology”, and “circRNA engineering.”

Results: Studies evaluating dengue virus immune responses demonstrated that afucosylated IgG antibodies exhibit increased binding to FcγRIIIa receptors. The binding enhances Fc-mediated viral uptake and increases disease severity, highlighting the importance of antibody quality in preventing ADE.² Comparative studies showed that circRNA exhibits greater resistance to exonuclease degradation than linear mRNA due to its covalently closed structure. This results in prolonged antigen expression and sustained protein production.³ CircRNA also demonstrated reduced innate immune activation, limiting interferon-mediated translational suppression through PKR-eIF2α signaling. Additional engineering studies showed that incorporation of internal ribosome entry sites (IRES) and intronic spacer sequences improved cap-independent translation and protein yield.⁴ Lipid nanoparticles (LNPs) in studies function as delivery systems and intrinsic adjuvants by inducing IL-6 signaling, promoting T follicular helper cell differentiation, germinal center formation, and affinity maturation of antibody responses.⁵ The primary ZIKV circRNA vaccine study demonstrated that a single-dose LNP-formulated circRNA vaccine encoding ZIKV EDIII and NS1 antigens generated strong neutralizing antibody responses, activated cellular immunity, provided complete protection against ZIKV challenge in murine models, and did not enhance dengue disease severity.¹

Conclusion: CircRNA vaccine platforms represent a possible next-generation mRNA vaccine strategy with the attraction of lower mRNA dose compared to current linear mRNA vaccines. This circRNA vaccine approach against  ZIKV combines prolonged antigen expression, specific targeted antigen design, and LNP-mediated immune activation to generate high-avidity neutralizing antibodies while minimizing ADE risk. Future studies should focus on the long-term durability of immune response, optimization of antigen and LNP design, and clinical translation in human populations.

Works Cited:

1. Liu X, Li Z, Li X, et al. A single-dose circular RNA vaccine prevents Zika virus infection without enhancing dengue severity in mice. Nat Commun. 2024;15(1):8932. Published 2024 Oct 16. doi:10.1038/s41467-024-53242-0
2. Bournazos S, Vo HTM, Duong V, et al. Antibody fucosylation predicts disease severity in secondary dengue infection. Science. 2021;372(6546):1102-1105. doi:10.1126/science.abc7303
3. Qu L, Yi Z, Shen Y, et al. Circular RNA vaccines against SARS-CoV-2 and emerging variants. Cell. 2022;185(10):1728-1744. doi:10.1016/j.cell.2022.03.044
4. Chen R, Wang SK, Belk JA, et al. Engineering circular RNA for enhanced protein production. Nat Biotechnol. 2023;41(2):262-272. doi:10.1038/s41587-022-01393-0
5. Alameh MG, Tombácz I, Bettini E, et al. Lipid nanoparticles enhance the efficacy of mRNA and protein subunit vaccines by inducing robust T follicular helper cell and humoral responses. Immunity. 2021;54(12):2877-2892.e7. doi:10.1016/j.immuni.2021.11.001
6. Crisanto-López IE, Jesús PL, López-Quecho J, Flores-Alonso JC. Congenital Zika syndrome. Síndrome congénito por virus Zika. Bol Med Hosp Infant Mex. 2023;80(1):3-14. doi:10.24875/BMHIM.22000110.
7. Tajik S, Farahani AV, Ardekani OS, et al. Zika virus tropism and pathogenesis: understanding clinical impacts and transmission dynamics. Virol J. 2024;21(1):271. Published 2024 Oct 29. doi:10.1186/s12985-024-02547-z
8. Vhp L, Aragão MM, Pinho RS, et al. Congenital Zika Virus Infection: a Review with Emphasis on the Spectrum of Brain Abnormalities. Curr Neurol Neurosci Rep. 2020;20(11):49. Published 2020 Sep 3. doi:10.1007/s11910-020-01072-0
9. Wong LP, Alias H, Lee HY, AbuBakar S, Lin Y, Hu Z. Has Zika been forgotten? A qualitative exploration of knowledge gaps, perceived risk and preventive practices in pregnant women in Malaysia. BMC Womens Health. 2024;24(1):190. Published 2024 Mar 21. doi:10.1186/s12905-024-02999-z