mRNA Co-expressing Membrane-Bound gE/gI Complex with CpG Adjuvant Enhances Efficacy in Preventing Herpes Zoster
Background
Varicella Zoster Virus (VZV) remains latent in ganglia following childhood chickenpox infection and reactivates during periods of weakened immunity, causing severe pain and skin lesions. As society ages, the prevalence and treatment burden of Herpes Zoster (HZ) are increasing. While recombinant protein vaccines have achieved superior efficacy compared to traditional live-attenuated vaccines, they possess clear limitations. The use of proprietary adjuvants to induce strong immunogenicity has frequently led to reported adverse reactions such as injection site pain, myalgia, and fever.
These side effects reduce vaccination compliance among the elderly and hinder the rate of completing the recommended two-dose regimen. Consequently, there is a continuous demand for vaccine formulations that maintain viral defense immunity equal to or greater than existing ones while reducing the burden of adverse reactions on patients. Recently, messenger RNA (mRNA) technology, which has emerged as a pillar of infectious disease prevention, is being actively explored as a promising alternative to protein-based formulations due to its ability to balance humoral and cellular immunity.
Key Findings
Researchers designed various mRNA candidates by focusing on the structural characteristics of Glycoprotein E (gE) and Glycoprotein I (gI), which are key envelope proteins on the VZV surface. They hypothesized that the depth of the induced immune response could vary depending on the combination of these two proteins involved in viral cell entry and spread. The researchers precisely compared the immunogenicity in mouse models based on the antigen's expression site and binding mechanism.
Experimental results showed that the membrane-bound gE, induced to localize on the cell membrane, elicited the highest and most sustained neutralizing antibody response. Co-expression of the gI antigen significantly enhanced T-cell immune responses essential for viral inhibition. The disparity according to the combination administration method was also clearly observed. The result showed that co-administration of membrane-localized gE and gI mRNA encapsulated in lipid nanoparticles (LNP) separately induced the strongest cellular immunity, compared to a single antigen form or a fusion form where two proteins were artificially linked.
To maximize the ability to induce cellular immunity, researchers added the CpG oligodeoxynucleotide (CpG-ODN) 1018 adjuvant, a Toll-like receptor 9 (TLR9) agonist. They confirmed immune response amplification in both virus-naive mice and mice with a simulated history of prior infection. The formulation combined with CpG-ODN 1018 not only significantly raised neutralizing antibody titers but also amplified CD4+ and CD8+ T-cell responses secreting antigen-specific interferon-gamma (IFN-γ), establishing a Th1-biased immune profile. This level was comparable to or exceeded that of the group administered Shingrix, a commercially available protein vaccine. In safety evaluations, no systemic toxicity or histopathological damage was observed, proving excellent tolerability.
Significance and Outlook
The strategy of co-expressing the gE and gI antigens as a membrane-bound complex within the cell proved superior in triggering immune responses compared to single-antigen-based formulations. The results demonstrated that combining the mRNA-LNP platform with the approved CpG-ODN 1018 adjuvant can raise both humoral and cellular responses to peak levels. Since suppressing the reactivation of latent viruses requires a robust T-cell response, this candidate demonstrated the advantage of inducing broad CD4+ and CD8+ T-cell responses.
Practical challenges remain before reaching the commercialization stage. It is uncertain whether the immunogenicity and safety confirmed in small rodents will be replicated at the same level in the human immune system. Subsequent verification must follow non-clinical primate testing and early-stage human clinical trials, with rigorous tracking of the frequency of adverse reactions and the long-term duration of the immune response.
Herpes zoster (HZ), caused by reactivation of latent varicella zoster virus (VZV), remains a growing health burden. Developing new HZ vaccines with high efficacy and improved tolerability could address limitations of current vaccines and increase vaccination uptake and completion rates. To identify an optimal antigen design, we systematically evaluated multiple mRNA candidates based on VZV glycoprotein E (gE) and I (gI). In mice, membrane-localized gE induced the strongest and most durable antibody responses, whereas inclusion of gI markedly enhanced T-cell responses. Co-delivery of membrane-localized gE and gI (gE+gI Lmix) elicited the most robust cellular responses, outperforming both single-antigen and fusion constructs. We therefore selected gE+gI Lmix for further optimization with CpG oligodeoxynucleotide (CpG-ODN) adjuvants. In both naïve and VZV-primed mice, CpG-ODN 1018 increased neutralizing antibody titers and significantly enhanced antigen-specific CD4+ T cell responses.
This newly designed dual-antigen mRNA vaccine formulation holds the potential to substantially improve vaccination compliance in clinical settings. The completion rate for the two-dose regimen of existing commercial vaccines was lower than expected, often due to systemic side effects such as severe fever and local pain following vaccination. The mRNA formulation combined with the safety-proven CpG-ODN 1018 is evaluated to mitigate vaccine hesitancy by reducing side effects while inducing a robust Th1 immune response. From an industrial perspective, utilizing the mRNA manufacturing process, which has a shorter production cycle and easier yield management compared to protein purification processes, is expected to contribute directly to the diversification of the global vaccine supply chain and cost reduction in the future.