Co-administered Nipah F and G mRNA Vaccines Show Neutralizing Activity in Mouse Sera
Background: An alternative model for evaluating vaccines against a high-risk virus
Mice given two mRNA vaccines encoding separate Nipah virus antigens together developed antigen-binding antibodies, and their sera showed in vitro neutralizing activity. Published in Frontiers in Immunology, the study presents a strategy for combining two independently prepared vaccine formulations and a pseudovirus assay for measuring the response. The findings concern antibody responses in mice; prevention of infection in humans was not evaluated.
Nipah virus (NiV) is a zoonotic pathogen that can spread between people and cause severe neurological and respiratory disease. The paper describes its high fatality rate and the lack of approved vaccines or treatments as the motivation for the research. Work with live virus requires biosafety level 4 (BSL-4) facilities, limiting the experimental settings available for evaluating vaccine candidates.
The researchers targeted the G protein, which mediates viral attachment to cells, and the F protein, which mediates membrane fusion. They separately formulated messenger RNA (mRNA) encoding each antigen in lipid nanoparticles (LNPs), then administered the two formulations together. The study focused on exploring a vaccine design that allows the antigen composition to be adjusted independently.
Key findings: Neutralizing activity detected in sera four weeks after the first dose
The experiments used six-week-old female BALB/c mice. The co-administration group received 10 μg each of F and G mRNA-LNP by intramuscular injection at weeks 0 and 2. Comparison groups received a plant-derived recombinant F+G protein vaccine or phosphate-buffered saline as a control. Each experiment included three mice per group, and two independent experiments were conducted; individual-animal data were pooled for analysis.
Four weeks after the first dose, both the mRNA-LNP and recombinant-protein groups showed antibody responses against F and G. Separately from binding-antibody detection, neutralizing activity in sera from the mRNA-LNP group was assessed using a vesicular stomatitis virus (VSV)-based Nipah pseudovirus. This approach uses particles that mimic cell entry to measure how much serum suppresses the infection signal, instead of using high-risk live Nipah virus. The researchers optimized washing steps and used anti-VSV-G antibody treatment to reduce nonspecific background infectivity.
At two weeks, neutralizing activity was not detected in most mice. By week four, the 50% neutralization titer (NT50) reached approximately 10³–10⁴ in every animal evaluated. NT50 is the serum dilution factor that reduces the infection signal by half and must be distinguished from a rate of infection prevention in humans. Because the study lacked single-antigen vaccine groups, it is difficult to determine whether co-administration outperformed either antigen alone or whether the two antigens had a synergistic effect.
Implications and outlook: Potential of antigen combinations and remaining validation
These results provide preclinical evidence that separately formulated F and G mRNA-LNPs can be administered together to induce an antibody response. Preparing each antigen formulation independently may help future studies adjust antigen composition and dosing ratios. The optimal ratio has not yet been established.
Protective efficacy and structural validation also remain outstanding. No live-virus challenge was performed, so whether the vaccine prevents infection or encephalitis is unknown. Although the antigens included domains intended to promote trimer formation, no analysis was performed to confirm whether trimeric structures actually formed. The pseudovirus assay also requires further validation of its specificity, and the procedures used to reduce background infectivity may lower yield. It is difficult to predict long-term immunity or efficacy in humans from antibody results at four weeks in a small mouse study. Further work should separately evaluate each antigen’s contribution and protection in vivo.
Source: Full text of the Frontiers in Immunology article
INTRODUCTION: Nipah virus (NiV) is a highly pathogenic zoonotic virus associated with a high case fatality rate and human-to-human transmission, and it is listed as a priority pathogen by the World Health Organization (WHO) due to the lack of approved therapeutics or vaccines. NiV is classified as a biosafety level 4 (BSL-4) pathogen, which severely limits experimental studies in the absence of specialized containment facilities. Therefore, the establishment of pseudovirus-based surrogate models is essential for NiV vaccine research. METHODS: In this study, single-antigen mRNA-lipid nanoparticle (mRNA-LNP) vaccines encoding the Nipah virus fusion protein (NiV-F) and attachment protein (NiV-G) were designed and evaluated using a co-administration strategy of independently formulated single-antigen mRNA-LNPs. A Vesicular stomatitis virus (VSV)-based NiV pseudovirus system was established and applied to assess neutralizing antibody responses in a mouse model. RESULTS: The synthesized mRNA-LNP vaccines exhibited high purity and relatively consistent physicochemical properties, indicating uniform formulation characteristics. The VSV-based NiV pseudovirus showed a robust infection signal compared to background controls, and optimization of the purification process effectively reduced non-specific background, enabling reliable evaluation of DISCUSSION: This study provides a foundation for future NiV mRNA-LNP vaccine development and presents a flexible vaccine design approach based on co-administration of independently formulated single-antigen mRNA-LNPs in which mixed administration of single-antigen mRNA-LNPs provides a flexible framework for independently modulating antigen composition and enabling antigen-specific immune responses. These findings provide a basis for future studies exploring diverse antigen combinations in NiV vaccine research.
Vaccine-development researchers can design follow-up experiments that prepare F and G as separate formulations, vary their dosing ratio, and compare antibody responses. Including single-antigen groups would help distinguish each antigen’s contribution to neutralizing activity from the benefits of co-administration. This study provides a basis for starting those comparisons; further experiments are needed to establish an optimal combination.
A VSV-based pseudovirus assay is a tool for assessing candidates’ in vitro neutralizing activity in settings where direct work with high-risk live Nipah virus is difficult. Its specificity and reproducibility need further evaluation before it is used for candidate screening. Whether vaccination actually prevents infection must be verified separately in live-virus protection studies, while applicability to humans remains a question for subsequent research.