mRNA Vaccine Against Large Yellow Croaker Vibriosis Shows 10-Week Stability at 25°C and Experimental Protection
Background: An experimental vaccine targeting vibriosis in large yellow croaker
An mRNA vaccine developed to prevent vibriosis in large yellow croaker (Larimichthys crocea) showed promise in room-temperature storage and pathogen challenge tests. The lyophilized formulation retained its physicochemical properties and in vitro antigenicity for 10 weeks at 25°C. In an experiment in which vaccinated fish were challenged with Vibrio harveyi, the 20 μg group had the greatest protective effect among the doses tested.
V. harveyi causes severe vibriosis in large yellow croaker, leading to mortality and economic losses in marine aquaculture. The researchers developed the vaccine against a backdrop of no effective commercial vaccine for this infection and concerns about resistance and environmental problems associated with antibiotic overuse. The target was FlaA, a flagellin protein involved in the bacterium’s virulence and immunogenicity. The formulation encapsulated messenger RNA (mRNA) encoding FlaA in lipid nanoparticles (LNPs).
Key findings: Formulation stability and survival after challenge
The researchers optimized the untranslated regions (UTRs), capping, LNP formulation, microfluidic encapsulation, and lyophilization conditions. Capping efficiency was 95.1%, and more than 50% of the mRNA introduced into kidney cells remained after 12 hours. This figure describes mRNA persistence in a cell experiment and should be distinguished from the duration of protection in vaccinated fish.
When stored at 25°C for 10 weeks, the lyophilized vaccine retained stable physicochemical properties and in vitro antigenicity, as well as its ability to induce neutralizing antibodies. However, the supplied abstract does not report measurements for individual physicochemical properties or acceptable ranges of variation. The stability findings therefore apply only to the stated temperature, duration, and evaluated properties.
After intramuscular injection into large yellow croaker, FlaA expression was observed in muscle tissue. Levels of specific immunoglobulin M (IgM) and neutralizing antibodies increased. Increased antioxidant and metabolic enzyme activity, along with expression of immune-related genes in immune tissues, was also reported. These findings show biological responses after vaccination, but the abstract alone does not establish that specific immune signaling pathways or the functions of cellular immunity have been elucidated.
In the V. harveyi challenge test, the 20 μg group had a reported survival rate of 77.7% and a relative percent survival (RPS) of 70.1%. The RPS of 70.1% is a separate measure from the vaccinated group’s actual survival rate of 77.7%. The 20 μg dose was the most effective among those tested; it has not been established as the optimal dose under other farming conditions.
Implications and outlook: Steps toward application in aquaculture
This study reports both room-temperature formulation stability and experimental protection for an mRNA-LNP vaccine targeting a bacterial disease in large yellow croaker. The researchers describe it as the first room-temperature-stable mRNA-LNP vaccine against aquatic bacterial pathogens. This claim of priority is the authors’ own; it cannot be independently verified against the full prior literature using the supplied materials alone.
The available materials consist of a journal indexing record and an abstract. Sample size, control-group composition, statistical uncertainty, challenge-test details, and duration of protection could not be confirmed. It is also difficult to assess superiority over existing vaccines or whether the candidate meets regulatory efficacy criteria. Before considering use on farms, protection under actual farming conditions, storage and transport conditions, and the practicality of intramuscular injection require further evaluation.
The findings can be checked in the abstract and bibliographic record for the Fish & Shellfish Immunology paper.
Vibrio harveyi causes severe vibriosis in the large yellow croaker (Larimichthys crocea), resulting in high mortality rates and significant economic losses in mariculture. Currently, there is no effective commercial vaccine available, and the overuse of antibiotics raises concerns about resistance and the environment. In this study, we developed a thermostable mRNA-LNP vaccine that encodes the FlaA flagellin, which is a key virulence and immunogenic antigen of V. harveyi. Through the optimisation of UTRs, capping, lipid nanoparticle (LNP) formulation, microfluidic encapsulation and lyophilisation, the vaccine achieved a capping efficiency of 95.1% and retained over 50% of the mRNA in kidney cells 12 h after transfection. The lyophilised vaccine remained stable with respect to physicochemical parameters and in vitro antigenicity at 25 °C for 10 wk, and retained the ability to induce neutralising antibodies. Intramuscular injection of the vaccine into croakers resulted in robust FlaA expression in muscle tissue, elevated levels of specific IgM and neutralising antibodies, increased antioxidant and metabolic enzyme activities, and expression of immune-related genes in immune tissues. A V. harveyi challenge demonstrated that a 20 μg dose was the most effective among the tested doses, with 77.7% survival and 70.1% relative percent survival. This is the first room-temperature-stable mRNA-LNP vaccine against an aquatic bacterial pathogen, offering a novel, eco-friendly strategy for controlling V. harveyi and advancing the development of mRNA vaccines for bacterial diseases in aquaculture.
Aquaculture vaccine development requires assessment of both protection following infection and storage and administration conditions. This study presents stability results for a lyophilized vaccine candidate against vibriosis in large yellow croaker at 25°C for 10 weeks, alongside survival results after pathogen challenge. It provides an initial basis for considering a candidate technology that could reduce the burden of refrigerated distribution.
For example, follow-up trials for potential farm use could assess whether formulation properties and protection are maintained after temperature fluctuations during transport, and whether individual intramuscular injections are practical in terms of time and cost. Duration of protection and effectiveness under actual farming conditions also need to be assessed. The current results do not establish that the vaccine can replace refrigerated distribution, reduce antibiotic use, or prevent economic losses.