Advanced eco-compatible mRNA vaccines for induction of protective immune responses in farmed fish – Fish-RNAvax

Infectious diseases in fish farming cost about 20% of the production value. In the context of ever expanding aquaculture industry, which already outgrows wild fish capture and is forecasted to double by 2050, disease prevention by vaccination has become crucial to reduce the aquaculture burden on the environment, by avoiding long term treatment with chemotherapeutics and antibiotics, and limiting the risk of infectious disease spread to wild fish populations. Indeed, vaccination has been highly beneficial for the control of bacterial disease in farmed fish (Norwegian Salmon for instance). Fish vaccines against many viral infections are, however, much needed. Although DNA vaccines afford full protection against a number of fish virus and a DNA vaccine (Apex-IHN®) was authorized for use in Salmon in Canada in 2005, no DNA vaccine has been approved to date for aquaculture in Europe. Indeed, if DNA vaccines are very efficient when injected intramuscularly, no efficient strategy of administration (by bath or mucosal route) have been set up, which rises costs and prevents fry vaccination. Moreover, there are strong concerns about DNA use, as suspected integration of GMO plasmid into DNA immunized fish may occur and pass to wild populations. The Fish-RNAvax project aims at developing new vaccines addressing these issues, by proposing mRNA vaccines as a safe and eco-compatible alternative to DNA (as done in human health), and by exploring mucosal routes of vaccine delivery.
mRNA will be transported using biodegradable particulate delivery systems developed by partner 1, which are naturally taken up by mucosal antigen presenting cells when administered by immersion in adult zebrafish (partner 1’s unpublished data). The project will combine the advantages of zebrafish, for genetic and imaging approaches to optimize vaccine strategies and characterize immune responses, and of rainbow trout, as a more relevant farm fish model. Our trans-disciplinary consortium gathers 4 partners, with synergistic expertise in immunology, nanotechnology, farm fish, and bio-imaging. Task 1 is dedicated to project management. In task 2, partner 1 will formulate vaccine candidates, using polylactic acid nanoparticles (PLA NPs) of 200 nm as a versatile platform to carry in vitro transcribed mRNA (or plasmid DNA, used as a benchmark in the different tasks). In task 3, partners 1 and 4 will select NP formulations and administration routes (with a focus on mucosal administration) leading to efficient in vivo transgene expression in zebrafish. A screen based on time cumulative expression of a bright reporter will be performed, using a Cre/loxP system. Then, the transgene expression from eGFP encoding NPs will be further characterized in mucosa, immune organs and immune cell types, by whole-body imaging approaches. In task 4, all partners will characterize the innate and humoral immune responses of zebrafish vaccinated against the G-protein of SVCV (Spring viremia of Carp Virus), and the protection efficiency obtained at adult or younger stages for selected vaccines. In task 5, strategy selected from task 3 or 4 will be evaluated by partner 2 in trout, for protection efficiency against the G-protein of the fish farm virus VHSV (Viral Haemorrhagic Septicaemia Virus) and for B-cell response characterization.
Thus, the Fish-RNAvax project will propose a unique and innovative NP-mRNA vaccine strategy dedicated to fish vaccination to address the sustainability challenges of aquaculture. This multidisciplinary approach at the cutting-edge of technologies will provide groundbreaking knowledge on immune fish responses and its modulation through diverse vaccine administration routes.