Biocompatibility of intraperitoneally implanted TEMPO-oxidized cellulose nanofiber hydrogels for antigen delivery in Atlantic salmon (salmo salar L.) vaccines

Authors: TURNER, SARAH - University Of Maine; KUKK, KORA - University Of Maine; SIDOR, INGA - University Of New Hampshire; BOUCHARD, DEBORAH - University Of Maine

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2024
Publication Date: 2/25/2025
Citation: Turner, S.M., Kukk, K., Sidor, I.F., Bouchard, D. 2025. Biocompatibility of intraperitoneally implanted TEMPO-oxidized cellulose nanofiber hydrogels for antigen delivery in Atlantic salmon (salmo salar L.) vaccines. Fish and Shellfish Immunology. 147.

Interpretive Summary: Presently, aquaculture is one of the fastest growing food production sectors worldwide. However, industry-wide losses to disease are a major limiting factor to successful sustainable aquaculture growth. High infectious pressure in the aquaculture setting necessitates developing effective vaccination strategies to protect against disease outbreaks while ideally reducing stress and intensive labor costs associated with handling fish during vaccination procedures. Vaccination by injection is a commonly used delivery method to administer small, concentrated known doses of antigens and can be produced in multivalent form to protect against multiple pathogen strains or diseases within one injection. Most injectable fish vaccines use oil-based adjuvants that act on the adaptive immune system, increasing both the humoral and/or cell-mediated immune responses of the fish. Negative consequences of vaccination can result from up-regulation of the innate immune response, causing inflammation, the formation of adhesions in and around the injection site, and strong infiltration of mononuclear cells. This response can further produce a significant growth penalty and go on to cause welfare issues such as adhesions and internal organ damage. These undesired reactions occur in Atlantic salmon (Salmo salar L.), a species that is extensively farmed as a high valued human food protein source rich in omega-3 fatty acids. Atlantic salmon are susceptible to a host of diseases and are routinely vaccinated by injection which has improved disease prevention and increased productivity. However, salmon are also negatively impacted by the adverse effects attributed to vaccination. Thus, the challenge remains to create a cost-effective and adequately robust immune response for long-lasting protection that minimizes adverse effects.

Technical Abstract: Disease outbreaks are a major impediment to aquaculture production, and vaccines are integral for disease management. Vaccines can be expensive, vary in effectiveness, and come with adjuvant-induced adverse effects, causing fish welfare issues and negative economic impacts. Three-dimensional biopolymer hydrogels are an appealing new technology for vaccine delivery in aquaculture, with the potential for controlled release of multiple immunomodulators and antigens simultaneously, action as local depots, and tunable surface properties. This research examined the intraperitoneal implantation of a cross-linked TEMPO cellulose nanofiber (TOCNF) hydrogel formulated with a Vibrio anguillarum bacterin in Atlantic salmon with macroscopic and microscopic monitoring to 600-degree days post-implantation. Results demonstrated a modified passive integrated transponder tagging (PITT) device allowed for implantation of the hydrogel. However, the Atlantic salmon implanted with TOCNF hydrogels exhibited a significant foreign body response (FBR) compared to sham-injected negative controls. The FBR was characterized by gross and microscopic external and visceral proliferative lesions, granulomas, adhesions, and fibrosis surrounding the hydrogel using Speilberg scoring of the peritoneum and histopathology of the body wall and coelom. Acutely, gross monitoring displayed rapid coagulation of blood in response to the implantation wound with development of fibrinous adhesions surrounding the hydrogel by 72 h post-implantation consistent with early stage FBR. While these results were undesirable for aquaculture vaccines, this work informs on the innate immune response to an implanted biopolymer hydrogel in Atlantic salmon and directs future research using cellulose nanomaterial formulations in Atlantic salmon for a new generation of aquaculture vaccine technology.