Prototype of a nanostructured multi-epitope vaccine for the control of Piscirickettsiosis: Proof-of concept in salmonid cells

The article focuses on the development of a nanostructured multi-epitope vaccine prototype to control Piscirickettsiosis, a serious bacterial infection caused by Piscirickettsia salmonis in salmonids. Piscirickettsiosis, one of the main causes of mortality in Chilean aquaculture, generates significant economic losses and extensive use of antibiotics, which represents risks to environmental and public health. Despite the existence of vaccines, their efficacy remains limited, especially under field conditions, where the genetic variability of the pathogen and other external factors compromise immunological protection. This research applies reverse vaccinology to identify specific antigenic epitopes of P. salmonis, particularly of the LF-89 and EM-90 genogroups, which are predominant in Chilean aquaculture. The study includes the design and production of four nanoparticles (NPs) with chimeric characteristics, called SkipZ, PulseJ, HopQ and Hoptech, derived from P. salmonis epitopes. These nanoparticles were expressed in Escherichia coli and purified for further immunogenic evaluation. The research analyses the uptake of these nanostructures by salmonid RTS-11 macrophage cells and their ability to induce antigen presentation and pro-inflammatory responses. The results show that the nanoparticles, especially SkipZ and HopQ, effectively stimulate the expression of key markers involved in antigen presentation, such as MHC-II, CD83 and CD86, as well as pro-inflammatory cytokines such as IL-1β and TNF-α, in a dose-dependent manner. These findings suggest that the selected epitopes are capable of enhancing immune responses in salmonid cells. This multi-epitope vaccine approach seeks to offer a more specific and effective strategy to control Piscirickettsiosis, potentially reducing the dependence on antibiotics and improving the long-term protection of salmonid populations. The work highlights the potential of using nanoparticle-based vaccines to induce robust cellular immunity, critical to combat intracellular pathogens such as P. salmonis. This proof-of-concept study paves the way for the development and optimization of vaccines tailored to the pathogen-specific genetic diversity in aquaculture environments.