Proteomics and First CRISPR-Cas9 Editing Point to New Liver Fluke Vaccine Targets

Fasciolosis, the parasitic disease caused by the liver fluke Fasciola hepatica, remains one of the most economically damaging infections of livestock worldwide and an underappreciated public health problem for humans. A new study published in Parasites & Vectors by researchers at the Institute of Natural Resources and Agrobiology of Salamanca (IRNASA-CSIC) in Spain offers a fresh, systematic route toward a long-sought vaccine. Led by Marta López-García, María Torres-Valle, Javier González-Miguel and Mar Siles-Lucas, the team combined comparative proteomics with a landmark proof-of-concept application of CRISPR-Cas9 gene editing in the parasite’s newly excysted juvenile stage, delivering both a shortlist of promising vaccine antigens and a technical milestone for the field.

The urgency of the work stems from a widening gap in disease control. For decades, fasciolosis has been managed almost exclusively with anthelmintic drugs, but drug-resistant parasite populations are increasingly emerging, eroding the reliability of chemical treatment. Vaccination would offer a sustainable alternative, yet despite numerous candidate antigens tested over the past twenty-five years, no effective commercial vaccine has materialized. A central obstacle, the authors note, has been the difficulty of selecting and validating suitable antigens, with protection often inconsistent across host species and experimental conditions.

To tackle that selection problem head-on, the researchers built a bioinformatic prioritization pipeline that integrates stage-specific proteomic datasets covering the earliest phase of infection. These datasets included ex vivo samples, in vivo material, and excretory-secretory products from the newly excysted juvenile stage, the brief window after the parasite emerges from its cyst in the host intestine and begins its invasive migration toward the liver. By demanding consistent detection across all of these datasets, the pipeline filtered out proteins whose presence might be an artifact of a single experimental condition and focused instead on a robust core set.

That comparative analysis converged on a core proteome of just six proteins consistently detected across every early-infection dataset examined. From this group, three candidates rose to the top after the team assessed structural stability, predicted solubility, and antigenic potential: cathepsin B3 (FhCB3), legumain 1 (FhLeg1), and serpin 1 (FhSrp1). Each represents a biologically plausible vaccine target. Cathepsins are proteases the fluke relies on to digest tissue and evade immune defenses during migration; legumain is another proteolytic enzyme implicated in parasite development; and serpins are protease inhibitors that parasites frequently deploy to manipulate host immune responses.

A critical requirement for any vaccine antigen is that the host immune system can actually see it. To verify this, the researchers expressed the three proteins recombinantly, confirmed their identity and molecular weights by Western blot, and then used confocal immunofluorescence microscopy to map their spatial localization in newly excysted juveniles and migratory stages. The results were encouraging: all three proteins were localized on the parasite surface, meaning they are exposed to the host immune system during the earliest and most vulnerable phase of infection. Surface exposure is precisely the property that allows antibodies to bind and potentially neutralize the parasite before it can establish itself.

The in silico characterization added further depth to the candidate profiles. Predicted three-dimensional structures, transmembrane topology, signal peptides, glycosylation sites, and solubility values were all computed for FhCB3, FhLeg1, and FhSrp1, providing a structural rationale for their stability and manufacturability as recombinant antigens. This kind of computational vetting matters practically as well as scientifically: proteins that are soluble and structurally stable are far easier to produce, purify, and formulate at scale, which is a prerequisite for any candidate hoping to move from the laboratory toward a commercial product.

The study’s second major contribution is methodological. For the first time, the team established a CRISPR-Cas9 gene editing workflow in F. hepatica newly excysted juveniles. Using ribonucleoprotein complexes delivering single-guide RNAs targeting the three candidate genes, introduced by electroporation, the researchers demonstrated that targeted mutations could be induced in the parasite genome. Editing efficiencies were modest but measurable: 3.2 percent for FhCB3 and 2.1 percent for FhLeg1. While these rates are far from sufficient for complete gene knockout on their own, they establish feasibility, showing that the juvenile stage, long considered technically challenging, can be genetically manipulated.

Why does this matter for vaccine development? Functional validation is the missing link in most antigen selection pipelines. Identifying that a protein is abundant, surface-exposed, and antigenic suggests but does not prove that it is essential to the parasite. Gene editing allows researchers to disrupt a candidate gene and observe the consequences for parasite survival, migration, and infectivity, turning a correlational shortlist into a causally validated target list. The authors’ demonstration that CRISPR-Cas9 can work in FhNEJ therefore converts their prioritization framework from a purely descriptive exercise into a platform capable of functional confirmation, a capability previously unavailable at this life stage.

The technical execution also addressed the practical pitfalls of working with a delicate multicellular parasite. Microscopy of electroporated juveniles tracked their condition at one, twenty-four, and forty-eight hours after treatment, distinguishing morphologically damaged individuals from viable ones, while PCR amplification of the target genes, with the nuclear ribosomal internal transcribed spacer 1 as an internal DNA quality control, confirmed the presence of editing events in treated groups. This combination of viability monitoring and molecular verification provides a template that other laboratories studying F. hepatica, and potentially related flatworm parasites, can adapt.

Taken together, the study establishes an integrated framework for the rational prioritization of vaccine candidates against fasciolosis, moving from multi-dataset proteomic comparison through structural and antigenic assessment to spatial validation and, finally, functional editing. The identification of FhCB3, FhLeg1, and FhSrp1 as host-exposed, early-stage antigens gives vaccine developers a focused set of targets grounded in consistent proteomic evidence rather than trial and error. And the first successful application of CRISPR-Cas9 in newly excysted juveniles opens the door to systematic functional genomics in a parasite for which such tools have been lacking. As drug resistance continues to spread, the combination of rational antigen selection and gene-editing validation may prove to be exactly the approach needed to finally deliver a sustainable vaccine against this globally significant fluke.

Subject of Research: Vaccine candidate discovery and CRISPR-Cas9 gene editing in the liver fluke Fasciola hepatica

Article Title: Uncovering early-stage vaccine candidates against Fasciola hepatica through integrative comparative proteomic analysis and proof-of-concept CRISPR-Cas9 gene editing

Article References: López-García, M., Torres-Valle, M., González-Miguel, J., & Siles-Lucas, M. (2026). Uncovering early-stage vaccine candidates against Fasciola hepatica through integrative comparative proteomic analysis and proof-of-concept CRISPR-Cas9 gene editing. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07699-1

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07699-1

Keywords: Fasciola hepatica, fasciolosis, vaccine candidates, proteomics, CRISPR-Cas9, gene editing, cathepsin B3, legumain, serpin, newly excysted juveniles, antigen discovery, drug resistance