Evaluation of Quillaja brasiliensis Saponin-Based Nanoparticles Combined with Leucine Aminopeptidases for Immunoprotection of Sheep Against Fasciola hepatica

<b>Background:</b><i>Fasciola hepatica</i> causes important economic losses in ruminants with only pharmacological treatments currently available, which produces several secondary problems. Because of this, vaccines have become an interesting alternative. Leucine aminopeptidases (LAPs) are attractive vaccine targets against fasciolosis since they play essential roles in the parasite such as host invasion and nutrient acquisition. To characterize immune responses, we produced two recombinant <i>F. hepatica</i> LAPs (<i>Fh</i>LAP1 and <i>Fh</i>LAP2), formulated with ISCOM-matrices (IMXs) nanoparticles from <i>Quillaja brasiliensis</i> saponins. <b>Methods:</b> Forty female Corriedale sheep were assigned to four groups (<i>n</i> = 10): <i>Fh</i>LAP1/IMX, <i>Fh</i>LAP1/<i>Fh</i>LAP2/IMX, IMX (control), and <i>Fh</i>LAP1/Adj50 (Adjuvac 50). Animals received two subcutaneous immunizations at weeks 0 and 4 and were challenged orally with 200 metacercariae at week 6. <b>Results:</b><i>Fh</i>LAP1 and <i>Fh</i>LAP1/<i>Fh</i>LAP2 induced specific IgG responses, with the predominance of the IgG1 response. However, these responses were lower than those generated by <i>Fh</i>LAP1 formulated with Adj50. A qPCR analysis revealed that <i>Fh</i>LAP1/IMX stimulated a Th1-type response profile before the challenge, but this profile was not sustained after infection. The post-infection profile of <i>Fh</i>LAP1/<i>Fh</i>LAP2/IMX was more congruent with expected values despite not achieving a robust IFN-γ expression. No significant differences in the fluke burden were observed. <b>Conclusions:</b> Further research on the optimal antigen/adjuvant combination in ruminants is encouraged. For instance, a higher concentration of adjuvant in the formulation used in this work may enhance the strength and duration of the inflammatory response and improve protective immunity against fasciolosis.