Protective response mediated by immunization with recombinant proteins in a murine model of toxocariasis and canine infection by Toxocara canis

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Toxocariasis is a neglected parasitic zoonosis of global importance. The development of a formulation that can be used as a vaccine would help the definitive control of the infection. Preclinical studies selected two recombinant T. canis proteins (rTcVcan and rTcCad) which significantly protected mice against larval migration. In the present work, these proteins plus three adjuvants (Alhydrogel®, PAM3CSK4®, and Quil-A®) were used to immunize mice against toxocariasis; blood samples were collected three times to measure IgG (total, IgG1, IgG2a), IgA, and IgE via indirect ELISA. Cytokines (IL-5, TNF-α, and IL-10) were measured in splenocytes supernatant, and T. canis larvae were quantified in tissues. The best protein + adjuvant pair found (rTVcan + QuialA®) was then used to immunize T. canis-free puppies (n = 18) that were experimentally infected with T. canis and T. canis naturally-infected puppies (n = 6). Immunoglobulin (IgA, IgE, IgG, IgG1, and IgG2a), parasite load (eggs in feces), number of expelled adults and eggs extracted from the female uterus, and their fertility percentages were analyzed. In mice, it was observed a highly significant reduction (73%) of tissue larvae, a mixed cytokine profile (Th1/Th2), and anti-T. canis antibody titers (IgG, IgG1, IgG2a) using rTVcan + QuialA® mix. In canines, rTVcan + QuialA® promoted reduction in the parasite eggs in feces (95%) and eggs reduction obtained from the uteri of pharmacologically expelled adult females (58.38%). In our knowledge this is the first canine clinical trial of a vaccine with T. canis recombinant proteins. The formulation used has been shown to efficiently stimulate the production of antibodies against infection by T. canis. In the canine, a significant reduction in the number of eggs expelled by the experimental animals that received the formulation prophylactically was evidenced. Future tests should be developed to evaluate the duration of the protective effect and analyze other immune pathways that could be stimulated by the formulation used.