Evaluation of the safety and immunogenicity of a peptide vaccine against canine leishmaniosis: a double-blind, multicenter, controlled clinical trial in dogs.

Current vaccines for canine leishmaniosis (CanL) provide limited protection, underscoring the need for improved immunization strategies. Multi-epitope peptide vaccine delivered via nanoparticle systems represents a promising alternative but remains underexplored in canine clinical trials. Here, we report the results of a double-blind clinical trial (499/ECV) evaluating the safety and immunogenicity of HisDTC, a peptide vaccine targeting Leishmania infantum, encapsulated in poly(lactic-co-glycolic acid) PLGA nanoparticles and adjuvanted with Toll-like receptor 2 (TLR2) and TLR3 ligands. Forty healthy dogs were immunized with different vaccine formulations and monitored over 12 months. Immune responses were assessed by flow cytometry, ELISA, and in vitro macrophage infection assays, while safety was evaluated through clinical follow-up. Vaccination with HisDTC elicited a protective cellular response, including sustained IFN-γ production by CD4+ and CD8+ T cells, an IgG2a-skewed humoral response, and expansion of CD4+CD8α+ double-positive memory T cells. Notably, only HisDTC-vaccinated dogs exhibited a >80% reduction in in vitro macrophage infection, with protective effects persisting for up to 8 months post-immunization. Importantly, the formulation was well tolerated, with no adverse effects reported. These findings demonstrate that HisDTC delivered via PLGA nanoparticles induces durable, protective immunity against L. infantum in dogs and supports its further evaluation under natural exposure conditions.