In Silico Design and Immunogenicity Evaluation of a Multiepitope Vaccine Candidate Against Leishmania tropica in BALB/c Mice.

BACKGROUND: Cutaneous leishmaniasis caused by Leishmania tropica remains a major neglected parasitic disease with limited therapeutic options and frequent treatment failure, highlighting the urgent need for effective vaccine-based interventions. Multiepitope vaccine (MEV) strategies provide a rational and targeted approach to induce defined cellular and humoral immune responses against Leishmania infection.

METHODS: In this study, a MEV candidate was designed using conserved cytotoxic T lymphocyte (CTL), helper T lymphocyte (HTL), and linear B-cell epitopes derived from immunodominant Leishmania antigens. Prior to experimental evaluation, protein-protein docking was performed to assess the interaction between the vaccine candidate and the TLR4 receptor. Molecular dynamics (MD) simulations were subsequently conducted using NAMD 3.0.0 with the CHARMM36 force field under physiological conditions (TIP3P water model, 0.15 M NaCl, pH 7.4). Structural parameters including root mean square deviation (RMSD), radius of gyration (Rg), and principal component analysis (PCA) were calculated. The recombinant construct was expressed in an Escherichia coli pET-20b (+) system and purified using affinity chromatography. The vaccine was evaluated in a BALB/c mouse model using a multidose subcutaneous immunization protocol followed by L. tropica challenge. Immunological responses were assessed by quantitative real-time PCR analysis of cytokine gene expression (IL-12, IFN-γ, and IL-4) and by Western blot analysis for detection of antigen-specific antibodies. Safety was evaluated based on survival and observation of apparent adverse effects during the experimental period.

RESULTS: Computational analysis demonstrated stable interaction between the vaccine candidate and the TLR4 receptor. MD simulations confirmed the formation of a stable and compact vaccine-TLR4 complex, supported by RMSD, Rg, and PCA analyses, indicating reduced conformational fluctuations and enhanced receptor stabilization compared with the unbound state. Immunological analysis revealed a strong Th1-skewed immune response characterized by significant upregulation of IFN-γ, modulation of IL-12 expression, and marked downregulation of IL-4 following challenge. Western blot analysis confirmed specific antigen recognition in vaccinated mice, whereas control groups showed no detectable reactivity. No mortality, behavioral changes, or apparent vaccine-related adverse effects were observed during the observation period, supporting the tolerability of the vaccine under the experimental conditions.

CONCLUSION: Overall, the MEV induced coordinated cellular immune responses together with antigen-specific antibody recognition. The observed cytokine gene expression profile and antibody reactivity indicate a robust immunogenic response and support the recombinant construct as a promising candidate for further preclinical evaluation against cutaneous leishmaniasis. Additional studies assessing protective efficacy, parasite burden, and long-term immune durability are warranted.