Safari MH; Hosseini SA; Ghiabi S; Ghiabi S; Siamian D; Majidiani H; Irannejad H; Asghari A · 2026 · Veterinary medicine and science
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BACKGROUND: Toxoplasma gondii is a protozoan parasite of medical and veterinary importance causing abortion. While current therapies are limited to address the chronic phase of infection, effective prophylactic vaccines are warranted. OBJECTIVES: In this study, we applied a rational vaccine design approach centred around immunodominant dense granule antigens (GRAs). METHODS: In silico epitope mapping was performed on six GRAs (GRA15, GRA60, GRA76, GRA83, GRA-α and GRA-β). Using web servers, B-cell, cytotoxic T-lymphocyte and helper T-lymphocyte epitopes were predicted and then filtered for antigenicity, solubility and allergenicity. We designed four vaccine constructs by fusing predicted epitopes with specific linkers and adjuvants (RS-09, RpfE/50S ribosomal protein of Mycobacterium tuberculosis, and human interferon gamma [IFN-γ]). Constructs were subjected to rigorous evaluation, which included physicochemical evaluation, 3D structural prediction and refinement, toll-like receptor-4 (TLR-4) docking, immune simulation and codon adaptation. RESULTS: All candidates exhibited high antigenicity (VaxiJen scores > 0.9) and solubility (> 0.6). Rpf-Toxo emerged optimal, with non-allergenic, antigenic (0.9148), soluble (0.658), stable (instability index: 35.41) and hydrophilic (grand average of hydropathicity: -0.641) properties. Docking revealed strong TLR-4 binding activity (affinity: -20.6 kcal/mol; K d: 7.3e-16 M) and immune simulation predicted robust responses, including antibody titers > 170,000, Th1-skewed IFN-γ (380,000 ng/mL) and memory cell activation; however, these in silico predictions need experimental validation. Codon optimization enhanced expression (CAI: 1.00; GC: 65.63%), and in silico cloning indicated compatibility with pET28a(+). CONCLUSION: These computational predictions require future experimental validation through in vitro and in vivo studies to confirm safety and protective efficacy.
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