In Silico Design and Evaluation of a Novel Chimeric Vaccine Candidate Based on SAG1, GRA1, and MIC4 Antigens of Toxoplasma gondii

Introduction/Background Toxoplasma gondii ( T. gondii ) is an intracellular protozoan parasite that poses serious risks to immunocompromised individuals and pregnant women. The adverse effects of current anti-toxoplasmosis drugs highlight the need for an effective vaccine. This study aimed to design a novel chimeric vaccine composed of selected epitopes from SAG1, GRA1, and MIC4 antigens using immunoinformatics approaches. Methods Immunodominant B- and T-cell epitopes were predicted using IEDB and PRED (BALB/c) tools. Selected epitopes were linked via an A(EAAAK)nA linker to construct the SGM (SAG1-GRA1-MIC4) chimeric protein. Structural properties, physicochemical characteristics, antigenicity, allergenicity, and solubility were evaluated using online bioinformatics servers. Results The SGM construct consisted of 395 amino acids with a predicted molecular weight (MW) of 42.62 kDa and an isoelectric point (pI) of 5.53. Structural validation indicated favorable stereochemical quality, with 96.08% of residues in favored regions of the Ramachandran plot. The protein was predicted to be stable, soluble, antigenic, and non-allergenic. Codon optimization analysis suggested efficient expression potential in the selected host system. Discussion The integration of immunodominant epitopes from three major T. gondii antigens into a single construct may enhance immune coverage and vaccine efficacy. In silico analyses support the structural stability and immunogenic potential of the designed construct, suggesting its suitability as a multi-epitope vaccine candidate. Conclusion The SGM construct represents a promising multi-epitope vaccine candidate against T. gondii ; however, experimental validation is required to confirm its immunoprotective efficacy.