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

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.

Immunodominant B- and T-cell epitopes were predicted using the Immune Epitope Database (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.

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.

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.

The SGM construct represents a promising multi-epitope vaccine candidate against T. gondii; however, experimental validation is required to confirm its immunoprotective efficacy.