In silico screening and identification of CTL and HTL epitopes in the secreted virulence factors of Mycobacterium tuberculosis.

Background: Mycobacterium tuberculosis (MTb) is a highly infectious pathogen and a global health threat due to its resilient cell wall and immune evasion strategies. Despite the availability of the antituberculosis Bacille Calmette-Guérin (BCG) vaccine, its efficacy varies (0%-80%) and gradually decreases over time. This study aimed to identify cytotoxic T-lymphocyte (CTL) and helper T-lymphocyte (HTL) epitopes in MTb secretory proteins using immunoinformatics tools.

Materials and methods: The Protein Variability Server was used to identify highly conserved sequences, and epitope population coverage was estimated for the Southeast Asian (SEA) region. Selected epitopes were also docked to their major histocompatibility complex alleles.

Results: Five secretory proteins critical to MTb pathogenesis and virulence were identified as antigenic (antigenicity score > 0.4). Predicted epitopes had IC₅₀ values ≤ 500 nM, indicating strong binding affinity, with an estimated 94% population coverage in SEA. All candidate epitopes were highly conserved (Shannon index ≤ 0.1) and showed no significant sequence similarity to human proteins, allergens, or toxic peptides. Docking analysis confirmed favorable binding to their corresponding HLA alleles, as indicated by low Gibbs free energy change (ΔG) values and dissociation constants (K _D nM).

Conclusions: Overall, this study identified immunoactive CTL and HTL epitopes that could serve as promising candidates for future antiTB vaccine development. Further in vitro and in vivo studies are required to validate these preliminary findings.