Bacillus Calmette-Guérin as adjuvant platform enhances immunogenicity of conserved epitopes from structural proteins of SARS-CoV-2.

The development of effective and broadly protective vaccines against SARS-CoV-2 remains a global priority. Conserved epitopes from viral structural proteins (E, M, N, and S) represent promising targets less affected by emerging mutations, while Bacillus Calmette-Guérin (BCG) offers unique adjuvant and delivery properties. This study aimed to validate conserved SARS-CoV-2 epitopes in combination with BCG and to design multiepitope vaccine constructs in silico. Dot blot assays confirmed recognition of five synthetic peptides by sera from convalescent patients. In vitro, BCG-peptide formulations activated the MAPK pathway and induced trained immunity signatures in macrophages. In vivo, immunized mice showed modulation of IgG subclasses and increased IL-6, TNF-α, and IFN-γ production. Splenocytes from vaccinated animals secreted high cytokine levels upon restimulation, suggesting memory responses. In silico modeling indicated stable, antigenic, and non-allergenic multiepitope constructs with favorable immune simulations. Together, these findings highlight BCG-epitope formulations as promising next-generation vaccine candidates against SARS-CoV-2.