5-MethylCytosine/BSA is an antigen-adjuvant conjugate composed of 5-MethylCytosine and bovine serum albumin (BSA). Conjugating the antigen with a protein adjuvant enhances the production of antigen-specific antibodies in vaccine models. This conjugate does not interfere with protein folding or disrupt major epitopes, and it promotes cross-presentation and the generation of antigen-specific T cells.