NP-BSA (4-Hydroxy-3-nitrophenylacetyl-bovine serum albumin) is an antigen-adjuvant conjugate that combines 4-Hydroxy-3-nitrophenylacetyl (NP) with bovine serum albumin (BSA), forming an immune complex. This conjugation enhances antigen-specific antibody production in vaccine models without altering protein folding or disrupting primary epitopes. It also improves cross-presentation and the generation of antigen-specific T cells.