25-OH Vitamin D3/KLH is an antigen-adjuvant conjugate formed by the coupling of 25-OH Vitamin D3 with keyhole limpet hemocyanin (KLH). This conjugation enhances the production of antigen-specific antibodies within vaccine models by attaching the antigen to a protein adjuvant. The conjugate does not alter protein folding or disrupt primary epitopes, and it also boosts cross-presentation and the generation of antigen-specific T cells.