The invention provides fusion proteins comprising antigens of infectious disease agents and cancer cells linked to multiple-trimer forms of TNF SuperFamily (TNFSF) ligands. The TNFSFs serve as vaccine adjuvants for increasing the immune response to the antigens. In particular, a fusion polypeptide strand that self-assembles inside cells into a multiple-trimer form of CD40 ligand (CD40L, TNFSF5) is provided. Other similar fusion proteins are also disclosed. The fusion proteins can be delivered to a host as isolated proteins, as nucleic acids used directly in DNA vaccination or carried and expressed by a viral vector such as adenovirus. In addition to use as a vaccine to prevent or ameliorate disease caused by an infectious agent, compositions of the invention may be used for the treatment of ongoing infection or for cancer immunotherapy.
