Provided herein are bioengineered immunomodulatory fusion proteins and uses thereof for modulating immune responses, as well as uses for improving a response of a subject to a vaccine, or uses for treating a disease or disorder, such as cancer or a pathogen infection. Provided herein is a single chain trimeric CD40L Fc fusion protein comprising (a) three CD40 ligand CD40L subunits covalently linked to one another by peptide linkers (CD40L trimer); and (b) an Fc monomer peptide.