This invention provides novel CD40L polypeptides and nucleic acids, as well as antigen presenting cells and vaccines comprising such CD40L polypeptides and/or nucleic acids, and related methods for preparing the antigen presenting cells and vaccines. The antigen presenting cells and vaccines are useful for enhancing an immune response. The invention provides a method for preparing mature dendritic cells (DCs), comprising the sequential steps of: (a) signaling isolated immature dendritic cells (iDCs) with a first signal comprising an interferon gamma receptor (IFN-?R) agonist and/or a tumor necrosis factor alpha receptor (TNF-?R) agonist to produce signaled dendritic cells； and (b) signaling said signaled dendritic cells with a second transient signal comprising an effective amount of a CD40 agonist to produce CCR7+ mature dendritic cells. Also provided by this invention are enriched populations of dendritic cells prepared by the methods of the invention. Such dendritic cells have enhanced immunostimulatory properties and increased IL-12 secretion and/or decreased IL-10 secretion. CD40 signaling can be initiated by one or more of polypeptide translated from an exogenous polynucleotide encoding CD40L (e.g., mRNA or DNA), an agonistic antibody to CD40 receptor or by CD40 ligand polypeptide. The enriched populations can be further modified by the administration of an immunogen to the DC. The DC will take up and process the immunogen on its cell surface.
