Generation of a multimeric form of CD40L with potent immunostimulatory activity using streptavidin as a chaperon

Effective aggregation of cell surface immune receptors with their ligands is critical in promoting humoral and cellular immune responses. Simulation of these interactions using soluble multimeric ligands having potent adjuvant effects may prove an effective alternative to agonistic antibodies as immunotherapeutics. Multimeric ligands may effectively engage their receptors, leading to aggregation and effective signal transduction. We exploited the structural characteristics of streptavidin (SA) for the generation of multimeric chimeric proteins. Streptavidin forms stable tetramers and oligomers under physiological conditions, and, as such, chimeric molecules with SA are expected to possess similar features. Two chimeric molecules consisting of the extracellular domains of human and mouse CD40L and a modified form of core streptavidin were generated. These proteins form stable oligomers that could only be dissociated into monomers by heating at 100°C, but not 60°C, under denaturing conditions. The chimeric proteins vigorously stimulated B cells, monocytes, and dendritic cells for the production of cytokines and chemokines and upregulation of immunostimulatory molecules. The use of SA as a chaperon presents a novel approach to generate multimeric immunological molecules with potent activities and their use as potential therapeutics for the treatment of cancer and other immune-based disorders.