Development of a CD28 receptor binding-based screen and identification of a biologically active inhibitor

CD28 is a T-cell costimulatory receptor which plays a pivotal role in antigen-induced T-cell response. We have developed a cell-free and scintillation-proximity assay-based screen to search for molecules that inhibit ligand binding to CD28. The assay was shown to be versatile and adaptable to automation for high-throughput screening. Using this assay, we identified an inhibitor of CD28, NP2214. The inhibitor was shown to be active in vitro by suppressing IL-2 synthesis and proliferation of peripheral blood mononuclear cells in response to CD28 costimulation. We also demonstrated the additive effects of NP2214 and cyclosporine A which act mechanistically distinctly in inhibiting costimulation-induced IL-2 synthesis.