Identification of CD4+ T-Cell-Stimulating Antigens by Expression Cloning

The antigens recognized by CD4(+) T cells are key to rational vaccine design, but have been difficult to identify due to limitations of conventional methods. A novel strategy for identifying CD4(+) T-cell-stimulating antigen genes is described here. Using antigen-specific, lacZ-expressing T cells as single-cell probes, a DNA library was screened as recombinant Escherichia coli. An antigen gene was isolated from the E. coli clone that, when ingested by the macrophages, allowed generation of the appropriate peptide/MHC class II complex and T-cell activation. This strategy was successfully applied to the identification of a previously unknown listeria gene product with characteristics of a membrane-bound lipoprotein.