Tetramer-guided epitope mapping: Rapid identification and characterizationof immunodominant CD4(+) T cell epitopes from complex antigens

T cell responses to Ags Involve recognition of selected peptide epitopes co ntained within the antigenic protein. In this report, we describe a new app roach for direct identification of CD4(+) T cell epitopes of complex Ags th at uses human class II tetramers to identify reactive cells. With a panel o f 60 overlapping peptides covering the entire sequence of the VP16 protein, a major Ag for HSV-2, we generated a panel of class II MHC tetramers loade d with peptide pools that were used to stain peripheral lymphocytes of an H SV-2 infected individual. With this approach, we identified four new DRA1*0 101/DRB1*0401- and two DRA1*0101/DRB1*0404-restricted, VP16-specific epitop es. By using tetramers to sort individual cells, we easily obtained a large number of clones specific to these epitopes. Although DRA1*0101/DRB1*0401 and DRA1*0101/DRB1*0404 are structurally very similar, nonoverlapping VP16 epitopes were identified, illustrating high selectivity of individual allel e polymorphisms within common MHC variants. This rapid approach to detectin g CD4(+) T cell epitopes from complex Ags can be applied to any known Ag th at gives a T cell response.