Tetramer Guided Epitope Mapping of Infuenza B epitopes. (A) Pool Mapping: T cells from a DR1401 donor were stimulated with overlapping peptide mixtures spanning Flu B HA and stained using pooled peptide loaded tetramers after two weeks. Peptide pools 3, 7, and 8 gave positive staining. (B) Individual peptide mapping: T cells from the tetramer positive panels shown in A were stained again using tetramers loaded with individual peptide from the corresponding peptide pools. Peptides p14, p15, p33, p34, and p40 were identified as peptides containing DR1401 restricted epitopes.