In vitro binding of HA-3^T and HA-3^M peptides to TAP. T1 cells were permeabilized with streptolysin O (15 U/mL) and incubated with radioiodinated reporter peptide TVNKTERAY plus the indicated concentration of test peptides. Reporter peptide binding in TAP-negative T2 cells was assessed as a negative control. Samples were done in duplicate except for T2 negative control and T1 cells with no inhibitor, which were done in triplicate.