The HLA class I ELISA is an enzyme immunoassay based on the detection of \u03b22-microglobulin subunit of HLA class I complexes, after capturing the complex through the conjugated biotin. To this end, biotinylated HLA class I complex is first captured in streptavidin coated microtiter wells. Subsequently, HRP-conjugated anti-human \u03b22-microglobulin is added to detect intact HLA class I complexes. Only intact HLA class I complexes are recognized. Peptides with high affinity binding will be clearly detected by this ELISA technique, while peptides with a moderate to low binding affinity for HLA class I provide a moderate to non-detectable signal. This protocol is designed to evaluate the efficiency of peptide exchange when using the Flex-T\u2122 system.