The Flex-T? system is designed to provide maximal flexibility in the study of antigen specific T cells. Flex-T? Monomer UVX products are a biotinylated HLA class I α-chain, associated with the β2-microglobulin chain, and stabilized by a UV-labile peptide. The C-terminus of the α-chain is biotinylated by the enzyme BirA. In the absence of proper peptide binding, the HLA class I complex quickly disassociates. Thus, by using UV radiation, it is possible to exchange the labile peptide with another peptide of interest. An ELISA was designed to verify this exchange process. A 96-well plate coated with Streptavidin captures the biotinylated α-chain, followed by detection of the associated β2-microglobulin with HRP-conjugated anti-β2-microglobulin antibody. The Flex-T? HLA Class I ELISA Control is a HLA class I α-chain associated with β2-microglobulin and stabilized with a high-affinity, non UV-labile peptide. This stable monomer serves as positive control for this ELISA.