Phage‐displayed libraries of peptide/major histocompatibility complexes

Characterizing peptide epitopes targeted by major histocompatibility complex (MHC)‐restricted T cells of unknown specificity would have broad implications. In this article we introduce and validate an original phage‐displayed library of noncovalent complexes of peptide and MHC (P/MHC). We show that soluble MHC molecules associate with peptides presented by a phage, thereby resulting in the formation of multivalent P/MHC phages. Complex formation is stabilized by the interaction of the soluble partner (MHC) with two components, peptide and β2‐microglobulin, both of which are covalently linked to the phage. As proof of concept, we have used this strategy to express peptide libraries in the context of H‐2Kb. Using monoclonal antibody 25D (specific for ovalbumin/H‐2Kb) as a template to screen the library, we were able to select a variant epitope functionally and structurally related to the wild‐type peptide. Interaction studies between monoclonal antibody 25D and cells suggest that the variant peptide has been selected on the basis of a decreased dissociation rate between the peptide/H‐2Kb complex and its ligand. A weak agonist of the N15 TCR (vesicular stomatitis virus/H‐2Kb‐specific) was also isolated from another P/MHC library. This strategy opens up new perspectives for antigen discovery and the manipulation of T cell responses.