Antigen discovery for t cell receptors isolated from patient tumors recognizing wild-type antigens and potent peptide mimotopes

A peptide antigen for a TCR, identified by the method comprising:

• contacting a TCR of interest with a population of host cells, which express on the cell surface a multiplexed library of at least 108 different polynucleotides encoding single chain polypeptides, the single chain polypeptides comprising:
• binding domains of the MHC protein;
• and
• a peptide ligand;
• selecting for host cells expressing a single chain polypeptide that binds to the TCR of interest;
• iterating the selecting step for at least three rounds;
• performing DNA sequencing of the polynucleotides present in the final selected population to determine a dataset of possible amino acids for each position of the peptide ligand;
• inputting the dataset to computer readable medium to generate a search algorithm;
• searching a sequence database with the search algorithm to identify the set of peptides that bind to the T cell receptor.