Abstract: Disclosed is a method that includes: (i) providing a plurality of initial nucleic acid cassettes that include: a) a first coding region encoding a first immunoglobulin variable domain, b) a second coding region encoding a second immunoglobulin variable domain, and c) a ribosomal binding site disposed between the first and second coding regions for translation of the second polypeptide in a first expression system, wherein the first and second coding regions are in the same translational orientation; (ii) modifying each nucleic acid cassette of the plurality in a single reaction mixture so that it is functional in a second expression system, wherein the first and second region remain physically attached during the modifying; (iii) introducing each modified nucleic acid cassette into a mammalian cell to produce a mixture of transfected cells; and (iv) expressing each modified nucleic acid cassette in the transfected cells.

Abstract: Disclosed are protein ligands comprising an immunoglobulin heavy chain variable (VH) domain and an immunoglobulin light chain variable (VL) domain, wherein the proteins bind a complex comprising an MHC and a peptide, do not substantially bind the MHC in the absence of the bound peptide, and do not substantially bind the peptide in the absence of the MHC, and the peptide is a peptide fragment of gp100, MUC1, TAX, or hTERT. Also disclosed are methods of using and identifying such ligands.