Soluble, high-affinity dimers of T-cell receptors and class II major histocompatibility complexes: Biochemical probes for analysis and modulation of immune responses

T cell receptors (TCR) and major histocompatibility complex (MHC) molecules are integral membrane proteins that have central roles in cell-mediated im mune recognition. Therefore, soluble analogs of these molecules would be us eful for analyzing and possibly modulating antigen-specific immune response s. However, due to the intrinsic low-affinity and inherent solubility probl ems, it has been difficult to produce soluble high-affinity analogs of TCR and class II MHC molecules. This report describes a general approach which solves this intrinsic low-affinity by constructing soluble divalent analogs using IgG as a molecular scaffold. The divalent nature of the complexes in creases the avidity of the chimeric molecules for cognate ligands. The gene rality of this approach was studied by making soluble divalent analogs of t wo different classes of proteins, a TCR (2C TCR(2)Ig) and a class II MHC (I -MCC. E-k (2)Ig) molecule, Direct flow cytometry assays demonstrate that th e divalent 2C TCR(2)Ig chimera retained the specificity of the native 2C TC R, while displaying increased avidity for cognate peptide/MHC ligands, resu lting in a high-affinity probe capable of detecting interactions that heret ofore have only been detected using surface plasmon resonance. TCR(2)IgG wa s also used in immunofluorescence studies to show ER localization of intrac ellular peptide-MHC complexes after peptide feeding. I-MCC-E-k (2)Ig chimer as were able to both stain and activate an MCC-specific T cell hybridoma. C onstruction and expression of these two diverse heterodimers demonstrate th e generality of this approach. Furthermore, the increased avidity of these soluble divalent proteins makes these chimeric molecules potentially useful in clinical settings for probing and modulating In vivo cellular responses . (C) 1999 Academic Press.