Using directed mutagenesis and phage display on a soluble fragment of the human immunoglobulin super-family receptor ILT2 (synonyms: LIR1, MIR7, CD85j), we have selected a range of mutants with binding affinities enhanced by up to 168,000-fold towards the conserved region of major histocompatibility complex (MHC) class I molecules. Produced in a dimeric form, either by chemical cross-linking with bivalent polyethylene glycol (PEG) derivatives or as a genetic fusion with human IgG Fc-fragment, the mutants exhibited a further increase in ligand-binding strength due to the avidity effect, with resident half-times (t(1/2)) on the surface of MHC I-positive cells of many hours. The novel compounds antagonized the interaction of CD8 co-receptor with MHC I in vitro without affecting the peptide-specific binding of T-cell receptors (TCRs). In both cytokine-release assays and cell-killing experiments the engineered receptors inhibited the activation of CD8(+) cytotoxic T lymphocytes (CTLs) in the presence of their target cells, with subnanomolar potency and in a dose-dependent manner. As a selective inhibitor of CD8(+) CTL responses, the engineered high affinity ILT2 receptor presents a new tool for studying the activation mechanism of different subsets of CTLs and could have potential for the development of novel autoimmunity therapies.
Amino Acid Sequence ; Antigens, CD ; chemistry ; genetics ; pharmacology ; Autoimmunity ; Biological Assay ; Cell Line ; Cytotoxicity, Immunologic ; genetics ; immunology ; Dose-Response Relationship, Immunologic ; Humans ; Immunoglobulins ; immunology ; metabolism ; Immunologic Factors ; chemistry ; genetics ; pharmacology ; Kinetics ; Leukocyte Immunoglobulin-like Receptor B1 ; Lymphocyte Activation ; genetics ; immunology ; Major Histocompatibility Complex ; genetics ; immunology ; Molecular Sequence Data ; Molecular Targeted Therapy ; Mutagenesis, Site-Directed ; Peptide Library ; Polyethylene Glycols ; Protein Binding ; genetics ; immunology ; Receptors, Immunologic ; chemistry ; genetics ; Recombinant Fusion Proteins ; genetics ; metabolism ; T-Lymphocytes, Cytotoxic ; immunology ; metabolism