EXPRESSION OF CONFORMATIONALLY CONSTRAINED ADHESION PEPTIDE IN AN ANTIBODY CDR LOOP AND INHIBITION OF NATURAL-KILLER-CELL CYTOTOXIC ACTIVITY BY AN ANTIBODY ANTIGENIZED WITH THE RGD MOTIF

We report that an antibody engineered to express three Arg-Gly-Asp (RG D) repeats in the third complementarity-determining region of the heav y chain (antigenized antibody) efficiently inhibits the lysis of human erythro-leukemia K-562 cells by natural killer (NK) cells. Synthetic peptides containing RGD did not inhibit. Inhibition was specific for t he (RGD)3-containing loop and required simultaneous occupancy of the F c receptor (CD16) on effector cells. The antigenized antibody inhibite d other forms of cytotoxicity mediated by NK cells but not cytotoxicit y mediated by major histocompatibility complex-restricted cytotoxic T lymphocytes (CTL). A three-dimensional model of the engineered antibod y loop shows the structure and physicochemical characteristics probabl y required for the ligand activity. The results indicate that an RGD m otif is involved in the productive interaction between NK and target c ells. Moreover, they show that peptide expression in the hypervariable loops of an antibody molecule is an efficient procedure for stabilizi ng oligopeptides within a limited spectrum of tertiary structures. Thi s is a new approach towards imparting ligand properties to antibody mo lecules and can be used to study the biological function and specifici ty of short peptide motifs, including those involved in cell adhesion.