Immunological Reviews 1992, No. 130 Published by Munksgaard, Copenhagen, Denmark No part may be reproduced by any process without written pcmussion from the author(s)

Theoretical and Practical Aspects of Antigenized Antibodies MAURIZIO ZANETTI,

FRANgoisE Rossi,

PAOLA LANZA, GILBERTO FILACI,

RICHARD H . LEE & ROSARIO BILLETTA

... "The study of immimity is a chapter in medical theory" ... Elie Mecthnikoff 1908

INTRODUCTION Antigenization of antibody is a new immunological concept (Zanetti 1992) that exemplifies MecthnikofTs words (Metchnikoff, reprinted in 1989) in a paradigmatic way. It was conceived with a two-fold purpose. One was to investigate directly the molecular basis of antibody antigenicity and immunogenicity. The other was to test from a molecular perspective one of the most controversial postulates ofthe idiotype network theory (Lindenmann 1973, Jeme 1974): antibodies as internal images of antigens. It soon became apparent, however, that antigenization of antibody was also a new, powerful way to provide a stable conformation to oligopeptides of general biological interest. Understanding the molecular and cellular requirements for antigenicity and immunogenicity of proteins is still a central issue in immunology. Antigenization of antibody may represent, therefore, a new alternative way to solve some of the puzzling aspects of immunology that still elude our understanding (e.g., the relationship between amino acid sequence, three-dimensional structure and function of soluble proteins and cell-surface receptors). In this article, we discuss the principles that have guided the development of antigenized antibodies (**Ab) and the directions of work we have undertaken to demonstrate their possible impact in immunology. The topics presented are organized into four main sections: I) discussion ofthe conceptual framework on which antigenization of antibody was developed, 2) brief description of the The Department of Medicine and Cancer Center, University of California San Diego 225 Dickinson Street San Diego, CA 92103-8420 and Biosym Technologies, 9685 Scranton Road, San Diego, CA 92121-2777, U.S.A.

126

ZANETTI ET AL.

methodological approach, 3) summary of our most representative experimental findings, and 4) speculation on ^^^Ab as a source of structural information and as potential therapeutic molecules. , ANTIGENIZATION: STRUCTURAL CONSIDERATIONS The synthesis of an antibody proceeds through a cascade of tissue-specific genetic events (Alt et al. 1987, Early et al. 1980). Variable {V) regions of both H and L chains are encoded by exons assembled upstream from the sequences that encode the constant (C) regions. During B-cell differentiation, three difTerent gene elements (VH, D and JH) in the H chain and two gene elements {VL and J J in the L chain {Early et al. 1980) join to create diversity of the V-region repertoire {i.e., antigen binding and idiotypy). X-ray crystal analysis (Poljak et al. 1973, SchifTer et al. 1973) has clarified the three-dimensional structure of the antibody molecule and its topology of sequence conservation. Framework regions {FRs) are organized as ^ strands interconnected with hypervariable {HV) loops. FRs are arranged in a ^ sheet sandwich {the "immunoglobulin fold"). The sandwich is filled with P sheets packed by hydrophobic side chains with invariant disulfide bond linking the opposing sheets. The constraints on the side chains necessary to preserve folding are sufficiently stringent to explain the sequence conservation of these regions. In contrast, it is well established that HV regions can drift in sequence and conformation with little or no effect on the structure of the FRs {Kabat et al. 1987). As discussed in following sections, both antigen binding and idiotypy localize to discrete areas of variability of V domains: HV regions or complementarity-determining regions (CDRs). The conformation of the six CDR loops, three in the H and three in the L chain, is the principal determinant of the architecture of the antigen-binding site and also the major contributor to antibody antigenicity. For at least five of the six loops of the two chains, a discrete repertoire of conformations {canonical structures) exists on which alternative combinations and side-chain diversity generate a wide range of binding sites and, consequently, antigenic structures {Chothia et al. 1985, 1987). A notable exception is the CDR3 of the H chain, which apparently does not use patterns of main conformation existing in the current structural data base for immunogiobulins. Antigenic determinants of immunogiobulins have been localized on the H chain (Kobzik et al. 1976, Zeldis et al. 1979, Rudikoff et al. 1983, Stanislawski et al. 1983, Gridley et al. 1985, Zavala et al. 1985, Borden et al. 1988, Sollazzo et al. 1989), on the L chain {Vrana et al. 1979, Chen et al. 1984) and on both H and L chains {Suzan et al. 1982, Kranz et al. 1983, Lee et al. 1983, Robbins et al. 1986). Some antigenic determinants of immunogiobulins have been mapped to a precise region in one polypeptide chain. Cumulative data indicate that residues in the CDR3 ofthe H chain {Rudkoff et al. 1983, Berek 1984, Gridley

*

Theoretical and practical aspects of antigenized antibodies.

Immunological Reviews 1992, No. 130 Published by Munksgaard, Copenhagen, Denmark No part may be reproduced by any process without written pcmussion fr...
8MB Sizes 0 Downloads 0 Views