Chapter 15 Designer antibodies

Abstract

This chapter discusses the antibody structure and biosynthesis, monoclonal antibodies in therapeutics, chimeric and humanized antibodies, expression of antibody fragments in Escherichia Coli , and designer antibody-targeted effector functions. Antibodies, or immunoglobulins (Ig), are glycoproteins that bind specific fluidphase antigen. Ig molecules are composed of four polypeptide chains, two identical heavy chains and two identical light chains. Each heavy chain is bonded to a light chain via hydrophobic interactions and a covalent disulfide bond. The heavy chain/light chain complexes are similarly joined by hydrophobic interactions and disulfide bonds. The heavy chain and light chain are composed of variable (V) domains and constant (C) domains. The heavy chain has one V domain (V H ) and four C domains (C H ) while, the light chain has one V domain (V L ) and one C domain (C L ). Both V and C domains have the characteristic structure of immunoglobulin domains. Like many types of proteins, the domain organization of antibody molecules makes them amenable to engineering because domains are modular. These modular properties include: (1) Both heavy and light chains can be altered by replacing domains within each chain since the heavy and light chains are built up from several immunoglobulin domains, (2) the relative spatial position and surface topology of V H and V L is well conserved. This allows different V H to combine fairly freely and interchangeably with different V L domains, (3) the double β-pleated sheet framework made by V H and V L form a nearly constant scaffold on which the antigen-binding site sits. This allows grafting of complementarity-determining regions from one antibody molecule to another without losing antigen binding specificity.