Tonto

REVIEW

REVIEW

mAbs 2:3, 221-232; May/June, 2010; © 2010 Landes Bioscience

Stability of IgG isotypes in serum
Ivan R. Correia
Abbott Bioresearch Center; Worcester, MA USA

Key words: serum, IgG isotypes, IgG1, IgG2, IgG3, IgG4, stability, primary, secondary, tertiary, Fab exchange, disulfide Abbreviations: FDA, Food and Drug Administration; IgG, immunoglobulin; MS, mass spectrometry;ER, endoplasmic reticulum; CDR, complementarity determining regions; PTM, post translational modification; cIEF, capillary isoelectric focusing; NA1F, asialo, monogalactosylated biantennary, core-substituted with fucose; NA2F, asialo, bigalactosylated biantennary, core-substituted with fucose; NGA2F, asialo, agalacto-, biantennary, core-substituted with fucose; NGA2F-GlcNAc, asialo, agalacto-,biantennary, core-substituted with fucose minus a bisecting N-acetylglucosamine; NA1F-GlcNAc, asialo, monogalactosylated biantennary, core-substituted with fucose minus a bisecting N-acetylglucosamine at various stages of development.1-4 Antibodies are attractive as therapeutics due to their specificity and safety. This is reflected in their relatively high approval success rate (∼25% for humanizedantibodies) compared with the ∼11% success rate for small molecule development.4-6 Other advantages of antibodies, in general, are that they are well tolerated, and the knowledge and experience gained from one antibody during development, manufacturing and clinical use has the potential to be readily transferred to other therapeutics in the pipeline of an organization.4,7 Two major disadvantages ofantibody therapeutics are that targets are restricted to molecules in circulation or those expressed on the surface of cells and they are expensive, primarily due to high doses needed for treatments.4,8 The structure of antibodies, with complete amino acid content and disulfide bond pairing, was elucidated by Gerald Edelman and Rodney Porter in the early 1960s, and they were awarded the NobelPrize in 1972 for this work.9-11 The Ig monomer is composed of two identical heavy chains (HC) and two identical light chains (LC) that are linked by disulfide bonds (inter-chain disulfides). Each of the HC and LC contain structural domains (Ig domains) that resemble immunoglobulin folds composed of two beta sheets linked by cysteine residues (intra-chain disulfides); the Ig domains are furtherclassified into variable (V) or constant (C) domains depending on structure and function.12,13 There are five classes of immunoglobulins that are classified on the basis of the constant region of the heavy chain; they are IgA, IgD, IgE, IgG and IgM. The constant heavy region of IgA, IgD and IgG has three Ig domains and a hinge region to provide flexibility; whereas, the constant regions of IgE and IgMhas four Ig domains. The IgG and IgA classes are further classified into six isotypes (IgG1, IgG2, IgG3, IgG4, IgA1 and IgA2). Despite the vast choice of immunoglobulin types to select for development of a therapeutic antibody, most antibody engineers have focused on the IgG class, although the IgG3 class is not used as a therapeutic candidate because it has a shorter half-life, a long hingeregion that is easily accessible to proteolysis, and allotypic polymorphism.1,4,5,14 The intra-chain disulfides of the HC and LC immunoglobulin domains for the four IgG isotypes are similar; however, the inter-chain disulfide brides are different (see Fig. 1). Differences

Drug development from early discovery to late stage commercialization is a long arduous process where a number of factors aretaken into consideration when deciding on a particular immunoglobulin isotype for a therapeutic purpose. There are no general rules for which isotype is selected; however, prior experiences, effector function and the specific therapy targeted, as well as extensive testing early in development help in paring the number of candidates. Over 20 monoclonal antibodies are FDA-approved, and most are IgG1...