FOCUS ON THERAPEUTIC ANTIBODIES PERSPECTIVES ‘validated targets’, either because prior anti- TIMELINE bodies have clearly shown proof of activity in humans (first-generation approved anti- Strategies and challenges for the bodies on the market for clinically validated targets) or because a vast literature exists next generation of therapeutic on the importance of these targets for the disease mechanism in both in vitro and in vivo pharmacological models (experi- antibodies mental validation; although this does not necessarily equate to clinical validation). Alain Beck, Thierry Wurch, Christian Bailly and Nathalie Corvaia Basically, the strategy consists of develop- ing new generations of antibodies specific Abstract | Antibodies and related products are the fastest growing class of for the same antigens but targeting other therapeutic agents. By analysing the regulatory approvals of IgG-based epitopes and/or triggering different mecha- biotherapeutic agents in the past 10 years, we can gain insights into the successful nisms of action (second- or third-generation strategies used by pharmaceutical companies so far to bring innovative drugs to antibodies, as discussed below) or even the market. Many challenges will have to be faced in the next decade to bring specific for the same epitopes but with only one improved property (‘me better’ antibod- more efficient and affordable antibody-based drugs to the clinic. Here, we ies). This validated approach has a high discuss strategies to select the best therapeutic antigen targets, to optimize the probability of success, but there are many structure of IgG antibodies and to design related or new structures with groups working on this class of target pro- additional functions. teins and freedom to operate is decreased. By contrast, one can identify new or less well studied target proteins that confer The research and development of mono- biotherapeutic agents in the past 10 years particular functions to cells that might clonal antibodies is a rapidly progressing (TIMELINE), we can gain insights into the be involved in pathogenic disorders. This field1,2. In the past 25 years, more than strategies developed by biopharmaceutical second ‘functional approach’ — in which 30 immunoglobulins (IgGs) and their companies. Here, we discuss strategies to antibodies are selected based on a func- derivatives have been approved for use in select therapeutic antigen targets based on tional screen, and the targets to which they various indications3,4 (TIMELINE). The cur- previous clinical or experimental valida- bind are then identified using proteomic rently marketed antibody-based drugs have tion or on functional approaches; strategies or cell-based approaches (reverse pharma- been approved not only to treat diseases to optimize the antibody structure and to cology), for example — is associated with affecting large numbers of patients (such design related or new structures with greater potential for innovation and intel- as cancer and inflammatory diseases) but additional functions; as well as challenges lectual property rights but increased risk of also for more specialized indications owing to bring more affordable treatments to development failure. to special regulatory procedures for rare the most appropriate patient populations medical conditions (orphan diseases), such screened for validated biomarkers. Clinically validated targets. ‘Blockbuster’ as paroxysmal nocturnal haemoglobinuria antibodies such as rituximab (Rituxan/ (for which, eculizumab (Soliris; Alexion Mabthera; Genentech/Roche/Biogen Idec), pharma ceuticals) therapy was approved in Since the first generation of… infliximab (Remicade; Centocor/Merck), 2007). Interestingly, 9 out of the 26 anti- IgG1 antibodies reached the trastuzumab (Herceptin; Genentech/ bodies currently in Phase III clinical trials market in the late 1990s, Roche) and cetuximab (Erbitux; ImClone (35%) have ‘orphan drug’ designation4. Systems), directed against now highly Since the first generation of mouse, the variety of antibody clinically validated targets such as CD20, chimeric and humanized IgG1 antibodies structures has been tumour necrosis factor (TNF), human epi- reached the market in the late 1990s, the considerably extended. dermal growth factor receptor 2 (HER2; variety of antibody structures has been also known as ERBB2) and epidermal considerably extended. Humanized and growth factor receptor (EGFR), respec- human antibodies of other IgG isotypes Strategies to select the best targets tively, are tremendous success stories1. (IgG2 and IgG4)5 have been developed, Antigen target selection can be classified in Second-generation antibodies directed as well as a large number of IgG-related broad terms into two main approaches. The against these same antigens have altera- products6. By analysing the success- first approach involves the development tions such as improved variable domains ful regulatory approvals of IgG-based of antibodies directed against so-called to decrease immunogenicity and/or to NATURE REVIEWS | IMMUNOLOGY VOLUME 10 | MAY 2010 | 345 © 2010 Macmillan Publishers Limited. All rights reserved PERSPECTIVES Timeline | The regulatory approval of IgG-based products in the past 24 years* • muromomab (CD3 Description of transgenic mice with • rituximab (CD20 • 131I–tositumomab (CD20-specific specific); 11 years human immunoglobulin genes by specific); first full length radio–immuno conjugate) The production of after the description L. L. Green et al. (Abgenix mice)70 and chimeric antibody • gemtuzumab • omalizumab (IgE-Fc specific) monoclonal antibodies of hybridomas by N. Lonberg et al. (Medarex mice)71 • daclizumab (CD25 ozogamicin • efalizumab (CD11a specific); by hybridoma specific); first humanized (CD33-specific– withdrawn from market in technology invented Antibody humanization • abciximab (glycoprotein IIβ specific antibody, 11 years after calicheamicin 2009 owing to risk of fatal by Cesar Milstein and first described by Fab); the first chimeric Fab, 10 years the description of antibody–drug brain infections Georges J. F. Köhler66 P. T. Jones et al.68 after the description of chimerization humanization conjugate) • alefacept (CD2-specific LFA3–Fc) 1975 1984 1986 1990 1994 1995 1997 1998 2000 2001 2002 2003 Antibody chimerization first Description of phage display • edrecolomab (EPCAM • basiliximab (CD25 specific) • alemtuzumab • 111In/90Y–ibritumomab described by S. L. Morrison et al.67 technology for the generation specific); approved in • palivizumab (RSV F protein (CD52 specific) tiuxetan (CD20-specific of fully human antibodies Germany, now specific) radio–immuno conjugate) Cesar Milstein and Georges J. F. Köhler by John McCafferty and withdrawn owing to • infliximab (TNF specific) • adalimumab (TNF specific); awarded the Nobel Prize in Physiology colleagues69 lack of efficacy • trastuzumab (HER2 specific) first fully human antibody, or Medicine for ‘the discovery of the • etanercept (TNF-specific 12 years after the principle for production of TNFR2–Fc) description of phage monoclonal antibodies’ display *Approved by the United States Food and Drug Administration (FDA), the European Medicines Agency (EMA), China’s State Food and Drug Administration and/or the Japanese Ministry of Health. The suffix of the international non-proprietary names for monoclonal antibodies denotes the antibody format: -omab, mouse IgG2 (4 approved products); -ximab, mouse–human chimeric IgG1 (5 approved products); -zumab, humanized IgG1 (14 approved products); -umab, human antibodies from phage display or transgenic mice (7 approved products); -cept, Fc-fusion protein (4 approved products); -stim, Fc-fusion peptide (1 approved product); -axomab, trifunctional (bispecific) mouse–rat hybrid (1 approved product). C5, complement component C5; CHPM, Committee for Medicinal Products for Human Use; CTLA4, cytotoxic T lymphocyte antigen 4; EGFR, epidermal growth factor receptor; EPCAM, epithelial cell adhesion molecule; HER2, human epidermal growth factor receptor 2; 131I, iodine-131; IL, interleukin; IL-1RAP, IL-1R accessory protein; 111In, indium-111; LFA3, lymphocyte function-associated antigen 3; PEG, polyethylene glycol; R, receptor; RANKL, receptor activator of nuclear factor-κB ligand; RSV, respiratory syncytial virus; TNF, tumour necrosis factor; TNFR2, TNF receptor 2; VEGFA, vascular endothelial growth factor A; 90Y, yttrium-90. target distinct epitopes with higher or lower review by the United States Food and Drug multifactorial, redundant and frequently affinity for their antigens7, and/or have dif- Administration (FDA) — and then by poorly understood. In addition, patients ferent antibody formats (such as conjugat- the third generation antibody MEDI-557 are becoming resistant to current cancer ing the Fab domain to polyethylene glycol (MedImmune) (a version of motavizumab treatments, leading to the expression of (PEGylation) and Fc-fusion proteins). These with engineered Fc domains for a longer new molecules (potential targets) that drive antibodies have been investigated in the serum half-life), which is in Phase I trials7. the tumour growth14. Another difficulty in clinic and recently approved for use in sev- oncology is to determine the best combina- eral diseases — for example, ofatumumab Experimentally validated targets. Most tion of drugs and drug targets, which is not (Arzerra; Genmab/GlaxoSmithKline) cytokines and associated receptors seem to be always predictable from pre-clinical studies, following rituximab, and adalimumab valuable