REVIEWS Antibody therapy of cancer Andrew M. Scott1, Jedd D. Wolchok2,3,4,5 and Lloyd J. Old3,4,5 Abstract | The use of monoclonal antibodies (mAbs) for cancer therapy has achieved considerable success in recent years. Antibody–drug conjugates are powerful new treatment options for lymphomas and solid tumours, and immunomodulatory antibodies have also recently achieved remarkable clinical success. The development of therapeutic antibodies requires a deep understanding of cancer serology, protein-engineering techniques, mechanisms of action and resistance, and the interplay between the immune system and cancer cells. This Review outlines the fundamental strategies that are required to develop antibody therapies for cancer patients through iterative approaches to target and antibody selection, extending from preclinical studies to human trials. Antibody-based therapy for cancer has become estab- Cancer serology Fc function The Fc portion of an antibody lished over the past 15 years and is now one of the most The idea that antibodies could serve as ‘magic bullets’ in can activate a number of successful and important strategies for treating patients the diagnosis and therapy of cancer has a long history, immunological pathways with haematological malignancies and solid tumours. The which started soon after their discovery in the late nine- leading to tumour cell killing. fundamental basis of antibody-based therapy of tumours teenth century. A considerable effort over the ensuing This includes complement activation, activation of dates back to the original observations of antigen expres- decades involved the immunization of various animal effector cells and phagocytosis sion by tumour cells through serological techniques in species with human cancer in the hope of generating of tumour cells. the 1960s1. The definition of cell surface antigens that are antisera with some degree of cancer specificity1. Despite expressed by human cancers has revealed a broad array repeated claims of success and much controversy, this of targets that are overexpressed, mutated or selectively approach yielded little of enduring value, with the nota- expressed compared with normal tissues2. A key challenge ble exception of the discovery of carcinoembryonic has been to identify antigens that are suitable for anti- antigen (CEA), which is a marker for colon cancer and body-based therapeutics. Such therapeutics can function other cancers, and α-fetoprotein, which is a marker for through mediating alterations in antigen or receptor func- hepatocellular cancer1,2. The development of inbred tion (such as agonist or antagonist functions), modulat- mice initiated a new era of serological investigation ing the immune system (for example, changing Fc function of cancer, with the emergence of the cytotoxic test as a and T cell activation) or delivering a specific drug that powerful tool to analyse the cell surface reactivity of is conjugated to an antibody that targets a specific anti- alloantibodies. This led to the recognition that the cell 1 Ludwig Institute for Cancer 2–5 Research; University of gen . Molecular techniques that can alter antibody surface is a highly differentiated structure. The identi- Melbourne; and Centre for pharmacokinetics, effector function, size and immunogenicity fication of cell surface differentiation antigens, which PET, Austin Hospital, have emerged as key elements in the development of new were initially used to distinguish lymphocyte subsets, Melbourne, Victoria 3084, antibody-based therapies. Evidence from clinical trials of set the stage for a revolution in biological and biomedi- Australia. antibodies in cancer patients has revealed the importance cal sciences. This revolution was fuelled by the develop- 2Department of Medicine; hybridoma technology 3Ludwig Institute for Cancer of iterative approaches for the selection of antigen targets ment of and analytical tools such as Research; and optimal antibodies, including the affinity and avidity fluorescence-activated cell sorting (FACS). In view 4Ludwig Center for Cancer of antibodies, the choice of antibody construct, the thera- of these remarkable advances, cancer immunologists Immunotherapy, Memorial peutic approach (such as signalling abrogation or immune renewed their search for human cancer-specific anti- Sloan-Kettering Cancer Center, New York, New York effector function) and the need to critically examine the gens and initiated a massive effort to dissect the surface 2 10065-6306, USA. pharmacokinetic and pharmacodynamic properties of structure of human cancer cells with mAbs . More recent 5Weill Cornell Medical antibodies in early clinical trials. This Review summarizes studies have shown that, in addition to changes in the College, New York, New York the steps that are necessary to transform monoclonal anti- surface antigenic structure of cancer cells, tumour stro- 10065-4896, USA. bodies (mAbs) into reagents for human use, the success mal and tumour vascular cells express novel antigens that Correspondence to A.M.S. 6–11 e-mail: andrew.scott@ludwig. of antibodies in the treatment of cancer patients, the chal- distinguish them from their normal counterparts . As edu.au lenges in target and construct selection, and the crucial a consequence, a detailed picture of the surface antigens doi:10.1038/nrc3236 role of the immune system in antibody therapy. of human cancers is emerging, and with bioinformatic 278 | APRIL 2012 | VOLUME 12 www.nature.com/reviews/cancer © 2012 Macmillan Publishers Limited. All rights reserved FOCUS ON TuMour iMMunoLoGY & iMMunotREVIEWSHerAPY 12,13 At a glance example, by cetuximab and trastuzumab) , the induc- tion of effector function primarily through ADCC (for • Antibody-based therapy for cancer has become established over the past 15 years example, by rituximab)14 and the immune modulation and is now one of the most successful and important strategies for treating patients of T cell function (for example, by ipilimumab)15 are the with haematological malignancies and solid tumours. approaches that have been most successful and that have • Evidence from clinical trials of antibodies in cancer patients has revealed the led to the approval of antibodies using these mechanisms importance of iterative approaches for the selection of antigen targets and optimal (discussed below). antibodies. Although most of the antibodies that have been suc- • The killing of tumour cells using monoclonal antibodies (mAbs) can result from direct cessful in the clinic are intact immunoglobulin G (IgG) action of the antibody (through receptor blockade, for example), immune-mediated molecules, multiple approaches for antibody construc- cell killing mechanisms, payload delivery, and specific effects of an antibody on the tion and for the delivery of conjugated cytotoxic drugs tumour vasculature and stroma. have been used (TABLE 1). The broad range of antibody • Tumour antigens that have been successfully targeted include epidermal growth engineering approaches that have been used in the clinic factor receptor (EGFR), ERBB2, vascular endothelial growth factor (VEGF), cytotoxic T 5,6,16 lymphocyte-associated antigen 4 (CTLA4), CD20, CD30 and CD52. has recently been reviewed . • Serological, genomic, proteomic and bioinformatic databases have also been used to Tumour antigens as antibody targets identify antigens and receptors that are overexpressed in tumour cell populations or that are linked to gene mutations identified as driving cancer cell proliferation, The safety and efficacy of therapeutic mAbs in oncol- including EGFRvIII, MET, CTLA4 and fibroblast activation protein (FAP). ogy vary depending on the nature of the target anti- • The successful development of candidate mAbs for the clinic involves a complex gen. Ideally, the target antigen should be abundant and process of scientific and preclinical evaluations that include identification of the accessible and should be expressed homogeneously, physical and chemical properties of the antibody; the detailed specificity analysis of consistently and exclusively on the surface of cancer antigen expression; the study of the immune effector functions and signalling cells. Antigen secretion should be minimal, as secreted pathway effects of the antibody; the analysis of in vivo antibody localization and antigens can bind the antibody in the circulation and distribution in transplanted or syngeneic tumour systems; and the observation of the could prevent sufficient antibody from binding to the in vivo therapeutic activity of the antibody. tumour. If the desired mechanism of action is ADCC or • A major objective for the clinical evaluation of mAbs has been determining the CDC, then it is desirable that the antigen–mAb complex toxicity and therapeutic efficacy of the antibody alone or as a delivery system for should not be rapidly internalized so as to maximize the radioisotopes or other toxic agents. It is also crucial to assess its in vivo specificity by availability of the Fc region to immune effector cells and determining its biodistribution in patients and to assess the ratio of antibody uptake complement proteins, respectively. By contrast, good in the tumour versus normal tissues. internalization is desirable for antibodies or proteins that • Twelve antibodies have received approval from the US Food and Drug Administration deliver toxins into the cancer cell and for antibodies the for the treatment of various solid tumours and haematological malignancies, and a action of which is primarily based on the downregulation