(D) The Fc stem is formed by the two C-terminal constant domains of the heavy chain (CH2 and CH3) and mediates the continuous circulatory half-life of the IgG1 molecule through conversation with FcRn and its various effector functions (CDC, ADCC, and ADCP) through interactions with complement component C1q as well as NK cells, macrophages, and other FcR-expressing myeloid and lymphoid cells. In cancer therapy, the natural effector functions are triggered upon arrayed engagement of the mAb with malignancy cell surface antigens. Collectively, the structural and functional modularity of the antibody molecule has served as a preferred canvas for protein engineers. years later, the top 15 drugs based on global sales across RETN all indications include five malignancy mAbs with combined revenues of approximately $40 billion [1]. This list is usually topped by immune checkpoint inhibitors (ICIs) pembrolizumab (Keytruda) and nivolumab (Opdivo) which both target PD1. The current quantity of FDA-approved and marketed antibody-based malignancy therapies is usually 43 and includes a variety of formats, targets, and indications (Table 1). Initially, the success of mAbs as pharmaceuticals was driven bynatural propertiesof the antibody molecule, such as high affinity and specificity to virtually any antigen, the ability to block receptor-ligand interactions, long circulatory half-life, and engagement of proteins and cells of the innate immune system and in doing so mediate complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC), and antibody-dependent cellular phagocytosis (ADCP) (marked in green inTable 1). Increasingly, mAbs withengineered propertiesnot found in nature are utilized for cancer therapy. These can be grouped into antibody therapeutics that either engage cytotoxic T cells or deliver cytotoxic payloads (marked in blue and orange, respectively, inTable 1). FDA-approved antibody therapeutics that deploy T cells as their mechanism of action (MOA) include seven ICIs, one T cell-engaging bispecific antibody (T-biAb), and five chimeric antigen receptor T cells (CAR-Ts). FDA-approved payload-delivering antibody therapeutics include one radioimmunoconjugate, nine antibody-drug conjugates (ADCs), Tacrine HCl Hydrate and one immunotoxin. A rich pipeline of antibody therapeutics from all three MOA categories is at various stages of preclinical and clinical investigations, with another record number of FDA approvals anticipated for 2021 [2]. == Table 1. FDA-approved and marketed antibody-based cancer therapies. == Currently, cancer patients in the United States have access to 43 different antibody therapeutics, with more than half added in the past five years. The differently colored rows indicate MOAs based on natural or enhanced natural properties of mAbs (green), on engaging cytotoxic T cells (blue), and on delivering cytotoxic payloads (orange). == Antibodies as pharmaceuticals == At the core of its success as a pharmaceutical is the highly stable and modular architecture of the antibody molecule, reflecting its evolution to a key guardian of the vertebrate Tacrine HCl Hydrate immune system adapted to physically, chemically, and biologically harsh extracellular environments. Its building block, the immunoglobulin (Ig) fold, is a -sandwich composed of two disulfide-linked antiparallel -sheets with protruding -turns. Both variable and constant domains of the antibody molecule are Tacrine HCl Hydrate Ig folds. In variable domains, three of the -turns serve as complementarity determining regions (CDRs) with hypervariable amino acid sequences. The most common format of both natural and synthetic human antibodies is the IgG1 molecule (Figure 1). Its concentration in the blood is 510 g/L, comprising more than half of all immunoglobulins. Of the 43 FDA-approved antibody-based cancer therapies 30 have an IgG1 format (Table 1). The ~150-kDa IgG1 molecule is composed of two identical ~25-kDa light chains and two identical ~50-kDa heavy chains that are covalently connected by four interchain disulfide bridges. Both light and heavy chain have an N-terminal variable domain (VLand VH, respectively), each contributing three CDRs which collectively comprise the paratope of the ~25-kDa Fv fragment that binds antigens with high affinity and specificity, followed by one and three constant domains, respectively. The ~50-kDa Fab fragment encompasses the Fv fragment and the adjacent constant domain of the light chain (CL) and first constant domain of the heavy chain (CH1). The two C-terminal constant domains of the heavy chain (CH2 and CH3) form the Fc fragment of the IgG1 Tacrine HCl Hydrate molecule which mediates its prolonged circulatory half-life through interaction with the neonatal Fc receptor (FcRn) and its effector functions through interaction with complement component C1q (triggering CDC) and Fc receptors (FcRs) I, IIA, and IIIA (triggering ADCC and ADCP) (Figure 1). The only conserved N-glycosylation site is an asparagine in CH2. The two branched glycans of.