Antibodies and related products are the fastest growing class of therapeutic agents. By analysing the regulatory approvals of IgG-based biotherapeutic agents in the past 10 years, we can gain insights into the successful strategies used by pharmaceutical companies so far to bring innovative drugs to the market. Many challenges will have to be faced in the next decade to bring more efficient and affordable antibody-based drugs to the clinic. Here, we discuss strategies to select the best therapeutic antigen targets, to optimize the structure of IgG antibodies and to design related or new structures with additional functions.
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- Antibody-dependent cellular cytotoxicity
(ADCC). A mechanism of cell-mediated immunity whereby effector cells of the immune system (mainly natural killer cells) actively lyse a target cell that has been bound by specific antibodies. It is one of the mechanisms by which antibodies, as part of the humoral immune response, can limit and contain infection.
- Biosimilar antibody
A generic version of an 'innovator' antibody with the same amino-acid sequence but produced from a different clone and manufacturing process, resulting in differences in glycosylation and other microvariations. Biosimilar antibodies are known as follow-on biologics in the United States.
- Bispecific antibody
(Also known as a bifunctional antibody). A monoclonal antibody that binds to two different epitopes. These can be on the same antigen or two different antigens, thereby triggering two different functions. Bispecific antibodies do not usually occur naturally.
- Chemistry, manufacture and control
(CMC). A part of pharmaceutical development that deals with the nature of the antibody drug substance and drug product, as well as the manner in which both are obtained, and by which the manufacturing process is quality controlled. Unfavourable physico-chemical characteristics of an antibody molecule that might result in difficulties to translate a research lead candidate into a scalable drug with appropriate pharmacokinetic and pharmacodynamic features are known as CMC liabilities (also referred to as 'drugability' or 'developability' issues).
- Complement-dependent cytotoxicity
A mechanism of antibody-mediated immunity whereby antibody binding to the complement component C1q activates the classical complement activation cascade leading to formation of the membrane attack complex, the cytolytic end product of the complement cascade.
- Complementarity-determining region
(CDR). A short sequence (up to 13 amino acids) found in the variable domains of immunoglobulins. The CDRs (six of which are present in IgG molecules) are the most variable part of immunoglobulins and contribute to their diversity by making contacts with a specific antigen, allowing immunoglobulins to recognize a vast repertoire of antigens with a high affinity.
- Fab fragment
The fragment of antigen binding is the region of an antibody that binds to antigens. It is composed of one constant and one variable domain of each of the heavy and light chains (VH and VL, respectively).
- Fc-fusion protein
An engineered recombinant protein carrying at its carboxy-terminal end the Fc portion (Hinge–CH2–CH3 domains) of an antibody and, at its amino-terminal end, any kind of protein or peptide such as a receptor-binding domain or a ligand. For example, etanercept, a product that is approved to treat rheumatoid arthritis by acting as a tumour necrosis factor inhibitor, is an Fc-fusion protein of IgG1 Fc with tumour necrosis factor receptor 2. The suffix -cept or -stim is used to identify Fc-fusion proteins or peptides, respectively.
- Humanized antibody
A humanized antibody is obtained by genetic engineering to increase its similarity to antibodies produced naturally in humans, thereby decreasing its potential immunogenicity. A common humanization method is known as CDR grafting; this involves introducing the CDRs from a non-human antibody of interest into a framework acceptor sequence of a human germline V gene that is closely related to the antibody of interest. The suffix -zumab is used to identify humanized antibodies.
- 'Me better' antibody
(Also known as a 'bio-better' antibody). We define this as an antibody targeting the same validated epitope as an existing antibody (having the same CDRs: 'me too') but with an optimized glycosylation profile (such as low fucose levels for enhanced ADCC) or an engineered Fc domain to increase the serum half-life.
Antibodies with small structural differences (such as amino-terminal pyroglutamic acid residues, carboxy-terminal clipped lysine residues, different glycoforms or disulphide bridge isomers) that are present in the drug substance, which might affect the pharmacokinetic and pharmacodynamic properties and that must be kept in comparable amounts during the production scale-up (toxicology studies, Phases I, II and III clinical trials and post-marketing batches).
- Orphan diseases
Rare diseases that affect only a small number of patients. Both the United States Food and Drug Administration and the European Medicines Agency have special development and regulatory procedures to stimulate research for such illnesses.
The antigen-binding site of an antibody composed of portions of the different CDRs of the antibody's heavy and light chain variable domains.
The covalent attachment of polyethylene glycol polymer chains to a Fab fragment to increase the serum half-life.
The study of the physiological effects of the antibody, the mechanisms of drug action and the relationship between antibody concentration and effect: what an antibody does to a body.
The study of antibody clearance in the serum: what the body does to an antibody.
- Protein scaffold
An engineered protein typically of small size (<100 amino acids) and containing a highly structured core associated with variable domains of high conformational tolerance, allowing insertions, deletions or other substitutions. These domains can create a putative binding interface for any targeted protein. The structure of protein scaffolds can be highly diverse (such as immunoglobulin-like molecules, loop-containing proteins, highly structured proteins and oligomeric proteins), but they are usually of human origin.
- Second-generation antibody
A first-generation follow-up antibody with improved variable domains (such as humanized or human variable domains or affinity matured CDRs).
- Third-generation antibody
A second-generation follow-up antibody with improved variable domains (such as humanized or human variable domains or affinity matured CDRs) and improved Fc domains (for example, glyco- or amino-acid engineered to increase effector functions or to improve half-life).
About this article
Molecular Biotechnology (2019)