Strategies and challenges for the next generation of therapeutic antibodies (1)
The research and development of mono-clonal antibodies is a rapidly progressing field 1,2
. In the past 25 years, more than 30 immunoglobulins (IgGs) and their derivatives have been approved for use in various indications 3,4
(Timeline). The cur-rently marketed antibody-based drugs have been approved not only to treat diseases affecting large numbers of patients (such as cancer and inflammatory diseases) but also for more specialized indications owing to special regulatory procedures for rare medical conditions (orphan diseases ), such as paroxysmal nocturnal haemoglobinuria (for which, eculizumab (Soliris; Alexion pharma c euticals) therapy was approved in 2007). Interestingly, 9 out of the 26 anti-bodies currently in Phase III clinical trials (35%) have ‘orphan drug’ designation 4
. Since the first generation of mouse, chimeric and humanized IgG1 antibodies reached the market in the late 1990s, the variety of antibody structures has been considerably extended. Humanized and human antibodies of other IgG isotypes (IgG2 and IgG4)5 have been developed, as well as a large number of IgG-related products 6
. By analysing the success-ful regulatory approvals of IgG-based biotherapeutic agents in the past 10 years (Timeline), we can gain insights into the strategies developed by biopharmaceutical companies. Here, we discuss strategies to select therapeutic antigen targets based on previous clinical or experimental valida-tion or on functional approaches; strategies to optimize the antibody structure and to design related or new structures with additional functions; as well as challenges to bring more affordable treatments to the most appropriate patient populations screened for validated biomarkers.Strategies to select the best targets Antigen target selection can be classified in broad terms into two main approaches. The first approach involves the development of antibodies directed against so-called ‘validated targets’, either because prior anti-bodies have clearly shown proof of activity in humans (first-generation approved anti-bodies on the market for clinically validated targets) or because a vast literature exists on the importance of these targets for the disease mechanism in both in vitro and in vivo pharmacological models (experi-mental validation; although this does not necessarily equate to clinical validation). Basically, the strategy consists of develop-ing new generations of antibodies specific
for the same antigens but targeting other epitopes and/or triggering different mecha-nisms of action (second- or third-generation antibodies , as discussed below) or even
specific for the same epitopes but with only
one improved property (‘me better’ antibod-ies ). This validated approach has a high probability of success, but there are many groups working on this class of target pro-teins and freedom to operate is decreased. By contrast, one can identify new or less well studied target proteins that confer
particular functions to cells that might
be involved in pathogenic disorders. This
second ‘functional approach’ — in which antibodies are selected based on a func-tional screen, and the targets to which they
bind are then identified using proteomic
or cell-based approaches (reverse pharma-cology), for example — is associated with greater potential for innovation and intel-lectual property rights but increased risk of development failure.Clinically validated targets. ‘Blockbuster’ antibodies such as rituximab (Rituxan/Mabthera; Genentech/Roche/Biogen Idec), infliximab (Remicade; Centocor/Merck), trastuzumab (Herceptin; Genentech/Roche) and cetuximab (Erbitux; ImClone
Systems), directed against now highly
clinically validated targets such as CD20,
tumour necrosis factor (TNF ), human epi-dermal growth factor receptor 2 (HER2; also known as ERBB2) and epidermal growth factor receptor (EGFR ), respec-tively, are tremendous success stories 1. Second-generation antibodies directed against these same antigens have altera-tions such as improved variable domains
to decrease immunogenicity and/or to
T I M E L I N E
Strategies and challenges for the next generation of therapeutic antibodies
Alain Beck, Thierry Wurch, Christian Bailly and Nathalie Corvaia
Abstract | 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.
Since the first generation of… IgG1 antibodies reached the
market in the late 1990s, the variety of antibody structures has been considerably extended.PersPectIves
target distinct epitopes with higher or lower affinity for their antigens7, and/or have dif-ferent antibody formats (such as conjugat-ing the Fab domain to polyethylene glycol (PeGylation) and Fc-fusion proteins). These antibodies have been investigated in the clinic and recently approved for use in sev-eral diseases — for example, ofatumumab (Arzerra; Genmab/GlaxoSmithKline) following rituximab, and adalimumab (Humira/Trudexa; Abbott), certolizumab pegol (Cimzia: uCB) and golimumab (Simponi; Centocor) following infliximab (Timeline). In addition, third-generation antibodies,targeting different epitopes, triggering other mechanisms of action and that are often engineered for improved
Fc-associated immune functions or half-life7, have also reached Phase I to III clinical trials8,9. For example, the third-generation CD20-specific antibody obinutuzumab (GA101; Biogen Idec/Roche/Glycart) is less immunogenic than rituximab, has a differ-ent mechanism of action and is glyco- engineered to trigger increased cytotoxicity8,9. Another example is the respiratory syncytial virus-specific monoclonal antibody palivizumab (Synagis; MedImmune/ Abbott), which has been followed by the second-generation antibody motavizumab (MEDI-524; MedImmune) — which
has affinity matured complementarity-determining regions (CDRs) and is under review by the united States Food and Drug
Administration (FDA) — and then by
the third generation antibody MEDI-557
(MedImmune) (a version of motavizumab
with engineered Fc domains for a longer
serum half-life), which is in Phase I trials7.
Experimentally validated targets.Most
cytokines and associated receptors seem to be
valuable targets for the treatment of immu-
nological disorders, as shown by the large
number of antibodies that have already been
approved (such as those specific for TNF,
interleukin-1 (Il-1), Il-2 receptor (Il-2R),
Il-6R, Il-12, Il-23 and receptor activator of
nuclear factor-κB ligand (RANKl)), as well
as the numerous candidates in clinical trials
(such as antibodies specific for Il-4, Il-6,
Il-13 and Il-17)10–12. In this area, there is
a lesser need to identify new targets, as the
mechanisms driving at least some inflam-
matory disorders are reasonably well known.
By contrast, diversification and validation
of new targets in oncology is a challenging
issue13 as the causes of malignancies are often
multifactorial, redundant and frequently
poorly understood. In addition, patients
are becoming resistant to current cancer
treatments, leading to the expression of
new molecules (potential targets) that drive
the tumour growth14.Another difficulty in
oncology is to determine the best combina-
tion of drugs and drug targets, which is not
always predictable from pre-clinical studies,
as shown by the adverse events (such as skin
toxicity, diarrhoea and infection) reported
for patients with colorectal cancer who were
administered with both EGFR- and vascular
endothelial growth factor A (vEGFA)-
specific antibodies15. Target selection will also
require an understanding of cooperative sig-
nalling involving, for example, growth factor
receptor heterodimers16 or integrin crosstalk
with growth factors17.
A source of potential new experimentally
validated targets in oncology is the abundant
literature documenting the important role
of tyrosine kinase receptors in malignancies.
For example, insulin-like growth factor 1
receptor (IGF1R) was proposed to be an
interesting oncoprotein more than 20 years
ago18, but patients have had to wait until now
to benefit from experimental treatments
involving IGF1R-specific antibodies; by the
end of 2009, nearly 100 clinical trials were
ongoing with at least 9 different IgGs specific
for IGF1R19. A similar lag phase existed his-
torically for the development of cetuximab,
functional approaches… allow the discovery of unknown cell surface antigens, but these new targets need extensive and careful clinical validation
a chimeric antibody that inhibits EGFR activation. Today, fortunately, the translation from research to clinic tends to occur more rapidly owing to the increasing knowledge of structure–function relationships for the newest monoclonal antibodies, such as those targeting vEGF receptors or the hepatocyte growth factor receptor MET. As a common feature, a tumour must be fully dependent on the antibody target for the therapeutic antibody to affect growth20, and the target must be overexpressed on tumour cells to avoid toxic effects.
Functionally validated targets.A more chal-lenging approach is to select monoclonal antibodies with a defined biological effect on tumour cells (such as the inhibition of proliferation or the induction of apoptosis) and to identify the recognized antigens by proteomics and alternative techniques21–23. These functional approaches (or reverse pharmacology) allow the discovery of unknown cell surface antigens, but these new targets need extensive and careful clini-cal validation, which is a high development risk and involves longer research timelines before entering into the clinic.
using this type of approach, the path-ways that control partial or complete resistance to current therapies should be better investigated to uncover putative targets that might translate into new and efficient therapies24. For example, it has
been reported that treatment with EGFR
inhibitors leads to MET overexpression25.
Similarly, resistance to HER2-specific anti-
bodies has been reported to be related to
IGF1R overexpression19.
In our opinion, companies should carry
out more research in these high-risk areas if
they are expecting new therapeutic break-
throughs. In addition to identifying new
antigen targets, another option to extend
the therapeutic use of antibodies is to mod-
ulate their structure and format, which is
discussed in the next section.
Strategies to optimize structures
A detailed knowledge of antibody structure
and activity now allows researchers to engi-
neer primary antibodies on a more rational
basis. This can yield more homogeneous and
stable molecules with additional properties
such as increased cytotoxicity or dual target-
ing, as well as IgG-related structures with
additional functions and specificities.
Improving pharmaceutical properties.
Most approved antibodies are chimeric,
humanized or human IgGs with similar
constant domains. Numerous studies look-
ing at the structure–function relationships
of these antibodies have been published in
the past five years with the aim of identifying
antibody microvariants26–28 and investigating
the influence of these variants on antigen
binding23, stability, pharmacokinetics29 and
pharmacodynamics(FiG. 1). This knowledge is
now being used to increase homogeneity and
mitigate the chemistry, manufacture and control
(CMC) liabilities of pre-clinical antibody
candidates by genetic engineering30–32. The
removal by mutation of instability or aggre-
gation hot spots in the antibody CDRs, and
the use of hinge-stabilized or aglycosylated
IgG4, are just a few examples of antibodies
with improved pharmacological properties
(such as decreased heterogeneity) that are
currently in development.
Improving antibody functions.The variable
fragment (Fv) of an antibody is responsible
for interactions with antigens and dictates
essential properties such as binding affinity
and target specificity. The origin of the Fv in
therapeutic antibodies can be diverse (such
as hybridomas, human antibody libraries,
rodents with a human antibody repertoire,
or primatized or humanized antibodies
from various species). Affinity maturation
allows the binding affinity of the Fv to
be improved and/or target selectivity to be
modulated. The constant fragment (Fc) of
an antibody is responsible for interactions
with immune cells33, and the associated
properties of the Fc can also be modulated
by engineering at several levels: altering the
glycosylation status to regulate anti- and
pro-inflammatory properties34, modulat-
ing antibody-dependent cellular cytotoxicity
(ADCC) by site-directed mutagenesis to
alter binding to Fc receptors, increasing
the serum half-life by Fc engineering to
increase binding to the neonatal Fc receptor
(FcRn) (which prevents IgG degradation)
and increasing complement activation by
isotype chimerism35(FiG. 2).
Second- and third-generation antibody–
drug conjugates. Additional functions can
be endowed on antibodies by conjugation
to other drugs. So far, the clinical success
of immunoconjugates is limited; only one
drug, namely gemtuzumab ozogamicin
(Mylotarg; Pfizer) has been approved in
the united States (but not in Europe) for the
treatment of patients with acute myeloid
leukaemia. Nevertheless, promising new
immunoconjugates — including optimized
linkers that are hydrolysable in the cyto-
plasm, resistant or susceptible to proteases,
or resistant to multi-drug resistance efflux
pumps — associated with highly cytotoxic
drugs are now being studied in advanced
clinical trials (such as trastuzumab–DM1
(Genentech) and inotuzumab–ozogamicin
Nature Reviews | Immunology in Phase III trials targeting HER2+ and CD22+ cells in patients with breast and various B cell lymphomas, respectively 36,37). IgGs have also been engineered to con-tain unique drug conjugation positions to obtain uniform and more homogeneous drug conjugates (such as thiomab–drug conjugates, which have a uniform stoichi-ometry of approximately two coupled drugs per antibody molecule 38), which should open new therapeutic avenues to deliver highly cytotoxic drugs with increased tolerability 38–40.
Bispecific antibodies. For most diseases, several mediators contribute to overall pathogenesis by either unique or over-lapping mechanisms. The simultaneous blockade of several targets might there-fore yield better therapeutic efficacy than inhibition of a single target. After many years of unsuccessful trials, the first
bispecific antibody , catumaxomab (Removab;
Fresenius Biotech/TRIoN Pharma), which binds to both epithelial cell adhesion mol-ecule (EPCAM) on tumour cells and CD3 on effector immune cells, was approved by the European Medicines Agency (EMA) in 2009 for the treatment of malignant ascites 41. Another promising example of a bispecific antibody is blinatumomab (MT103; Micromet/MedImmune), specific for tumour-associated CD19 and effec-tor cell-expressed CD3, which is being investigated in Phase II clinical trials for the therapy of minimal residual disease of B cell-precursor acute lymphoblastic leukaemia indication. Bispecific antibod-ies directed against two different tumour-associated or immunological antigen targets are another strategy that has been investi-gated, but with only limited success owing partly to the highly heterogeneous mixtures that result from the multiple possibilities of immunoglobulin chain association and also to scale-up and purification issues 42.
These difficulties have been recently overcome by the dual variable domain IgG (DvD-IgG) technology. This new type of immunoglobulin was obtained by combin-ing the variable domains of two already characterized monoclonal antibodies (two v l domains on the light chain and two v H domains on the heavy chain), as exempli-fied by an Il-12- and Il-18-specific anti-body or by an Il-1α- and Il-1β-specific antibody 33,43. This technology enables the different specificities of two monoclonal antibodies to be engineered into a single functional, dual-specific, tetravalent IgG-like molecule, and these antibodies can be made with good production yields in a scalable Chinese hamster ovary (CHo) cell line. Another elegant approach con-sisted of engineering an additional paratope in the variable domain of an existing antibody, which resulted in simultaneous binding to HER2 and vEGFA 44. In these two examples, the resulting proteins can be produced as a homogeneous single, functional species and with productivities similar to conventional IgGs, which is not the case for the previous bispecific antibody formats.
Polyclonal or oligoclonal antibodies. Another interesting concept is to design recombinant polyclonal or oligoclonal anti-bodies directed against the same or different targets: for example, the Rhesus D blood group antigen-specific polyclonal antibody rozrolimupab (Sym001; Symphogen A/S), which is a mixture of 25 unique recom-binant monoclonal antibodies 45, is currently in Phase II clinical trials for the treatment of chronic and acute idiopathic thrombo-cytopenic purpura. Synergistic preclinical in vivo antitumour efficacy was also recently reported for Sym004 (Symphogen A/S), a controlled mixture of two EGFR-specific antibodies that produces a superior response to cetuximab and panitumumab (vectibix; Amgen) alone 46, which has led to a Phase I clinical trial in patients with EGFR + breast cancer. As these recombinant mixtures are produced by a single cell type and are co-purified, this should result in a less
expensive drug product than the use of two or more separately produced monoclonal antibodies 47.
Engineering new protein scaffolds. As an alternative to antibodies, several small protein-based drugs and alterna-tive antibody formats are currently being investigated. These may be cheaper to produce and have advantages such as
resolution mass spectrometry methods in combination with ultra-performance separation techniques
are now routinely used at all stages of antibody discovery and development to assess antibody struc-ture. As a consequence, these new analytical tools have resulted in the identification of minor anti-body components, such as charge variants, glycoforms, disulphide bridge isoforms and other low level molecular species. As shown in the figure, lessons learned from the effects of these micro-variants on the stability and the pharmacokinetic and/or pharmacodynamic properties can be used for the design of the next generation of optimized antibodies with higher homogeneity, stability and potency. It is also important to consider the production system used to ensure low levels of xenobiotic glycans and humanized antibody glycosylation patterns. cDr, complementarity-determining region; c H , heavy chain constant domain; c L , light chain constant domain; v H , heavy chain variable domain; v L , light chain variable domain.
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Nature Reviews |Immunology
deeper tumour penetration associated with smaller size. Such protein scaffolds, with highly specific binding properties derived from natural human proteins, have now entered clinical trials48,49(TABle 1). Among them, ecallantide (Kalbitor/DX-88; Dyax) — a Kunitz domain-based scaffold that targets human plasma kallikrein — was approved in December 2009 by the FDA for the treatment of attacks of hereditary angioedema50,51. More than 10 protein scaffolds are currently in clinical trials, of which 6 are in Phase II trials. of interest, as one of the main disadvantages of these new drugs is their potential immunogenic-ity and safety profile52,53, it is encouraging that none of them elicited severe adverse reactions or anti-drug antibody responses during Phase I clinical trials. Nevertheless, these structures might have their own limi-tations in terms of pharmacokinetic and pharmacodynamic properties and potential for development, as each scaffold will need its own unique CMC package54.
Strategies to provide affordable treatments Antibodies are a successful class of thera-peutic agents, but many treaments remain costly, which may limit their use, particu-larly when synergistic combinations of IgGs are required55. Thus, decreasing costs is an important part of drug development. Decreasing production and processing costs.Although increased productivity is an important factor in decreasing costs, the greatest effect comes from combin-ing this with improved and less costly downstream processing. Improving the production yields of mammalian cell lines that produce already approved antibodies56 and improving the selection of alternative
purification and formulation methods (such as the use of chemical mimotopes rather than protein A for purifying IgG or large scale precipitation, which are much less expensive) are key steps that are being actively investigated by the biotechnol-ogy industry57, with significant progress in downstream processing already having been achieved. In addition, the design of less heterogeneous antibody structures will help to facilitate scale-up and proc-ess comparability and limit the need for extensive validation of new protocols. Alternative cell lines with simpler cul-ture media, higher productivity, shorter production times and no viral inactiva-tion steps are also important features to consider in terms of cost reduction. These might include, for example, the use of engineered yeast with humanized glyco-
sylation enzymes or plant cells (for the
production of fully functional glycosylated
antibodies) or the use of Escherichia coli
(for the production of Fab fragments or
non-glycosylated IgGs when effector
functions are not required)58. Such non-
mammalian production systems will not
require costly viral inactivation validation
steps, as are required for mammalian cell
lines that might be contaminated with
viruses that could infect humans.
Biosimilar or ‘me better’ antibodies?In
contrast to the low-cost generic versions
of small molecules that are off patent, it is
so far not possible to produce exact copies
of large proteins and glycoproteins, such
as antibodies, owing to their structural
complexity59. Nevertheless, since 2005,
the EMA has initiated regulatory approval
pathways for biosimilar products, currently
resulting in marketing authorization for
12 products encompassing three product
classes (human growth hormone, erythro-
poietin and granulocyte colony-stimulating
factor)60. Furthermore, biosimilar antibodies
(identical amino-acid sequence but only a
similar glycosylation profile compared with
a reference product), such as a biosimi-
lar antibody of rituximab, are approved
in countries such as India, China and
South Korea. Their possible emergence on
European markets was recently discussed
at a workshop organized by the EMA in
london61. Several laboratories also plan to Figure 2 | Antibody design to improve the pharmacological functions. A better knowledge of the structure–function relationships of antibody molecules allows fine-tuning of their associated pharmacological properties. the variable domain, which is associated with antigen binding (Fab moiety), can be tailored to modulate binding affinity and specificity using well-described phage display techniques. Fab fragments can be used as a monovalent non-activating format with a long half-life (conjugated to polyethylene glycol (PeGylated)) or with a short half-life (naked). Depending on its origin, humanization or de-immunization (that is, the substitution of key amino acids predicted to abrogate binding to human MHc class II molecules in order to reduce a t cell immune response) techniques can greatly decrease the potential immunogenicity of an antibody. With regard to the antibody Fc portion, better knowledge of the Fc receptors present on immune cells allows the tai-lored engagement of associated effector functions (such as antibody-dependent cellular cytotoxicity (ADcc), complement-dependent cytotoxicity or phagocytosis) by modulation of the binding affini-ties to these Fc receptors through mutations and/or glyco-engineering. the antibody Fc domain is also the major binding region to develop immunoconjugates, by association with a radioactive label, cytotoxic drug or protein. cDr, complementarity-determining region; c
H
, heavy chain constant domain; c
L
, light chain constant domain; Fcγr, Fc receptor for IgG; Fcrn, neonatal Fc receptor; v
H
, heavy chain variable domain; v
L
, light chain variable domain.
NATuRE REvIEwS |Immunology voluME 10 | MAy 2010 |349
bring ‘me better’ antibodies to the clinic, such as those with controlled and opti-mized glycosylation by producing them in glyco-engineered yeast strains 58 (for example, a copy of the rituximab amino acid sequence but with afucosylated glyco-forms resulting in a 100-fold increase in ADCC) and/or with increased plasma
half-life 62 (for example, a copy of rituximab but with a mutation of three amino acids in the Fc domain resulting in extended pharmaco k inetics). In both cases, the cost of treatment should decrease because of lower cost of the product or a less frequent administration regimen. Nevertheless, the development of biosimilar and ‘me better’ antibodies needs new regulations that must be discussed and validated by regulatory authorities 63. The first wave of biosimilar antibodies are copies of current important therapeutic antibodies such as a
biosimilar rituximab (Reditux; Dr Reddy’s laboratories), which is approved in India, and a biosimilar abciximab (Clotinab; Abu Abxis), which is appoved in South Korea; further biosimilar candidates include copies of infliximab, etanercept (Enbrel; Amgen/Pfizer), cetuximab and trastuzumab. Biomarker identification and selection of patients. The screening of patients with breast cancer for HER2 expression sta-tus before trastuzumab (HER2-specific) treatment is the paradigm of subset selec-tion for targeted treatment; in this case a subset of women with a HER2+ type of breast cancer (around 20%) are selected for HER2-targeted treatment 16. For EGFR-targeted therapy of colorectal cancer, it was originally thought that, because EGFR is overexpressed in tumour cells from more than 95% of patients, there was no need
for patient stratification; however, it has recently been found that only patients car-rying tumours with a wild-type KRAS phe-notype (60% of patients) will benefit from EGFR-specific cetuximab or panitumumab treatment 64. Similar observations apply to lung-targeted anti-cancer drugs 63 and to anti-angiogenic therapies 65. The identifica-tion of biomarkers and patient selection is becoming a paradigm for the development of targeted therapies that requires further investigation.
Conclusions and perspectives
The IgG-based biotherapeutic agents that have been approved in the past decade show that pharmaceutical laboratories have worked on the diversification and fine tailoring of antibody structures to bring new antibodies to the market. Following the success of the first generation of
table 1 |
Alternative protein and antibody scaffolds: early clinical proof-of-concept cell adhesion molecule; FDA, United states Food and Drug Administration; Her2, human epidermal growth factor receptor 2; IL, interleukin; LDL, low-density lipoprotein; NHL, non Hodgkin’s lymphoma; NscLc, non-small-cell lung carcinoma; r, receptor; scFv: single-chain variable domain antibody fragment; sMIP , small modular immunopharmaceutical; tNF , tumour necrosis factor; ttP , thrombotic thrombocytopenic purpura; veGF , vascular endothelial growth factor; v H , heavy chain variable domain; vHH, heavy chain variable domain (in camelids); v L , light chain variable domain; vWF , von Willebrand factor.
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monoclonal antibody blockbusters, second-generation antibodies were recently approved. In addition, many third-generation antibodies designed to trigger different mechanisms of action simultaneously (such as targeting growth factors, inhibit-ing angiogenesis and restoring apoptosis) and associated with enhanced or silenced effector functions (ADCC or complement-dependent cytotoxicity) are being investigated in clinical trials.
Among the challenges to be faced in the next 10 years are the identification and validation of new targets, addressing the resistance to current drug treatments and understanding target cross talk and regula-tion. In the meantime, efforts have to be made to decrease the costs of industrial
production by increasing the productivity
of the current cell lines, by developing alter-
native production systems and purification
processes and by optimizing the design
of more homogeneous and stable IgGs.
The availability of regulatory pathways to
register biosimilar antibodies might be
another way to decrease healthcare costs
and to generalize the use of monoclonal
antibodies. As an alternative to antibodies,
proof-of-concept of the clinical efficacy of
new protein scaffolds with different phar-
macological properties and less expensive
manufacturing processes might also help to
bring more affordable targeted biotherapies
to the market.
Alain Beck, Thierry Wurch, Christian Bailly and
Nathalie Corvaia are at the Centre d’Immunologie
Pierre Fabre (CIPF), 5 Avenue Napoléon III, F74160,
Saint-Julien-en-Genevois, France.
Correspondence to A.B.
e-mail: alain.beck@https://www.wendangku.net/doc/1414934813.html,
doi:10.1038/nri2727
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2. Beck, A., Reichert, J. M. & Wurch, T. 5th European
Antibody Congress 2009: November 30–December 2
2009. mAbs2, 108–128 (2010).
3. Beck, A., Wurch, T. & Corva?a, N. Editorial:
therapeutic antibodies and derivatives: from the
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421–422 (2008).
4. Reichert, J. M. Antibodies to watch in 2010. mAbs
2, 1–16 (2010).
5. Lonberg, N. Fully human antibodies from transgenic
mouse and phage display platforms. Curr. Opin.
Immunol.20, 450–459 (2008).
glossary
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 (V
H
and V
l
, respectively).
Fc-fusion protein
An engineered recombinant protein carrying at its
carboxy-terminal end the Fc portion (Hinge–C
H
2–C
H
3
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.
Microvariants
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.
Paratope
The antigen-binding site of an antibody composed of
portions of the different CDRs of the antibody’s heavy
and light chain variable domains.
PEGylation
The covalent attachment of polyethylene glycol polymer
chains to a Fab fragment to increase the serum half-life.
Pharmacodynamics
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.
Pharmacokinetics
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
immuno g lobulin-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).
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Competing interests statement
The authors declare competing financial interests: See Web
version for details.