Human therapeutic antibodies

Discovery-stage identification of drug-like antibodies using emerging experimental and computational methods

There is intense and widespread interest in developing monoclonal antibodies as therapeutic agents to treat diverse human disorders. During early-stage antibody discovery, hundreds to thousands of lead candidates are identified, and those that lack optimal physical and chemical properties must be deselected as early as possible to avoid problems later in drug development. It is particularly challenging to characterize such properties for large numbers of candidates with the low antibody quantities, concentrations, and purities that are available at the discovery stage, and to predict concentrated antibody properties (e.g., solubility, viscosity) required for efficient formulation, delivery, and efficacy. Here we review key recent advances in developing and implementing high-throughput methods for identifying antibodies with desirable in vitro and in vivo properties, including favorable antibody stability, specificity, solubility, pharmacokinetics, and immunogenicity profiles, that together encompass overall drug developability. In particular, we highlight impressive recent progress in developing computational methods for improving rational antibody design and prediction of drug-like behaviors that hold great promise for reducing the amount of required experimentation. We also discuss outstanding challenges that will need to be addressed in the future to fully realize the great potential of using such analysis for minimizing development times and improving the success rate of antibody candidates in the clinic.

Peptides, Antibodies, Peptide Antibodies and More

The applications of peptides and antibodies to multiple targets have emerged as powerful tools in research, diagnostics, vaccine development, and therapeutics. Antibodies are unique since they, in theory, can be directed to any desired target, which illustrates their versatile nature and broad spectrum of use as illustrated by numerous applications of peptide antibodies. In recent years, due to the inherent limitations such as size and physical properties of antibodies, it has been attempted to generate new molecular compounds with equally high specificity and affinity, albeit with relatively low success. Based on this, peptides, antibodies, and peptide antibodies have established their importance and remain crucial reagents in molecular biology.

Technical and ethical limitations in making human monoclonal antibodies (an overview)

In the broadest sense there are no longer any technical limitations to making human mAbs. Biological issues involving the type and nature of either a synthetic or a natural antibody, advantages of various B cell immunological compartments, and various assays needed to qualitate and quantitate mAbs have essentially been solved. If the target antigen is known then procedures to optimize antibody development can be readily planned out and implemented. When the antigen or target is unknown and specificity is the driving force in generating a human mAb then considerations about the nature and location of the B cell making the sought after antibody become important. And, therefore, the person the B cell is obtained from can be an ethical challenge and a limitation. For the sources of B cells special considerations must be taken to insure the anonymity and privacy of the patient. In many cases informed consent is adequate for antibody development as well as using discarded tissues. After the antibody has been generated then manufacturing technical issues become important that greatly depend upon the amounts of mAb required. For kilogram quantities then special considerations for manufacturing that include FDA guidelines will be necessary.

Monoclonal Antibodies: A Tool in Clinical Research

Monoclonal antibodies (MAbs) are an old immunological tool with applications in the fields of immunology, biotechnology, biochemistry, and applied biology. Production of monoclonal antibodies using hybridoma technology was discovered in 1975 by Georges Kohler of West Germany and Cesar Milstein of Argentina. Modern-day research on MAbs from laboratories worldwide is revealing additional applications in diverse branches of sciences. Recently, MAbs have been widely applied in the field of clinical medicine. Currently, MAbs account for one-third of all the new therapeutic treatments for breast cancer, leukemia, arthritis, transplant rejection, asthma, and psoriasis, with many more late-stage clinical trials being conducted. In this review, we outline the (i) production of MAbs, (ii) application of MAbs, (iii) antibody engineering, and (iv) pharmaceutical application of MAbs. The future prospect of this review lies in the applicability of monoclonal antibodies as a molecule for understanding and monitoring the biology of disease and its role in research, clinical, diagnostic, analytical, and pharmaceutical applications.

Antibody engineering reveals the important role of J segments in the production efficiency of llama single-domain antibodies in Saccharomyces cerevisiae

Variable domains of llama heavy-chain antibodies (VHH) are becoming a potent tool for a wide range of biotechnological and medical applications. Because of structural features typical of their single-domain nature, they are relatively easy to produce in lower eukaryotes, but it is not uncommon that some molecules have poor secretion efficiency. We therefore set out to study the production yield of VHH. We computationally identified five key residues that are crucial for folding and secretion, and we validated their importance with systematic site-directed mutations. The observation that all key residues were localised in the V segment, in proximity of the J segment of VHH, led us to study the importance of J segment in secretion efficiency. Intriguingly, we found that the use of specific J segments in VHH could strongly influence the production yield. Sequence analysis and expression experiments strongly suggested that interactions with chaperones, especially with the J segment, are a crucial aspect of the production yield of VHH.

Therapeutic antibodies: successes, limitations and hopes for the future

With more than 20 molecules in clinical use, monoclonal antibodies have finally come of age as therapeutics, generating a market value of $11 billion in 2004, expected to reach $26 billion by 2010. While delivering interesting results in the treatment of several major diseases including autoimmune, cardiovascular and infectious diseases, cancer and inflammation, clinical trials and research are generating a wealth of useful information, for instance about associations of clinical responses with Fc receptor polymorphisms and the infiltration and recruitment of effector cells into targeted tissues. Some functional limitations of therapeutic antibodies have come to light such as inadequate pharmacokinetics and tissue accessibility as well as impaired interactions with the immune system, and these deficiencies point to areas where additional research is needed. This review aims at giving an overview of the current state of the art and describes the most promising avenues that are being followed to create the next generation of antibody-based therapeutic agents.

Identification of a strongly activating human anti-CD40 antibody that suppresses HIV type 1 infection

We characterized the functional properties of a novel set of human anti-CD40 monoclonal antibodies originating from a human phage display library and identified an antibody that strongly activates cells via the CD40 receptor for potential use in HIV therapy. The anti-CD40 antibodies were converted from a single chain antibody fragment format (scFv) to an IgG format and produced in HEK293 cells, and the binding characteristics were evaluated. Next, their ability to (1) rescue a human B cell line from induced apoptosis, (2) stimulate B cell proliferation, and (3) block the CD40-CD40L interaction was determined. Finally, the most activating anti-CD40 antibody was tested for its ability to block HIV-1 infection in a monocyte-derived cell line. The different anti-CD40 antibodies, A24, B44, E30, F33, and A2-54, displayed a wide variety of binding and functional properties. In particular, B44 showed a very strong ability to activate normal human B cells and, in addition, did not block the CD40-CD40L interaction. This antibody was able to suppress HIV-1 infection in a human cell line (MonoMac 1) and may be a potential therapeutic candidate in HIV infection.

Construction of miniantibodies for the in vivo study of human autoimmune diseases in animal models

Background

Phage display antibody libraries have been made from the lymphocytes of patients suffering from autoimmune diseases in which the antibodies are known to play a role in the pathogenesis or are important for the diagnosis of the disease. In the case of Celiac Disease, the immune response is directed against the autoantigen tissue transglutaminase. However, despite numerous studies, the role of these antibodies in the pathogenesis of this disease has not been elucidated.

Results

We were able to engineer specific anti-transglutaminase antibody fragments in the form called "miniantibody". These are produced by genetic fusion of anti-tTG scFv to Human, Mouse or Rat Fc domains, making them suitable for in vivo expression. The results obtained here indicate that the miniantibody molecule is efficiently secreted, and that the reactivity to the antigen is retained even after fusion to heterologous Fc domains. Further analysis demonstrate that the molecule is secreted as homodimeric, mimicking original antibody structure. Finally, the in vivo expression in mice leads to detectable serum levels with no apparent gross immune response by the host.

Conclusion

In this work we demonstrated the usefulness of a method for the in vivo expression of miniantibodies specific to transglutaminase, corresponding to the autoimmune specificity of Celiac Disease. This can be proposed as a general method to study the pathogenic role of autoimmune antibodies in autoimmune diseases.

Applications of mass spectrometry for the structural characterization of recombinant protein pharmaceuticals

Therapeutic proteins produced using recombinant DNA technologies are generally complex, heterogeneous, and subject to a variety of enzymatic or chemical modifications during expression, purification, and long-term storage. The use of mass spectrometry (MS) for the evaluation of recombinant protein sequence and structure provides detailed information regarding amino acid modifications and sequence alterations that have the potential to affect the safety and activity of therapeutic protein products. General MS approaches for the characterization of recombinant therapeutic protein products will be reviewed with particular attention given to the standard MS tools available in most biotechnology laboratories. A number of recent examples will be used to illustrate the utility of MS strategies for evaluation of recombinant protein heterogeneity resulting from post-translational modifications (PTMs), sequence variations generated from proteolysis or transcriptional/translational errors, and degradation products which are formed during processing or final product storage. Specific attention will be given to the MS characterization of monoclonal antibodies as a model system for large, glycosylated, recombinant proteins. Detailed examples highlighting the use of MS for the analysis of monoclonal antibody glycosylation, deamidation, and disulfide mapping will be used to illustrate the application of these techniques to a wide variety of heterogeneous therapeutic protein products. The potential use of MS to support the selection of cell line/clone selection and formulation development for therapeutic antibody products will also be discussed.

PEGylation and multimerization of the anti-p185HER-2 single chain Fv fragment 4D5: effects on tumor targeting

A major goal in antibody design for cancer therapy is to tailor the pharmacokinetic properties of the molecule according to specific treatment requirements. Key parameters determining the pharmacokinetics of therapeutic antibodies are target specificity, affinity, stability, and size. Using the p185HER-2 (HER-2)-specific scFv 4D5 as model system, we analyzed how changes in molecular weight and valency independently affect antigen binding and tumor localization. By employing multimerization and PEGylation, four different antibody formats were generated and compared with the scFv 4D5. First, dimeric and tetrameric miniantibodies were constructed by fusion of self-associating, disulfide-linked peptides to the scFv 4D5. Second, we attached a 20-kDa PEG moiety to the monovalent scFv and to the divalent miniantibody at the respective C terminus. In all formats, serum stability and full binding reactivity of the scFv 4D5 were retained. Functional affinity, however, did change. An avidity increase was achieved by multimerization, whereas PEGylation resulted in a 5-fold decreased affinity. Nevertheless, the PEGylated monomer showed an 8.5-fold, and the PEGylated dimer even a 14.5-fold higher tumor accumulation than the corresponding scFv, 48 h post-injection, because of a significantly longer serum half-life. In comparison, the non-PEGylated bivalent and tetravalent miniantibodies showed only a moderate increase in tumor localization compared with the scFv, which correlated with the degree of multimerization. However, these non-PEGylated formats resulted in higher tumor-to-blood ratios. Both multimerization and PEGylation represent thus useful strategies to tailor the pharmacokinetic properties of therapeutic antibodies and their combined use can additively improve tumor targeting.

Structure-based Stability Engineering of the Mouse IgG1 Fab Fragment by Modifying Constant Domains

A semi-rational approach based on structural data was exploited in a search for CH1 and CL domains with improved intrinsic thermodynamic stabilities. Structural and amino acid level comparisons were carried out against known biophysically well-behaving and thermodynamically beneficial scFv and Fab fragments. A number of mutant Fab fragments were constructed by site-directed mutagenesis of regions in the CH1 and CL domains expected to be most sensitive under physical stress conditions. These mutations were located on three sites in the Fab constant domains; a mobile loop in the CH1 domain, residues surrounding the two largest solvated hydrophobic cavities located in the interface of the CH1 and CL domains and the hydrophobic core regions of both CH1 and CL. Expression levels of functional Fab fragments, denaturant-induced unfolding equilibria and circular dichroism spectroscopy were used to evaluate the relative stabilities of the wild-type and the mutant Fab fragments. The highest thermodynamic stability was reached through the mutation strategy, where the hydrophobicity and the packing density of the solvated hydrophobic cavity in the CH1/CL interface was increased by the replacement of the hydrophilic Thr178 in the CL domain by a more hydrophobic residue, valine or isoleucine. The midpoint of the transition curve from native to unfolded states of the protein, measured by fluorescence emission, occurred at concentrations of guanidine hydrochloride of 2.4 M and 2.6 M for the wild-type Fab and the most stable mutants, respectively. Our results illustrate that point mutations targeted to the CH1/CL interface were advantageous for the overall thermodynamic stability of the Fab fragment.

From Gene Expression Analysis to Tissue Microarrays

Mantle cell lymphoma (MCL) is an aggressive lymphoid malignancy for which better treatment strategies are needed. To identify potential diagnostic and therapeutic targets, a signature consisting of MCL-associated genes was selected based on a comprehensive gene expression analysis of malignant and normal B cells. The corresponding protein epitope signature tags were identified and used to raise monospecific, polyclonal antibodies, which were subsequently analyzed on paraffin-embedded sections of malignant and normal tissue. In this study, we demonstrate that the initial selection strategy of MCL-associated genes successfully allows identification of protein antigens either uniquely expressed or overexpressed in MCL compared with normal lymphoid tissues. We propose that genome-based, affinity proteomics, using protein epitope signature tag-induced antibodies, is an efficient way to rapidly identify a number of disease-associated protein candidates of both previously known and unknown identities.

Domain Interactions in the Fab Fragment: A Comparative Evaluation of the Single-chain Fv and Fab Format Engineered with Variable Domains of Different Stability

Recombinant antibody fragments, most notably Fab and scFv, have become important tools in research, diagnostics and therapy. Since different recombinant antibody formats exist, it is crucial to understand the difference in their respective biophysical properties. We assessed the potential stability benefits of changing the scFv into the Fab format, the influence of the variable domains on the stability of the Fab fragment, and the influence of the interchain disulfide bond in the Fab fragment. To analyze domain interactions, the Fab fragment was broken down into its individual domains, several two-domain assemblies and one three-domain assembly. The equilibrium denaturation properties of these constructs were then compared to those of the Fab fragment. It was found that mutual stabilization occurred across the VH/VL and the CH1/CL interface, whereas the direct interaction between the V) and the CL domain had no influence on the stability of either domain. This observation can be explained by the different interfaces used for interaction. In contrast, the whole CH1CL and VHVL unit showed significant mutual stabilization, indicating a high degree of cooperation between the VH/VL and CH1/CL interface. The interchain disulfide bond in the Fab fragment plays an essential role in this stabilization. In addition to the effects of domain association on the thermodynamic (equilibrium) stability, Fab fragments differ from scFv fragments of similar equilibrium stability by having a very slow unfolding rate. This kinetic stabilization may increase significantly the resistance of Fab fragments against short time exposure to adverse conditions.

Proteomics and leukocytes: an approach to understanding potential molecular mechanisms of inflammatory responses

Leukocytes play an important role in the progression of disease and leukocyte-derived proteins are associated with the pathogenesis of the disease. Leukocyte activation causes production of inflammatory mediators, over-expression of cell surface adhesion molecules, and an increase in migration and infiltration, phagocytosis, and degranulation, as well as receptor phosphorylation and signal transduction. An increasing number of studies on the application of leukocyte proteomics have appeared in mapping protein profiles of inflammatory cells, contributing to the understanding of potential mechanisms involved in leukocyte function. Together with improvements in proteomic technology in leukocyte research, leukocyte proteomic analysis becomes more simple, rapid, flexible, sensitive, and specific. This enables proteomic investigation of activated or non-activated leukocytes to be highly focused on defined suborgans or specific signaling pathways. Research in leukocyte proteomics is progressing from fingerprinting to functioning, human cell lines to primary leukocytes, non-activated cells to inflammatory mediator-stimulated cells, in vitro culture to in vivo challenge, and animal models to human disease. A number of newly identified proteins from leukocyte proteomics may offer new mechanism-orientated targets for drug discovery and development.

Profiling of internalizing tumor-associated antigens on breast and pancreatic cancer cells by reversed genomics

Human antibodies directed towards functionally associated tumor antigens have great potentials as adjuvant treatment in cancer therapy. Here we describe an efficient subtractive approach to select single chain Fv (scFv) antibodies, specifically binding to unknown rapidly internalizing tumor-associated antigens (TAA) on human breast and pancreatic carcinoma cell lines. After re-engineering the scFv into intact IgG molecules, these fully human antibodies displayed individual binding profiles to TAAs on breast, pancreatic, colorectal and prostate carcinomas, while showing no reactivity to lymphomas. The ability of the selected antibodies to undergo receptor-mediated internalization was verified by confocal microscopy, thus proving our strategy to provide a unique set of human antibodies, potentially useful in immunotherapy.

Affinity and epitope profiling of mouse anti-CD40 monoclonal antibodies

The CD40-CD40L interaction plays a critical role in both humoral and cellular immune responses and interfering antibodies have been suggested as an effective approach for the treatment of lymphomas and autoimmune diseases. In this study we have profiled a panel of mouse antihuman CD40 monoclonal antibodies (MoAbs), regarding their CD40 binding affinity and epitope-specificity relative to the CD40L binding in relation to their cellular activating potential. Despite a rather similar domain-recognition profile, the MoAbs blocked the CD40L binding to a varying degree, with MoAb 5C3 being the poorest inhibitor. There was no correlation between affinity and cellular activation potential. In contrast, a correlation between the ability to block CD40L-binding and activation potential could be seen. We believe that this analysis of several mouse anti-CD40 antibodies can be used to develop strategies for producing new human anti-CD40 antibodies that can more effectively induce or block B-cell proliferation.

Recombinant antibodies for cancer diagnosis and therapy

Recombinant antibodies currently represent over 30% of biopharmaceuticals in clinical trials, highlighted by the recent Food and Drug Administration (FDA) approvals of Zevalin(TM) (ibritumomab-tiuxetan; IDEC Pharmaceuticals, San Dieago, CA, USA) for cancer radioimmunotherapy and Humira(TM) (adalimumab; Abbott Laboratories, IL, USA) for rheumatoid arthritis. Together, these FDA approvals have excited the biotechnology industry, particularly since sales of recombinant antibodies are increasing rapidly to a predicted US dollar 4 billion per annum worldwide in 2003. To date, 10 engineered therapeutic antibodies have gained FDA approval and many others are in Phase III trials. Many recent FDA-approved antibodies are simple molecular designs that have taken 10 years to be developed into effective therapeutic reagents. Emerging new technologies have created a vast range of recombinant, antibody-based reagents, which specifically target clinical biomarkers of disease. Radiolabelling of antibodies has increased their potential for cancer imaging and targeting. Recombinant antibodies have also been reduced in size and rebuilt into multivalent molecules for higher affinity. In addition, antibodies have been fused with many molecules, including toxins, enzymes, drugs and viruses, for prodrug therapy, cancer treatment and gene delivery. Recombinant antibody technology has enabled clever manipulations in the construction of complex in vitro libraries for the selection of high-affinity reagents against refractory targets. Furthermore, innovative affinity maturation methods have been developed which enable rapid selection of extremely high-affinity reagents. This review focuses on developments in the last 12 months and describes the latest developments in the design, production and clinical use of recombinant antibodies for cancer diagnosis and therapy.