John McCafferty

Beyond natural antibodies: the power of in vitro display technologies

In vitro display technologies, best exemplified by phage and yeast display, were first described for the selection of antibodies some 20 years ago. Since then, many antibodies have been selected and improved upon using these methods. Although it is not widely recognized, many of the antibodies derived using in vitro display methods have properties that would be extremely difficult, if not impossible, to obtain by immunizing animals. The first antibodies derived using in vitro display methods are now in the clinic, with many more waiting in the wings. Unlike immunization, in vitro display permits the use of defined selection conditions and provides immediate availability of the sequence encoding the antibody. The amenability of in vitro display to high-throughput applications broadens the prospects for their wider use in basic and applied research.

Application of phage display to high throughput antibody generation and characterization

We have created a high quality phage display library containing over 1010 human antibodies and describe its use in the generation of antibodies on an unprecedented scale. We have selected, screened and sequenced over 38,000 recombinant antibodies to 292 antigens, yielding over 7,200 unique clones. 4,400 antibodies were characterized by specificity testing and detailed sequence analysis and the data/clones are available online. Sensitive detection was demonstrated in a bead based flow cytometry assay. Furthermore, positive staining by immunohistochemistry on tissue microarrays was found for 37% (143/381) of antibodies. Thus, we have demonstrated the potential of and illuminated the issues associated with genome-wide monoclonal antibody generation.

Cross-domain inhibition of TACE ectodomain

Proteolytic release from the cell surface is an essential activation event for many growth factors and cytokines. TNF-α converting enzyme (TACE) is a membrane-bound metalloprotease responsible for solubilizing many pathologically significant membrane substrates and is an attractive therapeutic target for the treatment of cancer and arthritis. Prior attempts to antagonize cell-surface TACE activity have focused on small-molecule inhibition of the metalloprotease active site. Given the highly conserved nature of metalloprotease active sites, this paradigm has failed to produce a truly specific TACE inhibitor and continues to obstruct the clinical investigation of TACE activity. We report the bespoke development of a specific TACE inhibitory human antibody using “two-step” phage display. This approach combines calculated selection conditions with antibody variable-domain exchange to direct individual antibody variable domains to desired epitopes. The resulting “cross-domain” human antibody is a previously undescribed selective TACE antagonist and provides a unique alternative to small-molecule metalloprotease inhibition.

Recombinant Antibodies and In Vitro Selection Technologies

Over the past decade, the accumulation of detailed knowledge of antibody structure and function has enabled antibody phage display to emerge as a powerful in vitro alternative to hybridoma methods for creating antibodies. Many antibodies produced using phage display technology have unique properties that are not obtainable using traditional hybridoma technologies. In phage display, selections are performed under controlled, in vitro conditions that are tailored to suit demands of the antigen and the sequence encoding the antibody is immediately available. These features obviate many of the limitations of hybridoma methodology, and because the entire process relies on scalable molecular biology techniques, phage display is also suitable for high-throughput applications. Thus, antibody phage display technology is well suited for genome-scale biotechnology and therapeutic applications. This review describes the antibody phage display technology and highlights examples of antibodies with unique properties that cannot easily be obtained by other technologies.

Generating a panel of highly specific antibodies to 20 human SH2 domains by phage display

To demonstrate the utility of phage display in generating highly specific antibodies, affinity selections were conducted on 20 related Src Homology 2 (SH2) domains (ABL1, ABL2, BTK, BCAR3, CRK, FYN, GRB2, GRAP2, LYN, LCK, NCK1, PTPN11 C, PIK3R1 C, PLCγ1 C, RASA1 C, SHC1, SH2D1A, SYK N, VAV1 and the tandem domains of ZAP70). The domains were expressed in Escherichia coli, purified and used in affinity selection experiments. In total, 1292/3800 of the resultant antibodies were shown to bind the target antigen. Of the 695 further evaluated in specificity ELISAs against all 20 SH2 domains, 379 antibodies were identified with unique specificity (i.e. monospecific). Sequence analysis revealed that there were at least 150 different clones with 1–19 different antibodies/antigen. This includes antibodies that distinguish between ABL1 and ABL2, despite their 89% sequence identity. Specificity was confirmed for many on protein arrays fabricated with 432 different proteins. Thus, even though the SH2 domains share a common three-dimensional structure and 20–89% identity at the primary structure level, we were able to isolate antibodies with exquisite specificity within this family of structurally related domains.

Generation of anti-Notch antibodies and their application in blocking Notch signalling in neural stem cells

Highlights ► Potent antibodies that antagonise mouse and human Notch signalling are generated. ► Receptor specific inhibition of Notch1 and 2 signalling is demonstrated. ► Antibody mediated inhibition of Notch influences neural stem cell differentiation.

Identification of soluble protein fragments by gene fragmentation and genetic selection

We describe a new method, which identifies protein fragments for soluble expression in Escherichia coli from a randomly fragmented gene library. Inhibition of E. coli dihydrofolate reductase (DHFR) by trimethoprim (TMP) prevents growth, but this can be relieved by murine DHFR (mDHFR). Bacterial strains expressing mDHFR fusions with the soluble proteins green fluroscent protein (GFP) or EphB2 (SAM domain) displayed markedly increased growth rates with TMP compared to strains expressing insoluble EphB2 (TK domain) or ketosteroid isomerase (KSI). Therefore, mDHFR is affected by the solubility of fusion partners and can act as a reporter of soluble protein expression. Random fragment libraries of the transcription factor Fli1 were generated by deoxyuridine incorporation and endonuclease V cleavage. The fragments were cloned upstream of mDHFR and TMP resistant clones expressing soluble protein were identified. These were found to cluster around the DNA binding ETS domain. A selected Fli1 fragment was expressed independently of mDHFR and was judged to be correctly folded by various biophysical methods including NMR. Soluble fragments of the cell-surface receptor Pecam1 were also identified. This genetic selection method was shown to generate expression clones useful for both structural studies and antibody generation and does not require a priori knowledge of domain architecture.

The INNs and outs of antibody nonproprietary names

An important step in drug development is the assignment of an International Nonproprietary Name (INN) by the World Health Organization (WHO) that provides healthcare professionals with a unique and universally available designated name to identify each pharmaceutical substance. Monoclonal antibody INNs comprise a –mab suffix preceded by a substem indicating the antibody type, e.g., chimeric (-xi-), humanized (-zu-), or human (-u-). The WHO publishes INN definitions that specify how new monoclonal antibody therapeutics are categorized and adapts the definitions to new technologies. However, rapid progress in antibody technologies has blurred the boundaries between existing antibody categories and created a burgeoning array of new antibody formats. Thus, revising the INN system for antibodies is akin to aiming for a rapidly moving target. The WHO recently revised INN definitions for antibodies now to be based on amino acid sequence identity. These new definitions, however, are critically flawed as they are ambiguous and go against decades of scientific literature. A key concern is the imposition of an arbitrary threshold for identity against human germline antibody variable region sequences. This leads to inconsistent classification of somatically mutated human antibodies, humanized antibodies as well as antibodies derived from semi-synthetic/synthetic libraries and transgenic animals. Such sequence-based classification implies clear functional distinction between categories (e.g., immunogenicity). However, there is no scientific evidence to support this. Dialog between the WHO INN Expert Group and key stakeholders is needed to develop a new INN system for antibodies and to avoid confusion and miscommunication between researchers and clinicians prescribing antibodies.

(Research Papers) Accelerated Screening of Phage-Display Output with Alkaline Phosphatase Fusions

When using multiple targets and libraries, selection of affinity reagents from phage-displayed libraries is a relatively time-consuming process. Herein, we describe an automation-amenable approach to accelerate the process by using alkaline phosphatase (AP) fusion proteins in place of the phage ELISA screening and subsequent confirmation steps with purified protein. After two or three rounds of affinity selection, the open reading frames that encode the affinity selected molecules (i.e., antibody fragments, engineered scaffold proteins, combinatorial peptides) are amplified from the phage or phagemid DNA molecules by PCR and cloned en masse by a Ligation Independent Cloning (LIC) method into a plasmid encoding a highly active variant of E. coli AP. This time-saving process identifies affinity reagents that work out of context of the phage and that can be used in various downstream enzyme linked binding assays. The utility of this approach was demonstrated by analyzing single-chain antibodies (scFvs), engineered fibronectin type III domains (FN3), and combinatorial peptides that were selected for binding to the Epsin N-terminal Homology (ENTH) domain of epsin 1, the c-Src SH3 domain, and the appendage domain of the gamma subunit of the clathrin adaptor complex, AP-1, respectively.

Identification of optimal protein binders through the use of large genetically encoded display libraries

The use of large genetically encoded binder libraries in co-operation with display technologies has matured over the past 25 years, and is now one of the primary methods used for selection of protein binders. Display technology has proven to be a robust and versatile method for generating binders to almost any antigen of interest. The evolution of this technology beyond antibody phage display has opened up new aspects for the concept of designer biologics. The ability to construct large populations of eukaryotic cells, including mammalian cells, where each cell expresses an individual antibody, peptide or engineered protein has added great value in identifying binders with desired properties. Here we review the evolution of display technology and highlight how it is being used today to generate binders with exquisite specificity, selectivity, affinity and developability characteristics.