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Antibody display technologies enable the successful isolation of antigen-specific antibodies with therapeutic potential. The key feature that facilitates the selection of an antibody with prescribed properties is the coupling of the protein variant to its genetic information and is referred to as genotype phenotype coupling. There are several different platform technologies based on prokaryotic organisms as well as strategies employing higher eukaryotes. Among those, phage display is the most established system with more than a dozen of therapeutic antibodies approved for therapy that have been discovered or engineered using this approach. In recent years several other technologies gained a certain level of maturity, most strikingly mammalian display. In this review, we delineate the most important selection systems with respect to antibody generation with an emphasis on recent developments.

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Here, we report the characterization of a VHH-derived IgG-like bi-and trispecific antibody platform that essentially relies on the replacement of the VH and VL regions of a conventional antibody by two independently functioning VHH domains. Consequently, a VHH is engrafted onto constant region CH1 while the other VHH-based paratope is engrafted on the constant region of the light chain, Cκ or Cλ, resulting in a tetravalent bispecific IgG-like molecule. Combined with a heavy chain heterodimerization technique, this platform allows facile engineering of bi-and trispecific antibodies with flexible valencies. We demonstrate the general applicability of this generic platform approach and elaborate on the limitations of specific formats.

Cystine-knot peptides sharing a common fold but displaying a notably large diversity within the primary structure of flanking loops have shown great potential as scaffolds for the development of therapeutic and diagnostic agents. In this study, we demonstrated that the cystine-knot peptide MCoTI-II, a trypsin inhibitor from Momordica cochinchinensis, can be engineered to bind to cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), an inhibitory receptor expressed by T lymphocytes, that has emerged as a target for the treatment of metastatic melanoma. Directed evolution was used to convert a cystine-knot trypsin inhibitor into a CTLA-4 binder by screening a library of variants using yeast surface display. A set of cystine-knot peptides possessing dissociation constants in the micromolar range was obtained; the most potent variant was synthesized chemically. Successive conjugation with neutravidin, fusion to antibody Fc domain or the oligomerization domain of C4b binding protein resulted in oligovalent variants that possessed enhanced (up to 400-fold) dissociation constants in the nanomolar range. Our data indicate that display of multiple knottin peptides on an oligomeric scaffold protein is a valid strategy to improve their functional affinity with ramifications for applications in diagnostics and therapy.

Activating NK cell receptors represent promising target structures to elicit potent antitumor immune responses. In this study, novel immunoligands were generated that bridge the activating NK cell receptor NKp30 on NK cells with epidermal growth factor receptor (EGFR) on tumor cells in a bispecific IgG-like format based on affinity-optimized versions of B7-H6 and the Fab arm derived from cetuximab. To enhance NKp30 binding, the solitary N-terminal IgV domain of B7-H6 (DB7-H6) was affinity matured by an evolutionary library approach combined with yeast surface display. Biochemical and functional characterization of 36 of these novel DB7-H6-derived NK cell engagers revealed an up to 45-fold-enhanced affinity for NKp30 and significantly improved NK cell-mediated, EGFR-dependent killing of tumor cells compared with the NK cell engager based on the wild-type DB7-H6 domain. In this regard, potencies (EC 50 killing) of the best immunoligands were substantially improved by up to 87-fold. Moreover, release of IFN-g and TNF-a was significantly increased. Importantly, equipment of the DB7-H6-based NK cell engagers with a human IgG1 Fc part competent in Fc receptor binding resulted in an almost 10-fold superior killing of EGFR-overexpressing tumor cells compared with molecules either triggering FcgRIIIa or NKp30. Additionally, INF-g and TNF-a release was increased compared with molecules solely triggering FcgRIIIa, including the clinically approved Ab cetuximab. Thus, incorporating affinity-matured ligands for NK cell-activating receptors might represent an effective strategy for the generation of potent novel therapeutic agents with unique effector functions in cancer immunotherapy.

Multivalent ligands of death receptors hold particular promise as tumor cell-specific therapeutic agents because they induce an apoptotic cascade in cancerous cells. Herein, we present a modular approach to generate death receptor 5 (DR5) binding constructs comprising multiple copies of DR5 targeting peptide (DR5TP) covalently bound to biomolecular scaffolds of peptidic nature. This strategy allows for efficient oligomerization of synthetic DR5TP-derived peptides in different spatial orientations using a set of enzyme-promoted conjugations or recombinant production. Heptameric constructs based on a short (60-75 residues) scaffold of a C-terminal oligomerization domain of human C4b binding protein showed remarkable proapoptotic activity (EC50=3 nm) when DR5TP was ligated to its carboxy terminus. Our data support the notion that inter-ligand distance, relative spatial orientation and copy number of receptor-binding modules are key prerequisites for receptor activation and cell killing.

Therapeutic proteins, including monoclonal antibodies, are typically manufactured using clonally‐derived, stable host cell lines, since consistent and predictable cell culture performance is highly desirable. However, selecting and preparing banks of stable clones takes considerable time, which inevitably extends overall development timelines for new therapeutics by delaying the start of subsequent activities, such as the scale‐up of manufacturing processes. In the context of the COVID‐19 pandemic, with its intense pressure for accelerated development strategies, we used a novel transposon‐based Leap‐In Transposase ® system to rapidly generate high‐titer stable pools and then used them directly for large scale‐manufacturing of an anti‐SARS‐CoV2 monoclonal antibody under cGMP. We performed the safety testing of our non‐clonal cell bank, then used it to produce material at a 200L‐scale for pre‐clinical safety studies and formulation development work, and thereafter at 2000L scale for supply of material for a Phase 1 clinical trial. Testing demonstrated the comparability of critical product qualities between the two scales and, more importantly, that our final clinical trial product met all pre‐set product quality specifications. The above expediated approach provided clinical trial material within 4.5 months, in comparison to 12‐14 months for production of clinical trial material via the conventional approach. This article is protected by copyright. All rights reserved.