Construction and development of a mammalian cell-based full-length antibody display library for targeting hepatocellular carcinoma

Advancements in mammalian display technology for therapeutic antibody development and beyond: current landscape, challenges, and future prospects

The evolving development landscape of biotherapeutics and their growing complexity from simple antibodies into bi- and multi-specific molecules necessitates sophisticated discovery and engineering platforms. This review focuses on mammalian display technology as a potential solution to the pressing challenges in biotherapeutic development. We provide a comparative analysis with established methodologies, highlighting key aspects of mammalian display technology, including genetic engineering, construction of display libraries, and its pivotal role in hit selection and/or developability engineering. The review delves into the mechanisms underpinning developability-driven selection via mammalian display and their broader implications. Applications beyond antibody discovery are also explored, alongside advancements towards function-first screening technologies, precision genome engineering and AI/ML-enhanced libraries, situating them in the context of mammalian display. Overall, the review provides a comprehensive overview of the current mammalian display technology landscape, underscores the expansive potential of the technology for biotherapeutic development, addresses the critical challenges for the full realisation of this potential, and examines advances in related disciplines that might impact the future application of mammalian display technologies.

Construction and Applications of Mammalian Cell-Based DNA-Encoded Peptide/Protein Libraries

DNA-encoded peptide/protein libraries are the starting point for protein evolutionary modification and functional peptide/antibody selection. Different display technologies, protein directed evolution, and deep mutational scanning (DMS) experiments employ DNA-encoded libraries to provide sequence variations for downstream affinity- or function-based selections. Mammalian cells promise the inherent post-translational modification and near-to-natural conformation of exogenously expressed mammalian proteins and thus are the best platform for studying transmembrane proteins or human disease-related proteins. However, due to the current technical bottlenecks of constructing mammalian cell-based large size DNA-encoded libraries, the advantages of mammalian cells as screening platforms have not been fully exploited. In this review, we summarize the current efforts in constructing DNA-encoded libraries in mammalian cells and the existing applications of these libraries in different fields.

A novel and effective approach to generate germline-like monoclonal antibodies by integration of phage and mammalian cell display platforms

Phage display technology allows for rapid selection of antibodies from the large repertoire of human antibody fragments displayed on phages. However, antibody fragments should be converted to IgG for biological characterizations and affinity of antibodies obtained from phage display library is frequently not sufficient for efficient use in clinical settings. Here, we describe a new approach that combines phage and mammalian cell display, enabling simultaneous affinity screening of full-length IgG antibodies. Using this strategy, we successfully obtained a novel germline-like anti-TIM-3 monoclonal antibody named m101, which was revealed to be a potent anti-TIM-3 therapeutic monoclonal antibody via in vitro and in vivo experiments, indicating its effectiveness and power. Thus, this platform can help develop new monoclonal antibody therapeutics with high affinity and low immunogenicity.

Engineered mRNA-expressed antibodies prevent respiratory syncytial virus infection

The lung is a critical prophylaxis target for clinically important infectious agents, including human respiratory syncytial virus (RSV) and influenza. Here, we develop a modular, synthetic mRNA-based approach to express neutralizing antibodies directly in the lung via aerosol, to prevent RSV infections. First, we express palivizumab, which reduces RSV F copies by 90.8%. Second, we express engineered, membrane-anchored palivizumab, which prevents detectable infection in transfected cells, reducing in vitro titer and in vivo RSV F copies by 99.7% and 89.6%, respectively. Finally, we express an anchored or secreted high-affinity, anti-RSV F, camelid antibody (RSV aVHH and sVHH). We demonstrate that RSV aVHH, but not RSV sVHH, significantly inhibits RSV 7 days post transfection, and we show that RSV aVHH is present in the lung for at least 28 days. Overall, our data suggests that expressing membrane-anchored broadly neutralizing antibodies in the lungs could potentially be a promising pulmonary prophylaxis approach.

Engineered neutralizing antibodies are potential therapeutics for numerous viruses, such as respiratory syncytial virus (RSV). Here, the authors develop an mRNA-based approach to express membrane-anchored neutralizing antibodies in the lung and demonstrate that it inhibits RSV infections in mice.

Domain structure of growth signalobodies critically affects the outcome of antibody library selection

Wide applications of antibodies have demanded rapid and easy methods for isolating high-affinity antibodies. We recently developed an antibody screening system in mammalian cells using a growth signalobody, which is a single-chain Fv (scFv) library/cytokine receptor chimera that can transduce a growth signal in response to a target oligomeric antigen. However, we have never investigated how the domain structure of signalobodies affects the outcome of library screening. In this study, we screened naïve scFv library-inserted signalobodies having distinct extracellular and transmembrane (TM) domains. Although the previously constructed signalobody with the extracellular D1/D2 domains of erythropoietin receptor had recovered the clones with high affinity against a target antigen and with low background cell growth, its D1/D2-deficient variant which was tested in this study recovered the clones with low affinity against a target antigen and with considerable background cell growth. In addition, mutagenesis in the TM domain lowered the level of the background cell growth. These results suggest that the D1/D2 domains increase a threshold to activate signalobodies, thereby selecting clones with high affinity against a target antigen and that the TM domain could be engineered to minimize background growth signalling.

A novel platform for antibody library selection in mammalian cells based on a growth signalobody

While many antibody-screening methods in vitro have been developed, these methods need repeated cycles of panning or sorting procedures to isolate antigen-specific antibodies. Here we developed a new antibody selection system based on antigen-dependent growth of mammalian cells. In this system, a growth signalobody library, which is a naïve single-chain Fv (scFv) library/cytokine receptor chimera that can transduce a growth signal in response to a specific antigen, is expressed in murine interleukin-3-dependent Ba/F3 cells. Simple culture of the cells in an antigen-containing medium results in growing cells with a high-affinity scFv gene, leading to selection of the scFv specific to the target antigen without panning/sorting procedures. To demonstrate this system, we used the SD1D2g signalobody having the signaling domain of gp130 and fluorescein-conjugated BSA as a target antigen, and investigated whether a fluorescein-specific scFv could be selected from a naïve scFv library. As a result, we successfully obtained fluorescein-binding scFv clones, and the scFv clone with the highest affinity was most abundantly selected, having the same sequence as the clone, which had been obtained through phage display. These results demonstrate the utility of our system as an affinity-based scFv selection method based on growth advantage of mammalian cells.

Monoclonal antibody preparation of Golgi phosphoprotein 2 and preliminary application in the early diagnosis of hepatocellular carcinoma

Golgi phosphoprotein 2 (Golph2) is a type II Golgi‑specific membrane protein, which has been found to be overexpressed in hepatocellular carcinoma (HCC) patients. The sensitivity of diagnosis of HCC using Golph2 (76%) was markedly elevated compared with alpha‑fetoprotein (AFP) (70%), and Golph2 is expected to be a novel and effective serum biomarker for the diagnosis of HCC. The aim of this study was to prepare monoclonal antibodies against Golph2 and to establish double-antibody sandwich enzyme-linked immunosorbent assay (s-ELISA), which will be used in diagnostics, therapeutics and as a tool in understanding the role of Golph2 in the pathogenesis of liver diseases and cancer. In this study, fusion protein TRX-Golph2 was expressed and purified using an Escherichia coli system. BALB/c mice were immunized with TRX-Golph2 recombinant protein. The hybridoma technique was used for the production of anti-Golph2 monoclonal antibody. Hybridoma clones were screened using indirect ELISA and anti-Golph2 monoclonal antibody was produced in the ascites of BALB/c mice. The specificity of anti-Golph2 monoclonal antibody was detected by western blot analysis and immunocytochemistry. s-ELISA was established using horseradish peroxidase (HRP)‑labeled anti-Golph2 monoclonal antibody and used to detect the antigen in the serum of HCC patients. As a result, five stable hybridoma cell clones (5C6D5, 5B7F5, 7F5F3, 8A7B4, 8C9E8) producing anti-Golph2 monoclonal antibody were established. The highest titer of anti-Golph2 monoclonal antibody (5C6D5) was 1:51,200. Western blot analysis revealed that anti-Golph2 monoclonal antibody had a high specificity for Golph2 protein. Anti-Golph2 monoclonal antibody was HRP-labeled and the optimal working concentration was found to be 1:500. The levels of antigen in a proportion of HCC patients were shown to be significantly higher compared to those found in healthy controls.