"Diabodies": small bivalent and bispecific antibody fragments

Connexin Hemichannel Inhibition and Human Genodermatoses

Pathogenic variants in genes encoding connexins that cause skin diseases, such as keratitis-ichthyosis-deafness (KID) syndrome and hidrotic ectodermal dysplasia (HED) or Clouston syndrome, display increased hemichannel activity. Mechanistic insights derived from biophysical studies of the variant connexins support the hypothesis that inhibition of the acquired hemichannel activity could alleviate epidermal pathology. Use of pharmacological blockers and engineered mAbs in mouse models of HED and KID confirm that hemichannel inhibition is a promising target for new therapeutic approaches to KID and HED. Insights from this work could apply to other connexin-based genetic skin diseases in which hemichannel activity is elevated.

IgStrand: A universal residue numbering scheme for the immunoglobulin-fold (Ig-fold) to study Ig-proteomes and Ig-interactomes

The Immunoglobulin fold (Ig-fold) is found in proteins from all domains of life and represents the most populous fold in the human genome, with current estimates ranging from 2 to 3% of protein coding regions. That proportion is much higher in the surfaceome where Ig and Ig-like domains orchestrate cell-cell recognition, adhesion and signaling. The ability of Ig-domains to reliably fold and self-assemble through highly specific interfaces represents a remarkable property of these domains, making them key elements of molecular interaction systems: the immune system, the nervous system, the vascular system and the muscular system. We define a universal residue numbering scheme, common to all domains sharing the Ig-fold in order to study the wide spectrum of Ig-domain variants constituting the Ig-proteome and Ig-Ig interactomes at the heart of these systems. The "IgStrand numbering scheme" enables the identification of Ig structural proteomes and interactomes in and between any species, and comparative structural, functional, and evolutionary analyses. We review how Ig-domains are classified today as topological and structural variants and highlight the "Ig-fold irreducible structural signature" shared by all of them. The IgStrand numbering scheme lays the foundation for the systematic annotation of structural proteomes by detecting and accurately labeling Ig-, Ig-like and Ig-extended domains in proteins, which are poorly annotated in current databases and opens the door to accurate machine learning. Importantly, it sheds light on the robust Ig protein folding algorithm used by nature to form beta sandwich supersecondary structures. The numbering scheme powers an algorithm implemented in the interactive structural analysis software iCn3D to systematically recognize Ig-domains, annotate them and perform detailed analyses comparing any domain sharing the Ig-fold in sequence, topology and structure, regardless of their diverse topologies or origin. The scheme provides a robust fold detection and labeling mechanism that reveals unsuspected structural homologies among protein structures beyond currently identified Ig- and Ig-like domain variants. Indeed, multiple folds classified independently contain a common structural signature, in particular jelly-rolls. Examples of folds that harbor an "Ig-extended" architecture are given. Applications in protein engineering around the Ig-architecture are straightforward based on the universal numbering.

Disulfide-stabilized diabodies enable near-atomic cryo-EM imaging of small proteins: A case study of the bacterial Na+/citrate symporter CitS

Diabodies are engineered antibody fragments with two antigen-binding Fv domains. Previously, we demonstrated that they are often highly flexible but can be rigidified by introducing a disulfide bond at the Fv interface. In this study, we explored the potential of disulfide-bridged, bispecific diabodies for near-atomic cryoelectron microscopy (cryo-EM) imaging of small proteins because they can predictably link target proteins to "structural marker" proteins. As a case study, we used the bacterial citrate transporter CitS as the target protein, and the horseshoe-shaped ectodomain of human Toll-like receptor 3 (TLR3) as the marker. We show that diabodies containing one or two disulfide bonds enabled the 3D reconstruction of CitS at resolutions of 3.3 Å and 3.1 Å, respectively. This resolution surpassed previous crystallographic results and allowed us to visualize the high-resolution structural features of the transporter. Our work expands the application of diabodies in structural biology to address a key limitation in the field.

Protein-Based Degraders: From Chemical Biology Tools to Neo-Therapeutics

The nascent field of targeted protein degradation (TPD) could revolutionize biomedicine due to the ability of degrader molecules to selectively modulate disease-relevant proteins. A key limitation to the broad application of TPD is its dependence on small-molecule ligands to target proteins of interest. This leaves unstructured proteins or those lacking defined cavities for small-molecule binding out of the scope of many TPD technologies. The use of proteins, peptides, and nucleic acids (otherwise known as "biologics") as the protein-targeting moieties in degraders addresses this limitation. In the following sections, we provide a comprehensive and critical review of studies that have used proteins and peptides to mediate the degradation and hence the functional control of otherwise challenging disease-relevant protein targets. We describe existing platforms for protein/peptide-based ligand identification and the drug delivery systems that might be exploited for the delivery of biologic-based degraders. Throughout the Review, we underscore the successes, challenges, and opportunities of using protein-based degraders as chemical biology tools to spur discoveries, elucidate mechanisms, and act as a new therapeutic modality.

Sequence and Configuration of a Novel Bispecific Antibody Format Impacts Its Production Using Chinese Hamster Ovary (CHO) Cells

There are a number of new format antibody-inspired molecules with multiple antigen binding capabilities in development and clinical evaluation. Here, we describe the impact of the sequence and configuration of a unique bispecific antibody format (termed BYbe) using a panel of four BYbe's and the three IgG1s from which they were derived on their production in a Chinese hamster ovary (CHO) cell expression system. Following transfection and selection, one bispecific antibody format yielded fewer mini-pools in comparison to the other bispecific cell pools. When the top 12 expressing stable mini-pools of all BYbe configurations and sequences were evaluated, both the dsscFv sequence and antibody chain configuration or placement directly impacted productivity. The cell-specific productivity (qP, pg/cell/day) was lower in all BYbe cell pools compared to the IgG1 cell lines. However, when the actual molecules/cell/day produced were considered, three of the four bispecific cell pools outproduced the parental IgG1 cell pools. While gene copy number did not correlate to productivity, mRNA analysis showed that for specific BYbe formats there was a strong correlation with productivity. In summary, we describe how bispecific antibody format configuration impacts the cell line construction process and yield of product from CHO cells.

The Evolving Applications of Bispecific Antibodies: Reaping the Harvest of Early Sowing and Planting New Seeds

After decades of gradual progress from conceptualization to early clinical trials (1960-2000), the therapeutic potential of bispecific antibodies (bisp Abs) is now being fully realized. Insights gained from both successful and unsuccessful trials are helping to identify which mechanisms of action, antibody formats, and targets prove most effective, and which may benefit from further refinement. While T-cell engagers remain the most commonly used class of bisp Abs, current efforts aim to increase their effectiveness by co-engaging costimulatory molecules, reducing escape mechanisms, and countering immunosuppression. Strategies to minimize cytokine release syndrome (CRS) are also actively under development. In addition, novel antibody formats that are selectively activated within tumors are an exciting area of research, as is the precise targeting of specific T-cell subsets. Beyond T cells, the recruitment of macrophages and dendritic cells is attracting increasing interest, with researchers exploring various macrophage receptors to promote phagocytosis or to carry out specialized functions, such as the immunologically silent clearance of amyloid-beta plaques in the brain. While bisp Abs targeting B cells are relatively limited, they are primarily aimed at inhibiting B-cell activity in autoimmune diseases. Another evolving application involves the forced interaction between proteins. Beyond the successful development of Hemlibra for hemophilia, bispecific antibodies that mimic cytokine activity are being explored. Additionally, the recruitment of cell surface ubiquitin ligases and other enzymes represents a novel and promising therapeutic strategy. In regard to antibody formats, some applications such as the combination of T-cell engagers with costimulatory molecules are driving the development of trispecific antibodies, at least in preclinical settings. However, the increasing structural complexity of multispecific antibodies often leads to more challenging development paths, and the number of multispecific antibodies in clinical trials remains low. The clinical success of certain applications and well-established production methods position this therapeutic class to expand its benefits into other therapeutic areas.

Experimental and Computational Studies on Domain-Swapped Structure Stabilization of an Antibody Light Chain by Disulfide Bond Introduction

Development of different platforms would be useful for designing functional antibodies to improve the efficiency of antibody-based drugs. Three-dimensional domain swapping (3D-DS) may occur in the variable region of antibody light chain #4C214A, and a pair of domain-swapped dimers may interact with each other to form a tetramer. In this study, to stabilize the 3D-DS dimer structure in #4C214A, Val2 in strand A (swapping region) and Thr97 in strand G were replaced with Cys residues, generating #4 V2C/T97C/C214A with a Cys2-Cys97 disulfide bond that cross-links strands A and G of different protomers. The #4 V2C/T97C/C214A tetramer did not dissociate into monomers at low protein concentration (6 μM); however, some of the tetramers were converted to monomers by disulfide bond reduction. Two-dimensional free energy profile analysis for the tetramerization of two 3D-DS dimers was performed by molecular dynamics simulation. These results show that disulfide bond introduction is useful for controlling the dimerization/dissociation of the variable region through 3D-DS.

Efficient combinatorial adaptor-mediated targeting of acute myeloid leukemia with CAR T-cells

CAR T-cell products targeting lineage-specific cell-of-origin antigens, thereby eliminating both tumor and healthy counterpart cells, are currently clinically approved therapeutics in B- and plasma-cell malignancies. While they represent a major clinical improvement, they are still limited in terms of efficacy by e.g. single, sometimes low-expressed antigen targeting, and in terms of safety by e.g., lack of on-off activity. Successful cell-of-origin non-discriminative targeting of heterogeneous hematopoietic stem and progenitor cell malignancies, such as acute myeloid leukemia (AML), will require antigen-versatile targeting and off-switching of effectors in order to then allow rescue by hematopoietic stem cell transplantation (HSCT), preventing permanent myeloablation. To address this, we developed adaptor-CAR (AdFITC-CAR) T-cells targeting fluoresceinated AML antigen-binding diabody adaptors. This platform enables the use of adaptors matching the AML-antigen-expression profile and conditional activity modulation. Combining adaptors significantly improved lysis of AML cells in vitro. In therapeutic xenogeneic mouse models, AdFITC-CAR T-cells co-administered with single diabody adaptors were as efficient as direct CAR T-cells, and combinatorial use of adaptors further enhanced therapeutic efficacy against both, cell lines and primary AML. Collectively, this study provides proof-of-concept that AdFITC-CAR T-cells and combinations of adaptors can efficiently enhance immune-targeting of AML.

The Multifaceted Role of Epithelial Membrane Protein 2 in Cancer: from Biomarker to Therapeutic Target

Tetraspanin superfamily proteins not only facilitate the trafficking of specific proteins to distinct plasma membrane domains but also influence cell-to-cell and cell-extracellular matrix interactions. Among these proteins, Epithelial Membrane Protein 2 (EMP2), a member of the growth arrest-specific gene 3/peripheral myelin protein 22 (GAS3/PMP22) family, is known to affect key cellular processes. Recent studies have revealed that EMP2 modulates critical signaling pathways and interacts with adhesion molecules and growth factor receptors, underscoring its potential as a biomarker for cancer diagnosis and prognosis. These findings suggest that EMP2 expression patterns could provide valuable insights into tumorigenesis and metastasis. Moreover, EMP2 has emerged as a promising therapeutic target, with approaches aimed at inhibiting or modulating its activity showing potential to disrupt tumor growth and metastasis. This review provides a comprehensive overview of recent advances in understanding the multifaceted roles of EMP2 in cancer, with a focus on its underlying mechanisms and clinical significance.

Mechanism of Action and Pharmacokinetics of Approved Bispecific Antibodies

Bispecific antibodies represent a significant advancement in therapeutic antibody engineering, offering the ability to simultaneously target two distinct antigens. This dual-targeting capability enhances therapeutic efficacy, especially in complex diseases, such as cancer and autoimmune disorders, where drug resistance and incomplete target coverage are prevalent challenges. Bispecific antibodies facilitate immune cell engagement and disrupt multiple signaling pathways, providing a more comprehensive treatment approach than traditional monoclonal antibodies. However, the intricate structure of bispecific antibodies introduces unique pharmacokinetic challenges, including issues related to their absorption, distribution, metabolism, and excretion, which can significantly affect their efficacy and safety. This review provides an in-depth analysis of the structural design, mechanisms of action, and pharmacokinetics of the currently approved bispecific antibodies. It also highlights the engineering innovations that have been implemented to overcome these challenges, such as Fc modifications and advanced dimerization techniques, which enhance the stability and half-life of bispecific antibodies. Significant progress has been made in bispecific antibody technology; however, further research is necessary to broaden their clinical applications, enhance their safety profiles, and optimize their incorporation into combination therapies. Continuous advancements in this field are expected to enable bispecific antibodies to provide more precise and effective therapeutic strategies for a range of complex diseases, ultimately improving patient outcomes and advancing precision medicine.

Elucidation of the Reversible Self-Association Interface of a Diabody-Interleukin Fusion Protein Using Hydrogen-Exchange Mass Spectrometry and In Silico Modeling

Reversible self-association (RSA) of therapeutic proteins presents major challenges in the development of high-concentration formulations, especially those intended for subcutaneous administration. Understanding self-association mechanisms is therefore critical to the design and selection of candidates with acceptable developability to advance to clinical trials. The combination of experiments and in silico modeling presents a powerful tool to elucidate the interface of self-association. RSA of monoclonal antibodies has been studied extensively under different solution conditions and have been shown to involve interactions for both the antigen-binding fragment and the crystallizable fragment. Novel modalities such as bispecific antibodies, antigen-binding fragments, single-chain-variable fragments, and diabodies constitute a fast-growing class of antibody-based therapeutics that have unique physiochemical properties compared to monoclonal antibodies. In this study, the RSA interface of a diabody-interleukin 22 fusion protein (FP-1) was studied using hydrogen-deuterium exchange coupled with mass spectrometry (HDX-MS) in combination with in silico modeling. Taken together, the results show that a complex solution behavior underlies the self-association of FP-1 and that the interface thereof can be attributed to a specific segment in the variable light chain of the diabody. These findings also demonstrate that the combination of HDX-MS with in silico modeling is a powerful tool to guide the design and candidate selection of novel biotherapeutic modalities.

Looking ahead to CD3, T-cell engager bispecific antibodies for hematological malignancies

INTRODUCTION

Since the approval of the bispecific antibody blinatumomab in 2017 for the treatment of acute lymphoblastic leukemia in relapse, the development of numerous bispecific antibody constructs has dramatically expanded in hematologic malignancies. Many have recently received Food Drug Administration and European Medicines Agency approvals in various stages of treatment for lymphomas, leukemias, and multiple myeloma.

AREAS COVERED

The purpose of this review is to provide an overview of bispecific antibody treatment including the mechanisms leading to effector T cells targeting tumor-associated antigens, the treatment indications, efficacies, toxicities, and challenges of the different constructs. A literature search was performed through access to PubMed and clinicaltrials.gov.

EXPERT OPINION

While there has been substantial success in the treatment of NHL, MM, and ALL, there are still hematologic malignancies such as AML where there has been limited progress. It is important to continue to investigate new designs, tumor antigen targets, and further refine where current approved bispecific antibodies fit in terms of sequencing of therapy. Hopefully, with the knowledge gained in recent years and the explosion of these therapies, patients with blood cancers will continue to benefit from these treatments for years to come.

Higher Order Structure Characterization of Two Interdomain Disulfide Bond Variants of a Bispecific Monoclonal Antibody

Characterization and understanding of protein higher order structure (HOS) is essential at all stages of biologics development. Here, two folding variants of a bispecific monoclonal antibody, the correctly folded form and an alternative configuration with reduced potency, were characterized by several HOS characterization techniques. Specifically, differential scanning calorimetry (DSC), circular dichroism (CD), Fourier-transform infrared spectroscopy (FTIR), Raman and Raman optical activity (ROA) spectroscopy were used together to elucidate the impacts of disulfide bond scrambling in the fused scFv domains on the structure and thermal stability of the antibody. This study illustrates the importance of selecting appropriate biophysical characterization techniques based on the nature and magnitude of the HOS change.

Engineered Antibodies to Improve Efficacy against Neurodegenerative Disorders

Antibodies that can selectively remove rogue proteins in the brain are an obvious choice to treat neurodegenerative disorders (NDs), but after decades of efforts, only two antibodies to treat Alzheimer's disease are approved, dozens are in the testing phase, and one was withdrawn, and the other halted, likely due to efficacy issues. However, these outcomes should have been evident since these antibodies cannot enter the brain sufficiently due to the blood-brain barrier (BBB) protectant. However, all products can be rejuvenated by binding them with transferrin, preferably as smaller fragments. This model can be tested quickly and at a low cost and should be applied to bapineuzumab, solanezumab, crenezumab, gantenerumab, aducanumab, lecanemab, donanemab, cinpanemab, and gantenerumab, and their fragments. This paper demonstrates that conjugating with transferrin does not alter the binding to brain proteins such as amyloid-β (Aβ) and α-synuclein. We also present a selection of conjugate designs that will allow cleavage upon entering the brain to prevent their exocytosis while keeping the fragments connected to enable optimal binding to proteins. The identified products can be readily tested and returned to patients with the lowest regulatory cost and delays. These engineered antibodies can be manufactured by recombinant engineering, preferably by mRNA technology, as a more affordable solution to meet the dire need to treat neurodegenerative disorders effectively.

Stepping forward: T-cell redirecting bispecific antibodies in cancer therapy

T cell-redirecting bispecific antibodies are specifically designed to bind to tumor-associated antigens, thereby engaging with CD3 on the T cell receptor. This linkage between tumor cells and T cells actively triggers T cell activation and initiates targeted killing of the identified tumor cells. These antibodies have emerged as one of the most promising avenues within tumor immunotherapy. However, despite success in treating hematological malignancies, significant advancements in solid tumors have yet to be explored. In this review, we aim to address the critical challenges associated with T cell-redirecting bispecific antibodies and explore novel strategies to overcome these obstacles, with the ultimate goal of expanding the application of this therapy to include solid tumors.

Structural and functional characterization of IgG- and non-IgG-based T-cell-engaging bispecific antibodies

Bispecific T-cell-engaging antibodies are a growing class of therapeutics with numerous molecules being tested in clinical trials and, currently, seven of them have received market approval. They are structurally complex and function as adaptors to redirect the cytotoxicity of T cells to kill tumor cells. T-cell-engaging bispecific antibodies can be generally divided into two categories: IgG/IgG-like and non-IgG-like formats. Different formats may have different intrinsic potencies and physiochemical properties, and comprehensive studies are needed to gain a better understanding of how the differences in formats impact on structural and functional characteristics. In this study, we designed and generated bispecific T-cell-engaging antibodies with IgG-like (DVD-Ig) and non-IgG (BiTE) formats. Both target the same pair of antigens (EGFR and CD3) to minimize the possible influence of targets on functional characterization. We performed a side-by-side comparison to assess differences in the physiochemical and biological properties of these two bispecific T-cell-engaging antibodies using a variety of breast and ovarian cancer cell-based functional assays to delineate the structural-functional relationships and anti-tumor activities/potency. We found that the Fc portion of T-cell-engaging bispecific antibodies can significantly impact antigen binding activity, potency, and stability in addition to eliciting different mechanisms of action that contribute the killing of cancer cells.

Current Landscape of Cancer Immunotherapy: Harnessing the Immune Arsenal to Overcome Immune Evasion

Cancer immune evasion represents a leading hallmark of cancer, posing a significant obstacle to the development of successful anticancer therapies. However, the landscape of cancer treatment has significantly evolved, transitioning into the era of immunotherapy from conventional methods such as surgical resection, radiotherapy, chemotherapy, and targeted drug therapy. Immunotherapy has emerged as a pivotal component in cancer treatment, harnessing the body's immune system to combat cancer and offering improved prognostic outcomes for numerous patients. The remarkable success of immunotherapy has spurred significant efforts to enhance the clinical efficacy of existing agents and strategies. Several immunotherapeutic approaches have received approval for targeted cancer treatments, while others are currently in preclinical and clinical trials. This review explores recent progress in unraveling the mechanisms of cancer immune evasion and evaluates the clinical effectiveness of diverse immunotherapy strategies, including cancer vaccines, adoptive cell therapy, and antibody-based treatments. It encompasses both established treatments and those currently under investigation, providing a comprehensive overview of efforts to combat cancer through immunological approaches. Additionally, the article emphasizes the current developments, limitations, and challenges in cancer immunotherapy. Furthermore, by integrating analyses of cancer immunotherapy resistance mechanisms and exploring combination strategies and personalized approaches, it offers valuable insights crucial for the development of novel anticancer immunotherapeutic strategies.

Engineered polyspecific antibodies: A new frontier in the field of immunotherapeutics

The 21st-century beginning remarked with the huge success of monospecific MAbs, however, in the last couple of years, polyspecific MAbs (PsAbs) have been an interesting topic and show promise of being biobetter than monospecific MAbs. Polyspecificity, in which a single antibody serves multiple specific target binding, has been hypothesized to contribute to the development of a highly effective antibody repertoire for immune defence. This polyspecific MAb trend represents an explosion that is gripping the whole pharmaceutical industry. This review is concerned with the current development and quality enforcement of PsAbs. All provided literature on monospecific MAbs and polyspecific MAbs (PsAbs) were searched using various electronic databases such as PubMed, Google Scholar, Web of Science, Elsevier, Springer, ACS, Google Patent and books via the keywords Antibody engineering, Polyspecific antibody, Conventional antibody, non-conventional antibody, and Single domain antibody. In the literature, there are more than 100 different formats to construct PsAb by quadroma technology, chemical conjugation and genetic engineering. Till March 2023, nine PsAb have been approved around the world, and around 330 are in advanced developmental stages, showing the dominancy of PsAb in the growing health sector. Recent advancements in protein engineering techniques and the fusion of non-conventional antibodies have made it possible to create complex PsAbs that demonstrate higher stability and enhanced potency. This marks the most significant achievement for cancer immunotherapy, in which PsAbs have immense promise. It is worth mentioning that seven out of the nine PsAbs have been approved as anti-cancer therapy. As PsAbs continue to acquire prominence, they could pave the way for the development of novel immunotherapies for multiple diseases.

Modular design of bi- and multi-specific knob domain fusions

Introduction

The therapeutic potential of bispecific antibodies is becoming widely recognised, with over a hundred formats already described. For many applications, enhanced tissue penetration is sought, so bispecifics with low molecular weight may offer a route to enhanced potency. Here we report the design of bi- and tri-specific antibody-based constructs with molecular weights as low as 14.5 and 22 kDa respectively.

Methods

Autonomous bovine ultra-long CDR H3 (knob domain peptide) modules have been engineered with artificial coiled-coil stalks derived from Sin Nombre orthohantavirus nucleocapsid protein and human Beclin-1, and joined in series to produce bi- and tri-specific antibody-based constructs with exceptionally low molecular weights.

Results

Knob domain peptides with coiled-coil stalks retain high, independent antigen binding affinity, exhibit exceptional levels of thermal stability, and can be readily joined head-to-tail yielding the smallest described multi-specific antibody format. The resulting constructs are able to bind simultaneously to all their targets with no interference.

Discussion

Compared to existing bispecific formats, the reduced molecular weight of the knob domain fusions may enable enhanced tissue penetration and facilitate binding to cryptic epitopes that are inaccessible to conventional antibodies. Furthermore, they can be easily produced at high yield as recombinant products and are free from the heavy-light chain mispairing issue. Taken together, our approach offers an efficient route to modular construction of minimalistic bi- and multi-specifics, thereby further broadening the therapeutic scope for knob domain peptides.

A Detailed Protocol for Constructing a Human Single-Chain Variable Fragment (scFv) Library and Downstream Screening via Phage Display

The development of monoclonal antibodies (mAbs) represents a significant milestone in both basic research and clinical applications due to their target specificity and versatility in therapeutic and diagnostic applications. The innovative strategy of mAb screening, utilizing phage display, facilitates the in vitro screening of antibodies with high affinity to target antigens. The single-chain variable fragment (scFv) is a subset of mAb derivatives, known for its high binding affinity and smaller size-just one-third of that of human IgG. This report outlines a detailed and comprehensive procedure for constructing a scFv phagemid library derived from human patients, followed by screening via phage display affinity selection. The protocol utilizes 348 primer combinations spanning the entire human antibody repertoire to minimize sequence bias and maintain library diversity during polymerase chain reaction (PCR) for scFv generation, resulting in a library size greater than 1 × 108. Furthermore, we describe a high-throughput phage display screening protocol using enzyme-linked immunosorbent assay (ELISA) to evaluate more than 1200 scFv candidates. The generation of a highly diverse scFv library, coupled with the implementation of a phage display screening methodology, is expected to provide a valuable resource for researchers in pursuit of scFvs with high affinity for target antigens, thus advancing both research and clinical endeavors.

Polyvalency: an emerging trend in the development of clinical antibodies

Medicine has benefited greatly from the development of monoclonal antibody (mAb) technology. First-generation mAbs have seen significant success in the treatment of major diseases, such as autoimmune, inflammation, cancer, infectious, and cardiovascular diseases. Developing next-generation antibodies with improved potency, safety, and non-natural characteristics is a booming field of mAb research. In this review, we discuss the significance of polyvalency and polyvalent antibodies, as well as important findings from preclinical studies and clinical trials involving polyvalent antibodies. We then review the role of tumor necrosis factor-alpha (TNF-α) in inflammatory diseases and the need for polyvalent anti-TNF-α antibodies.

Facilitating high throughput bispecific antibody production and potential applications within biopharmaceutical discovery workflows

A major driver for the recent investment surge in bispecific antibody (bsAb) platforms and products is the multitude of distinct mechanisms of action that bsAbs offer compared to a combination of two monoclonal antibodies. Four bsAb products were granted first regulatory approvals in the US or EU during 2023 and the biopharmaceutical industry pipeline is brimming with bsAb candidates across a broad range of therapeutic applications. In previously reported bsAb discovery campaigns, following a hypothesis-based choice of two specific target proteins, selections and screening activities have often been performed in mono-specific formats. The conversion to bispecific modalities has usually been positioned toward the end of the discovery process and has involved small numbers of lead molecules, largely due to challenges in expressing, purifying, and analyzing large numbers of bsAbs. In this review, we discuss emerging strategies to facilitate the production of expanded bsAb panels, focusing particularly upon combinatorial methods to generate bsAb matrices. Such technologies will enable screening in. bispecific formats at earlier stages of discovery campaigns, not only widening the accessible protein space to maximize chances of success, but also advancing empirical bi-target validation activities to assess initial target selection hypotheses.

Bispecific antibodies revolutionizing breast cancer treatment: a comprehensive overview

Breast cancer (BCa) is known as a complex and prevalent disease requiring the development of novel anticancer therapeutic approaches. Bispecific antibodies (BsAbs) have emerged as a favorable strategy for BCa treatment due to their unique ability to target two different antigens simultaneously. By targeting tumor-associated antigens (TAAs) on cancer cells, engaging immune effector cells, or blocking critical signaling pathways, BsAbs offer enhanced tumor specificity and immune system involvement, improving anti-cancer activity. Preclinical and clinical studies have demonstrated the potential of BsAbs in BCa. For example, BsAbs targeting human epidermal growth factor receptor 2 (HER2) have shown the ability to redirect immune cells to HER2-positive BCa cells, resulting in effective tumor cell killing. Moreover, targeting the PD-1/PD-L1 pathway by BsAbs has demonstrated promising outcomes in overcoming immunosuppression and enhancing immune-mediated tumor clearance. Combining BsAbs with existing therapeutic approaches, such as chemotherapy, targeted therapies, or immune checkpoint inhibitors (ICIs), has also revealed synergistic effects in preclinical models and early clinical trials, emphasizing the usefulness and potential of BsAbs in BCa treatment. This review summarizes the latest evidence about BsAbs in treating BCa and the challenges and opportunities of their use in BCa.

Functional integration of protein A binding ability to antibody fragments for convenient and tag-free purification

Although the development of small therapeutic antibodies is important, the affinity tags used for their purification often result in heterogeneous production and immunogenicity. In this study, we integrated Staphylococcus aureus protein A (SpA) binding ability into antibody fragments for convenient and tag-free purification. SpA affinity chromatography is used as a global standard purification method for conventional antibodies owing to its high binding affinity to the Fc region. SpA also has a binding affinity for some variable heavy domains (VH) classified in the VH3 subfamily. Through mutagenesis based on alignment and structural modeling results using the SpA-VH3 cocrystal structure, we integrated the SpA-binding ability into the anti-CD3 single-chain Fv. Furthermore, we applied this mutagenesis approach to more complicated small bispecific antibodies and successfully purified the antibodies using SpA affinity chromatography. The antibodies retained their biological function after purification. Integration of SpA-binding ability into conventional antibody fragments simplifies the purification and monitoring of the production processes and, thus, is an ideal strategy for accelerating the development of small therapeutic antibodies. Furthermore, because of its immunoactivity, the anti-CD3 variable region with SpA-binding ability is an effective building block for developing engineered cancer therapeutic antibodies without the Fc region.

Revolutionizing cancer immunotherapy: unleashing the potential of bispecific antibodies for targeted treatment

Recent progressions in immunotherapy have transformed cancer treatment, providing a promising strategy that activates the immune system of the patient to find and eliminate cancerous cells. Bispecific antibodies, which engage two separate antigens or one antigen with two distinct epitopes, are of tremendous concern in immunotherapy. The bi-targeting idea enabled by bispecific antibodies (BsAbs) is especially attractive from a medical standpoint since most diseases are complex, involving several receptors, ligands, and signaling pathways. Several research look into the processes in which BsAbs identify different cancer targets such angiogenesis, reproduction, metastasis, and immune regulation. By rerouting cells or altering other pathways, the bispecific proteins perform effector activities in addition to those of natural antibodies. This opens up a wide range of clinical applications and helps patients with resistant tumors respond better to medication. Yet, further study is necessary to identify the best conditions where to use these medications for treating tumor, their appropriate combination partners, and methods to reduce toxicity. In this review, we provide insights into the BsAb format classification based on their composition and symmetry, as well as the delivery mode, focus on the action mechanism of the molecule, and discuss the challenges and future perspectives in BsAb development.

Structure and Dynamics Guiding Design of Antibody Therapeutics and Vaccines

Antibodies and other new antibody-like formats have emerged as one of the most rapidly growing classes of biotherapeutic proteins. Understanding the structural features that drive antibody function and, consequently, their molecular recognition is critical for engineering antibodies. Here, we present the structural architecture of conventional IgG antibodies alongside other formats. We emphasize the importance of considering antibodies as conformational ensembles in solution instead of focusing on single-static structures because their functions and properties are strongly governed by their dynamic nature. Thus, in this review, we provide an overview of the unique structural and dynamic characteristics of antibodies with respect to their antigen recognition, biophysical properties, and effector functions. We highlight the numerous technical advances in antibody structure prediction and design, enabled by the vast number of experimentally determined high-quality structures recorded with cryo-EM, NMR, and X-ray crystallography. Lastly, we assess antibody and vaccine design strategies in the context of structure and dynamics.

Noninvasive In Vivo Imaging of T-Cells during Cancer Immunotherapy Using Rare-Earth Nanoparticles

Only a minority of patients respond positively to cancer immunotherapy, and addressing this variability is an active area of immunotherapy research. Infiltration of tumors by immune cells is one of the most significant prognostic indicators of response and disease-free survival. However, the ability to noninvasively sample the tumor microenvironment for immune cells remains limited. Imaging in the near-infrared-II region using rare-earth nanocrystals is emerging as a powerful imaging tool for high-resolution deep-tissue imaging. In this paper, we demonstrate that these nanoparticles can be used for noninvasive in vivo imaging of tumor-infiltrating T-cells in a highly aggressive melanoma tumor model. We present nanoparticle synthesis and surface modification strategies for the generation of small, ultrabright, and biocompatible rare-earth nanocrystals necessary for deep tissue imaging of rare cell types. The ability to noninvasively monitor the immune contexture of a tumor during immunotherapy could lead to early identification of nonresponding patients in real time, leading to earlier interventions and better outcomes.

Single-chain dimers from de novo immunoglobulins as robust scaffolds for multiple binding loops

Antibody derivatives have sought to recapitulate the antigen binding properties of antibodies, but with improved biophysical attributes convenient for therapeutic, diagnostic and research applications. However, their success has been limited by the naturally occurring structure of the immunoglobulin dimer displaying hypervariable binding loops, which is hard to modify by traditional engineering approaches. Here, we devise geometrical principles for de novo designing single-chain immunoglobulin dimers, as a tunable two-domain architecture that optimizes biophysical properties through more favorable dimer interfaces. Guided by these principles, we computationally designed protein scaffolds that were hyperstable, structurally accurate and robust for accommodating multiple functional loops, both individually and in combination, as confirmed through biochemical assays and X-ray crystallography. We showcase the modularity of this architecture by deep-learning-based diversification, opening up the possibility for tailoring the number, positioning, and relative orientation of ligand-binding loops targeting one or two distal epitopes. Our results provide a route to custom-design robust protein scaffolds for harboring multiple functional loops.

Cross-linking disulfide bonds govern solution structures of diabodies

In the last years, antibodies have emerged as a promising new class of therapeutics, due to their combination of high specificity with long serum half-life and low risk of side-effects. Diabodies are a popular novel antibody format, consisting of two Fv domains connected with short linkers. Like IgG antibodies, they simultaneously bind two target proteins. However, they offer altered properties, given their smaller size and higher rigidity. In this study, we conducted the-to our knowledge-first molecular dynamics (MD) simulations of diabodies and find a surprisingly high conformational flexibility in the relative orientation of the two Fv domains. We observe rigidifying effects through the introduction of disulfide bonds in the Fv -Fv interface and characterize the effect of different disulfide bond locations on the conformation. Additionally, we compare VH -VL orientations and paratope dynamics between diabodies and an antigen binding fragment (Fab) of the same sequence. We find mostly consistent structures and dynamics, indicating similar antigen binding properties. The most significant differences can be found within the CDR-H2 loop dynamics. Of all CDR loops, the CDR-H2 is located closest to the artificial Fv -Fv interface. All examined diabodies show similar VH -VL orientations, Fv -Fv packing and CDR loop conformations. However, the variant with a P14C-K64C disulfide bond differs most from the Fab in our measures, including the CDR-H3 loop conformational ensemble. This suggests altered antigen binding properties and underlines the need for careful validation of the disulfide bond locations in diabodies.

Natural Killer Cell Engagers (NKCEs): a new frontier in cancer immunotherapy

Natural Killer (NK) cells are a type of innate lymphoid cells that play a crucial role in immunity by killing virally infected or tumor cells and secreting cytokines and chemokines. NK cell-mediated immunotherapy has emerged as a promising approach for cancer treatment due to its safety and effectiveness. NK cell engagers (NKCEs), such as BiKE (bispecific killer cell engager) or TriKE (trispecific killer cell engager), are a novel class of antibody-based therapeutics that exhibit several advantages over other cancer immunotherapies harnessing NK cells. By bridging NK and tumor cells, NKCEs activate NK cells and lead to tumor cell lysis. A growing number of NKCEs are currently undergoing development, with some already in clinical trials. However, there is a need for more comprehensive studies to determine how the molecular design of NKCEs affects their functionality and manufacturability, which are crucial for their development as off-the-shelf drugs for cancer treatment. In this review, we summarize current knowledge on NKCE development and discuss critical factors required for the production of effective NKCEs.

Rational design of a Nivolumab-based ANTI-PD-1 single chain variable fragment that blocks the interaction between PD-1 expressed on T-CELLS and PD-L1 ON CHO cells

Antibodies that block the interaction between PD-1 expressing T-cells and cancer cells expressing PD-L1 play a central role in contemporary immunotherapy regimes [1-3]. We previously reported the isolation of a single chain variable fragment (scFv) of the monoclonal anti-PD-1 antibody Nivolumab, that binds to purified PD-1 and blocked its interaction with PD-L1 [4]. This anti-PD-1 scFv did not, however, function in a cell-based assay designed to detect the disruption of the PD-1/PD-L1 interaction, a result likely due to its poor solubility in tissue culture media. Herein we report that following a series of structure-based rational design analyses, including Aggreescan3D, we have isolated a variant of the anti-PD-1 scFv having significantly improved solubility in tissue culture medium. Moreover, this soluble anti-PD-1 scFv variant disrupted the interaction between PD-1 expressed on Jurkat Cells and PD-L1 expressed on CHO cells. These findings are discussed in terms of the related observation that the residues mutated to form the anti-PD-1 variant are conserved in many other scFvs; thus, the properties of a range of scFvs will likely be enhanced by similar mutations of the conserved residues.

VERITAS: Harnessing the power of nomenclature in biologic discovery

We are entering an era in which therapeutic proteins are assembled using building block-like strategies, with no standardized schema to discuss these formats. Existing nomenclatures, like AbML, sacrifice human readability for precision. Therefore, considering even a dozen such formats, in combination with hundreds of possible targets, can create confusion and increase the complexity of drug discovery. To address this challenge, we introduce Verified Taxonomy for Antibodies (VERITAS). This classification and nomenclature scheme is extensible to multispecific therapeutic formats and beyond. VERITAS names are easy to understand while drawing direct connections to the structure of a given format, with or without specific target information, making these names useful to adopt in scientific discourse and as inputs to machine learning algorithms for drug development.

TRYBE®: an Fc-free antibody format with three monovalent targeting arms engineered for long in vivo half-life

TrYbe® is an Fc-free therapeutic antibody format, capable of engaging up to three targets simultaneously, with long in vivo half-life conferred by albumin binding. This format is shown by small-angle X-ray scattering to be conformationally flexible with favorable 'reach' properties. We demonstrate the format's broad functionality by co-targeting of soluble and cell surface antigens. The benefit of monovalent target binding is illustrated by the lack of formation of large immune complexes when co-targeting multivalent antigens. TrYbes® are manufactured using standard mammalian cell culture and protein A affinity capture processes. TrYbes® have been formulated at high concentrations and have favorable drug-like properties, including stability, solubility, and low viscosity. The unique functionality and inherent developability of the TrYbe® makes it a promising multi-specific antibody fragment format for antibody therapy.

AXL-Receptor Targeted 14FN3 Based Single Domain Proteins (Pronectins™) from 3 Synthetic Human Libraries as Components for Exploring Novel Bispecific Constructs against Solid Tumors

A highly specific AXL-receptor targeted family of non-immunoglobulin, single domain protein binders (Pronectins™) have been isolated from three (3) synthetic libraries that employ the human scaffold of the 14th domain of Fibronectin III (14FN3) and evolutionary CDRs diversity of over 25 billion loop sequences. The three libraries, each containing diversity in two loops, were designed to expand upon a human database of more than 6000 natural scaffold sequences and approximately 3000 human loop sequences. We used a bioinformatic-based approach to maximize "human" amino acid loop diversity and minimize or prevent altogether CDR immunogenicity created by the use of mutagenesis processes to generate diversity. A combination of phage display and yeast display was used to isolate 59 AXL receptor targeted Pronectins with KD ranging between 2 and 100 nM. FACS analysis with tumor cells over-expressing AXL and the use of an AXL knock-out cell line allowed us to identify Pronectin candidates with exquisite specificity for AXL receptor. Based upon several in vitro cell-based tests, we selected the best candidate, AXL54, to further characterize its in vitro cancer cells killing activity. Finally, AXL54 was used to produce the first bi-specific T cell engager protein (AXL54 [Pronectin]-linker-scFV CD3), a "new in class" protein for further testing of its anti-tumor activity in vitro and in vivo.

Evaluation and selection of a lead diabody for interferon-γ PET imaging

INTRODUCTION

Interferon-γ (IFN-γ) is an appealing target to evaluate immune response in cancer immunotherapy as it is a hallmark of an active immune system. Imaging and detection via immunopositron emission tomography (immunoPET) of this soluble cytokine has been made feasible using a ⁸⁹Zr-labeled (t _1/2 ~ 3.27 d) monoclonal antibody (mAb). Because of its size, using a full-length mAb as an imaging vector is not ideal for repeat serial imaging because of its prolonged blood pool residency and tumor accumulation resulting in lengthier wait times between administration and imaging. This consequently impacts the potential to image a dynamic immune response in real time. This work compares ⁸⁹Zr-labeled diabodies (Db) designed with variable linker lengths between the V_H and V_L regions with the goal of selecting a lead Db for future studies.

METHODS AND RESULTS

Four Db fragments with various linker lengths (HL-n, n = 7-13 amino acids) were each conjugated to desferrioxamine (DFO). The number of attached chelates was analyzed via mass spectrometry with all immunoconjugates exhibiting one unit of DFO attached. Db-DFO conjugates were subsequently radiolabeled with zirconium-89. All constructs radiolabeled with high yields. Each radioimmunoconjugate was tested for reactivity to IFN-γ. All tracers except for [⁸⁹Zr]Zr-DFO-NCS-anti-IFN-γ HL-9 exhibited comparable immunoreactivities (>90 %) to the radiolabeled parent mAb (95.8 %). At 24 h post-labeling, the IRF values were retained except for the HL-13 construct. Imaging scans and tissue distribution studies acquired in mice bearing CT26 syngeneic colorectal tumors between 1 and 24 h post-tracer administration demonstrated variable clearance kinetics and tumor localization of each radiotracer. HL-7 had higher binding in non-tumor tissues compared to HL-11 and HL-13 at 3 h p.i. Competitive binding studies versus unmodified parent mAb (AN-18) demonstrated blocking of radiolabeled HL-11 and HL-13. [⁸⁹Zr]Zr-DFO-NCS-anti-IFN-γ HL-7 was inadequately blocked.

CONCLUSION

Despite nuanced differences in linker lengths, our data demonstrates that [⁸⁹Zr]Zr-DFO-NCS-anti-IFN-γ HL-11 exhibited the best radiotracer properties for the assessment of IFN-γ production in vivo. Work is currently underway to test the potential of using shorter-lived isotopes, like copper-64 (t_1/2 ~ 12.7 h) to match pharmacokinetics and half-lives.

Current landscape and future directions of bispecific antibodies in cancer immunotherapy

Recent advances in cancer immunotherapy using monoclonal antibodies have dramatically revolutionized the therapeutic strategy against advanced malignancies, inspiring the exploration of various types of therapeutic antibodies. Bispecific antibodies (BsAbs) are recombinant molecules containing two different antigens or epitopes identifying binding domains. Bispecific antibody-based tumor immunotherapy has gained broad potential in preclinical and clinical investigations in a variety of tumor types following regulatory approval of newly developed technologies involving bispecific and multispecific antibodies. Meanwhile, a series of challenges such as antibody immunogenicity, tumor heterogeneity, low response rate, treatment resistance, and systemic adverse effects hinder the application of BsAbs. In this review, we provide insights into the various architecture of BsAbs, focus on BsAbs' alternative different mechanisms of action and clinical progression, and discuss relevant approaches to overcome existing challenges in BsAbs clinical application.

IgG-like bispecific antibodies with potent and synergistic neutralization against circulating SARS-CoV-2 variants of concern

Monoclonal antibodies are a promising approach to treat COVID-19, however the emergence of SARS-CoV-2 variants has challenged the efficacy and future of these therapies. Antibody cocktails are being employed to mitigate these challenges, but neutralization escape remains a major challenge and alternative strategies are needed. Here we present two anti-SARS-CoV-2 spike binding antibodies, one Class 1 and one Class 4, selected from our non-immune human single-chain variable fragment (scFv) phage library, that are engineered into four, fully-human IgG-like bispecific antibodies (BsAb). Prophylaxis of hACE2 mice and post-infection treatment of golden hamsters demonstrates the efficacy of the monospecific antibodies against the original Wuhan strain, while promising in vitro results with the BsAbs demonstrate enhanced binding and distinct synergistic effects on neutralizing activity against circulating variants of concern. In particular, one BsAb engineered in a tandem scFv-Fc configuration shows synergistic neutralization activity against several variants of concern including B.1.617.2. This work provides evidence that synergistic neutralization can be achieved using a BsAb scaffold, and serves as a foundation for the future development of broadly reactive BsAbs against emerging variants of concern.

A 33-residue peptide tag increases solubility and stability of Escherichia coli produced single-chain antibody fragments

Single-chain variable fragments (scFvs), composed of variable domains of heavy and light chains of an antibody joined by a linker, share antigen binding capacity with their parental antibody. Due to intrinsically low solubility and stability, only two Escherichia coli-produced scFvs have been approved for therapy. Here we report that a 33-residue peptide, termed P17 tag, increases the solubility of multiple scFvs produced in Escherichia coli SHuffle strain by up to 11.6 fold. Hydrophilic sequence, especially charged residues, but not the predicted α-helical secondary structure of P17 tag, contribute to the solubility enhancement. Notably, the P17 tag elevates the thermostability of scFv as efficiently as intra-domain disulfide bonds. Moreover, a P17-tagged scFv targeting hepatitis B virus surface proteins shows over two-fold higher antigen-binding affinity and virus-neutralizing activity than the untagged version. These data strongly suggest a type I intramolecular chaperone-like activity of the P17 tag. Hence, the P17 tag could benefit the research, production, and application of scFv.

Low solubility and stability of Escherichia coli produced single chain variable fragments (scFvs) restrict their applications. Here the authors report a 33-residue peptide tag which simultaneously increases the solubility and thermostability of multiple scFvs produced in Escherichia coli SHuffle strain.

Directing HIV-1 for degradation by non-target cells, using bi-specific single-chain llama antibodies

While vaccination against HIV-1 has been so far unsuccessful, recently broadly neutralizing antibodies (bNAbs) against HIV-1 envelope glycoprotein were shown to induce long-term suppression in the absence of antiretroviral therapy in patients with antibody-sensitive viral reservoirs. The requirement of neutralizing antibodies indicates that the antibody mediated removal (clearance) of HIV-1 in itself is not efficient enough in these immune compromised patients. Here we present a novel, alternative approach that is independent of a functional immune system to clear HIV-1, by capturing the virus and redirecting it to non-target cells where it is internalized and degraded. We use bispecific antibodies with domains derived from small single chain Llama antibodies (VHHs). These bind with one domain to HIV-1 envelope proteins and with the other domain direct the virus to cells expressing epidermal growth factor receptor (EGFR), a receptor that is ubiquitously expressed in the body. We show that HIV envelope proteins, virus-like particles and HIV-1 viruses (representing HIV-1 subtypes A, B and C) are efficiently recruited to EGFR, internalized and degraded in the lysosomal pathway at low nM concentrations of bispecific VHHs. This directed degradation in non-target cells may provide a clearance platform for the removal of viruses and other unwanted agents from the circulation, including toxins, and may thus provide a novel method for curing.

Bispecific Antibody-Based Immune-Cell Engagers and Their Emerging Therapeutic Targets in Cancer Immunotherapy

Cancer is the second leading cause of death worldwide after cardiovascular diseases. Harnessing the power of immune cells is a promising strategy to improve the antitumor effect of cancer immunotherapy. Recent progress in recombinant DNA technology and antibody engineering has ushered in a new era of bispecific antibody (bsAb)-based immune-cell engagers (ICEs), including T- and natural-killer-cell engagers. Since the first approval of blinatumomab by the United States Food and Drug Administration (US FDA), various bsAb-based ICEs have been developed for the effective treatment of patients with cancer. Simultaneously, several potential therapeutic targets of bsAb-based ICEs have been identified in various cancers. Therefore, this review focused on not only highlighting the action mechanism, design and structure, and status of bsAb-based ICEs in clinical development and their approval by the US FDA for human malignancy treatment, but also on summarizing the currently known and emerging therapeutic targets in cancer. This review provides insights into practical considerations for developing next-generation ICEs.

Therapeutic bispecific antibodies against intracellular tumor antigens

Bispecific antibodies (BsAbs)-based therapeutics have been identified to be one of the most promising immunotherapy strategies. However, their target repertoire is mainly restricted to cell surface antigens rather than intracellular antigens, resulting in a relatively limited scope of applications. Intracellular tumor antigens are identified to account for a large proportion of tumor antigen profiles. Recently, bsAbs that target intracellular oncoproteins have raised much attention, broadening the targeting scope of tumor antigens and improving the efficacy of traditional antibody-based therapeutics. Consequently, this review will focus on this emerging field and discuss related research advances. We introduce the classification, characteristics, and clinical applications of bsAbs, the theoretical basis for targeting intracellular antigens, delivery systems of bsAbs, and the latest preclinical and clinical advances of bsAbs targeting several intracellular oncotargets, including those of cancer-testis antigens, differentiation antigens, neoantigens, and other antigens. Moreover, we summarize the limitations of current bsAbs, and propose several potential strategies against immune escape and T cell exhaustion as well as some future perspectives.

Effect of non-repetitive linker on in vitro and in vivo properties of an anti-VEGF scFv

Single chain antibody fragments (scFvs) are favored in diagnostic and therapeutic fields thanks to their small size and the availability of various engineering approaches. Linker between variable heavy (V_H) and light (V_L) chains of scFv covalently links these domains and it can affect scFv’s bio-physical/chemical properties and in vivo activity. Thus, scFv linker design is important for a successful scFv construction, and flexible linkers are preferred for a proper pairing of V_H–V_L. The flexibility of the linker is determined by length and sequence content and glycine-serine (GS) linkers are commonly preferred for scFvs based on their highly flexible profiles. Despite the advantage of this provided flexibility, GS linkers carry repeated sequences which can cause problems for PCR-based engineering approaches and immunogenicity. Here, two different linkers, a repetitive GS linker and an alternative non-repetitive linker with similar flexibility but lower immunogenicity are employed to generate anti-Vascular Endothelial Growth Factor scFvs derived from bevacizumab. Our findings highlight a better in vitro profile of the non-repetitive linker such as a higher monomer ratio, higher thermal stability while there was no significant difference in in vivo efficacy in a zebrafish embryonic angiogenesis model. This is the first study to compare in vivo efficacy of scFvs with different linkers in a zebrafish model.

Bispecific antibodies-effects of point mutations on CH3-CH3 interface stability

A new format of therapeutic proteins is bispecific antibodies, in which two different heavy chains heterodimerize to obtain two different binding sites. Therefore, it is crucial to understand and optimize the third constant domain (CH3-CH3) interface to favor heterodimerization over homodimerization, and to preserve the physicochemical properties, as thermal stability. Here, we use molecular dynamics simulations to investigate the dissociation process of 19 CH3-CH3 crystal structures that differ from each other in few point mutations. We describe the dissociation of the dimeric interface as a two-steps mechanism. As confirmed by a Markov state model, apart from the bound and the dissociated state, we observe an additional intermediate state, which corresponds to an encounter complex. The analysis of the interdomain contacts reveals key residues that stabilize the interface. We expect that our results will improve the understanding of the CH3-CH3 interface interactions and thus advance the developability and design of new antibodies formats.

Development and characterization of functional antibodies targeting NMDA receptors

N-methyl-D-aspartate receptors (NMDARs) are critically involved in basic brain functions and neurodegeneration as well as tumor invasiveness. Targeting specific subtypes of NMDARs with distinct activities has been considered an effective therapeutic strategy for neurological disorders and diseases. However, complete elimination of off-target effects of small chemical compounds has been challenging and thus, there is a need to explore alternative strategies for targeting NMDAR subtypes. Here we report identification of a functional antibody that specifically targets the GluN1-GluN2B NMDAR subtype and allosterically down-regulates ion channel activity as assessed by electrophysiology. Through biochemical analysis, x-ray crystallography, single-particle electron cryomicroscopy, and molecular dynamics simulations, we show that this inhibitory antibody recognizes the amino terminal domain of the GluN2B subunit and increases the population of the non-active conformational state. The current study demonstrates that antibodies may serve as specific reagents to regulate NMDAR functions for basic research and therapeutic objectives.

Selective targeting individual subtypes of N-methyl-D-aspartate receptors (NMDARs) is a desirable therapeutic strategy for neurological disorders. Here, the authors report identification of a functional antibody that specifically targets and allosterically down-regulates ion channel activity of the GluN1—GluN2B NMDAR subtype.

Emerging new therapeutic antibody derivatives for cancer treatment

Monoclonal antibodies constitute a promising class of targeted anticancer agents that enhance natural immune system functions to suppress cancer cell activity and eliminate cancer cells. The successful application of IgG monoclonal antibodies has inspired the development of various types of therapeutic antibodies, such as antibody fragments, bispecific antibodies, and antibody derivatives (e.g., antibody-drug conjugates and immunocytokines). The miniaturization and multifunctionalization of antibodies are flexible and viable strategies for diagnosing or treating malignant tumors in a complex tumor environment. In this review, we summarize antibodies of various molecular types, antibody applications in cancer therapy, and details of clinical study advances. We also discuss the rationale and mechanism of action of various antibody formats, including antibody-drug conjugates, antibody-oligonucleotide conjugates, bispecific/multispecific antibodies, immunocytokines, antibody fragments, and scaffold proteins. With advances in modern biotechnology, well-designed novel antibodies are finally paving the way for successful treatments of various cancers, including precise tumor immunotherapy, in the clinic.

Initial evaluation of 99m Tc-labeled anti-CEA scFv for micro-SPECT imaging in mice with colorectal cancer

Carcinoembryonic antigen (CEA) has emerged as an important molecular target for several neoplastic diseases, including colorectal cancer with CEA over-expression. In this study, we report the production and radiolabeling of a novel anti-CEA single-chain fragment variable (scFv-96NRT, concentration for 50% of maximal effect 46 ng/mL), and evaluation of [^99m Tc]Tc-scFv-96NRT in non-invasive detection of CEA expression. [^99m Tc]Tc-scFv-96NRT was synthesized by one step reduction in labeling yield of > 95% with radiochemical purity of > 98% and molar activity of 10-11 GBq/μmol. [^99m Tc]Tc-scFv-96NRT showed high stability in 0.01 M phosphate buffered saline (PBS), and 5% human serum albumin (HSA). It exhibited elevated uptake in CEA over-expressing cells. Bio-distribution studies in BALB/c mice revealed that the probe was cleared from blood rapidly, and the highest retention was observed in the kidneys. The micro-single photon emission computed tomography (micro-SPECT) imaging of [^99m Tc]Tc-scFv-96NRT showed a specific accumulation pattern, as blocking experiment with excess scFv-96NRT suppressed the tumor uptake. These preliminary results suggest that [^99m Tc]Tc-scFv-96NRT is a potential non-invasive molecular probe for imaging tumors with CEA over-expression.

Natural Receptor- and Ligand-Based Chimeric Antigen Receptors: Strategies Using Natural Ligands and Receptors for Targeted Cell Killing

Chimeric antigen receptor (CAR) T-cell therapy has been widely successful in the treatment of B-cell malignancies, including B-cell lymphoma, mantle cell lymphoma, and multiple myeloma; and three generations of CAR designs have led to effective FDA approved therapeutics. Traditionally, CAR antigen specificity is derived from a monoclonal antibody where the variable heavy (V_H) and variable light (V_L) chains are connected by a peptide linker to form a single-chain variable fragment (scFv). While this provides a level of antigen specificity parallel to that of an antibody and has shown great success in the clinic, this design is not universally successful. For instance, issues of stability, immunogenicity, and antigen escape hinder the translational application of some CARs. As an alternative, natural receptor- or ligand-based designs may prove advantageous in some circumstances compared to scFv-based designs. Herein, the advantages and disadvantages of scFv-based and natural receptor- or ligand-based CAR designs are discussed. In addition, several translational aspects of natural receptor- and ligand-based CAR approaches that are being investigated in preclinical and clinical studies will be examined.

[Bispecific antibodies: An old story with a bright future… with CAR-T cells!]

CAR-T cells originate from two different approaches, cellular immunotherapy based on tumor immunosurveillance by T lymphocytes, combined with molecular engineering of bispecific antibodies and antibody fragments. The latter makes it possible to retarget immune effector cytotoxic cells (such as NK cells and T lymphocytes) to tumor cells through the binding to tumor-associated antigens. We present herein the history of bispecific antibodies, highlighting how such antibodies played a major role in CAR-T cell development. We will first evoke how antibody engineering led to the construction of various bispecific formats, in particular using the single chain Fv fragment (scFv) which has been used as the initial building block to generate chimeric bi-, tri- or multifunctional molecules. We will also describe how bispecific antibodies, either full IgG or as scFv or F(ab')₂ format, directed against Fcγ receptors or CD3ɛ and against tumor-associated antigens, induce a potent anti-tumor cytotoxicity following the recruitment and activation of immune effector cells, including CD3⁺ T lymphocytes. These anti-tumor effects have been translated into the clinics, especially to treat malignant hemopathies. At last, recently generated bispecific CAR-T cells suggest that the embrace between cell therapy and bispecific antibodies is not over and that we are yet to witness further discoveries enabling these cells to be even more efficient.

Concepts in Oncolytic Adenovirus Therapy

Oncolytic adenovirus therapy is gaining importance as a novel treatment option for the management of various cancers. Different concepts of modification within the adenovirus vector have been identified that define the mode of action against and the interaction with the tumour. Adenoviral vectors allow for genetic manipulations that restrict tumour specificity and also the expression of specific transgenes in order to support the anti-tumour effect. Additionally, replication of the virus and reinfection of neighbouring tumour cells amplify the therapeutic effect. Another important aspect in oncolytic adenovirus therapy is the virus induced cell death which is a process that activates the immune system against the tumour. This review describes which elements in adenovirus vectors have been identified for modification not only to utilize oncolytic adenovirus vectors into conditionally replicating adenoviruses (CRAds) that allow replication specifically in tumour cells but also to confer specific characteristics to these viruses. These advances in development resulted in clinical trials that are summarized based on the conceptual design.