Therapeutic Antibody Targeting Research Articles

Post-translational modifications optimize the ability of SARS-CoV-2 spike for effective interaction with host cell receptors.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein is the prime target for vaccines, diagnostics, and therapeutic antibodies against the virus. While anchored in the viral envelope, for effective virulence, the spike needs to maintain structural flexibility to recognize the host cell surface receptors and bind to them, a property that can heavily depend upon the dynamics of the unresolved domains, most prominently the stalk. Construction of the complete, membrane-bound spike model and the description of its dynamics are critical steps in understanding the inner working of this key element of the viral infection by SARS-CoV-2. Combining homology modeling, protein-protein docking, and molecular dynamics (MD) simulations, we have developed a full spike structure in a native membrane. Multimicrosecond MD simulations of this model, the longest known single trajectory of the full spike, reveal conformational dynamics employed by the protein to explore the surface of the host cell. In agreement with cryogenic electron microscopy (cryo-EM), three flexible hinges in the stalk allow for global conformational heterogeneity of spike in the fully glycosylated system mediated by glycan-glycan and glycan-lipid interactions. The dynamical range of the spike is considerably reduced in its nonglycosylated form, confining the area explored by the spike on the host cell surface. Furthermore, palmitoylation of the membrane domain amplifies the local curvature that may prime the fusion. We show that the identified hinge regions are highly conserved in SARS coronaviruses, highlighting their functional importance in enhancing viral infection, and thereby, provide points for discovery of alternative therapeutics against the virus.

A Bioinformatics Assessment Indicating Better Outcomes With Breast Cancer Resident, Immunoglobulin CDR3-MMP2 Binding.

The recombination of V, D, and J immunoglobulin (IG) gene segments leads to many variations in the amino acids (AAs) encoded at that site, the complementarity determining region-3 (CDR3). Thus, cancer patients may have varying degrees of CDR3 AA binding specificity for cancer proteases, for example, matrix metalloproteinase 2 (MMP2). MMP2 in breast cancer has been found to contribute to metastasis and is used as a marker for tumor staging. Thus, this report evaluated the tumor resident, patient specific IG CDR3 binding affinities to cancer proteases to test the hypothesis that greater binding affinities would be associated with a better outcome. Using two independent bioinformatics tools, we evaluated the IG CDR3-MMP2 binding affinities throughout the cancer genome atlas breast cancer (TCGA-BRCA) dataset. Results indicated that the better the CDR3-MMP2 binding, the better the survival probability. An analogous evaluation for four other proteases, including calpain-1 and thermolysin, displayed no such associations with survival probabilities. This study is consistent with the possibility that patient IG-cancer protease interactions could impact outcomes and raises the question of whether therapeutic antibody targeting of MMP2 would reduce breast cancer mediated tissue destruction and breast cancer mortality rates.

Therapeutic Anti-Jagged1 Antibody Targeting Osteoblast-Related Myeloid Dysplasia to Overcome Standard of Care Resistance

Acute myeloid leukemia (AML) and myelodysplasia (MDS) are increasingly recognized as not only genetic but niche-dependent malignancies prompting the question of whether targeting signals from supporting stromal cells may provide a more stable target for therapy than emerging leukemic clones. Whereas standard of care and malignant cell targeted therapies fail to eliminate resistant clones or prevent the expansion of new ones, inhibition of oncogenic or tumor promoting signals from the stroma could overcome mutation dependance and clonal resistance and be an efficient approach to manage disease and prevent relapse. Here, we inhibited a potent, niche-driven tumorigenic pathway, constitutive activation of b-catenin/Jagged1 signaling in osteoblasts. This pathway is activated following hypermethylation of its regulators in MDS patients; is activated in approximately 40% of MDS and AML patients; its activation levels increase with disease severity and progression; correlate with MDS to AML transformation and del(5q)-associated myeloid malignancies and leads to MDS rapidly progressing to AML in mice. To examine the therapeutic potential of targeting this pathway we generated a human-mouse chimeric antibody that efficiently and specifically binds JAG1 (anti-JAG1) and inhibits Notch1 signaling. Administration of anti-JAG1 in leukemic mice with osteoblastic active b-catenin rescued anemia, thrombocytopenia, neutrophilia and lymphocytopenia, restored LT-HSCs (the leukemia initiating population), relieved myeloid differentiation block and eliminated blasts. Body weight increased and lethality was abrogated in treated mice. In contrast, chemotherapy at a dose simulating induction regimen used in humans, dramatically exacerbated anemia, thrombocytopenia and lymphocytopenia without decreasing blasts leading to increased lethality due to bone marrow failure. A lower chemotherapy dose induced a physiologically relevant response in wild type mice, but failed to improve hematopoiesis and myeloid differentiation block in leukemic mice and as a result AML progression and lethality was not affected. Emphasizing relevance to human disease, anti-JAG1 treatment of patient-derived samples with activated b-catenin in their osteoblasts, inhibited MDS and AML cell growth and survival and promoted myeloid and erythroid differentiation irrespective of disease category through its actions on osteoblasts. These findings suggest anti-JAG1 may provide a broad therapeutic approach that is effective in 1/3 of MDS and AML patients with cytogenetically distinct types of disease. The therapeutic potential of targeting the bone marrow stromal niche in hematological malignancies can be a treatment strategy that may evade relapse and overcome standard of care resistance and toxicity.

MM-324 Effects of Soluble and Microvesicle-Bound Therapeutic Anti-CD38 Antibodies on Immune Effector Cells in Multiple Myeloma

CD38 is a pleiotropic cell surface molecule with a short cytoplasmic tail. This molecule is highly expressed by multiple myeloma (MM) cells, and it was chosen as the target of therapeutic monoclonal antibodies, such as daratumumab (Dara). This work aims at investigating how Dara interacts with target and immune cells and what effects are induced on natural killer (NK) cells and myeloid-derived suppressor cells (MDSCs). Experiments were conducted on MM-derived cell lines stabilized in our laboratory and fresh human myeloma cells. Microvesicles (MVs) were collected through serial centrifugations. MVs' surface phenotype and internalization were evaluated by flow cytometry. Functional experiments were performed on cells purified from peripheral blood or bone marrow mononuclear cells and analyzed by flow cytometry. As previously reported, CD38 engagement by Dara on MM cells in conditions of membrane fluidity is followed by the release of MVs with peculiar phenotype and cargo. To extend these observations, the activity of both soluble and insolubilized Dara was assessed by exposing NK cells and MDSC to Dara. The results indicate that Dara treatment of NK cells is followed by increased expression of CD69 (activation marker) and CD107 (degranulation marker) and decreased IFNγ production by the latter cells. NK proliferation was reduced by Dara treatment, thus confirming in-vivo observations. On MDSCs, Dara treatment was followed by increased nitrite release and iNos expression. Cell viability was not altered by Dara treatment. MVs were also incubated with dendritic cells, and a high internalization rate was observed, the consequences of which are under investigation. The results of this work indicate that MVs obtained from Dara-treated MM cells may be a particulate system to modulate the immune response, either locally in the bone marrow niche or at distance. Moreover, these observations provide evidence that Dara enhances NK degranulation and activation while paradoxically decreasing their proliferation. These phenomena were observed with both the soluble and insolubilized forms of the antibody. Our data may describe a mechanism underlying Dara effectiveness and may also partially explain the onset of Dara resistance. In conclusion, our results may pave the way for new strategies to improve treatment efficacy and avoid the onset of resistance.

Posttranslational modifications optimize the ability of SARS-CoV-2 spike for effective interaction with host cell receptors

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein is the prime target for vaccines, diagnostics, and therapeutic antibodies against the virus. While anchored in the viral envelope, for effective virulence, the spike needs to maintain structural flexibility to recognize the host cell surface receptors and bind to them, a property that can heavily depend upon the dynamics of the unresolved domains, most prominently the stalk. Construction of the complete, membrane-bound spike model and the description of its dynamics are critical steps in understanding the inner working of this key element of the viral infection by SARS-CoV-2. Combining homology modeling, protein-protein docking, and molecular dynamics (MD) simulations, we have developed a full spike structure in a native membrane. Multimicrosecond MD simulations of this model, the longest known single trajectory of the full spike, reveal conformational dynamics employed by the protein to explore the surface of the host cell. In agreement with cryogenic electron microscopy (cryo-EM), three flexible hinges in the stalk allow for global conformational heterogeneity of spike in the fully glycosylated system mediated by glycan-glycan and glycan-lipid interactions. The dynamical range of the spike is considerably reduced in its nonglycosylated form, confining the area explored by the spike on the host cell surface. Furthermore, palmitoylation of the membrane domain amplifies the local curvature that may prime the fusion. We show that the identified hinge regions are highly conserved in SARS coronaviruses, highlighting their functional importance in enhancing viral infection, and thereby, provide points for discovery of alternative therapeutics against the virus.

Complexity of Viral Epitope Surfaces as Evasive Targets for Vaccines and Therapeutic Antibodies.

The dynamic interplay between virus and host plays out across many interacting surfaces as virus and host evolve continually in response to one another. In particular, epitope-paratope interactions (EPIs) between viral antigen and host antibodies drive much of this evolutionary race. In this review, we describe a series of recent studies examining aspects of epitope complexity that go beyond two interacting protein surfaces as EPIs are typically understood. To structure our discussion, we present a framework for understanding epitope complexity as a spectrum along a series of axes, focusing primarily on 1) epitope biochemical complexity (e.g., epitopes involving N-glycans) and 2) antigen conformational/dynamic complexity (e.g., epitopes with differential properties depending on antigen state or fold-axis). We highlight additional epitope complexity factors including epitope tertiary/quaternary structure, which contribute to epistatic relationships between epitope residues within- or adjacent-to a given epitope, as well as epitope overlap resulting from polyclonal antibody responses, which is relevant when assessing antigenic pressure against a given epitope. Finally, we discuss how these different forms of epitope complexity can limit EPI analyses and therapeutic antibody development, as well as recent efforts to overcome these limitations.

Abstract 332: Development of a novel therapeutic CLDN18.2 monoclonal antibody and antibody drug conjugate for the treatment of CLDN18.2 positive cancers

Abstract Background: Claudin 18 is a member of the claudin family of tight junction tetraspan cell surface proteins. The 18.2 isoform of claudin 18 (CLDN18.2) is expressed in healthy gastric mucosa cells and largely absent from other normal adult cell types. In contrast to the low expression in healthy tissues, CLDN18.2 is highly overexpressed in many cancer types including gastric and pancreatic malignancies at high frequencies (50-80%). The high tumor-normal expression differential of CLDN18.2 make it an attractive target for both therapeutic monoclonal antibodies (mAbs) and antibody drug conjugate (ADCs). Here, we describe the preclinical development of a novel therapeutic CLDN18.2 mAb and ADC. Materials and Methods: CLDN18.2 specific mAbs were generated through a multiplexed immunization strategy by which mice were immunized with either peptides spanning loop 2 of the CLDN18.2 extracellular domain or mouse NIH3T3 cells overexpressing the full length CLDN18.2 protein. Antibody clones were screened by flow cytometry for selective binding to cell surface CLDN18.2. A CLDN18.2-directed ADC was generated from the fully humanized clinical candidate CLDN18.2 mAb by MMAE conjugation with a cleavable linker. CLDN18.2 positivity in cell line (CDX) and patient derived xenograft (PDX) models was determined by IHC assay. Results: Selective binding of the CLDN18.2-mAb to CLDN18.2, without cross reactivity to the more widely expressed CLDN18.1 isoform, was confirmed in human cancer cell lines and cells engineered to overexpress each isoform. The CLDN18.2-mAb demonstrated strong induction of both antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cell-mediated phagocytosis (ADCP) in in vitro assays; suggesting that Fc effector function is a key component of the mechanism of action of the mAb. Treatment of CLDN18.2 positive gastric and pancreatic CDXs with CLDN18.2-mAb monotherapy induced significant inhibition of tumor growth in CD-1 nude mice. Binding of CLDN18.2-mAb or CLDN18.2-ADC to the cell surface CLDN18.2 induced internalization of the protein-antibody complex. Complete regression of CDX tumors was observed in response to treatment with the CLDN18.2-ADC in three separate CLDN18.2 positive models (two pancreas, one gastric). Moreover, complete loss of xenograft tumor burden was also observed in 4/5 CLDN18.2 positive pancreas PDX models. No impact on xenograft tumor growth as observed in response to treatment with either the CLDN18.2-mAb or CLDN18.2-ADC in CLDN18.2 negative CDX/PDX models. Discussion: These data support the clinical development of this CLDN18.2-mAb and CLDN18.2-ADC for the treatment of CLDN18.2 positive cancers. Each of these molecules will begin phase 1 clinical testing in early 2022. Citation Format: Neil A. O'brien, Martina S. McDermott, Jun Zhang, Ke Wei Gong, Ming Lu, Benjamin G. Hoffstrom, Dylan Conklin, Tong Luo, Kevin Chau, Min Liang, Timothy R. Donahue, John A. Glaspy, Leonard Presta, Dennis J. Slamon. Development of a novel therapeutic CLDN18.2 monoclonal antibody and antibody drug conjugate for the treatment of CLDN18.2 positive cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 332.

CD38 Monoclonal Antibodies in Relapsed/Refractory Multiple Myeloma

Multiple myeloma remains an incurable disease. CD38 is a desirable target for therapeutic antibodies, including isatuximab and daratumumab. Nurse practitioners working in the oncology setting play an essential role in the management and education of patients receiving these therapies. This article provides a practical overview of anti-CD38 antibodies for oncology nurse practitioners, including infusion reaction mitigation, laboratory interpretation, and clinical decision making.

The ART of tumor immune escape

ABSTRACT We recently identified the adenosine-5′-diphosphate (ADP)–ribosyltransferase-1 (ART1) as a novel immune checkpoint expressed by cancer cells. ART1 utilizes free nicotinamide adenine dinucleotide (NAD+) in the tumor microenvironment (TME) to mono-ADP-ribosylate (MARylate) the P2X7 receptor (P2X7R) on CD8 T cells, resulting in NAD-induced cell death (NICD) and tumor immune resistance. This process is blocked by therapeutic antibody targeting of ART1.

Application of quantitative protein mass spectrometric data in the early predictive analysis of target engagement by monoclonal antibodies.

Model‐informed drug discovery is endorsed by the US Food and Drug Administration (FDA) to improve the flow of medicines from bench to bedside. In the case of monoclonal antibodies, this necessitates taking into account not only the pharmacokinetic (PK) properties of the drug, but also the tissue distribution, concentration, and turnover of the target to guide dose and affinity selection, as well as serve as a link to downstream pharmacology. Relevant information (e.g., tissue proteomic data from quantitative mass spectrometry), is increasingly available from public domain data repositories, although not necessarily in the form that is directly usable for the purpose of quantitative, predictive, and mechanistic PK/pharmacodynamic (PD) modeling based on molarity or similar frameworks instead. Using secreted plasma protein concentrations measured both by immunochemical methods and mass spectrometry, we addressed this gap and derived an optimized nonlinear empirical function that establishes the correlation between the two data sets and validated the approach taken using a wider data set of all proteins found in plasma. In addition, we present a semimechanistic framework for the plasma half‐life of soluble proteins where clearance is expressed as a nonlinear function of the molecular weight of the protein. Finally, we apply the approach to two established therapeutic antibody targets: complement factor C5 and PCSK9 to demonstrate how the described framework can be applied to predictive PK/PD modeling.

Multiple SARS-CoV-2 Variants Exhibit Variable Target Cell Infectivity and Ability to Evade Antibody Neutralization.

The continuous emergence of SARS-coronavirus 2 (SARS-CoV-2) variants, especially the variants of concern (VOC), exacerbated the impact of the coronavirus disease 2019 (COVID-19) pandemic. As the key of viral entry into host cells, the spike (S) protein is the major target of therapeutic monoclonal antibodies (mAbs) and polyclonal antibodies elicited by infection or vaccination. However, the mutations of S protein in variants may change the infectivity and antigenicity of SARS-CoV-2, leading to the immune escape from those neutralizing antibodies. To characterize the mutations of S protein in newly emerging variants, the proteolytic property and binding affinity with receptor were assessed, and the vesicular stomatitis virus (VSV)-based pseudovirus system was used to assess the infectivity and immune escape. We found that some SARS-CoV-2 variants have changed significantly in viral infectivity; especially, B.1.617.2 is more likely to infect less susceptible cells than D614G, and the virus infection process can be completed in a shorter time. In addition, neutralizing mAbs and vaccinated sera partially or completely failed to inhibit host cell entry mediated by the S protein of certain SARS-CoV-2 variants. However, SARS-CoV-2 variant S protein-mediated viral infection can still be blocked by protease inhibitors and endocytosis inhibitors. This work provides a deeper understanding of the rise and evolution of SARS-CoV-2 variants and their immune evasion.

Concerted hinge motions in SARS-CoV-2 spike modulated by glycan-glycan and glycan-lipid interactions

SARS-CoV-2 binds to the host cells through its spike glycoprotein, making it a key target for therapeutic antibodies. The anchoring of the spike to the viral envelope through the stalk domain allows it to function as extended viral antennae for recognition by the host cell surface receptors, and the construction of the complete membrane-bound spike model and description of its dynamics remain the first and most critical steps in understanding the working of this key component of the viral infection machinery.

TMEM176B Regulates AKT/mTOR Signaling and Tumor Growth in Triple-Negative Breast Cancer.

TMEM176B is a member of the membrane spanning 4-domains (MS4) family of transmembrane proteins, and a putative ion channel that is expressed in immune cells and certain cancers. We aimed to understand the role of TMEM176B in cancer cell signaling, gene expression, cell proliferation, and migration in vitro, as well as tumor growth in vivo. We generated breast cancer cell lines with overexpressed and silenced TMEM176B, and a therapeutic antibody targeting TMEM176B. Proliferation and migration assays were performed in vitro, and tumor growth was evaluated in vivo. We performed gene expression and Western blot analyses to identify the most differentially regulated genes and signaling pathways in cells with TMEM176B overexpression and silencing. Silencing TMEM176B or inhibiting it with a therapeutic antibody impaired cell proliferation, while overexpression increased proliferation in vitro. Syngeneic and xenograft tumor studies revealed the attenuated growth of tumors with TMEM176B gene silencing compared with controls. We found that the AKT/mTOR signaling pathway was activated or repressed in cells overexpressing or silenced for TMEM176B, respectively. Overall, our results suggest that TMEM176B expression in breast cancer cells regulates key signaling pathways and genes that contribute to cancer cell growth and progression, and is a potential target for therapeutic antibodies.

Conformational epitopes exposed on misfolded toxic forms of amyloid-beta, tau and alpha-synuclein directly contribute to their seeding activity.

Misfolded, toxic aggregates of proteins capable of prion-like propagation from cell to cell have been implicated in the pathogenesis of neurodegenerative disorders. For example, toxic oligomers of amyloid-beta (Abeta) as well as oligomers and small soluble fibrils of tau and alpha-synuclein (Asyn) have been reported to contribute to neuronal damage and progression of Alzheimer's disease as well as various tauopathies (e.g. FTLD, progressive supranuclear palsy) and synucleinopathies (e.g. Parkinson's, Lewy body dementia, multiple system atrophy). Misfolding of these proteins into toxic forms leads to the exposure of conformational epitopes not normally present on the healthy form of the protein. In these studies, we sought to determine whether these small misfolded regions may not only represent a target for therapeutic antibodies but also directly contribute to the pathogenic seeding activity of misfolded proteins. Computational modeling was used to predict conformational epitopes likely to become solvent-exposed on toxic aggregates of Abeta, tau and Asyn but not on non-toxic forms of the proteins. Antibodies raised against cyclic peptide scaffolds replicating these conformational epitopes were tested for binding to various forms of each protein by surface plasmon resonance (SPR) to confirm restricted expression on toxic species. The seeding activity of the conformational peptide epitope scaffolds was tested in a thioflavin T (ThT) propagation assay by measuring the fibrillogenic aggregation of protein monomers with and without the addition of peptide epitope over time. Antibodies raised against predicted conformational epitopes of misfolded Abeta, Asyn and tau showed selective recognition of toxic species by SPR indicating that the epitopes are not exposed on normal, healthy forms of these proteins. The conformational cyclic peptide scaffolds, but not the linear versions of the same peptides, showed seeding activity in ThT propagation assays for all 3 proteins. Small misfolded regions (conformational epitopes) exposed on misfolded toxic proteins can, on their own, replicate the seeding activity of the full-length protein suggesting that they contribute to its prion-like pathogenicity. These results also indicate that these conformational epitopes represent a biologically relevant target for therapeutic antibodies.

Treating Iron Overload Disorders with a Novel Therapeutic Antibody Targeting TMPRSS6

Iron is an essential element for almost all living organisms as it participates in a wide variety of metabolic processes. Disorders of iron metabolism are among the most prevalent human diseases, ranging from anemia to hemochromatosis. Excessive iron accumulations in major organs of iron overload patients can lead to high mortality. Hepcidin, a HAMP-encoded liver hormone, is the master regulator of iron homeostasis. By binding to the sole iron exporter ferroportin and causing internalization and degradation of the complex, hepcidin inhibits cellular iron efflux, thereby lowers plasma iron levels. Inappropriately suppressed/low hepcidin production is central to iron overload. Transmembrane protease serine-6 (TMPRSS6), a type II transmembrane serine protease primarily expressed in liver, downregulates hepcidin expression through BMP-SMAD pathway. TMPRSS6 deficiencies have been shown to cause hepcidin overexpression in both TMPRSS6-mutant mice and in patients with iron-refractory iron deficiency anemia (IRIDA). Therefore, TMPRSS6 is a viable therapeutic target for iron overload disorders.Here we report the generation of an anti-TMPRSS6 antibody through a hybridoma campaign using a DNA-based immunization approach, followed by humanization and sequence optimization. Lead antibody, hzMWTx-003 selectively binds human TMPRSS6 with low nanomolar affinity (KD: 7.6nM), and is cross-reactive to rodent (mouse and rat) and monkey (cynomolgus and rhesus) TMPRSS6. Single-dose injection of hzMWTx-003 was able to significantly elevate serum hepcidin and liver HAMP RNA levels in wildtype mice, resulting in significantly reduced serum iron level. The Hbb th3/+ mouse model of β-thalassemia, like its human counterpart, is characterized by iron overload, ineffective erythropoiesis and splenomegaly. Treatment of Hbb th3/+mice with MWTx-003 effectively increased hepcidin expression at both protein and RNA levels, leading to significantly reduced serum iron and liver non-heme iron content. MWTx-003 also dramatically improved anemia and ineffective erythropoiesis, and alleviated splenomegaly in these mice.CMC development of hzMWTx-003 confirms outstanding biophysical properties. Preliminary studies in cynomolgus monkey using GLP-grade material demonstrated good pharmacokinetics of hzMWTx-003 and expected pharmacodynamic response where reduction of serum iron could be sustained for 21 days after single dose administration. A single dose toxicology study in cynomolgus monkey revealed no safety concerns, and no production of anti-idiotype antibodies was detected. In summary, anti-TMPRSS6 antibody MWTx-003 represents a promising therapy for iron overload disorders such as β-thalassemia, and potentially other diseases where iron restriction is beneficial. DisclosuresChen: Mabwell Therapeutics Inc: Current Employment. Wang: Mabwell Therapeutics Inc: Current Employment. Zheng: Mabwell (Shanghai) Bioscience Co. Ltd: Current Employment. Huang: Mabwell Therapeutics Inc: Current Employment. Mao: Mabwell (Shanghai) Bioscience Co. Ltd.: Current Employment. Ouyang: Mabwell (Shanghai) Bioscience Co. Ltd.: Current Employment. Du: Mabwell Therapeutics Inc: Current Employment.

Membrane fusion and immune evasion by the spike protein of SARS-CoV-2 Delta variant.

The Delta variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has outcompeted previously prevalent variants and become a dominant strain worldwide. We report the structure, function, and antigenicity of its full-length spike (S) trimer as well as those of the Gamma and Kappa variants, and compare their characteristics with the G614, Alpha, and Beta variants. Delta S can fuse membranes more efficiently at low levels of cellular receptor angiotensin converting enzyme 2 (ACE2), and its pseudotyped viruses infect target cells substantially faster than the other five variants, possibly accounting for its heightened transmissibility. Each variant shows different rearrangement of the antigenic surface of the amino-terminal domain of the S protein but only makes produces changes in the receptor binding domain (RBD), making the RBD a better target for therapeutic antibodies.

Cryo-Electron Microscopy Structure and Interactions of the Human Cytomegalovirus gHgLgO Trimer with Platelet-Derived Growth Factor Receptor Alpha.

ABSTRACTHuman cytomegalovirus (HCMV) is a herpesvirus that produces disease in transplant patients and newborn children. Entry of HCMV into cells relies on gH/gL trimer (gHgLgO) and pentamer (gHgLUL128–131) complexes that bind cellular receptors. Here, we studied the structure and interactions of the HCMV trimer, formed by AD169 strain gH and gL and TR strain gO proteins, with the human platelet-derived growth factor receptor alpha (PDGFRα). Three trimer surfaces make extensive contacts with three PDGFRα N-terminal domains, causing PDGFRα to wrap around gO in a structure similar to a human hand, explaining the high-affinity interaction. gO is among the least conserved HCMV proteins, with 8 distinct genotypes. We observed high conservation of residues mediating gO-gL interactions but more extensive gO variability in the PDGFRα interface. Comparisons between our trimer structure and a previously determined structure composed of different subunit genotypes indicate that gO variability is accommodated by adjustments in the gO-PDGFRα interface. We identified two loops within gO that were disordered and apparently glycosylated, which could be deleted without disrupting PDGFRα binding. We also identified four gO residues that contact PDGFRα, which when mutated produced markedly reduced receptor binding. These residues fall within conserved contact sites of gO with PDGFRα and may represent key targets for anti-trimer neutralizing antibodies and HCMV vaccines. Finally, we observe that gO mutations distant from the gL interaction site impact trimer expression, suggesting that the intrinsic folding or stability of gO can impact the efficiency of trimer assembly.

Abstract 3193: Development and functional characterization of NC762, a novel therapeutic antibody targeting B7-H4, for the treatment of malignancies

Abstract Human B7 homolog 4 (B7-H4) is a transmembrane protein in the B7 family of molecules that is expressed on tumor cells in the tumor microenvironment (TME). High protein expression on tumors and low expression on healthy tissue makes B7-H4 an attractive molecule for direct targeting with low off-target toxicity. NC762 is a humanized immunoglobulin gamma 1, kappa (IgG1κ) monoclonal antibody specific for human B7-H4 that is being developed for the treatment of cancer and demonstrates an excellent safety profile in IND-enabling studies. The IgG1κ region of NC762 contains three-point mutations (S239D/A330L/I332E a.k.a. DLE) which enhances binding to CD16a (FcγRIIIa) in order to increase antibody-dependent cellular cytotoxicity (ADCC) activity. NC762 binds to human B7-H4 on SKBR3 cells, a breast cancer cell line that endogenously expresses B7-H4 and induces in vitro ADCC activity. Despite the high homology, NC762 does not cross-react with rodent B7-H4, therefore, in vivo testing was performed in a humanized xenograft murine model in NSG mice, where NC762 restricted tumor growth in a dose-dependent manner. Depleting human natural killer (NK) cells prior to tumor inoculation reduced anti-B7-H4 parent antibody activity, supporting a role for NK-cell mediated ADCC in tumor growth retardation. However, in the absence of human PBMCs, NC762 also achieved significant anti-tumor activity. Furthermore, a mutant of NC762 with a low FcγR binding IgG1 domain showed similar activity as the DLE IgG1, demonstrating an ADCC-independent mechanism of tumor growth restriction mediated by B7-H4 mAb treatment. Together, these results indicate that even with the ADCC-enhanced IgG1κ region, NC762 is able to mediate ADCC-independent anti-tumor activity for the eradication of B7-H4 expressing tumors; and is expected to provide benefit in multiple oncology indications. Citation Format: Kristina Archer, Justine Ceradoy, Tiffany Coupet, Jason Bosiacki, Chang Song, Ido Weiss, Sue Niu, Tete Obot, Jinglin Xu, Tom O'Neill, Alison Ferrell, Hasan Abukharma, Zac Cusumano, Dallas Flies, Sol Langermann, Linda N. Liu. Development and functional characterization of NC762, a novel therapeutic antibody targeting B7-H4, for the treatment of malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3193.

Use of Lateral Flow Immunoassay to Characterize SARS-CoV-2 RBD-Specific Antibodies and Their Ability to React with the UK, SA and BR P.1 Variant RBDs.

Identifying anti-spike antibodies that exhibit strong neutralizing activity against current dominant circulating variants, and antibodies that are escaped by these variants, has important implications in the development of therapeutic and diagnostic solutions and in improving understanding of the humoral response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We characterized seven anti-SARS-CoV-2 receptor binding domain (RBD) antibodies for binding activity, pairing capability, and neutralization activity to SARS-CoV-2 and three variant RBDs via lateral flow immunoassays. The results allowed us to group these antibodies into three distinct epitope bins. Our studies showed that two antibodies had broadly potent neutralizing activity against SARS-CoV-2 and these variant RBDs and that one antibody did not neutralize the South African (SA) and Brazilian P.1 (BR P.1) RBDs. The antibody escaped by the SA and BR P.1 RBDs retained binding activity to SA and BR P.1 RBDs but was unable to induce neutralization. We demonstrated that lateral flow immunoassay could be a rapid and effective tool for antibody characterization, including epitope classification and antibody neutralization kinetics. The potential contributions of the mutations (N501Y, E484K, and K417N/T) contained in these variants’ RBDs to the antibody pairing capability, neutralization activity, and therapeutic antibody targeting strategy are discussed.

More Is Always Better Than One: The N-Terminal Domain of the Spike Protein as Another Emerging Target for Hampering the SARS-CoV-2 Attachment to Host Cells.

Although the approved vaccines are proving to be of utmost importance in containing the Coronavirus disease 2019 (COVID-19) threat, they will hardly be resolutive as new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, a single-stranded RNA virus) variants might be insensitive to the immune response they induce. In this scenario, developing an effective therapy is still a dire need. Different targets for therapeutic antibodies and diagnostics have been identified, among which the SARS-CoV-2 spike (S) glycoprotein, particularly its receptor-binding domain, has been defined as crucial. In this context, we aim to focus attention also on the role played by the S N-terminal domain (S1-NTD) in the virus attachment, already recognized as a valuable target for neutralizing antibodies, in particular, building on a cavity mapping indicating the presence of two druggable pockets and on the recent literature hypothesizing the presence of a ganglioside-binding domain. In this perspective, we aim at proposing S1-NTD as a putative target for designing small molecules hopefully able to hamper the SARS-CoV-2 attachment to host cells.