Native Antibody Research Articles

Comparative Characteristics of Immunochromatographic Test Systems for Tylosin Antibiotic in Meat Products.

Tylosin (TYL) is a macrolide antibiotic widely used in animal husbandry. Due to associated health risks, there is a demand for sensitive methods for mass screening of TYL in products of animal origin. This article describes the development of lateral flow immunoassays (LFIAs) for TYL detection using direct (anti-TYL antibodies conjugated with nanoparticles) and indirect antibody labeling (anti-species antibodies conjugated with nanoparticles and combined with native anti-TYL antibodies). The choice of LFIA conditions, such as concentrations of hapten-protein conjugates, specific antibodies, and gold nanoparticle (GNP) conjugates with antibodies, as well as incubation time of reagents and the concentration of detergent in the sample buffer, is presented. The achieved limits of TYL detection using LFIAs with indirect labeling were 0.8 ng/mL (visual) and 0.07 ng/mL (instrumental), compared to 4 ng/mL (visual) and 0.4 ng/mL (instrumental) for the case of direct labeling. The sensitivity of the LFIA using the indirect format was up to seven times higher, allowing the determination of the target analyte at low concentrations. TYL detection in ground meat using LFIA with indirect antibody labeling ranged from 76-119%.

Selection of antibody-binding covalent aptamers

Aptamers are oligonucleotides with antibody-like binding function, selected from large combinatorial libraries. In this study, we modified a DNA aptamer library with N-hydroxysuccinimide esters, enabling covalent conjugation with cognate proteins. We selected for the ability to bind to mouse monoclonal antibodies, resulting in the isolation of two distinct covalent binding motifs. The covalent aptamers are specific for the Fc region of mouse monoclonal IgG1 and are cross-reactive with mouse IgG2a and other IgGs. Investigation into the covalent conjugation of the aptamers revealed a dependence on micromolar concentrations of Cu2+ ions which can be explained by residual catalyst remaining after modification of the aptamer library. The aptamers were successfully used as adapters in the formation of antibody-oligonucleotide conjugates (AOCs) for use in detection of HIV protein p24 and super-resolution imaging of actin. This work introduces a new method for the site-specific modification of native monoclonal antibodies and may be useful in applications requiring AOCs or other antibody conjugates.

Biophysical cartography of the native and human-engineered antibody landscapes quantifies the plasticity of antibody developability

Designing effective monoclonal antibody (mAb) therapeutics faces a multi-parameter optimization challenge known as “developability”, which reflects an antibody’s ability to progress through development stages based on its physicochemical properties. While natural antibodies may provide valuable guidance for mAb selection, we lack a comprehensive understanding of natural developability parameter (DP) plasticity (redundancy, predictability, sensitivity) and how the DP landscapes of human-engineered and natural antibodies relate to one another. These gaps hinder fundamental developability profile cartography. To chart natural and engineered DP landscapes, we computed 40 sequence- and 46 structure-based DPs of over two million native and human-engineered single-chain antibody sequences. We find lower redundancy among structure-based compared to sequence-based DPs. Sequence DP sensitivity to single amino acid substitutions varied by antibody region and DP, and structure DP values varied across the conformational ensemble of antibody structures. We show that sequence DPs are more predictable than structure-based ones across different machine-learning tasks and embeddings, indicating a constrained sequence-based design space. Human-engineered antibodies localize within the developability and sequence landscapes of natural antibodies, suggesting that human-engineered antibodies explore mere subspaces of the natural one. Our work quantifies the plasticity of antibody developability, providing a fundamental resource for multi-parameter therapeutic mAb design.

First site-specific conjugation method for native goat IgG antibodies via glycan remodeling at the conserved Fc region.

Despite their triumph in treating human diseases, antibody therapies for animals have gained momentum more slowly. However, the first approvals of animal antibodies for osteoarthritic pain in cats and dogs may herald the dawn of a new era. For example, goats are vital to economies around the world for their milk, meat, and hide products. It is therefore imperative to develop therapies to safeguard goats-with antibodies at the forefront. Goat antibodies will be crucial in the development of therapeutic antibodies, for example, as tracers to study antibody distribution in vivo, reagents to develop other therapeutic antibodies, and therapeutic agents themselves (e.g., antibody-drug conjugates). Hamstringing this effort is a still-burgeoning understanding of goat antibodies and their derivatization. Historically, goat antibody conjugates were generated through stochastic chemical modifications, producing numerous attachment sites and modification ratios, thereby deleteriously impacting antigen binding. Site-specific methods exist but often require substantial engineering and have not been demonstrated with goat antibodies. Nevertheless, we present herein a novel method to site-specifically conjugate native goat antibodies: chemo-enzymatic remodeling of the native Fc N-glycan introduces a reactive azide handle, after which click chemistry with strained alkyne partners affords homogeneous conjugates labeled only on the Fc domain. This process is robust, and resulting conjugates retain their antigen binding and specificity. To our knowledge, our report is the first for site-specific conjugation of native goat antibodies. Furthermore, our approach should be applicable to other animal antibodies-even with limited structural information-with similar success.

Biospecific Chemistry for Covalent Linking of Biomacromolecules.

Interactions among biomacromolecules, predominantly noncovalent, underpin biological processes. However, recent advancements in biospecific chemistry have enabled the creation of specific covalent bonds between biomolecules, both in vitro and in vivo. This Review traces the evolution of biospecific chemistry in proteins, emphasizing the role of genetically encoded latent bioreactive amino acids. These amino acids react selectively with adjacent natural groups through proximity-enabled bioreactivity, enabling targeted covalent linkages. We explore various latent bioreactive amino acids designed to target different protein residues, ribonucleic acids, and carbohydrates. We then discuss how these novel covalent linkages can drive challenging protein properties and capture transient protein-protein and protein-RNA interactions in vivo. Additionally, we examine the application of covalent peptides as potential therapeutic agents and site-specific conjugates for native antibodies, highlighting their capacity to form stable linkages with target molecules. A significant focus is placed on proximity-enabled reactive therapeutics (PERx), a pioneering technology in covalent protein therapeutics. We detail its wide-ranging applications in immunotherapy, viral neutralization, and targeted radionuclide therapy. Finally, we present a perspective on the existing challenges within biospecific chemistry and discuss the potential avenues for future exploration and advancement in this rapidly evolving field.

Repurposing of therapeutic antibodies against dengue virus envelope protein receptor binding domain.

Dengue virus (DENV) is the leading cause of numerous deaths every year due to its high infectivity. In this study we have tried to target the DENV envelope protein receptor binding domain, the region crucial for binding to host receptors which leads to membrane fusion and entry of the viral genome into the human host cell. We have taken 13 known FDA approved antiviral therapeutic antibodies from therapeutic antibody database and tried to repurpose them against the DENV envelope protein. Based on the humanness analysis, 10 antibodies were selected against the DENV envelope protein. Computational affinity maturation of the 10 selected antibodies was performed to increase their binding affinity and specificity against the DENV envelope protein which ultimately led to 8 mutant antibodies having better binding affinity than the native ones. Molecular Dynamics (MD) simulation shows that, the stability of the complexes involving both the native and mutant antibodies were found to be the same although the binding energy between the protein and the respective antibodies was seen to improve upon computational affinity maturation. Contact analyses show similar robustness of the interaction for both the mutant and native antibodies during complex formation with the DENV envelope protein. This has led to the selection of total 18 antibodies including 10 natural and 8 affinity matured mutants which have a high probability of interacting with the DENV envelope protein. Finally, based on all these analyses along with heated MD simulation, Bamlanivimab, Etesivimab and Tixagevimab with a mutation of residue 100 of the heavy chain from serine to tyrosine were selected as prospective therapeutic antibodies to combat DENV infection. This study may open a new avenue in designing therapeutics to combat Dengue viral infection.

Antibody-Drug Conjugate Made of Zoledronic Acid and the Anti-CD30 Brentuximab-Vedotin Exert Anti-Lymphoma and Immunostimulating Effects.

Relevant advances have been made in the management of relapsed/refractory (r/r) Hodgkin Lymphomas (HL) with the use of the anti-CD30 antibody-drug conjugate (ADC) brentuximab-vedotin (Bre-Ved). Unfortunately, most patients eventually progress despite the excellent response rates and tolerability. In this report, we describe an ADC composed of the aminobisphosphonate zoledronic acid (ZA) conjugated to Bre-Ved by binding the free amino groups of this antibody with the phosphoric group of ZA. Liquid chromatography-mass spectrometry, inductively coupled plasma-mass spectrometry, and matrix-assisted laser desorption ionization-mass spectrometry analyses confirmed the covalent linkage between the antibody and ZA. The novel ADC has been tested for its reactivity with the HL/CD30+ lymphoblastoid cell lines (KMH2, L428, L540, HS445, and RPMI6666), showing a better titration than native Bre-Ved. Once the HL-cells are entered, the ADC co-localizes with the lysosomal LAMP1 in the intracellular vesicles. Also, this ADC exerted a stronger anti-proliferative and pro-apoptotic (about one log fold) effect on HL-cell proliferation compared to the native antibody Bre-Ved. Eventually, Bre-Ved-ZA ADC, in contrast with the native antibody, can trigger the proliferation and activation of cytolytic activity of effector-memory Vδ2 T-lymphocytes against HL-cell lines. These findings may support the potential use of this ADC in the management of r/r HL.

Sialic acids from the Group B Streptococcus (GBS) capsule dampen mast cell activation through Siglec-9

Abstract GBS is a leading cause of bacterial infection in newborns, adult diabetics, pregnant women, and the elderly. A key virulence factor of GBS is its surface capsular polysaccharide, which displays terminal sialic acids that suppress host innate immune responses by engaging host inhibitory receptors like Sialic acid-binding immunoglobin-like lectin- 9 (Siglec-9). We reported that human mast cells (MC) express Siglec-9 and that engaging it with native ligands or antibodies results in reduced mast cell activation in vitro. We hypothesized that capsular sialic acids engage Siglec-9 to impair MC ability to initiate the host response. Mice expressing human Siglec -7 and -9 were infected with WT GBS or a sialic acid deficient strain, ΔcpsK, and the ΔcpsK infected mice showed reduced bacterial burden and less dissemination. Using bone marrow-cultured MC from a transgenic mouse expressing Siglec-9, we confirmed that GBS interacts with MC Siglec-9, which inhibited the release of the pro-inflammatory cytokine IL-6. Challenge of primary human MC with WT, ΔcpsK, or ΔneuA, another sialic acid deficient GBS strain, showed that MC interact more with ΔcpsK and ΔneuA GBS, and that MC kill sialic acid deficient GBS. MC challenged with ΔcpsK or ΔneuA GBS also produce more IL-8 and undergo cell death more than WT infected MC. Together, this data shows that sialylated GBS capsule engages MC Siglec-9 to dampen activation, which reduces the immune response and benefits the pathogen.

Exploring Pre-Pandemic SARS-CoV-2-Specific B Cell Responses in the West African Population.

Abstract The emergence of the novel coronavirus, SARS-CoV-2, during the COVID-19 pandemic prompted investigations into pre-existing immunity in human populations. Despite being a new coronavirus, individuals had previous exposure to common seasonal human coronaviruses. In this study, we examined SARS-CoV-2-specific memory B cells in six pre-pandemic Lassa virus-infected patients from West Africa. By incorporating a SARS-CoV-2 Spike Antigen (WA-1 strain) into a broader antigen panel that included Lassa virus GPC and a control, we identified and sorted antigen-positive B cells. Further analysis revealed a distinct population of SARS-CoV-2-specific memory B cells. Native paired monoclonal antibody (mAb) sequences were recovered from 598 SARS-CoV-2 Spike-positive B cells, demonstrating a surprisingly high frequency of pre-existing SARS-CoV-2-specific B cells. Remarkably, Spike-specific mAbs were recovered from all six donors, each contributing to at least one expanded clonal lineage. Notably, most IgM antibodies belonged to the same lineages. These findings suggest a notable prevalence of pre-existing immunity to SARS-CoV-2 in pre-pandemic patients, potentially influencing susceptibility to the virus and contributing to adverse COVID-19 outcomes. This study provides insights for risk management and supports the development of universal coronavirus vaccines by highlighting the complex interplay between pre-existing immunity and susceptibility to SARS-CoV-2.

AJICAP-M: Traceless Affinity Peptide Mediated Conjugation Technology for Site-Selective Antibody-Drug Conjugate Synthesis.

A traceless site-selective conjugation method, "AJICAP-M", was developed for native antibodies at sites using Fc-affinity peptides, focusing on Lys248 or Lys288. It produces antibody-drug conjugates (ADCs) with consistent drug-to-antibody ratios, enhanced stability, and simplified manufacturing. Comparative in vivo assessment demonstrated AJICAP-M's superior stability over traditional ADCs. This technology has been successfully applied to continuous-flow manufacturing, marking the first achievement in site-selective ADC production. This manuscript outlines AJICAP-M's methodology and its effectiveness in ADC production.

EGFR-Targeted Antibody-Drug Conjugate to Different Aminobisphosphonates: Direct and Indirect Antitumor Effects on Colorectal Carcinoma Cells.

Antibody--drug conjugates (ADCs) are a promising delivery system that involves linking a monoclonal antibody (mAb) to a specific drug, such as a cytotoxic agent, to target tumor cells. This new class of antitumor therapy acts as a "biological missile" that can destroy tumor cells while increasing the therapeutic index and decreasing toxicity. One of the most critical factors in ADC design is selecting a target antigen that is highly expressed on the surface of cancer cells. In this study, we conjugated Cetuximab (Cet), a monoclonal antibody that targets the epidermal growth factor receptor (EGFR), to aminobisphosphonates (N-BPs) such as ibandronate (IBA) or risedronate (RIS) or zoledronate (ZA). Cetuximab is administered to patients with metastatic colorectal carcinoma (mCRC) with a wild-type (WT) EGFR transduction pathway. Also, it is well established that N-BPs can trigger the antitumor activity of Vδ2 T cells in both in vitro and in vivo experimental models. The resulting ADCs were added in co-culture to assess the effect on CRC cell line proliferation and sensitivity to Vδ2 T antitumor lymphocytes in comparison with the native antibody. These assays have been performed both in conventional and 3D spheroid cultures. We found that all three ADCs can increase the inhibitory effect on cell proliferation of the WT-EGFR cell line Caco-2 while only Cet-RIS and Cet-ZA can increase the cytotoxicity mediated by Vδ2 T cells against both WT and EGFR-mutated CRC cell lines (Caco-2, DLD-1, and HCT-116). Also, the ADCs can trigger the cell proliferation of Vδ2 T cells present in peripheral blood and tumor specimens. Our findings indicate that anti-EGFR antibodies bound to N-BPs can improve the antitumor effects of the native antibody possibly increasing the therapeutic effect.

Abstract 4077: T cell targeting with PD-1-selective immune cell engagers based on GlycoConnect™ (GC™-ICEs) show excellent efficacy and tolerability

Abstract Engagement of T cell cells to harness a patient’s immune system is a promising approach in immuno-oncology. An immunocytokine, i.e. a tumor-targeting antibody (fragment) genetically fused to an immunostimulatory cytokine, is specifically designed for this purpose. Fusion antibody-immunocytokines, based on molecular architectures generated by a variant of DNA recombinant technologies, have recently entered the clinic. Earlier we have demonstrated how GlycoConnect™, a site-specific conjugation technology anchoring on the native antibody glycan1, can be applied for attachment of various cytokines, including RLI or IL-15, without prior antibody engineering. The immunostimulatory activity of these GlycoConnect™ immune cell engagers (GC™-ICEs) can be modulated by tailoring linker design and payload stoichiometry. In this presentation, we demonstrate the GC™-ICE with either IL-15 or RLI can be applied to selective targeting of T cells, based on PD-1-selective binding and activation, using either protease-sensitive or non-cleavable linkers. We will show how such T cell targeting can be achieved leading to significant tumor volume reductions in syngeneic mouse models. Moreover, we have found that the GC-ICE™ can be applied without inducing systemic immune activation, thereby displaying a promising therapeutic index. In vitro and in vivo studies will be presented to showcase the biological activity of these GC™-ICEs in comparison to conventional immunocytokines obtained via genetic engineering.1Wijdeven et al., Enzymatic glycan remodeling-metal free click (GlycoConnect™) provides homogenous antibody-drug conjugates with improved stability and therapeutic index without sequence engineering. mAbs 2022, 14, DOI: 10.1080/19420862.2022.2078466. Citation Format: Remon van Geel, Mick Verhagen, Elias Post, Willem Vugs, Sorraya Popal, Sander van Berkel, Floris van Delft. T cell targeting with PD-1-selective immune cell engagers based on GlycoConnect™ (GC™-ICEs) show excellent efficacy and tolerability [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4077.

Abstract 3149: Development of a novel site-specific ADC glycan platform with potential for improved in vivo efficacy and stability of the ADC in animal studies

Abstract Antibody-drug conjugates (ADCs) represent a promising modality for delivering cytotoxic drugs to targeted tumor cells while avoiding off-tumor toxicities. Despite successes in the past 20 years, development of effective ADCs with broad therapeutic window remains challenging due to the complexity of conjugation technologies and the instability of the linkers. Most platforms currently in the market as well as under clinical development may face limitations ascribed to the heterogeneity of ADCs with various drug-to-antibody ratio (DAR). This likely resulted from random conjugation and poor overall biophysical characteristics caused by linker hydrophobicity. The limitations may impact the efficacy, safety, bioavailability, and the robustness of manufacturing process of these therapeutic agents. OBI developed a unique glycan ADC platform (GlycOBI) to enable a site-specific conjugation, which is in a 'Plug and Play' format and compatible with any antibodies, linkers, and payloads in various DAR. This is an efficient and scalable process to generate homogenous ADCs. This platform overcomes the limitations of traditional ADCs, resulting in the improvement of efficacy and stability. We developed a non-genetic, engineering-free approach to generate site-specific homogenous ADCs. This was achieved by utilizing OBI proprietary enzymatic technology (EndoSymeOBI), followed by the click chemistry to conjugate the hydrophilic linker-payload via the glycan site that naturally occurs on the antibody’s Fc region. The conjugation process avoids disrupting the antibody structure, ensuring the related ADC has similar biophysical characteristics compared to native antibody. Furthermore, OBI linker technology improves the conjugation efficiency of the payload, as well as reduces the aggregation propensity, and expands the half-life of the ADC products. Anti-TROP2 and anti-HER2 ADCs are developed based on OBI glycan ADC platform (GlycOBI) using a topoisomerase I inhibitor, exatecan, as the payload. Both ADCs demonstrated greater chemical stability in serum stability studies compared to competitor ADCs. Additionally, they showed broad activity against different cancer cell lines in vitro as well as in mouse xenograft models. The preclinical data presented here suggest that GlycOBI is an outstanding ADC platform to improve the performance of ADCs. Further investigations, including studies in the clinical settings, are warranted. Citation Format: Teng-Yi Huang, Yin-Cheng Hsieh, Ka-Shu Fung, Yu-Chao Huang, Chi-Sheng Shia, Ming-Feng Chiang, Nan-Hsuan Wang, Wan-Fen Li, Ming-Tain Lai. Development of a novel site-specific ADC glycan platform with potential for improved in vivo efficacy and stability of the ADC in animal studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3149.

Site-Specific Conjugation of Native Antibody: Transglutaminase-Mediated Modification of a Conserved Glutamine While Maintaining the Primary Sequence and Core Fc Glycan via Trimming with an Endoglycosidase.

A versatile chemo-enzymatic tool to site-specifically modify native (nonengineered) antibodies is using transglutaminase (TGase, E.C. 2.3.2.13). With various amines as cosubstrates, this enzyme converts the unsubstituted side chain amide of glutamine (Gln or Q) in peptides and proteins into substituted amides (i.e., conjugates). A pleasant surprise is that only a single conserved glutamine (Gln295) in the Fc region of IgG is modified by microbial TGase (mTGase, EC 2.3.2.13), thereby providing a highly specific and generally applicable conjugation method. However, prior to the transamidation (access to the glutamine residue by mTGase), the steric hindrance from the nearby conserved N-glycan (Asn297 in IgG1) must be reduced. In previous approaches, amidase (PNGase F, EC 3.5.1.52) was used to completely remove the N-glycan. However, PNGase F also converts a net neutral asparagine (Asn297) to a negatively charged aspartic acid (Asp297). This charge alteration may markedly change the structure, function, and immunogenicity of an IgG antibody. In contrast, in our new method presented herein, the N-glycan is trimmed by an endoglycosidase (EndoS2, EC 3.2.1.96), hence retaining both the core N-acetylglucosamine (GlcNAc) moiety and the neutral asparaginyl amide. The trimmed glycan also reduces or abolishes Fc receptor-mediated functions, which results in better imaging agents by decreasing nonspecific binding to other cells (e.g., immune cells). Moreover, the remaining core glycan allows further derivatization such as glycan remodeling and dual conjugation. Practical and robust, our method generates conjugates in near quantitative yields, and both enzymes are commercially available.

Chimeric antigens displaying GPR65 extracellular loops on a soluble scaffold enabled the discovery of antibodies, which recognized native receptor

ABSTRACT GPR65 is a proton-sensing G-protein coupled receptor associated with multiple immune-mediated inflammatory diseases, whose function is relatively poorly understood. With few reagents commercially available to probe the biology of receptor, generation of an anti-GPR65 monoclonal antibody was desired. Using soluble chimeric scaffolds, such as ApoE3, displaying the extracellular loops of GPR65, together with established phage display technology, native GPR65 loop-specific antibodies were identified. Phage-derived loop-binding antibodies recognized the wild-type native receptor to which they had not previously been exposed, generating confidence in the use of chimeric soluble proteins to act as efficient surrogates for membrane protein extracellular loop antigens. This technique provides promise for the rational design of chimeric antigens in facilitating the discovery of specific antibodies to GPCRs.

Transglutaminase-mediated proximity labeling of a specific Lys residue in a native IgG antibody.

The fusion protein of an engineered zymogen of microbial transglutaminase (EzMTG) with a protein G variant, EzMTG-pG, enabled the proximity-based, tag-free labeling of Lys65 in the heavy chain of a native IgG antibody (trastuzumab) with a Gln-donor peptidyl substrate functionalized with a fluorescent molecule.

New approach to generating of human monoclonal antibodies specific to the proteolytic domain of botulinum neurotoxin A.

Botulinum neurotoxins (BoNTs) cause botulism and are the most potent natural toxins known. Immunotherapy with neutralizing monoclonal antibodies (MAbs) is considered to be the most effective immediate response to BoNT exposure. Hybridoma technology remains the preferred method for producing MAbs with naturally paired immunoglobulin genes and with preserved innate functions of immune cells. The affinity-matured human antibody repertoire may be ideal as a source for antibody therapeutics against BoNTs. In an effort to develop novel BoNT type A (BoNT/A) immunotherapeutics, sorted by flow cytometry plasmablasts and activated memory B cells from a donor repeatedly injected with BoNT/A for aesthetic botulinum therapy could be used due to obtain hybridomas producing native antibodies. Plasmablasts and activated memory B-cells were isolated from whole blood collected 7 days after BoNT/A injection and sorted by flow cytometry. The sorted cells were then electrofused with the K6H6/B5 cell line, resulting in a producer of native human monoclonal antibodies (huMAbs). The 3 antibodies obtained were then purified by affinity chromatography, analyzed for binding by Western blot assay and neutralization by FRET assay. We have succeeded in creating 3 hybridomas that secrete huMAbs specific to native BoNT/A and the proteolytic domain (LC) of BoNT/A. The 1B9 antibody also directly inhibited BoNT/A catalytic activity in vitro. The use activated plasmablasts and memory B-cells isolated at the peak of the immune response (at day 7 of immunogenesis) that have not yet completed the terminal stage of differentiation but have undergone somatic hypermutation for hybridization allows us to obtain specific huMAbs even when the immune response of the donor is weak (with low levels of specific antibodies and specific B-cells in blood). A BoNT/A LC-specific antibody is capable of effectively inhibiting BoNT/A by mechanisms not previously associated with antibodies that neutralize BoNT. Antibodies specific to BoNT LC can be valuable components of a mixture of antibodies against BoNT exposure.

Infliximab aggregates produced in severe and mild elevated temperature stress conditions induce an extended specific CD4 T-cell response

Aggregation has been widely described as a factor contributing to therapeutic antibody immunogenicity. Although production of high-affinity anti-drug antibodies depends on the activation of CD4 T lymphocytes, little is known about the T-cell response induced by antibody aggregates, especially for aggregates produced in mild conditions resulting from minor handling errors of vials. Large insoluble infliximab (IFX) aggregates produced in severe elevated temperature stress conditions have been previously shown to induce human monocyte-derived dendritic cell (moDC) maturation. We here showed that large IFX aggregates recruit in vitro a significantly higher number of CD4 T-cells compared to native IFX. Moreover, a larger array of T-cell epitopes encompassing the entire variable regions was evidenced compared to the native antibody. We then compared the responses of moDCs to different types of aggregates generated by submitting IFX to mild conditions of various times of incubation at an elevated temperature. Decreasing stress duration reduced aggregate size and quantity, and subsequently altered moDC activation. Of importance, IFX aggregates generated in mild conditions and not altering moDC phenotype generated an in vitro T-cell response with a higher frequency of CD4 T cells compared to native IFX. Moreover, cross-reactivity studies of aggregate-specific T cells showed that some T cells could recognize both native and aggregated IFX, while others responded only to IFX aggregates. Taken together, our results suggest that aggregation of antibodies in mild elevated temperature stress conditions is sufficient to alter moDC phenotype in a dose-dependent manner and to increase T-cell response.

Abstract A149: Characterization of HER3 targeted radioligand therapy using molecular imaging

Abstract Background: Radioligand therapy (RLT) is an emerging treatment modality that has shown potential to improve survival in cancer patients that often have limited or non-effective therapeutic options. We previously demonstrated that anti-HER3 antibody radioconjugate (HER3 ARC) has antitumor efficacy against HER3 expressing tumor xenograft models. One important step in the early development of RLT is to understand the targeting properties and the distribution of the RLT in vivo. Non-invasive molecular imaging such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) offer unique opportunities to understand drug behavior in vivo, permitting real time drug targeting and distribution analysis. In this study, we assessed the targeting properties and distribution of our HER3 ARC in HER3 expressing preclinical xenograft tumor models using both SPECT and PET. Methods: HER3 monoclonal antibody was conjugated with p-SCN-Bn-deferoxamine (DFO) or p-SCN-Bn-DOTA (DOTA) then labeled with Zirconium-89 (89Zr) or Indium-111 (111In), respectively. Flow cytometry and gamma counting was used to characterize HER3 ARC biological activity in HER3-expressing tumor cell lines. Balb/c mice subcutaneously inoculated with HER3-expressing xenograft tumors (lung, ovarian and colorectal) were intravenously administered with 89Zr-DFO-HER3 or 111In-DOTA-HER3. PET or SPECT scans were acquired 72 and 120-144hrs post injection of the radiotracer. Separate cohorts of mice were simultaneously administered with 89Zr-DFO-HER3 or 111In-DOTA-HER3 and 20-fold excess of native HER3 antibody as control to block radiotracer binding. Tissue uptake was quantified by drawing 3D or 2D regions of interest (ROI) for PET or SPECT images, respectively. Results: HER3 ARC radiotracers were successfully prepared and demonstrated similar binding to HER3 expressing cells compared to native HER3 antibody. In tumor-bearing mice, 89Zr-DFO-HER3 and 111In-DOTA-HER3 specifically accumulated in HER3 expressing tumors and cleared throughout the reticuloendothelial system. High tumor uptake was observed 120hrs post radiotracer injection using both imaging modalities. In mice pre-treated with 20-fold excess of native antibody, tumor uptake was significantly lower, showing tumor binding specificity of ARC. PET and SPECT images showed similar tracer distribution profile in the HER3 tumors. As expected, radiotracer clearance organ signals were also visualized. Conclusions: In this study we show that PET or SPECT imaging using 89Zr or 111In, respectively, offers the potential to assess the distribution of HER3 targeted radioligand therapy during early stages of drug development. HER3 ARC showed highly specific HER3 tumor uptake that remained at least 120hrs post injection. Our findings warrant further investigation to support advancement of HER3 ARC as a therapeutic option. Citation Format: Sumit Mukherjee, Debbie Lewis, Jason Li, Le-Cun Xu, Amanda Chin, Mary Chen, Monideepa Roy, Patrik Brodin, William van der Touw, Helen Kotanides, Denis Beckford-Vera. Characterization of HER3 targeted radioligand therapy using molecular imaging [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A149.

Framework-Directed Amino-Acid Insertions Generated over 55-Fold Affinity-Matured Antibody Fragments That Enabled Sensitive Luminescent Immunoassays of Cortisol.

We generated three single-chain Fv fragments (scFvs) specific to cortisol according to our original affinity-maturation strategy and verified their utility in developing immunoassays. These scFv mutants (m-scFvs) had insertion of one, four, or six amino acid(s) in the framework region 1 of the VH-domain and showed >55-fold higher affinity (Ka, 2.0 - 2.2 × 1010 M-1) than the unmodified scFv (wt-scFv). Each m-scFv was fused with NanoLuc luciferase (NLuc) for the use in enzyme-linked immunosorbent assays (ELISAs). In these ELISA, the m-scFv-NLuc fusions were competitively reacted with immobilized cortisol residues and cortisol standards, and then the bound NLuc activity was monitored luminometrically. The luminescent ELISAs generated dose-response curves with extremely low midpoints (approx. 3 pg/assay) and were >150-fold more sensitive than the colorimetric ELISAs using wt-scFv and >8000-fold more sensitive than the ELISA using the parental native antibody. The luminescent ELISAs showed acceptable cross-reactivity patterns with related steroids, and the determination of control sera afforded cortisol levels in the reference range with satisfactory parallelism.