Antigen Binding Research Articles

Abstract 6713: TICTE, A trispecific T-cell engager with immune checkpoint modulation for solid tumors

Abstract Background: Bispecific T-cell engager (BiTE) is a targeted cancer immunotherapy which bridges T-cells to cancer cells, leading to activation of T-cells and killing cancer cells. While BiTEs have shown promising therapeutic efficacy in the treatment of hematological malignancies, therapeutic benefit of T-cell engagers are still in exploration for the treatment of solid tumors. Upregulation of immune checkpoints presents one of the major resistant mechanisms of the BiTE therapy. Here, we report a Trispecific Immune Check-point T-Cell Engager (TICTE) platform that targets both CD3 and PD-L1 simultaneously, which activates the T-cells as well as modulates the immune checkpoint blockade through the PD/PD-L1 axis, respectively. Our in vitro and in vivo studies demonstrate that the TICTEs induce dramatic and superior antitumor activity compared to its counterpart BiTE alone and the BiTE with anti-PD-L1 combination. These studies suggest that the TICTE (CD3xTAAxPD-L1), a single-agent with dual function of T-cell activation and immune checkpoint modulation, may provide an efficacious therapy to patients with solid tumors. Methods: Various TICTEs and BiTEs formats using the human IgG like architecture in three different TAA examples were generated. Their biophysical and biological activities were characterized. The cell binding activity and antigen density of cell lines were determined using flow cytometry. TDCC activity was measured using xCELLigence RTCA eSight system. In vitro efficacy was evaluated with multiple cancer cell lines and toxicity was evaluated with normal cell lines. The humanized xenograft models were utilized to investigate the TICTEs efficacy in vivo. Results: All TICTEs adopted their intended forms and showed robust biophysical properties. The TICTEs demonstrated the blockade activity of PD1/PD-L1 axis, as well preferentially targeted tumor cells expressed both TAAs and PD-L1. Large therapeutic windows were observed in three TAA (cMET, Her2 and Trop2) TICTEs. TICTEs showed a superior efficacy compared to counterpart BiTEs and combination of BiTE with a PD-L1 inhibitor in vitro and in vivo. Low cytokine release was observed compared to combination of BiTEs with a PD-L1 inhibitor, signifying the reduced risk of cytokine release syndrome (CRS) often associated with BiTE therapy. Conclusion: A single agent of the TICTE platform with unique biological property, superior efficacy and low cytokine release could represent an alternative combination immunotherapy for solid tumors. Citation Format: Xiufeng Wu, Xiaoshan Min, Yinan Wu, Lin Liu, Jing Zhou, Silvia Hudson, Shih-ping Chen, Jennifer Li, Will Draper, Subhadra Dash, Shidong Ma, Hang Chen, Zhulun Wang. TICTE, A trispecific T-cell engager with immune checkpoint modulation for solid tumors [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 6713.

Abstract 2720: Engineering sweeping antibodies for the clearance of tumor-derived, pro-tumorigenic cytokines

Abstract Soluble, tumor-derived, pro-tumorigenic (STP) cytokines have been shown to contribute to cancer cell proliferation and drug resistance. But therapeutic targeting of STP cytokines by monoclonal antibodies is limited by high concentrations and persistent production of antigen. We hypothesize that the ability of sweeping antibodies (swAbs) to actively clear soluble antigens will overcome these limitations. SwAbs differ from conventional antibodies via (1) pH-dependent binding of antigen, and (2) increased binding to the neonatal Fc receptor (FcRn). SwAbs facilitate clearance of soluble antigens by releasing antigen in the low pH environment of FcRn-expressing cells. SwAbs are then recycled via FcRn for repeated clearance of antigen.We are developing swAbs against four STP cytokines contributing to cancer cell proliferation, survival, migration or intra-tumoral angiogenesis: hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF), transforming growth factor-β (TGF-β) and interleukin 16 (IL-16). We selected four existing neutralizing antibodies against these cytokines with available crystal structures and generated a second antibody targeting interleukin 16 with high affinity (clone 3B6; KD = 13 nM) de novo using phage display. We are using bio-layer interferometry and custom recycling/clearance assays for antibody characterization and pre-clinical validation. To introduce pH dependency into the four antibodies with crystal structures, we performed targeted histidine mutagenesis of residues at the interface with the respective target antigens. For the de novo-generated interleukin-16 antibody, we performed an unbiased histidine scanning approach by mutating residues across all six complementarity-determining regions (CDRs), which resulted in slight increases in pH sensitivity. We then performed a second round of mutagenesis of the most pH-sensitive 3B6 variants by replacing additional residues considered developability liabilities with histidine residues. We found that this approach significantly increased expression and affinity at pH 7 of the resulting 3B6 variants but only modestly increased pH sensitivity. In contrast, replacing a single residue in the heavy CDR1 in clone 14.1, a pre-clinical anti-IL-16 antibody, resulted in substantially increased pH sensitivity (KD(pH=7) = 2 nM; KD(pH<6) = n.b.). We are currently performing pH-sensitivity screenings for the three additional STP-specific antibodies. Our findings indicate that the ability to introduce pH sensitivity is largely dependent on the parental antibody and that some antibodies may not be amenable to this process. In addition, we show that histidine mutagenesis can be an effective approach to enhance expressibility and binding, while also increasing pH sensitivity. This project will answer the question whether anti-STP cytokine swAbs are an effective approach to treat patients with cancer. Citation Format: Jillian M. Baker, Nevil J. Singh, Tim Luetkens. Engineering sweeping antibodies for the clearance of tumor-derived, pro-tumorigenic cytokines [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 2720.

Abstract 6705: A novel tri-specific T cell engager targeting the intracellular oncoprotein WT1

Abstract Background: Wilms' tumor gene 1 (WT1) is considered an oncogenic factor, with high expression observed in several hematological malignancies and solid tumors. However, its expression is rarely found in normal adult tissue. WT1 can be degraded by the proteasome, processed and presented on the cell surface as major histocompatibility complex (MHC) I epitopes and recognized by T cell receptors (TCR). Here, we described the development of WT1-TOPAbody, a novel tri-specific T cell engager (TCE), that activated T cells by both CD3 and 4-1BB signaling upon recognition of WT1 in the context of HLA-A02, leading to superior anti-tumor efficacy. Materials and Methods: WT1-TOPAbody was evaluated for its antigen binding activity and target specificity by a series protein/peptide and cell-based assays. In vitro cytotoxicity and T cell activation mediated by WT1-TOPAbody was further assessed in a panel of WT1+ tumor cell lines in coculture with effector cells. Anti-tumor activity was investigated in a humanized syngeneic mice model bearing WT1/HLA-A02 expressing tumors. Safety assessment including cytokine release assay (CRA) and preliminary CMC developability was also performed. Results: WT1-TOPAbody exhibited superior binding affinity to the WT1/HLA-A02 complex while displaying lower binding to off-target peptides and CD34+ HSC from healthy donor than clinical benchmark WT1-CD3 bispecific antibody, RG-6007. WT1-TOPAbody effectively induced tumor lysis in multiple WT1+ tumors including leukemia, ovarian, breast, and colon cancer cells. Moreover, serial killing of tumor cells were observed in WT1-TOPAbody treated T cells, accompanied by lower exhaustion markers expressed, suggesting a prolonged anti-tumor inhibition effect of WT1-TOPAbody. In a humanized CD3e/4-1BB/HLA-A2.1 mouse model, WT1-TOPAbody significantly inhibited tumor growth in a dose-dependent manner and the efficacy was superior than that of the benchmark. Additionally, IL-6 release was minimal in PBMC upon treatment of the antibody, indicating a reduced risk of inducing cytokine release syndrome (CRS). Drug developability assessment indicated that the leading WT1-TOPAbody was a reasonably developable molecule to be taken forward. Conclusion: WT1-TOPAbody is a differentiated WT1/HLA-A02 targeted T cell engagers that displayed potent and durable anti-tumor activity. These results collectively support the potential of WT1-TOPAbody as a novel therapeutic agent against WT1/HLA-A02+ cancers and warrant its further development. Citation Format: Shan Gao, Liu Yang, Jun Du, Wenqing Jiang, Lei Fang. A novel tri-specific T cell engager targeting the intracellular oncoprotein WT1 [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 6705.

Abstract 5811: Ultralong CDR3 engineered interleukin-15 antibody fusion for T and NK cell expansion

Abstract Interleukin (IL)-15 is a promising immunotherapeutic cytokine for cancer treatment because it can stimulate the proliferation and cytotoxicity of CD8+ T lymphocytes and nature killer (NK) cells, similar to the action of IL-2, which has been used to treat metastatic melanoma and renal cancer. IL-15 may have improved pharmacologic properties over IL-2 because it doesn’t cause vascular leak syndrome or stimulate regulatory T cells. However, IL-15 is difficult to express as a stable soluble protein and has a short half-life in vitro and in vivo. To solve the problem, we designed an IL-15 ultralong CDR3 humanized bovine antibody fusion. Bovine ultralong CDR3 antibodies have a unique “stalk and knob” structure in which two antiparallel β-strands support a disulfide bonded knob protruding out of the antibody surface and forms a mini antigen binding domain. By replacing the knob domain with IL-15, we have created a chimeric CDR3-IL-15 IgG which functions as IL-15 in vitro and in vivo but can be easily produced in mammalian cells with increased stability. Thus, the CDR3 can stabilize IL-15 in the absence of its high affinity receptor α (Rα) chain. Furthermore, as IL-15 utilizes Rα for increased trans signaling to the receptor β and γ subunits, one variant candidate (CDR3-IL-15_Rα) was produced by co-expressing Rα sushi domain with the chimeric IgG. Both constructs have been demonstrated to be highly active in stimulating proliferation of NK cells and CD8+ T cells in vitro as well as in stimulating proliferation of NK cells and CD8+ T cells in rats and non-human primates (NHP). Although the CDR3-IL-15_Rα exhibited higher in vitro signaling activity than CDR3-IL-15, both were equally potent in stimulating the proliferation of NK cells and CD4+ and CD8+ T cells in NHP without any immunogenicity detected. Moreover, in vivo studies in NHP indicated that CDR3-IL-15 acted faster than CDR3-IL-15_Rα in stimulating the proliferation of these lymphocytes. CDR3-IL-15 is the first thermodynamically stabilized variant of IL-15 produced in the absence of its Rα chain, is highly active in vivo, and has multiple potential cancer applications as an T and NK cell stimulating agent. Citation Format: Ruiqi Huang, Duncan McGregor, Vaughn Smider. Ultralong CDR3 engineered interleukin-15 antibody fusion for T and NK cell expansion [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 5811.

Abstract 2124: Validation of the intelligent glycotransferase-dependent conjugation (iGDC) platform: A groundbreaking approach for next-generation HER2-targeting ADC GQ1012 with enhanced druggability, potency, and safety

Abstract Background: Antibody glycan remodeling has emerged as a promising site-specific conjugation technology to develop ADCs, while most reported cases suffer from complicated CMC process and scalability challenges. We report herein an innovative, streamlined one-enzyme, one-step glycan remodeling technology, i.e. intelligent Glycotransferase-Dependent Conjugation (iGDC), that enables the site-specific conjugation of various biologic modalities including monoclonal antibody, bispecific antibody and Fc fusion proteins. Employing immobilized enzymes and a continuous-flow process, iGDC efficiently tethers payloads to the N-297 glycan site without requiring antibody engineering. In contrast to alternative conjugation techniques, iGDC offers superior versatility, product quality, process efficiency, scalability, and cost-effectiveness. Validation of the iGDC platform is exemplified by GQ1012, a HER2-targeting ADC featuring the potent Topoisomerase I inhibitor, TopoIx. Preclinical studies demonstrated GQ1012's outstanding anti-tumor efficacy in diverse in vitro and in vivo models, displaying robust synergistic effects with anti-PD-1 therapy and excellent tolerability in pre-tox studies involving monkeys with no signs of lung diseases, surpassing those of Enhertu. Results: GQ1012, developed through iGDC, utilized a highly hydrophilic, stable branch linker to conjugate TopoIx to an anti-HER2 antibody, achieving high conjugation efficiency confirmed by DAR analysis. The ADC maintained comparable antigen binding affinity and internalization compared to the parental antibody, exhibiting potent cytotoxicity against HER2-positive cancer cells. Despite glycan remodeling with iGDC leading to the removal of ADCC function, GQ1012 demonstrated no off-target cytotoxicity in HER2-negative cells and displayed a robust bystander killing ability in co-culture assays. In various in vivo models, GQ1012 demonstrated similar or superior antitumor efficacy compared to Enhertu, showcasing strong synergy with anti-PD-1 therapy. Stability studies confirmed GQ1012 maintains a highly stable linker, minimizing DAR reduction. Preliminary toxicity studies in monkeys following repeated intravenous infusions of GQ1012 showcased excellent safety and pharmacokinetics at specified doses and the potential for an extended therapeutic window compared to Enhertu. Conclusion: The validation of the iGDC platform through GQ1012 highlights its adaptability and efficiency in producing highly homogeneous next-generation ADCs without requiring antibody engineering. GQ1012 presents promising potential as a next generation HER2 ADC with an expanded therapeutic window compared to Enhertu, supported by extensive in vitro, in vivo assessments, and preliminary toxicity studies. Citation Format: Meijun Xiong, Zengyan Mu, Meiling Xu, Chong Liu, Bo Dai, Junhao Wang, Xinju Gao, Lili Shi, Paul H. Song, Gang Qin. Validation of the intelligent glycotransferase-dependent conjugation (iGDC) platform: A groundbreaking approach for next-generation HER2-targeting ADC GQ1012 with enhanced druggability, potency, and safety [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 2124.

Abstract 6317: Developing a fully human heavy chain only Claudin-18.2-specific CAR-T cell therapy

Abstract Camelid VHH/nanobodies have been widely applied as the antigen binding domain of CAR-T cell therapies due to a smaller size and simpler structure compared to the traditionally used single chain variable fragment (scFv). Additionally, camelid VHH/nanobodies provide greater flexibility for dual-targeting CAR-T cell therapies. However, camelid VHH/nanobodies require laborious and costly humanization and still have a significant risk of inducing anti-drug antibodies when administered to patients. Transgenic mice exclusively harboring the most stable human VH genes (HCAb Harbour Mice®) provide one of the best solutions to get fully human heavy chain only antibodies (HCAbs). To efficiently identify lead HCAb VHs for Claudin-18.2-targeting CAR-T cells, we developed an innovative direct CAR-function based HCAb library screening platform. From Claudin-18.2-immunized HCAb Harbour Mice®, we constructed a total VH library in a CAR lentiviral vector that we developed in-house. After producing the lentiviral particle library, we transduced a Jurkat-NFAT-GFP reporter cell line and stimulated with Claudin-18.2 overexpression cell line. Subsequently, GFP positive reporter cells, representing Claudin-18.2-specific CARs, were isolated through FACS sorting, expanded, and further stimulated with Claudin-18.2-positive NUGC-4 tumor cells. Then, Next Generation Sequencing and abundance ranking was performed on VHs recovered from sorted CAR-reporter cells. Lead VH candidates were cloned into the CAR-P2A-RFP lentiviral vector, and many of these VH clones exhibited superior Claudin-18.2-specific functionality compared to a clinically-validated reference scFv in both reporter and primary CAR-T cells. Many lead VH clones also exhibited excellent developability as soluble HCAbs. These data suggest that this innovative method of combining our fully human HCAb and CAR-based library screening platform will provide new avenues for CAR-T cell therapies. Citation Format: Jason Noon, Yao Lu, Itishree Kaushik, Oyku Ay, Adam Luk, Bradley Delaney, David DeMeritt, Musheng Bao. Developing a fully human heavy chain only Claudin-18.2-specific CAR-T cell therapy [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 6317.

Abstract 6323: Preclinical evaluation of CB-012, an allogeneic anti-CLL-1 CAR-T cell therapy, that exhibits specific and potent toxicity in acute myeloid leukemia (AML) xenograft models

Abstract Background: CLL-1 is a compelling therapeutic target for AML as it is highly expressed on AML tumor cells and leukemic stem cells but is not expressed on hematopoietic stem cells. CB-012 was engineered with a next-generation Cas12a CRISPR hybrid RNA-DNA (chRDNA) genome-editing technology and leverages both checkpoint disruption and immune cloaking armoring strategies to potentially improve antitumor activity. The CB-012 anti-CLL-1 CAR was developed with a fully human scFv and the CD28 costimulatory domain and is currently in development for the treatment of relapsed or refractory AML (r/r AML). Here we describe preclinical studies that supported the CB-012 IND clearance by the FDA in October 2023. Methods: Cas12a chRDNA guides were implemented to generate five genome edits in the manufacture of CB-012. A multiplex genome-editing strategy was designed to enhance the antitumor activity of CB-012 through prevention of GvHD, PD-1 checkpoint disruption, and suppression of allograft rejection. In vitro and in vivo studies evaluated the specificity of antigen binding, antigen-dependent activity, and toxicologic potential. Results: CB-012 demonstrated potent antigen-dependent expansion and cytotoxic activity against CLL-1+ human AML cell lines and patient-derived cells in co-cultures. In AML xenograft models, a single dose of CB-012 CAR-T cells resulted in robust tumor control, leading to significant prolongation of survival. CB-012 co-culture with multiple CLL-1-negative cell types representing vital tissues demonstrated that the anti-CLL-1 scFv does not exhibit tissue cross-reactivity. In an unbiased cell surface protein microarray, the anti-CLL-1 scFv demonstrated highly specific interaction with human CLL-1, with no detectable non-specific interactions. CB-012 CAR-T cells exhibited limited tissue infiltration and expansion in treatment naïve, immunocompromised murine models. Conclusion: CB-012, the first allogeneic anti-CLL-1 CAR-T cell therapy using both checkpoint disruption and immune cloaking armoring, demonstrated specific and potent CLL-1-targeted cytolytic activity in vitro and in vivo. Specificity of the anti-CLL-1 scFv was demonstrated in an unbiased protein-binding study and no adverse safety signals were observed from CB-012 in murine toxicology models. These preclinical studies supported the IND clearance of CB-012, which is being evaluated in the AMpLify trial, a Phase 1, first-in-human clinical trial for patients with r/r AML (NCT06128044). Citation Format: Brian Francica, Elizabeth Garner, Sai Namburi, Cian Colgan, Tristan Fowler, Devin Mutha, Art Aviles, Morena Stanaway, Raymond Guo, Zili An, Erin Kelly, Emilie Degagne, George Kwong, Leslie Edwards, Emma Jakes, McKay Shaw, Benjamin Schilling, Jeremy Huynh, Ricky Luu, Max Sidorov, Rhonda Mousali, Mikk Otsmaa, Peter Lauer, Justin Skoble, Steven Kanner. Preclinical evaluation of CB-012, an allogeneic anti-CLL-1 CAR-T cell therapy, that exhibits specific and potent toxicity in acute myeloid leukemia (AML) xenograft models [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 6323.

Abstract 3107: SMASH: Single molecule antibody screening with high-throughput imaging system

Abstract Larger, more diverse antibody libraries are being screened in recent years. Despite enabling the high-throughput screening of extensive libraries, the process for identification and characterization of antibodies remains laborious and time-intensive. Here we report a platform that not only compiles hit finding and validation processes, but also provides high-resolution binding affinity as well as rank order among the library being screened. We streamlined the library construction and affinity screening via microscale transient expression in HEK293T cells with designed antibody sequence and direct quantification of antibody-antigen binding affinity which reduced the timeline from multiple weeks to a single week. We constructed the single-chain fragment antigen binding (scFab) libraries by replacing the duplex DNA fragment in CDR of interest while preserving the human framework of Fab. We have demonstrated that the SPID technique allows to detect antibody-antigen interactions from just dozens of pg of scFabs in total. This allowed us to bypass the conventional DNA cloning or even PCR amplification to achieve the minimum amount of DNA plasmids for expressing scFabs to be analyzed such as BLI and SPR. Therefore, we assembled the DNA plasmids through in vitro ligation with high efficiency and directly introduced it to HEK293T in 96-well microplate with microscale (200 ul) for transient transfection, which only takes three days for library generation. Next, we utilized SPID to quantify the number of single molecules between free and antigen-bound fractions of scFab, resulting in occupancy at the antibody-antigen binding equilibrium. This technique facilitated the determination of binding affinity (KD) for 200 antibody-antigen pairs within a 6-hour TAT encompassing both measurement and analysis. In total, we utilized 4,000 times less antibody for characterization while achieving enhanced sensitivity compared to both BLI and SPR methods. As a proof-of-concept, we generated a library consisting of 720 variants of Trastuzumab in scFab format to probe the landscape of CDRs affecting affinities against HER2 showing nM to low uM dynamic range of KD. Out of 720 analyzed variants, 5% were deleterious, 38% provided substantial changes, 40% showed little/no change, 17% enhanced affinity to HER2. To validate the robustness of the platform, we extensively expanded the library screening, assessing over 2,000 antibody variants for their affinity against more than three different therapeutic targets. To conclude, we demonstrated an efficient approach for monitoring changes in affinity resulting from single mutations in scFab. This rapid screening of site-saturated libraries would lead to a combinational variant library that our platform can screen. Ultimately, our platform aims to identify potential candidates for therapeutic antibody development throughput the phases of antibody discovery, maturation, and engineering. Citation Format: Jihye Jo, Changju Chun, Byeong-Kwon Sohn, Booyoung Yu, Jiyu Lee. SMASH: Single molecule antibody screening with high-throughput imaging system [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 3107.

Abstract 3131: Novel CDH17-targeting antibody-drug conjugate exhibits anti-tumor efficacy in preclinical models of gastrointestinal cancers

Abstract Antibody-drug conjugates (ADC) for oncology indications have been developed, however, only few of them are approved for the treatment of gastrointestinal (GI) cancers, which represent as a huge unmet medical need. As such, we developed a novel ADC of which monomethyl auristatin E (MMAE), an antimitotic agent, was conjugated to a cadherin-17 (CDH17)-targeting monoclonal antibody via protease-cleavable peptide valine-citrulline linker. CDH17 is highly restricted to the intestinal adherent junctions which is not accessible in healthy individuals. In contrast, it is overexpressed and becomes reachable in over half of the gastric and pancreatic cancer patients and in more than 95% of patients with colorectal cancer, making it a perfect target for ADC. Our ADC is designed to deliver MMAE specifically to CDH17-expressing tumors to exert the cytotoxic effect of MMAE on cancer cell, mitigating the undesired off-target cytotoxicity. LC/MS analysis revealed that MMAE was conjugated in a drug-to-antibody ratio of 4 with a yield of higher than 75%. ELISA showed that the binding of naked antibody and ADC to CDH17 was comparable (EC50, 0.17 nM & 0.3 nM, respectively), indicating the conjugation process did not affect antigen binding. This ADC also bound to different CDH17-expressing cell lines, including pancreatic AsPC1 and gastric AGS (EC50, 2.1 nM & 1.53 nM, respectively). By labelling the ADC with pH-sensitive fluorescent indicator, we illustrated that ADC internalization only occurred in CDH17+ but not CDH17- cells, suggesting the high specificity of the ADC. Similarly, the ADC showed selective killing on CDH17+ cells (EC50, 0.02-0.5 nM), and the data together proposed a positive correlation between ADC internalization level and its cytotoxicity (R2 = 0.4307). This supported the specificity and safety of the ADC in killing CDH17+ cancer cells only without affecting normal cells. Furthermore, a preliminary in-vivo study on subcutaneous AsPC1 xenograft model demonstrated that the ADC significantly suppressed tumor growth without causing any changes in body weight. Our ADC would potentially be a “First-in-class” ADC for the treatment of GI cancers with minimal adverse systemic toxicity. Further pharmacokinetics, safety, and other IND-enabling studies are underway. Citation Format: Po Yee Wong, Lin He, Kronos Chow, Kwan Wa Wong, Chui Yee O, Dennis Wong, John Moon Luk, Pui-Chi Lo, Kwong Fai Wong. Novel CDH17-targeting antibody-drug conjugate exhibits anti-tumor efficacy in preclinical models of gastrointestinal cancers [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 3131.

Abstract 2735: High affinity and potent anti-tumor efficacy of Nivo813, an anti-PD-1/ALK-1 bispecific antibody, in pre-clinical studies for solid tumors

Abstract Background: The activin-like kinase receptor 1 (ALK-1, encoded by ACVRL1) is a member of the transforming growth factor β (TGF-β) superfamily. Combination treatment using anti-PD-1/PD-L1 agents with anti-angiogenetic reagents might bring additional benefits, such as establishing a favorable TME leading to better responses towards immunotherapy. In the phase II clinical trial (NCT03893695) of combination therapy of ALK-1 (GT90001) and Nivolumab for the second line therapy in patients with metastatic hepatocellular carcinoma (“HCC”) in Taiwan, among the 20 evaluable patients, the overall response rate is 40%, and the side effects were well tolerated and manageable. Nowadays, the combination of GT90001 and nivolumab shows a remarkable long-tail effect, since 7 patients are still alive as of March 30, 2023, 6 of them had received no further systematic anti-tumor therapy after trial completion. Among them, 4 patients are still on progression free status. Our pre-clinical data demonstrated that Nivo813 has improved cell-binding potency and potent anti-tumor effects, lighting up its potential capacity as a therapeutic drug in the treatment of human cancers. Methods: The antigen binding activity of Nivo813 with PD-1 and ALK-1 were assessed by ELISA, Fortebio and flow cytometry. Endothelial cell tube formation assay was performed to identify the anti-angiogenesis function of Nivo813. The anti-tumor activity of Nivo813 was investigated in PBMC implanted with MDA-MB-231 breast cancer cells. Results:Nivo813 could specifically bind to human PD-1 and ALK-1 with high affinity. Intriguingly, Nivo813 was found to have much higher affinity (40-fold, nM) to cell surface PD-1 than that of nivolumab. Meanwhile, Nivo813 exhibited dose-dependent anti-angiogenesis activity in vitro. Nivo813 demonstrated greater anti-tumor efficacy compared to nivolumab in mice model. Conclusions: Nivo813, a dual-blocking anti-PD-1/ALK-1 bispecific antibody, shows improved binding potency to cell surface PD-1 and ALK-1 simultaneously, and displays dose-dependent anti-angiogenesis in vitro and great anti-tumor efficacy in vivo, supporting its clinical potentials for the treatment of human cancers. Citation Format: Qingqing Zhou, Rong Tang, Lanfang Zhuang, Jianyu Huang, Jiang Qian, Zhihua Ren, Youzhi Tong. High affinity and potent anti-tumor efficacy of Nivo813, an anti-PD-1/ALK-1 bispecific antibody, in pre-clinical studies for solid tumors [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 2735.

Analytical Insights into Protein-Alum Interactions and Their Impact on Conformational Epitope.

Several alum-adjuvanted vaccines have been licensed in the past 40 years. Despite its extensive and continuous use, the immune mechanism of action of alum adjuvants is not yet completely understood. Many different variables during the formulation process have been assessed as critical for alum-adjuvanted vaccines, although most of them are still not yet fully understood. The absence of a clear understanding of all the possible variables regulating the mechanism of action and the behavior that alum adjuvant imposes on the protein antigen may also be related to analytical challenges. For this reason, there is an urgent need for a fast and simple tool that is possible without a preliminary sample manipulation and is able to control the amount and the degree of antigen adsorption levels and their consistency across different production processes. This work attempts to develop new analytical tools with the aim of directly quantifying and assessing both the content and/or the purity of formulated alum-adsorbed antigens, without any preliminary sample manipulation (e.g., antigen desorption) being reported. In addition, the different confirmation/behavior in terms of the response to specific monoclonal antibodies in the presence of different ratios of alum-OH adsorbent antigens have been investigated. As a proxy to develop new analytical tools, three recombinant protein adsorbed models were used as follows: Neisseria adhesin A (NadA), Neisserial Heparin Binding Antigen (NHBA), and factor H binding protein (fHbp) as antigens, as well as aluminum hydroxide (AH) as an adjuvant system. The selection of the adjuvanted system model was dictated due to the substantial quantity of the literature regarding the protein structure and immunological activities, meaning that they are well characterized, including their adhesion rate to alum. In conclusion, three different analytical tools were explored to quantify, detect, and study the behavior of antigens in the presence of the alum adjuvant.

A gradient of the HD-Zip regulator Woolly regulates multicellular trichome morphogenesis in tomato.

Homeodomain (HD) proteins regulate embryogenesis in animals such as the fruit fly (Drosophila melanogaster), often in a concentration-dependent manner. HD-leucine zipper (Zip) IV family genes are unique to plants and often function in the L1 epidermal cell layer. However, our understanding of the roles of HD-Zip IV family genes in plant morphogenesis is limited. In this study, we investigated the morphogenesis of tomato (Solanum lycopersicum) multicellular trichomes, a type of micro-organ in plants. We found that a gradient of the HD-Zip IV regulator Woolly (Wo) coordinates spatially polarized cell division and cell expansion in multicellular trichomes. Moreover, we identified a TEOSINTE BRANCHED1, CYCLOIDEA, and PROLIFERATING CELL NUCLEAR ANTIGEN BINDING FACTOR (TCP) transcription factor-encoding gene, SlBRANCHED2a (SlBRC2a), as a key downstream target of Wo that regulates the transition from cell division to cell expansion. High levels of Wo promote cell division in apical trichome cells, whereas in basal trichome cells, Wo mediates a negative feedback loop with SlBRC2a that forces basal cells to enter endoreduplication. The restricted high and low activities of Wo pattern the morphogenesis of tomato multicellular trichomes. These findings provide insights into the functions of HD-Zip IV genes during plant morphogenesis.

MIB Guides: Measuring the Immunoreactivity of Radioimmunoconjugates

Immunoglobulins, both full-length antibodies and smaller antibody fragments, have long been regarded as effective platforms for diagnostic and therapeutic radiopharmaceuticals. The construction of radiolabeled immunoglobulins (i.e., radioimmunoconjugates) requires the manipulation of the biomolecule through the attachment of a radiohalogen or the bioconjugation of a chelator that is subsequently used to coordinate a radiometal. Both synthetic approaches have historically relied upon the stochastic modification of amino acids within the immunoglobulin, a process which poses a risk to the structural and functional integrity of the biomolecule itself. Not surprisingly, radioimmunoconjugates with impaired antigen binding capacity will inevitably exhibit suboptimal in vivo performance. As a result, the biological characterization of any newly synthesized radioimmunoconjugate must include an assessment of whether it has retained its ability to bind its antigen. Herein, we provide straightforward and concise protocols for three assays that can be used to determine the immunoreactivity of a radioimmunoconjugate: (1) a cell-based linear extrapolation assay; (2) a cell-based antigen saturation assay; and (3) a resin- or bead-based assay. In addition, we will provide a critical analysis of the relative merits of each assay, an examination of the inherent limitations of immunoreactivity assays in general, and a discussion of other approaches that may be used to interrogate the biological behavior of radioimmunoconjugates.

The Incredible Adventure of Omalizumab.

The basis of our current understanding of allergies begins with the discovery of IgE in the mid-1960s. The whole theory of the physiology and pathophysiology of allergic diseases, including rhinitis and asthma, dates from that period. Among the key regions of IgE identified were the FAB (fragment antigen binding) portion that has the ability to capture allergens, and the Cε3 domain, through which IgE binds to its membrane receptor. It was then postulated that blocking IgE at the level of the Cε3 domain would prevent it from binding to its receptor and thus set in motion the allergic cascade. This was the beginning of the development of omalizumab, a monoclonal antibody with an anti-IgE effect. In this article, we review the pathophysiology of allergic disease and trace the clinical development of omalizumab. We also review the benefits of omalizumab treatment that are apparently unrelated to allergies, such as its effect on immunity and bronchial remodeling.

Establishment of COS-BK cells persistently infected with archetype BK polyomavirus.

BK polyomavirus (BKPyV) was the first human polyomavirus to be isolated from an immunosuppressed kidney transplant recipient in 1971. BKPyV reactivation causes BKPyV-associated nephropathy and hemorrhagic cystitis. However, the mechanisms underlying BKPyV replication remain unclear. In the present study, we performed the long-term cultivation of COS-7 cells transfected with archetype KOM-5 DNA, which were designated as COS-BK cells. BKPyV derived from COS-BK cells was characterized by analyzing the amount of the virus based on hemagglutination, viral replication, and the production of viral protein 1 (VP1). Immunostaining showed that VP1-positive cells accounted for a small percentage of COS-BK cells. The nucleotide sequences encompassing the origin of the DNA replication of BKPyV derived from COS-BK cells were generated from KOM-5 by the deletion of an 8-bp sequence, which did not involve T antigen binding sites. BKPyV replicated most efficiently in COS-BK cells in DMEM containing 2% fetal bovine serum. These results indicate that COS-BK cells are a suitable culture system for studying the persistent infection of archetype BKPyV.

Circular RNA as a source of neoantigens for cancer vaccines

BackgroundThe effectiveness of somatic neoantigen-based immunotherapy is often hindered by the limited number of mutations in tumors with low to moderate mutation burden. Focusing on microsatellite-stable colorectal cancer (CRC), this...

A Novel Dual-Fc Bispecific Antibody with Enhanced Fc Effector Function.

Bispecific antibodies (BsAbs) are undergoing continued development for applications in oncology and autoimmune diseases. While increasing activity by having more than one targeting arm, most BsAb engineering employs single Fc engagement as monoclonal antibodies. Here, we designed a novel immunoglobulin gamma-1 (IgG1)-derived dual-Fc BsAb containing two Fc regions and two distinct asymmetric antigen binding arms comprising a Fab arm and another VHH domain. In conjunction with the knob-into-hole technology, dual-Fc BsAbs could be produced with a high yield and good stability. We explore how Fc engineering effects on dual-Fc constructs could boost the desired therapeutic efficacy. This new format enabled simultaneous bispecific binding to corresponding antigens. Furthermore, compared to the one-Fc control molecules, dual-Fc BsAbs were shown to increase the avidity-based binding to FcγRs to result in higher ADCC and ADCP activities by potent avidity via binding to two antigens and Fc receptors. Overall, this novel BsAb format with enhanced effector functionalities provides a new option for antibody-based immunotherapy.

Noninvasive Evaluation of Tumoral PD-L1 Using a Novel 99mTc-Labeled Nanobody Tracer with Rapid Renal Clearance.

The expression level of PD-L1 in tumor tissue is considered one of the effective biomarkers to guide PD-1/PD-L1 therapy. Quantifying whole-body PD-L1 expression by SPECT imaging may help in selecting patients that potentially respond to PD-1/PD-L1 therapy. Nanobody is the smallest antibody fragment with antigen-binding ability that is well suited for radionuclide imaging. Nevertheless, high retention of radioactivity in the kidney may limit its clinical translation. The present study aimed to screen, design, and prepare a nanobody-based SPECT probe with rapid renal clearance to evaluate the PD-L1 expression level in vivo noninvasively. A phage library was constructed by immunizing alpaca with recombinant human PD-L1 protein, and 17 anti-PD-L1 nanobodies were screened by the phage display technique. After sequence alignment and flow cytometry analysis, APN09 was selected as the candidate nanobody, and a GGGC chelator was attached to its C-terminus for 99mTc labeling to prepare a SPECT imaging probe. The affinity and specificity of 99mTc-APN09 were evaluated by protein and cell-binding experiments, and SPECT imaging and biodistribution were performed in a mouse model with bilateral transplantation of A549 and A549PD-L1 tumors. The ability of 99mTc-APN09 to quantify the PD-L1 expression level in vivo was validated in tumor models with different PD-L1 expression levels. 99mTc-APN09 had a radiochemical purity higher than 99% and a binding equilibrium dissociation constant of 21.44 ± 1.65 nM with hPD-L1, showing high affinity. SPECT imaging results showed that 99mTc-APN09 could efficiently detect PD-L1-positive tumors within 0.5 h, and the quantitative results of SPECT were well correlated with the expression level of PD-L1 in cell lines. SPECT imaging and biodistribution results also showed that 99mTc-APN09 was rapidly cleared from the kidney in 2 h postinjection. 99mTc-APN09 was a simple and stable tool for visualizing PD-L1 expression in the whole body. In addition, due to its significant reduction in renal retention, it has better prospects for clinical translation.

The Evolving Role of Dendritic Cells in Atherosclerosis.

Atherosclerosis, a major contributor to cardiovascular morbidity and mortality, is characterized by chronic inflammation of the arterial wall. This inflammatory process is initiated and maintained by both innate and adaptive immunity. Dendritic cells (DCs), which are antigen-presenting cells, play a crucial role in the development of atherosclerosis and consist of various subtypes with distinct functional abilities. Following the recognition and binding of antigens, DCs become potent activators of cellular responses, bridging the innate and adaptive immune systems. The modulation of specific DC subpopulations can have either pro-atherogenic or atheroprotective effects, highlighting the dual pro-inflammatory or tolerogenic roles of DCs. In this work, we provide a comprehensive overview of the evolving roles of DCs and their subtypes in the promotion or limitation of atherosclerosis development. Additionally, we explore antigen pulsing and pharmacological approaches to modulate the function of DCs in the context of atherosclerosis.

An Efficient Approach to the Accurate Prediction of Mutational Effects in Antigen Binding to the MHC1.

The major histocompatibility complex (MHC) can recognize and bind to external peptides to generate effective immune responses by presenting the peptides to T cells. Therefore, understanding the binding modes of peptide-MHC complexes (pMHC) and predicting the binding affinity of pMHCs play a crucial role in the rational design of peptide vaccines. In this study, we employed molecular dynamics (MD) simulations and free energy calculations with an Alanine Scanning with Generalized Born and Interaction Entropy (ASGBIE) method to investigate the protein-peptide interaction between HLA-A*02:01 and the G9209 peptide derived from the melanoma antigen gp100. The energy contribution of individual residue was calculated using alanine scanning, and hotspots on both the MHC and the peptides were identified. Our study shows that the pMHC binding is dominated by the van der Waals interactions. Furthermore, we optimized the ASGBIE method, achieving a Pearson correlation coefficient of 0.91 between predicted and experimental binding affinity for mutated antigens. This represents a significant improvement over the conventional MM/GBSA method, which yields a Pearson correlation coefficient of 0.22. The computational protocol developed in this study can be applied to the computational screening of antigens for the MHC1 as well as other protein-peptide binding systems.