Cell-engaging Bispecific Antibodies Research Articles

Management of Toxicities Associated with BCMA, GPRC5D, and FcRH5-Targeting Bispecific Antibodies in Multiple Myeloma.

The introduction of bispecific antibodies is one of the most significant recent advances in the treatment of relapsed/refractory multiple myeloma. This review will summarize the management of the toxicities associated with newly approved T cell-engaging bispecific antibodies and those which may be approved in the near future. Numerous trials have shown that bispecific antibodies can be both effective and tolerable when adverse events are properly managed. Cytokine release syndrome and increased infections are observed across all bispecific antibodies. Additional adverse events are target-specific, such as the more severe hypogammaglobulinemia and infections of BCMA bispecific antibodies and the dysgeusia, nail dystrophy, and skin changes of GPRC5D bispecific antibodies. Bispecific antibodies will surely become a mainstay of multiple myeloma therapy given their efficacy and accessibility. Their unique toxicities must be carefully considered and managed to ensure they are utilized safely.

T Cell-Engaging Bispecific Antibodies Targeting gp100 and PRAME: Expanding Application from Uveal Melanoma to Cutaneous Melanoma.

Uveal melanoma represents a rare and aggressive subtype of melanoma with limited treatment options and poor prognosis, especially in the metastatic setting. Tebentafusp, a bispecific fusion protein, offers a promising therapeutic approach by targeting gp100, an antigen highly expressed in uveal melanoma cells, and redirecting T cell-mediated cytotoxicity towards tumor cells. This review provides an overview of the preclinical and clinical data on tebentafusp in the management of metastatic uveal melanoma. We summarize the mechanism of action, clinical efficacy, safety profile, and ongoing research efforts surrounding this innovative immunotherapy. Preclinical studies have demonstrated the ability of tebentafusp to induce potent and specific anti-tumor immune responses against gp100-expressing uveal melanoma cells. Clinical trials have shown encouraging results, with tebentafusp exhibiting meaningful clinical activity in a subset of patients with metastatic uveal melanoma. Importantly, tebentafusp has also demonstrated a manageable safety profile. By specifically targeting tumor cells expressing gp100, tebentafusp offers a promising therapeutic avenue for individuals with metastatic uveal melanoma, meeting a significant clinical need in this context. Continued clinical trials will provide additional insights into the impact of tebentafusp on treatment-resistant metastatic cutaneous melanoma. Furthermore, we are exploring the potential of T cell engagers directed against the cancer testis antigen PRAME, which could have widespread utility in the treatment of cutaneous melanoma as well as other PRAME-expressing malignancies.

Quantitative systems pharmacology (QSP) model to predict combination activity of CD19-targeted antibody drug conjugate (loncastuximab tesirine) co-dosed with a CD20/CD3 T-cell bispecific (epcoritamab) in patients with diffuse large B-cell lymphoma (DLBCL).

e19059 Background: Loncastuximab tesirine-lpy (Lonca) is an antibody-drug conjugate comprising an anti-CD19 antibody conjugated to a pyrrolobenzodiazepine dimer cytotoxin. Epcoritamab-bysp (Epco) is a CD20×CD3 T cell-engaging bispecific antibody (bsAb) that redirects T-cells to eliminate malignant B-cells. Epco and Lonca target different B-cell surface antigens and combining both is expected to have additive or synergistic efficacy. Previously, a novel QSP model for Lonca was developed (Utsey K et al. Clin Pharmacol Drug Dev. 2023;12:123-125) and validated with clinical data from patients with R/R DLBCL (Caimi P et al. Blood. 2022;140:9548-9550). A combination QSP model for Lonca with Epco in R/R DLBCL was described to predict potential anti-tumor synergies in proposed clinical trials. Methods: The model reduced previous Lonca model complexity while maintaining core functionality and was combined with a published QSP model for T-cell bsAbs (Hosseini I et al. Npj Syst Bio Appl. 2020;6(1):1-11) to predict tumor dynamics after Lonca and/or Epco treatment. Assumptions included: 1) Lonca or Epco induce healthy and malignant B-cell killing; 2) tumor comprises malignant B- & T-cells; 3) tumor volume is based on malignant B-cell count; 4) T-cells can enter or leave tumor as with other tissues; 5) CD19-/low CD20+ B-cells account for tumor heterogeneity from cells insensitive to Lonca treatment. Results: Tumor growth inhibition (TGI) was predicted to plateau by Cycle (C) 2 with Epco monotherapy. By end of C3, however, predicted median normalized tumor volume reduction with co-dosing Lonca and Epco was approximately 1 log order greater than Epco alone. Maximum activity of Lonca and Epco therapy was not observed until C4 or later as depth of tumor regression increased with additional treatment cycles. Since patients with DLBCL may present with low T-cell counts (Hutchings et al. Lancet. 2021) the effect of T-cell count at baseline was evaluated. A 50% decrease at baseline from 2000-1000 T-cells/µL significantly reduced antitumor effect with Epco alone but made no difference with Lonca in combination. Conclusions: These results resemble predictions for Lonca in combination with other bsAbs (Lonca plus mosunetuzumab or glofitamab; abstract submitted to AACR 2024). By end of C3, Lonca plus Epco was predicted to promote substantially more TGI than Epco or Lonca alone. While increased doses of Lonca from 90-150 µg/kg in combination had limited additional therapeutic benefit, combination treatment beyond C3 was predicted to increase depth of tumor regression. Response from Lonca and Epco co-dosing was predicted to be less affected by suppressed T-cell counts at baseline compared to Epco alone; a feature that may enhance responsiveness when T-cell level is moderate.

Preclinical efficacy and pharmacokinetics of an RNA-encoded T cell-engaging bispecific antibody targeting human claudin 6.

We present the preclinical pharmacology of BNT142, a lipid nanoparticle (LNP)-formulated RNA (RNA-LNP) encoding a T cell-engaging bispecific antibody that monovalently binds the T cell marker CD3 and bivalently binds claudin 6 (CLDN6), an oncofetal antigen that is absent from normal adult tissue but expressed on various solid tumors. Upon BNT142 RNA-LNP delivery in cell culture, mice, and cynomolgus monkeys, RNA is translated, followed by self-assembly into and secretion of the functional bispecific antibody RiboMab02.1. In vitro, RiboMab02.1 mediated CLDN6 target cell-specific activation and proliferation of T cells, and potent target cell killing. In mice and cynomolgus monkeys, intravenously administered BNT142 RNA-LNP maintained therapeutic serum concentrations of the encoded antibody. Concentrations of RNA-encoded RiboMab02.1 were maintained longer in circulation in mice than concentrations of directly injected, sequence-identical protein. Weekly injections of mice with BNT142 RNA-LNP in the 0.1- to 1-μg dose range were sufficient to eliminate CLDN6-positive subcutaneous human xenograft tumors and increase survival over controls. Tumor regression was associated with an influx of T cells and depletion of CLDN6-positive cells. BNT142 induced only transient and low cytokine production in CLDN6-positive tumor-bearing mice humanized with peripheral blood mononuclear cells (PBMCs). No signs of adverse effects from BNT142 RNA-LNP administration were observed in mice or cynomolgus monkeys. On the basis of these and other findings, a phase 1/2 first-in-human clinical trial has been initiated to assess the safety and preliminary efficacy of BNT142 RNA-LNP in patients with CLDN6-positive advanced solid tumors (NCT05262530).

Heterodimerization of T cell engaging bispecific antibodies to enhance specificity against pancreatic ductal adenocarcinoma

BackgroundEGFR and/or HER2 expression in pancreatic cancers is correlated with poor prognoses. We generated homodimeric (EGFRxEGFR or HER2xHER2) and heterodimeric (EGFRxHER2) T cell-engaging bispecific antibodies (T-BsAbs) to direct polyclonal T cells to these antigens on pancreatic tumors.MethodsEGFR and HER2 T-BsAbs were constructed using the 2 + 2 IgG-[L]-scFv T-BsAbs format bearing two anti-CD3 scFvs attached to the light chains of an IgG to engage T cells while retaining bivalent binding to tumor antigens with both Fab arms. A Fab arm exchange strategy was used to generate EGFRxHER2 heterodimeric T-BsAb carrying one Fab specific for EGFR and one for HER2. EGFR and HER2 T-BsAbs were also heterodimerized with a CD33 control T-BsAb to generate ‘tumor-monovalent’ EGFRxCD33 and HER2xCD33 T-BsAbs. T-BsAb avidity for tumor cells was studied by flow cytometry, cytotoxicity by T-cell mediated 51Chromium release, and in vivo efficacy against cell line-derived xenografts (CDX) or patient-derived xenografts (PDX). Tumor infiltration by T cells transduced with luciferase reporter was quantified by bioluminescence.ResultsThe EGFRxEGFR, HER2xHER2, and EGFRxHER2 T-BsAbs demonstrated high avidity and T cell-mediated cytotoxicity against human pancreatic ductal adenocarcinoma (PDAC) cell lines in vitro with EC50s in the picomolar range (0.17pM to 18pM). They were highly efficient in driving human polyclonal T cells into subcutaneous PDAC xenografts and mediated potent T cell-mediated anti-tumor effects. Both EGFRxCD33 and HER2xCD33 tumor-monovalent T-BsAbs displayed substantially reduced avidity by SPR when compared to homodimeric EGFRxEGFR or HER2xHER2 T-BsAbs (∼150-fold and ∼6000-fold respectively), tumor binding by FACS (8.0-fold and 63.6-fold), and T-cell mediated cytotoxicity (7.7-fold and 47.2-fold), while showing no efficacy against CDX or PDX. However, if either EGFR or HER2 was removed from SW1990 by CRISPR-mediated knockout, the in vivo efficacy of heterodimeric EGFRxHER2 T-BsAb was lost.ConclusionEGFR and HER2 were useful targets for driving T cell infiltration and tumor ablation. Two arm Fab binding to either one or both targets was critical for robust anti-tumor effect in vivo. By engaging both targets, EGFRxHER2 heterodimeric T-BsAb exhibited potent anti-tumor effects if CDX or PDX were EGFR+HER2+ double-positive with the potential to spare single-positive normal tissue.

Optimizing the Design and Geometry of T Cell-Engaging Bispecific Antibodies Targeting CEA in Colorectal Cancer.

Metastatic colorectal cancer remains a leading cause of cancer-related deaths, with a 5-year survival rate of only 15%. T cell-engaging bispecific antibodies (TCBs) represent a class of biopharmaceuticals that redirect cytotoxic T cells toward tumor cells, thereby turning immunologically "cold" tumors into "hot" ones. The carcinoembryonic antigen (CEA) is an attractive tumor-associated antigen that is overexpressed in more than 98% of patients with colorectal cancer. In this study, we report the comparison of four different TCB formats employing the antibodies F4 (targeting human CEA) and 2C11 (targeting mouse CD3ε). These formats include both antibody fragment-based and IgG-based constructs, with either one or two binding specificities of the respective antibodies. The 2 + 1 arrangement, using an anti-CEA single-chain diabody fused to an anti-CD3 single-chain variable fragment, emerged as the most potent design, showing tumor killing at subnanomolar concentrations across three different CEA+ cell lines. The in vitro activity was three times greater in C57BL/6 mouse colon adenocarcinoma cells (MC38) expressing high levels of CEA compared with those expressing low levels, highlighting the impact of CEA density in this assay. The optimal TCB candidate was tested in two different immunocompetent mouse models of colorectal cancer and showed tumor growth retardation. Ex vivo analysis of tumor infiltrates showed an increase in CD4+ and CD8+ T cells upon TCB treatment. This study suggests that bivalent tumor targeting, monovalent T-cell targeting, and a short spatial separation are promising characteristics for CEA-targeting TCBs.

Abstract 2374: Bispecific and trispecific GPRC5D antibodies with potent cell-killing activity against multiple myeloma

Abstract Background: GPRC5D is a G protein-coupled receptor that is expressed on multiple myeloma cells but absent from most healthy tissues except for hair follicles. It is an attractive target for anti-tumor modalities including T cell-engaging bispecific antibodies. Recent clinical data demonstrate that combination therapy of T cell-engaging molecules individually targeting GPRC5D and BCMA on tumor cells offers unprecedented therapeutic benefits in relapsed/refractory multiple myeloma patients. A trispecific antibody that simultaneously engages these molecules while activating T cells is expected to provide comparable and additional benefits as a monotherapy. Methods: Multipass membrane proteins are valuable therapeutic targets but are largely inaccessible for antibody discovery due to structural complexity and high conservation. We developed an antibody discovery platform (MPS) tailored for membrane proteins that utilizes advanced immunization techniques including DNA, mRNA, and Lipoparticles (virus-like particles) and evolutionarily divergent host species. From the parental antibodies isolated, we engineered panels of GPRC5DxCD3 bispecific and GPRC5DxBCMAxCD3 trispecific antibodies using multiple formats and CD3 arms that encompass different geometries and binding stoichiometries. GPRC5D multispecific antibodies were tested for target specificity using Integral Molecular’s Membrane Proteome Array (MPA), and epitope residues were defined using alanine scanning mutagenesis. Both bispecific and trispecific antibodies were tested for in vitro potency and cytokine release using MM.1R and RPMI 8226 multiple myeloma cell lines. In vivo efficacy for a subset of antibodies was determined using xenograft models in PBMC-engrafted mice. Results: We immunized chickens with GPRC5D to obtain high-titer immune responses and configured resulting antibodies as T cell-engaging bispecific molecules with a CD3 binding arm. A subset of GPRC5DxCD3 bispecific antibodies displayed potent T cell-mediated cytotoxicity with picomolar potency on multiple myeloma cell lines. Antibody specificity profiling showed high specificity binding, and epitope mapping helped to explain why only some GPRC5D antibodies were active as multispecific antibodies. Bispecific molecules were then re-engineered as trispecific antibodies with additional binding to BCMA, a well-validated multiple myeloma target. GPRC5DxBCMAxCD3 trispecifics showed improved cytotoxic activity against multiple myeloma cells. Both bispecific and trispecific antibodies demonstrated a large window between cell killing and cytokine release. We will present in vivo efficacy data for a panel of bi- and trispecific molecules against MM.1R xenografts in PBMC-engrafted mice. Citation Format: Hayley Roth, Daniel Rogers, Ileine Sanchez, Breanna Tyrell, Trevor Barnes, Ami Snyder, Nenna Nowgu, Kyle Doolan, Benjamin J. Doranz, Ross Chambers, Joseph B. Rucker. Bispecific and trispecific GPRC5D antibodies with potent cell-killing activity against multiple myeloma [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 2374.

Preclinical Characterization of the Anti-Leukemia Activity of the CD33/CD16/NKG2D Immune Modulating TriNKET ® BMS-986357 (CC-96191)

CD33 is widely expressed by myeloid cells and is a validated drug target in acute myeloid leukemia (AML), as shown by the benefit of some patients from the CD33 antibody-drug conjugate gemtuzumab ozogamicin (GO). However, GO is often ineffective and toxic, prompting interest in more potent CD33-directed therapies. Success of T cell-engaging bispecific antibodies in lymphoid malignancies has raised enthusiasm for similar agents targeting CD33, but toxicities from activated T cells cause significant challenges for their use and provide a strong rationale to explore drugs engaging natural killer (NK) cells. Here, we investigated BMS-986357, a TriNKET ® that activates NK cells via CD16 and NKG2D receptors while targeting CD33. This format was chosen because simultaneous engagement of multiple activating NK cell receptors yields greater cytotoxic activity against neoplastic cells than engagement via a single activating receptor. Surface plasmon resonance analyses showed BMS-986357 simultaneously binds CD33, NKG2D, and CD16a, and co-engagement of NKG2D and CD16a increases the avidity. In the presence of primary human NK cells from healthy donors or a human NK cell line, the TriNKET ® demonstrated broad cytolytic anti-leukemia activity in a strictly CD33-dependent manner using a panel of CD33-expressing or CD33-deficient/deleted acute leukemia cells. Consistent with this, removing the CD33 binding domain rendered BMS-986357 ineffective against CD33+ AML cells. Drug-induced cytotoxicity was greater with BMS-986357 than with monoclonal CD33 antibodies, including lintuzumab and an afucosylated antibody with enhanced NK function, demonstrating the benefit of the TriNKET ® format. Compared to BMS-986357, substantially less cytotoxicity was observed with an Fc-mutant variant of BMS-986357 that abrogates binding to CD16a or an NKG2D dead-arm TriNKET ®, and cytolytic effects were reduced with a CD16-deficient NK cell line vs. a CD16-expressing subline, indicating maximal efficacy of BMS-986357 required co-engagement of CD16a and NKG2D. Using sublines of OCI-AML3 and KG-1 cells (both cell lines with low endogenous CD33 expression) to overexpress wild-type CD33 at increasing levels, we found low abundance of CD33 curtailed BMS-986357-induced cytotoxicity. Flow cytometric binding studies identified BMS-986357 to recognize the membrane-distal V-set domain of CD33. Unlike GO, BMS-986357-mediated cytolysis was not affected by over-expression of ABC transporter proteins by AML cells. The potency but not maximal activity of BMS-986357 was reduced by super-physiologic concentrations of soluble CD33; in contrast, the soluble form of the NKG2D ligand MICA did not impact TriNKET ® activity. In the presence of CD33+ AML cells, BMS-986357 activated NK cells but not T cells from healthy donor peripheral blood mononuclear cells and produced similar levels of maximum cytolysis as a CD33/CD3 bispecific antibody. Despite this, BMS-986357 elicited 10 to >100-fold lower soluble cytokine levels including IFN-γ, TNF, IL-6, and GM-CSF than a CD33/CD3 bispecific antibody, suggesting BMS-986357 has the potential for CD33/CD3 bispecific-like efficacy without the associated risk of cytokine release syndrome. Finally, in bone marrow specimens from patients with AML, BMS-986357 killed AML cells but not normal monocytes, suggesting selectivity of drug-induced cytotoxicity toward neoplastic cells, consistent with the notion NK cells are capable to differentiate between healthy and leukemic CD33+ cells. This selectivity suggests BMS-986357 may produce less myelosuppressive toxicity than what has been observed with CD33 targeting antibody-drug conjugates. In summary, our findings demonstrate that BMS-986357 TriNKET ® has potent CD33-dependent cytolytic activity in vitro against human AML cells, supporting the drug's exploration in early phase clinical trials. One such trial (NCT04789655) has opened accrual for adults with relapsed/refractory AML.

Sequential T-Cell Engagement for Myeloma (“STEM”) Trial: A Phase 2 Study of Cevostamab Consolidation Following BCMA CAR T Cell Therapy

Background and significance: The BCMA-targeted CAR T products idecabtagene vicleucel (ide-cel) and ciltacabtagene autoleucel (cilta-cel) are currently approved for relapsed/refractory multiple myeloma (RRMM) patients with ≥4 prior lines of therapy, including an IMID, proteasome inhibitor, and CD38 antibody. However, despite unprecedented response rates, CAR T cells are not curative in these late-line patients, even for those in complete remission. Mechanisms of resistance may include lack of persistence or poor function of persisting CAR T cells, as well as BCMA-low or -negative residual tumor cells that serve as a reservoir for relapse. FcRH5 is another MM cell surface antigen, with expression independent of BCMA. Cevostamab is an FcRH5-targeted, T cell-engaging bispecific antibody (bsAb) with demonstrated activity in RRMM, including in patients with prior BCMA-directed therapies (Trudel et al, ASH 2021, #157). We hypothesize that consolidating BCMA CAR T cell therapy with a bsAb targeting a different antigen may re-invigorate persisting CAR+ T cells against residual BCMA+ tumor cells, while also activating endogenous T cells against FcRH5+, BCMA-low/negative tumor cells, ultimately improving rates of sustained minimal residual disease (MRD)-negativity and durability of response. Study design and methods: This is a single-institution, investigator-initiated study (NCT05801939) sponsored by the University of Pennsylvania, with funding support from Genentech. Targeted population are patients with RRMM who have received a commercially available CAR T cell product (ide-cel or cilta-cel) according to the FDA label, within the past 8 weeks, with stable disease or better. Major inclusion criteria include absolute neutrophil count ≥ 1, hemoglobin ≥ 7, platelets ≥ 50, and creatinine clearance ≥ 30 ml/min. Major exclusion criteria include prior cytokine release syndrome or ICANS ≥ grade 3, or any grade hemophagocytic lymphohistiocytosis (HLH) or Parkinsonism, or any active infection. The study schema is shown in Figure 1. Cevostamab is initiated 8-10 weeks after CAR T cell infusion. This timepoint was chosen to allow recovery from acute CAR T cell-related toxicities, but while CAR T cells may still be detectable in circulation. Cevostamab is given at a step-up dose of 3.6mg intravenously (IV) on Cycle 1, Day 1 (C1D1), followed by full dose of 160mg IV on C1D8. Subjects are hospitalized for 48 hours after each C1 dose to monitor for CRS and ICANS. They then continue cevostamab every 3 weeks for total of 8 cycles. If they are in an MRD-negative complete response (CR) after 8 cycles (Adaptive Clonoseq assay, at 10e-5 sensitivity), they stop therapy and are observed. If not, or if bone marrow results are indeterminate, they get another 8 cycles of cevostamab, then stop and are observed. The primary endpoint is frequency of MRD-negative CR at 12 months post-CAR T cell therapy. Assuming a roughly equal proportion of patients enrolling after ide-cel and cilta-cel, the null hypothesis is that the true MRD-negative CR rate at 12 months is 35%. Twenty-six evaluable subjects will be accrued in a single-stage design. The null hypothesis will be rejected if 14 or more subjects meet the primary endpoint. This design yields a one-sided type I error rate of 0.05 and power of 0.84 for an exact test when the true 12-month MRD-negative CR rate is 60%. Secondary endpoints include feasibility, safety/tolerability, and other efficacy measures (overall and CR rates, PFS, OS). Exploratory endpoints include 1) impact of cevostamab on pre- and post-therapy frequency and phenotype of both CAR+ and CAR-negative T cells in blood and marrow, assessed by multiparameter flow cytometry; 2) pre- and post-therapy expression of BCMA and FcRH5 on myeloma cells (when available), serum concentrations of soluble BCMA and FcRH5, and relationship of these factors to clinical outcome measures, and 3) pre- and post-therapy genotypic and phenotypic make-up of bone marrow microenvironment, assessed by single cell RNA sequencing (scRNAseq) and multiparameter flow cytometry, and relationship of these factors to clinical outcome measures. Conclusions: This phase 2 study is exploring the efficacy, safety, and feasibility of cevostamab consolidation following BCMA-directed CAR T cell therapy for RRMM, with the goal of sequential T cell engagement against 2 different antigens to eliminate residual disease. Accrual started in July 2023.

New Biological Therapies for Multiple Myeloma.

Multiple myeloma is a cancer of bone marrow plasma cells that represents approximately 10% of hematologic malignancies. Though it is typically incurable, a remarkable suite of new therapies developed over the last 25 years has enabled durable disease control in most patients. This article briefly introduces the clinical features of multiple myeloma and aspects of multiple myeloma biology that modern therapies exploit. Key current and emerging treatment modalities are then reviewed, including cereblon-modulating agents, proteasome inhibitors, monoclonal antibodies, other molecularly targeted therapies (selinexor, venetoclax), chimeric antigen receptor T cells, T cell-engaging bispecific antibodies, and antibody-drug conjugates. For each modality, mechanism of action and clinical considerations are discussed. These therapies are combined and sequenced in modern treatment pathways, discussed at the conclusion of the article, which have led to substantial improvements in outcomes for multiple myeloma patients in recent years.

Incorporation of a repeated polypeptide sequence in therapeutic antibodies as a universal masking procedure: A case study of T cell-engaging bispecific antibodies

Prodrug design is a promising approach for reducing the off-target effects of therapeutic antibodies, particularly bispecific antibodies (bsAbs) that recruit T cells for activation; this design uses masking sequences that inhibit antibody binding until they reach the tumor microenvironment, where they are removed. In this study, we propose PAS, a polypeptide sequence composed of repeated Pro, Ala, and Ser residues, as a universal masking sequence. PAS has no specificity, but can inhibit antibody binding through steric hindrance caused by its large fluid dynamic radius and disordered structure; additionally, its length can be adjusted. We fused PAS to the N-terminus of an anti-CD3 single-chain variable fragment (scFv) and a bsAb, that targets both the epidermal growth factor receptor and CD3, via a recognition sequence cleaved by cancer-related proteases. PAS integration inhibited anti-CD3 scFv binding with higher efficacy than the epitope sequence, and the extent of inhibition was proportional to the length of the PAS sequence. For masked bsAbs, T cell-binding ability, cancer growth inhibition effects, and T cell activation effects were also reduced depending on the length of PAS and were fully restored upon removing PAS sequences using protease. The masking procedure using PAS was successfully applied to another scFv. The provision to adjust the masking effects of PAS by tuning its length, makes PAS fusion a valuable tool for the universal design of prodrug antibodies.

Suppression of MUC1-Overexpressing Tumors by a Novel MUC1/CD3 Bispecific Antibody.

Mucin1 (MUC1) is abnormally glycosylated and overexpressed in a variety of epithelial cancers and plays a critical role in tumor progression. MUC1 has received remark attention as an oncogenic molecule and is considered a valuable tumor target for immunotherapy, while many monoclonal antibodies (mAbs) targeting MUC1-positive cancers in clinical studies lack satisfactory results. It would be highly desirable to develop an effective therapy against MUC1-expressing cancers. In this study, we constructed a novel T cell-engaging bispecific antibody (BsAb) targeting MUC1 and CD3 with the Fab-ScFv-IgG format. A high quality of MUC1-CD3 BsAb can be acquired through a standard method. Our study suggested that this BsAb could specifically bind to MUC1- and CD3-positive cells and efficiently enhance T cell activation, cytokine release, and cytotoxicity. Furthermore, our study demonstrated that this BsAb could potently redirect T cells to eliminate MUC1-expressing tumor cells in vitro and significantly suppress MUC1-positive tumor growth in a xenograft mouse model. Thus, T cell-engaging MUC1/CD3 BsAb could be an effective therapeutic approach to combat MUC1-positive tumors and our MUC1/CD3 BsAb could be a promising candidate in clinical applications for the treatment of MUC1-positive cancer patients.

Binding domain on CD22 molecules contributing to the biological activity of T cell-engaging bispecific antibodies

CD22, as the B-cell malignancies antigen, has been targeted for immunotherapies through CAR-T cells, antibody-drug conjugates (ADCs) and immunotoxins via interaction of antibodies with binding domains on the receptor. We hypothesized that avidity and binding domain of antibody to target cells may have significant impact on the biological function in tumor immunotherapy, and T cell-engaging bispecific antibody (TCB) targeting CD22 could be used in the therapy of hematologic malignancies. So, to address the question, we utilized the information of six previously reported CD22 mAbs to generate CD22-TCBs with different avidity to different domains on CD22 protein. We found that the avidity of CD22-TCBs to protein was not consistent with the avidity to target cells, indicating that TCBs had different binding mode to the protein and cells. In vitro results indicated that CD22-TCBs mediated cytotoxicity depended on the avidity of antibodies to target cells rather than to protein. Moreover, distal binding domain of the antigen contributed to the avidity and biological activity of IgG-[L]-scfv-like CD22-TCBs. The T cells' proliferation, activation, cytotoxicity as well as cytokine release were compared, and G5/44 BsAb was selected for further in vivo assessment in anti-tumor activity. In vivo results demonstrated that CD22-TCB (G5/44 BsAb) significantly inhibited the tumors growth in mice. All these data suggested that CD22-TCBs could be developed as a promising candidate for B-cell malignancies therapy through optimizing the design with avidity and binding domain to CD22 target in consideration.

The expanding success of T cell-engaging bispecific antibodies.

The expanding success of T cell-engaging bispecific antibodies.

Tracking Bispecific Antibody-Induced T Cell Trafficking Using Luciferase-Transduced Human T Cells.

T cell-engaging bispecific antibodies (T-BsAbs) are in various stages of preclinical development and clinical testing for solid tumors. Factors such as valency, spatial arrangement, interdomain distance, and Fc mutations affect the anti-tumor efficacy of these therapies, commonly by influencing the homing of T cells to tumors, which remains a major challenge. Here, we describe a method to transduce activated human T cells with luciferase, allowing in vivo tracking of T cells during T-BsAb therapy studies. The ability of T-BsAbs to redirect T cells to tumors can be quantitatively evaluated at multiple time points during treatment, allowing researchers to correlate the anti-tumor efficacy of T-BsAbs and other interventions with the persistence of T cells in tumors. This method alleviates the need to sacrifice animals during treatment to histologically assess T cell infiltration and can be repeated at multiple time points to determine the kinetics of T cell trafficking during and after treatment.

Identification of immunotherapy and radioimmunotherapy targets on desmoplastic small round cell tumors.

Development of successful antibody-based immunotherapeutic and radioimmunotherapeutic strategies rely on the identification of cell surface tumor-associated antigens (TAA) with restricted expression on normal tissues. Desmoplastic small round cell tumor (DSRCT) is a rare and generally neglected malignancy that primarily affects adolescent and young adult males. New therapies capable of treating disseminated disease are needed for DSRCT, which is often widespread at diagnosis. We used immunohistochemistry (IHC) on fresh frozen surgical specimens and patient-derived xenograft (PDX) tumors and flow cytometry on DSRCT cell lines to evaluate expression of TAAs in these tumors. In vitro cytotoxicity assays were used to evaluate the efficacy of T cell-engaging bispecific antibodies (T-BsAbs) directed at these targets. In vivo, we used an intraperitoneal xenograft mouse model of DSRCT to test T-BsAbs against several TAAs. In DSRCT specimens we found widespread expression of B7-H3, EGFR, GD2, HER2, mesothelin, and polysialic acid, clinical targets for which specific antibody therapeutics are available. The expression of B7-H3, EGFR, HER2, and mesothelin was confirmed on the cell surface of DSRCT cell lines. In vitro cytotoxicity assays confirmed the efficacy of T cell-engaging bispecific antibodies (T-BsAbs) directed at these targets against DSRCT cells. Remarkably, a HER2xCD3 T-BsAb was capable of completely shrinking established tumors in an intraperitoneal mouse model of DSRCT. We propose that these TAAs should be further investigated in preclinical models as targets for immunotherapy and radioimmunotherapy with the hope of providing a rationale to extend these therapies to patients with advanced DSRCT.

Abstract 6305: Bispecific claudin 18.2 and GPRC5D antibodies with potent cell-killing activity for cancer therapeutics

Abstract Tumor-associated antigens with little or no expression in healthy tissue are attractive targets for anti-tumor modalities including T cell-engaging bispecific antibodies. CLDN18.2 is a transmembrane adhesion protein undetectable in most healthy adult tissues but highly expressed in gastric, pancreatic, esophageal, and lung cancers. GPRC5D is a G protein-coupled receptor that is absent from most healthy tissues except for hair follicles but expressed on multiple myeloma cells. Both CLND18.2 and GPRC5D are novel oncology targets with no clinically approved therapies against them. Using our discovery platform tailored to complex transmembrane proteins, we have developed bispecific antibodies with the ability to potently kill CLDN18.2-positive or GPRC5D-positive cells. Multipass membrane proteins are valuable therapeutic targets in oncology and other disease areas but are largely inaccessible as antibody targets due to their poor expression, membrane-dependent structure, small extracellular regions, and poor immunogenicity due to sequence conservation. We developed an antibody discovery platform (MPS) that specifically addresses each of these challenges. This platform utilizes advanced immunization techniques including DNA, mRNA, and Lipoparticles (virus-like particles). It also employs chickens as an evolutionarily divergent host species for robust immune responses against conserved targets. Antibodies raised in chickens are directly humanized prior to isolation, reducing the need for downstream engineering. In two separate campaigns, we immunized chickens with CLDN18.2 and GPRC5D and obtained high-titer immune responses. We were successful in isolating high-affinity antibodies specific to each of these targets. Our CLDN18.2 antibodies showed specificity for their target and did not bind the closely related splice variant CLND18.1, which is highly expressed in healthy lung tissue. Additionally, the antibodies showed no binding to ~6,000 other proteins that were screened using a Membrane Proteome Array. A subset of antibodies from both discovery programs were configured as bispecific molecules using a CD3-targeting arm to bring tumor cells into close proximity with cytotoxic T cells that mediate cell killing. The panels of molecules encompassed multiple bispecific formats bearing different stoichiometries, geometries, and sizes to enable identification of lead molecules with favorable activities and safety profiles. Both CLDN18.2 and GPRC5D bispecifics showed potent T cell-mediated cytotoxicity with picomolar potency. They also showed good cytokine release and developability profiles. GPRC5D x CD3 and CLDN18.2 x CD3 bispecifics hold promise as potent and safe therapeutics for different cancer types. Citation Format: Ileine Sanchez, Hayley Roth, Brad Screnci, David Tucker, Nick Molino, Trevor Barnes, Paige Murphy, Kyle Guldner, Tim Phillips, Kristen Shema, Thomas Charpentier, Alyssa Cunningham, Janae Latta, Breanna Tyrell, Meghan Pitts, Carmen Navia, Charles Azuelos, Anna Lobley, Jawhara Karam, Valerie Fiers, Daniela Reyes, Kate Slovik, Alison Snyder, Marianne Assogba, Kai-Ti Chang, Riley Payne, Kyle Doolan, Ross Chambers, Joe Rucker, Benjamin Doranz. Bispecific claudin 18.2 and GPRC5D antibodies with potent cell-killing activity for cancer therapeutics. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6305.

Abstract C022: Heterodimeric bispecific antibodies for highly specific treatment of EGFR(+)HER2(+) pancreatic ductal adenocarcinoma

Abstract Background: EGFR and HER2 are highly expressed in many pancreatic cancers which strongly correlate with poorer prognoses. We tested homodimeric (EGFRxEGFR or HER2xHER2) and heterodimeric (EGFRxHER2) T cell-engaging bispecific antibodies (BsAbs) to direct polyclonal T cells to these antigens on pancreatic tumors. Methods: We used the 2+2 IgG(L)-scFv format to create BsAbs, previously shown to have exceptional anti-tumor properties compared to other structural platforms. These BsAbs utilize two anti-CD3 scFvs attached to the light chains of an IgG to engage T cells while retaining bivalent binding to tumor antigens with both Fab arms. Anti-EGFR was based on the Cetuximab and anti-HER2 on the Trastuzumab amino acid sequences. Using a ‘knob-into-hole’ strategy, we generated an EGFRxHER2 heterodimeric BsAb bearing one Fab specific for EGFR and one for HER2. T cells were tagged with luciferase for tracking by bioluminescence for in vivo trafficking studies. Results: The EGFRxEGFR, HER2xHER2, and EGFRxHER2 BsAbs demonstrate high avidity (KD: 2pM to 300 pM) and T cell-mediated cytotoxicity against several human pancreatic ductal adenocarcinoma (PDAC) cell lines in vitro with EC50s in the picomolar range (0.17pM to 18pM). They mediate potent T cell-mediated antitumor effects against subcutaneous PDAC xenografts and were highly efficient in driving human polyclonal T cells into tumors as measured by bioluminescence. To examine the importance of anti-tumor valency in antitumor effects, EGFR and HER2 BsAbs were heterodimerized with a CD33 control BsAb to generate EGFRxCD33 and HER2xCD33 BsAbs. Both EGFRxCD33 and HER2xCD33 BsAbs showed modest reductions in target avidity by surface plasmon resonance (2.7-fold and 12.6-fold, respectively), cell binding strength by FACS (8.0-fold and 63.6-fold) and cytotoxicity (7.7-fold and 47.2-fold) compared to their homodimeric counterparts and, remarkably, showed no therapeutic efficacy against SW1990 cell line-derived and patient-derived PDAC xenografts, correlating with reduced tumor-infiltrating bioluminescent T cells, when compared to EGFRxHER2 BsAb. When tested against SW1990 with CRISPR-mediated target KOs, only HER2xHER2 BsAb treatment could eliminate EGFR-KO tumors, while EGFRxEGFR and EGFRxHER2 BsAbs were ineffective. Conversely, in HER2-KO SW1990 tumors, while EGFRxEGFR BsAb demonstrated strong tumor control, HER2xHER2 and EGFRxHER2 BsAbs demonstrated only weak activity. Conclusion: EGFR and HER2 were useful targets for driving T cell infiltration and tumor ablation. HER2 was overall more effective as a target when compared to EGFR for pancreatic cancer in vivo. Bivalent Fab binding to tumor was critical for robust anti-tumor effect in vivo even when in vitro differences of monovalent BsAb were less obvious. EGFRxHER2 heterodimeric BsAb exhibited potent antitumor efficacy against EGFR(+)HER2(+) double positive PDAC xenografts, but not single-positive tumors, and could offer a strategy to spare healthy single-positive tissues to reduce ‘on target/off tumor’ side effects. Citation Format: Alan W. Long, Brian Santich, Hongfen Guo, Nai-Kong Cheung. Heterodimeric bispecific antibodies for highly specific treatment of EGFR(+)HER2(+) pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C022.

P389: BISPECIFIC ANTIBODIES ACTIVATE AUTOLOGOUS LEUKEMIA-REACTIVE T CELLS IN ACUTE MYELOID LEUKEMIA

Background: Acute myeloid leukemia (AML) is a highly immunosuppressive disease with a high risk of relapse. This makes the finding of effective immunotherapy-based treatments important, but also difficult. T cell-engaging bispecific antibodies (TCEs) are designed to bind to both T cells and target cells, activate the T cells and thus induce an immune response against the leukemia cells without employing the MHC-T cell receptor (TCR) interaction. Several therapies of this kind are under development for treatment of AML. Surprisingly, both in vitro and in vivo, a subset of these TCE immunocoached T cells (ICTs) can subsequently target autologous AML cells and mediate efficient TCR-MHC-dependent AML cell killing in the absence of the TCE. This points to that a) a portion of the T cells present in an AML are leukemia-reactive but have been immunosuppressed - a suppression that can be reversed by the addition of a TCE, b) that this anti-AML T cell reactivation may play an important part of the mechanism of action of AML-targeted TCEs and c) that by understanding this reactivation mechanism, we will be able to design improved AML immunotherapies in the future. Aims: To understand the mechanisms by which a TCE induces reactivation of leukemia-reactive T cells (LRTs) in AML. Methods: T cells in biobanked AML patient bone marrow samples were activated with either an anti-CD3 x anti-CD123 TCE or a conventional anti-CD3 antibody for 5 days before isolating the ICTs. ICT assay: ICTs were washed to remove the TCE, and isolated ICTs were co-cultured with additional autologous bone marrow cells at different E:T ratios. Killing efficiency and T cell expansion were determined over several days using flow cytometry. Trogocytosis assay: ICTs were co-cultured with stained additional autologous AML cells for 1 h and T cell populations of interest were isolated using FACS. T cell repertoires were analyzed by targeted RNAseq of the TCR. Results: ICTs generated with a TCE kill autologous AML cells efficiently without further addition of the TCE. Adding additional TCE at this stage also does not increase the AML killing efficiency of the ICTs. ICTs generated with an activating anti-CD3 antibody show a similar AML killing efficiency and a similar trogocytotic behavior as TCE ICTs. Most of the TCR clones present in the AML bone marrow pre-stimulation were also represented among the ICTs and trogocytotic ICTs (ICTs that are directly targeting the AML cells after either TCE or anti-CD3 stimulation; Figure 1), suggesting that the bulk of T cells in an AML bone marrow represent heterogeneous immunosuppressed LRTs which can be equally well reactivated by a TCE or an anti-CD3 antibody. Trogocytotic ICTs generated from both types of T cell activation have a similar TCR distribution. ICTs derived from the bone marrow target autologous AML cells more efficiently than ICTs from peripheral blood. Image:Summary/Conclusion: Similarities between TCE ICTs and CD3 ICTs in regards to TCR distributions and killing efficiencies suggest that the TCE reactivates leukemia-reactive T cells via a CD3-dependent mechanism rather than a more complex proximity mechanism. Our data further suggests that T cells in the AML bone marrow are highly heterogeneous and leukemia targeted to a very high degree. In summary, AML bone marrow ICTs are targeting and killing leukemic cells efficiently in a polyclonal fashion and our results highlight that boosting this mechanism can leverage the clinical impact of AML TCEs and be utilized in other novel AML immunotherapy approaches.

Abstract 2077: Preclinical characterization of a next-generation CD19/CD3-bispecific T cell engager with extended serum half-life and superior potency against CD19-low target cells

Abstract T cell therapies targeting the B cell antigen CD19 have profoundly changed the way we treat various B cell malignancies. Both the CD19-specific T cell-engaging bispecific antibody blinatumomab and various autologous CAR-T cell therapies have exhibited robust clinical activity in relapsed/refractory acute lymphocytic leukemia (ALL) and non-Hodgkin lymphoma (NHL). While CAR-T cell therapies show high complete response rates, bispecific antibodies have room for improvement. Both therapies, however, fail in patients where tumor cells escape selective pressure by expressing very low or undetectable levels of the CD19 antigen.We developed a novel CD19/CD3-bispecific antibody construct called CLN-978. Like blinatumomab, CLN-978 has tandemly arranged CD19- and CD3-specific single-chain Fv (scFv) fragments. Uniquely, a single-domain antibody specific for serum albumin was N-terminally fused to enable a prolonged serum half-life, eliminating the need for continuous IV infusion. CLN-978 is composed of novel humanized CD19-, CD3- and albumin-binding elements that are cross-reactive with non-human primate (NHP) orthologs and lacks a hexahistidine tag. It is produced at g/L levels in CHO cells and enables protein A affinity purification. CLN-978 has a 100-fold higher binding affinity for CD19 than blinatumomab. Side-by-side comparison with blinatumomab showed that the higher CD19 binding affinity translates into superior T cell-mediated cytotoxicity (TDCC) of CLN-978 with both target cell lines expressing high or very low levels of CD19. Superior efficacy was similarly observed in xenotransplant mouse tumor models. Preclinical studies in primates are in progress assessing safety, pharmacology, pharmacokinetics (PK) and pharmacodynamics (PD) of CLN-978 administered either through intravenous or subcutaneous delivery. CLN-978 has the potential to have superior TDCC against cells expressing very low levels of CD19 as are selected following treatment with CD19-directed therapies. This may translate into higher response rates and longer response duration in ALL and NHL patients expressing normal and very low levels of CD19 on malignant B cells. The cross-reactivity of CLN-978 to the NHP orthologs of CD19, CD3 and albumin enables assessment of depletion of normal B cells, strategies to mitigate cytokine release, PK and PD properties, and exploration of dosing routes. CLN-978 holds promise as a CD19-targeted therapeutic that can be easily and conveniently administered to patients with diverse B cell malignancies. Citation Format: Patrick A. Baeuerle, Naveen K. Mehta, Kristan Meetze, Bochong Li, Jennifer S. Michaelson. Preclinical characterization of a next-generation CD19/CD3-bispecific T cell engager with extended serum half-life and superior potency against CD19-low target cells [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 2077.