Trispecific Killer Engager Research Articles

Chondroitin sulfate proteoglycan 4: An attractive target for antibody-based immunotherapy.

Multifunctional molecules involved in tumor progression and metastasis have been identified as valuable targets for immunotherapy. Among these, chondroitin sulfate proteoglycan 4 (CSPG4), a significant tumor cell membrane-bound proteoglycan, has emerged as a promising target, especially in light of advances in chimeric antigen receptor (CAR) T-cell therapy. The profound bioactivity of CSPG4 and its role in pivotal processes such as tumor proliferation, migration, and neoangiogenesis underline its therapeutic potential. We reviewed the molecular intricacies of CSPG4, its functional attributes within tumor cells, and the latest clinical-translational advances targeting it. Strategies such as blocking monoclonal antibodies, conjugate therapies, bispecific antibodies, small-molecule inhibitors, CAR T-cell therapies, trispecific killer engagers, and ribonucleic acid vaccines against CSPG4 were assessed. CSPG4 overexpression in diverse tumors and its correlation with adverse prognostic outcomes emphasize its significance in cancer biology. These findings suggest that targeting CSPG4 offers a promising avenue for future cancer therapy, with potential synergistic effects when combined with existing treatments.

Tri-specific killer engager: unleashing multi-synergic power against cancer.

Cancer continues to be a global health concern, necessitating innovative solutions for treatment. Tri-specific killer engagers (TriKEs) have emerged as a promising class of immunotherapeutic agents, offering a multifaceted approach to cancer treatment. TriKEs simultaneously engage and activate natural killer (NK) cells while specifically targeting cancer cells, representing an outstanding advancement in immunotherapy. This review explores the generation and mechanisms of TriKEs, highlighting their advantages over other immunotherapies and discussing their potential impact on clinical trials and cancer treatment. TriKEs are composed of three distinct domains, primarily antibody-derived building blocks, linked together by short amino acid sequences. They incorporate critical elements, anti-cluster of differentiation 16 (CD16) and interleukin-15 (IL-15), which activate and enhance NK cell function, together with specific antibody to target each cancer. TriKEs exhibit remarkable potential in preclinical and early clinical studies across various cancer types, making them a versatile tool in cancer immunotherapy. Comparative analyses with other immunotherapies, such as chimeric antigen receptor-T (CAR-T) cell therapy, immune checkpoint inhibitors (ICIs), cytokine therapies, and monoclonal antibodies (mAbs), reveal the unique advantages of TriKEs. They offer a safer pathway for immunotherapy by targeting cancer cells without hyperactivating T cells, reducing off-target effects and complications. The future of TriKEs involves addressing challenges related to dosing, tumor-associated antigen (TAA) expression, and NK cell suppression. Researchers are exploring innovative dosing strategies, enhancing specificity through tumor-specific antigens (TSAs), and combining TriKEs with other therapies for increased efficacy.

Abstract 1241: Enhancing NK cell therapy for head and neck cancer within the solid tumor microenvironment using a B7H3-targeting tri-specific killer engager (TriKE)

Abstract With an annual incidence rate exceeding 660,000 cases, and a death toll surpassing 325,000 per year, head and neck cancer (HNC) ranks as the seventh most common cancer in the world. Surgery, radiation and chemotherapy are used to treat HNC patients with modest and variable clinical success. However, these treatments prove less effective for human papillomavirus negative (HPV-) HNC patients, a subset of HNC patients with markedly worse prognosis. While significant advancements have been made in cancer immunotherapy over the past decade, its success also remains elusive for HNC due to factors such as the hypoxic solid tumor microenvironment (TME). To address the critical need for an improved therapeutic intervention, we leveraged the ability of natural killer (NK) cells in killing cancer cells without prior sensitization by developing a novel tri-specific killer engager (TriKE) that can direct NK cell killing of tumor within the hypoxic solid TME. The TriKE is composed of three domains: a humanized nanobody arm binding the activating receptor CD16 on NK cells, an interleukin (IL)-15 moiety that can drive expansion of NK cells, and a nanobody arm binding B7H3, a protein which high expression can be negatively correlated with overall survival of HPV- HNC patients. B7H3 is a prime target candidate because it is highly expressed on HPV- HNC cells, but minimally expressed on healthy tissues. In vitro testing using HPV- HNC patient blood samples revealed that B7H3 TriKE enhances activation (measured by NK cell degranulation and interferon-gamma production) and expansion of NK cells from these patients at levels equivalent to those observed in healthy controls. Furthermore, B7H3 TriKE is efficacious in its ability to drive high NK cell cytotoxicity in both acute (<48-hours) and prolonged (7-days) hypoxic (1% oxygen) models of HNC. Under acute hypoxia, B7H3 TriKE induces significantly more killing of targets by NK cells compared to IL-15 treatment, where NK cell cytotoxicity is impaired. In addition, B7H3 TriKE can boost the killing efficacy of NK cells exposed to prolonged hypoxia, surpassing limitations seen with IL-15 treatment. These findings strongly suggest that the B7H3 TriKE can bypass hypoxic suppression of NK effector functions in the solid TME. In vivo studies using immunocompromised mice engrafted with HPV- HNC cells revealed that B7H3 TriKE treatment significantly extends the survival of mice, compared to IL-15 treatment. Moreover, NK cells persisted in the blood of B7H3 TriKE-treated mice 28 days post-NK cell injection, highlighting the promising clinical translation of this immunotherapy. More in-depth characterization of NK cells from HPV- HNC patients are underway but altogether, these robust pre-clinical data present a novel avenue for the management of HNC for these patients. We plan to translate results from these studies to clinical trials in fall 2024. Citation Format: Melissa Khaw, Nicholas A. Zorko, Carly Selleck, Laura Bendzick, Zachary Davis, Peter Hinderlie, Madison Shackelford, Ann Lu, James Lim, Naomi Fujioka, Margaret MacMillan, John Wagner, Martin Felices, Jeffrey S. Miller. Enhancing NK cell therapy for head and neck cancer within the solid tumor microenvironment using a B7H3-targeting tri-specific killer engager (TriKE) [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 1241.

Abstract 1240: Enhancing NK cell function in the ‘cold’ tumor microenvironment of prostate cancer with a novel tri-specific killer engager

Abstract Introduction: Natural killer (NK) cells are associated with good prognosis in patients with metastatic castration-resistant prostate cancer (mCRPC). However, NK cell function is hindered in the immunosuppressive and hypoxic tumor microenvironment (TME) of mCRPC. To improve NK cell-mediated responses against mCRPC, we designed a novel Tri-specific Killer Engager (TriKE®) that engages with NK cell activating receptor CD16, binds to prostate-specific membrane antigen (PSMA) that is highly and specifically expressed on mCRPC, and has an interleukin (IL)-15 moiety that is essential for NK cell survival, proliferation, and priming. Methods: PSMA TriKE was produced using the mammalian expression system and tested using healthy donor and prostate cancer patient-derived NK cells. Flow cytometry-based functional and dye dilution proliferation assays were used to compare activation and proliferation of NK cells treated with PSMA TriKE or IL-15. NK cell cytolytic capacity against C4-2 cells, a PSMA-expressing prostate cancer line, was measured using IncuCyte live cell imaging. In various assays, hypoxic (1% oxygen) culture condition and cytokine-induced myeloid-derived suppressor cells (MDSC) were incorporated to better examine PSMA TriKE function in the physiological setting of mCRPC. In vivo testing of the PSMA TriKE was performed using C4-2 xenograft model and expanded NK cells in NSG mice. Results: PSMA TriKE significantly enhanced expansion of peripheral blood NK cells derived from healthy donors up to 8-fold. Additionally, PSMA TriKE induced significantly higher NK cell degranulation and intracellular IFNγ and TNFα buildup, when compared to IL-15 treatment, after incubation with C4-2 cells. Responses of NK cells derived from prostate cancer patients were equivalent to healthy controls. Although NK cell activation was not observed against PSMA knockout (KO) C4-2, indicating specificity of PSMA TriKE treatment, bystander killing of PSMA-KO C4-2 was achieved with PSMA TriKE treatment when wildtype C4-2 cells were cocultured. This suggests potential PSMA TriKE benefit in controlling tumor antigen escape, through natural cytotoxicity once primed. In settings that mimic the TME of mCRPC, NK cells treated with PSMA TriKE in prolonged exposure to hypoxia showed retention of cytotoxicity against C4-2 while IL-15 treated NK cells showed greatly impaired cytotoxicity. Similarly, MDSC suppressed NK cell cytotoxicity in the presence of IL-15, but PSMA TriKE treatment abrogated MDSC-induced suppression. Finally, PSMA TriKE enhanced tumor control and improved survival of mice as compared to IL-15 and no treatment groups in vivo. Conclusion: PSMA TriKE demonstrates potential in overcoming suppression of NK cells in the TME of mCRPC and is a promising candidate for advanced prostate cancer therapy. Citation Format: Shee Kwan Phung, Yvette Soignier, Nicholas Zorko, Rhett L. Waller, Josh Walker, Trygve Nelson, Carly Selleck, Laura Bendzick, Philippa Kennedy, Jeffrey S. Miller, Martin Felices. Enhancing NK cell function in the ‘cold’ tumor microenvironment of prostate cancer with a novel tri-specific killer engager [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 1240.

Abstract P20: Anti-CD123 CAR NK cells and cam161533 Trispecific Killer Engager have synergistic activity against Acute Myeloid Leukemia

Abstract P20: Anti-CD123 CAR NK cells and cam161533 Trispecific Killer Engager have synergistic activity against Acute Myeloid Leukemia

Abstract B040: Trispecific killer engagers against IGF1R and fetal form of insulin receptor induce human natural killer cell mediated killing of hormone receptor positive breast cancer in vitro and in vivo

Abstract Patients with hormone receptor-positive (HR+) breast cancers frequently recur with metastatic disease 5-20 years after the initial diagnosis and completion of chemotherapy and prolonged treatment with hormonal therapy. Thus, patients with metastatic HR+ breast cancer need new therapeutic options. A potential mechanism of therapeutic resistance in HR+ patients is the presence of slow-growing, well-differentiated cancer cells that result in clinically detectable metastases after a prolonged latency. One way to eliminate these cancer cells is with immunotherapy (IT). Unfortunately HR+ breast cancers have not responded to current T-cell based IT. The objective of this study is to target HR+ breast cancers using a natural killer (NK) cell based approach that targets cell surface receptors in HR+ breast cancer. The type I IGF receptor (IGF1R) is expressed on HR+ breast cancers and its expression is tightly related to ER function. Endocrine therapy resistance is associated with increased expression of the A-isoform or fetal form of IR (IR-A) and depend on IR signaling. We hypothesized that a drug that would target NK cells to IGF1R or IR-A expressing HR+ cells will be effective in killing them. We generated IGF1R or IR-A specific Tri specific Killer Engagers (TriKE) that leverage expression of IGF1R and IR-A on HR+ cells to cause NK directed death. The IGF1R TriKE consists of humanized single domain antibody (VHH) sequence of a CD16 nanobody to engage and activate NK cells, a humanized VHH of a nanobody against IGF1R to target HR+ breast cancer cells, and an IL-15 molecule between them to drive NK cell expansion and survival. The IGF1R TriKE did not bind embryonal fibroblasts from IGF1R knock out mice (R- cells) but bound R-/IGF1R cells (R- cells engineered to express human IGF1R) and to IGF1R+ MCF-7 and T47D breast cancer cells indicating specific binding to IGF1R on cells. It did not cause downregulation of IGF1R levels in multiple HR+ breast cancer cells and did not inhibit signaling via IGF1R. It specifically induced NK cell degranulation, measured by surface CD107a expression and intracellular IFNγ, against IGF1R+ target breast cancer cells (MCF-7, T-47D, ZR-75-1) in a functional assay compared to the anti-IGF1R nanobody. It did not induce degranulation of NK cells against IGF1R negative cells suggesting that the functionality was specific for IGF1R expressing targets. The IGF1R TriKE enhanced cell killing of HR+ breast cancer cells as measured by cytotoxicity assays. IGF1R TriKE combined with human NK cells inhibited tumor growth of MCF-7 tumors in NSG mice compared to control groups. Human NK cells persisted in peripheral blood three weeks after final NK infusion based on flow cytometry assessment. The IR-A TriKE incorporated a novel engineered non-immunoglobulin IR-A specific peptide binder. Our preliminary data show that the IR-A TriKE degranulated NK cells against breast cancer cells overexpressing IR-A. These data indicate that this strategy could be an effective treatment for HR+ metastatic breast cancer and make them responsive to IT. Citation Format: Courtney Baar, Emily Chiu, Yvette Soignier, Behiye Kodal, Jeffrey S Miller, Martin Felices, Deepali Sachdev. Trispecific killer engagers against IGF1R and fetal form of insulin receptor induce human natural killer cell mediated killing of hormone receptor positive breast cancer in vitro and in vivo [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B040.

B7-H3 Inhibitors in Oncology Clinical Trials: A Review.

B7-H3 is a transmembrane receptor highly prevalent on malignant cells and plays an important role in adaptive immunity that is not fully elucidated. Targeted B7-H3 inhibitors, including antibody-drug conjugates, radioimmunotherapy, and monoclonal antibodies, are a new class of antineoplastic agents showing promising preliminary clinical efficacy, observed with several of these agents against multiple tumor types. Particularly promising treatments are enoblituzumab for prostate cancer, 131I-omburtamab for central nervous system malignancies, and HS-20093 for small-cell lung cancer but further studies are warranted. There are clinical trials on the horizon that have not yet enrolled patients examining chimeric antigen receptor T-cell therapies, bi- and tri-specific killer engagers, and dual-affinity retargeting proteins. These data will be telling of the efficacy of B7-H3 inhibitors in both hematologic and solid malignancies. This study aimed to compile available results of B7-H3 inhibitors in oncology clinical trials.

Effect of camelid B7-H3 tri-specific killer engagers on natural killer cells in patients with prostate cancer.

155 Background: Recombinant human (rh) IL-15, the homeostatic factor for natural killer (NK) cells, is being clinically developed, but it has little antitumor activity alone. B7H3 (CD276) is an immune checkpoint inhibitor that is associated with poorer prognosis and is highly-expressed on prostate cancer. NK cells can be given as allogeneic products and, unlike T cells, do not induce cytokine-release syndrome or neurotoxicity. Here we developed a B7H3 targeting Tri-Specific Killer Engager (TriKE) as a novel dual camelid (cam) TriKE containing WT IL-15 and two cam engagers targeting CD16 on NK cells and B7H3 on tumor targets, making NK cells antigen specific. We have previously demonstrated that NK cells infiltrate prostate cancer tumors. As proof of concept, a clinical trial of a CD33-targeted TriKE for AML (NCT03214666) induced endogenous NK cell expansion and activation in refractory AML patients. Methods: Prostate cancer cell lines or patient-derived xenografts (PDX) were incubated with healthy donor or prostate cancer patient NK cells with or without B7H3 TriKE. PDX were propagated in NSG mice and then homogenized for in vitro assays. NK cell function was measured by flow cytometry and IncuCyte live tumor imaging assays. Castration-sensitive and -resistant prostate cancer (CSPC and CRPC, respectively) patient or normal donor peripheral blood mononuclear cells (PBMC) were immunophenotyped using 42-marker NK specific or broad immune cytometry time-of-flight (CyToF) panels. Results: B7H3 TriKE resulted in a dose-dependent proliferation of NK cells, but not T cells. This was in marked contrast to rhIL-15, which stimulated both cell types. camB7H3 was broadly expressed on prostate, head and neck, ovarian and glioblastoma cancers as well as multiple myeloma. We observed a B7H3 TriKE dose-dependent increase in CD107a degranulation and inflammatory cytokines to all B7H3 positive targets that was highly specific, with no response seen with B7H3 negative hematologic targets and CRISPR KO controls. Compared to rhIL-15, B7H3 TriKE given at molar equivalent dosing induced B7H3+ target killing in in a dose-dependent manner above that seen with rhIL-15 induced natural cytotoxicity. Using CSPC and CRPC patient PBMC (n=11-15), we demonstrated that there is no significant loss in NK cell degranulation/interferon gamma production or target cytotoxicity compared to healthy age- and sex-matched donors when treated with B7H3 TriKE. CyToF analysis of CSPC and CRPC patient PBMC is ongoing. In vivo activity in xenogeneic models of human tumor is underway. Conclusions: B7H3 TriKE delivers an NK cell specific IL-15 signal to expand NK cells and is highly specific against B7H3+ prostate cancer cell lines and PDX. Clinical-grade B7H3 TriKE is undergoing validation and a Phase 1/2 clinical trial is planned to open in the 3rd Quarter of 2024 for CRPC patients progressing on one or more therapies the CRPC setting.

355 Unraveling and targeting the innate immune response in Multisystem Inflammatory Syndrome in Children (MIS-C)

OBJECTIVES/GOALS: The innate immune responses to Multisystem Inflammatory Syndrome in Children (MIS-C) are not fully known. Using samples from MIS-C, we will assess the cellular responses and develop a novel Tri-Specific Killer Engager (TRiKE) that engages innate immune cells to improve those responses. METHODS/STUDY POPULATION: We collected blood samples from 60 pediatric patients from which we isolated plasma and peripheral blood mononuclear cells. We received blood samples from 13 MIS-C, 32 severe acute COVID, 5 COVID-19 asymptomatic, and 15 COVID-19 negative patients. Using plasma, we then performed ELISAs to determine IgG antibody levels against SARS-CoV-2 and plaque reduction neutralization tests to determine neutralizing antibody functions. We isolated DNA to look at Fc receptor genetics. We also utilized utilize flow cytometry assays determine the phagocytosis and killing abilities of the innate cells from these patients. This data will be correlated with clinical outcomes. Additionally, we have developed a novel SARS-CoV-2 TRiKE which directs natural killer (NK) cell killing specifically to of COVID-19 infected cells. RESULTS/ANTICIPATED RESULTS: MIS-C patients had higher IgG antibody titers against SARS-CoV-2 compared to children with symptomatic or asymptomatic COVID. MIS-C patients also neutralized SARS-CoV-2 more effectively than children with acute symptomatic or asymptomatic COVID-19. We found natural killer cells and monocytes are dysfunctional in MIS-C patients and do not kill SARS-CoV-2 infected cells as well. Specifically, NK cells do not kill COVID-19 infected cells as well. To combat this, we have successfully generated and are now testing a Tri-Specific Killer engager (TRiKE) which binds one ends to NK cells, one end to the Spike protein on COVID-19 infected cells and contains IL-15 to improve NK cell function. We anticipate that we can improve NK cell killing of COVID-19 infected cells with this TRiKE. DISCUSSION/SIGNIFICANCE: We found that MIS-C patients have antibodies that can neutralize SARS-CoV-2 but that that innate immune cells that engage antibodies are dysfunctional. We are have successfully developed and are targeting this response with a TRiKE to improve innate immune cell functional; this may serve as an adjunctive therapeutic if proven successful.

A tri-specific killer engager against mesothelin targets NK cells towards lung cancer.

New treatments are required to enhance current therapies for lung cancer. Mesothelin is a surface protein overexpressed in non-small cell lung cancer (NSCLC) that shows promise as an immunotherapeutic target in phase I clinical trials. However, the immunosuppressive environment in NSCLC may limit efficacy of these therapies. We applied time-of-flight mass cytometry to examine the state of circulating mononuclear cells in fourteen patients undergoing treatment for unresectable lung cancer. Six patients had earlier stage NSCLC (I-IVA) and eight had highly advanced NSCLC (IVB). The advanced NSCLC patients relapsed with greater frequency than the earlier stage patients. Before treatment, patients with very advanced NSCLC had a greater proportion of CD14- myeloid cells than patients with earlier NSCLC. These patients also had fewer circulating natural killer (NK) cells bearing an Fc receptor, CD16, which is crucial to antibody-dependent cellular cytotoxicity. We designed a high affinity tri-specific killer engager (TriKE®) to enhance NK cytotoxicity against mesothelin+ targets in this environment. The TriKE consisted of CD16 and mesothelin binding elements linked together by IL-15. TriKE enhanced proliferation of lung cancer patient NK cells in vitro. Lung cancer lines are refractory to NK cell killing, but the TriKE enhanced cytotoxicity and cytokine production by patient NK cells when challenged with tumor. Importantly, TriKE triggered NK cell responses from patients at all stages of disease and treatment, suggesting TriKE can enhance current therapies. These pre-clinical studies suggest mesothelin-targeted TriKE has the potential to overcome the immunosuppressive environment of NSCLC to treat disease.

526 - An ADAM17-Binding Antibody (MEDI-1) Enhances Proliferation of NK Cells from Multiple Myeloma Patients and Improves Killing with a B7-H3 Tri-Specific Killer Engager (TriKE)

526 - An ADAM17-Binding Antibody (MEDI-1) Enhances Proliferation of NK Cells from Multiple Myeloma Patients and Improves Killing with a B7-H3 Tri-Specific Killer Engager (TriKE)

A Novel Dual-Antigen Targeting Approach Enables Off-the-Shelf CAR NK Cells to Effectively Recognize and Eliminate the Heterogenous Population Associated with AML

While acute myeloid leukemia (AML) treatment has improved, relapse is still common, even after reduced intensity conditioning allogeneic transplantation. Natural killer (NK) cells are a promising allogeneic cell immunotherapy without the risk of graft-versus-host disease or cytokine release syndrome. We and others have reported that haploidentical NK cells can safely result in 30-50% complete remissions in advanced AML patients when given with high-dose lymphodepleting chemotherapy and exogenous cytokine support. However, while NK cell natural cytotoxicity has a clinical signal in AML, increased specificity and multi-dosing are likely to enhance the efficacy and durability of this treatment strategy. A number of stress ligands, including the MHC-I polypeptide-related sequence A and B (MICA/B), bind to the NK cell activating receptor NKG2D and initiate NK cell killing of transformed and infected cells, and several groups have shown promising results in clinical trials by developing NK cells that carry a NKG2D chimeric antigen receptor (CAR). However, the distal α1 and α2 domains of MICA/B that are recognized by NKG2D can be proteolytically cleaved from the surface of the tumor by metalloproteases, allowing for escape from NK cell-mediated detection and elimination. Wucherpfennig and colleagues have described that the membrane proximal α3 domain remains on the cell surface and may be a potential target for immunotherapy across many cancers, including AML. However, since AML is heterogenous, we hypothesized that clinical success would require dual-targeting and selected CD33 as the ideal complementary targeting approach since CD33 is a validated marker expressed on greater than 80% of AML blasts. To this end, our lab has developed a Tri-specific Killer Engager (TriKE) capable of agonistically ligating the CD16 Fc receptor to CD33 found on AML along with IL-15 co-stimulation to further activate the NK cell response. Here, we demonstrate the efficacy of a multiplexed-gene edited induced pluripotent stem-cell (iPSC) derived NK cell (iNK) product that expresses a high-affinity, non-cleavable version of CD16 (hnCD16), a membrane-bound IL-15 fusion receptor, CD38 knockout to enhance metabolic fitness, and a CAR against the α3 domain of MICA/B (α3 MICA/B) to drive a potent response against AML alone and when combined with anti-CD33 TriKE. In the initial study, the iNK cell backbone (iNK cells without the α3 MICA/B CAR) induced potent activity against the AML cell line HL60, and displayed further enhancement of activity with the addition of anti-CD33 TriKE (GTB-3650), representing combined effects of natural cytotoxicity and antibody-dependent cellular cytotoxicity. To show specificity for α3 MICA/B targeting, the AML cell line THP-1 was stained for the presence of MICA/B by flow cytometry using the 6D4 clone that recognizes the α1/2 domains of MICA/B or the 7C6 clone that uniquely recognizes the α3 domain +/- proteolytic cleavage with trypsin (Fig. 1A-B). Significant expression of the α3 domain was observed on THP-1 cells using the 7C6 antibody, which was highly expressed even after protease treatment. On the other hand, the α1/2 domains of MICA/B were detectable at lower levels using the 6D4 antibody and were undetectable after protease treatment (Fig. 1A-B). To assess a dual targeting approach, THP-1 cells were used as targets in live imaging functional assays under standard conditions (Effector:Target [E:T] 2:1). The iNK cell backbone had modest natural cytotoxicity at 3 hours that was significantly enhanced by the addition of α3 MICA/B CAR. The effect was further improved with more rapid killing kinetics when combined with the anti-CD33 TriKE (Fig. 1C). To evaluate the efficacy of dual-targeting in a more stringent physiologic manner, we mimicked "stress” conditions by minimizing the E:T ratio to 0.25:1. While all effector conditions induced immediate killing in 4 hours at the low E:T ratio, sustained tumor control was only observed with dual-antigen targeting (Fig. 1D). Studies with primary AML targets, +/- preincubation of decitabine and all-trans retinoic acid, known to upregulate NKG2D ligands in AML, are in progress and will be discussed. In summary, dual-targeting strategies using off-the-shelf CAR NK cells targeting α3 MICA/B in combination with antigen-specific TriKE targeting CD33 represent an ideal clinical strategy to enhance efficacy and durability of treatment in advanced AML. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

B7-H3 Trike Enhances Killing of Myeloid Derived Suppressor Cells in Multiple Myeloma

Multiple myeloma (MM) is sensitive to Natural Killer (NK) cell-mediated killing but develops methods to attenuate NK cell function. One method to enhance NK cell specificity against myeloma is antibody dependent cellular cytotoxicity through the CD16 receptor. We developed a tri-specific killer engager (TriKE®) with a camelid single-domain antibody (sdAb) fragment against CD16 (on NK cells) as well as a linker region containing IL-15, to enhance NK cell survival. Delivery of IL-15 by TriKE supports NK cell proliferation while avoiding off-target effects on T cells. The second sdAb targets B7-H3 (CD276), a tumor antigen that is expressed on myeloma and is associated with decreased progression free survival. B7-H3 is differentially expressed on myeloma tumor lines MM1S, RPMI-8226, U266, and H929 but all four MM lines are significantly killed by peripheral blood NK cells in the presence of 3nM B7-H3 TriKE compared to NK cells alone. Bone marrow aspirates from 5 MM patients (3 newly diagnosed and 2 relapsed) were analyzed by flow cytometry and showed 58-96% expression of B7-H3 on CD138+ plasma cells. The bone marrow biopsy aspirates also showed monocytic myeloid derived suppressor cells (Mo-MDSC, CD14+, CD11b+) that expressed B7-H3 (38-87%) as well as the damage associated molecular pattern (DAMP) S100A8/9. In comparison, CD14+ cells from the peripheral blood of healthy donors expressed very low levels of B7-H3 or S100A8/9 (<5%). Mo-MDSC are important to the pathogenesis of MM because they support MM growth and contribute to suppression of NK in the tumor microenvironment. B7-H3 is highly expressed on mature osteoclasts and MDSC can develop into osteoclasts in mouse models of MM and breast cancer. We saw that Mo-MDSC expressing B7-H3 also co-expressed RANK, a receptor necessary for signaling osteoclastic development. We developed Mo-MDSC from CD33+ myeloid cells from healthy donors using IL-6 and GM-CSF or co-culture with MM cell lines at 1:1000 ratio. Both types of MDSC suppressed NK proliferation. Peripheral blood derived MDSC expressed >80% B7-H3 and RANK. We separated B7-H3 positive and negative populations by flow cytometry and attempted to develop osteoclasts with M-CSF and RANK-L over 14 days. Tartrate resistant acid phosphatase (TRAP) staining was performed but both groups were negative and exhibited no phenotypic changes by light microscopy. We then isolated CD14+ cells from the bone marrow of an MM patient who was in complete remission (CR) after autologous stem cell transplant but had a distinct population of B7-H3+, RANK+, S100A8/9+ Mo-MDSC in her surveillance bone marrow aspirate. After fourteen days of culture with M-CSF and RANK-L, TRAP staining was positive, and cells had grown larger, consistent with osteoclastic differentiation (Figure 1A). We tested the ability of B7-H3 TriKE to eliminate MDSC by NK cells, therefore diminishing there immune suppression. Cytotoxicity assays were conducted over 48 hours with NK cells with or without B7-H3 TriKE. Killing was significantly enhanced by B7-H3 TriKE (Figure 1B). Since MDSC are known to suppress NK cell function, we assessed metabolic fitness in NK cells with MDSC at 1:1 ratio for 48 hours with or without 3nM B7-H3 TriKE and found that B7-H3 TriKE improved both the oxygen consumption and extracellular acidification rates. These data show that B7-H3 TriKE enhances NK cell killing of MM through direct targeting and eliminates suppressive Mo-MDSC. B7-H3+ Mo-MDSC can differentiate into osteoclasts and persist even in patients who are in CR, possibly contributing to relapse. B7-H3 TriKE may be particularly useful for patients with bone lesions or as consolidative therapy. Commercial manufacturing of B7-H3 TriKE (GTB-5550) has begun, and a phase I trial is expected in late 2023. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

TEM8 Tri-specific Killer Engager binds both tumor and tumor stroma to specifically engage natural killer cell anti-tumor activity

BackgroundThe tumor microenvironment contains stromal cells, including endothelial cells and fibroblasts, that aid tumor growth and impair immune cell function. Many solid tumors remain difficult to cure because of tumor-promoting...

755P B7H3-targeted tri-specific killer engagers deliver IL-15 to NK cells but not T-cells, and specifically target solid tumors as a pan-tumor antigen strategy mediated through NK cells

IL-15, the homeostatic factor for NK cells is being clinically developed but it has little antitumor activity alone. We hypothesized that targeted delivery of IL-15 to NK cells along with ADCC would impart NK cells with specificity to tumor antigens. As proof of concept, a clinical trial of GTB-3550 (a CD33-targeted Tri-specific Killer Engager [TriKE] in AML) induced endogenous NK cell expansion and activation in refractory AML patients. Here we developed GTB-5550 (a B7H3 TriKE) as a novel dual camelid (cam) TriKE containing WT IL-15 and comprised of two cam engagers: targeting CD16 on NK cells and B7H3 on multiple solid tumors.

New Frontiers in Monoclonal Antibodies for the Targeted Therapy of Acute Myeloid Leukemia and Myelodysplastic Syndromes.

Acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) represent an unmet clinical need whose prognosis is still dismal. Alterations of immune response play a prominent role in AML/MDS pathogenesis, revealing novel options for immunotherapy. Among immune system regulators, CD47, immune checkpoints, and toll-like receptor 2 (TLR2) are major targets. Magrolimab antagonizes CD47, which is overexpressed by AML and MDS cells, thus inducing macrophage phagocytosis with clinical activity in AML/MDS. Sabatolimab, an inhibitor of T-cell immunoglobulin and mucin domain-containing protein 3 (TIM3), which disrupts its binding to galectin-9, has shown promising results in AML/MDS, enhancing the effector functions of lymphocytes and triggering tumor cell death. Several other surface molecules, namely CD33, CD123, CD45, and CD70, can be targeted with monoclonal antibodies (mAbs) that exert different mechanisms of action and include naked and conjugated antibodies, bispecific T-cell engagers, trispecific killer engagers, and fusion proteins linked to toxins. These novel mAbs are currently under investigation for use as monotherapy or in combination with hypomethylating agents, BCL2 inhibitors, and chemotherapy in various clinical trials at different phases of development. Here, we review the main molecular targets and modes of action of novel mAb-based immunotherapies, which can represent the future of AML and higher risk MDS treatment.

P618: SECOND-GENERATION CD19 TARGETING TRI-SPECIFIC KILLER ENGAGER DRIVES ROBUST NK CELL FUNCTION AGAINST B CELL MALIGNANCIES

Background: Chronic Lymphocytic Leukemia (CLL) involves uncontrollable clonal expansion of CD5+/CD19+ B lymphocytes. While patients can sometimes coexist with CLL for years, eventually there is progression to bulky adenopathy and pancytopenia from marrow suppression requiring therapy. In recent years, targeted therapies, including utilization of the inhibitors for B cell receptor (BCR) signaling and for B cell lymphoma 2 (Bcl-2) protein, have been effective treatment options. However, these treatments are associated with limitations such as development of drug resistance and the lower treatment efficacy ratio in high-risk patients. Meanwhile, CAR-T cell immunotherapy failed to produce effective treatment outcomes against CLL, mostly due to defects in the effector T cells leading to product failures, as well as being associated with high levels of off-target cytotoxicity. Aims: Thus, approaches to CLL treatment are necessary and NK cell immunotherapy presents a viable and non-toxic option to this problem. Methods: Our group previously demonstrated the immunotherapeutic potential of utilizing first-generation CD19-targeting 161519 Tri-Specific Killer Engager (TriKE®) to drive natural killer (NK) cell cytotoxicity against B-cell malignancies. We have now produced a novel second-generation CD19 TriKE, ‘CAM161519’, utilizing a humanized camelid anti-CD16 VHH single domain antibody (sdAb) ‘CAM16’, a wild-type IL-15 component, and anti-CD19 tumor antigen scFv all linked via short peptide linkers. The TriKE primarily works by generating a cytolytic bridge between NK cells and CD19 expressing B cell malignancies while also providing an expansion and survival signal to the NK cells. Using flow-based assays and imaging based cytolytic assays we explored the capability of CAM161519 to target a variety of B cell lines (Raji, Daudi, and Nalm6) and primary B cell malignancies from patients with CLL and B cell acute lymphoblastic leukemia (B-ALL). Expanded NK cells were incubated with primary CLL targets from 6 different patients and no treatment (NT), rhIL-15 (30 nM), Rituximab (10 ug/mL), or CAM16159 (30 nM). NK cell degranulation and IFNg production was evaluated after 5 hours of co-culture (Figure). CLL killing was evaluated in a similar co-culture, but with a staining mix containing CD5 and CD19, to identify CLL tumor cells in order to determine the percent CLL targets killed normalized to incubation of CLL cells with NK cells alone (Figure Image). Results: The CAM161519 robustly activated NK cell degranulation (CD107a) and inflammatory cytokine production (IFNg) against B cell lines. The activation was specific as it was strongly reduced against CD19 knockout Nalm6 cells. The TriKE also induced specific NK cell proliferation. IncuCyte imaging based cytolytic assays demonstrated strong killing activity against Raji targets. When evaluating activity against primary targets, CAM161519 induced enhanced NK cell degranulation, cytokine production, and cytotoxicity using flow cytometry-based assays against primary CLL (Figure Image) and B-ALL targets when compared to IL-15 treatment. CAM161519 also rescued functionality of NK cells from CLL patients against their autologous CLL cells. Image:Summary/Conclusion: Taken together, these data are indicative of the potential for clinical translation of the CAM161519 TriKE in the CLL and B-ALL settings alone or in combination with cellular products.

Abstract 3435: GTB-5550 (cam16-IL15-camB7H3) trispecific killer engager (TriKE®) drives natural killer cell activation and antibody dependent cellular cytotoxicity against head and neck squamous cell carcinomas

Abstract Worldwide, Head and Neck Squamous Cell Carcinomas (HNSCC) account for about 900,000 cases and 400,000 deaths. In some settings, like Fanconi anemia (FA), patients receive curative treatments (allogeneic stem cell transplantation), only to develop HNSCC in early adulthood at a high rate of incidence. Current treatment strategies for non-FA HNSCC patients include surgery, chemotherapy and radiotherapy. However, these are not viable treatment options for FA HNSCC patients due to their low tolerance for the high toxicity levels of chemotherapy and radiation. Therefore, there is a critical need for novel and targeted therapeutic interventions for the treatment of FA HNSCC patients. B7H3, a checkpoint member of the B7 and CD28 families, is overexpressed on several solid tumors but is absent or not expressed on healthy tissues. It is a promising target for immunotherapy, and recent basket trials, particularly in the prostate cancer, have demonstrated strong clinical signals. Here we developed and tested the ability of GTB-5550, a tri-specific killer engager (TriKE) that includes a B7H3 targeting component, to direct NK cell killing to B7H3-expressing Head and Neck cancer targets. This TriKE molecule includes an NK cell engaging domain containing a humanized camelid nanobody against CD16, a camelid nanobody against B7H3 and a wild type IL-15 sequence between the two engagers. We assessed B7H3 expression by flow cytometry of wild-type HNSCC cells and a paired version with a CRISPER KO of the FANCA gene and determined that the KO had no effect on B7H3 expression. Thus, GTB-5550 activity against HNSCC should be present on both normal HNSCC and FA-HNSCC settings. NK cell responses against HNSCC lines in the presence of GTB-5550 were assessed through either flow cytometry based functional assays, to evaluate NK cell degranulation and cytokine secretion, or IncuCyte imaging assays, to directly assess target killing. NK cell degranulation and IFN-gamma production of GTB-3550-treated samples were higher compared to that of control samples treated with B7H3 single domain or IL-15 alone. GTB-5550 also induced more HNSCC target cell killing by NK cells compared to treatment with the B7H3 single domain or IL-15 alone irrespective of the FANCA gene. Ongoing experiments will evaluate functionality of GTB-5550 on FA patient samples as well as in spheroid assays. Taken together, this data shows that a GTB-5550 is able to drive NK cell activity against B7H3-expressing HNSCC cells, which presents potential for a B7H3-targeted TriKE to be used to be implemented clinically to treat HNSCC or FA-HNSCC patients. Citation Format: Melissa Khaw, Zachary Davis, Nicholas Zorko, Greg Berk, Gavin Choy, Margaret MacMillan, Martin Felices, Jeffrey S. Miller. GTB-5550 (cam16-IL15-camB7H3) trispecific killer engager (TriKE®) drives natural killer cell activation and antibody dependent cellular cytotoxicity against head and neck squamous cell carcinomas [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 3435.

Abstract 2878: Mediating NK cell function against solid tumors, via targeting of tumor stroma, using a TEM8-targeting Tri-specific Killer Engager (TriKE®)

Abstract Immunotherapies for solid tumors need to overcome barriers within the solid tumor microenvironment (TME), including stromal cells, cancer-associated fibroblasts, endothelial cells, pericytes, and immune cells. These can comprise a significant portion of the tumor mass in many common carcinomas and contribute to immune cell dysfunction within the tumor. Stromal cells support cancer cells through several mechanisms and can promote metastasis. Tumor vasculature supplies cancer cells with nutrients and oxygen necessary for tumor growth and dissemination. Thus, targeting these components of cancer can enhance tumor rejection directly and increase sensitization of surviving tumors to immune infiltration and chemotherapeutic treatments through weakening of the tumor architecture. While there are current antiangiogenic therapies being tested clinically, they have associated toxicities in normal angiogenic processes, limiting clinical efficacy. Tumor Endothelial Marker 8 (TEM8, encoded by the ANTXR1 gene) is a highly conserved integrin-like adhesion molecule that was discovered on the endothelium of colorectal cancer, and subsequent studies identified its expression on multiple stromal cells—endothelial cells, fibroblasts, and pericytes—in the tumor microenvironment of diverse human cancer types. Little to no expression has been demonstrated in normal human stroma, indicating that this would be a good target for immunotherapy. Using a mammalian expression system, we designed and expressed a TEM8 targeting TriKE (cam1615TEM8) consisting of a humanized anti-CD16 single domain antibody, a wild-type IL-15 moiety, and an anti-TEM8 scFv. cam1615TEM8 induces NK cell degranulation and cytokine production against TEM8+ tumor and stromal cell lines (endothelial cells and fibroblasts). Using TEM8- cancer lines and a TEM8-CRISPR knockout version of A549 lung cancer lines, we show that cam1615TEM8 only activates NK cells in the presence of tumor antigen. cam1615TEM8 also preferentially stimulates TEM8+ tumor spheroid killing. Moreover, the camelid anti-CD16 nanobody selectively enhances signaling by the IL-15 moiety to NK cells, specifically promoting NK cell survival and proliferation in vitro and in vivo. In an in vivo xenogeneic mouse model, containing human NK cells and tumor, cam1615TEM8-treated mice had enhanced NK cell tumor infiltration, significantly decreased tumor growth, and enhanced survival when compared to IL-15 treated mice. Since TEM8 is highly conserved, and the scFv within the TriKE is reactive to mouse TEM8, we were able to show reduced tumor endothelial density in the tumors of mice treated with cam1615TEM8. Given the findings of this study cam1615TEM8 could be leveraged in several clinical settings by inducing NK cell specific targeting of the tumor itself and/or the tumor endothelium and stroma. Citation Format: Martin Felices, Michael Kaminski, Peter Hinderlie, Rachel Hopps, Laura Bendzick, Melissa Geller, Jeffrey S. Miller. Mediating NK cell function against solid tumors, via targeting of tumor stroma, using a TEM8-targeting Tri-specific Killer Engager (TriKE®) [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 2878.

126P Novel B7-H3 targeting dual nanobody NK cell engagers display robust activity against a broad spectrum of solid and hematologic malignancies

B7-H3 is a checkpoint molecule under intense investigation as an immune therapy target. We previously showed that dual camelid nanobody tri-specific killer engager (TriKE) (GTB-5550) specifically bound B7-H3 on PC3/C4-2 prostate cancer (PCa) cells and activated peripheral blood (PB) NK cells. We have since developed a dual camelid bispecific killer engager (BiKE) targeting B7-H3 and show that both GTB-5550, which harbors wild-type IL-15, and BiKE display broad activity against B7-H3-expressing tumors.