Bispecific T-Cell Engager Antibodies in Multiple Myeloma- a Systematic Review of Phase 1 Clinical Trials

Introduction One of the emerging targeted strategies for treatment of multiple myeloma (MM) is the use of robust immune responses via T cell activation against tumor cells. B-Cell Maturation Antigen (BCMA), a cell surface protein, remains a potential target for therapeutic interventions. Recently, bispecific T cell engager therapy, targeting BCMA and CD3 antigens on plasma and T cells respectively, have shown promising results in preclinical and early clinical studies in the context of relapsed/refractory myeloma (RRMM). We conducted a systematic review of phase 1 trials to report the efficacy and safety of Bispecific T-Cell Engager antibodies for MM. Methodology: We systematically searched multiple databases, including PubMed, Embase, Cochrane, and Clinicaltrials.gov. We also searched major conferences for oral or poster presentations. MeSH terms and keywords for MM and bispecific antibodies were utilized. We included all original studies reported in English language published from 1990 until June 2021. The primary database search yielded 390 articles. After excluding review articles, duplicates, irrelevant articles, and non-human studies, six phase 1 clinical trials were included to evaluate the efficacy and safety outcomes. Results: A total of 253 patients were identified from the six phase 1 studies, among whom 247 were evaluable for response, while the safely analysis involved all the patients. A study conducted by Krishan et al. (n= 40) stated an overall response rate (ORR) of 65% among patients receiving subcutaneous (SQ) teclistamab with a median of five prior therapies, 30% and 58% of the responders had a complete response (CR) and very good partial response (VGPR), respectively. A similar ORR of 63% was reported in 28 patients with a median of 5.5 prior therapies receiving SQ talquetamab by Berdeja et al. Cohen et al reported an ORR of 51.7% in patients receiving IV BFCR4350A at doses ≥3.6/20mg (Partial response (PR):17.2% and CR: 10.3%). SQ elranatamab achieved an ORR of 75% in 17 patients who received doses ≥215 μg/kg. Madduri et al. evaluated REGN5458 monotherapy with dose escalation from 3 to 96 mg among 45 patients and reported an ORR of 60% at the highest dose levels. ORR of 31% was reported in 42 patients receiving IV BI836909/AMG 420 by Topp et al. The median time to response (TTP) was 1 month in the majority of the studies. (Table 1) The most common grade three or higher hematological toxicities were neutropenia and anemia, while among non-hematological toxicities, infections were the most common. The incidence of cytokine release syndrome and neurotoxicity varied from 24% to 74% and 2 % to 20%, respectively. (Table 3) Conclusion: The early clinical data of Bispecific T-Cell Engager therapy in heavily pretreated RRMM patients shows promising results regarding its efficacy and safety profile. It represents a whole new horizon of targeted approach towards RRMM. Phase II / III studies are being conducted to evaluate this potential treatment approach in patients with MM. Figure 1 Figure 1. Disclosures Anwer: GlaxoSmithKline: Research Funding; BMS / Celgene: Honoraria, Research Funding; Allogene Therapeutics: Research Funding; Janssen pharmaceutical: Honoraria, Research Funding.

A Novel Bispecific T Cell Engager (UMG2-BTCE) Targeting CD1a-CD3ε Is Effective Against Cortical-Derived Acute Lymphoblastic Leukemia

Caterina Riillo*and Daniele Caracciolo*equally contributed to the work. Background: T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive and orphan hematological disease derived from malignant transformation of thymic T cell precursors. At present, the prognosis of relapsed/refractory patients remains poor. While immunotherapy has significantly improved the outcome of B cell acute lymphoblastic leukemia (B-ALL), the lack of tumor-restricted T cell antigens hampers its efficacy in T-ALL. (Caracciolo D, Riillo C, et al. Therapeutic afucosylated monoclonal antibody and bispecific T-cell engagers for T-cell acute lymphoblastic leukemia. J Immunother Cancer. 2021) Therefore, the development of novel immune-therapeutics is eagerly awaited. CD1a is a cell surface glycoprotein restricted to cortical T-ALL subtype expressed only by cortical thymocytes and Langerhans's cells among human healthy tissue and might represent a valuable therapeutic target for the treatment of T-ALL. On this basis, we develop an asymmetric monovalent 2 +1 bispecific T cell engager (BTCE) derived from a novel humanized UMG2 mAb directed against an original CD1a epitope selectively expressed by cortical T-ALL cells. Methods. To evaluate if UMG2 recognizes a specific CD1a epitope, HEK293T cell line, negative for CD1a expression, has been transfected with a plasmid encoding for CD1a (HEK293T/CD1a) and with a negative control vector and UMG2 reactivity has been evaluated by flow cytometry. A competitive binding assay between UMG2 and commercially available CD1a antibodies was performed. The UMG2 expression profile was evaluated on healthy donor peripheral blood cells and on a panel of cortical T-ALL cell lines. To develop a UMG2 targeting immunotherapeutic construct with a limited unspecific T cell activation, an asymmetric 2+1 UMG2-CD3 bispecific T cell engager (BTCE) was generated using knobs into holes technology. UMG2-CD3 BTCE in vitro T cell-mediated activity was evaluated on HEK293T CD1a antigen-negative cell line, on HEK293T/CD1a, on patient-derived and T-ALL cell lines, co-cultured with healthy donors derived peripheral blood mononuclear cells (PBMCs), CD4/CD8 depleted and CD56 enriched lymphocytes at 10:1 E:T ratio. T cell activation, degranulation, proliferation, and pro-inflammatory cytokine secretion were assessed by flow cytometry on primary blasts and on T-ALL cells with effector lymphocytes. To evaluate UMG2-CD3 BTCE anti-tumor activity against CD1a expressing T-ALL cell line in vivo, Hu-PBMCs NSG mouse model was generated, and tumor growth was assessed by fluorescent imaging probe. Results UMG2 mAb recognizes a previously uncharacterized CD1a epitope and does not compete with any of the commercially available anti-CD1a mAbs. While a strong UMG2 reactivity is observed on both patient-derived samples and T-ALL cells, no binding is found on normal blood cells, indicating the tumor-restricted pattern of reactivity of UMG2. UMG2-CD3 BTCE specifically binds CD1a on leukemic cells and activates CD3ε downstream signaling pathway on T lymphocytes, as demonstrated by the concentration-dependent increase of T cell proliferation, cytotoxic degranulation (CD107a), expression of cell surface activation markers (CD25, CD69), and pro-inflammatory cytokine secretion (IL-2, TNF-α, IFN-γ). UMG2-CD3 BTCE mediates strong and concentration-dependent specific T cell re-directed cytotoxicity only on CD1a expressing leukemic cells in the presence of T lymphocytes. Minimal UMG2-CD3 BTCE residual anti-tumor activity is observed in CD4/CD8 depleted and CD56 enriched lymphocytes, while CD56 depleted and Fc-blocked PBMCs are able to induce an anti-T-ALL activity comparable to total PBMCs, demonstrating that UMG2-BTCE could not recruit monocytes and NK cells through Fc-FcyR interaction by reducing the risk of immune-mediated adverse events. Most importantly, in an in vivo of immune-humanized NSG mice engrafted with human T-ALL cells, UMG2-BTCE significantly inhibits tumor growth translating into the survival advantage of treated animals. Conclusion: Taken together, all these results provide a framework for the clinical development of UMG2-CD3 BTCE potentially offering a novel therapeutic path for cortical-derived T-ALL. Disclosures No relevant conflicts of interest to declare.

788 A novel T- lymphocyte binding aptamer assembled into a bispecifc compound for the treatment of solid tumors

BackgroundT-cell engagers are bispecific molecules directed against the CD3 complex on one end and a tumor specific antigen on the other end, allowing a physical link of T cell to a tumor cell, resulting in tumor killing and immune activation. Bispecific molecules harnessing and redirecting T-cells towards tumor cells are a promising therapeutic agents. Aptamers are single stranded oligonucleotides with binding and recognition propensities similar to those of antibodies. Aptamers have a number of advantages over bispecific antibodies including shorter generation time and low immunogenicity. Thus, aptamers capable of targeting T cells would have great potential for use as anti-cancer therapeuticsMethodsSystematic evolution of ligands by exponential enrichment (SELEX) methodology was employed in order to identify a novel CD3e binding aptamer. CD3 binding aptamer was subsequently linked into a bispecific T cell engager structure with a tumor-targeting aptameric arm. The tumor-targeting aptamer is developed by Aummune's proprietary tailored therapeutic platform.1 based on identifying functional aptamer sequences capable of specifically killing targeted tumor cells and sparing healthy tissue .Exemplary bispecific aptamers were tested for T cell stimulation by flow cytometry. In vivo antitumor activity was investigated in syngeneic and in xenograft tumor models.ResultsWe have successfully identified a novel CD3e –targeting aptamer with a Kd of 31nM. A bispecific T cell engager comprised of this aptamer and a tumor-targeting aptamer induced a potent stimulation of T cells in vitro, resulting in CD69 upregulation and IFNg secretion.Next, the CD3e targeting aptamer was hybridized to tumoricidal aptamers identified by Aummune's platform (VS12) to target either the human colon carcinoma HCT116 cells or (VS32) the murine triple negative breast cancer 4T1 cells. Both bispecific entities (CS6-VS12 and CS6-VS32) effectively lead to inhibition of tumor growth in vivo and increased survival in the corresponding models.ConclusionsOur data above provide a proof-of-concept for Aummune's Bispecific Aptamer efficacy and provide a framework for the clinical development of this novel tailored immune therapeutic agents. Indeed, we are currently in the process of developing a first-in-human clinical study in subjects with solid tumors.ReferenceMamet N, et al, Commun Biol 2020.

Immunotherapy combinations overcome resistance to bispecific T cell engager treatment in T cell–cold solid tumors

Therapeutic approaches are needed to promote T cell–mediated destruction of poorly immunogenic, “cold” tumors typically associated with minimal response to immune checkpoint blockade (ICB) therapy. Bispecific T cell engager (BiTE) molecules induce redirected lysis of cancer cells by polyclonal T cells and have demonstrated promising clinical activity against solid tumors in some patients. However, little is understood about the key factors that govern clinical responses to these therapies. Using an immunocompetent mouse model expressing a humanized CD3ε chain (huCD3e mice) and BiTE molecules directed against mouse CD19, mouse CLDN18.2, or human EPCAM antigens, we investigated the pharmacokinetic and pharmacodynamic parameters and immune correlates associated with BiTE efficacy across multiple syngeneic solid-tumor models. These studies demonstrated that pretreatment tumor-associated T cell density is a critical determinant of response to BiTE therapy, identified CD8+ T cells as important targets and mediators of BiTE activity, and revealed an antagonistic role for CD4+ T cells in BiTE efficacy. We also identified therapeutic combinations, including ICB and 4-1BB agonism, that synergized with BiTE treatment in poorly T cell–infiltrated, immunotherapy-refractory tumors. In these models, BiTE efficacy was dependent on local expansion of tumor-associated CD8+ T cells, rather than their recruitment from circulation. Our findings highlight the relative contributions of baseline T cell infiltration, local T cell proliferation, and peripheral T cell trafficking for BiTE molecule–mediated efficacy, identify combination strategies capable of overcoming resistance to BiTE therapy, and have clinical relevance for the development of BiTE and other T cell engager therapies.

Emerging therapies for relapsed/refractory multiple myeloma: CAR-T and beyond

The pace of innovation of multiple myeloma therapy in recent years is remarkable with the advent of monoclonal antibodies and the approval of novel agents with new mechanisms of action. Emerging therapies are on the horizon for clinical approval with significant implications in extending patient survival and advancing closer to the goal of a cure, especially in areas of immunotherapy such as chimeric antigen receptor T cells, bispecific T cell engager antibodies, antibody drug conjugates, newer generations of monoclonal antibodies, and small molecule inhibitor and modulators. This review provides an update of current myeloma therapeutics in active preclinical and early clinical development and discusses the mechanism of action of several classes of novel therapeutics.