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BACKGROUND: Relapsed/refractory (R/R) B-cell non-Hodgkin lymphoma (B-NHL) remains an area of high unmet patient need and no curative options are currently available. Odronextamab (REGN1979) is a first-in-class, hinge-stabilized, fully human IgG4-based bispecific antibody that binds to CD20-expressing cells and CD3 on T cells, targeting CD20+ cells via T-cell-mediated cytotoxicity independent of T-cell receptor recognition. The safety, tolerability, and anti-tumor activity of odronextamab monotherapy was evaluated in a global, multicenter, Phase 1 study in heavily pretreated patients with R/R B-NHL (NCT02990951; Bannerji et al, ASH 2019). Intravenous infusion of odronextamab has demonstrated an acceptable safety profile at doses up to 320 mg weekly (QW), and the maximum tolerated dose was not reached. Broad and durable anti-tumor responses were observed in both indolent and aggressive lymphomas, including in patients who progressed after prior CAR T-cell therapy. An assessment of pharmacokinetics, efficacy and safety data from the Phase 1 study informed the recommended Phase 2 dosing regimens. METHODS: This global, Phase 2, open-label, multi-cohort study (R1979-ONC-1625; NCT03888105) is designed to assess the anti-tumor activity and safety of odronextamab in patients with B-NHL. There are five disease-specific cohorts, each with independent parallel enrollment. The study includes patients with: (1) R/R follicular lymphoma (FL) Grade 1-3a after ≥2 prior lines of systemic therapy, including an anti-CD20 antibody and an alkylating agent; (2) R/R diffuse large B-cell lymphoma (DLBCL) after ≥2 lines of systemic therapy, including an anti-CD20 antibody and an alkylating agent; (3) R/R mantle cell lymphoma (MCL) following or with failure to tolerate Bruton's tyrosine kinase inhibitor therapy; (4) R/R marginal zone lymphoma (MZL) after ≥2 lines of systemic therapy; (5) other R/R B-NHL subtypes, excluding Waldenström macroglobulinemia, after ≥2 lines of systemic therapy (Fig. 1). Estimated total enrollment is 481 patients. Key eligibility criteria are: age ≥18 years; not appropriate for other approved therapy with established benefit; ≥1 bi-dimensionally measurable nodal lesion of ≥1.5 cm; Eastern Cooperative Oncology Group performance status ≤1; and adequate bone marrow, renal, and hepatic function. Key exclusion criteria are: prior anti-CD20 x CD3 bispecific antibody therapy; prior CAR T-cell therapy; primary central nervous system (CNS) lymphoma or known involvement by non-primary CNS NHL; and history of allogeneic hematopoietic stem cell transplantation. Odronextamab is administered using a step-up dose schedule consisting of an initial dose at Week (W)1, an intermediate dose at W2, and thereafter, a fixed weekly dose until W12 followed by maintenance Q2W dosing until progression or discontinuation (Fig. 2). The dose for indolent B-NHL is 80 mg QW followed by 160 mg Q2W, and for aggressive B-NHL is 160 mg QW followed by 320 mg Q2W. All patients with durable complete responses of 9 months will transition from Q2W to Q4W dosing. The primary endpoint for each cohort is objective response rate (ORR) by independent central review, as assessed from first dose until completion of 28 weeks of study treatment, or study withdrawal. Secondary endpoints include complete response (CR) rate, progression-free survival, duration of response, disease control rate (DCR), overall survival, incidence and severity of treatment-emergent adverse events, pharmacokinetics, immunogenicity, and patient-reported outcomes. ORR, CR rate and DCR with a two-sided 95% confidence interval (CI) will be summarized. Time-to-event endpoints will be summarized by median and corresponding 95% CI using the Kaplan-Meier method. The study is actively accruing patients at sites across North America, Europe, and Asia-Pacific. Disclosures Kim: AstraZeneca: Consultancy; Novartis: Consultancy; Takeda: Consultancy; Sanofi: Consultancy; F. Hoffmann-La Roche Ltd/Genentech, Inc.: Consultancy; Voronoi: Consultancy; Boryung: Consultancy; AstraZeneca and Korea Health Industry Development Institute: Research Funding. Stevens:Amgen, MorphoSys: Consultancy. Poon:Astrazeneca, Pfizer, Takeda, Janssen, Roche, Novartis: Honoraria. Le Gouill:Loxo Oncology at Lilly: Consultancy; Roche Genentech, Janssen-Cilag and Abbvie, Celgene, Jazz pharmaceutical, Gilead-kite, Loxo, Daiichi-Sankyo and Servier: Honoraria. Carpio:Takeda, Regeneron: Consultancy. Keating:Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Taiho: Membership on an entity's Board of Directors or advisory committees; Shire: Membership on an entity's Board of Directors or advisory committees; Servier: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Consultancy; Sanofi: Membership on an entity's Board of Directors or advisory committees; Merck: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Hoffman La Roche: Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Adriaens:Regeneron Pharmaceuticals, Inc: Current Employment, Current equity holder in publicly-traded company, Patents & Royalties: Dosing regime that mitigates cytokine release syndrome for therapeutic antibodies (status: pending). Ufkin:Regeneron Pharmaceuticals, Inc: Current Employment, Current equity holder in publicly-traded company. Sabir:Regeneron Pharmaceuticals, Inc: Current Employment, Current equity holder in publicly-traded company. Li:Regeneron Pharmaceuticals, Inc: Current Employment, Current equity holder in publicly-traded company. Jankovic:Regeneron Pharmaceuticals, Inc: Current Employment, Current equity holder in publicly-traded company. Zhu:Regeneron Pharmaceuticals, Inc: Current Employment, Current equity holder in publicly-traded company. Brouwer-Visser:Regeneron Pharmaceuticals, Inc: Current Employment, Current equity holder in publicly-traded company. Leng:Regeneron Pharmaceuticals, Inc: Current Employment, Current equity holder in publicly-traded company. Sirulnik:Regeneron Pharmaceuticals, Inc.: Current Employment, Current equity holder in publicly-traded company. Chaudhry:Regeneron Pharmaceuticals, Inc: Current Employment, Current equity holder in publicly-traded company. Ambati:Regeneron Pharmaceuticals, Inc: Current Employment, Current equity holder in publicly-traded company. Won Seog:Roche, Takeda, J&J, Kyowa-Kirin, Celltrion ,Pfizer, Donga: Research Funding. OffLabel Disclosure: The Trial in Progress abstract will report on use of odronextamab in a Phase 2 clinical trial of patients with B-NHL

Introduction REGN1979 is an anti-CD20 x anti-CD3 bispecific IgG4 antibody (Ab) modified to reduce Fc binding. Engaging both targets results in CD20-specific, local T-cell activation and cytotoxicity, a mechanism of action distinct from standard anti-CD20 Abs. We report updated promising efficacy results of a Phase 1 trial of REGN1979 in patients (pts) with relapsed/refactory (R/R) B-NHL previously treated with anti-CD20 Abs. Methods The primary objectives of the study are to determine safety, tolerability, and occurrence of dose limiting toxicities (DLTs). Other objectives include assessment of preliminary antitumor activity, pharmacokinetics (PK), and pharmacodynamics. Eligible pts with R/R NHL must have received at least 1 prior CD20-directed therapy. Treatment consists of 12 weekly doses of REGN1979 followed by every 2 week dosing for 12 doses for a total of 36 weeks. Guidelines are provided for management of cytokine release syndrome (CRS) and include steroids and/or tocilizumab at investigator discretion. Results As of June 1, 2018, 54 pts with B-NHL were treated with REGN1979 monotherapy: DLBCL (pt number [n]=30), FL (n=16), MCL (n=5), MZL (n=2), and WM (n=1). The median number of prior regimens was 3 (range, 1-11); 41 pts were refractory to their last prior systemic therapy, 18 had bulky disease, and 6 had prior HSCT. Pts were treated with REGN1979 0.03-27 mg and received a median of 7 (range, 1-24) doses. Eight pts remain on treatment, 13 completed treatment, and 33 discontinued therapy prior to the planned 36 wks (majority [n=22] due to progressive disease [PD]). There have been no DLTs to date. The most common treatment-related treatment-emergent adverse events (TR-TEAEs) included infusion-related reactions (IRR) or CRS; 26 pts experienced CRS (Grade 1-2, n=23; Grade 3, n=3) with a median duration of CRS of 2 (range 1-15) days. Six pts received tocilizumab. The severity of CRS symptoms declined through optimized pre-medication even with REGN1979 dose escalation. Other common Grade ≥3 TR-TEAEs were lymphocytopenia/ decreased lymphocyte count (n=8); neutropenia/ decreased neutrophil count (n=7); and thrombocytopenia/ decreased platelet count, hypotension, hypophosphatemia, and anemia (each n=3). Seventeen pts experienced a nervous system event including headache, dizziness, paraesthesia, dysgeusia, and peripheral neuropathy with no Grade ≥3 events; no neurologic event required termination of study drug. Seven pts died on study: PD (n=5), gastric perforation (n=1), and cardiac arrest (n=1). TEAEs leading to premature discontinuation of REGN1979 were Grade 3 fatigue (n=1), Grade 3 hemolysis (n=1), and Grade 2 pyrexia/Grade 2 tachycardia (n=1). Among 27 pts treated with REGN1979 ≥5 mg (dose associated with tumor killing in pre-clinical data), the overall response rate (ORR) was 55.6% (5 complete response [CR] and 10 partial response [PR]; Table/Figure). Responses were seen in 7/7 FL Grade 1-3a pts (5 CR, 2 PR), 6/15 DLBCL pts (all PR), 2/2 MCL pts (all PR). At 18 mg and 27 mg of REGN1979, 4 of 4 pts with DLBCL had best response of PR. Post data cut-off, 1 pt with a DLBCL best response of PR converted to CR. PK and pharmacodynamic assessments suggest that for pts treated with REGN1979 5-18 mg, best exposures in the first 3 weeks appear to linearly increase with dose. In pts treated with up to REGN1979 18 mg, a maximum mean Ctrough of 1.6 mcg/mL was observed in the first 3 weeks of weekly dosing. Studies of peripheral blood biomarkers demonstrated depletion of peripheral B lymphocytes, transient margination of circulating T-cells, and elevated circulating cytokines following REGN1979 dosing. Increased peak cytokine levels (IL-6, IL-10, and TNF-alpha) were observed in pts with CRS. Immunohistological analysis of malignant lymph node tissue demonstrated a decrease of CD20 expression in responding pts; among the responders, subsequent relapse was associated with either maintenance of CD20 expression or further CD20 loss, suggesting antigen-dependent and independent disease escape mechanisms. Conclusions REGN1979 displays efficacy and an acceptable safety profile in pts with R/R B-NHL. Most TR-TEAEs were IRR/CRS and have been well managed with supportive care. No significant neurological toxicity has been observed. At doses of 5-27 mg of REGN1979, the preliminary ORR was 100% in pts with FL Grade 1-3a and 40.0% in pts with DLBCL. This promising efficacy warrants further clinical investigation. Disclosures Bannerji: Regeneron Pharmaceuticals, Inc.: Consultancy; AbbVie, Inc.: Consultancy. Arnason:Regeneron Pharmaceuticals, Inc.: Consultancy. Advani:Bayer Healthcare Pharmaceuticals: Other: Consultancy/Advisory Role; Janssen Pharmaceutical: Other: Institutional Research Support; Bristol Myers Squibb: Other: Consultancy/Advisory role and Institutional Research Support; Pharmacyclics: Other: Institutional Research Support; Takeda: Other: Consultancy/Advisory Role; Millenium: Other: Institutional Research Support; Gilead/Kite: Other: Consultancy/Advisory Role; Infinity: Other: Institutional Research Support; Merck: Other: Institutional Research Support; Forty Seven, Inc: Other: Institutional Research Support; Cell Medica: Other: Consultancy/Advisory Role; Agensys: Other: Institutional Research Support; Celgene: Other: Institutional Research Support; Seattle Genetics: Other: Consultancy/Advisory role, Institutional Research Support; Kura: Other: Institutional Research Support; Roche/Genentech: Other: Consultancy/Advisory Role, Institutional Research Support; Kyowa: Other: Consulting/Advisory Role; Regeneron Pharmaceuticals, Inc.: Other: Institutional Research Support; Autolus: Other: Consultancy/Advisory Role; AstraZeneca: Other: Consultancy/Advisory Role. Brown:Acerta / Astra-Zeneca: Membership on an entity's Board of Directors or advisory committees; Verastem: Consultancy, Research Funding; Pharmacyclics: Consultancy; Celgene: Consultancy; Genentech: Consultancy; TG Therapeutics: Consultancy; Morphosys: Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy; Abbvie: Consultancy; Gilead: Consultancy, Research Funding; Sun Pharmaceutical Industries: Research Funding; Sunesis: Consultancy; Loxo: Consultancy; Beigene: Membership on an entity's Board of Directors or advisory committees; Invectys: Membership on an entity's Board of Directors or advisory committees; Roche/Genentech: Consultancy; Boehringer: Consultancy. Allan:Genentech: Membership on an entity's Board of Directors or advisory committees; Verastem: Membership on an entity's Board of Directors or advisory committees; Sunesis: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Acerta: Consultancy. Ansell:Bristol-Myers Squibb: Research Funding; Affimed: Research Funding; Regeneron: Research Funding; Merck & Co: Research Funding; LAM Therapeutics: Research Funding; Seattle Genetics: Research Funding; Trillium: Research Funding; Celldex: Research Funding; Takeda: Research Funding; Pfizer: Research Funding. O'Brien:Kite Pharma: Research Funding; Aptose Biosciences Inc.: Consultancy; Pharmacyclics: Consultancy, Research Funding; GlaxoSmithKline: Consultancy; Astellas: Consultancy; Sunesis: Consultancy, Research Funding; Alexion: Consultancy; Amgen: Consultancy; TG Therapeutics: Consultancy, Research Funding; Pfizer: Consultancy, Research Funding; Vaniam Group LLC: Consultancy; Regeneron: Research Funding; Janssen: Consultancy; Celgene: Consultancy; Abbvie: Consultancy; Acerta: Research Funding; Gilead: Consultancy, Research Funding. Chavez:Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Merck: Research Funding; Kite: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen: Speakers Bureau; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Humanigen: Consultancy. Lowy:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Charnas:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Sternberg:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Ambati:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Adriaens:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Ufkin:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Yan:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Li:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Navarro:Regeneron Pharmaceuticals, Inc.: Employment. Gasparini:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Jankovic:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Fiaschi:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Zhang:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Hamon:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Thurston:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Topp:Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Research Funding; F. Hoffmann-La Roche Ltd: Membership on an entity's Board of Directors or advisory committees, Research Funding; Boehringer Ingelheim: Research Funding; Regeneron Pharmaceuticals, Inc.: Honoraria, Research Funding.

TPS3089 Background: REGN1979 is a human bispecific antibody based on an IgG4 isotype modified to reduce Fc binding, designed to bridge CD20-expressing cells to cytotoxic T-cells by binding to the C...

TPS2618 Background: REGN910 is a selective, fully human Angiopoietin-2 (ANG-2) MAb, which potently blocks signaling through the Tie2 receptor. Ziv-aflibercept (ZAFL) is a recombinant human fusion protein that acts as a decoy receptor for vascular endothelial growth factor (VEGF)-A, VEGF-B, and placental growth factor (PlGF), thereby preventing the interaction of these ligands with their receptors. In several mouse xenograft models, combination of the 2 anti-angiogenic compounds, REGN910 and ZAFL, demonstrated significantly enhanced tumor growth inhibition relative to either agent alone, suggesting that dual angiogenic blockade is worth exploring in cancer patients. Methods: This phase 1b study employs a standard 3+3 dose escalation design exploring 5 different combination treatment dose levels of REGN910 and ZAFL. Once the recommended phase 2 dose (RD) of the combination treatment is determined, additional patients will be enrolled in a safety expansion cohort, for a planned total enrollment of up to 40 patients. The primary study objectives are to evaluate the safety and determine the RD of the 2 drugs in combination when both are administered IV every 2 weeks in patients with advanced solid tumors. Secondary endpoints include characterization of the PK and potential immunogenicity of REGN910 and ZAFL when given in combination, evaluation of correlative PD biomarkers related to REGN910 and ZAFL, and identification of antitumor activity. Enrollment to cohorts 1 and 2 has been completed without DLT. Enrollment to cohort 3 opened in December 2012. Updated enrollment status will be presented. Reference: ClinicalTrials.gov Identifier: NCT01688960. Clinical trial information: NCT01688960.

2517 Background: REGN910 is a selective, fully human Ang2 MAb that potently blocks signaling through the Tie2 receptor regulating tumor angiogenesis and growth. In multiple mouse xenograft models of human solid tumors, REGN910 inhibits tumor growth. Methods: This first-in-human phase I study (3+3 design) explored the safety, recommended phase II dose (RP2D), pharmacokinetics (PK), pharmacodynamics (PD) and antitumor activity of REGN910 as a single agent. REGN910 was given IV at escalating doses. At RP2D, expansion cohorts were initiated to confirm safety and assess anti-tumor activity in about 20 patients (pts). Results: 37 pts [17M/20F; median age 57 (range 22-82); ECOG PS 0(9)/1(28)] were enrolled. Twenty-three (23) pts were enrolled in the dose escalation cohorts. No DLTs were reported, and a MTD was not reached. Most common G1/2 treatment-related adverse events (TRAEs) were fatigue 7(19%), peripheral edema 6(17%), diarrhea 5(14%), abdominal distension 4(11%), and decreased appetite 4(11%). There were no ≥ Grade 3 TRAEs. A confirmed sustained PR (16 wks) was observed in 1 pt with adrenocortical cancer treated at 1 mg/kg. SD (range 6.9-46.8 wks) was reported for 17 of 32 (53%) pts evaluable for efficacy. Fourteen pts received treatment >16 wks. One pt with thyroid cancer had SD for 46 wks, and 1 pt with hepatocellular cancer had SD for 16 wks with ≥50% decline in alpha-fetoprotein. Across all dose levels, REGN910 pharmacokinetics appeared linear and dose-proportional. The PK profile was characterized by an initial distribution and a single mono-exponential elimination phase. Total circulating serum Ang2 levels appeared saturated following treatment in all cohorts, indicating systemic target engagement at all doses tested. Conclusions: Administration of REGN910 in patients with advanced cancer is well tolerated, with generally mild and moderate TRAEs. Dose escalation is completed, and enrollment to the expansion cohorts continues. The safety profile supports combination with chemotherapy and/or other anti-angiogenic agents. Clinical trial information: NCT01271972.

2502 Background: Dll4, a Notch receptor ligand, may have a role in tumor angiogenesis and is an emerging anticancer target. REGN421 (R) is a fully human IgG1mAb that binds human Dll4 and disrupts Notch-mediated signaling. Methods: Primary objectives of the dose escalation (3+3 design) trial were to determine safety and a recommended phase II dose (RP2D) of R in patients (pts) with advanced cancer. R was given IV at doses of 0.25, 0.5, 1, 2 and 4mg/kg every 3 weeks (Q3W) or 0.75, 1, 1.5, and 3mg/kg every 2 weeks (Q2W). Secondary objectives were PK, immunogenicity, and antitumor activity. Results: 53 pts (M/F=22/31, ECOG 0/1=18/35) were enrolled; 31 pts were treated Q3W at doses of 0.25 - 4 mg/kg; 22 pts were treated Q2W at doses of 0.75 - 3 mg/kg. Two DLTs occurred: Grade 3 (Gr3) nausea (0.5mg/kg Q3W) and Gr3 abdominal pain (1 mg/kg Q2W). A maximum tolerated dose was not reached on either schedule. Grade 3/4 AEs occurred in 29 pts; nausea, abdominal pain, dyspnea, hypoxia, and hypertension (HTN) were reported in ≥ 5%. Most frequent treatment related AEs were fatigue (30%), headache (26%), HTN (26%), and nausea (15%). Six treatment related SAEs (all reversed off treatment) were reported in 4 patients: BNP increase (0.25mg/kg, Gr1), troponin I increase (4mg/kg, Gr3), right ventricular dysfunction (1.5mg/kg, Gr3), left ventricular dysfunction (3mg/kg, Gr3) and 2 events of pulmonary HTN (1.5mg/kg, Gr 3, and 3mg/kg Gr3). Laboratory abnormalities (≥ Gr3) were neutropenia (3) and anemia (2), and elevated ALP (7), ALT (3), bilirubin (3), AST (2), and decreased albumin (1). Anti-tumor activity included 2 PRs (NSCLC BAL-type with a beta-catenin mutation and ovarian cancer [OvCa]), and 16 pts with SD (3 pts had SD > 6 months). Two of 8 pts with OvCa had CA125 responses. R had non-linear target-mediated PK without accumulation. The half-life of R at 3mg/kg Q2W was 7 days. No immunogenicity was observed. Conclusions: REGN421 had an acceptable safety profile, and RP2Ds of 4mg/kg Q3W and 3mg/kg Q2W. Responses and prolonged SD were noted in OvCa pts and other solid tumors. Dose escalation has concluded and disease specific expansion cohorts are ongoing. Clinical trial information: NCT00871559.

TPS159 Background: Angiopoietin-2 (Ang2) is a secreted growth factor that functions as a critical regulator of angiogenesis, blood vessel maturation and integrity of the vascular endothelium. The e...