Allan, John N.

7078 Background: Lisaftoclax is a novel, oral, highly selective, potent BCL-2 inhibitor in development. In an ibrutinib-resistant patient-derived WM xenograft/preclinical model, lisaftoclax + ibrutinib has a strong synergistic effect. This report provides updated efficacy and safety data of lisaftoclax-based therapies (including combinations with ibrutinib) in pts with WM. Methods: In this global, open-label, phase 1b/2 multicenter study, pts with WM were enrolled in 3 arms: Arm A (lisaftoclax) included BTKi-resistant/intolerant pts; Arm B (lisaftoclax + ibrutinib), treatment-naïve pts; and Arm C (lisaftoclax + rituximab), BTKi-naïve relapsed/refractory pts. Lisaftoclax was escalated from 400 to 1,200 mg using a modified toxicity probability interval design. A 3-day ramp-up was used for pts at high risk of tumor lysis syndrome (TLS). Objectives were efficacy, safety, and pharmacokinetics (PK) assessments (responses assessed per IWWM criteria). Results: As of January 25, 2024, 46 pts were enrolled and treated at doses of up to 1,000 (Arm A), 1,200 (Arm B), and 800 mg (Arm C; Table). The median (range) treatment duration was 11 (1-28; Arm A), 23.5 (1-34; B), and 11.5 (5-33; C) months. Objective response rates (PR, VGFR, CR) were: 41.7% (Arm A), 90.9% (B), and 37.5% (C). In Arm A, pts with wild-type CXCR4 (n = 7) had better overall response to lisaftoclax than the CXCR4mut group (n = 3). No significant difference was observed between pts with/without CXCR4mut in Arms B and C. In Arm B, 1 DLT (grade 3 clinical TLS due to preexisting renal impairment) was reported at 1,200 mg; 1 grade 3 laboratory TLS, primarily attributed to dehydration and concomitant symptomatic therapies, occurred at 1,000 mg; abnormal electrolytes resolved after 1 day of drug interruption, without recurrence. Grade ≥ 3 lisaftoclax-related AEs included neutropenia (15.2%), thrombocytopenia (4.3%), decreased leukocytes (4.3%), TLS (4.3%), anemia (2.2%), weight loss (2.2%), and septic shock (2.2%). Ventricular arrhythmia was not observed. One pt required dose reduction because of neutropenia. The MTD was not reached. Lisaftoclax + ibrutinib showed a PK exposure comparable to lisaftoclax or ibrutinib alone, indicating no potential drug-drug interactions. Conclusions: Lisaftoclax alone and combined with ibrutinib or rituximab was well tolerated and demonstrated measurable effects in pts with naïve or BTKi-treatment-failed WM. (CT.gov: NCT04260217; Internal ID: APG2575WU101) *Co-first authors: ML and SA. Clinical trial information: NCT04260217 . [Table: see text]

Abstract Although Bruton tyrosine kinase inhibitors (BTKis) are generally well tolerated and less toxic than chemotherapy alternatives used to treat lymphoid malignancies, BTKis like ibrutinib have the potential to cause new or worsening hypertension (HTN). Little is known about the optimal treatment of BTKi-associated HTN. Randomly selected patients with lymphoid malignancies on a BTKi and antihypertensive drug(s) and with at least 3 months of follow-up data were sorted into 2 groups: those diagnosed with HTN before BTKi initiation (prior-HTN), and those diagnosed with HTN after BTKi initiation (de novo HTN). Generalized estimating equations assessed associations between time varying mean arterial pressures (MAPs) and individual anti-HTN drug categories. Of 196 patients included in the study, 118 had prior-HTN, and 78 developed de novo HTN. Statistically significant mean MAP reductions were observed in patients with prior-HTN who took β blockers (BBs) with hydrochlorothiazide (HCTZ), (−5.05 mmHg; 95% confidence interval [CI], 10.0 to −0.0596; P = .047), and patients diagnosed with de novo HTN who took either an angiotensin converting enzyme inhibitor (ACEi) or angiotensin receptor blocker (ARB) with HCTZ (−5.47 mmHg; 95% CI, 10.9 to −0.001; P = .05). These regimens also correlated with the greatest percentages of normotensive MAPs. Treatment of HTN in patients taking a BTKi is challenging and may require multiple antihypertensives. Patients with prior-HTN appear to benefit from combination regimens with BBs and HCTZ, whereas patients with de novo HTN appear to benefit from ACEi/ARBs with HCTZ. These results should be confirmed in prospective studies.

Background: Richter Transformation (RT) refers to the development of an aggressive lymphoma in the setting of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). Small molecule inhibitors (SMI), such as the Bruton tyrosine kinase inhibitors (BTKi) and BCL2 inhibitors (BCL2i), have revolutionized the treatment of CLL/SLL. Prior studies evaluated outcomes of patients (pts) with RT in an era where chemoimmunotherapy (CIT) was typically used to treat CLL/SLL. Now that SMI are standard of care, fewer pts with CLL/SLL receive CIT, therefore we sought to determine which variables predict survival in pts who developed RT without prior CIT exposure for CLL/SLL. Methods: We conducted an international multicenter retrospective study of pts from 11 academic centers. Pts with RT occurring as large B-cell lymphoma who did not previously receive CIT (e.g., fludarabine, cyclophosphamide, bendamustine, chlorambucil) for their CLL/SLL were included. We collected pt, disease, and treatment (tx) characteristics. RT was categorized into 3 groups: “Concurrent RT,” defined as RT and CLL/SLL diagnosed simultaneously (within 3 months [mos]); “RT w/o prior CLL/SLL tx,” defined as RT and CLL/SLL diagnosed >3 mos apart with the CLL/SLL never treated; and “RT with prior non-CIT tx for CLL/SLL” defined as having received prior CLL/SLL tx. Overall survival (OS) was measured from RT diagnosis (Dx) and estimated using the Kaplan-Meier method. Cox regression model was used to identify prognostic factors associated with OS. Results: 242 pts were identified. At CLL/SLL Dx, 66% of pts had unmutated IGHV, 37% had del17p/ TP53 disruption, and 20% had trisomy 12. At RT Dx, 56% of the RT with prior non-CIT tx for CLL/SLL group had a del17p/ TP53 disruption versus 27% for the concurrent RT group and 18% for the RT w/o prior CLL/SLL tx groups. Median time from CLL/SLL Dx to RT Dx was 47 mos (range 3-394) for RT w/o prior CLL/SLL tx and 46 mos (range 4-218) for RT with prior non-CIT tx for CLL/SLL. Pts with prior non-CIT tx for CLL/SLL received a median of 1 (range 1-5) prior tx. 86% of pts previously received a BTKi or a BCL2i for tx of CLL/SLL (54% BTKi only, 5% BCL2i only, 27% both). The remaining 14% had been treated with an anti-CD20 monoclonal antibody (MoAb), steroids, lenalidomide, radiation, or alemtuzumab. 85% of pts developed RT while on active tx with SMI. Median age at RT Dx was 69 years (range 37-92). At RT Dx, 38% and 21% of pts had del17p/ TP53 disruption, and trisomy 12 in CLL/SLL tissue, respectively. At RT Dx, there was no difference in highest SUV on PET (median 16, range 2.9-65.6), LDH (median 325, range 103-8162, ULN range 180-271), largest lymph node in diameter (median 4.9 cm, range 0-17.1), Ki-67 (median 80%, range 5%-100%), rate of GCB subtype (27%), presence of MYC translocation (20%), or CLL/SLL and RT clonal relationship (81%) for those pts tested amongst the 3 groups ( Table). The most common 1 st line tx for RT was CIT with or w/o radiation and/or steroids (76%), followed by CIT plus SMI (13%), SMI single agent or combination (7%), and other (4%, which includes anti-CD20 MoAb). Median follow-up from RT Dx was 42.3 mos; the median OS for the entire cohort was 25.8 mos (95% CI: 16.8-49.1). Pts with RT after non-CIT tx for CLL/SLL had a significantly worse OS (median 8.2 mos [95% CI: 5.6-14.3]) than pts with concurrent RT (median 46.3 mos [95% CI: 23.8-96.9]) and RT w/o prior CLL/SLL tx (median 63.5 mos [95% CI: 28.3-70.3]) ( Figure). From an exploratory univariable analysis, we found RT after non-CIT tx for CLL/SLL compared to concurrent RT (HR 2.32 [95% CI: 1.55-3.46]), RT Dx age (HR for 5-year increase 1.14 [95% CI: 1.05-1.23]), del17p/ TP53 disruption (HR 2.27 [95% CI: 1.45-3.56]), and LDH (HR for 2-fold increase 1.37 [95% CI: 1.20-1.58]) were prognostic for worse OS. Conclusions: This is the largest cohort of pts who developed RT having received only SMI with no CIT for their CLL reported, thus reflecting the current treatment landscape. Despite being CIT-naïve, pts in our series who received tx for their CLL/SLL and then developed RT had a short OS, underscoring the need to develop better therapies for these pts. In contrast, as in other published analyses (Wang Haematologica 2020), pts w/o prior tx for CLL/SLL had more favorable outcomes, with a median OS of approximately 5 years. Further analysis to determine PFS and OS by tx for RT for pts who have been treated with SMI for their CLL/SLL is ongoing.

Background Chimeric antigen receptor (CAR) T-cell therapies have recently been established as an important option for the management of relapsed/refractory (R/R) DLBCL. However, real-world studies suggest that approximately half of all patients (pts) receiving commercial CAR-T therapies will relapse within 6 months. These pts have a poor prognosis, with estimated overall survival (OS) of only 5 months, indicating a significant unmet need. Odronextamab is a novel, off-the-shelf, CD20×CD3 bispecific antibody that has demonstrated activity in both R/R follicular lymphoma and R/R DLBCL. We have previously reported encouraging results with odronextamab from the Phase 1 ELM-1 study (NCT02290951) in pts with R/R DLBCL post CAR-T therapy (Bannerji R, et al. Lancet Haematol. 2022). These results were consistent with the antitumor activity seen in pts with R/R DLBCL from the Phase 2 ELM-2 study (Kim WS, et al. ASH 2022). Here, we present an updated analysis of outcomes in a prespecified cohort of post CAR-T patients from ELM-1. Methods Intravenous odronextamab was administered weekly in 21-day cycles during Cycles (C) 1-4. Revisions to the step-up regimen were reported previously (Bannerji R, et al. Lancet Haematol. 2022). Odronextamab was administered with steroid prophylaxis and step-up doses of 0.7/4/20 mg during C1 to mitigate the risk of cytokine release syndrome (CRS), followed by 160 mg on Days (D) 1, 8, and 15 of C2-4. After C4, odronextamab maintenance treatment continued at 320 mg every 2 weeks until disease progression or unacceptable toxicity. Those pts who achieved a complete response (CR) that was durable for ≥9 months transitioned to dosing with 320 mg every 4 weeks. The primary endpoint was objective response rate (ORR), assessed by independent central review (ICR) according to the Lugano classification. Key secondary endpoints included duration of response (DoR), progression-free survival (PFS), and OS. Immune biomarker assessment was an exploratory endpoint. Results As of Dec 20, 2022, 46 pts were treated (safety-evaluable), with 44 pts evaluable for efficacy. For safety-evaluable pts, median age was 63 years (range 27-82), 67% male, 74% Ann Arbor stage III-IV, and 72% were refractory to CAR-T therapy administered in any prior line. 44 pts were evaluable for efficacy after 4.9 months median duration of follow-up. The ORR and CR rate by ICR were 48% (21/44) and 30% (13/44), respectively. Responses were durable, and both median DoR and median duration of CR were not reached. The probability of maintaining a response for 12 months was 62% and the probability of maintaining a CR for 9 months was 86%.A responder analysis of the subgroup of pts who achieved a CR will be presented. The CAR-T treated pts with DLBCL who were evaluable for biomarker analysis (n=10) had lower T-cell counts at baseline compared with CAR-T naive DLBCL pts (n=41 comparable pts who received odronextamab in ELM-2), yet the fold-change of T-cell expansion at C4D15 was greater in CAR-T treated pts versus CAR-T naive pts. T-cell dynamics, such as changes in activation, exhaustion, and memory subsets, will be presented. Safety was generally consistent with that previously reported. Six (13%) pts permanently discontinued odronextamab due to a treatment-emergent AE (device-related infection, pneumonia, dysphagia, gait disturbance, leukemia, and encephalopathy [n=1 each]). The most common treatment-emergent AE was CRS (any grade, 52%). The highest grade of CRS reported was Grade 2, and low-grade CRS events occurred in 46% of pts with the 0.7/4/20 mg step-up regimen. No cases of ICANS were reported in pts with the 0.7/4/20 mg regimen. Grade ≥3 infections occurred in 10 (22%) pts, with no Grade 5 events. No cases of tumor flare were reported. Conclusions Odronextamab monotherapy demonstrates encouraging antitumor activity in heavily pretreated pts who have progressed after CAR-T therapy, with a generally manageable safety profile. Durable CRs were achieved in this difficult-to-treat setting. These data support the potential role of odronextamab in the treatment paradigm for R/R DLBCL. Further studies to evaluate the optimal sequencing and combinations of odronextamab with CAR-T therapy are warranted.

7569 Background: B-cell lymphoma 2 inhibitors (BCL-2i) are well tolerated and effective in treating B-cell lymphoproliferative disorders such as CLL. Investigational agent lisaftoclax is a novel, oral, highly selective and potent BCL-2i. Preclinical data show a strong synergistic effect of lisaftoclax plus ibrutinib in an ibrutinib-insensitive PDXWM1 model. Methods: This global, open-label, multicenter study evaluates the safety and efficacy of lisaftoclax alone and combined with ibrutinib or rituximab in pts with WM. Pts were enrolled in 3 arms: Arm A (lisaftoclax), BTKi-resistant/intolerant pts; Arm B (lisaftoclax plus ibrutinib), treatment-naïve pts; and Arm C (lisaftoclax plus rituximab), BTKi-naïve relapsed/refractory pts. Lisaftoclax was escalated from 400 to 1,200 mg using a modified toxicity probability interval design. A 3-day ramp-up was used for pts at high TLS risk. Primary objectives were pharmacokinetics (PK), safety, and efficacy assessments; responses were assessed per IWWM criteria. Results: As of January 25, 2023, 46 pts were enrolled (Arm A [n = 14]; up to 1,000 mg; Arm B [n = 24]; up to 1,200 mg; Arm C [n = 8]; up to 800 mg). Baseline characteristics are shown in the table. Median (range) treatment duration was 6 (1-18; Arm A), 14 (1-27; B), and 8 (2-26; C) months. Overall response rates (ORRs) were: Arm A, 25% (median time to response [MTTR], 4.3 months); Arm B, 90.9% (MTTR, 1.9); Arm C, 37.5% (MTTR, 4.4). No significant difference was observed between pts with and without CXCR4-mut. At 1,200 mg, 1 DLT (grade 3 clinical TLS), due to pre-existing renal impairment, was reported. At 1,000 mg, 1 grade 3 laboratory TLS occurred in Arm B because of dehydration and active symptomatic therapies; abnormal electrolytes resolved after 1 day of drug interruption, without recurrence. Grade ≥ 3 lisaftoclax-related AEs included neutropenia (13%), leukocytopenia (4.3%), anemia (2.2%), weight loss (2.2%), and septic shock (2.2%). Ventricular arrhythmias were not observed. Only 1 pt required dose reduction (due to neutropenia). MTD has not been reached. A total of 14 pts discontinued study treatment because of disease progression (n = 5) and AE (n = 1). Lisaftoclax plus ibrutinib showed a PK exposure comparable to ibrutinib alone, indicating no potential DDI. Conclusions: Lisaftoclax alone or combined with ibrutinib/rituximab demonstrated measurable effects in pts with naïve or BTKi-treatment-failed WM. Internal study identifier: APG2575WU101. *SA and ML are co-first authors. Clinical trial information: NCT04260217 . [Table: see text]

AbstractRichter syndrome (RS) represents the transformation of chronic lymphocytic leukemia (CLL), typically to an aggressive lymphoma. Treatment options for RS are limited and the disease is often fatal. Receptor tyrosine kinase–like orphan receptor 1 (ROR1) is expressed on CLL cells and other cancers but not on healthy adult tissues, making it an attractive, tumor-specific therapeutic target. VLS-101 is being developed as an antibody-drug conjugate (ADC) for therapy of ROR1-expressing (ROR1+) cancers. VLS-101 comprises UC-961 (a humanized immunoglobulin G1 monoclonal antibody that binds an extracellular epitope of human ROR1), a maleimidocaproyl-valine-citrulline-para-aminobenzoate linker, and the antimicrotubule cytotoxin monomethyl auristatin E (MMAE). VLS-101 binding to ROR1 results in rapid cellular internalization and delivery of MMAE to induce tumor cell death. We studied 4 RS patient-derived xenografts (RS-PDXs) with varying levels of ROR1 expression (11%, 32%, 85%, and 99% of cells). VLS-101 showed no efficacy in the lowest-expressing RS-PDX but induced complete remissions in those with higher levels of ROR1 expression. Responses were maintained during the posttherapy period, particularly after higher VLS-101 doses. In systemic ROR1+ RS-PDXs, VLS-101 dramatically decreased tumor burden in all RS-colonized tissues and significantly prolonged survival. Animals showed no adverse effects or weight loss. Our results confirm ROR1 as a target in RS and demonstrate the therapeutic potential of using an ADC directed toward ROR1 for the treatment of hematological cancers. A phase 1 clinical trial of VLS-101 (NCT03833180) is ongoing in patients with RS and other hematological malignancies.

BACKGROUND: Odronextamab (REGN1979) is a first-in-class, hinge-stabilized, fully human IgG4-based CD3 x CD20 bispecific antibody (bsAb) that has demonstrated encouraging safety, tolerability and preliminary efficacy in a first-in-human study of patients (pts) with relapsed/refractory (R/R) B-cell non-Hodgkin lymphoma (B-NHL). We report updated safety and efficacy data from the dose escalation and early dose expansion phase of the ongoing Phase (P)1 study (NCT02290951). METHODS: Odronextamab was 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. Dexamethasone premedication was used to mitigate the risk for cytokine release syndrome (CRS). Key primary objectives were to assess safety and dose-limiting toxicities (DLTs), and to establish a maximum tolerated dose (MTD) and recommended P2 dosing regimen (RP2DR). Secondary objectives included a preliminary assessment of anti-tumor activity. RESULTS: As of Jun 25, 2020, 127 pts with R/R B-NHL have been treated at doses ranging from 0.03-320 mg. The study included pts with diffuse large B-cell lymphoma (DLBCL; n=71), follicular lymphoma (FL) Grade (Gr) 1-3a (n=37), mantle cell lymphoma (MCL; n=11), marginal zone lymphoma (n=6), and other B-NHLs (n=2). Pts were highly refractory (80.3%) and had received a median of 3 (range: 1‒11) prior lines of therapy; 29 pts (22.8%) received prior CAR T therapy (FL: 2; DLBCL: 25; MCL: 2) and 85 pts (66.9%) were double refractory to alkylator and anti-CD20 antibody, in any line of therapy. Median follow-up was 3.9 (0.4‒37.6) months (mo). No DLTs were reported during dose escalation and MTD was not reached with odronextamab doses up to 320 mg weekly. The most frequent treatment-related adverse events (AEs) of any grade were pyrexia (76.4%), CRS (62.2%), and chills (48.0%). Gr 3 CRS occurred in 8 pts (6.3%) and a Gr 4 CRS occurred in 1 pt (0.8%). Most of the CRS events occurred during the first 2 weeks of step-up dosing and resolved within a median of 2 days (range 1-41) with supportive care measures. No pts discontinued odronextamab treatment due to CRS. Gr 3 neurologic AEs were noted in 5 pts, of which only 3 (2.3%) were considered treatment-related: somnolence, syncope, and encephalopathy. None of these events required treatment discontinuation. There were no Gr 4 or higher neurologic AEs. Overall, 7 pts (5.5%) discontinued treatment due to treatment-related AEs. In pts with R/R FL Gr 1-3a, odronextamab demonstrated a broad window of therapeutic activity. In pts treated at doses of ≥5 mg (n=28), objective response rate (ORR) was 92.9%, and complete response (CR) rate was 75.0%; median duration of response (DoR) was 7.7 mo (range 0+-20.9+), with 13 of 21 CRs ongoing at last tumor assessment. The median duration of complete response (DoCR) was 8.1 mo (range 0+-19.9+) and follow-up is ongoing (Table). In pts with R/R DLBCL, encouraging activity was observed at higher odronextamab dose levels. In DLBCL pts who had not received prior CAR T therapy, treated at doses ≥80 mg (n=10), ORR and CR rate were 60%; median observed DoR was 10.3 mo (range 2.9-18.6+), with 4 of 6 CRs ongoing at last tumor assessment. The median DoCR was 9.5 mo (range 2.9-18.6+) and follow-up is ongoing. In DLBCL pts who were refractory to prior CAR T therapy, treated at doses ≥80 mg (n=21), ORR was 33.3%, and CR rate was 23.8%; median observed DoR was 2.8 mo (range 0+-18.9+), with 5 of 5 CRs ongoing at last tumor assessment. The median DoCR was 4.4 mo (range 0+-18.9+) and follow-up is ongoing. Based on an evaluation of preliminary antitumor activity and PK, RP2DR was identified for dose expansion cohorts. CONCLUSIONS: Odronextamab has demonstrated encouraging single agent antitumor activity in highly refractory pts with B-NHLs. Durable CRs have been observed in both indolent and aggressive B-NHL pts, including in pts refractory to CAR T therapy. Most CRs are ongoing at time of data cutoff, and updated data will be presented. Odronextamab has an acceptable safety and tolerability profile. Dexamethasone premedication and step-up dosing mitigates the risk for CRS and allows odronextamab administration up to 320 mg weekly without DLTs. A global P2 trial investigating odronextamab in R/R B-NHL is ongoing. Disclosures Bannerji: Regeneron Pharmaceuticals: Research Funding; AbbVie: Research Funding; Sanofi-Pasteur: Other: Spouse is employee; F. Hoffmann-La Roche Ltd/Genentech, Inc and Pharmacyclics LLC, an AbbVie Company: Research Funding. Allan:Acerta, Genentech, Abbvie, Sunesis, Ascentage, Pharmacyclics, Janssen, AstraZeneca, BeiGene: Consultancy; Abbvie, Janssen, AstraZeneca, Pharmacyclics: Honoraria; Celgene, Genentech, Janssen, TG Therapeutics: Research Funding. Arnason:Regeneron: Consultancy; Juno: Consultancy. Brown:Catapult: Consultancy; Sun: Research Funding; Loxo: Consultancy, Research Funding; Verastem: Consultancy, Research Funding; TG Therapeutics: Consultancy; Sunesis: Consultancy; Rigel Pharmaceuticals: Consultancy; Pfizer: Consultancy; Octapharma: Consultancy; Novartis: Consultancy; Nextcea: Consultancy; MEI Pharma: Consultancy; Kite: Consultancy; Juno/Celgene: Consultancy; Eli Lilly and Company: Consultancy; Dynamo Therapeutics: Consultancy; BeiGene: Consultancy; Gilead: Consultancy, Research Funding; Invectys: Membership on an entity's Board of Directors or advisory committees, Other: DSMC; Acerta: Consultancy; Genentech: Consultancy; Pharmacyclics: Consultancy; Morphosys: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other; Astra-Zeneca: Consultancy; Janssen: Honoraria; AbbVie: Consultancy. Advani:Celgene, Forty Seven, Inc., Genentech/Roche, Janssen Pharmaceutical, Kura, Merck, Millenium, Pharmacyclics, Regeneron, Seattle Genetics: Research Funding; Astra Zeneca, Bayer Healthcare Pharmaceuticals, Cell Medica, Celgene, Genentech/Roche, Gilead, KitePharma, Kyowa, Portola Pharmaceuticals, Sanofi, Seattle Genetics, Takeda: Consultancy. Ansell:Bristol Myers Squibb: Research Funding; Takeda: Research Funding; Trillium: Research Funding; ADC Therapeutics: Research Funding; Affimed: Research Funding; Seattle Genetics: Research Funding; Regeneron: Research Funding; AI Therapeutics: Research Funding. O'Brien:Gilead, Pharmacyclics, TG Therapeutics, Pfizer, Sunesis: Consultancy, Research Funding; Kite, Regeneron, Acerta: Research Funding; Amgen, Astellas, Celgene, GlaxoSmithKline, Janssen Oncology, Aptose Biosciences Inc. Vaniam Group, AbbVie, Alexion, Verastem, Eisai, Juno Therapeutics, Vida Ventures: Consultancy. Duell:Morphosys: Research Funding. Martin:Sandoz: Consultancy; Karyopharm: Consultancy, Research Funding; Celgene: Consultancy; Teneobio: Consultancy; I-MAB: Consultancy; Bayer: Consultancy; Beigene: Consultancy; Cellectar: Consultancy; Incyte: Consultancy; Kite: Consultancy; Morphosys: Consultancy; Regeneron: Consultancy; Janssen: Consultancy. Li:Regeneron Pharmaceuticals, Inc: Current Employment, Current equity holder in publicly-traded company. Flink: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. Weinreich:Regeneron Pharmaceuticals, Inc.: Current Employment, Current equity holder in publicly-traded company. Yancopoulos: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. Topp:Amgen, Boehringer Ingelheim, KITE, Regeneron, Roche: Research Funding; Amgen, KITE, Novartis, Regeneron, Roche: Consultancy. OffLabel Disclosure: The data described in the abstract will report on use of odronextamab in a Phase 1 clinical trial of patients with B-NHL

Background : The presence of TP53 aberrations (defined as del(17p) or TP53 gene mutation) is a strong negative predictor of survival in patients (pts) with CLL. First-line chemoimmunotherapy is suboptimal in pts with CLL bearing TP53 aberrations, with 3-year progression-free survival (PFS) and overall survival (OS) rates of only 18% and 38%, respectively, with fludarabine, cyclophosphamide, and rituximab (Hallek, Lancet 2010). Ibrutinib is the only once-daily Bruton's tyrosine kinase (BTK) inhibitor with significant PFS and OS benefit demonstrated in multiple randomized phase 3 studies (eg, RESONATE-2, ECOG1912) in the first-line treatment of CLL/small lymphocytic lymphoma (SLL). Previous reports of single-agent ibrutinib or ibrutinib-based combination treatments have further demonstrated favorable PFS benefit in pts with TP53 aberrations in both the first-line and relapsed/refractory settings. Despite these study-specific subgroup analyses, there are limited data on long-term outcomes in pts with TP53 aberrations treated with first-line BTK inhibitors. We performed a pooled analysis of data across 4 studies to evaluate the long-term efficacy and safety of first-line ibrutinib-based therapy in pts with CLL bearing TP53 aberrations. Methods : Data for first-line ibrutinib treatment in pts with TP53 aberrations were pooled across 4 clinical trials in CLL/SLL: PCYC-1122e (NCT01500733; single-agent ibrutinib; n=34), PCYC-1130 (NCT02264574; ibrutinib + obinutuzumab; n=18), ECOG1912 (NCT02048813; ibrutinib + rituximab; n=26), and RESONATE-2 (NCT01722487; single-agent ibrutinib; n=11). ECOG1912 and RESONATE-2 excluded pts with del(17p) but did not exclude pts with TP53 mutations. Long-term PFS (assessed by investigator), OS, and safety are reported. Results : Eighty-nine pts with TP53 aberrations receiving first-line ibrutinib treatment were included in this pooled analysis. Median age was 65 years (range 33-87), and 69% of pts were male. At baseline, 53% had Rai stage III/IV, 38% had bulky disease (lymph nodes ≥5 cm), and 69% (of 87 evaluable) had unmutated IGHV. All patients had either del(17p) or TP53 mutation; 53% (of 89 evaluable) had del(17p) and 91% (of 58 evaluable) had TP53 mutation. Among 16 pts with del(17p) who had TP53 sequencing results available, 11 (69%) had both del(17p) and TP53 mutation. Forty-five pts received ibrutinib as a single agent and 44 received ibrutinib in combination with an anti-CD20 agent. With a median follow-up of 50 months (range 0.1 to 95.9 months), median PFS was not reached (95% CI: 67 months to not estimable; Figure 1A). At 48 months, the PFS rate was 79% and the OS rate was 88% (Figure 1B). Median duration of ibrutinib treatment was 46 months (range 0.1 to 95.5 months). Reasons for treatment discontinuation were progressive disease (20%), study closure (12%), adverse event (10%), withdrawal by pt (7%), death (3%), and other (physician decision due to scheduled pt surgery; 1%). Grade ≥3 adverse events of clinical interest with up to 8 years of treatment with ibrutinib were infection (22%; most commonly pneumonia in 7%), hypertension (13%), atrial fibrillation (12%), and major hemorrhage (7%). With the current follow-up, 46% of pts with TP53 aberrations remained on ibrutinib treatment. Conclusions : With a median follow-up of 4 years, first-line ibrutinib-based treatment resulted in sustained efficacy with high PFS and OS rates in CLL pts with TP53 aberrations, a population with historically poor outcomes. Although pts with TP53 aberrations remain at risk for progression, first-line treatment with ibrutinib has partially overcome the poor prognosis in this high-risk population with 4-year PFS and OS rates of 79% and 88%, respectively. No new safety signals were identified in this analysis. These results from a large, pooled, multi-study dataset demonstrated the long-term benefit of first-line ibrutinib-based treatment in pts with TP53 aberrations. Disclosures Allan: Janssen, AbbVie, and AstraZeneca: Other: Travel/accommodations/expenses; Celgene, Genentech, AstraZeneca, TG Therapeutics, and Janssen: Research Funding; AstraZeneca, Pharmacyclics LLC, an AbbVie Company, Genentech, AbbVie, Ascentage, and Cellectar: Consultancy; Janssen, AstraZeneca, and AbbVie: Honoraria. Shanafelt:Genentech, Pharmacyclics LLC, an AbbVie Company, AbbVie, GlaxoSmithKline, and Merck: Research Funding; Mayo Clinic: Patents & Royalties: and other intellectual property. Wiestner:Pharmacyclics LLC, an AbbVie Company; Acerta, Merck, Nurix, Verastem, and Genmab: Research Funding; National Institutes of Health: Patents & Royalties: and other intellectual property. Moreno:Janssen, AbbVie, Sunesis, and AstraZeneca: Consultancy; AbbVie and Janssen: Research Funding; Janssen: Speakers Bureau. O'Brien:Eisai: Consultancy; Juno Therapeutics: Consultancy; Aptose Biosciences: Consultancy; GlaxoSmithKline: Consultancy; Sunesis: Research Funding; Acerta: Research Funding; Amgen: Consultancy; Celgene: Consultancy; Pfizer: Research Funding; Pharmacyclics: Research Funding; Astellas: Consultancy; Gilead: Consultancy; TG Therapeutics: Research Funding; Vida Ventures: Consultancy; KITE: Research Funding; Vaniam Group LL: Consultancy; Alexion: Consultancy; Regeneron: Research Funding; AbbVie: Consultancy; Verastem: Consultancy; Janssen Oncology: Consultancy. Braggio:DASA: Consultancy; Bayer: Other: Stock Owner; Acerta Pharma: Research Funding. Liu:AbbVie: Current equity holder in publicly-traded company; Pharmacyclics LLC, an AbbVie Company: Current Employment. Dean:AbbVie: Current equity holder in publicly-traded company; Pharmacyclics LLC, an AbbVie Company: Current Employment. Lai:Pharmacyclics LLC, an AbbVie Company: Current Employment; AbbVie and Bristol-Myers Squibb: Current equity holder in publicly-traded company; AbbVie: Other: Travel/accommodations/expenses.

Background 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. Dose escalation is complete and a recommended Ph 2 dose has been determined. We report Ph 1 safety and efficacy results of REGN1979 in patients (pts) with R/R B-NHL previously treated with anti-CD20 Abs, including pts with progressive disease after anti-CD19 CAR T-cell (CAR T) therapy. Methods Primary objectives are to determine safety, tolerability, and occurrence of dose limiting toxicities (DLTs). Other objectives are to assess antitumor activity, pharmacokinetics (PK), and pharmacodynamics. Eligible pts with R/R B-NHL must have received prior CD20-directed therapy. Treatment consists of 12 weekly intravenous doses of REGN1979 followed by every 2-week dosing for 12 doses (36 weeks total). Results As of June 3, 2019, 96 pts (diffuse large cell B-cell lymphoma [DLBCL] [n=53], follicular lymphoma [FL] grade [Gr] 1-3a [n=25], mantle cell lymphoma [n=6], marginal zone lymphoma [n=6], or other [FL Gr 3b, FL unknown, FL ungraded, or Waldenström macroglobulinemia ] [n=6]) were treated with REGN1979 0.03-320 mg and received a median of 9 doses (range 1-24). Pts had a median of 3 prior lines of therapy (range 1-11); 12 pts with prior CAR T therapy were included in the safety analysis of which 6 were included in the efficacy analysis. Twenty-four pts remain on treatment; 18 completed treatment; 54 discontinued early (35 due to progressive disease [PD]). No pts with B-NHL experienced a DLT. The most common treatment-emergent adverse events (AEs) were pyrexia (n=74), CRS (n=55), chills (n=49), infections and infestations (n=47), fatigue (n=36), increased C-reactive protein (n=32), and anemia (n=32). Seven pts experienced Gr 3 CRS. The severity of CRS symptoms declined through optimized pre-medication even with REGN1979 dose escalation. Most common Gr 3 or 4 AEs were anemia (n=19), decreased lymphocytes/lymphopenia (n=19), infections and infestations (n=18), decreased neutrophils/neutropenia (n=17), and hypophosphatemia/decreased blood phosphorus (n=16). No pts had seizures or grade 4/5 neurologic AEs. Gr 3 neurologic AEs included depressed level of consciousness (unrelated), somnolence, and syncope (n=1 each). Neurological events were transient and none required permanent treatment termination. Five pts discontinued due to AEs: Gr 3 hemolysis; Gr 3 fatigue; Gr 2 and Gr 3 pneumonia; and Gr 3 neck abscess (1 each). Eleven pts died on study: PD (n=6), gastric perforation (n=1), cardiac arrest (n=1), lung infection (n=1), multi-organ failure (n=1), pneumonia (n=1). The Table and Figure show efficacy and duration of response for R/R DLBCL by dose level. Pts who had opportunity for response assessment at Week 12 were included in the analysis of response. Emerging data suggest increasing efficacy with higher doses in R/R DLBCL, with 5 of 8 pts treated at 80/160/320 mg achieving CR; at these doses 2 of 3 pts achieved CR after failure of CAR T therapy. Data also suggest increasing efficacy with increasing doses in R/R FL, but maximum efficacy appears to be achieved at lower doses than in DLBCL; in pts with FL Gr 1-3a treated at ≥5 mg, the ORR was 93% (13/14), and the CR rate was 71.4% (10/14). REGN1979 concentrations in serum increased linearly with dose during the first five weeks. Elevated levels of serum cytokines were observed, mostly in week 1, and no correlation was observed with clinical efficacy. Immunohistological analysis of malignant lymph node tissue demonstrated that pts with high and low CD20 expression achieved clinical response. Relapse among responders was seen with either maintenance or loss of CD20 expression, suggesting antigen-dependent and independent disease escape mechanisms. Conclusions/Summary Tolerability of REGN1979 has been demonstrated at doses up to the final dose level of 320 mg weekly, with no observed DLTs in pts with B-NHL. No pts discontinued due to neurologic AE. Activity was observed broadly in heavily pretreated R/R B-NHL pts treated with REGN1979. With increasing dose, more resistant tumors such as R/R DLBCL are showing benefit, even in pts with prior CAR T therapy failure. Based on these efficacy findings, a global Ph 2 study is underway to evaluate REGN1979 monotherapy in R/R FL Gr 1-3a, R/R DLBCL, and other R/R B-NHL subtypes. Disclosures Bannerji: AbbVie, Inc: Consultancy, travel support; Gilead: Other: travel support; Gilead: Other: travel support; Pharmacyclics: Other: travel support; Merck: Other: travel support, Patents & Royalties: IP rights; AbbVie, Inc: Consultancy; Regeneron Pharmaceuticals, Inc.: Consultancy, Other: travel support, Research Funding; Regeneron Pharmaceuticals, Inc.: Consultancy, Other: travel support, Research Funding; Celgene: Consultancy; Celgene: Consultancy; Merck: Other: travel support, Patents & Royalties: IP rights; Pharmacyclics: Other: travel support. Allan:Acerta Pharma: Consultancy; Sunesis Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees; AbbVie, Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics LLC, an AbbVie company: Consultancy; Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bayer: Consultancy; Verastem Oncology, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria. Arnason:Celgene/Juno: Consultancy; Regeneron Pharmaceuticals, Inc.: Consultancy. Brown:AstraZeneca: Consultancy; Acerta Pharma: Consultancy; Morphosys: Other: Data safety monitoring boards ; Sun Pharmaceuticals, Inc: Research Funding; Sun: Research Funding; Verastem: Consultancy, Research Funding; TG Therapeutics: Consultancy; Teva: Honoraria; Sunesis: Consultancy; Pharmacyclics: Consultancy; Pfizer: Consultancy; Janssen: Honoraria; Invectys: Other: other; Loxo: Consultancy, Research Funding; Novartis: Consultancy; Octapharma: Consultancy; Kite: Consultancy, Research Funding; Dynamo Therapeutics: Consultancy; Catapult Therapeutics: Consultancy; BeiGene: Consultancy; Gilead: Consultancy, Research Funding; Genentech/Roche: Consultancy. Advani:Kyowa Kirin Pharmaceutical Developments, Inc.: Consultancy; Seattle Genetics: Consultancy, Research Funding; Celmed: Consultancy, Membership on an entity's Board of Directors or advisory committees; Forty-Seven: Research Funding; Roche/Genentech: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Kura: Research Funding; Bayer: Consultancy, Membership on an entity's Board of Directors or advisory committees; Millennium: Research Funding; Gilead Sciences, Inc./Kite Pharma, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding; Infinity Pharma: Research Funding; Janssen: Research Funding; Merck: Research Funding; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees; Cell Medica, Ltd: Consultancy; Autolus: Consultancy, Membership on an entity's Board of Directors or advisory committees; Agensys: Research Funding; AstraZeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees; Stanford University: Employment, Equity Ownership; Regeneron: Research Funding; Pharmacyclics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Ansell:Seattle Genetics: Research Funding; Trillium: Research Funding; Seattle Genetics: Research Funding; Trillium: Research Funding; Regeneron: Research Funding; Mayo Clinic Rochester: Employment; Regeneron: Research Funding; LAM Therapeutics: Research Funding; Seattle Genetics: Research Funding; Seattle Genetics: Research Funding; Mayo Clinic Rochester: Employment; Mayo Clinic Rochester: Employment; LAM Therapeutics: Research Funding; Bristol-Myers Squibb: Research Funding; Regeneron: Research Funding; Bristol-Myers Squibb: Research Funding; Trillium: Research Funding; Bristol-Myers Squibb: Research Funding; Affimed: Research Funding; Bristol-Myers Squibb: Research Funding; LAM Therapeutics: Research Funding; Seattle Genetics: Research Funding; Affimed: Research Funding; Mayo Clinic Rochester: Employment; Seattle Genetics: Research Funding; Seattle Genetics: Research Funding; Affimed: Research Funding; Affimed: Research Funding; Trillium: Research Funding; LAM Therapeutics: Research Funding; Affimed: Research Funding; Bristol-Myers Squibb: Research Funding; LAM Therapeutics: Research Funding; Regeneron: Research Funding; Regeneron: Research Funding; Affimed: Research Funding; Affimed: Research Funding; Regeneron: Research Funding; Bristol-Myers Squibb: Research Funding; LAM Therapeutics: Research Funding; Bristol-Myers Squibb: Research Funding; LAM Therapeutics: Research Funding; Trillium: Research Funding; Seattle Genetics: Research Funding; Affimed: Research Funding; Regeneron: Research Funding; Trillium: Research Funding; LAM Therapeutics: Research Funding; LAM Therapeutics: Research Funding; Trillium: Research Funding; Mayo Clinic Rochester: Employment; Regeneron: Research Funding; Trillium: Research Funding; Seattle Genetics: Research Funding; Bristol-Myers Squibb: Research Funding; Trillium: Research Funding; Affimed: Research Funding; Bristol-Myers Squibb: Research Funding; Mayo Clinic Rochester: Employment; Mayo Clinic Rochester: Employment; Mayo Clinic Rochester: Employment; Regeneron: Research Funding; Mayo Clinic Rochester: Employment. O'Brien:Pfizer: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria; Acerta: Research Funding; Alexion: Consultancy; Amgen: Consultancy; Aptose Biosciences, Inc: Consultancy; Astellas: Consultancy; Celgene: Consultancy; Eisai: Consultancy; Gilead: Consultancy, Research Funding; GlaxoSmithKline: Consultancy; Kite: Research Funding; Janssen: Consultancy, Honoraria; Pharmacyclics LLC, an AbbVie Company: Consultancy, Research Funding; Regeneron: Research Funding; Verastem: Consultancy; Sunesis: Consultancy, Research Funding; Vaniam Group LLC: Consultancy; TG Therapeutics: Consultancy, Research Funding. Chavez:Janssen Pharmaceuticals, Inc.: Speakers Bureau; Kite Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees; Genentech: Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees. Duell:Regeneron Pharmaceuticals, Inc.: Research Funding. Martin:I-MAB: Consultancy; Karyopharm: Consultancy; Celgene: Consultancy; Janssen: Consultancy; Sandoz: Consultancy; Teneobio: Consultancy. Charnas: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. Zhu:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Li:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Gasparini:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Ibrahim:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Jankovic:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Fiaschi:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Aina:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Zhang:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Deering:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Hamon:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Thurston:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Murphy:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Weinreich:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Yancopoulos:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Lowy:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Sternberg:Regeneron Pharmaceuticals, Inc.: Employment, Equity Ownership. Topp:Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Boehringer Ingelheim: Membership on an entity's Board of Directors or advisory committees, Research Funding; KITE: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Regeneron Pharmaceuticals, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees. OffLabel Disclosure: The data described in the abstract will report on use REGN1979 in a Phase 1 clinical trial of patients with B-NHL.

Abstract Introduction: REGN1979 is a hinge-stabilized CD20xCD3bispecific full-length antibody (Ab) based on an IgG4isotype modified to reduce Fc binding. It is designed to bind T cells (via CD3) and CD20-expressing cells. Cross-linking results in specific, local T cell activation and engagement ofcytolytic functions, independent of T cell receptor mediated recognition. This mechanism of action (MOA) is distinct from approved anti-CD20 Abs, and may provide additional therapeutic benefit. This report describes safety and clinical outcomes in 25 patients (pts) treated with REGN1979. Methods: The study uses a 3+3 design to assess safety, pharmacokinetics (PK), pharmacodynamics (PD), and activity of REGN1979 inpts with NHL and CLL, in separate dose escalation cohorts. REGN1979 is administered IV over 1-4 hours, weekly (QW) for 4 doses followed by every 4 weeks (Q4W) for 5 doses. Each dose level (DL) consists of an initial starting dose followed by a higher (step-up) dose.Pts with either progressive disease (PD) after initial response or suboptimal initial response could be retreated. Results: As of clinical cut-off, 25pts had been enrolled and treated with REGN1979 at flat doses ranging from 0.03 - 3.0 mg: 20pts with NHLand 5pts with CLL. NHL subtypes included DLBCL (n=12), FL (n=6), and MCL (n=2). Allpts hada medianof3 (range 1-7) prior regimens, and received a median of 5 (range 2-9) doses of REGN1979. Sixpts remained on initial treatment, 3pts completed treatment, and 16pts discontinued treatment (14 for PD; 2 subject decision). Of 4pts who entered retreatment, 2pts remained ongoing. The most common treatment-related treatment-emergent AEs (TR-TEAEs) were pyrexia (56%), infusionrelated reaction (IRR) (40%), chills (36%), cytokine release syndrome (CRS) (28%), fatigue (24%), tachycardia (24%), hypomagnesaemia (20%) and hypotension (20%). Grade >= 3 TR-TEAEs occurred in 8 pts(32%): IRR (12%), CRS (8%), hypotension (8%), and pyrexia, tachycardia, dyspnea, anemia, hypoxia, hypertension, tachypnea, transaminases increased, and tumor pain each in 1 pt(4%). All were grade 3 with the exception of 1 ptwith grade 4 hypotension. There were no protocol-defined DLTs, nor grade 5 TEAE. No ptsdiscontinued REGN1979 due to TR-TEAE. IRR and CRS events were most commonly reported with the first administration of both initial and step-up dose with incidence and severity decreasing with increasing exposure. Tenptsreported at least one TR-SAE: CRS (24%), IRR (20%), and increased AST and tumor pain, each in 1pt(4%). Threeptswith aggressive lymphoma who discontinued REGN1979 due to PD died of their disease within 30 days of their last dose. Notably, modifications to pre-medication(s) and drug administration instructions have improved tolerability (fewer and less severe IRR/CRS). No clinically significant CNS TEAEs have been observed. CT-based (Cheson, 2007) anti-tumor activity was observed in 11 ptswith NHL: PR [n=4,median duration of 50d];SD [n=7, median duration of >196d]. The overall response rate (ORR) in NHL ptsacross DLs was 20%. In 2 highest dose levels, ORR was 27% (Fig 1). Of the 14pts evaluated by PET, 4pts had a partial metabolic response, withmedian duration of 244d perLugano Criteria. Twopts with CLL attained SD as best overall response. PK: REGN1979 concentrations in serum increased with increasing DL and were variable across pts. Variability was less at higher DLs and also decreased over time during therapy. At DLs tested, REGN1979 concentrations did not notably increase over time during treatment. PD/Cytokines: At the lowest dose tested, 0.03 mg, transient B-cell depletion was observed inpts with measurable circulating B cells.Samples from 12pts were available for cytokine analysis. Interim analysis indicates REGN1979 induces cytokine release as expected based on MOA. An increase in IL-6, IL-10 and to lesser extent IFN-γ was observed. The magnitude of cytokine response generally correlated with symptomatic IRR/CRS. Conclusion: REGN1979 demonstrated an acceptable safety profile at flat doses of 0.03 - 3.0 mg (< 1% of rituximab dose) inpts with NHL and CLL. Most TEAEs were associated with IRR/CRS, and were managed with supportive therapy and modification to REGN1979 administration. No clinically significant neurological toxicity was observed. Preliminary antitumor activity demonstrates increased activity at higher doses. Dose escalation and treatment schedule optimization continue. Disclosures Brown: Acetylon, Gilead: Research Funding; Celgene, Roche/Genentech, Gilead, Infinity, Janssen, Pharmacyclics, ProNai, Sun BioPharma: Consultancy. Arnason:Gilead: Consultancy. O'Brien:Pharmacyclics, LLC, an AbbVie Company: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria. Chavez:Janssen: Speakers Bureau. Ansell:BMS, Seattle Genetics, Merck, Celldex and Affimed: Research Funding. Topp:Amgen: Consultancy, Honoraria, Other: travel, Speakers Bureau; Roche: Honoraria, Other: travel; Boehringer: Consultancy, Other: Travel, Research Funding; Jazz: Consultancy; Pfizer: Consultancy, Other: Travel. Adriaens:Regeneron Pharmaceuticals Inc.: Employment, Equity Ownership. Ufkin:Regeneron Pharmaceuticals Inc.: Employment, Equity Ownership. Kostic:Regeneron Pharmaceuticals Inc.: Employment, Equity Ownership. Paccaly:Regeneron Pharmaceuticals Inc.: Employment, Equity Ownership. Gao:Regeneron Pharmaceuticals Inc: Employment, Equity Ownership. Trail:Regeneron Pharmaceuticals Inc: Employment, Equity Ownership. Lowy:Regeneron Pharmaceuticals Inc: Employment, Equity Ownership. Brownstein:Regeneron Pharmaceuticals Inc: Employment, Equity Ownership.