Citations

Candida species cause hundreds of thousands of invasive infections with high mortality each year. Developing novel antifungal agents is challenging due to the many similarities between fungal and human cells. Maintaining phosphate balance is essential for all organisms but is achieved completely differently by fungi and humans. A protein that imports phosphate into fungal cells, Pho84, is not present in humans and is required for normal cell wall stress resistance and cell wall integrity signaling in C. albicans . Nucleotide sugars, which are phosphate-containing building block molecules for construction of the cell wall, are diminished in cells lacking Pho84. Cell wall-constructing enzymes may be slowed by lack of these building blocks, in addition to being inhibited by drugs. Combined targeting of Pho84 and cell wall-constructing enzymes may provide a strategy for antifungal therapy by which two sequential steps of cell wall maintenance are blocked for greater potency.

8015 Background: Multiple myeloma (MM) is a heterogeneous disease with varying survival outcomes depending on the presence of certain genetic abnormalities. Common abnormalities include trisomies, translocations involving chromosome 14, and amplifications or deletions of chromosomes 1, 13, and 17. t(11;14), occurring in approx. 15% of patients (pts) with MM, is considered a standard risk abnormality, but recent data suggest that the prognosis may be inferior to what had been expected. This is of particular relevance as new therapeutic options such as the BCL-2 inhibitor venetoclax has been shown to be effective in t(11;14) pts. Methods: This was a multicenter study designed and conducted by the IMWG, to identify the outcomes of pts with t(11;14) using a retrospective cohort of pts. Pts with MM diagnosed between 2005 and 2015 with t(11;14) identified on FISH performed within six months (mos) of diagnosis, and with treatment details available and if alive, a minimum of 12 mos of follow up, were enrolled. Results: The current analysis includes 848 pts with a median age of 64.4 years; 60.0% are male. The median follow-up from diagnosis for the entire cohort was 45.7 mos; 84.7% of the pts were alive at the last follow up. ISS stage distribution included: Stage 1 (35.3%), Stage II (38.9%) and stage III (25.8%). The distribution of FISH abnormalities included: del 13q (14.5%), 1q amp (12.1%), del 17p or monosomy 17 (6.1%). Pts received initial therapy with different regimens: IMiD-24.3%, PI-41.0%, both-20.8% and 13.8% had no novel agent. The drug classes by line of therapy are shown in table. An early stem cell transplant (SCT) was used in 40.8% of pts. The median time to next treatment (TTNT) after initial treatment was 15.0 (95% CI: 12.2 to 17.7) mos. The median overall survival from diagnosis for the entire cohort was 82.5 (95% CI: 73.5 to 95.8) mos. Conclusions: This is the first study to examine the outcomes of a large group of myeloma pts with t(11;14) abnormality. Pts receiving a combination if a PI and an IMiD appear to have the best survival outcomes and thse receiving an early SCT appear to have excellent survival with median OS approaching 10 years. Additional pts are being accrued to this study and additional analysis examining the variables affecting response duration and survival will be presented. [Table: see text]

8006 Background: IBER is a novel cereblon E3 ligase modulator (CELMoD) with enhanced tumoricidal and immunostimulatory activities. Preclinically, IBER overcomes immunomodulatory drug (IMiD) resistance and has synergy with daratumumab (DARA), bortezomib (BORT), and DEX. Methods: A phase 1b/2a multicenter, open-label, dose-escalation study evaluated the maximum tolerated dose (MTD), recommended phase 2 dose (RP2D), safety, and preliminary efficacy of IBER. Eligible pts had RRMM and must have received ≥ 2 prior regimens including lenalidomide (LEN) and/or pomalidomide (POM), and a proteasome inhibitor (PI). All pts had progressed on or within 60 days of last MM therapy. Escalating doses of IBER were given on days 1–21, in combination with DEX 40 mg (20 mg in pts age > 75 years) on days 1, 8, 15, and 22, of each 28-day cycle. Dose escalation was reviewed by a dose escalation committee. Results: As of Jan 2019,58 pts received IBER + DEX. Median age was 64.5 years (range 33–79), and median number of prior regimens was 5 (2–12). Prior therapies included autologous stem cell transplant (79%), LEN (100%), POM (69%), PIs (100%), and DARA (66%). IBER dose ranged from 0.3 to 1.2 mg; MTD/RP2D was not reached. Median duration of therapy was 12+ weeks (range 4–109). Grade 3–4 adverse events (AEs) were reported in 41 (72%) pts and were not related to dose. Grade 3–4 neutropenia, thrombocytopenia, neuropathy, and fatigue occurred in 26%, 11%, 2%, and 0% pts, respectively. Three pts discontinued treatment due to AEs. Clinical activity occurred early and was observed across all dose levels (Table); 20 of 51 pts remain on treatment (2–27+ cycles). Conclusions: IBER + DEX showed favorable efficacy and safety in heavily pretreated pts with RRMM who failed multiple prior therapies. This study is ongoing, including combinations of IBER with DARA or BORT. Clinical trial information: NCT02773030. [Table: see text]

7059 Background: Patients with chronic myelomonocytic leukemia (CMML) have historically poor outcomes, with ~6-7 mos median OS in relapsed/refractory (r/r) setting. Splenomegaly is a poor prognostic factor and potential target in CMML. CD123 is detected on blasts, monocytes, and neoplastic microenvironmental plasmacytoid dendritic cell (pDC) infiltrates part of the CMML malignant clone (Solary, et al). Tagraxofusp, a novel CD123 targeted therapy, demonstrated high levels of activity in BPDCN, an aggressive hematologic malignancy derived from CD123-expressing pDCs, and is FDA approved in BPDCN. As such, tagraxofusp may offer a novel approach in CMML. Methods: Multicenter, 2-stage Ph1/2 enrolling patients (pts) with r/r CMML. Objectives: determine optimal dose, evaluate safety and efficacy. Stage 1 dose escalation: IV tagraxofusp (7, 9, and 12 mcg/kg/day) dosed on days 1-3 every 21 days (C1-4), 28 days (C5-7), and 42 days (C8+). Stage 2 (ongoing), pts receive optimal S1 dose (12 mcg/kg/day; no MTD). Results: 20 pts (12 CMML-1; 8 CMML-2) enrolled. 18 pts 2nd-line (2 pts in 1L), HMAs most common prior therapy. Median age 69 (43-80); 81% male. 11 (52%) had baseline splenomegaly (spleen palpable below left costal margin by physical exam) of 2-27 cm. Most common TRAEs: hypoalbuminaemia (35%), thrombocytopenia (35%), nausea (30%), vomiting (30%), and fatigue (20%). Most common ≥Gr3 TRAEs were thrombocytopenia (35%) and nausea (5%). Capillary leak syndrome in 3 pts (15%; all Gr1&2). 100% (10/10) of pts with splenomegaly had spleen response: 80% (8/10) had reductions ≥50% and 67% (4/6) with spleen size ≥5 cm had reductions ≥50%. 3 pts achieved bone marrow complete responses, including 1 pt bridged to SCT in remission. Conclusions: Tagraxofusp demonstrated single agent activity in CMML as 80% of pts showed ≥50% reduction in splenomegaly by palpation. Splenomegaly in CMML, as in myelofibrosis, is a major cause of morbidity and associated with poor prognosis and impaired QoL. Targeting splenomegaly in myeloid neoplasms with proliferative features may be an important therapeutic goal. Given CD123 expression on CMML blasts, monocytes, and malignant pDCs, tagraxofusp may offer a targeted approach, especially in pts with splenomegaly. Updated safety and efficacy data to be presented. Registrational trial planned. Clinical trial information: NCT02268253.

8514 Background: MLN9708 is an investigational, orally bioavailable, potent, reversible, specific inhibitor of the 20S proteasome that has demonstrated antitumor activity in in vivo models of MM. We report safety, activity and pharmacokinetics (PK) of weekly oral MLN9708 in a phase 1 trial in patients (pts) with relapsed and/or refractory MM after full enrollment (NCT00963820). Methods: Pts received MLN9708 (days 1, 8, 15; 28-day cycles) at 0.24–3.95 mg/m2 (dose-escalation phase) and at the MTD, 2.97 mg/m2, in relapsed and refractory (RR), bortezomib (btz)-relapsed, PI-naïve, and prior carfilzomib (CZ) expansion cohorts. Adverse events (AEs) were graded by NCI-CTCAE v3.0. Response was assessed by IMWG uniform criteria. Results: 60 pts (33 male, median age 64 yrs [40–79]) were enrolled, 32 in the dose-escalation phase and 31 to the expansion cohorts (11 RR, 10 btz-relapsed, 6 PI-naïve, 4 CZ; 2 RR and 1 btz-relapsed pts included from MTD dose-escalation cohort). Median time from MM diagnosis was 4.9 yrs (1.5–18.8). Median number of prior regimens was 6 (2–18), including btz, lenalidomide, thalidomide, and CZ in 83%, 95%, 52%, and 13%, respectively; 76% were refractory to last therapy (17% btz-refractory). At data cut-off (Nov 29, 2012) pts had received a median of 2 cycles (1–11); 5 pts remained on treatment. All-grade/grade ≥3 drug-related AEs were seen in 83%/52% of pts; common drug-related grade ≥3 AEs were thrombocytopenia (33%), diarrhea, neutropenia (17%), decreased appetite, fatigue, and lymphopenia (8%). 6 pts (10%) had drug-related PN (no grade ≥3). 5 pts discontinued due to drug-related AEs; 1 pt died on study due to an unrelated AE. By investigator assessment in 41 evaluable pts, responses included1 VGPR, 5 PR, 1 MR, and 15 with SD. MLN9708 was rapidly absorbed, with a terminal half-life of 4–12 days (supporting weekly dosing) and a proportional increase in plasma AUC with dose (0.8–3.95 mg/m2). PK data were similar across expansion cohorts. Conclusions: Current data suggest weekly oral MLN9708 is generally well tolerated with infrequent PN, and shows activity in this heavily pretreated population with prior exposure to immunomodulatory drugs and btz. Clinical trial information: NCT00963820.

8033 Background: MLN9708 is an oral, reversible 20S proteasome inhibitor. The feasibility of combining a proteasome inhibitor with an immunomodulatory drug and a steroid in previously untreated MM has been demonstrated with the RVD regimen. This is the first study of MLN9708 in combination with lenalidomide and dexamethasone (NCT01217957). Here we report the phase (Ph) 1 MTD and preliminary Ph 2 results. Methods: Pts with previously untreated MM, aged ≥18 yrs with measurable disease received oral MLN9708 (phase 1: 1.68–3.95 mg/m2) days 1, 8, and 15, lenalidomide 25 mg days 1–21, and dexamethasone 40 mg days 1, 8, 15, and 22, for up to twelve 28-day cycles. Primary objectives were determination of safety, MTD, and recommended phase 2 dose (RP2D) (Ph 1), and CR+VGPR rate (Ph 2). Results: At data cut-off (Dec 1, 2011), 29 pts had been enrolled (15 Ph 1, 14 Ph 2). Median age was 64 yrs (range 40–82); 69% ISS stage II/III. In Ph 1, the MLN9708 MTD was determined as 2.97 mg/m2 and the RP2D as 2.23 mg/m2; for Ph 2, the RP2D was converted to a 4.0 mg fixed dose based on population PK results. Ph 1 pts have received a median of 6 treatment cycles (range 1–11), 8 received ≥6 cycles; 6 stopped to receive ASCT, 7 are ongoing. Ph 2 pts received a median of 1 (range 1–2), all are ongoing. Grade ≥3 hematologic toxicity was reversible and included anemia (n=2) and thrombocytopenia (n=1). Grade ≥3 nonhematologic toxicity included erythematous rash, syncope, and vomiting (2 pts each). All-grade drug-related peripheral neuropathy was seen in 6 pts (21%), including grade 2 with pain in 2 (both Ph 1 at doses above the MTD). Two pts discontinued due to AE; there were 5 pts who had serious drug-related AE (all Ph 1). Of 19 response-evaluable pts (Ph 1 + Ph 2), all achieved ≥PR, including 5 CR (1 sCR), 4 VGPR, and 10 PR; all remain in response with duration of confirmed response of up to 9.5 months. Of 4 response-evaluable Ph 2 pts, 1 has achieved VGPR and 3 PR to date. Conclusions: Oral MLN9708 plus lenalidomide and dexamethasone appears well tolerated with manageable toxicity. These data show antitumor activity at the RP2D in pts with previously untreated MM, with ≥PR in all pts to date.

8034 Background: Phase 1 studies are evaluating IV and oral dosing of the reversible proteasome inhibitor MLN9708 in multiple tumor types. We report the safety, MTD, pharmacokinetics (PK), pharmacodynamics, and preliminary responses with weekly oral MLN9708 in pts with relapsed/refractory MM (NCT00963820). Methods: Pts aged ≥18 yrs received MLN9708 on d 1, 8, and 15 of 28-d cycles. In the dose-escalation phase, pts required ≥2 prior therapies (including bortezomib, thalidomide/lenalidomide, and corticosteroids). At the MTD, pts were to be enrolled to relapsed and refractory (RR), bortezomib-relapsed (VR), proteasome inhibitor (PI) naïve, and carfilzomib (CZ) expansion cohorts. Results: 36 pts have been enrolled to date (data cut-off: Dec 1, 2011), 32 in the dose-escalation phase (0.24–3.95 mg/m2) and 8 to expansion cohorts (2 RR, 5 VR, 1 PI naïve; RR and VR cohorts each include 2 pts from MTD dose-escalation cohort). Median age was 64.5 yrs (range 40–79), 53% were male, and median number of prior lines of therapy was 3.5 (range 1-13), including 92%, 92%, 56%, and 8% who had prior bortezomib, lenalidomide, thalidomide, and carfilzomib, respectively. Pts have received a median of 2 cycles (range 1–11); 5 pts remain on treatment. Among 24 DLT-evaluable pts, 3 DLTs were seen: 2 at 3.95 mg/m2 (1 grade 3 rash, 1 grade 3 GI AEs) and 1 at 2.97 mg/m2 (grade 3 GI AEs). The MTD was determined as 2.97 mg/m2. Overall, 69% of pts had drug-related AEs, and 28% had related grade ≥3 AEs, including thrombocytopenia (17%), diarrhea (11%), nausea, neutropenia, and fatigue (each 8%). Only 3 (8%) pts had drug-related peripheral neuropathy (PN; no grade ≥3). 2 pts discontinued due to AEs. In 18 response-evaluable pts, 1 had a VGPR at 3.95 mg/m2, 1 had a PR at 2.97 mg/m2, and 8 have achieved SD durable for up to 9.5 mos. PK analyses showed linear plasma PK (0.8–3.95 mg/m2), Tmax of 0.5-2 hr, and terminal half-life of 7 d for MLN2238 (biologically active hydrolysis product). There was a trend for a dose-dependent increase in whole blood 20S proteasome inhibition. Conclusions: Current data suggest weekly oral MLN9708 is generally well tolerated with infrequent PN, and shows early signs of antitumor activity.

Abstract Stearoyl‐CoA desaturases (SCD) are endoplasmic reticulum (ER)‐associated enzymes that catalyze the synthesis of the monounsaturated fatty acids (MUFAs). As such, SCD play important roles in maintaining the intracellular balance between saturated fatty acid (SFAs) and MUFAs. The roles of SCD in CD4 + T‐helper cell responses are currently unexplored. Here, we have found that murine and human follicular helper T (T FH ) cells express higher levels of SCD compared to non‐T FH cells. Further, the expression of SCD in T FH cells is dependent on the T FH lineage‐specification transcription factor BCL6. We found that the inhibition of SCD impaired T FH cell maintenance and shifted the balance between T FH and follicular regulatory T (T FR ) cells in the spleen. Consequently, SCD inhibition dampened germinal center B‐cell responses following influenza immunization. Mechanistically, we found that SCD inhibition led to increased ER stress and enhanced T FH cell apoptosis in vitro and in vivo. These results reveal a possible link between fatty acid metabolism and cellular and humoral responses induced by immunization or potentially, autoimmunity.

Treatment of polycythemia vera (PV) with the Murine Double Minute 2 (MDM2) antagonist, idasanutlin, in a phase 1 trial was reported by our group to be well tolerated with a high overall response rate (Mascarenhas et al, Blood. 2019 Jun 5). A global, phase 2 trial is currently underway evaluating idasanutlin in hydroxyurea (HU) resistant/intolerant PV patients (NCT03287245). MDM2, a negative regulator of TP53 is upregulated in PV CD34+ cells and inhibition of MDM2 targets PV hematopoietic stem/progenitor cells (HSPC) (Lu et al, Blood. 2014;124(5):771-90). Additional trials of MDM2 antagonists have shown promise, however, there is concern that these agents have the potential to induce TP53 mutations or promote expansion of TP53 mutated clones. Resistance to MDM2 inhibitors has been evaluated in solid tumor cell lines and attributed to either the emergence of de novoTP53 mutations or the selection of TP53 mutated clones. (Michaelis et al, Cell Death Dis. 2011;2:e243; Skalniak et al, Cancers. 2018;10(11)). The effect of MDM2 inhibition on TP53 mutant clones is of particular interest in myeloproliferative neoplasms (MPNs). TP53 mutations have been reported with a low allele burden in ~15% of chronic MPN patients (Kubesova et al, Leukemia. 2018;32(2):450-61), however, TP53 loss of heterozygosity and rapid expansion of TP53 mutant clones is associated with transformation to blast phase (Lundberg et al, Blood 2014,123:2220-8). As reported, in the idasanutlin PV trial, 1/13 patients were identified to have a baseline pathogenic TP53 mutation in hematopoietic cells (VAF 5.5%), using a deep sequencing assay with a limit of detection (LOD) of VAF 0.5%. This patient was a non-responder to idasanutlin and upon treatment had an increasing JAK2V617F and TP53 mutant VAF. End of study hematopoietic cell specimens of all patients were deep sequenced (LOD 0.1%) and revealed that 4 additional patients harbored detectable TP53 mutations after idasanutlin treatment with VAF ranging from 1-12%. In each sample, 1-5 unique TP53 mutations were identified, all within the hotspot domain of the TP53 gene. Deeper sequencing of baseline and follow-up samples revealed these mutations were present at a subclonal level (VAF 0.1-5.5%) and increased over time, indicating that treatment with the MDM2 antagonist promoted expansion of already existing TP53 mutant clones (Table 1, Figure 1). None of the patients who lacked a TP53 mutation at baseline developed a TP53 mutant clone with idasanutlin treatment. There was no clear association of presence of TP53 mutations with prior HU, anagrelide or interferon exposure. There has been careful monitoring of patients to determine whether the expanding TP53 clone has clinical ramifications. Patients were on study for a median of 54 weeks (23-131). The only patient who exemplified resistance to idasanutlin was the single patient with a high burden TP53 mutation (37%). All other patients were taken off study due to patient choice/toxicity. Furthermore, all TP53 mutant and non-mutant patients have had stable disease with no evidence of progression to MF or AML. Sequencing of 2 patients post-discontinuation of idasanutlin revealed that the VAF of the TP53 mutant clones decreased since the agent was discontinued. Updated patient molecular data post-treatment discontinuation will be reported at the meeting. To investigate whether idasanutlin induces de novo TP53 mutations in PV myeloid cells we performed long term HSPC cultures. Mononuclear cells from 6 distinct PV patients were treated continuously with idasanutlin (500 nM) over ~6 weeks and DNA from both treated and untreated colonies were analyzed using next generation sequencing with a LOD of 2% VAF and no TP53 mutations were detected. The combined in vitro and clinical data reveals that treatment with an MDM2 antagonist is not associated with the emergence of de novoTP53 mutations but rather the expansion of prior existing TP53 clones. This does not appear to have clinical repercussions, however, close monitoring of these patients is essential. We recommend that patients be screened for TP53 mutations prior to treatment with an MDM2 antagonist and that if present the TP53 mutant VAF be followed during their treatment course. Resistance to MDM2 inhibition is likely dependent on the TP53 mutant VAF and further studies will need to clarify the ideal dosing schedule of MDM2 antagonists and/or combinatorial therapy to prohibit TP53 mutant clonal expansion. Disclosures Houldsworth: Cancer Genertics: Other: stock in; Sema4: Employment. Rossi:Sema4: Employment. Kiladjian:AOP Orphan: Honoraria, Research Funding; Celgene: Consultancy; Novartis: Honoraria, Research Funding. Rampal:Agios, Apexx, Blueprint Medicines, Celgene, Constellation, and Jazz: Consultancy; Constellation, Incyte, and Stemline Therapeutics: Research Funding. Mascarenhas:Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding; Roche: Consultancy, Research Funding; Merck: Research Funding; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; CTI Biopharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Research Funding; Promedior: Research Funding; Merus: Research Funding; Pharmaessentia: Consultancy, Membership on an entity's Board of Directors or advisory committees. Hoffman:Merus: Research Funding.

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.