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Background Prognosis is poor for patients (pts) with relapsed/refractory multiple myeloma (RRMM; median overall survival: Methods This multicenter, phase 1, open-label, dose-escalation/expansion study (NCT03933735) enrolled pts with RRMM (≥3 prior lines of therapy that included a proteasome inhibitor, an immunomodulatory drug, and an anti-CD38 monoclonal antibody), estimated glomerular filtration rate ≥30 mL/min as calculated by the Modification of Diet in Renal Disease formula, and ECOG performance status ≤2. Prior BCMA-targeted therapy is prohibited. Primary objectives include safety/tolerability, pharmacokinetics (PK), and determination of recommended phase 2 dose (RP2D); secondary objectives include assessment of clinical activity (per IMWG criteria 2016). TNB-383B is administered intravenously over 1-2 hours every 3 weeks (Q3W) with the first dose administered inpatient. The study uses a 3+3 design with backfilling for dose and permits intrapatient dose escalation to highest safe dose. Dose expansion was initiated on selection of RP2D. Pts are treated until progression, unacceptable toxicity, or other discontinuation criteria are met. The efficacy-evaluable population includes all pts who received at least 1 dose of TNB-383B and have at least 1 postdose assessment. The safety population includes all pts who received at least 1 dose of study drug; adverse events (AEs) are graded according to NCI CTCAE v5.0. Results As of 10 May 2021, 103 pts (dose escalation, n=73; dose expansion, n=30) have been treated with TNB-383B (0.025-120 mg). The RP2D of 60 mg Q3W was selected on the basis of tolerability, safety, PK, and clinical activity. Pt demographics and baseline characteristics are summarized in Table 1. Three dose-limiting toxicities were reported in dose escalation (platelet count decreased: grade [Gr] 4, 60 mg; cytokine release syndrome [CRS]: Gr 3, 90 mg and 120 mg); none were reported as serious. Treatment-related AEs (TRAEs) were reported in 79 (77%) pts, with Gr ≥3 and serious AEs occurring in 33 (32%) and 23 (22%) pts, respectively. The most common TRAEs (Table 2) include CRS (n=54, 52%), neutropenia (n=18, 17%), and fatigue (n=14, 14%). At the RP2D (n=39), the Gr ≥3 CRS rate was 3% (n=1). Onset of CRS typically occurred on the same or next day following the first dose and all pts recovered using tocilizumab or standard supportive care measures. Treatment-emergent AEs (TEAEs) of infusion-related reactions were reported in 8 (8%) pts and infections occurred in 29 (28%) pts; pneumonia (n=5, 5%) and upper respiratory tract infection (n=4, 4%) were the most common. Five deaths from TEAEs were reported; all were unrelated to study drug. Forty-two (40%) pts discontinued treatment due to disease progression. In the dose-escalation cohorts of ≥40 mg Q3W (n=24), the objective response rate (ORR) was 79% (19/24), with a very good partial response or better (≥VGPR) rate of 63% (15/24), and a complete response (CR) rate of 29% (7/24) at the data cutoff date; these pts have the longest follow-up (ie, mature data) with median time on study of 6.1 months (Figure 1). At doses ≥40 mg in the combined dose-escalation and -expansion cohorts (n=44), the observed ORR, ≥VGPR, and CR rates were 64% (28/44), 43% (19/44), and 16% (7/44), respectively; these pts have shorter follow-up (ie, immature data) with median time on study of 3.1 months. Twenty-nine (66%) of the 44 pts administered ≥40 mg were triple-class refractory and reported an ORR of 55% (16/29). Conclusions TNB-383B in pts with RRMM is well tolerated with an ORR of 79% observed at doses ≥40 mg in the dose-escalation cohorts. Despite having a shorter follow-up period, this trend was also observed at doses ≥40 mg in the combined dose-escalation/expansion cohorts (ORR: 64%). Enrollment into the dose-expansion arm is ongoing; updated data will be presented at the meeting. Figure 1 Figure 1. Disclosures Kumar: Novartis: Research Funding; Carsgen: Research Funding; KITE: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astra-Zeneca: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Research Funding; Roche-Genentech: Consultancy, Research Funding; Bluebird Bio: Consultancy; Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Research Funding; Beigene: Consultancy; Oncopeptides: Consultancy; Antengene: Consultancy, Honoraria; Tenebio: Research Funding; BMS: Consultancy, Research Funding; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Adaptive: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Research Funding. D'Souza: Imbrium, Pfizer, BMS: Membership on an entity's Board of Directors or advisory committees; Sanofi, Takeda, Teneobio, CAELUM, Prothena: Research Funding; Janssen, Prothena: Consultancy. Shah: Oncopeptides: Consultancy; Nektar: Research Funding; Poseida: Research Funding; Janssen: Research Funding; Indapta Therapeutics: Consultancy; GSK: Consultancy; CareDx: Consultancy; BMS/Celgene: Research Funding; Bluebird Bio: Research Funding; CSL Behring: Consultancy; Teneobio: Research Funding; Kite: Consultancy; Sutro Biopharma: Research Funding; Karyopharm: Consultancy; Amgen: Consultancy; Precision Biosciences: Research Funding; Sanofi: Consultancy. Rodriguez: Takeda: Consultancy, Speakers Bureau; Karyopharm: Consultancy, Speakers Bureau; Janssen: Consultancy, Speakers Bureau; BMS: Consultancy, Speakers Bureau; Oncopeptides: Consultancy, Honoraria; Amgen: Consultancy, Speakers Bureau. Voorhees: AbbVie Inc, Bristol-Myers Squibb Company; Consulting Agreement: GlaxoSmithKline, Novartis, Oncopeptides: Other: Advisory Committee; Bristol-Myers Squibb Company.: Other: Data Safety & Monitoring. Bueno: AbbVie: Current Employment, Current equity holder in publicly-traded company. Buelow: Teneobio, Inc.: Current Employment, Current holder of stock options in a privately-held company. Freise: Abbvie, Inc.: Current Employment, Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company. Yue: Abbvie, Inc.: Current Employment, Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company. Pothacamury: AbbVie: Current Employment, Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company. Polepally: Abbvie, Inc.: Current Employment, Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company. Vij: BMS: Research Funding; Takeda: Honoraria, Research Funding; Sanofi: Honoraria, Research Funding; BMS: Honoraria; GSK: Honoraria; Oncopeptides: Honoraria; Karyopharm: Honoraria; CareDx: Honoraria; Legend: Honoraria; Biegene: Honoraria; Adaptive: Honoraria; Harpoon: Honoraria.

Background: Therapeutic advances in multiple myeloma (MM) have greatly improved the rate and depth of response. Venetoclax (Ven) is a highly selective, potent, oral BCL-2 inhibitor that has synergistic activity with carfilzomib (K) and dexamethasone (d), and is currently under investigation as a targeted therapy in relapsed/refractory (R/R) MM. Using next-generation sequencing (NGS) and 18F-Fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT), we aimed to comprehensively evaluate minimal residual disease (MRD) in R/R MM patients (pts) treated with VenKd. Methods: In this phase 2, dose-escalation study (NCT02899052), R/R MM (1 - 3 prior lines of therapy and no prior K exposure) pts received VenKd: Ven 400 mg/day + K 27 mg/m2 d1,2,8,9,15,16 + d 40 mg d1,8,15,22 (Cohort 1), same regimen but with Ven 800 mg/day (Cohort 2), Ven 800 mg/day + K 70 mg/m2 d1,8,15 + d 40 mg d1,8,15, 22 (Cohort 3/expansion cohort), or Ven 800 mg + K 56 mg/m2 d1,2,8,9,15,16 + d 40 mg d1,2,8,9,15,16,22,23 (Cohort 4). The following biomarker analyses were performed by central laboratory assessments of CD138-enriched bone marrow mononuclear cells collected at baseline: BCL2 gene expression by quantitative PCR and cytogenetic abnormalities by interphase fluorescence in situ hybridization. MRD assessments by NGS (clonoSEQ®) were performed on bone marrow aspirates at cycle 3 day 1 in pts achieving VGPR or better, time of suspected CR/sCR, and 6- and 12-months post confirmation of CR/sCR with negativity determined at Results: As of 14 Feb 2020, 49 pts were enrolled (4 in cohort 1, 3 in cohort 2, 7 in cohort 4 and 35 in cohort 3 + expansion). Pts had received a median of 2 (1-3) prior lines of therapy, 96% were exposed to PI (57% refractory), 90% exposed to IMiD (71% refractory), and 86% exposed to PI + IMiD (45% double refractory). Median age was 60 years (37 - 79), 61% had ISS II/III disease, 27% had t(11;14), and 45% were BCL2high. Of note, 8 out of the 22 (36.4%) BCL2high pts were t(11;14) positive. Overall response rate (ORR) was 80% (≥PR), including 65% ≥ VGPR and 41% ≥CR (Table 1). Among t(11;14) pts, ORR was 92%, ≥ VGPR 85%, and ≥CR 54%; while among BCL2high pts ORR was 86%, ≥ VGPR 77%, and ≥CR 41%. Of the 19 pts assessed for MRD by NGS, 15 (79%) had clonotypes identified at baseline. Of these 15 pts, 6 (40%) achieved MRD negativity ( Conclusions: The combination of VenKd demonstrates promising efficacy in pts with R/R MM, including high rates of MRD, particularly in the t(11;14) and BCL2high subgroups. Overall, MRD assessments by NGS and FDG-PET/CT were highly concordant in this study and may be complementary for assessment of disease clearance in MM. Disclosures Costa: Sanofi: Consultancy, Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Genentech: Consultancy; BMS: Consultancy, Honoraria; Amgen: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy; Celgene: Consultancy, Honoraria. Burwick:AbbVie: Research Funding. Jakubowiak:AbbVie, Amgen, BMS/Celgene, GSK, Janssen, Karyopharm: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive, Juno: Consultancy, Honoraria. Kaufman:Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Tecnopharma: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Karyopharm: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy; Celgene: Consultancy, Honoraria; TG Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Honoraria; Bristol-Myers Squibb: Consultancy, Honoraria; Sanofi/Genyzme: Consultancy, Honoraria; Takeda: Consultancy, Honoraria. Cabanillas:AbbVie: Research Funding. Dail:Genentech: Current Employment, Current equity holder in publicly-traded company. Karve:AbbVie: Current Employment, Current equity holder in publicly-traded company. Masud:AbbVie: Current Employment, Other: may hold stock or stock options . Yang:Abbvie: Current Employment, Current equity holder in publicly-traded company. Bueno:AbbVie: Current Employment, Current equity holder in publicly-traded company. Mudd:AbbVie: Current Employment, Current equity holder in publicly-traded company. Ross:AbbVie: Current Employment, Current equity holder in publicly-traded company. Davies:Oncopeptides: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene/BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Adaptive Biotech: Honoraria; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Background: Novel and more effective therapies for multiple myeloma (MM) have led to increasing overall survival, but most patients (pts) will eventually relapse or become refractory (RR). The proteasome inhibitor (PI) bortezomib (V), the anti-CD38 antibody daratumumab (D), and dexamethasone (d) are key agents for combination therapy in first-line and RR settings. Venetoclax (Ven) is a highly selective, potent, oral BCL-2 inhibitor that induces apoptosis in BCL-2-dependent MM cells in vitro. Encouraging clinical efficacy has been observed with Ven monotherapy in t(11;14) pts, and with VenV in pts irrespective of disease genetic background. In view of MM intraclonal heterogeneity, the addition of D to Ven +/- PI is postulated to further enhance antitumor activity of Ven-based regimens in RRMM. Methods: M15-654 (NCT03314181) is an ongoing Phase 1/2, nonrandomized, multicenter study of combination therapy consisting of VenDd +/- V in pts with RRMM. The primary objective is to evaluate the safety, tolerability, and preliminary efficacy of VenDd +/- V. In Part 1, VenDd was evaluated in t(11;14) MM pts who received ≥1 prior line of therapy that included a PI and an immunomodulatory drug (IMiD). In Part 2, VenDVd was evaluated in MM pts irrespective of t(11;14) status who were non-refractory to PIs and received 1 - 3 prior lines of therapy. Each regimen was evaluated in a dose escalation and expansion phase. In each part, Ven dose escalation was initiated at 400 mg daily (QD) and escalated to 800 mg QD if acceptable safety and tolerability were observed. Escalation cohorts had ≥3 pts, and escalation decisions were based on a Bayesian optimal interval design and the number of pts with a dose limiting toxicity (DLT). In Part 1, cycles (C) were 28-day: Ven QD + D 16 mg/kg intravenous (IV) (C1, 2: Days 1, 8, 15, 22; C3 - 6: Days 1, 15; C7+: Day 1) + d 40 mg total weekly. In Part 2, C1 - 8 were 21-day, C9+ were 28-day: Ven QD + D 16 mg/kg IV (C1 - 3: Days 1, 8, 15; C4+: Day 1) + V 1.3 mg/m2 subcutaneous (C1 - 8, Days 1, 4, 8, 11) + d 20 mg (C1 - 3: Days 1, 2, 4, 5, 8, 9, 11, 12, 15; C4 - 8, Days 1, 2, 4, 5, 8, 9, 11, 12) and 40 mg weekly for C9+. Results: As of 13 May 2019, 48 pts were enrolled. Of 24 t(11;14) pts treated in Part 1 with VenDd, median age was 63 (range, 51 - 76), median prior lines of therapy was 2.5 (range, 1 - 8), 14 (58%) had ISS II/III disease, and 24 (100%) received both prior PI and IMiD (46% refractory to PI, 71% refractory to IMiD, 42% double refractory). Of 24 pts treated in Part 2 with VenDVd, median age was 64 (range, 41 - 80), median prior lines of therapy was 1 (range, 1 - 3), 14 (58%) had ISS II/III disease, and 6 (25%) were t(11;14). Twenty-two (92%) pts received prior PI, 17 (71%) received prior IMiD (33% refractory), and 15 (63%) received prior PI + IMiD. The most common adverse events (AEs; VenDd/VenDVd) were fatigue (54%/21%), diarrhea (50%/42%), nausea (33%/38%), insomnia (29%/42%), cough (21%/8%), headache (21%/4%), upper respiratory tract infection (21%/17%), constipation (8%/33%), infusion related reaction (8%/33%), peripheral neuropathy (4%/25%), and dyspepsia (4%/21%). Grade 3/4 AEs were seen in 63%/54% of pts. The most common Grade 3/4 AEs in pts receiving VenDd were neutropenia (13%), fatigue, hyperglycemia, and hypertension (8% each); in pts receiving VenDVd, the most common were insomnia (17%), diarrhea, and thrombocytopenia (8% each). There were 6 pts with infection-related Grade 3/4 AEs (3 VenDd, 3 VenDVd). No AEs of tumor lysis syndrome were observed. Eleven pts had a serious AE (5 VenDd, 6 VenDVd), the most common being pyrexia in 3 pts. One pt treated with VenDd had a DLT of febrile neutropenia, and 1 pt treated with VenDVd died due to progressive disease. No infection-related deaths were seen. Pharmacokinetic analyses demonstrated that addition of D and V did not impact Ven exposure. Median time on study is 3.6 months (m; 8.1 m escalation, 2.8 m expansion) in the VenDd arm and 3.1 m (5.8 m escalation, 2.4 m expansion) in the VenDVd arm. The objective response rate (ORR) was 92% and 88% in pts receiving VenDd and VenDVd, respectively (Table). Conclusions: This first analysis of pts treated with VenDd +/- V demonstrate a tolerable safety profile with encouraging efficacy, notably among t(11;14) pts treated with VenDd who had an ORR of 92%. No new safety signals were observed. Although the study is currently on partial clinical hold, enrolled pts continue to be followed. Analysis will be updated at presentation. Disclosures Bahlis: Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria. Baz:Bristol-Myers Squibb: Research Funding; AbbVie: Research Funding; Merck: Research Funding; Sanofi: Research Funding; Karyopharm: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding. Harrison:Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen Cilag: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; GSK: Consultancy, Research Funding; AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: investigator on studies, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Quach:Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; Sanofi: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees. Ho:Celgene: Membership on an entity's Board of Directors or advisory committees. Vangsted:Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria; Jansen: Honoraria. Moreau:Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Takeda: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria. Gibbs:BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Salem:AbbVie: Employment, Other: Stock/stock options. Ross:AbbVie: Employment, Other: Stock/stock options. Pesko:AbbVie: Employment, Other: Stock/stock options. Westrup:AbbVie: Employment, Other: Stock/stock options. Vue:AbbVie: Employment, Other: Stock/stock options. Maciag:AbbVie: Employment, Other: Stock/stock options. Bueno:AbbVie: Employment, Other: Stock/stock options. Kaufman:Takeda: Consultancy; Amgen: Consultancy; AbbVie: Consultancy; Winship Cancer Institute of Emory University: Employment; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Incyte: Consultancy; Karyopharm: Membership on an entity's Board of Directors or advisory committees; TG Therapeutics: Consultancy; Janssen: Honoraria; Bristol-Myers Squibb: Consultancy; Celgene: Consultancy. OffLabel Disclosure: Venetoclax is a BCL-2 inhibitor that is FDA-approved in some indications. This presentation will focus on venetoclax for treatment of multiple myeloma, which is not an approved indication.

Background: The BCL-2 family of anti-apoptotic proteins (e.g., BCL-2, BCL-XL, MCL-1) are important regulators of lymphocyte development and are therapeutic targets for hematologic malignancies, including multiple myeloma (MM). Venetoclax (Ven) is a highly selective, potent, oral BCL-2 inhibitor that induces apoptosis in MM cells and has shown synergistic activity with bortezomib (Velcade; V) and dexamethasone (Dex or d). Combination of the CD38 monoclonal antibody (mAb) daratumumab (D) with Ven is hypothesized to further increase anti-myeloma activity based upon dual mechanisms of pro-apoptotic effects on tumor cells as well as enhanced immune stimulation. Pre-clinically and in healthy human subjects, Ven treatment leads to enrichment of CD8+ T effector memory cells, while resulting in loss of CD4+ and CD8+ naïve T-cells, however the potential immunomodulatory effect of Ven in MM is unknown. Results presented herein describe the pharmacodynamic changes observed in immune cell subsets in relapsed/refractory (R/R) MM patients (pts) treated with VenDex, VenDd, and VenDVd. Methods: Peripheral blood samples were collected at day 1 of cycles 1-5 to characterize pharmacodynamic changes in B- and T-cell sub-populations by multicolor flow cytometry in Ven MM clinical trials M13-367 (NCT01794520) and M15-654 (NCT03314181). M13-367 is a phase 1/2 study of VenDex in t(11;14) R/R MM, and M15-654 is a phase 1/2 study of VenDd in t(11;14) R/R MM (Part 1) and VenDVd in R/R MM (Part 2). As of 12 June 2019, 15 out of 31 pts treated with VenDex in phase 2 of M13-367, 19 out of 24 pts treated in Part 1 (VenDd), and 19 out of 24 pts treated in Part 2 (VenDVd) of M15-654 had baseline and post-treatment specimens available for analysis. Results: Consistent with previous findings that B-cells are highly dependent upon BCL-2 for cell survival, each Ven-containing regimen (VenDex, VenDd, and VenDVd) resulted in rapid and sustained reduction (~90% decrease from baseline by end of cycle 1) in peripheral B-cell (CD19+/CD5-) counts (Figure). In subgroup analyses, naïve B-cells (CD27-/IgM+) were significantly reduced in pts treated with each regimen, however regulatory B-cells (CD27+/CD24+) remained largely unaffected. In addition, a decrease in plasmablasts (CD27+CD38+CD20-) were only observed in pts treated with D-containing regimens (VenDd and VenDVd), which is consistent with expression of CD38 in this subgroup. In contrast to B-cells, CD3+ T-cells were minimally reduced (~20-30% reduction from baseline through end of cycle 4) with VenDex and VenDd treatment. A more prominent reduction was observed in pts treated with VenDVd (~50-60% reduction from baseline through end of cycle 4). CD4+ T-cells were more sensitive than CD8+ T-cells to VenDex and VenDd, while both CD4+ and CD8+ T-cells were reduced in VenDVd treated pts (Figure). T-cell subgroup analyses were also performed, including naïve T-cells (CD45RA+/CD197+), effector (CD45RA+/CD197-), effector memory (CD45RA-/CD197-), and central memory (CD45RA-/CD197+). Overall, there were no significant changes in the composition of the T-cell pool (Tnaive, TCM, TEM, TEMRA) or in Th1 (CD4+/CD183+/CD196-), Th2 (CD4+/CD183-/CD196-), and Th17 (CD4+/CD183-/CD196+) cells in pts treated with VenDex, VenDd, or VenDVd. Finally, a decrease in Tregs (CD4+/CD25+/CD127low/CD194+) was observed in VenDd and VenDVd treated pts, but not in VenDex treated pts (Figure). While no reduction in overall Tregs was observed with VenDex, a decrease in the relative proportion of activated Tregs (HLA-DR+/CD45RO+) to naïve (HLA-DR-/CD45RO-) and memory (HLA-DR-/CD45RO+) Tregs was observed. Conclusions: Comprehensive immunophenotyping studies were conducted to characterize the potential effects of Ven in B- and T-cell subsets when used in combination with standard of care anti-myeloma agents of various mechanisms of action (i.e. glucocorticoid, CD38 mAb and/or proteasome inhibitor). While each Ven combination regimen resulted in significant reductions in circulating B-cells, T-cell effects were largely dependent upon the combination regimen. Minimal reduction in total T-cell counts were observed with VenDex and VenDd, which were primarily due to reduction in CD4+ T-cells. However, the extent of T-cell depletion (CD4+ and CD8+ T-cells) was greatest in pts treated with the bortezomib-containing regimen VenDVd. Correlative studies between immune profiles and pt outcomes are ongoing. Disclosures Vishwamitra: AbbVie: Employment, Other: stock or other options. Mantis:AbbVie Inc: Employment, Other: Stock/stock options. Haribhai:AbbVie: Employment, Other: stock or other options. Uziel:AbbVie: Employment, Other: stock or other options. Leverson:AbbVie Inc: Employment, Other: Stock or options. Pauff:AbbVie Inc: Employment, Other: may own stock or stock options. Bueno:AbbVie: Employment, Other: Stock/stock options. Maciag:AbbVie: Employment, Other: Stock/stock options. Ross:AbbVie: Employment, Other: Stock/stock options.

We have studied effects of ferric transferrin (FeTF), ferric lactoferrin (FeLF), ferric complexes of pyridoxal- or salicylaldehyde- isonicotinoyl hydrazone, (Fe-PIH, Fe-SIH), and ferric ammonium citrate (FAC) on expression of protein kinase C (PKC) mRNA transcripts in a variety of cultured cell lines. FeTF supported an increase of PKC-beta mRNA transcripts in T-lymphoblastoid (CCRF-CEM; Jurkat), B- lymphoblastoid (Daudi; Raji), promyelocyte (HL-60), erythroleukemia (K562), and monocyte (U937) cell lines. By contrast, FeLF, Fe-PIH, and Fe-SIH did not support an increase of PKC-beta mRNA transcripts in any of these cell lines. Furthermore, FAC supported an increase of PKC-beta mRNA transcripts in HL-60, K562, and U937 cells only. Preincubation of cells with desferrioxamine (DF), a cell-permeable iron chelator, abolished the increments of PKC-beta mRNA observed in response to FeTF or FAC. In contrast to results with PKC-beta, neither FeTF nor FAC caused an increase of PKC-alpha transcripts in any cell line. To locate iron-responsive DNA regulatory elements of the PKC-beta gene, we prepared genetic constructs containing various portions of the human PKC-beta 52-flanking DNA linked to the firefly luciferase gene. Constructs were cotransfected with the neomycin resistance plasmid, Pwl- neo, into HRE H9 cells, and stable transfectants were selected in G418. Treatment with FeTF of transfectants bearing chimeric gene constructs with 2,200 bp of the PKC-beta 52-flanking region increased luciferase activity and mRNA transcripts 2.5-fold. This increase was blocked by DF. Neither luciferase activity nor mRNA increased with FeTF in stable transfectants bearing constructs with 342 bp or 587 bp of the PKC-beta 52-flanking region. These data provide direct confirmation that iron is involved in regulation of PKC-beta but not PKC-alpha gene expression in many cell lines. The form in which iron is presented to these cell lines appears to affect its availability for this function, and cells vary in their capabilities to use nontransferrin iron to support PKC- beta gene expression. Finally, transcriptional upregulation of PKC-beta by FeTF is mediated by DNA sequences located between -2200 bp and -587 bp in the 52-flanking region of the human PKC-beta gene.

Iron-transferrin (FeTF) is an essential growth factor required for proliferation of lymphoid cells. FeTF activates protein kinase C (PKC) in the lymphoblastoid T-cell line, CCRF-CEM. We have treated CEM cells with human FeTF, then examined levels of PKC mRNA by hybridization analysis using cDNA probes specific for alpha-, beta-, and gamma-PKC subspecies. CEM cell mRNA hybridized with the beta-subspecies probe but not with probes for alpha- or gamma-subspecies. After exposure to FeTF an increase in PKC-beta mRNA was detectable at 10 minutes, peaked at 12 hours, and was sustained for 72 hours. Nuclear transcription assays demonstrated that rates of PKC-beta mRNA transcription were increased in FeTF-treated cells. By contrast, steady state levels of PKC-beta mRNA did not increase after treatment of cells with apotransferrin or gallium TF. Similarly, treatment with soluble iron as ferric ammonium citrate did not increase steady state levels of PKC-beta mRNA, despite producing a marked increase in cellular ferritin content. Ferritin increased from a baseline value of 63 ng/10(6) cells to 98 and 100 ng/10(6) cells in CEM cells treated for 1 hour with ferric ammonium citrate or FeTF, respectively. FeTF did not increase cytoplasmic-free calcium in CEM cells loaded with fura-2, indicating that binding of FeTF to transferrin receptors did not open membrane Ca2+ channels or release intracellular Ca2+. In addition, pretreatment of cells with desferrioxamine, but not ferrioxamine, blocked the FeTF-induced increase in PKC-beta transcripts. Therefore, iron as FeTF (not soluble iron or nonferric TF) stimulates transcription of the CEM cell PKC-beta gene. Transcriptional rate of the PKC-beta gene does not correlate with cellular iron content as judged by ferritin measurements. Furthermore, the requirement for FeTF does not appear to reflect activation of a classic agonist pathway as judged by stable cellular Ca2+. These data suggest that delivery of iron by FeTF to one or more specific cellular compartments may stimulate PKC-beta gene transcription in CEM cells.