Search

Extracellular histones have been shown to play an important pathogenic role in many diseases, primarily through their cytotoxicity toward nucleated cells and their ability to promote platelet activation with resultant thrombosis and thrombocytopenia. In contrast, little is known about the effect of extracellular histones on erythrocyte function. We demonstrate in this study that histones promote erythrocyte aggregation, sedimentation, and using a novel in vitro shear stress model, we show that histones induce erythrocyte fragility and lysis in a concentration-dependent manner. Furthermore, histones impair erythrocyte deformability based on reduced passage of erythrocytes through an artificial spleen. These in vitro results were mirrored in vivo with the injection of histones inducing anemia within minutes of administration, with a concomitant increase in splenic hemoglobin content. Thrombocytopenia and leukopenia were also observed. These findings suggest that histones binding to erythrocytes may contribute to the elevated erythrocyte sedimentation rates observed in inflammatory conditions. Furthermore, histone-induced increases in red blood cell lysis and splenic clearance may be a significant factor in the unexplained anemias seen in critically ill patients.

Interleukin 10 (IL-10)-producing B cells (regulatory B cells [Bregs]) regulate autoimmunity in mice and humans, and a regulatory role of IL-10-producing plasma cells has been described in mice. Dysfunction of B cells that maintain homeostasis may play a role in the pathogenesis of chronic graft-versus-host disease (cGVHD) after allogeneic stem cell transplantation. Here, we found a relation between decreased Breg frequencies and cGVHD severity. An impaired ability of B cells to produce IL-10, possibly linked to poor signal transducer and activator of transcription 3 and extracellular signal-regulated kinase phosphorylation, was found in patients with active cGVHD. IL-10 production was not confined to a single B-cell subset, but enriched in both the CD24(hi)CD27(+) and CD27(hi)CD38(hi) plasmablast B-cell compartments. In vitro plasmablast differentiation increased the frequency of IL-10-producing B cells. We confirmed that allogeneic transplant recipients had an impaired reconstitution of the memory B-cell pool. cGVHD patients had less CD24(hi)CD27(+) B cells and IL-10-producing CD24(hi)CD27(+) B cells. Patients with cGVHD had increased plasmablast frequencies but decreased IL-10-producing plasmablasts. These results suggest a role of CD24(hi)CD27(+) B-cell and plasmablast-derived IL-10 in the regulation of human cGVHD.

Background: B cell maturation antigen (BCMA) has recently emerged as a promising candidate antigen for therapeutic targeting in multiple myeloma (MM), with several targeted agents in clinical studies including antibody-drug conjugates and bispecific T cell engagers as well as CAR T cells. The Antibody-Coupled T cell Receptor (ACTR) platform is a universal, engineered autologous T cell therapy developed to mediate anti-tumor activity in combination with tumor-targeting antibodies. The ACTR construct is composed of the ectodomain of CD16 fused to intracellular co-stimulatory and CD3ζ signaling domains (Kudo et al., Cancer Res. 2014), which allow ACTR T cells to exert antibody-dependent cell-mediated cytotoxicity, a function otherwise physiologically limited to CD16-expressing natural killer cells and macrophages. ACTR087 expresses a 4-1BB-containing receptor and has been evaluated in combination with rituximab in subjects with relapsed or refractory (R/R) CD20+ B cell lymphoma as previously reported (Akard et al., Blood 2017). SEA-BCMA is a novel, humanized non-fucosylated anti-BCMA IgG1 antibody that has been demonstrated pre-clinically to bind to ACTR087 T cells to mediate ACTR T cell activation, cytotoxicity, cytokine release, and proliferation in the presence of BCMA-expressing MM cell lines. These functional activities were demonstrated to be BCMA-specific and SEA-BCMA dose-dependent (Cheema et al., AACR 2017). Here we present preliminary findings from the first 2 single-subject cohorts of the ATTCK-17-01 study (NCT03266692), an ongoing Phase 1 study of ACTR087 in combination with the first-in-human administration of SEA-BCMA. Methods: ATTCK-17-01 is a multicenter, Phase 1, dose-escalation study of ACTR087 in combination with SEA-BCMA. The primary objectives are to characterize the safety and to determine the recommended Phase 2 dose of ACTR087 in combination with SEA-BCMA in subjects with R/R MM. The secondary objectives include evaluation of anti-myeloma activity, ACTR T cell persistence, cytokines, and SEA-BCMA pharmacokinetics (PK); exploratory objectives include the anti-myeloma activity of SEA-BCMA alone. Subjects must have measurable disease and must have received at least 3 prior lines of therapy including treatment with a proteasome inhibitor and an immunomodulatory agent, and hematopoietic stem cell transplant (HSCT) for HSCT-eligible subjects. BCMA expression on MM cells was not a condition of eligibility. Dose escalation of the 2 investigational agents, ACTR087 and SEA-BCMA, is determined according to adaptive design principles. After study enrollment and leukapheresis, subjects receive SEA-BCMA by IV infusion once every 3 weeks until disease progression or treatment discontinuation. After the third dose of SEA-BCMA and lymphodepleting chemotherapy (cyclophosphamide 300 mg/m2 and fludarabine 30 mg/m2, each daily for 3 days), subjects receive a single dose of ACTR087. Results: Two subjects enrolled and received ACTR087 at the first dose level in combination with the first 2 dose levels of SEA-BCMA. First-in-human dosing of SEA-BCMA was well tolerated, with no reported SEA-BCMA-related adverse events (AEs) or dose-limiting toxicities (DLTs). Following ACTR087 infusion, ACTR+ T cells were detectable in the peripheral blood and demonstrated expansion post-infusion. No DLTs were observed with the combination of ACTR087 and SEA-BCMA in the first 2 cohorts. Grade 3 or higher treatment-emergent AEs experienced by at least 1 subject, regardless of causality assessment, include cytopenias, increased ALT, and bone pain. Conclusions: ACTR087 in combination with SEA-BCMA was well tolerated in the first 2 subjects treated, with no DLTs or AEs leading to treatment discontinuation. These results support the continued dose escalation of ACTR087 in combination with SEA-BCMA. Enrollment in Cohort 3 is ongoing. Updated data, including SEA-BCMA PK, biomarkers, and preliminary Cohort 3 data, will be presented. Disclosures Holmes: Unum: Research Funding; Seattle Genetics: Research Funding, Speakers Bureau; Novartis: Research Funding; Genentech: Research Funding; Celgene: Research Funding; Rigel: Consultancy; Gilead: Consultancy, Research Funding, Speakers Bureau; Bayer: Consultancy. Hari:Kite Pharma: Consultancy, Honoraria; Janssen: Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Amgen Inc.: Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Spectrum: Consultancy, Research Funding; Sanofi: Honoraria, Research Funding. Sachs:Unum Therapeutics Inc.: Employment. Exter:Unum Therapeutics Inc.: Employment. Ranger:Unum Therapeutics Inc.: Employment. Cheema:Unum Therapeutics Inc.: Employment. Sienczylo:Unum Therapeutics Inc.: Employment. O'Meara:Seattle Genetics: Employment, Equity Ownership. Sussman:Seattle Genetics: Employment. Akard:Gilead: Speakers Bureau; Celgene: Speakers Bureau; Takeda: Speakers Bureau; Novartis: Speakers Bureau; Bristol-Myers Squibb: Speakers Bureau.

Introduction : Hairy cell leukemia (HCL) is a chronic mature B-cell neoplasm with a very indolent clinical course and patients may survive for many decades. First-line treatment with purine analogues such as cladribine (Cld) is considered standard of care since it is very efficient and induces profound remissions. However, patients with HCL often relapse after purine analogues and repeated treatment may increase morbidity and mortality. Despite good clinical evidence of long term control of the disease by several mainly single center studies of patients treated with purine analogues, there is only one study analyzing mainly subcutaneous (sc) treated patients based on registry data. We therefore performed a pooled long-term follow-up analysis of our prospective multicenter studies treating patients with sc Cld focusing on survival, secondary malignancy and retreatment. Materials and Methods : The SAKK included patients treated for HCL in 4 studies between 1993 and 2005. Three studies focused on first-line regimens with sc Cld, whereas the fourth protocol focused on the effect of Rituximab monotherapy in patients pretreated with Cld. Classical morphologic, immunohistochemistry and flow cytometry criteria were used as inclusion criteria and response was assessed by established criteria. Treatment algorithms in the 4 studies were as follows: 1) 5 days of Cld 0.14mg/kg sc followed by max 2 cycles of 7 days of Cld 0.1mg/kg sc in case of minor response or no response (SAKK 32/93); 2) Single shot of Cld 0.25mg/kg sc followed by a maximum of 2 cycles of 0.14mg/kg sc for 5 day in case of minor response, no response or relapse (SAKK 32/95); 3) 5 consecutive days of Cld 0.14mg/kg sc versus the same dose in 5 weekly applications (SAKK 32/98); 4) Rituximab 375 mg/m2iv weekly for 4 weeks in relapsed patients (SAKK 31/98). SAKK 32/93 included 63, SAKK 32/95 74 and SAKK 32/98 100 patients. Of the 26 patients registered in 31/98 20 were already in SAKK 32/93, 32/95 and 32/98. Therefore, we also included the treatment information and follow-up data of these 20 patients. All patients were subject to life-long follow-up within the clinical trials. Further information including secondary malignancies and retreatments were obtained by sending out questionnaires to the treating physicians of the study patients. Of the 237 patients 4 patients were in two of the studies and 10 patients have been excluded because of non-classical HCL phenotype. Therefore, a total of 223 patients were included in the analysis. Overall survival and follow-up time were assessed by Kaplan-Meier and reverse Kaplan-Meier method, respectively. Results : The median age of patients at the time of diagnosis was 55 (range 21 to 96) years, 50 patients were female (22.4%) and 173 (77.6%) male. At the time of data analysis, the median follow-up time was 12.1 (95%-CI 10.0 to 14.0) years. A total of 129 (57.8%) patients had the last follow-up information more than two years prior to the data cut-off in May 2016, however, the available information of all patients was used for the sub-analyses including secondary malignancies or retreatment. By the cut-off date, 49 patients have died, 14 (28.6%) due to secondary malignancies and 7 (14.3%) due to HCL progression. Median overall survival from diagnosis was 31.6 (95%-CI 31.6 to 37.8) years. Retreatment was necessary in 53 (23.7%) patients after a mean of 6 (0.2 to 20.4) years and first retreatment was mainly Cld (64%), rituximab (19%) or Cld and rituximab (13%). 21 patients (9.4%) required more than one retreatment with a mean number of 1.57 (range 1 to 5) treatments. A total of 42 (18.8%) patients developed secondary malignancies with an average time to occurrence of 7.1 (range: 0.1 to 17.7) years. The majority of the secondary malignancies were of non-hematological origin (85.9%), most frequently skin cancer (31.0%), followed by prostate cancer (19.0%) and colorectal cancer (16.7%). Six patients (14.4%) developed hematological secondary malignancies with a predominance of B-lymphoid neoplasms. Conclusion : Long-term overall survival in HCL patients treated with sc Cld was excellent and comparable to studies using iv Cld. Despite the long follow-up, sc Cld had a curative potential and relapses requiring re-treatment were observed only in a minority of patients. Secondary malignancies were predominantly non-hematological. These data indicate that patients need to be followed carefully with a special focus on secondary malignancies. Disclosures Chalandon: Roche: Membership on an entity's Board of Directors or advisory committees, Other: Travel costs.

Background CD33is expressed in approximately 90% of AML cases, representing a promising target despite age, prior therapies, or mutational heterogeneity. Vadastuximab talirine (33A) is a CD33-directed antibody conjugated to 2 molecules of a pyrrolobenzodiazepine (PBD) dimer. Upon binding, 33A is internalized and transported to the lysosomes where PBD dimer is released via proteolytic cleavage of the linker, crosslinking DNA, and leading to cell death. Methods The dose-escalation portion of this phase 1 study (NCT01902329) was designed to evaluate the safety, tolerability, pharmacokinetics, and antileukemic activity of 33A as monotherapy. After dose escalation, 40 mcg/kg was identified as the recommended monotherapy dose. Eligible patients (ECOG status 0-1) in this expansion cohort must have had CD33-positive AML and considered ineligible for or declined conventional induction/consolidation. 33A monotherapy was administered outpatient IV every 3 weeks for up to 2 cycles, followed by optional low-dose maintenance treatment for patients who achieved a CR/CRi. Investigator assessment of response was per IWG criteria; CRi required either platelet count of ≥100,000/µL or neutrophils of ≥1,000/µL (Cheson 2003). Results Twenty-seven treatment naive patients (48% male) with a median age of 74 years (range, 67-89) were treated with 40 mcg/kg of 33A. Most patients had intermediate (70%) or adverse (26%) cytogenetic risk by MRC and 48% of patients had underlying myelodysplasia. Twenty-four patients were considered unfit for intensive therapy and 3 patients declined intensive therapy. At baseline, patients had a median of 47% BM blasts. Three patients remain on treatment. The most common Grade 3 or higher adverse events (AE) were thrombocytopenia (44%), febrile neutropenia (41%), anemia (33%), fatigue, and pneumonia (19% each). Other common treatment-emergent AEs regardless of relationship to 33A were decreased appetite, diarrhea, fatigue, peripheral edema, thrombocytopenia (44% each), febrile neutropenia (41%), dizziness (37%), anemia, chills, cough, dyspnea, and epistaxis (33% each). The 30- and 60-day mortality rates were 0% and 15%. Of the 26 efficacy evaluable treatment naive patients, 6 patients (23%) achieved a best clinical response of CR, 8 (31%) achieved CRi, and 5 patients (19%) achieved a morphologic leukemia-free state. Most remissions were achieved after 1 cycle and were observed in many patients with adverse risk including underlying myelodysplasia (6/12, 50%), FLT3/ITD+ (3/4, 75%), and in patients ≥75 years of age (8/12, 67%). Of the responding patients with available minimal residual disease (MRD) data, 6 of 13 (46%) achieved MRD negativity by flow cytometry. In patients who achieved at least a CRi, the median time to full count recovery from first dose was 6.1 weeks for neutrophils (≥1,000/µL) and 5.1 weeks for platelets (≥100,000/µL). Median OS continues to evolve with 10 patients (37%) alive at the time of this data cut. Pharmacokinetic data for treatment naive patients is consistent with previously reported results; 33A exhibits rapid elimination consistent with target-mediated drug disposition. Conclusions In an expansion cohort of 33A monotherapy at 40 mcg/kg, AEs observed were generally manageable and commonly associated with on-target myelosuppression. 33A has demonstrated favorable antileukemic activity as a single agent with 54% achieving a CR+CRi in this high risk treatment naive older AML population, more than doubling the response rate expected with standard non-intensive therapies such as hypomethylating agents or low-dose cytarabine. The rapid clearance of marrow blasts, high rate of MRD-negative remissions, and low early mortality rate are encouraging. These data support exploration of 33A in combination with standard induction, consolidation, and pre- and post-transplant regimens. Disclosures Stein: Celgene: Research Funding; Stemline Therapeutics: Consultancy, Research Funding; Argios: Research Funding; Amgen: Consultancy, Research Funding, Speakers Bureau; Seattle Genetics: Research Funding. Fathi:Agios Pharmaceuticals: Other: Advisory Board participation; Bexalata: Other: Advisory Board participation; Seattle Genetics: Consultancy, Other: Advisory Board participation, Research Funding; Celgene: Consultancy, Research Funding; Merck: Other: Advisory Board participation. Kovacsovics:Seattle Genetics: Research Funding. Levy:Seattle Genetics: Research Funding; Jansen: Speakers Bureau; Amgen: Speakers Bureau; Millennium: Speakers Bureau. Erba:Daiichi Sankyo: Consultancy; Jannsen: Consultancy, Research Funding; Celator: Research Funding; Incyte: Consultancy, DSMB, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; Juno: Research Funding; Astellas: Research Funding; Ariad: Consultancy; Millennium Pharmaceuticals, Inc.: Research Funding; Pfizer: Consultancy; Agios: Research Funding; Novartis: Consultancy, Speakers Bureau; Gylcomimetics: Other: DSMB; Seattle Genetics: Consultancy, Research Funding; Amgen: Consultancy, Research Funding; Sunesis: Consultancy. Jillella:Seattle Genetics: Research Funding. Ravandi:Seattle Genetics: Consultancy, Honoraria, Research Funding; BMS: Research Funding. Stein:Novartis: Consultancy; Seattle Genetics: Research Funding; Agios Pharmaceuticals: Other: Advisory Board, Research Funding; Celgene: Other: Advisory Board, Research Funding. Faderl:Astellas: Research Funding; Pfizer: Research Funding; Seattle Genetics: Research Funding; Celator Pharmaceuticals: Research Funding; BMS: Research Funding; Ambit Bioscience: Research Funding; Karyopharm: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; JW Pharma: Consultancy; Amgen: Speakers Bureau. DeAngelo:Baxter: Consultancy; Amgen: Consultancy; Novartis: Consultancy; Incyte: Consultancy; Pfizer: Consultancy; Ariad: Consultancy; Celgene: Consultancy. Ho:Seattle Genetics: Employment, Equity Ownership. O'Meara:Seattle Genetics: Employment, Equity Ownership. Voellinger:Seattle Genetics: Employment, Equity Ownership. Advani:Seattle Genetics: Consultancy, Research Funding.

Background Treatment of AML among the elderly is challenging due to intolerance of intensive therapy and greater prevalence of therapy-resistant biology. Hypomethylating agents (HMAs) are commonly used in this setting, but yield suboptimal remission rates and modest survival (Dombret 2015, Kantarjian 2012). Vadastuximab talirine (33A) is a CD33-directed antibody conjugated to 2 molecules of a pyrrolobenzodiazepine (PBD) dimer. Upon binding, 33A is internalized and transported to the lysosomes where PBD dimer is released via proteolytic cleavage of the linker, crosslinking DNA, and leading to cell death. In preclinical studies, HMA priming followed by 33A resulted in upregulated CD33 expression, increased DNA incorporation of the PBD dimer, and enhanced cytotoxicity. Methods A combination cohort in a phase 1 study (NCT01902329) was designed to evaluate the safety, tolerability, pharmacokinetics, and antileukemic activity of 33Ain combination with an HMA. Eligible patients (ECOG status 0-1) must have had previously untreated CD33-positive AML andhad declined intensive therapy. A single dose level of 33A, 10 mcg/kg,was administered outpatient IV every 4 weeks on the last day of HMA (azacitidine or decitabine [5-day regimen], standard dosing). Investigator assessment of response was per IWG criteria; CRi required either platelet count of ≥100,000/µL or neutrophils of ≥1,000/µL (Cheson 2003). Results Fifty-three patients (median age 75 years; range, 60-87) have been treated with 33A+HMA. All patients had adverse (38%) or intermediate (62%) cytogenetic risk by MRC criteria; 40 patients (75%) were considered unfit for intensive therapy and 13 patients (25%) declined intensive therapy.Of the patients with secondary AML (23/53, 43%), median age was 77 years (range 60-87) with most of the patients ≥75 years (70%). The median treatment duration is currently 19.3 weeks (range, 2-86) with 13 patients remaining on treatment; no DLTs or infusion reactions were reported. G3 or higher AEs reported in ≥15% of patients were thrombocytopenia (55%), anemia (43%), febrile neutropenia (43%), neutropenia (38%), pneumonia (19%), and leukopenia (17%); no G4 or 5 bleeding events were observed. Other non-hematologic treatment-emergent AEs regardless of relationship to study treatment and reported in ˃25% of patients were fatigue (58%), nausea (47%), constipation (43%), decreased appetite, peripheral edema (40% each), pyrexia (32%), dyspnea (28%), diarrhea (26%), and dizziness (25%). 30- and 60-day mortality rates were 2% and 8% with no treatment-related deaths reported. A total of 37% (90/246) of doses were delayed due to AEs primarily related to myelosuppression (neutropenia 16%, thrombocytopenia 6%, febrile neutropenia 4%).Thirty-six of the 49 efficacy evaluable patients (73%)achieved CR (21, 43%) or CRi (15, 31%); an additional 4 patients were not efficacy evaluable by protocol definition, due to death (n=2) or withdrawal of consent (n=2) before a response assessment marrow could be obtained. Remissions were achieved after a median of 2 cycles (range, 1-4) and were observed in most of the patients with adverse risk disease including antecedent myelodysplasia (16/22, 73%), adverse cytogenetics (15/18, 83%), FLT3/ITD (5/5, 100%), and patients≥75 years (17/26, 65%). Seventeen of 22 efficacy-evaluable patients with secondary AML (77%) achieved CR (11, 50%) or CRi (6, 27%). Of all responding patients, 17 of 36 (47%) achieved MRD negativity by flow cytometry. The median relapse-free survival was 9.1 months (range, 0.1-16.5+) andOS continues to evolve with22 patients (42%) alive with a median follow-up of 10 months. Conclusions The combination of 33A+HMA is well tolerated with no identified pattern of off-target toxicity. Activity with the combination appears markedly improved when compared to the historical experience of HMA monotherapy in this patient population (Table 1). The CR+CRi rate of 73% in older AML patients with poor risk factors in the setting of low early mortality is particularly encouraging. Activity was maintained even in the highest risk patient groups (adverse risk cytogenetics, underlying myelodysplasia, secondary AML, FLT3/ITD). Survival data are evolving and compare favorably to historical controls. CASCADE, a phase 3 trial investigating 33A+HMA v. HMA alone in older AML patients is now enrolling (NCT02785900). Disclosures Fathi: Merck: Other: Advisory Board participation; Agios Pharmaceuticals: Other: Advisory Board participation; Bexalata: Other: Advisory Board participation; Seattle Genetics: Consultancy, Other: Advisory Board participation, Research Funding; Celgene: Consultancy, Research Funding. Erba:Gylcomimetics: Other: DSMB; Millennium Pharmaceuticals, Inc.: Research Funding; Jannsen: Consultancy, Research Funding; Ariad: Consultancy; Sunesis: Consultancy; Pfizer: Consultancy; Celator: Research Funding; Juno: Research Funding; Seattle Genetics: Consultancy, Research Funding; Agios: Research Funding; Astellas: Research Funding; Novartis: Consultancy, Speakers Bureau; Incyte: Consultancy, DSMB, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; Amgen: Consultancy, Research Funding; Daiichi Sankyo: Consultancy. Stein:Celgene: Other: Advisory Board, Research Funding; Agios Pharmaceuticals: Other: Advisory Board, Research Funding; Seattle Genetics: Research Funding; Novartis: Consultancy. Ravandi:Seattle Genetics: Consultancy, Honoraria, Research Funding; BMS: Research Funding. Faderl:JW Pharma: Consultancy; Amgen: Speakers Bureau; Karyopharm: Consultancy, Research Funding; Ambit Bioscience: Research Funding; BMS: Research Funding; Celator Pharmaceuticals: Research Funding; Astellas: Research Funding; Pfizer: Research Funding; Seattle Genetics: Research Funding; Celgene: Consultancy, Research Funding. Advani:Seattle Genetics: Consultancy, Research Funding. DeAngelo:Baxter: Consultancy; Pfizer: Consultancy; Amgen: Consultancy; Celgene: Consultancy; Ariad: Consultancy; Incyte: Consultancy; Novartis: Consultancy. Kovacsovics:Seattle Genetics: Research Funding. Jillella:Seattle Genetics: Research Funding. Levy:Seattle Genetics: Research Funding; Jansen: Speakers Bureau; Amgen: Speakers Bureau; Millennium: Speakers Bureau. O'Meara:Seattle Genetics: Employment, Equity Ownership. Ho:Seattle Genetics: Employment, Equity Ownership. Stein:Seattle Genetics: Research Funding; Amgen: Consultancy, Research Funding, Speakers Bureau; Stemline Therapeutics: Consultancy, Research Funding; Argios: Research Funding; Celgene: Research Funding.

Background Older patients with AML who are not candidates for intensive therapy are typically treated with hypomethylating agents (HMAs) or other low intensity therapy. HMAs have been shown to upregulate CD33 and to increase sensitivity to cytotoxic chemotherapy by decreasing apoptotic threshold in tumor cells. SGN-CD33A (or 33A) is a CD33-directed antibody conjugated to 2 molecules of a pyrrolobenzodiazepine (PBD) dimer. Upon binding, 33A is internalized and transported to the lysosomes where PBD dimer is released via proteolytic cleavage of the linker, crosslinking DNA, and leading to cell death. In preclinical studies combining 33A with an HMA (azacitidine and decitabine), synergy has been demonstrated in multidrug resistant AML models (Sutherland ASH 2014). Methods A combination cohort in a phase 1 study (NCT01902329) was designed to evaluate the safety, tolerability, pharmacokinetics (PK), and anti-leukemic activity of 33A in combination with an HMA. Eligible patients (ECOG 0-1) must have previously untreated CD33-positive AML, and have declined intensive therapy. A single dose level of 33A, 10 mcg/kg, was administered outpatient IV every 4 weeks on the last day of HMA (azacitidine or decitabine [5 day regimen], standard dosing). Patients with clinical benefit may continue treatment until relapse or unacceptable toxicity. Investigator assessment of response is per IWG criteria; CRi requires either platelet count of ≥100,000/µL or neutrophils of ≥1,000/µL (Cheson 2003). Results To date, 24 patients (63% male) with a median age of 77 years (range, 66-83) have been treated with the combination therapy. 42% of patients had adverse cytogenetics (MRC), 23 patients were treatment naïve and 1 patient had received prior low intensity therapy for MDS. At baseline, patients had a median of 60% BM blasts (range, 2%-90%) and a median of WBC of 2.2 (range, 1-132). At the time of this interim analysis, patients were on treatment for a median of 13.5+ weeks with 17 patients continuing treatment; no DLTs have been reported. Grade 3 or higher adverse events (AE) reported in >20% of patients were fatigue (54%), febrile neutropenia (46%), anemia (25%), neutropenia (25%), and thrombocytopenia (21%). Other treatment-emergent AEs regardless of relationship to study treatment reported in ˃20% of patients were nausea (29%), decreased appetite (25%), and constipation (21%). Thirty- and 60-day mortality rates are 0% and 4% respectively with no treatment-related deaths reported. Fifteen of the 23 efficacy evaluable patients (65%) achieved CR (5) or CRi (10). Remissions were generally obtained after 2 cycles of treatment and were observed in many patients with adverse risk including underlying myelodysplasia (6/8, 75%) and adverse cytogenetics (8/9, 89%). Median OS has not been reached with 20 patients alive at the time of this data cut. Conclusions The combination of 33A with HMA appears to be well-tolerated, active, and has no identified off-target toxicities. Activity with the combination compares favorably with historical experience with HMAs alone in this patient population. The CR+CRi rate of 65% in AML patients with poor risk factors with the observed low 60-day mortality (4%) are particularly encouraging. These promising data warrant further evaluation in future trials. Disclosures Fathi: Agios Pharmaceuticals: Other: Advisory Board participation; Merck: Other: Advisory Board participation; Seattle Genetics: Other: Advisory Board participation, Research Funding. Off Label Use: SGN-CD33A is an investigational agent being studied in patients with CD33-positive AML. SGN-CD33A is not approved for use.. Erba:GlycoMimetics; Janssen: Other: Data Safety & Monitoring Committees; Sunesis;Pfizer; Daiichi Sankyo; Ariad: Consultancy; Millennium/Takeda; Celator; Astellas: Research Funding; Seattle Genetics; Amgen: Consultancy, Research Funding; Novartis; Incyte; Celgene: Consultancy, Patents & Royalties. Lancet:Seattle Genetics: Consultancy; Pfizer: Research Funding; Boehringer-Ingelheim: Consultancy; Kalo-Bios: Consultancy; Amgen: Consultancy; Celgene: Consultancy, Research Funding. Stein:Seattle Genetics, Inc.: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees. Walter:Pfizer, Inc.: Consultancy; Covagen AG: Consultancy; AstraZeneca, Inc.: Consultancy; CSL Behring: Research Funding; AbbVie, Inc.: Research Funding; Amgen: Research Funding; Amphivena Therapeutics, Inc.: Consultancy, Research Funding; Seattle Genetics, Inc.: Consultancy, Research Funding. DeAngelo:Incyte: Consultancy; Amgen: Consultancy; Pfizer: Consultancy; Ariad: Consultancy; Bristol Myers Squibb: Consultancy; Novartis: Consultancy; Celgene: Consultancy; Agios: Consultancy. Faderl:Celator: Research Funding; Ambit: Research Funding; BMS: Research Funding; Astellas: Research Funding; Karyopharm: Consultancy, Research Funding; Seattle Genetics, Inc.: Research Funding; JW Pharma: Consultancy; Celgene: Consultancy, Research Funding, Speakers Bureau; Pfizer: Research Funding; Onyx: Speakers Bureau. Jillella:Seattle Genetics, Inc.: Research Funding. Bixby:Seattle Genetics, Inc.: Research Funding. Kovacsovics:Seattle Genetics, Inc.: Research Funding. O'Meara:Seattle Genetics, Inc: Employment, Equity Ownership. Kennedy:Seattle Genetics, Inc.: Employment, Equity Ownership. Stein:Amgen: Speakers Bureau.

Acute myeloid leukemia (AML) remains a therapeutic challenge. Long-term survival rates, in particular for older AML patients, remain poor, highlighting the need for improved and well-tolerated treatment options. AML patients who are unfit for high dose chemotherapy in the US are often prescribed hypomethylating agents (azacitidine or decitabine) although the efficacy of these agents in this population was modest (Estey, Leukemia 2013). SGN-CD33A is a CD33-directed antibody drug conjugate (ADC) that is comprised of a cysteine-engineered anti-CD33 antibody, a cleavable dipeptide linker that is highly stable in circulation, and a PBD dimer that binds DNA with high intrinsic affinity. The ADC is active as a single agent in preclinical models of AML that are characteristically resistant to chemotherapy (multi-drug-resistant, MDR-positive) (Sutherland et al. Blood 2013). In the present study, we tested the activity of SGN-CD33A in combination with hypomethylating agents (HMA), azacitidine or decitabine. We hypothesized that the combination of SGN-CD33A with an HMA will have greater impact on the DNA repair pathway in leukemic cells, furthering the processes of apoptosis and cell death. MDR-positive AML cells were treated for 96 hours with SGN-CD33A and each of the HMAs alone and in combination, evaluating both simultaneous as well as sequential administration. Enhanced tumor cell killing was observed when AML cells were treated concomitantly with the combination of SGN-CD33A and an HMA or pre-treated with HMAs prior to the addition of SGN-CD33A. Superior anti-leukemic activity of subtherapeutic doses of SGN-CD33A in combination with HMAs was observed in mouse xenograft models generated with MDR-positive AML cell lines. In the difficult to treat HEL9217 model, decitabine or a single dose of 200 mcg/kg SGN-CD33A delayed tumor growth, while significant reductions in tumor growth were observed for the combination treatment (p=0.0001). Improved antitumor activity in this model was also observed for SGN-CD33A in combination with azacitidine. SGN-CD33A in combination with decitabine significantly reduced tumor burden compared to either agent alone in the TF1-α AML model (p=0.0002). Similarly, sequenced dosing of azacitidine followed by a subtherapeutic dose of 30 mcg/kg SGN-CD33A in mice bearing KG-1 xenografts delivered greater antitumor activity compared to the individual agents (p=0.0001). To investigate the mechanism underlying the enhancement in antileukemic activity, we looked at the impact of HMAs alone and in combination with SGN-CD33A on myeloid marker expression, PBD drug release, and impact on the DNA damage and apoptotic pathways. In AML cell lines that did not show improved cytotoxic activity with the combination of SGN-CD33A and HMA, HMA treatment appeared to have no positive effect on the cell surface levels of CD33. However in responsive cell lines such as TF1-α, HMA treatment resulted in time- and dose-dependent increases in the levels of CD33. Significant increases in expression were observed between 2 and 4 days with decitabine and after 4 days with azacitidine. In addition, more PBD dimer drug from SGN-CD33A was incorporated into DNA in HMA treated cells. Concomitant, the treatment of AML cells with the combination of SGN-CD33A and HMA resulted in greater DNA damage and apoptosis as shown by the increased levels of the early DNA damage marker, γH2AX, and the formation of cleaved PARP, an apoptosis marker, compared to either agent alone. Studies are in progress to investigate the effects on other components of the DNA repair and cell cycle pathways. These findings demonstrate that SGN-CD33A can be successfully combined with hypomethylating agents to deliver marked antitumor activity in preclinical drug-resistant models of AML. Disclosures Sutherland: Seattle Genetics, Inc.: Employment. Yu:Seattle Genetics, Inc.: Employment. O'Day:Seattle Genetics,Inc: Employment. Alley:Seattle Genetics,Inc.: Employment. Anderson:Seattle Genetics, Inc.: Employment. Emmerton:Seattle Genetics, Inc.: Employment. Zeng:Seattle Genetics, Inc.: Employment. O'Meara:Seattle Genetics, Inc: Employment, Equity Ownership. Feldman:Seattle Genetics,Inc: Employment. Kennedy:Seattle Genetics,Inc: Employment, Equity Ownership, Honoraria, Speakers Bureau. Ryan:Seattle Genetics, Inc.: Employment. Benjamin:Seattle Genetics, Inc: Employment.

Background CD33is expressed in approximately 90% of AML, representing a promising target despite age, prior therapies, or mutational heterogeneity. SGN-CD33A (or 33A) is a CD33-directed antibody conjugated to 2 molecules of a pyrrolobenzodiazepine (PBD) dimer. Upon binding, 33A is internalized and transported to the lysosomes where PBD dimer is released via proteolytic cleavage of the linker, crosslinking DNA, and leading to cell death. Methods The dose-escalation portion of this phase 1 study (NCT01902329) is designed to evaluate the safety, tolerability, pharmacokinetics (PK), and antileukemic activity of 33A as monotherapy. Eligible patients (ECOG 0-1) must have CD33-positive AML, and have either relapsed disease following initial remission (CR) of >3 months, or have declined conventional induction/consolidation. 33A monotherapy is administered outpatient via IV every 3 weeks for up to 2 cycles, followed by optional low-dose maintenance treatment for patients who achieve a CR/CRi. Investigator assessment of response is per IWG criteria; CRi requires either platelet count of ≥100,000/µL or neutrophils of ≥1,000/µL (Cheson 2003). Results To date, 87 patients (62% male) with a median age of 74 years (range, 27-89) have been treated. 34 patients had relapsed AML after 1st CR with intensive therapy; 52 had declined conventional intensive therapy (40 of these patients had received 1-2 prior low intensity therapies, primarily hypomethylating agents). Most patients had intermediate I-II (51%) or adverse (31%) risk by ELN classification and 54% of patients had AML with underlying myelodysplasia-related changes. 9% of patients displayed NPM1 mutations without FLT3 mutation (NPM1+/FLT3-). Dose levels ranged from 5-60 mcg/kg (n=75) and also included fractionated dosing of 20 mcg/kg on Day 1 and Day 4 (n=12). Five patients remain on treatment. Six dose-limiting toxicities were reported in the monotherapy escalation cohorts: 2 Grade 4 bone marrow failures (40 and 60 mcg/kg), 2 mucositis (Grade 3 at 50 mcg/kg; Grade 3 at fractionated 20+20 mcg/kg), Grade 3 pulmonary embolism (20 mcg/kg), and Grade 5 sepsis (50 mcg/kg). The most common Grade 3 or higher adverse events (AE) reported were febrile neutropenia (69%), thrombocytopenia (29%), and anemia (23%). Increased myelosuppression was observed at doses higher than 40 mcg/kg and the fractionated dosing cohort, including febrile neutropenia observed in 68% of patients and sepsis observed in 26% of patients. Other common treatment-emergent AEs regardless of relationship to study treatment were fatigue (48%), decreased appetite (28%), constipation, diarrhea, dyspnea, nausea (26% each), and peripheral edema (25%). The 30-day mortality was 6%. Across all dose levels, the CR+CRi rate was 86% in the patients with NPM1+/FLT3- disease (n=7). Of the 21 efficacy evaluable patients treated at 40 mcg/kg, 3 patients achieved a best clinical response of CR, 4 achieved CRi, and 5 had morphologic leukemia-free state (mLFS). Three of 5 treatment-naïve patients within the 40 mcg/kg dose level achieved a CR or CRi. In patients across dose levels who achieved at least mLFS, the mean time to full count recovery was 5 weeks for neutrophils (≥1,000/µL) and 6 weeks for platelets (≥100,000/µL). Median OS in patients treated at 40 mcg/kg is 10 months with 17 patients alive at the time of this data cut. Across all dose levels, 8 patients went on to receive an allogeneic SCT. PK data demonstrated generally dose-dependent increase in plasma ADC exposures and target-mediated rapid clearance. Conclusions Dose escalation is complete and a recommended monotherapy 33A dose of 40 mcg/kg was identified. AEs observed were generally manageable, often associated with underlying myelosuppression. 33A has demonstrated favorable antileukemic activity with 33% achieving a CR+CRi at the 40 mcg/kg dose level (60% CR+CRi in treatment naïve patients). The rapid clearance of marrow blasts in patients with poor risk factors and low 30-day mortality (6%) are encouraging. Enrollment is ongoing in multiple expansion cohorts, including previously untreated AML patients who declined intensive therapy, relapsed NPM1 mutant disease, and relapsed APL. In addition, a study evaluating 33A with intensive therapy in newly diagnosed patients with AML is ongoing. Disclosures Stein: Amgen: Speakers Bureau. Off Label Use: SGN-CD33A is an investigational agent being studied in patients with CD33-positive AML. SGN-CD33A is not approved for use. Walter:Pfizer, Inc.: Consultancy; Covagen AG: Consultancy; AstraZeneca, Inc.: Consultancy; CSL Behring: Research Funding; AbbVie, Inc.: Research Funding; Amgen: Research Funding; Amphivena Therapeutics, Inc.: Consultancy, Research Funding; Seattle Genetics, Inc.: Consultancy, Research Funding. Erba:GlycoMimetics; Janssen: Other: Data Safety & Monitoring Committees; Sunesis; Pfizer; Daiichi Sankyo; Ariad: Consultancy; Millennium/Takeda; Celator; Astellas: Research Funding; Seattle Genetics; Amgen: Consultancy, Research Funding; Novartis; Incyte; Celgene: Consultancy, Patents & Royalties. Fathi:Agios Pharmaceuticals: Other: Advisory Board participation; Seattle Genetics: Other: Advisory Board participation, Research Funding; Merck: Other: Advisory Board participation. Lancet:Seattle Genetics: Consultancy; Pfizer: Research Funding; Boehringer-Ingelheim: Consultancy; Kalo-Bios: Consultancy; Amgen: Consultancy; Celgene: Consultancy, Research Funding. Kovacsovics:Seattle Genetics, Inc.: Research Funding. DeAngelo:Pfizer: Consultancy; Amgen: Consultancy; Ariad: Consultancy; Bristol Myers Squibb: Consultancy; Novartis: Consultancy; Incyte: Consultancy; Agios: Consultancy; Celgene: Consultancy. Bixby:Seattle Genetics, Inc.: Research Funding. Faderl:Onyx: Speakers Bureau; BMS: Research Funding; Seattle Genetics, Inc.: Research Funding; JW Pharma: Consultancy; Karyopharm: Consultancy, Research Funding; Celgene: Consultancy, Research Funding, Speakers Bureau; Pfizer: Research Funding; Astellas: Research Funding; Celator: Research Funding; Ambit: Research Funding. Jillella:Seattle Genetics, Inc.: Research Funding. O'Meara:Seattle Genetics, Inc: Employment, Equity Ownership. Zhao:Seattle Genetics, Inc.: Employment, Equity Ownership. Stein:Seattle Genetics, Inc.: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees.

Higher levels of procoagulant factors and factor XII deficiency may be risk factors for first venous thromboembolism (VTE). We studied associations of coagulation factors IX through XIII with risk of future VTE in 2 general population samples. Using a nested case-control study combining the 21 860 participants of the Atherosclerosis Risk in Communities study and the Cardiovascular Health Study, we determined antigenic levels of these coagulation factors in primarily pre-event blood samples from 462 participants who subsequently developed VTE and 1047 participants who remained free of VTE. Only elevated levels of factors IX and XI were associated with increased risk of VTE after adjustment for age, sex, race, and study. For factor IX, the odds ratio (OR) was 1.4 (95% confidence interval [CI], 1.0-2.0) comparing the top to bottom quintile. The OR for factor XI was higher: 2.0 (95% CI, 1.4-2.9). With further adjustment for body mass index and diabetes, only elevated factor XI remained associated with VTE risk: OR 1.8 (95% CI, 1.3-2.7). Associations were similar by study and whether the thrombosis was idiopathic or secondary. Factor XII deficiency was not related to VTE risk. Among these procoagulant factors, only elevated factor XI was a risk factor for VTE.

Background CD33 is expressed on the surface of myeloblasts in 85 to 90% of patients with AML and represents a promising target regardless of age, risk factors, or underlying mutational heterogeneity. SGN-CD33A is an anti-CD33 engineered cysteine antibody conjugated to an average of 2 molecules of a pyrrolobenzodiazepine (PBD) dimer, a highly potent DNA crosslinking agent. Upon binding to the cell surface, SGN-CD33A is internalized and transported to the lysosomes where PBD dimer is released within the cell through proteolytic cleavage of the linker, crosslinking DNA and leading to cell death. Methods This phase 1, open-label, 3+3 dose-escalation study (NCT01902329) is designed to evaluate the safety, tolerability, pharmacokinetics (PK), and anti-leukemic activity of SGN-CD33A. Eligible patients (ECOG 0-1) must have CD33-positive AML, and have either relapsed disease following initial remission (CR) of > 3 months, or have declined conventional induction/consolidation. SGN-CD33A is administered outpatient IV every 3 weeks for up to 4 cycles (Part A), followed by optional maintenance treatment for patients achieving a CR/CRi (Part B). Investigator assessment of response is per IWG criteria (Cheson 2003). Results To date, 40 patients (48% female) with a median age of 75 years (range, 27-86) have been treated. Twenty patients had relapsed AML after 1st CR with intensive therapy (3 of these had intensive frontline therapy plus 1 additional line of low intensity therapy); 20 had declined conventional intensive therapy (13 of these patients had received 1-2 prior low intensity therapies, primarily hypomethylating agents). Of the patients enrolled, 45% had underlying myelodysplasia and most had disease with intermediate (70%) or adverse (18%) cytogenetic risk, 8% with mutated NPM1 (without FLT3 mutation) and 13% with mutated FLT3. Dose levels tested were 5 mcg/kg (n=3), 10 mcg/kg (n=3), 20 mcg/kg (n=13), 40 mcg/kg (n=18), and 60 mcg/kg (n=3). To date, a maximum of 4 cycles was received in Part A and 10 cycles in Part B (total median of 2 cycles on treatment; range, 1-13 cycles). Thirteen patients remain on treatment and enrollment is ongoing. Two dose-limiting toxicities have been reported, a Grade 3 pulmonary embolism (20 mcg/kg) and a Grade 4 hypocellular marrow (>28 days; 40 mcg/kg). The only Grade 3 or higher adverse event (AE) reported in >10% of patients was febrile neutropenia (55%). Other treatment-emergent AEs regardless of relationship to study treatment reported in ˃10% of patients were fatigue (48%), diarrhea (20%), constipation (18%), cough (18%), dyspnea (18%), epistaxis (18%), peripheral edema (18%), malaise (15%), hypokalemia (13%), and pleural effusion (13%). The 30-day mortality was 2.5%, with no treatment-related deaths occurring during that time; 1 elderly patient died from a traumatic fall unrelated to SGN-CD33A. Blast clearance in marrow was obtained in 16 of 38 efficacy evaluable patients (42%) across all dose levels. A dose-response relationship is evolving with rapid and marked decreases in bone marrow blasts at 40 and 60 mcg/kg in 19 of 21 patients (Figure 1). Of 17 efficacy evaluable patients treated at 40 mcg/kg, 8 experienced clearance of marrow blasts; these patients achieved a best clinical response of CR (2), CRi (3), and morphologic leukemia-free state (mLFS; 3) thus far. In addition, complete remissions were observed at 5 mcg/kg (1 CR), 10 mcg/kg (1 CRi), and 20 mcg/kg (2 CRis). Preliminary PK data demonstrated rapid clearance of ADC, suggesting target-mediated disposition. Plasma ADC exposure generally increased with increasing dose levels. Conclusions A MTD for SGN-CD33A is not yet identified and enrollment continues. AEs observed were generally manageable, often associated with underlying myelosuppression. To date, SGN-CD33A has demonstrated antileukemic activity with 47% achieving blast clearance at the 40 mcg/kg dose level. The observed low 30-day mortality (2.5%) and rapid clearance of marrow blasts in patients with poor risk factors (median age 75, predominantly intermediate and adverse cytogenetic risk, and 45% underlying myelodysplasia) with outpatient administration are encouraging. Enrollment is ongoing to further define optimal dose and schedule. In addition, combinations of SGN-CD33A with standard AML and MDS agents will be evaluated. Figure 1: Bone Marrow Blasts Over Time Figure 1:. Bone Marrow Blasts Over Time Disclosures Stein: Seattle Genetics, Inc.: Research Funding; Janssen Pharmaceuticals: Consultancy. Off Label Use: SGN-CD33A is an investigational agent being studied in patients with AML. SGN-CD33A is not approved for use. Stein:Seattle Genetics, Inc.: Research Funding. Walter:Seattle Genetics, Inc.: Consultancy, Research Funding; Amphivena Therapeutics, Inc.: Consultancy; Amgen: Research Funding; Amphivena Therapeutics, Inc.: Consultancy; Amgen: Research Funding. Fathi:Exelixis: Research Funding; Takeda Pharmaceuticals International Co.: Research Funding; Ariad: Consultancy; Seattle Genetics, Inc.: Consultancy, Research Funding. Lancet:Seattle Genetics, Inc.: Consultancy, Research Funding. Kovacsovics:Seattle Genetics, Inc.: Research Funding. Advani:Seattle Genetics, Inc.: Research Funding. DeAngelo:Seattle Genetics, Inc.: Research Funding. O'Meara:Seattle Genetics, Inc.: Employment, Equity Ownership. Zhao:Seattle Genetics, Inc.: Employment, Equity Ownership. Kennedy:Seattle Genetics, Inc.: Employment, Equity Ownership. Erba:Incyte: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Celgene: Consultancy, Speakers Bureau; Seattle Genetics, Inc.: Consultancy, Research Funding.

Multiple myeloma (MM) is a malignancy of post-germinal centre B-cells whose pathogenesis is only partially understood. Chromosomal hyperdiploidy and recurrent immunoglobulin gene locus rearrangements are frequent, but are insufficient for malignant transformation, which is associated with additional events such as somatic mutations, epigenomic aberrations, and chromosomal copy-number changes. To investigate genomic event underlying MM pathogenesis and evolution, we used whole exome sequencing, copy number profiling and cytogenetics in 67 patients and 84 samples. For 15 patients, 2 or 3 serial samples (median 299 days apart) were available. Exome reads were used to call substitutions and indels. We used the Genome-Wide SNP Array 6.0 or exome reads to estimate the allele-specific copy number of the tumor. To cluster variants and estimate the clonal architecture of each sample and its evolution over time, we used the mutation burden, corrected for copy number and normal cell contamination. Analysis of the clonal structure of the tumors showed at least one subclone in 94% of patients at diagnosis, suggesting that myeloma is a heterogeneous disease at presentation. Interestingly, many mutations of known MM driver genes (KRAS, NRAS, BRAF, TP53, FAM46C) were subclonal at diagnosis. In 5/67 patients, BRAF and KRAS/NRAS mutations co-existed in the same sample, raising therapeutic implications given the paradoxical ERK-activating effect of BRAF inhibitors in RAS-mutated cells. Furthermore, only 3/10 BRAF variants were V600E, the current target of most inhibitors. Altogether, only the 5 previously known genes were significantly enriched in our cohort, highlighting marked heterogeneity of the spectrum of candidate driver gene mutations across MM patients. Nevertheless, we identified several new recurrent gene lesions: inactivating mutations of SP140 (7.5%), a gene previously linked to germline susceptibility to CLL, and in ROBO1 (7.5%), a gene recently implicated in pancreatic cancer; clustered missense substitutions in EGR1 (6%), a gene previously implicated in plasma cell apoptosis; clustered truncating mutations in LTB (4.5%), a TNF-family protein implicated in lymphoid development. The subclonal structure of the sample changed over time in 72% paired samples, highlighting genomic evolution at relapse. We described 4 different scenarios with striking concordance between mutations and chromosomal copy number changes: no change, linear evolution (a new clone appears in the later sample), differential clonal response (the relative proportions of the subclones change over time), and branching evolution (new clones emerge, while others decline in frequency or disappear). All subclonal variants in known driver myeloma genes increased their clonal fraction at the later time-point, consistent with the expected positive selection for the subclones harboring them. To investigate mutational processes responsible for the generation of the mutational repertoire in MM, we extracted the variant context and analyzed the mutational signatures. We found two signatures in our samples. The most represented one is enriched for spontaneous deamination of methylated cytosines, a common process in cancer and aged cells. The second signature was more represented in samples showing extremely high numbers of variants, sometimes clustered in small regions of ∼200 bp (kataegis). We hypothesize that it results from aberrant activity of the APOBEC family of cytosine deaminases, recently described in breast cancer. Interestingly, cases of extramedulary relapse were always associated with branching evolution and showed increased contribution from this APOBEC signature. In conclusion, in our cohort of MM samples we show: 1) evidence of tumor heterogeneity at the time of diagnosis; 2) discernable genetic changes and shifts in the clonal structure of disease at the time of progression; 3) different mutational processes responsible for an heterogeneous mutational repertoire across patients, and over time in the same patient; 4) a comprehensive list of recurrent variants, many of which are previously unreported. Our study provides new insights into the genomic architecture of MM, and will help identify molecular alterations associated with progression of disease and development of drug resistance. Disclosures: Tai: Onyx: Consultancy. Richardson:Millennium: Membership on an entity’s Board of Directors or advisory committees; Johnson & Johnson: Membership on an entity’s Board of Directors or advisory committees; Novartis: Membership on an entity’s Board of Directors or advisory committees. Moreau:Celgene: Honoraria, Speakers Bureau. Attal:CELGENE: Honoraria, Speakers Bureau; JANSSEN: Honoraria, Speakers Bureau. Anderson:Celgene, Millennium, BMS, Onyx: Membership on an entity’s Board of Directors or advisory committees; Acetylon, Oncopep: Scientific Founder , Scientific Founder Other.

Introduction Hodgkin lymphoma (HL) in patients aged ≥60 years has disproportionately inferior outcomes as compared to HL in younger patients. This can be mostly attributed to treatment-related factors that compromise cure rates. Comorbidities in older patients are associated with higher rates of treatment-related toxicities and can prevent delivery of standard intensity and/or duration of chemotherapy. A retrospective multicenter analysis showed an increased incidence of bleomycin-associated pulmonary toxicity (32%; with a mortality rate of 25%) in HL patients aged ≥ 60 who received ABVD for frontline therapy (Evens 2012). Novel therapeutic approaches with improved efficacy and tolerability are needed for this population. Brentuximab vedotin (ADCETRIS®) is an antibody-drug conjugate that comprises an anti-CD30 antibody conjugated by a protease-cleavable linker to a microtubule-disrupting agent, monomethyl auristatin E. Robust antitumor activity and acceptable toxicity has been demonstrated in HL patients who relapse after conventional chemotherapy or autologous stem cell transplant. A retrospective analysis of patients aged ≥60 years with relapsed/refractory CD30+ lymphomas across 7 single-agent brentuximab vedotin studies showed antitumor activity and clinical response duration consistent with those observed in younger patients (Fanale 2012). Thus, this ongoing phase 2, single-arm, open-label study was initiated to evaluate the efficacy, safety, and tolerability of brentuximab vedotin as frontline monotherapy for HL patients aged ≥60 years (NCT01716806). Methods The population to be enrolled includes ∼30 treatment-naïve patients with classical HL (Stages I–IV). Eligible patients must be aged ≥60 years, have an ECOG status ≤3, and be ineligible for or have declined conventional chemotherapy. Brentuximab vedotin 1.8 mg/kg is administered every 3 weeks by IV infusion. Patients achieving stable disease (SD) or better can receive up to 16 cycles of treatment, after which therapy can be continued for those experiencing clinical benefit. The primary endpoint is objective response rate (ORR) as assessed by the Revised Response Criteria for Malignant Lymphoma (Cheson 2007). Response assessments are performed at Cycles 2, 4, 8, 12, and EOT (including PET at Cycles 2, 8, and EOT). Results Thirteen patients with treatment-naïve classical HL have been enrolled to date. Median age was 75 years (range, 64 to 92) and approximately half of the patients were male (54%). Seven patients (54%) had moderate age-related renal insufficiency at baseline (creatinine clearance ≥30 and Of the 11 patients with a response assessment (see table), the ORR was 82% (n=9) and the complete remission (CR) rate was 64% (n=7). For the 10 patients who had interim PET scans after 2 cycles of therapy, the mean decrease in maximum standardized uptake value (SUVmax) between baseline and Cycle 2 was 83%. Cycle 2 PET scans were negative (Deauville Score 1-3) in 36% of patients, and the range of duration of response was 0.1+ to 20.6+ weeks thus far. Treatment-related adverse events (AEs) occurring in ≥15% of patients included neutrophil count decreased, peripheral sensory neuropathy, pruritus, and rash (n=2 each); most events were Grade 1 or 2. Grade 3 treatment-related AEs included neutrophil count decreased, rash, and orthostatic hypotension (n=1 each). No Grade 4 or 5 events have been observed to date. Conclusions In this interim analysis of patients aged ≥60 years with newly diagnosed HL, compelling antitumor activity with single-agent brentuximab vedotin has been demonstrated. To date, a response rate of 82% has been shown in this historically challenging population of patients who either declined or were not eligible for standard chemotherapy. Preliminary safety data demonstrate tolerability in this patient population and the data are consistent with the current safety profile of brentuximab vedotin. Disclosures: Yasenchak: Seattle Genetics, Inc.: Research Funding. Off Label Use: Brentuximab vedotin is indicated for treatment of patients with Hodgkin lymphoma after failure of autologous stem cell transplant or after failure of at least two prior multi-agent chemotherapy regimens in patients who are not ASCT candidates and for the treatment of patients with systemic anaplastic large cell lymphoma after failure of at least one prior multi-agent chemotherapy regimen. Chen:Seattle Genetics, Inc.: Consultancy, Research Funding, Speakers Bureau, Travel expenses Other. Sharman:Seattle Genetics, Inc.: Research Funding, Travel expenses Other; Genentech: Research Funding; Gilead: Research Funding. Boccia:Seattle Genetics, Inc.: Honoraria, Research Funding. Holkova:Seattle Genetics, Inc.: Research Funding. Rosen:Seattle Genetics, Inc.: Advisory/scientific board membership Other, Honoraria, Research Funding. Friedberg:Seattle Genetics, Inc.: Research Funding. O'Meara:Seattle Genetics, Inc.: Employment, Equity Ownership. Forero-Torres:Seattle Genetics, Inc.: Research Funding, Speakers Bureau.

Abstract 1331 BET (bromodomain and extra-terminal) proteins bind to acetylated lysine residues on histones and thereby directly and selectively regulate the expression of genes relevant to cancer. Small molecule inhibition of BET protein binding to chromatin suppresses the transcription of MYC, a subset of NF-κB-dependent genes, and BCL-2. Because of the clinical potential of this novel mechanism, we have discovered selective and potent small molecule inhibitors of BET bromodomains with physical and pharmacokinetic properties that are favorable for clinical development. CPI-267232 is representative of a series of small molecule BET inhibitors with these characteristics. In a biochemical binding assay it has an IC50 126 nM against BD1 of BRD4, and in the MV4-11 leukemia cell line it suppresses the transcription of MYC with an EC50 of 170 nM and inhibits its growth with a GI50of 120 nM. In a panel of more than 100 cancer cell lines CPI-267232 and other structurally dissimilar BET inhibitors demonstrate growth inhibitory activity most potently and consistently against cell lines of hematologic origin. Cells treated with CPI-267232 undergo a G1 arrest with the more sensitive lines undergoing apoptosis with longer periods of drug exposure (> 48 hrs). CPI-267232 has high oral bioavailability in mice (∼80%) but is cleared rapidly, with an elimination half-life of approximately 3 hrs (in dogs, oral bioavailability is 94% with an elimination half-life of 9 hrs). PK-PD studies conducted in mice bearing subcutaneous xenografts of Raji Burkitt's lymphoma demonstrated that maximal (80%) suppression of MYC expression was achieved 4 hours following a single 30 mg/kg oral dose; MYC expression returned to baseline levels by 12 hours, consistent with the rapid elimination of the compound. Efficacy studies in nude mice bearing xenografts were subsequently conducted, with a 30 mg/kg PO bid regimen yielding a %T/C value of 23% (Raji) or regression (MV4-11) after 21 days of treatment. Evaluation of the relationships between various measurements of drug exposure and efficacy revealed that efficacy is primarily driven by maintaining drug concentration above a minimum value rather by total AUC or Cmax. This observation is consistent with the importance of exposure duration in effecting growth arrest and cell killing in tissue culture. Although the transcription of MYC is frequently suppressed, the overall effects of BET inhibition on gene transcription vary across cell lines of different origin. Genome-wide expression profiling of 2 myeloma and 3 leukemia cells lines at 4 and 24 hours after exposure to a small molecule BET inhibitor resulted in the identification of approximately 200 genes that were commonly either up- or down-regulated by at least 2-fold with statistical significance. In addition, a small set of BET inhibitor-sensitive genes has been identified in peripheral blood mononuclear cells. The discovery of novel BET inhibitors with optimized potency, selectivity, and pharmacokinetic properties, coupled with these insights into the pharmacokinetic and pharmacodynamic determinants of anti-tumor activity, provides an opportunity for the rational development of BET inhibition in the treatment of patients with hematologic malignancies. Disclosures: Sims: Constellation Pharmaceuticals: Employment. Normant:Constellation Pharmaceuticals: Employment. Sandy:Constellation Pharmaceuticals: Employment. Mertz:Constellation Pharmaceuticals: Employment. Bryant:Constellation Pharmaceuticals: Employment. O'Meara:Constellation Pharmaceuticals: Employment. Green:Constellation Pharmaceuticals: Employment. Cooper:Constellation Pharmaceuticals: Employment. Audia:Constellation Pharmaceuticals: Employment.

Abstract 1958 Background: Hurler syndrome (HS), the most severe phenotype in the spectrum of Mucopolysaccharidosis type I, is caused by a deficiency of the lysosomal enzyme alpha-L-iduronidase. HS is clinically characterized by a progressive and ultimately fatal multi-system deterioration with involvement of the central nervous system. At present, hematopoietic stem cell transplantation (HSCT) is the only treatment that prevents disease progression in the central nervous system and is therefore considered the treatment of choice in HS. Long-term follow-up of outcomes of HSCT for HS are sparse and risk factors for favorable long-term outcomes are still largely unknown. Therefore, an international multicenter study was initiated to describe the long-term outcomes of successfully transplanted HS patients. Methods: HS-patients transplanted between 1980 and 2007 within the leading transplantation centers in Europe and the United States were include in this study. Patient, donor, and transplantation-related variables which may influence long-term outcome were analyzed. Patients who were ‘alive and engrafted (donor-chimerism >10%)' with a follow up of at least three years after HSCT were included. The functional outcomes assessed for the various organ systems - orthopedic, cardiac, ophthalmologic, respiratory and audiologic - were analyzed using multivariate Cox proportional hazards and logistic regression models. Results: 197 Hurler patients were included from 8 different transplant centers. This is estimated to be about 70–80% of the successfully transplanted HS patients worldwide during that time period. These patients had a median age of 16 (2–80) months at HSCT with a median follow up of 88 (36–258) months after successful HSCT. Seventy-nine % of the patients received a graft from an unaffected (non-carrier) donor. Seventy-two % of the patients achieved full (>95%)-donor-chimerism and 28% mixed-chimerism. After HSCT, normal enzyme-levels (EL; according to the local reference range) were found in 75% of the patients while 25% had EL below lower limit of normal; either due to mixed-chimerism or carrier-donorship). Multivariate analyses ( table 1 ) showed having a “normal EL” after HSCT and younger (below the median age of 16mths) “age at transplantation” were associated with less serious orthopedic complications requiring surgical interventions; e.g. cord compression, genu-valgum surgery, carpal tunnel surgery. Genotype (double non-sense vs. any other genotype) was associated with a lower probability of requiring hip dysplasia surgery as well as with the occurrence of retinopathy. For other endpoints; e.g progression valve insufficiency, progression corneal clouding and development of retinopathy and the need for hearing aids having a normal EL as well as age at HSCT ( Conclusion: The long-term outcome of clinical manifestations in HS-patients after successful HSCT is promising although residual disease burden remains. Predictors, favorably influencing the long-term outcomes are suggested to be 1) enzyme level (normal vs. below LLN) after HSCT, 2) genotype and 3) age at HSCT. Achieving normal enzyme levels at an early age might significantly impact the prognosis of Hurler syndrome patients. Newborn screening (resulting in early HSCT), the use of non-carrier donors and achieving full-donor chimerism may be crucial in optimizing long-term outcomes. Table 1 . Multivariate analyses HR p-value Cord Compression Surgery normal enzymes (>LLN) 0,081 0,021 age at transplantation 0,075 0,025 Carpal Tunnel Surgery normal enzymes (>LLN) 0,021 0,011 age at transplantation 0,21 0,005 Hip Dysplasia Genotype (double nonsence vs. rest) 4,83 0,005 Genu Valgum Surgery normal enzymes (>LLN) 0,224 0,002 Mitral Insufficiency - Progression normal enzymes (>LLN) 0,32 0,044 age at transplantation 0,36 0,053 Corneal Clouding - Progression normal enzymes (>LLN) 0,21 0,015 age at transplantation 0,14 0,007 Retinopathy - Occurence Genotype (double nonsence vs. rest) 5,36 0,038 age at transplantation 0,05 0,008 Hearing Aids normal enzymes (>LLN) 0,29 0,011 Disclosures: No relevant conflicts of interest to declare.

Abstract 3353 Iron store depletion is a common side effect of whole-blood donation. Iron loss may lead to iron deficiency symptoms such as fatigue, decreased physical and job performance then gradually result in iron deficiency anemia. As of 2004, routine serum ferritin testing was implemented at our Center. We analyzed the impact of this measure on our donor population with regard to hemoglobin level, anemia occurrence and donor deferral due to low hemoglobin. A total of 160'612 intended donations of 23'557 healthy blood donors at a single institution (Blutspendezentrum beider Basel, Basel, Switzerland) between 1996 and 2009 were analyzed. At each visit, complete blood counts were taken from fingerprick samples and donors were deferred if the capillary hemoglobin concentration proved Disclosures: No relevant conflicts of interest to declare.

Abstract 3460 Autoimmune diseases (AD) have been reported after haematopoetic stem cell transplantation (HSCT) and most commonly autoimmune cytopenias (AIC) are observed. Proposed risk factors are unrelated donor HSCT and presence of chronic graft-versus-host disease (GVHD). Use of CB cells is increasing as an alternative source of adults HSC for allotransplant however incidence and risk factors of AD after CBT have not been described. Since CB lymphocytes are immature and most of the CBT are HLA mismatched, we hypothesize a high incidence and diversity of secondary AD and. Therefore, we conducted a retrospective study in order to describe incidence, nature and risk factors for secondary AD after CBT. We include CBT recipients reported to EUROCORD up to December 2008. All centres were asked to participate to the survey even if they did not observe any case of AD after CBT. For those with AD, detailed information on diagnosis, treatment and outcome were asked. Median follow-up was 44 months (3.2-217). 42 out of 651 patients (pts) from 35 centres had developed at least one secondary AD at a median of 198 days (27-4267) after CBT. The remaining 609 pts without secondary AD served as control group (nonAD). Characteristics of both groups are given in table 1. Cumulative incidence of secondary AD after CBT was 5±1% after 3 years and 6.5±1% after 10 years. Diagnosis of secondary AD were autoimmune haemolytic anemia (AIHA) in 16, autoimmune thrombopenia (ITP) in 9, EVANS syndrome in 6, autoimmune thyroiditis in 3, glomerulonephritis in 2, Graves disease, psoriasis, psoriasis arthritis, immune neutropenia, ulcerative colitis and vasculitis in 1 patient each. Three pts developed ITP followed by AIHA. Median time to develop a AIC was 180 days (27-4267) and non-hematological AD was 322 days (70-1117), respectively (p=0.13). At onset of AD, 3 pts had acute GvHD, 6 chronic GvHD and in 10 pts an infection. In multivariate analysis adjusted for differences between the two groups, the following factors were associated with higher incidence of secondary AD: 1) age Table 1: Characteristics of pts developing AD or not (nonAD) Pts characteristics AD pts nonAD pts P female sex 36% 45% age at HSCT 2.23 (0.2–43.24) years 10.7 (0.11–66.5) years 0.0001 year of HSCT 2006 (95–08) 2006 (92–08) 0.04 Type of donor unrelated 95% 90% 0.26 Indication for HSCT (n) ALL 10 184 AML 2 150 MDS 4 67 AA 5 52 SCID 6 51 CML 3 24 NHL 0 21 Hemoglobinopathy 0 15 Histiocytosis 2 14 Metabolic diseases 9 19 others 1 11 Graft Single cord 85% 77% 0.25 Double cord 14% 23% HLA compatibility 5/6+6/6 68% 48% 0.02 Conditioning RIC 80% 73% 0.34 TBI 20% 43% 0.0004 Serotherapy 73% 74% 0.86 Host CMV status positive 45% 58% 0.11 Disclosures: No relevant conflicts of interest to declare.