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BCR-ABL1 kinase inhibitors have improved the prognosis of Philadelphia-chromosome-positive (Ph+)-acute lymphoblastic leukemia (ALL). Ph-like (or BCR-ABL1-like) ALL does not express BCR-ABL1 but commonly harbors other genomic alterations of signaling molecules that may be amenable to therapy. Here, we report a case with a NUP214-ABL1 fusion detected at relapse by multiplexed, targeted RNA sequencing. It had escaped conventional molecular work-up at diagnosis, including cytogenetic analysis and fluorescence in situ hybridization for ABL1 rearrangements. The patient had responded poorly to initial multi-agent chemotherapy and inotuzumab immunotherapy at relapse before the fusion was revealed. The addition of dasatinib targeting NUP214-ABL1 to inotuzumab resulted in complete molecular remission, but recurrence occurred rapidly with dasatinib alone. However, deep molecular remission was recaptured with a combination of blinatumomab and ponatinib, so he could proceed to allotransplantation. This case illustrates that next-generation sequencing approaches designed to discover cryptic gene fusions can benefit patients with Ph-like ALL.

We sought to assess the safety of adding ixazomib, an oral proteasome inhibitor, to a multi-agent treatment regimen for older adults with acute lymphoblastic leukemia (ALL). Patients 51 to 75 years of age with newly diagnosed ALL were screened. Induction consisted of prednisone (P), vincristine (V), and doxorubicin (D). For BCR-ABL1+ patients, dasatinib was added. On Days 1, 8, 15 of induction, ixazomib was given orally. After induction patients received 1 cycle of consolidation in which ixazomib was given on Days 1, 8, 15. After consolidation, patients in remission (CR) were offered stem cell transplantation. Among the 19 patients treated, 15 (79%) [90% CI, 58-92%] achieved CR or CRi. At 2 years, the overall survival was 47% [95%CI, 29-72%]. In this study the dose of 2.3 mg of ixazomib in combination was the MTD for older patients with ALL and is the recommended dose for future phase 2 studies.

A Man with Sore Throat, Epistaxis, and Oropharyngeal Petechiae A 21-year-old man with sickle cell trait presented with sore throat, epistaxis, and petechiae of the oropharynx. The hemoglobin level ...

Summary Background Genome-edited donor-derived allogeneic anti-CD19 chimeric antigen receptor (CAR) T cells offer a novel form of CAR-T-cell product that is available for immediate clinical use, thereby broadening access and applicability. UCART19 is one such product investigated in children and adults with relapsed or refractory B-cell acute lymphoblastic leukaemia. Two multicentre phase 1 studies aimed to investigate the feasibility, safety, and antileukaemic activity of UCART19 in children and adults with relapsed or refractory B-cell acute lymphoblastic leukaemia. Methods We enrolled paediatric or adult patients in two ongoing, multicentre, phase 1 clinical trials to evaluate the safety and antileukaemic activity of UCART19. All patients underwent lymphodepletion with fludarabine and cyclophosphamide with or without alemtuzumab, then children received UCART19 at 1·1–2·3 × 106 cells per kg and adults received UCART19 doses of 6 × 106 cells, 6–8 × 107 cells, or 1·8–2·4 × 108 cells in a dose-escalation study. The primary outcome measure was adverse events in the period between first infusion and data cutoff. These studies were registered at ClinicalTrials.gov, NCT02808442 and NCT02746952. Findings Between June 3, 2016, and Oct 23, 2018, seven children and 14 adults were enrolled in the two studies and received UCART19. Cytokine release syndrome was the most common adverse event and was observed in 19 patients (91%); three (14%) had grade 3–4 cytokine release syndrome. Other adverse events were grade 1 or 2 neurotoxicity in eight patients (38%), grade 1 acute skin graft-versus-host disease in two patients (10%), and grade 4 prolonged cytopenia in six patients (32%). Two treatment-related deaths occurred; one caused by neutropenic sepsis in a patient with concurrent cytokine release syndrome and one from pulmonary haemorrhage in a patient with persistent cytopenia. 14 (67%) of 21 patients had a complete response or complete response with incomplete haematological recovery 28 days after infusion. Patients not receiving alemtuzumab (n=4) showed no UCART19 expansion or antileukaemic activity. The median duration of response was 4·1 months with ten (71%) of 14 responders proceeding to a subsequent allogeneic stem-cell transplant. Progression-free survival at 6 months was 27%, and overall survival was 55%. Interpretation These two studies show, for the first time, the feasibility of using allogeneic, genome-edited CAR T cells to treat patients with aggressive leukaemia. UCART19 exhibited in-vivo expansion and antileukaemic activity with a manageable safety profile in heavily pretreated paediatric and adult patients with relapsed or refractory B-cell acute lymphoblastic leukaemia. The results this study are an encouraging step forward for the field of allogeneic CAR T cells, and UCART19 offers the opportunity to treat patients with rapidly progressive disease and where autologous CAR-T-cell therapy is unavailable. Funding Servier.

The prognosis for adults with relapsed or refractory B-cell acute lymphoblastic leukaemia remains poor. UCART19, an allogeneic genome-edited anti-CD19 chimeric antigen receptor (CAR) T-cell product derived from healthy donors and available for immediate clinical use, offers a potential therapeutic option for such patients. The CALM trial is a first-in-human study evaluating the safety and antileukaemic activity of UCART19 in adult patients with relapsed or refractory B-cell acute lymphoblastic leukaemia.This phase 1, open-label study was conducted at eight centres across France, the UK, the USA, and Japan. Adult patients aged 16-70 years with CD19-positive relapsed or refractory B-cell acute lymphoblastic leukaemia who had morphological relapse or a minimal residual disease level of at least 1 × 10Between Aug 1, 2016, and June 30, 2020, 25 patients were enrolled in the study and treated with UCART19. Median duration of follow-up was 12·8 months (IQR 2·8-24·8). Median age was 37 years (IQR 28-45). 14 (56%) patients were male and 11 (44%) female. 17 (68%) patients were White, two (8%) Black, two (8%) Asian, and four (16%) from other racial or ethnic groups. Three patients developed dose-limiting toxicities (one at each dose level); one had grade 4 cytokine release syndrome and two had grade 4 prolonged cytopenias. Grade 3 or higher cytokine release syndrome was reported in six (24%) patients and grade 3 or higher neurological toxicity in one (4%) patient. Grade 3 or higher infections occurred in seven (28%) patients, and grade 4 prolonged cytopenia in four (16%) patients. Two (8%) patients developed grade 1 acute cutaneous graft-versus-host disease. 14 patients died, nine from progressive disease and five from infections or other complications, of which four were considered to be related to UCART19 or lymphodepletion, or both. After a median of follow-up of 12·8 months (IQR 2·8-24·8), overall response rate was 48% (95% CI 28-69; 12 of 25 patients), duration of response and median relapse-free survival were 7·4 months (95% CI 1·8 to not calculable), progression-free survival was 2·1 months (95% CI 1·2-2·8), and overall survival was 13·4 months (95% CI 4·8-23·0).UCART19 had a manageable safety profile, and showed evidence of antileukaemic activity in heavily pretreated adult patients with relapsed or refractory B-cell acute lymphoblastic leukaemia. This study shows that allogeneic off-the-shelf CAR T cells can be used safely to treat patients with relapsed B-cell acute lymphoblastic leukaemia.Servier.

Background Outcomes for patients with relapsed/refractory acute myeloid leukemia (R/R AML) remain poor. Novel therapies specifically targeting AML are of high interest. Brentuximab vedotin (BV) is an antibody-drug conjugate that is specific for human CD30. In this phase 1 dose escalation study, the authors evaluated the safety of BV combined with mitoxantrone, etoposide, and cytarabine (MEC) re-induction chemotherapy for patients with CD30-expressing R/R AML. Methods Using a standard dose escalation design, the authors evaluated 3 dose levels of BV (0.9 mg/kg, 1.2 mg/kg, and 1.8 mg/kg) administered once on day 1 followed by MEC on days 3 through 7. Results There were no dose-limiting toxicities noted and the maximum tolerated dose was not reached. The recommended phase 2 dose of BV was determined to be 1.8 mg/kg when combined with MEC. The side effect profile was similar to that expected from MEC chemotherapy alone, with the most common grade ≥3 toxicities being febrile neutropenia, thrombocytopenia, and anemia (toxicities were graded using the National Cancer Institute Common Terminology Criteria for Adverse Events [version 4.0]). Among the 22 patients enrolled on the trial, the composite response rate was 36%, with a composite response rate of 42% noted among those who received the highest dose of BV. The median overall survival was 9.5 months, with a median disease-free survival of 6.8 months observed among responders. Approximately 55% of patients were able to proceed with either allogeneic hematopoietic stem cell transplantation or donor lymphocyte infusion. Conclusions The combination of BV with MEC was found to be safe in patients with CD30-expressing R/R AML and warrants further study comparing this combination with the use of MEC alone in this population (ClinicalTrials.gov identifier NCT01830777). Lay summary The outcomes for patients with relapsed/refractory acute myeloid leukemia (R/R AML) are exceptionally poor. New and emerging treatment combinations are actively being studied in an effort to improve outcomes. The authors examined the combination of brentuximab vedotin, an antibody product that recognizes a marker called CD30, with mitoxantrone, etoposide, and cytarabine (MEC), a common chemotherapy regimen, in patients with R/R AML that expressed the CD30 marker. The authors found that the combination was safe and well tolerated. Future studies comparing this new combination with the use of MEC alone can help to inform its effectiveness for this patient population.

Antifungal prophylaxis during induction for acute myeloid leukemia (AML) varies according to local rates of invasive fungal infections (IFIs). We evaluated fluconazole prophylaxis and no antifungal prophylaxis, as a natural interrupted time-series study to assess survival and infection complications.We identified patients with AML ≥ 18 years old undergoing induction chemotherapy during 2 time periods: period 1, fluconazole prophylaxis from August 1, 2013 to September 30, 2015, and period 2, no prophylaxis from October 1, 2015 to December 31, 2017. The primary outcome was incidence of proven or probable IFI. Secondary outcomes included types of IFIs and 60-day overall survival (OS). IFI was defined by the 2002 European Organization for Research and Treatment of Cancer/Mycoses Study Group Consensus criteria.One hundred forty-four patients received induction chemotherapy over the 2 time periods. In the prophylaxis versus no-prophylaxis groups, the rate of proven or probable IFIs was 4 (5%) of 87 versus 12 (21%) of 57 (P = .01). The total number of proven IFIs was 3 (3%) of 87 versus 4 (7%) of 57 (P = .44), whereas probable IFIs were 1 (1%) of 87 versus 8 (14%) of 57 (P .01). No difference was observed in fungemia. Incidence of IFIs was too low to detect resistance patterns. OS at 60 days was improved in with fluconazole prophylaxis compared with no prophylaxis (hazard ratio, 0.329; 95% confidence interval, 0.12-0.89; P = .028).Observed rates of proven or probable IFI were lower in the fluconazole prophylaxis group versus the no-prophylaxis group. Sixty-day OS was higher with fluconazole prophylaxis. Further study is required to evaluate how fluconazole may impart the differences in survival seen in this analysis.

Transcriptional control of dendritic cell (DC) functions is poorly understood. Lau, Tiniakou, et al. report that transcription factor ETV6 optimizes gene expression in DCs and facilitates their ability to cross-prime T cells and initiate tumor-specific immune responses., An IRF8-dependent subset of conventional dendritic cells (cDCs), termed cDC1, effectively cross-primes CD8+ T cells and facilitates tumor-specific T cell responses. Etv6 is an ETS family transcription factor that controls hematopoietic stem and progenitor cell (HSPC) function and thrombopoiesis. We report that like HSPCs, cDCs express Etv6, but not its antagonist, ETS1, whereas interferon-producing plasmacytoid dendritic cells (pDCs) express both factors. Deletion of Etv6 in the bone marrow impaired the generation of cDC1-like cells in vitro and abolished the expression of signature marker CD8α on cDC1 in vivo. Moreover, Etv6-deficient primary cDC1 showed a partial reduction of cDC-specific and cDC1-specific gene expression and chromatin signatures and an aberrant up-regulation of pDC-specific signatures. Accordingly, DC-specific Etv6 deletion impaired CD8+ T cell cross-priming and the generation of tumor antigen–specific CD8+ T cells. Thus, Etv6 optimizes the resolution of cDC1 and pDC expression programs and the functional fitness of cDC1, thereby facilitating T cell cross-priming and tumor-specific responses.

Neurologic complications (NCs) may be a significant source of morbidity and mortality after hematopoietic cell transplantation (HCT). We performed a retrospective study of 263 consecutive patients undergoing allogeneic HCT for hematological malignancies to determine the incidence, risk factors and clinical impact of NCs in the first 5 years after HCT. We determined the incidence of central nervous system (CNS) infection, intracranial hemorrhage, ischemic stroke, metabolic encephalopathy, posterior reversal encephalopathy syndrome, seizure and peripheral neuropathy. In all, 50 patients experienced 63 NCs-37 early (⩽day +100), 21 late (day +101 to 2 years) and 5 very late (2 to 5 years). The 1- and 5-year cumulative incidences of all NCs were 15.6% and 19.2%, respectively, and of CNS complication (CNSC; all of the above complications except peripheral neuropathy) were 12.2 and 14.5%. Risk factors for CNSC were age (hazard ratio (HR)=1.06 per year, P=0.0034), development of acute GvHD grade III-IV (HR=2.78, P=0.041), transfusion-dependent thrombocytopenia (HR=3.07, P=0.025) and delayed platelet engraftment (>90th centile; HR=2.77, P=0.043). CNSCs negatively impacted progression-free survival (HR=2.29, P=0.0001), overall survival (HR=2.63, P

The ETV6 (also known as TEL) gene encodes a transcriptional repressor that plays a critical role in hematopoiesis and in embryonic development. While somatic ETV6 translocations and missense mutations are frequently observed in human cancers, the role of ETV6 in malignant transformation was unclear. Recently, autosomal dominant germline ETV6 mutations were discovered in families with inherited thrombocytopenia and a propensity to develop hematological malignancy, unequivocally demonstrating a role for ETV6 in leukemogenesis. Studies of germline ETV6 mutations also uncovered an important function of ETV6 in megakaryocyte development. Here we discuss our current understanding of the role of ETV6 in malignancy and in hematopoiesis.

Characterization of pathogenic alterations in acute myeloid leukemia (AML) has led to development of promising targeted therapies, including FLT3 (FLT3i) and IDH1/2 inhibitors (IDHi), with several approved for use; midostaurin (MIDO), gilteritinib, enasidenib (ENA), and ivosidenib (IVO). A proportion of patients (pts) have concurrentFLT3andIDHmutations at diagnosis or develop a second mutation during therapy.FLT3mutations, in particular, are associated with poor response rates to IDHi therapy, and treatment-emergentFLT3mutations also appear to confer therapeutic resistance to these agents. There is therefore growing interest to study combined therapies that target multiple pathways, but the clinical experience with combined IDHi and FLT3i therapy has not yet been reported. We performed a retrospective data collection and analysis at 5 institutions (Massachusetts General Hospital, University of Pennsylvania, Johns Hopkins University, University of California San Francisco, and MD Anderson). Using de-identified information from institutional databases, pts treated with concurrent IDHi and FLT3i were identified. Collected data included demographic data, date of initial diagnosis, number of prior therapies, prior hematopoietic cell transplant (HCT), prior targeted therapy, type ofIDHandFLT3mutation, concurrent mutations and cytogenetics, duration of concurrent therapy, therapy-related toxicity, best response, toxicities, and vital status. We identified 12 pts who received concurrent IDHi and FLT3i therapy, 11 of which had relapsed/refractory (R/R) AML. Median age was 57 (range 31-84) and 9 (75%) were male. 7 (58%) were Caucasian, 3 (25%) African American, and 2 (17%) Asian. All pts had intermediate-risk cytogenetics.IDH1R132 mutations were detected in 3 (25%), andIDH2R140 mutations in 9 (75%) pts. OneIDH2mutation arose at relapse. All pts hadFLT3-ITDmutations, and for 3 (38%), this mutation was known to have emerged at relapse. Common concurrent mutations includedDNMT3A(75%) andNPM1(58%). Median number of prior lines of therapy was 2 (range 0-6), and 4 pts (33%) had underwent prior HCT. Six pts (50%) had received FLT3i monotherapy in a prior line of treatment; 4 sorafenib, 1 gilteritinib, 1 MIDO, and 1 with FF-10101 (one pt had 2 prior lines of FLT3i). Six pts were initiated on concurrent therapy in simultaneous fashion, and the remainder were sequential; 2 pts (17%) were on IDHi therapy to which the FLT3i was added, and 4 (33%) had been on FLT3i with subsequent IDHi addition. Four pts (33%) received concurrent gilteritinib and ENA, 3 (25%) received gilteritinib and IVO, 3 (25%) received sorafenib and ENA, and 2 (17%) MIDO and ENA. Three pts received hypomethylating therapy concurrent with combined FLT3i/IDHi therapy; 2 received azacitidine (AZA) with ENA/MIDO, and 1 received AZA with ENA/gilteritinib. Pts were on concurrent therapy for a median of 75 days (range 9-343). Two pts had rash attributable to sorafenib, leading to temporary treatment pause in one and discontinuation in the other. No other toxicities were thought to be related to concurrent treatment. Four pts (33%) achieved CR or CRi (2 CR, 2 CRi), all with persistence of molecular residual disease (MRD). The median duration of remission for these pts was 310 days (range 85-326), and 3 have since relapsed. One pt experienced MLFS, 1 had peripheral blast reduction and 1 had improvement in platelets. An additional pt had MRD(+) CR (byNPM1PCR) on gilteritinib prior to addition of ENA, and then achieved MRD(-) CR with dual therapy. The 4 remaining pts did not respond to concurrent treatment. Two pts (17%) were effectively bridged to HCT following dual therapy. Five pts (42%) remain alive. In this retrospective analysis, a notable proportion of pts benefitted from concurrent FLT3i and IDHi therapy. Composite remission rate was 33%, and overall response rate (CR+CRi+MLFS) was 42% among a largely R/R patient cohort, the majority of whom had received IDHi or FLT3i monotherapy in a prior line of treatment. An additional pt in MRD(+) CR cleared MRD following concurrent treatment. Concurrent therapy appeared to be largely well-tolerated. These response rates are particularly intriguing, given the presence ofFLT3/ITDmutations, alterations thought to confer resistance to IDHi monotherapy. Larger, prospective studies are needed to fully assess the promise of concurrent FLT3i and IDHi therapy in co-mutated pts with AML. Disclosures Fathi: Amphivena:Consultancy;Astellas:Consultancy;Trillium:Consultancy;Amgen:Consultancy;Seattle Genetics:Consultancy, Research Funding;Abbvie:Consultancy;Pfizer:Consultancy;Newlink Genetics:Consultancy;Forty Seven:Consultancy;Trovagene:Consultancy;Kite:Consultancy;BMS/Celgene:Consultancy, Research Funding;Novartis:Consultancy;Daiichi Sankyo:Consultancy;Kura Oncology:Consultancy;Blueprint:Consultancy;PTC Therapeutics:Consultancy;Agios:Consultancy, Research Funding;Takeda:Consultancy, Research Funding;Jazz:Consultancy;Boston Biomedical:Consultancy.Perl:Arog Pharmaceuticals Inc:Other: uncompensated consulting, travel costs for meetings;Astellas:Consultancy, Honoraria, Other: writing/editorial support, travel costs for meeting presentations related to study, Research Funding;AbbVie Inc:Consultancy, Honoraria, Other, Research Funding;Syndax:Consultancy, Honoraria;Takeda:Honoraria, Other: Travel costs for meeting;Leukemia & Lymphoma Society, Beat AML:Consultancy;Novartis:Honoraria, Other, Research Funding;Actinium Pharmaceuticals Inc:Consultancy, Honoraria, Research Funding;Daiichi Sankyo:Consultancy, Honoraria, Other: Writing/editorial support, travel costs for meetings, Research Funding;FUJIFILM Pharmaceuticals USA, Inc:Research Funding;New Link Genetics:Honoraria, Other;Bayer HealthCare Pharmaceuticals:Research Funding;Biomed Valley Discoveries:Research Funding;Loxo Oncology Inc, a wholly owned subsidiary of Eli Lilly & Company:Consultancy, Honoraria, Other;Jazz:Honoraria, Other;Agios:Consultancy, Honoraria, Other;FORMA Therapeutics:Consultancy, Honoraria, Other.Levis:Menarini:Honoraria;Amgen:Honoraria;FujiFilm:Honoraria, Research Funding;Daiichi-Sankyo:Honoraria;Astellas:Honoraria, Research Funding.Smith:Daiichi Sanyko:Consultancy, Honoraria;Abbvie:Other: Research Support, Research Funding;FujiFilm:Other: Research support, Research Funding;Astellas Pharma:Honoraria, Other: Research Support, Research Funding;Revolution Medicines:Other: Research Support, Research Funding;Sanofi:Honoraria.Brunner:Forty-Seven Inc:Membership on an entity's Board of Directors or advisory committees;AstraZeneca:Research Funding;Takeda:Research Funding;Celgene:Membership on an entity's Board of Directors or advisory committees, Research Funding;Novartis:Research Funding;Jazz Pharmaceuticals:Membership on an entity's Board of Directors or advisory committees.Amrein:Amgen:Research Funding;AstraZeneca:Consultancy, Research Funding;Takeda:Research Funding.Hobbs:Merck:Research Funding;Constellation:Honoraria, Research Funding;Incyte:Research Funding;Bayer:Research Funding;Celgene/BMS:Honoraria;Novartis:Honoraria;Jazz:Honoraria.Narayan:Sanofi-Genzyme:Other: Current Spouse employment ;Takeda:Other: Prior Spouse employment within 24 months;Genentech:Other: Prior Spouse employment within 24 months and prior spouse equity divested within past 24 months.Daver:Pfizer:Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding;Karyopharm:Research Funding;Servier:Research Funding;Daiichi Sankyo:Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding;Genentech:Research Funding;AbbVie:Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding;Astellas:Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding;Novimmune:Research Funding;Gilead:Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding;Amgen:Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding;Trovagene:Research Funding;Fate Therapeutics:Research Funding;ImmunoGen:Research Funding;Novartis:Consultancy, Membership on an entity's Board of Directors or advisory committees;Celgene:Consultancy, Membership on an entity's Board of Directors or advisory committees;Jazz:Consultancy, Membership on an entity's Board of Directors or advisory committees;Trillium:Consultancy, Membership on an entity's Board of Directors or advisory committees;Syndax:Consultancy, Membership on an entity's Board of Directors or advisory committees;Amgen:Consultancy, Membership on an entity's Board of Directors or advisory committees;KITE:Consultancy, Membership on an entity's Board of Directors or advisory committees;Agios:Consultancy, Membership on an entity's Board of Directors or advisory committees;Bristol-Myers Squibb:Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.DiNardo:Calithera:Research Funding;Celgene:Consultancy, Honoraria, Research Funding;Agios:Consultancy, Honoraria, Research Funding;Syros:Honoraria;Daiichi Sankyo:Consultancy, Honoraria, Research Funding;Notable Labs:Membership on an entity's Board of Directors or advisory committees;Jazz:Honoraria;ImmuneOnc:Honoraria;Takeda:Honoraria;MedImmune:Honoraria;Novartis:Consultancy;AbbVie:Consultancy, Honoraria, Research Funding. OffLabel Disclosure: Midostaurin for relapsed/refractory AML Sorafenib for relapsed/refractory AML

Characterization of molecular alterations in acute myeloid leukemia (AML) has led to development of targeted therapies, including FLT3 and IDH1/2 inhibitors. Maintenance therapy following hematopoietic cell transplantation (HCT) has shown substantial promise. Enasidenib (ENA), a selective IDH2 inhibitor, was associated with impressive rates of response in relapsed/refractory (R/R) AML and is now FDA-approved for this indication. We sought to assess the tolerability and define the maximum tolerated dose (MTD) of ENA as maintenance following HCT for IDH2-mutated myeloid malignancy. HCT-eligible patients (pts) ≥ 18 years with AML in remission, or myelodysplastic syndrome (MDS) with 1000/µL and platelets > 50000/µL). Those with prior HCT, active disease, QTc ≥450ms, and active infections were excluded. ENA was initiated between day 30 and 90 after HCT, at which time the following were required: chimerism ≥70% of donor origin among blood/marrow cells, no acute graft versus host disease (aGVHD) requiring ≥0.5mg/kg/day prednisone or equivalent, and no relapse. ENA was taken orally (po) daily (qd) in 28-day cycles. The period for dose-limiting toxicity (DLT) evaluation was the first cycle, escalation to successive levels was guided by DLT incidence, and 2 levels (50mg,100mg) were studied. Following establishment of MTD or recommended phase 2 dose (RP2D), 10 pts would be enrolled in an expansion cohort. Pts were monitored for relapse and toxicity and continued until disease progression, intolerable toxicity, or receipt of 12 cycles. Nineteen pts have been registered prior to HCT at 3 sites, Massachusetts General Hospital, Dana Farber Cancer Institute, and Johns Hopkins Hospital. Three pts could not initiate ENA following HCT; 2 due to logistic challenges of the COVID pandemic and 1 due to relapse. The remaining 16 pts initiated ENA treatment. The median age was 61 years (range 31-76); 12 (75%) were male, and 13 (81%) were Caucasian. Fourteen (88%) had AML, of which 6 were AML with MDS related changes and 2 had antecedent myeloproliferative neoplasm. Two pts (13%) had MDS. Among these 16 pts, 9 (56%) had IDH2 R140, and 5 (25%) had IDH2 R172 mutations. IDH2 subtype data was unavailable for 2 pts. Of 15 pts with available data from time of diagnosis, 11 (73%) had intermediate-risk and 4 (27%) had adverse-risk cytogenetics. Among these 15 pts, common concurrent mutations were DNMT3A (47%), SRSF2 (33%), and RUNX1 (33%). Eleven AML pts (85%) received intensive versus non-intensive therapies (15%) prior to HCT, and among all pts, 7 (44%) had received ENA prior to HCT. HCT data was available for all 16 pts; 4 pts (25%) received myeloablative, and 12 (75%) received reduced-intensity conditioning. Nine pts (56%) had a matched unrelated, 6 (38%) had haploidentical, and 1 (6%) had a matched related donor HCT. Three pts were enrolled at the 50mg dose level, 6 pts at 100mg, and after no DLTs were detected, the remaining were enrolled in an expansion cohort at 100mg qd. Median follow-up (F/U) for surviving patients is currently 11.7 months (range 1.5-18.9). 2 pts (13%) have relapsed during F/U, at 96 and 364 days post HCT. Additional ≥grade (G) 3 toxicities detected during treatment, possibly or probably related to ENA, included neutropenia, anemia, and bilirubinemia. Six pts (38%) required dose interruptions lasting a median 19 days (range 7-25), 4 required a dose reduction to 50mg, and 1 stopped treatment due to G3 bilirubinemia. In total, 3 pts (18%) discontinued study treatment, 1 for aforementioned G3 bilirubinemia, 1 to pursue a GVHD trial, and 1 for relapse. Six pts have completed the 12-month f/u without relapse, and 7 remain on study. 15 of 16 pts remain alive. Thus far, 3 pts have experienced ≥ G2 aGVHD, and 4 had moderate chronic GVHD. Serial measurement of 2HG is being conducted on samples, and these will be reported. Enasidenib is well-tolerated as post-HCT maintenance therapy for myeloid malignancy at the RP2D of 100mg qd. No DLTs have been detected, and a low rate of post-HCT relapse has been identified to date, although longer f/u is needed. Larger, randomized studies of ENA in the post-SCT setting would determine the true efficacy of this agent as maintenance therapy. Disclosures Fathi: Blueprint: Consultancy; Jazz: Consultancy; Amgen: Consultancy; Newlink Genetics: Consultancy; Pfizer: Consultancy; Abbvie: Consultancy; Seattle Genetics: Consultancy, Research Funding; Agios: Consultancy, Research Funding; PTC Therapeutics: Consultancy; Takeda: Consultancy, Research Funding; Boston Biomedical: Consultancy; Amphivena: Consultancy; BMS/Celgene: Consultancy, Research Funding; Kite: Consultancy; Trovagene: Consultancy; Forty Seven: Consultancy; Novartis: Consultancy; Daiichi Sankyo: Consultancy; Astellas: Consultancy; Trillium: Consultancy; Kura Oncology: Consultancy. Soiffer:Gilead: Consultancy; Novartis: Consultancy; Juno: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; VOR Biopharma: Consultancy; alexion: Consultancy; Rheos Therapeutics: Consultancy; Cugene: Consultancy; Precision Bioscience: Consultancy; Be the Match/ National Marrow Donor Program: Membership on an entity's Board of Directors or advisory committees; Kiadis: Membership on an entity's Board of Directors or advisory committees; Mana Therapeutics: Consultancy. Levis:Menarini: Honoraria; Amgen: Honoraria; FujiFilm: Honoraria, Research Funding; Astellas: Honoraria, Research Funding; Daiichi-Sankyo: Honoraria. Mims:Novartis: Speakers Bureau; Kura Oncology: Membership on an entity's Board of Directors or advisory committees; Leukemia and Lymphoma Society: Other: Senior Medical Director for Beat AML Study; Agios: Consultancy; Syndax Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Other: Data Safety Monitoring Board; Abbvie: Membership on an entity's Board of Directors or advisory committees. Devine:Magenta Therapeutics: Consultancy. Defilipp:Incyte: Research Funding; Regimmune: Research Funding; Syndax Pharmaceuticals: Consultancy. Spitzer:Jazz Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees; Bluebird Bio: Membership on an entity's Board of Directors or advisory committees. Frigault:Celgene: Consultancy; Arcellx: Consultancy; Novartis: Consultancy, Research Funding; Gilead/Kite: Consultancy, Research Funding. Amrein:Amgen: Research Funding; AstraZeneca: Consultancy, Research Funding; Takeda: Research Funding. Hobbs:Incyte: Research Funding; Merck: Research Funding; Bayer: Research Funding; Constellation: Honoraria, Research Funding; Jazz: Honoraria; Celgene/BMS: Honoraria; Novartis: Honoraria. Brunner:Janssen: Research Funding; Acceleron Pharma Inc.: Consultancy; GSK: Research Funding; Xcenda: Consultancy; Takeda: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; Jazz Pharma: Consultancy; Forty Seven, Inc: Consultancy; Celgene/BMS: Consultancy, Research Funding; Biogen: Consultancy; Astra Zeneca: Research Funding. Narayan:Genentech: Other: Prior Spouse employment within 24 months and prior spouse equity divested within past 24 months; Takeda: Other: Prior Spouse employment within 24 months; Sanofi-Genzyme: Other: Current Spouse employment . Chen:AbbVie: Other: Data and Safety Monitoring Board Member; Incyte Corporation: Consultancy; Takeda: Consultancy; Actinium: Other: Data and Safety Monitoring Board Member; Equillium: Other: Data and Safety Monitoring Board Member; Magenta: Consultancy; Kiadis: Consultancy. OffLabel Disclosure: Enasidenib as post-transplant maintenance therapy

BACKGROUND: Angiogenesis is increasingly known to play a role in pathogenesis of hematologic malignancies, including myeloid neoplasms. Regorafenib is a multikinase inhibitor that targets angiogenic, stromal and oncogenic kinases including VEGF- 1, 2, 3, TIE-2, PDGFR-β,c-KIT, rRET, RAF-1, FGFR-1, BRAF and p38 MAP kinase. As a result of regorafenib's broad inhibition of kinases and its effects on angiogenesis, this drug has the potential to overcome the limitations of more selective kinase inhibitors and may be associated with efficacy in various myeloid neoplasms, including acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), and myeloproliferative neoplasms (MPN). METHODS: We conducted a single-center, open-label, dose-escalation and expansion phase I trial in patients with relapsed/refractory AML, MPN, or MDS to assess the safety, tolerability, and preliminary efficacy of regorafenib and identify the recommended phase 2 dose (RP2D). A 3+3 dose escalation design was used with 2 planned dose levels (120 mg or 160 mg daily in 28-day cycles), as well as 1 de-escalation level (80 mg daily). An additional 10 patients were treated on an expansion cohort. RESULTS: Six patients were enrolled during the dose escalation phase (3 at 120 mg daily followed by 3 at 160 mg daily), with no DLTs, as defined by a Grade >3 toxicity occurring within the first 28 days after initiation of treatment, and unrelated to the myeloid neoplasm. Therefore, the RP2D of regorafenib was identified as 160 mg daily. Ten additional patients were enrolled on this dose during the expansion phase. The median age was 74 (range 36-84), and 13 (81%) patients were male. Diagnoses included 7 AML, 6 MDS, and 3 MPN patients (Table 1). Dose modifications and delays occurred in 5 and 4 patients, respectively. The median duration of treatment was 56 days or 2.5 cycles (range: 5-410 days, 1-15 cycles). Of the 16 patients, the best overall disease response as measured by IWG criteria included partial remission (in 1 patient with AML), stable disease in 12 (2 de novo AML, 2 secondary AML, 3 MPN, and 5 MDS) patients, and progressive disease in 3 (1 MDS and 2 secondary AML) patients. An initial improvement in absolute neutrophil count and/or hemoglobin was observed in the 6 MDS patients, although this did not meet criteria for hematologic improvement by IWG criteria. All patients have discontinued off treatment. The most frequent Grade 3-4 adverse effects (AEs) included liver function test abnormalities (5.1%), fatigue (4.3%), thrombocytopenia (3.4%), and neutropenia (3.4%) (Table 2). The majority of AEs were grades 1-2. CONCLUSIONS: Regorafenib demonstrates an acceptable safety profile in relapsed/refractory myeloid malignancy patients, a population where few treatment options exist. The majority of patients achieved stable disease. Modest improvements in cell counts were observed in MDS patients, and we are performing correlative studies to clarify regorafenib's mechanism of action and identify populations which may benefit from treatment. Disclosures Amrein: AstraZeneca: Consultancy, Research Funding; Takeda: Research Funding; Amgen: Research Funding. Brunner:Novartis: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Research Funding; AstraZeneca: Research Funding; Forty-Seven Inc: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Fathi:Kura Oncology: Consultancy; Trillium: Consultancy; Boston Biomedical: Consultancy; Pfizer: Consultancy; Daiichi Sankyo: Consultancy; Jazz: Consultancy; Agios: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; PTC Therapeutics: Consultancy; Amphivena: Consultancy; Astellas: Consultancy; Amgen: Consultancy; Seattle Genetics: Consultancy, Research Funding; Abbvie: Consultancy; Blueprint: Consultancy; Kite: Consultancy; Trovagene: Consultancy; Forty Seven: Consultancy; Newlink Genetics: Consultancy; Novartis: Consultancy; BMS/Celgene: Consultancy, Research Funding. Narayan:Sanofi-Genzyme: Other: Current Spouse employment ; Takeda: Other: Prior Spouse employment within 24 months; Genentech: Other: Prior Spouse employment within 24 months and prior spouse equity divested within past 24 months. Neuberg:Pharmacyclics: Research Funding; Madrigak Pharmaceuticals: Current equity holder in publicly-traded company; Celgene: Research Funding. Chen:Takeda: Consultancy; Magenta: Consultancy; Equillium: Other: Data and Safety Monitoring Board Member; AbbVie: Other: Data and Safety Monitoring Board Member; Incyte Corporation: Consultancy; Actinium: Other: Data and Safety Monitoring Board Member; Kiadis: Consultancy. Hobbs:Merck: Research Funding; Constellation: Honoraria, Research Funding; Incyte: Research Funding; Jazz: Honoraria; Novartis: Honoraria; Celgene/BMS: Honoraria; Bayer: Research Funding. OffLabel Disclosure: Regorafenib was used to assess safety and preliminary efficacy in advanced myeloid malignancies

Introduction: Outcomes for acute myeloid leukemia (AML) among older patients has remained largely unchanged for decades. Long-term survival for patients aged >60 years is poor (median survival 10.5 months). Targeting the proteasome in AML is attractive, since leukemia stem cells have demonstrated sensitivity to proteasome inhibition in preclinical models, perhaps through down regulation of nuclear NF-KB (Guzman, Blood 2001). AML cell lines are susceptible to synergistic cytotoxicity when bortezomib, a proteasome inhibitor, is combined with daunorubicin and cytarabine. We have shown that adding bortezomib to standard treatment in AML results in a high remission rate, although grade 2 sensory neurotoxicity was noted in approximately 12% of treated patients. A newer generation proteasome inhibitor, ixazomib, is less frequently associated with neurotoxicity, and, therefore, was selected for combination with conventional chemotherapy in this phase I trial. The primary objective of this study was to determine the maximum tolerated dose (MTD) of ixazomib in combination with conventional induction and consolidation chemotherapy for AML. Herein are the initial results of this trial. Methods: Adults >60 years of age with newly diagnosed AML were screened for eligibility. Patients with secondary AML were eligible, including those with prior hypomethylating agent therapy for myelodysplastic syndromes (MDS). We excluded those with promyelocytic leukemia. There were 2 phases in this study. In the first phase (A), the induction treatment consisted of the following: cytarabine 100 mg/m2/day by continuous IV infusion, Days 1-7; daunorubicin 60 mg/m2/day IV, Days 1, 2, 3, and ixazomib was provided orally at the cohort dose, Days 2, 5, 9, and 12. Consolidaton or transplant was at the discretion of the treating physician in phase A. In the second phase (B), induction was the same as that with the determined MTD of ixazomib. All patients were to be treated with the following consolidation: cytarabine at 2 g/m2/day, days 1-5 with ixazomib on days 2, 5, 9, and 12 at the cohort dose for consolidation. A standard 3 + 3 patient cohort dose escalation design was used to determine whether the dose of ixazomib could be safely escalated in 3 cohorts (1.5 mg/day, 2.3 mg/day, 3.0 mg/day), initially in induction (phase A) and subsequently in consolidation (phase B). The determined MTD of ixazomib in the first portion (A) of the trial was used during induction in the second portion (B), which sought to determine the MTD for ixazomib during consolidation. Secondary objectives included rate of complete remission, disease-free survival, and overall survival (OS). Results: Thirty-six patients have been enrolled on study, and 28 have completed dose levels A-1 through A-3 and B1 through B-2. Full information on cohort B-3 has not yet been obtained, hence, this report covers the experience with the initial 28 patients, cohorts A-1 through B-2. There were 12 (43%) patients among the 28 with secondary AML, either with prior hematologic malignancy or therapy-related AML. Nineteen patients (68%) were male, and the median age was 68 years (range 61-80 years). There have been no grade 5 toxicities due to study drug. Three patients died early due to leukemia, 2 of which were replaced for assessment of the MTD. Nearly all the grade 3 and 4 toxicities were hematologic (Table). There was 1 DLT (grade 4 platelet count decrease extending beyond Day 42). There has been no grade 3 or 4 neurotoxicity with ixazomib to date. Among the 28 patients in the first 5 cohorts, 22 achieved complete remissions (CR) and 2 achieved CRi, for a composite remission rate (CCR) of 86%. Among the 12 patients with secondary AML 8 achieved CR and 2 achieved CRi, for a CCR of 83%. The median OS for the 28 patients has not been reached (graph). The 18-month OS estimate was 65% [90% CI, 50-85%]. Conclusions: The highest dose level (3 mg) of ixazomib planned for induction in this trial has been reached safely. For consolidation there have been no serious safety issues in the first 2 cohorts with a dose up to 2.3 mg, apart from 1 DLT in the form of delayed platelet count recovery. The recommended phase 2 dose of ixazomib for induction is 3 mg. Accrual to cohort B-3 is ongoing. Notably, to date, no grade 3 or 4 neurotoxicity has been encountered. The remission rate in this older adult population with the addition of ixazomib to standard chemotherapy appears favorable. Figure Disclosures Amrein: Amgen: Research Funding; AstraZeneca: Consultancy, Research Funding; Takeda: Research Funding. Attar:Aprea Therapeutics: Current Employment. Brunner:Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Forty-Seven Inc: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Research Funding; Takeda: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding. Hobbs:Constellation: Honoraria, Research Funding; Novartis: Honoraria; Incyte: Research Funding; Merck: Research Funding; Bayer: Research Funding; Jazz: Honoraria; Celgene/BMS: Honoraria. Neuberg:Celgene: Research Funding; Madrigak Pharmaceuticals: Current equity holder in publicly-traded company; Pharmacyclics: Research Funding. Fathi:Blueprint: Consultancy; Boston Biomedical: Consultancy; BMS/Celgene: Consultancy, Research Funding; Novartis: Consultancy; Kura Oncology: Consultancy; Trillium: Consultancy; Amgen: Consultancy; Seattle Genetics: Consultancy, Research Funding; Abbvie: Consultancy; Pfizer: Consultancy; Newlink Genetics: Consultancy; Forty Seven: Consultancy; Trovagene: Consultancy; Kite: Consultancy; Daiichi Sankyo: Consultancy; Astellas: Consultancy; Amphivena: Consultancy; PTC Therapeutics: Consultancy; Agios: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; Jazz: Consultancy. OffLabel Disclosure: Ixazomib is FDA approved for multiple myeloma. We are using it in this trial for acute myeloid leukemia.

Summary Background Increased aurora A kinase (AAK) expression occurs in acute myeloid leukaemia; AAK inhibition is a promising therapeutic target in this disease. We therefore aimed to assess the activity of alisertib combined with 7 + 3 induction chemotherapy in previously untreated patients with high-risk acute myeloid leukaemia. Methods We did a single-arm, phase 2 trial of patients recruited from the Dana–Farber/Harvard Cancer Center in the USA. Eligible patients had previously untreated acute myeloid leukaemia, an Eastern Cooperative Oncology Group performance status of 0–2, and were at high risk of disease as defined by the presence of an adverse-risk karyotype, the presence of secondary acute myeloid leukaemia arising from previous myelodysplastic syndrome or myeloproliferative neoplasm, the presence of therapy-related acute myeloid leukaemia, or being 65 years or older. Enrolled patients received 7 + 3 induction chemotherapy of continuous infusion of cytarabine (100 mg/m2 per day on days 1–7) and intravenous bolus of idarubicin (12 mg/m2 per day on days 1–3). Oral alisertib (30 mg) was given twice per day on days 8–15. Patients could receive up to four consolidation cycles with cytarabine and alisertib, and alisertib maintenance for 12 months. The primary endpoint was a composite including the proportion of patients achieving complete remission and those with a complete remission with incomplete neutrophil or platelet count recovery. Analyses were per-protocol. This study is registered with Clinicaltrials.gov , number NCT02560025 , and has completed enrolment. Findings Between Dec 31, 2015, and Aug 1, 2017, we enrolled a total of 39 eligible patients. 19 (49%) of 39 patients had secondary acute myeloid leukaemia and three (8%) had therapy-related acute myeloid leukaemia. At mid-induction, 33 (85%) of 39 patients showed marrow aplasia, six (15%) received re-induction. The median follow-up was 13·7 months (IQR 12·7–14·4). Composite remission was 64% (two-stage 95% CI 48–79), with 20 (51%) of 39 patients achieving complete remission and five (13%) achieving complete remission with incomplete neutrophil or platelet count recovery. The most common grade 3 or 4 adverse events included febrile neutropenia (16 [41%] of 39), neutropenia (12 [31%]), thrombocytopenia (13 [33%]), anaemia (11 [28%]), anorexia (nine [23%]), and oral mucositis (four [10%]). No treatment-related deaths were observed. Interpretation These results suggest that alisertib combined with induction chemotherapy is active and safe in previously untreated patients with high-risk acute myeloid leukaemia. This study met criteria to move forward to a future randomised trial. Funding Millennium Pharmaceuticals.

The Mst1 and 2 cytosolic serine/threonine protein kinases are the mammalian orthologs of the Drosophila Hippo protein. Mst1 has been shown previously to participate in T-cell and B-cell trafficking and the migration of lymphocytes into secondary lymphoid organs in a cell intrinsic manner. We show here that the absence of Mst1 alone only modestly impacts B cell homing to lymph nodes. The absence of both Mst1 and 2 in hematopoietic cells results in relatively normal B cell development in the bone marrow and does not impact migration of immature B cells to the spleen. However, follicular B cells lacking both Mst1 and Mst2 mature in the splenic white pulp but are unable to recirculate to lymph nodes or to the bone marrow. These cells also cannot traffic efficiently to the splenic red pulp. The inability of late transitional and follicular B cells lacking Mst 1 and 2 to migrate to the red pulp explains their failure to differentiate into marginal zone B cell precursors and marginal zone B cells. Mst1 and Mst2 are therefore required for follicular B cells to acquire the ability to recirculate and also to migrate to the splenic red pulp in order to generate marginal zone B cells. In addition B-1 a B cell development is defective in the absence of Mst1.

Stem cells have been identified in two locations in small intestinal crypts; those intercalated between Paneth cells and another population (which retains DNA label) are located above the Paneth cell zone, at cell position 4. Because of disadvantages associated with the use of DNA label, doxycycline-induced transient transgenic expression of histone 2B (H2B)-green fluorescent protein (GFP) was investigated. H2B-GFP-retaining putative stem cells were consistently seen, with a peak at cell position 4, over chase periods of up to 112 days. After a 28-day chase, a subpopulation of the H2B-GFP-retaining cells was cycling, but the slow cycling status of the majority was illustrated by lack of expression of pHistone H3 and Ki67. Although some H2B-GFP-retaining cells were sensitive to low-dose radiation, the majority was resistant to low- and high-dose radiation-induced cell death, and a proportion of the surviving cells proliferated during subsequent epithelial regeneration. Long-term retention of H2B-GFP in a subpopulation of small intestinal Paneth cells was also seen, implying that they are long lived. In contrast to the small intestine, H2B-GFP-retaining epithelial cells were not seen in the colon from 28-day chase onward. This implies important differences in stem cell function between these two regions of the gastrointestinal tract, which may have implications for region-specific susceptibility to diseases (such as cancer and ulcerative colitis), in which epithelial stem cells and their progeny are involved.

SummaryL3mbtl2 has been implicated in transcriptional repression and chromatin compaction but its biological function has not been defined. Here we show that disruption of L3mbtl2 results in embryonic lethality with failure of gastrulation. This correlates with compromised proliferation and abnormal differentiation of L3mbtl2−/− embryonic stem (ES) cells. L3mbtl2 regulates genes by recruiting a Polycomb Repressive Complex1 (PRC1)-related complex, resembling the previously described E2F6-complex, and including G9A, Hdac1, and Ring1b. The presence of L3mbtl2 at target genes is associated with H3K9 dimethylation, low histone acetylation, and H2AK119 ubiquitination, but the latter is neither dependent on L3mbtl2 nor sufficient for repression. Genome-wide studies revealed that the L3mbtl2-dependent complex predominantly regulates genes not bound by canonical PRC1 and PRC2. However, some developmental regulators are repressed by the combined activity of all three complexes. Together, we have uncovered a highly selective, essential role for an atypical PRC1-family complex in ES cells and early development.

In mice lacking both Mst1 and Mst2 in the lymphoid compartment, thymocyte development is normal, but single-positive thymocytes exhibit excessive apoptosis and greatly diminished thymic egress, accompanied by loss of chemokine activation of RhoA and Rac1., The Mst1 kinase is an important regulator of murine T cell adhesion, migration, proliferation, and apoptosis. In this study, we analyze mice lacking both Mst1 and Mst2 in hematopoietic cells. Compared with wild-type mice, these double knockout (DKO) mice exhibit a severe reduction in the number of mature T cells in the circulation and in secondary lymphoid organs (SLOs). CD4+CD8− and CD4−CD8+ single-positive (SP) thymocytes in DKO mice resemble mature T cells of wild-type mice but undergo excessive apoptosis, and their egress from the thymus is reduced by >90%. Even when placed directly in the circulation, DKO SP thymocytes failed to enter SLOs. In SP thymocytes, deficiency of Mst1 and Mst2 abolished sphingosine-1 phosphate– and CCL21-induced Mob1 phosphorylation, Rac1 and RhoA GTP charging, and subsequent cell migration. When phosphorylated by Mst1 or Mst2, Mob1 binds and activates the Rac1 guanyl nucleotide exchanger Dock8, which is abundant in the thymus. Thus, the Mst1 and Mst2 kinases control Rho GTPase activation and the migratory responses of SP thymocytes.

Introduction: Treatment of acute myeloid leukemia (AML) has remained largely unchanged for several decades despite the emergence of new agents. Long-term survival for patients aged >60 years is less than 10% (median survival 10.5 months). Targeting the proteasome in treating AML is attractive, since leukemia stem cells have demonstrated sensitivity to proteasome inhibition, perhaps through down regulation of nuclear NF-KB (Guzman, Blood 2001). Preclinical studies in leukemia cell lines revealed synergistic cytotoxicity when bortezomib, a proteasome inhibitor, was combined with the standard agents daunorubicin and cytarabine. We have shown that adding bortezomib to standard treatment in AML results in a high remission rate, although neurotoxicity was noted among treated patients, 12% grade 3 sensory (Attar, …, Amrein, et al. Clin Cancer Res 2008, Attar, … Amrein, J Clin Oncol 2012). The next generation proteasome inhibitor, ixazomib, which is less frequently associated with neurotoxicity, was therefore selected for combination with conventional chemotherapy in this phase I trial. The primary objective was to determine the maximum tolerated dose (MTD) in the combination, initially in induction, and then in combination with consolidation in a subsequent portion of the overall study. We report here the results of the induction portion of the study, which has been completed. Methods: Adults >60 years of age with newly diagnosed AML were screened for eligibility. Patients with secondary AML were eligible, including those with prior hypomethylating agent therapy for myelodysplastic syndromes (MDS). We excluded those with promyelocytic leukemia. The induction treatment consisted of the following: cytarabine 100 mg/m2/day by continuous IV infusion, Days 1-7; daunorubicin 60 mg/m2/day IV, Days 1, 2, 3; ixazomib orally at the cohort dose, Days 2, 5, 9, and 12 A standard 3 + 3 patient cohort dose escalation design was used to determine whether the dose of ixazomib could be safely escalated in 3 cohorts (1.5 mg/day, 2.3 mg/day, 3.0 mg/day), initially in induction and subsequently in consolidation. The dose of 3.0 mg/day was the maximum planned for this study. The determined MTD of ixazomib in the first portion of the trial would be used during induction in the second portion, which seeks to test dose escalation of ixazomib during consolidation. Secondary objectives included rate of complete remission and disease-free survival. Results: Fourteen patients have been analyzed for toxicity and activity during the induction portion of the study. There were 4 (28%) patients with either secondary AML or treatment related AML, 9 (64%) were male, and the median age was 67 years (range 62-80 years). There have been no grade 5 toxicities due to study drug. Three patients died early due to leukemia, 2 of which were replaced for assessment of the MTD. Nearly all the grade 3 and 4 toxicities were hematologic (Table). There was 1 DLT (grade 3 thrombocytopenia) indicated at the highest dose level. There has been no neurotoxicity with ixazomib to date. Among the 14 patients, there have been 10 complete remissions (CR's) and 1 CRi for a remission rate of 79%. Conclusions: The highest dose level planned for this portion of the trial, 3.0 mg of ixazomib, was reached with 1 DLT and is the recommended dose for induction in the next portion of this study, which will seek to determine a safe ixazomib dose in combination with conventional consolidation therapy. That no neurotoxicity was encountered was reassuring, and the remission rate in this older adult population is favorable. Table. Table. Disclosures Amrein: Takeda: Research Funding. Attar:Agios: Employment, Equity Ownership. Brunner:Takeda: Research Funding; Novartis: Research Funding; Celgene: Consultancy, Research Funding. Fathi:Celgene: Consultancy, Honoraria, Research Funding; Boston Biomedical: Consultancy, Honoraria; Astellas: Honoraria; Agios: Honoraria, Research Funding; Jazz: Honoraria; Seattle Genetics: Consultancy, Honoraria; Takeda: Consultancy, Honoraria.

Background: Aurora kinases play essential roles in regulating cell division, and increased expression has been noted in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). We previously conducted a phase I study of alisertib combined with "7+3" induction chemotherapy in untreated patients with AML, and found the combination to have an adverse event profile similar to 7+3 alone, with promising efficacy, particularly for patients with high-risk disease, such as those who were older, with high-risk molecular features, or with secondary AML. These patients collectively have a historically grim prognosis, with an approximate rate of remission, in trials, of 45%. CPX-351, a liposomal daunorubicin-cytarabine product, was recently approved for use in secondary AML after it was demonstrated to be superior to 7+3 induction, with a median survival of 9.6 months versus 5.9 months among older patients, in a phase 3 trial. We recently completed accrual to a phase II study of alisertib plus induction chemotherapy in patients with untreated, high-risk AML. Methods: Patients were eligible if they had AML defined by WHO 2016 and either an adverse-risk karyotype (European Leukemia Net Guidelines), secondary (post-MDS/MPN) AML, therapy-related AML, or age ≥ 65 vears. We used a Simon two-stage design, assuming a null composite remission rate (complete remission [CR] and CR with incomplete count recovery [CRi]) of 45%. Patients could be enrolled prior to cytogenetic classification, but those without adverse-risk karyotype who lacked other eligibility criteria were removed before day 8 and replaced. All patients received continuous infusion cytarabine 100mg/m2 on days 1-7 [D1-7] and idarubicin 12mg/m2 [or daunorubicin 60mg/m2] D1-3 (7+3). On D8 through D15, alisertib at 30mg BID orally (PO) was administered. All underwent a mid-induction marrow biopsy to assess for residual disease, which if present, was treated with 5+2 re-induction without alisertib. Following remission, patients could receive up to 4 consolidation cycles with cytarabine (3g/m2 BID D1,3,5 for age Results: 39 eligible patients were enrolled. The median age was 67 (range 33-83); 25 (64%) were male, and 33 (85%) were Caucasian. 22 patients (56%) had secondary AML (16 with antecedent MDS, 2 with antecedent CMML, 1 with antecedent MPN, and 3 with therapy-related AML). 13 (33%) exhibited adverse risk karyotype. FLT3 mutations were seen in 7 (18%), NPM1 in 7 (18%), IDH1 in 5 (13%), IDH2 in 5 (13%), CEBPA in 3 (8%), and TP53 mutations in 4 (10%) patients. 33 patients (85%) demonstrated an ablated marrow at mid-treatment, and six (15%) received re-induction at mid-treatment. 8 patients (21%) were refractory to induction, and five (13%) died prior to response assessment due to infection or bleeding. The 30-day and 60-day mortality rates were 8% and 13%, respectively. Patients experienced expected grade 4 toxicities of leukopenia, anemia, thrombocytopenia, and febrile neutropenia; no new attributable safety signals were detected. The CR+CRi rate was 64% (2-stage 95% CI 48-79%) with 20 patients (51%) achieving CR and 5 (13%) achieving Cri. The CR+CRi rate was 59% (13 of 22) in those with secondary AML, 67% (18 of 27) in those aged ≥ 65, 77% (10 of 13) in those with adverse risk karyotype, and 75% (3 of 4 patients) in patients with TP53 mutations. One (3%) patient achieved a partial remission. Based on the composite remission rate of 64%, the combination was deemed effective per study design. 5 patients have relapsed to date. 10 have received at least 1 cycle of consolidation, 16 patients (41%) have gone on to SCT. With a median follow-up of 14 months (Figure), the 12-month overall survival (OS) is 51% (37-65%). Although the data continues to mature, median OS is 12.2 months (90% CI 8.8-NA). In the subset of patients achieving a CR+CRi, the 12-month relapse-free survival was 52% (90% CI 34-67%). Conclusions: Alisertib, a novel aurora A kinase inhibitor, combined with conventional induction, is efficacious and demonstrates a promising rate of remission and survival among patients with previously untreated high-risk AML. Larger randomized studies are under consideration to better assess the promise of this novel combination. Figure. Figure. Disclosures Brunner: Takeda: Research Funding; Novartis: Research Funding; Celgene: Consultancy, Research Funding. DeAngelo:Glycomimetics: Research Funding; ARIAD: Consultancy, Research Funding; BMS: Consultancy; Novartis Pharmaceuticals Corporation: Consultancy, Honoraria; Shire: Honoraria; BMS: Consultancy; Amgen: Consultancy; Pfizer Inc: Consultancy, Honoraria; Incyte: Consultancy, Honoraria; Glycomimetics: Research Funding; ARIAD: Consultancy, Research Funding; Amgen: Consultancy; Takeda: Honoraria; Blueprint Medicines: Honoraria, Research Funding. Amrein:Takeda: Research Funding. Steensma:Acceleron: Consultancy; Amphivena: Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; H3 Biosciences: Research Funding; Janssen: Consultancy, Research Funding; Kura: Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees; Onconova: Consultancy; Otsuka: Membership on an entity's Board of Directors or advisory committees; Syros: Research Funding; Takeda: Consultancy. Garcia:Celgene: Consultancy. Rosenblatt:Bristol-Myers Squibb: Research Funding; Celgene: Research Funding; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Merck: Membership on an entity's Board of Directors or advisory committees. Chen:Magenta Therapeutics: Consultancy; REGiMMUNE: Consultancy; Incyte: Consultancy, Membership on an entity's Board of Directors or advisory committees; Takeda Pharmaceuticals: Consultancy. Fathi:Astellas: Honoraria; Seattle Genetics: Consultancy, Honoraria; Boston Biomedical: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria; Agios: Honoraria, Research Funding; Jazz: Honoraria.

Introduction: While progress has been made in the treatment of childhood leukemia, the outlook for patients >60 years of age with acute lymphoblastic leukemia (ALL) is poor with complete remission rates of approximately 60% and 3-year survivals of less than 15% (Larson R., Hematology 2005). Ixazomib is an oral proteasome inhibitor, which has shown single agent activity and promising combination activity in pediatric ALL patients (Messinger, Blood 2012). We sought to assess the safety and tolerability, as well as an early appreciation of the therapeutic promise, of adding ixazomib to standard multi-agent standard treatment for older adults with ALL. Methods: Patients aged 51 to 75 years of age with newly diagnosed B-ALL and T-ALL were screened for eligibility. Excluded were patients with mature ALL (including Burkitt's). Patients with Philadelphia chromosome positive ALL (BCR-ABL1+) were eligible and tyrosine kinase inhibitor therapy was added to the chemotherapy on Day 10 for these patients. The induction treatment consisted of the following: Prednisone 40 mg/m2/day, Days 2-22 for patients Prednisone 40mg/m2/day Days 2-8 for patients ≥ 60 years of age; Vincristine (V) 2 mg IV on Days 2, 9, 16, 23; Doxorubicin (D) 30mg/m2/day on Days 2 and 3; intrathecal cytarabine 50 mg on Day 2; Intrathecal methotrexate 12 mg Day 29; G-CSF 300 mcg/kg sc or IV was started on Day 5 and continued until ANC was >2000 for 2 consecutive days. On Days 1, 8, 15, ixazomib was given orally at the dose prescribed according to 3 dose-escalation cohorts: 2.3 mg/day, 3.0mg/day, or 4.0 mg/day. A standard 3 +3 patient cohort dose escalation design was used to determine the dose of ixazomib for each patient. The primary objective of the study was to determine the maximum tolerated dose (MTD) of ixazomib during induction for these patients. After induction patients received consolidation I consisting of the following: cyclophosphamide 750 mg/m2/day, Days 2-3; prednisone 40 mg/m2/day, Days 2-6; PEG-asparaginase 500 units/m2 IV on Day 2 (for Ph- patients only); intrathecal methotrexate 12 mg on Days 2 and 15. On Days 1, 8, 15 of consolidation I, ixazomib was given orally at the dose previously prescribed for them during induction. After consolidation I, patients in complete remission (CR) with a suitable donor were offered stem cell transplantation as per institutional guidelines. Those not going to transplantation proceeded to continuation therapy as follows: CNS Phase: Intrathecal methotrexate 12 mg, cytarabine 40 mg, hydrocortisone 50 mg on days 1, 8, 15, vincristine Day 1, doxorubicin on Day 1, 6-MP Days 1-14, dexamethasone (DEX) Days 1-5, PEG-ASP Day 1+15 Consolidation II: 8 cycles of V + D + 6-MP + DEX + PEG-ASP; Maintenance Phase: V + DEX + 6+MP + oral methotrexate (ends after 18 months of remission). Results: The dose escalation phase completed with 9 patients. Among these patients, 4 harbored BCR-ABL1 rearrangements, all had B-ALL, the median age was 65 years, 78% were male, and 78% were performance status 1. The MTD was 2.3 mg of ixazomib, as 2 patients at 3.0 mg developed DLT's, a grade 3 peripheral neuropathy and a grade 5 acute kidney injury. Grade 3 and 4 toxicities included grade 4 neutropenia in 8 patients and grade 4 thrombocytopenia in 7 patients. Two patients experienced grade 3 thrombocytopenia. There was 1 patient with a grade 2 neuropathy that did not meet the definition of DLT. Among the 9 patients, 7 (78%) achieved CR, and 2 patients went on to stem cell transplantation. Conclusions: A dose of 2.3 mg of ixazomib was well-tolerated in combination with induction chemotherapy among older patients with ALL, and is being tested in the expansion phase of this trial. The remission rate in this older adult population appears favorable in both Ph-negative and Ph-positive patients. Table. Table. Disclosures Amrein: Takeda: Research Funding. Fathi:Agios: Honoraria, Research Funding; Astellas: Honoraria; Boston Biomedical: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Jazz: Honoraria; Seattle Genetics: Consultancy, Honoraria; Takeda: Consultancy, Honoraria.

Background: Brentuximab vedotin (BV) is an antibody-drug conjugate (ADC) consisting of an antibody specific for human CD30, an anti-microtubule agent monomethyl auristatin E (MMAE), and a protease-cleavable linker attaching MMAE to the antibody. BV is efficacious therapy against certain CD30-expressing malignancies, including classical Hodgkin lymphoma and anaplastic large cell lymphoma, and is currently approved for use in these diseases. We and others previously demonstrated CD30 expression on a sizeable proportion of primary AML samples as well as cell lines. Given this data, we conducted a phase I dose-escalation trial of BV in combination with re-induction chemotherapy (MEC) for patients with relapsed or refractory AML. Methods: In this phase I, 3+3 cohort dose-escalation study, BV was administered 3 days prior to initiation of MEC re-induction for relapsed or refractory AML. Eligibility for enrollment included adults over age 18, adequate organ function, an ECOG performance status of ≤ 2, and a diagnosis of relapsed or refractory AML with > 20% CD30 expression (as assessed by immunohistochemistry or flow cytometric analysis). On day 1 of the trial, all enrolled participants were initiated on therapy with BV intravenously using three sequential dosing levels (0.9 mg/kg, 1.2 mg/kg, 1.8mg/kg). On day 3, patients were initiated on MEC re-induction chemotherapy (Mitoxantrone 10mg/m2 IV administration for five days [D3-8], etoposide 100mg/m2 IV D3-8, cytarabine 1000mg/m2 IV D3-8). The period of dose limiting toxicity (DLT) assessment occurred during the period of re-induction (approximately D1-35). Once dose escalation for BV reached a dose of 1.8 mg/kg IV, no further escalation would occur. An additional cohort of ten patients were to be treated at this maximum dose, or if a maximum tolerated dose (MTD) was reached, an additional 10 patients were to be treated at this dose. Thereafter, maintenance therapy with BV could be initiated, and administered IV every 21 days, as per dose level during prior re-induction, and continued for up to 12 months. Those eligible for stem cell transplant (SCT) were removed from study for this purpose. Results: 22 eligible patients were enrolled on study. The median age was 58 (range 23-72); 15 (68%) were male, and 20 (91%) were Caucasian. 7 patients (32%) had secondary AML (6 with antecedent MDS and 1 with therapy related AML). 6 (27%) exhibited adverse risk karyotype. FLT3 mutations were seen in 7 (32%), NPM1 in 4 (18%), and CEBPA in 2 (9%). The median degree of blast CD30 expression in those assessed by flow cytometry was 92% (range 30-98%). 6 patients had refractory disease, while the remaining had relapsed AML at time of enrollment. 10 patients (46%) had undergone prior allogeneic stem cell transplantation (SCT), one of whom had undergone two prior stem cell transplants. Three patients were treated at dose level 1, 5 at dose level 2, and 4 at dose level 3. Two of the patients treated at dose level 2 were removed prior to end of DLT period due to lack of response and were replaced, and 1 patient treated at dose level 3 died due to infectious complications prior to end of DLT monitoring period and was replaced. No new attributable toxicities apart from that expected from MEC re-induction alone were seen with the combination therapy. No DLTs were detected, and the recommended phase 2 dose (RP2D) was deemed to be dose level 3 (1.8 mg/kg). An additional 10 patients were treated at the RP2D. Overall, 4 patients achieved a complete remission (CR) and 4 achieved a complete remission with incomplete hematologic recovery (CRi), for a composite remission rate (CCR) of 36% (8/22). Among the 14 patients treated at the RP2D of 1.8mg/kg, 6 achieved a CR or CRi (CCR 43%). Of the remaining cases, one was replaced prior to response assessment and the others experienced progressive disease. The degree of baseline CD30 expression by flow cytometry did not appear to predict for response in this phase 1 dose escalation study, although study of correlative samples is ongoing. Conclusions: BV is well tolerated when administered in conjunction with conventional re-induction chemotherapy in patients with relapsed-refractory AML, in whom CD30 is an intriguing target. Adverse events on this study were predominantly expected and related to marrow suppression from MEC re-induction. No DLT was identified. Additional and larger studies are needed to more comprehensively assess the efficacy of CD30-targeted therapy in AML. Disclosures Fathi: Jazz: Honoraria; Boston Biomedical: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Astellas: Honoraria; Agios: Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria. Emadi:NewLink Genetics: Research Funding. Brunner:Takeda: Research Funding; Novartis: Research Funding; Celgene: Consultancy, Research Funding. Amrein:Takeda: Research Funding.

Objective Neutrophils represent a prominent component of inflammatory joint effusions and are required for synovial inflammation in mouse models, but mechanisms are poorly understood. We developed a system to test the importance of production of specific factors by neutrophils in a mouse model of arthritis.

Hematopoietic stem cells (HSCs) save lives in routine clinical practice every day, as they are the key element in transplantation-based therapies for hematologic malignancies. The success of clinical stem cell transplantation critically relies on the ability of stem cells to reconstitute the hematopoietic system for many decades after the administration of the powerful chemotherapy and/or irradiation that is required to eradicate malignant cells, but also irreversibly ablates patients’ own blood forming capacity. Surprisingly, despite enormous efforts and continuous progress in the field, our understanding of the basic biology of HSCs is still rather incomplete. Several recent studies substantially refine our understanding of the cells at the very top of the hematopoietic hierarchy, and suggest that we may need to revise the criteria we typically use to identify and define HSCs.

The reprogramming of somatic cells into induced pluripotent stem (iPS) cells upon overexpression of the transcription factors Oct4, Sox2, Klf4 and cMyc is extremely inefficient. It has been assumed that the somatic differentiation state provides a barrier for efficient reprogramming; however, direct evidence for this notion is lacking. Here, we have tested the susceptibilities of hematopoietic cells at different stages of differentiation to be reprogrammed into iPS cells. Surprisingly, hematopoietic stem and progenitor cells give rise to iPS cells up to 300 times more efficiently compared with terminally differentiated B and T cells, yielding reprogramming efficiencies of up to 28%. Our data provide evidence that the differentiation stage of the starting cell has a critical influence on the efficiency of reprogramming into iPS cells. Moreover, we identify adult hematopoietic progenitors as an attractive cell type for applications of iPS technology in research and therapy.

Hematopoietic stem cells (HSCs) are thought to divide infrequently based on their resistance to cytotoxic injury targeted at rapidly cycling cells1, 2 and have been presumed to retain labels such as the nucleotide analogue 5-bromodeoxyuridine (BrdU). However, recently it has been demonstrated that BrdU-retention is neither sensitive nor specific for HSCs3. Here we show that transient, transgenic expression of a Histone2B (H2B)-Green Fluorescent Protein (GFP) fusion protein in mice allows superior labeling of HSCs and permits improved analysis of their turnover in combination with other markers. Mathematical modeling of H2B-GFP dilution in HSCs, identified with a highly stringent marker combination (L−K+S+CD48−CD150+)4, revealed unexpected heterogeneity in their proliferation rates and suggests that ~ 20% of HSCs turn over at an extremely low rate (≤ 0.8–1.8% per day). Prospective isolation and transplantation of L−K+S+CD48−CD150+ HSCs with different H2B-GFP levels revealed that higher H2B-GFP label retention correlates with superior long-term repopulation potential.

SummaryTo better understand the cellular origin of breast cancer, we developed a mouse model that recapitulates expression of the ETV6-NTRK3 (EN) fusion oncoprotein, the product of the t(12;15)(p13;q25) translocation characteristic of human secretory breast carcinoma. Activation of EN expression in mammary tissues by Wap-Cre leads to fully penetrant, multifocal malignant breast cancer with short latency. We provide genetic evidence that, in nulliparous Wap-Cre;EN females, committed alveolar bipotent or CD61+ luminal progenitors are targets of tumorigenesis. Furthermore, EN transforms these otherwise transient progenitors through activation of the AP1 complex. Given the increasing relevance of chromosomal translocations in epithelial cancers, such mice serve as a paradigm for the study of their genetic pathogenesis and cellular origins, and generation of preclinical models.

Gfi-1, originally identified as a transcriptional repressor in lymphoid cells, is now recognized to have essential, independent functions in neutrophil maturation and hematopoietic stem cell biology. Here we review recent studies pertaining to Gfi-1 and its cell context specific functions in hematopoietic development.Progress in mapping the precise timing of requirements for myeloid transcription factors during hematopoietic development reveals a more refined picture of their sequence of action. We contrast Gfi-1's role in neutrophil development with PU.1, C/EBPalpha, and C/EBPepsilon. Gfi-1 has been found to be a major regulator of adult hematopoietic stem cells. It is required for restricting the proliferation of hematopoietic stem cells and maintaining their functional integrity. We discuss its role and compare its function with that of other regulators recently implicated in the biology of hematopoietic stem cells.Considerable progress has been made in understanding Gfi-1's context-sensitive roles at defined stages of hematopoietic differentiation.

Haematopoietic stem cells (HSCs) sustain blood production throughout life. HSCs are capable of extensive proliferative expansion, as a single HSC may reconstitute lethally irradiated hosts1. In steady-state, HSCs remain largely quiescent and self-renew at a constant low rate, forestalling their exhaustion during adult life2,3. Whereas nuclear regulatory factors promoting proliferative programmes of HSCs in vivo and ex vivo have been identified4,5,6, transcription factors restricting their cycling have remained elusive. Here we report that the zinc-finger repressor Gfi-1 (growth factor independent 1), a cooperating oncogene in lymphoid cells7,8, unexpectedly restricts proliferation of HSCs. After loss of Gfi-1, HSCs display elevated proliferation rates as assessed by 5-bromodeoxyuridine incorporation and cell-cycle analysis. Gfi-1-/- HSCs are functionally compromised in competitive repopulation and serial transplantation assays, and are rapidly out-competed in the bone marrow of mouse chimaeras generated with Gfi-1-/- embryonic stem cells. Thus, Gfi-1 is essential to restrict HSC proliferation and to preserve HSC functional integrity.

The production of blood cells is sustained throughout the lifetime of an individual by haematopoietic stem cells (HSCs). Specification of HSCs from mesoderm during embryonic development requires the stem cell leukaemia SCL/tal-1 gene product. Forced expression of SCL/tal-1 strongly induces blood formation in embryos, indicating that this gene has a dominant role in commitment to haematopoiesis. In the adult haematopoietic system, expression of SCL/tal-1 is enriched in HSCs and multipotent progenitors, and in erythroid and megakaryocytic lineages, consistent with roles for this factor in adult haematopoiesis. Here we assess by conditional gene targeting whether SCL/tal-1 is required continuously for the identity and function of HSCs. We find that SCL/tal-1 is dispensable for HSC engraftment, self-renewal and differentiation into myeloid and lymphoid lineages; however, the proper differentiation of erythroid and megakaryocytic precursors is dependent on SCL/tal-1. Thus, SCL/tal-1 is essential for the genesis of HSCs, but its continued expression is not essential for HSC functions. These findings contrast with lineage choice mechanisms, in which the identity of haematopoietic lineages requires continuous transcription factor expression.

Strict, lineage-intrinsic requirement for continuous adult Gfi-1b expression at two distinct critical stages of erythropoiesis and megakaryopoiesis., The zinc finger transcriptional repressor Gfi-1b is essential for erythroid and megakaryocytic development in the embryo. Its roles in the maintenance of bone marrow erythropoiesis and thrombopoiesis have not been defined. We investigated Gfi-1b’s adult functions using a loxP-flanked Gfi-1b allele in combination with a novel doxycycline-inducible Cre transgene that efficiently mediates recombination in the bone marrow. We reveal strict, lineage-intrinsic requirements for continuous adult Gfi-1b expression at two distinct critical stages of erythropoiesis and megakaryopoiesis. Induced disruption of Gfi-1b was lethal within 3 wk with severely reduced hemoglobin levels and platelet counts. The erythroid lineage was arrested early in bipotential progenitors, which did not give rise to mature erythroid cells in vitro or in vivo. Yet Gfi-1b−/− progenitors had initiated the erythroid program as they expressed many lineage-restricted genes, including Klf1/Eklf and Erythropoietin receptor. In contrast, the megakaryocytic lineage developed beyond the progenitor stage in Gfi-1b’s absence and was arrested at the promegakaryocyte stage, after nuclear polyploidization, but before cytoplasmic maturation. Genome-wide analyses revealed that Gfi-1b directly regulates a wide spectrum of megakaryocytic and erythroid genes, predominantly repressing their expression. Together our study establishes Gfi-1b as a master transcriptional repressor of adult erythropoiesis and thrombopoiesis.

Developmental ‘road maps’ chart the steps from simple cells to mature, specialized cells. A newly discovered variety of blood-cell progenitor doesn't fit into the accepted blood map, but should that map be redrawn?

Foxp3(+) regulatory T (T(reg)) cells are essential for the maintenance of self-tolerance and immune homeostasis. The majority of T(reg) cells is generated in the thymus as a specific subset of CD4(+) T cells, known as thymus-derived or natural T(reg) (nT(reg)) cells, in response to signals from T-cell receptors, costimulatory molecules, and cytokines. Recent studies have identified intracellular signaling and transcriptional pathways that link these signals to Foxp3 induction, but how the production of these extrinsic factors is controlled remains poorly understood. Here, we report that the transcription repressor growth factor independent 1 (Gfi1) has a key inhibitory role in the generation of nT(reg) cells by a noncell-autonomous mechanism. T cell-specific deletion of Gfi1 results in aberrant expansion of thymic nT(reg) cells and increased production of cytokines. In particular, IL-2 overproduction plays an important role in driving the expansion of nT(reg) cells. In contrast, although Gfi1 deficiency elevated thymocyte apoptosis, Gfi1 repressed nT(reg) generation independently of its prosurvival effect. Consistent with an inhibitory role of Gfi1 in this process, loss of Gfi1 dampens antitumor immunity. These data point to a previously unrecognized extrinsic control mechanism that negatively shapes thymic generation of nT(reg) cells.

Introduction: Myelodysplastic syndromes (MDS) comprise a broad spectrum of hematologic malignancies with varying clinical courses; although most deaths are attributed to MDS, many patients will die of other attributable causes, independent of or potentially augmented by their underlying cancer. Cardiovascular (CV) disease is a frequently attributed cause of death in these patients, and may be influenced by CV care patterns in a patient's county of residence. Patients who live in counties with worse CV outcomes may be at greater risk of CV complications and death. We sought to determine whether regional quality of CV care in the US, measured by the rate of CV death in a county, impacts the cumulative incidence of death attributed to CV disease among MDS patients. Methods: We used the Surveillance, Epidemiology, and End Results (SEER) database from the National Cancer Institute to identify patients, age 15 and older, with a new diagnosis of MDS between 2001 and 2011. We identified 29,571 patients with a known age at diagnosis and follow-up, for whom MDS was the first cancer diagnosed in SEER. We grouped patients into lower risk disease (RA, RT, RN, and RARS), intermediate risk disease (MDS-unclassified, del(5q), RCMD, and t-MDS) and higher risk disease (RAEB and RAEB-T) according to SEER classifications. The incidence of a given cause of death (COD) was estimated by the cumulative incidence method identifying each COD as competing risks using R statistical software, and tested using the Gray test. We identified population rates of CV-specific mortality, according to the National Center for Health Statistics and available through SEER*Stat, in all counties with at least one MDS diagnosis over the study period. If the rate of death due to cardiovascular disease in a county was below the 25th percentile, then the CV performance was considered "good", if above the 75th percentile then the CV performance was considered "poor", and all others were considered "intermediate." Patients with MDS were grouped into a county CV performance quartile according to the rate of CV death in that county at the time of diagnosis. Results: The median age at diagnosis was 76 years (range 15-109) and the patients were 54% male. Patients were divided among lower risk (21%), intermediate risk (66%), and higher risk MDS (13%). Cause of death was reported for 29,344 patients. 602 counties had 1 diagnosis of MDS between 2001 and 2011, 599 of which reported overall CV mortality rates. A total of 15,856 MDS patients (54%) lived in counties with good CV performance (less than or equal to the 25th percentile of CV mortality) during the study period, while 11,845 (40%) lived in counties with intermediate CV performance, and 1817 (6%) lived in poor CV performance counties. MDS patients living in poor CV performance counties had a cumulative incidence of death attributed to cardiovascular disease of 7.2% at 12 months, compared to 4.8% and 5.1% among intermediate and good CV performance counties, respectively (p=0.0001). Death attributed to MDS was 15.7%, 15.6%, and 14.5% at 12 months for patients living in good, intermediate, and poor CV performance counties, respectively (Table 1). When looking specifically at MDS risk groups, it appeared that county CV performance had a greater impact on patients with intermediate and higher risk MDS (Table 1). Patients with higher risk MDS living in poor CV performance counties had a 12-month cumulative incidence of death due to CV disease of 9.3% compared to 4.2% and 3.6% in good and intermediate CV performance counties (p Conclusions: Most MDS patients live in counties with good CV performance; MDS patients living in counties with higher cardiovascular mortality have higher rates of death attributed to cardiovascular disease than do MDS patients living in intermediate or low cardiovascular mortality regions, while death attributed to MDS or other causes is relatively stable. This is more apparent among patients with higher risk MDS. These findings suggest that cardiovascular disease may be a modifiable risk factor for MDS patients. Table 12-Month Cumulative Incidence of Death due to MDS, CAD, and other causes. Table. 12-Month Cumulative Incidence of Death due to MDS, CAD, and other causes. Figure Cause of Death According to County Cardiovascular Performance. Figure. Cause of Death According to County Cardiovascular Performance. Disclosures Hobbs: Incyte: Other: participation in advisory board; Agios: Other: participation in advisory board. Fathi:Seattle Genetics: Consultancy, Other: Advisory Board participation, Research Funding; Bexalata: Other: Advisory Board participation; Celgene: Consultancy, Research Funding; Merck: Other: Advisory Board participation; Agios Pharmaceuticals: Other: Advisory Board participation.

Introduction: A significant source of morbidity and mortality related to allogeneic hematopoietic cell transplantation (HCT) is neurologic complication. We performed a retrospective chart review to determine the incidence, risk factors, timing, and impact of neurologic complications in the first five years after HCT. Methods: We performed a retrospective chart review of patients undergoing allogeneic HCT for hematological disorders at the Massachusetts General Hospital between January 2000 and December 2010, focusing on neurologic complications after HCT. We determined the incidence of central nervous system (CNS) infections, intracranial hemorrhage, thromboembolic events, metabolic encephalopathy, posterior reversal encephalopathy syndrome (PRES), seizures, CNS malignancy, and peripheral neuropathy. We classified neurological events as either early (day -7 to day +100), late (day +101 to 2 years) or very late (2 years to 5 years). Risk factors studied were demographics (age, gender, race), disease-related factors (diagnosis, disease status, prior autologous transplant),transplant factors (myeloablative or reduced-intensity conditioning, use of antithymocyte globulin (ATG), stem cell source and GVHD prophylaxis). Outcome variables were neutrophil and platelet engraftment, progression free survival (PFS) and overall survival (OS). Results: There were 263 consecutive patients (median age 54 years, range 18 to 76 years). The diseases were acute myeloid leukemia n=91 (34.6%), non-Hodgkin lymphoma n=64 (24.3%), myelodysplastic syndrome n=41 (15.6%), acute lymphoblastic leukemia n=21 (8.0%), myeloproliferative neoplasm n=13 (4.9%), chronic lymphocytic leukemia n=12 (4.6%), Hodgkin lymphoma n=11 (4.2%), multiple myeloma n=10 (3.8%). Conditioning was myeloablative n=86 (33%), or reduced-intensity n= 177 patients (67%). Donor source was matched related donor n=153 (58.1%), matched unrelated donor n=52 (19.8%), haploidentical n=35 (13.3%), umbilical cord blood n=20 (7.6%), and mismatched unrelated donor n=3 (1.1%). The median days to ANC > 500x106/L, and platelet count > 20,000 x106/L unsupported were 15 (range 7 to 37 days) and 19 (range 7 to 167 days), respectively. The incidence of acute GVHD grades II-IV was 22% and the 1-year incidence of extensive chronic GVHD was 8.9%. The 5-year overall and progression free survivals were 37% and 29% respectively. The major cause of death was relapsed or progressive malignancy. 15 patients (5.7%) experienced 19 clinically active neurologic events without having relapsed or progressed at the time, as follows: CNS infection n=0,CNS hemorrhage n=2, CNS thromboembolic event n=1, metabolic encephalopathy n=4, PRES n=3, seizure n=4, CNS malignancy n=4, and peripheral neuropathy n=5 (Table 1). 4 patients experienced CNS relapse as their first neurologic event post transplant. Patients who relapsed or progressed had a higher incidence of neurologic complications -55 of those patients (38.4% of patients who relapsed) experienced 79 neurologic events: CNS infection n=16,CNS hemorrhage n=14, CNS thromboembolic event n=14, metabolic encephalopathy n=14, PRES n=3, seizure n=9, CNS disease n=7, and peripheral neuropathy n=12(Table 2). After 100 days post transplant, neurologic complications were rare in patients who had not relapsed or progressed (2.2% of patients). In a multivariate analysis, risk factors for neurologic complication were relapsed/progressive disease, grade II-IV acute GVHD and use of sirolimus in GVHD prophylaxis. 4 of 17 patients who received sirolimus had a neurologic event (1 thromboembolic stroke, 1 seizure/PRES, 1 seizure/PRES/metabolic encephalopathy and 1 peripheral neuropathy). Neutrophil and platelet engraftment were not affected by neurologic complications. Neurologic complications negatively impacted OS (Hazard Ratio (HR) 3.5, p In summary, (1) Neurologic complications are uncommon after allogeneic HCT (5.7%); (2) Neurologic complications are more common in patients with relapsed or progressive disease (38.4%); (3) Neurologic complications are more common in patients receiving sirolimus-containing GVHD prophylaxis (23.5%), although limited by small numbers; (4) Neurologic complications are uncommon after 100 days (2.2%); (5) Neurologic complications were associated with decreased PFS and OS. Disclosures Chen: Novartis: Research Funding; Incyte Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.

In this study, we show the high frequency of spontaneous γδ T-cell leukemia (T-ALL) occurrence in mice with biallelic deletion of enhancer of zeste homolog 2 (Ezh2). Tumor cells show little residual H3K27 trimethylation marks compared with controls. EZH2 is a component of the PRC2 Polycomb group protein complex, which is associated with DNA methyltransferases. Using next-generation sequencing, we identify alteration in gene expression levels of EZH2 and acquired mutations in PRC2-associated genes (DNMT3A and JARID2) in human adult T-ALL. Together, these studies document that deregulation of EZH2 and associated genes leads to the development of mouse, and likely human, T-ALL.

Expression of the interleukin (IL)-2 receptor beta chain in the IL-7-dependent pre-B cell line IxN/2B permitted growth in presence of either IL-2 or IL-7, allowing for a direct comparison of intracellular signaling events. Protein tyrosine phosphorylation was essential for IL-2 and IL-7-induced signal transduction since the tyrosine kinase inhibitor herbimycin A blocked proliferation in response to both factors. Western blot analysis of tyrosine-phosphorylated proteins revealed that both IL-2 and IL-7 stimulation led to enhanced phosphorylation of proteins of 170-, 145-, 115- and 99-kDa, as well as induction of phosphorylation of a 96-kDa protein. However, a 55- and a 155-kDa protein were only phosphorylated after IL-2 stimulation. The 55-kDa protein specifically phosphorylated by IL-2 could be identified as p52shc which has recently been shown to be critically involved in Ras activation. Shc tyrosine phosphorylation as a result of IL-2 stimulation was consistently found in CTLL-2 cells and human T lymphoblasts. Taken together our results indicate that the IL-2- and IL-7-stimulated intracellular pathways are partially different and that Shc is a target of IL-2-, but not IL-7-, stimulated tyrosine phosphorylation.

The receptors for IL-3, IL-5 and GM-CSF belong to the hematopoetic receptor superfamily and have no intrinsic tyrosine kinase activity but nevertheless indirectly induce protein tyrosine phosphorylation. In order to directly compare the effects of IL-3, IL-5 and GM-CSF on protein tyrosine phosphorylation we analyzed the murine cell line FDCP-1 which proliferates equally well in response to IL-3 and GM-CSF and the cell line B13 which responds to both IL-3 and IL-5. The protein tyrosine phosphorylation pattern induced by IL-3, IL-5 and GM-CSF in these cell lines was shown to be remarkably similar and all three cytokines induced tyrosine phosphorylation of Shc, a src homology domain-2 containing protein which has been shown to be involved in Ras activation by tyrosine kinase receptors.

Interleukin (IL)-2, IL-4, IL-7, tumor necrosis factor (TNF), or interferon-gamma (IFN-gamma) has been shown to be able to induce tumor rejection if produced locally by the tumor cells after gene transfer. To analyze whether the cellular rejection mechanisms are different or redundant we have expressed the cytokines in the same tumor cell line (J558L). Cell depletion experiments revealed that all cytokines required CD8+ T cells for complete long-term tumor eradication, although effective but transient host-dependent tumor suppression was also observed in the complete absence of CD8+ T cells. The transient tumor suppression induced by IL-2, IL-4, TNF, or IFN-gamma was also operative in nude and severe combined immunodeficient mice, whereas only tumor suppression induced by IL-7 was dependent on the presence of CD4+ T cells and was not evident in nude mice. The T-cell-independent effector arm of IL-2 and IFN-gamma but not IL-4 and TNF was mediated in part by natural killer cells. The transience of tumor suppression in the absence of T cells reflected loss of cytokine production in the case of TNF, IL-2, and IL-4 but not IFN-gamma. Immunohistologic analysis revealed all cytokine-producing tumors to be heavily infiltrated by macrophages. IL-4 and IL-7 tumors additionally contained eosinophils. The infiltration by T cells did not necessarily reflect their contribution to tumor rejection. Thus, the different cytokines activate heterogeneous transient tumor-suppressive mechanisms but always require CD8+ T cells for complete tumor rejection.

Tumor necrosis factor (TNF) produced by tumor cells after gene transfer can effectively suppress the growth of locally growing tumors. We wanted to test the effects of "local" TNF on the growth of a highly metastatic cell line. Therefore, a recombinant retrovirus allowing expression of the TNF gene by the beta-actin promotor has been constructed and used to infect the two tumor cell lines EB and ESB, which grow as solid tumor or metastasize, respectively. Expression of TNF by EB cells resulted in their rapid and dose-dependent rejection. In sharp contrast, mice injected with ESB cells producing similar amounts of TNF showed no signs of tumor suppression, but rather had reduced survival rates that correlated with enhanced hepatic metastases. The accelerated formation of liver metastases by ESB TNF cells could be reversed by an anti-TNF mAb. These results demonstrate the opposite effects TNF may have on tumor growth: suppression of a locally growing tumor and promotion of metastasis formation.

We have determined the sequence of the light and heavy chains of mAb 3G-10 (IgGl), a monoclonal antibody competing with interleukin 2 (IL2) for binding to the human IL2 receptor Tac protein. The antibody-encoding genes were chimerized by introducing splice donor and part of the intron sequences into the cDNA and subsequently linking it to the constant parts of the human IgG 1 gene. The chimeric mAb was produced in mouse myeloma cells and purified. Murine and chimeric mAbs showed similar properties with respect to inhibition of T-cell proliferation. In contrast to its murine counterpart, the chimeric mAb exhibited Ab-dependent cellular cytotoxicity and, when combined with an Ab recognizing a different epitope on the IL2 receptor Tac protein, was able to activate human complement. The chimerized mAb might therefore have improved therapeutic efficacy.

The potential of interleukin 7 (IL-7) to induce an antitumor response in vivo was analyzed. Therefore, the IL-7 gene was expressed in the plasmacytoma cell line J558L. Although the growth of IL-7-producing cells was not retarded in vitro, the IL-7-producing cells were completely rejected upon injection into mice. Tumor rejection was observed only in syngeneic but not in nude mice. The tumor-suppressive effect could be abolished by the parallel injection of an anti-IL-7 monoclonal antibody. Immunohistochemical analysis revealed IL-7-dependent infiltration of the tumor tissue by CD4+ and CD8+ T lymphocytes, and also type 3 complement receptor-positive (CR3+) cells, predominantly macrophages. Depletion of T cell subsets in tumor-bearing mice showed the absolute dependence of the antitumor response on CD4+ cells, whereas tumor rejection was unaffected by depletion of CD8+ cells. In addition to CD4+ cells, CR3+ cells were also needed for tumor rejection. The antitumor effect of IL-7 was confirmed by expression of the IL-7 gene in a second tumor cell line of different cellular origin. Together, our results demonstrate that a high local IL-7 concentration at the tumor site obtained by tumor cell-targeted gene transfer leads to tumor rejection involving a cellular mechanism that seems to be different from the ones observed in analogous experiments with other cytokines.