ALBERT

Description: Abstract 2665 Background: Hematologic and solid tumors are associated with hypercoagulability the reason for which has not been delineated. Prothrombinase named fibrinogen-like protein 2 (FGL-2) is a 70 kD transmembrane protein that was found to have a quality of a serine protease capable of directly cleaving prothrombin to thrombin. FGL-2 is synthesized by monocytes, T-lymphocytes and endothelial cells. FGL-2 protein and its mRNA have been previously found within different tumor cells. Aim: To study the role of FGL-2 in patients with lymphoproliferative disorders. Our hypothesis is that upregulation of FGL-2 activity in patients with B-cell malignancies may contribute to tumorigenesis via generation of thrombin leading to increased angiogenesis and spread/metastasis of malignant cells. Methods: Thrombin generation reflecting FGL-2 activity was measured in homogenized peripheral blood mononuclear cells (PBMC) from 29 patients with active lymphoproliferative disorders and 107 normal controls. Informed consent was obtained from every participant. PBMC extracts were incubated with an equal volume of human prothrombin (final concentration10 μM) for 30 min at 37 °C. Thrombin generation was measured at 405 nm using an automated plate reader after addition of chromogen S-2238. The thrombin activity of each sample was calculated by comparison with absorbance curve generated by known concentrations of human thrombin. FGL-2 was immunoprecipitated (IP) from PBMC with an anti-FGL-2 antibody and EZview Red Protein A Affinity Gel (sigma # P6486). The activity of IP FGL-2 was measured by thrombin generation assay. The expression of FGL-2 was analyzed in HUVEC and PBMC in the presence or absence of IF-γ at 20 ng/ml. Total RNA was isolated using RNAqueous™ (Ambion #AM1912) and RT-PCR, analysis was performed using Rotor-gene RG-3000 (Corbett). The difference in cycle time (ΔCT) was measured by comparing FGL-2 gene with ABL-1 gene (house keeping gene). The relative quantification was calculated by the formula RQ= 2−ΔCT. HUVEC were transfected with 0.5 μM SiRNA synthesized complementary to FGL-2 (Target SiRNA) using Dharmacon ON-TARGET plus SMART pool reagent (Thermo Fisher Scientific) according to manufacturer instructions. FGL-2 expression following addition of target SiRNA was compared to that obtained following addition of non-specific (non-target) SiRNA. Student's t-test was used for all comparisons. Results: As shown in the table, almost 3-fold increase in FGL-2 activity in PBMC was observed among patients with active B-cell lymphoma, either aggressive or indolent, as compared to that of healthy controls (p

Description: Somatic mutations in calreticulin (CALR), an endoplasmic reticulum (ER) chaperone protein, are found in up to 40% of patients with myeloproliferative neoplasms (MPN). All pathologic CALR mutations are out-of-frame insertion and/or deletions (indels) in exon 9, generating a 1 base-pair (bp) frame shift and a common mutant-specific C-terminus, with the most common mutation being a 52 bp deletion (del52). The observation that CALR mutations are mutually exclusive with other MPN-initiating mutations such as JAK2V617F suggests a key pathogenic role for mutant CALR. To determine if mutant CALR alone is sufficient to induce MPN we began by over-expressing CALR-del52 in a retroviral bone marrow transplant (BMT) mouse model. We found that CALR-del52-expressing mice develop thrombocytosis and megakaryocytic hyperplasia, recapitulating the megakaryocyte-specific phenotype of CALR-mutant MPN patients. These findings suggest that the thrombopoietin receptor, MPL plays a key role in the pathogenesis of mutant CALR-driven MPN. To evaluate the role of MPL in mutant CALR driven oncogenesis, we over-expressed CALR-del52 in interleukin-3 (IL-3)-dependent Ba/F3 hematopoietic cells. We found that CALR-del52 over-expression results in transformation to IL3-independent growth only in Ba/F3 cells co-expressing MPL, but not in parental Ba/F3 cells or Ba/F3 cells co-expressing the EPO receptor (EPOR) or the G-CSF receptor (GCSFR). We found similar results in human cytokine-dependent UT-7 cells. We also introduced +1 frameshift mutations into the endogenous Calr locus in Ba/F3-MPL cells using CRISPR/Cas9 gene editing and successfully engendered IL-3 independent growth, indicating that endogenous levels of mutant Calr expression are sufficient for transformation. Together, these data indicate that MPL is specifically required for the transforming capacity of mutant CALR. Using RNA-sequencing followed by gene set enrichment analysis (GSEA), we confirmed that mutant CALR transformed Ba/F3-MPL cells display strong enrichment of Stat5 and Stat3 gene expression signatures. Concordantly, we also saw differential phosphorylation of Stat5 and Stat3 in these cells. Furthermore, we found that the IL-3 independent proliferation of mutant CALR expressing Ba/F3-MPL cells is decreased upon shRNA-mediated knockdown of Jak2, and that differential activation of Stat5 and Stat3 is abrogated by the JAK2 inhibitor, ruxolitinib. Together, these data demonstrate that mutant CALR signals through the JAK/STAT axis downstream of MPL. We next sought to define the specific domains within mutant CALR required for oncogenic transformation. We found that neither expression of the mutant C-terminus alone nor expression of CALR lacking the C-terminus leads to cytokine-independent growth, suggesting that the novel C-terminus is necessary (but not sufficient) for transformation. We therefore generated an extensive series of truncation, domain deletion and point mutations within the C-terminus and assessed their respective transforming capabilities. Surprisingly, we found that the oncogenic activity of mutant CALR is not encoded within a specific sequence or domain of the mutant C-terminus. Rather, we found that the positive electrostatic charge of the mutant C-terminus is critical for its transforming capacity. Mutagenizing all 18 lysine/arginine residues (positively charged) within the C-terminus to a neutral glycine residue abrogates CALR-del52 transformation activity. In contrast, mutagenizing the 18 non-lysine/arginine residues within the C-terminus to glycine does not affect transforming activity, a remarkable finding considering that, in this mutant, 50% of the amino acids have been modified. Finally, using co-immunoprecipitation assays we found that mutant CALR, but not wild-type CALR, physically interacts with MPL, and that neither the mutant C-terminus alone nor mutant CALR lacking the C-terminus can bind to MPL. This suggests that the tertiary structure of mutant CALR is required for binding to MPL. Moreover, we found that the ability of our engineered CALR mutants to bind MPL perfectly correlates with their ability to mediate transformation, suggesting that the interaction with MPL is critical for mutant CALR-mediated transformation. Together, our findings elucidate a novel mechanism of pathogenesis in MPN and provide insights into how CALR mutations drive the development of MPN. Disclosures: No relevant conflicts of interest to declare.

Description: Background: Survival of adult patients with Ph-negative acute lymphoblastic leukemia (ALL) with conventional therapeutic approaches remains poor. Given the ability to safely perform allogeneic stem-cell transplant (alloSCT) in this age cohort, older patients with ALL in first complete remission (CR1) are increasingly offered consolidation with this modality. We asked whether alloSCT in CR1 offers a survival advantage in older patients with ALL as compared to post remission chemotherapy. Methods: One hundred and seven patients ≥40 years were treated at the Dana Farber Cancer Institute for Ph-negative ALL from 1/1/2006 to 12/31/2013; of the 99 patients treated with curative intent, 80 patients (age 54.5 years; range 41-83) achieved first remission (81%; CR and CRi). Baseline characteristics of the chemotherapy and alloSCT post remission groups were compared using the Fisher exact and Wilcoxon rank-sum tests for categorical and continuous variables, respectively. The comparison of outcomes between the alloSCT and chemotherapy cohorts was made using a modified Mantel-Byar test to account for the waiting time to transplant. For graphical comparisons, the method of left-truncation was used to adjust for the time of wait from first CR/CRi to transplant. In Cox modeling of overall survival (OS) and disease free survival (DFS), treatment was included as a time-dependent variable. The cumulative incidence of relapse (CIR) and non-relapse mortality (NRM) were calculated and compared between groups from the time of CR/CRi to the time of the event with each considered as competing events. Retrospectively determining the reason for choosing one post remission approach over the other was not always possible. Furthermore, MRD status was available in a minority of patients. The effect and relation of these factors to patient selection and outcome therefore could not be assessed. Results: Eighty patients in first CR/CRi were analyzed. B-cell ALL was diagnosed in 86% of patients and T-cell origin was identified in 14% of patients; 6% of patients had therapy-related ALL. Median WBC, platelet and Hb levels at diagnosis were 5.3X109/L, 61X109/L and 9.6mg/dL, respectively. Cytogenetics were available for 63 patients (cytogenetics were not reported for referred patients (n=11) or were unsuccessful (n=6)) and were diploid (52%), near hyperploid (25%), hyperploid (11%), near hypoploid (5%) and hypoploid (2%). MLL rearrangement was identified in 12.5% of patients. Most patients had an ECOG performance status of 0-1; the median modified Charlson co-morbidity index score was 2 (range 0-10) and 56% of patients had ≥1 co-morbidities. In the alloSCT group, myeloablative and reduced-intensity conditioning were used in 55% and 45% of patients, respectively. Matched related and matched unrelated donors were used in 40% and 48% of patients, respectively, with the remainder receiving alternative donor sources. Forty patients received alloSCT in first remission and 40 patients were treated with chemotherapy only. Baseline characteristics did not significantly differ between the 2 groups except for lower Hb in the alloSCT group (p=0.028). Nine of 10 patients with MLL rearrangement were allocated to the alloSCT group. The median follow-up in the alloSCT and chemotherapy groups was 3.7 and 2.6 years, respectively. OS (Figure 1) and DFS did not differ between the groups at 3 years; the significantly higher CIR rate in the chemotherapy group was offset by the higher NRM in the alloSCT group (Table 1). Univariate Cox Modeling of 13 patient, disease and treatment-related factors including post remission modality were analyzed, none of which were shown to affect OS or DFS. WBC at diagnosis (≥20K vs.

Description: Introduction: The phase III RATIFY study (Stone et al, NEJM 2017) demonstrated that the addition of the FLT3 inhibitor midostaurin to intensive induction and consolidation courses improves outcome in younger FLT3-positive AML patients. The toxicity and efficacy profile of adding midostaurin to chemotherapy in patients not originally included in the RATIFY study is unknown. We sought to characterize midostaurin use in a 'real-world' setting. Methods: Patients (〉18 years) with FLT3-positive AML (ITD/TKD) were eligible to receive midostaurin through the Novartis extended access program that was launched in Israel in April 2016. In order to control for toxicity and efficacy outcomes in the midostaurin-treated patients, a historical control cohort was created that included patients with FLT3-positive AML from 2 participating centers that were not treated with midostaurin (all patients diagnosed after January 2015). Data were extracted from electronic patient records and were collected from several medical centers in Israel. Base-line characteristics, disease- and patient- specific parameters as well as relapse-rates and overall survival were analyzed and compared between the midostaurin treated and untreated cohorts. We used Cox regression to analyze predictors for survival. This study was approved by the Institutional Review Board. Results: Thirty-five patients were included in the analysis. The median age of the patients was 62 years (range 27-78); 40% and 20% of patients were over the age of 65 and 70 years, respectively. FLT3-ITD mutations were detected in 32 patients (91%) and 3 patients had TKD mutations (9%). Eight patients (23%) had secondary leukemia, 83% had normal karyotype and 57% were NPM1-mutated. No differences were noted between the midostaurin-treated group (n=21) and the historical control cohort (n=14) in terms of age, gender, leukemia ontogeny, cytogenetics, presenting blood counts, extramedullary involvement, performance status and comorbidity scales. More patients in the midostaurin group were found to be NPM1-mutated (66 vs. 44%, p=0.03). Furthermore, no differences were noted between the groups in terms of daunorubicin dose for induction (45, 60 and 90 mg/m2/dayin 20, 30 and 50% of patients, respectively), number of consolidations (median number of cycles - 2), cytarabine dose or allogeneic transplantation rate (45 and 36% in the midostaurin and control group, respectively). The full 14 day midostaurin course was given in most patients during induction (73%). In 5 patients midostaurin was initiated only at the post-induction courses due to technical delays in drug supply. Only 4 patients experienced dose reductions or interruptions during therapy: 3 during induction (septic shock, drug interaction and QT prolongation) and 1 during consolidation (new onset atrial fibrillation). Toxicity was comparable between the cohorts. Febrile neutropenia during induction was noted in 95 and 93% of patients in the midostaurin and control groups, respectively. Time to neutrophil and platelet recovery were also comparable (25 vs. 24 days and 24 vs. 20 days in the midostaurin and control groups respectively). Other toxicities were uncommon and not significantly different between the groups. CR/CRi rates were 85% and 58% in the midostaurin and control cohorts, respectively (p=0.17). The median follow-up time for surviving patients in the midostaurin and control cohorts were 426 and 517 days, respectively (p=0.55). During follow-up, 7 deaths occurred in the midostaurin group and 9 in the control arm. Median survival was not reached for the midostaurin treated group and was 281 days for the control group (Figure 1, p=0.42). Nine and 6 patients in remission relapsed in the midostaurin and control group, respectively, translating into a relapse-rate of 53% and 86%, respectively (p=0.19). No difference in early death rate was noted between the groups. The only factor that significantly affected overall survival in the COX-regression analysis was white blood cell count at diagnosis (p=0.03). Conclusions: In the off-trial setting, midostaurin is administered across all age groups and various FLT3-positive subtypes. In this 'real-life' setting, midostaurin is well tolerated and does not significantly add to the toxicity of chemotherapy. Longer follow-up and more patients are needed to assess the efficacy of adding midostaurin to chemotherapy in this group of patients. Figure 1. Figure 1. Disclosures Ofran: Novartis: Other: Served on a Novartis advisory board.

Description: Introduction: Skin eruptions in acute myeloid leukemia (AML) patients are not uncommon. Skin biopsy is a minimal invasive procedure, yet potential complications, such as infection and bleeding, might be expected in these patients due to immunosuppression and thrombocytopenia. Data are scarce regarding the prevalence, etiology and characteristics of skin eruptions among AML patients during intensive therapies. Even less is known regarding the safety and diagnostic yield of skin biopsies in this setting. We sought to evaluate the diagnostic yield and safety of skin biopsies obtained from adult AML patients during hospitalization for intensive chemotherapy. Methods: This is a single-center retrospective cohort study of adult AML patients who underwent skin biopsies for histopathology and tissue culture during induction and consolidation treatment for AML at our hemato-oncology unit between 1.1.2007-1.9.2018. Data collection included demographic details, AML characteristics, chemotherapy regimens, clinical description of rush and associated symptoms (mainly fever, pruritus) and laboratory tests. We recorded whether biopsy results had an impact on patients' care. This study was approved by the Institutional Review Board. Results: 37 skin biopsies from AML patients were identified in our cohort during the study period. Patient demographics and rash characteristics are presented in Table 1. 22% of the skin biopsies were performed at AML presentation prior to chemotherapy, and the remainder after chemotherapy commencement, i.e. after starting either induction or post-induction (consolidation or salvage) treatment (70% and 8%, respectively). Most skin eruptions were grade 1 (53%) or 2 (26%) in severity. Only 21% were grade 3 and 4 rashes. The most common body parts involved were the limbs (51%) and trunk (33%). At the time of skin biopsy 43% of patients had associated fever and 11% had bacteremia. Most patients (62%) had grade 4 neutropenia and 38% and 19% of patients had grade 3 and 4 thrombocytopenia, respectively. Elevated prothrombin time was evident in 66% of patients, whereas 5.5% of patients had an elevated partial thromboplastin time at the time of biopsy. Rash etiology according to skin biopsies histopathological findings consistent with drug eruptions (24.3%), infections (11%), leukemia cutis (16.2%), Sweet syndrome (5.5%) or a reactive process (8%). 35% of biopsies results were inconclusive. In 16 cases (43%) tissue cultures were performed and of those, 4 cultures were positive. However, only in 1 patient the positive culture result has led to a change of antimicrobial coverage. A proactive approach following biopsy results was conducted in 2 additional patients, when a suspected drug leading to the eruption was discontinued (n=1), and systemic steroids were prescribed instead of acyclovir (n=1). Hence, skin biopsy results changed patients' management only in 8% of cases (n=3). Skin biopsies were generally safe and only 1 patient suffered from a complication directly attributed to the biopsy - i.e. she became febrile and suffered from a local hemorrhagic bulla formation, necessitating administration of vancomycin. Conclusions: We suggest that skin biopsies from AML patients hospitalized for intensive chemotherapy treatment are relatively safe. Nevertheless, their diagnostic yield is limited and does not alter the management of most patients. Increased physician discretion should be exercised prior to performing a skin biopsy in this patient population, to avoid unnecessary usage of medical resources and invasive procedures. Further studies are needed to establish the role of skin biopsies in these patients. Disclosures Wolach: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Speaker; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Speaker.

Description: Introduction - Patients who experience relapse of acute myeloid leukemia or progress after exposure to hypomethylating agents (HMA's) have a dismal prognosis. Specifically, elderly patients lack effective salvage therapies in this setting. Venetoclax is a BCL-2 inhibitor that has shown substantial anti-leukemia activity in several early phase trials. We hypothesized that the addition of venetoclax to patients who previously failed HMA's might overcome resistance and improve outcome. Methods - Patients (≥18 years) were eligible if leukemia relapsed after or was refractory to HMA. In general, in addition to venetoclax, patients continued HMA's or other low intensity therapies. Patients who previously underwent allogeneic hematopoietic stem-cell transplantation (HSCT) were also eligible; however they did not continue HMA and received donor lymphocyte infusion in addition to venetoclax. Data were analyzed on June 2018. The following domains were analyzed for correlation with CR and duration of survival: % of blasts in marrow and peripheral blood, LDH levels, age, acute leukemia ELN subgroup at diagnosis, number of previous chemotherapy lines, number of previous episodes of progression and the dose of venetoclax given. We used logistic regression to analyze predictors for response and Cox regression to analyze predictors for survival. Results - Between October 2016 and March 2018 we treated 22 patients with acute myeloid leukemia that was refractory to HMA (azacitidine, n=20; decitabine, n=2). Median follow-up was 8.9 (range, 2.3-13.1) months. Table 1 depicts patients' characteristics. Median age was 76 (range, 41-92) years. Patients were given different doses of venetoclax (100mg, n=3; 200mg, n=9; 400 mg, n=8; 600mg, n=1; 800mg, n=1). After adjustment for concomitant medications (mainly azoles), only 2 patients were given less than the recommended 400 mg dose (both 200 mg). 17 patients (77%) developed at least one infectious episode. None experienced a major bleeding episode. Nine patients (41%) achieved CR. Median time to CR was 62 days (range, 28-102). High LDH levels and a lower venetoclax dose were associated with lower incidence of CR (OR=.882, p=.047, and OR=.93, p=.087, respectively). Four patients are in ongoing remission (5, 5.8, 7.1, and 11 months post venetoclax). Median overall survival was 5.5 months (95% CI 5.1-5.9) for the whole group, while for patients achieving CR, the median OS was 12.5 months (95% CI 6.6-18.3), Figure 1. The following factors were associated with shorter survival - higher percentage of blasts in marrow (HR-1.035, p=.013), higher LDH levels (HR-1.29, p=.022), and peripherally circulating blasts (HR-1.03, p=.01). For the subgroup of patients that relapsed after allogeneic HSCT (n=5), CR was achieved in 3 patients (60%) and the median OS was 12.4 months. 4/5 patients were given DLI in addition to venetoclax. One patient developed GVHD. Conclusions - the addition of venetoclax to patients with HMA-refractory AML may result in a substantial anti-leukemic activity, specifically in those achieving complete remission. This should be further tested in a well designed prospective trial. Disclosures Zuckerman: Cellect Biotherapeutics Ltd: Consultancy.

Description: Introduction - Acinetobacter baumannii is a Gram-negative strictly aerobic non-fermentative coccobacillus, widely distributed in nature. Multidrug resistant strains, including carbapenem antibiotic resistant, have been associated with fulminant severe sepsis and high overall mortality rate, ranging between 25 and 54%. This is true mainly for intensive care unit (ICU) and immunocompromised patients. Although CRAB bacteremia has previously been reported, studies involving hemato-oncological patients have rarely been reported. Aim - To investigate factors associated with 7 day mortality, defined as death within 7 days of documented bacteremia among hemato-oncological patients with CRAB bacteremia in a tertiary medical center in Israel. Methods - A retrospective analysis of all patients with CRAB bacteremia treated in a large tertiary care hospital January 2008 to June 2018 was performed. Among them, 46 hemato-oncological patients were identified and analyzed. Baseline patient and infection characteristics were collected from electronic medical records. In addition, antibiotic management and outcomes were documented. Univariable and multivariable analysis of risk factors for 7 day mortality were performed. Variables statistically significant in the univariable analysis were introduced into the regression model. Results - A total of 46 hemato-oncological patients with CARB bacteremia were included in this study. At the time that bacteremia occurred - 18 (39.5%) patients were hospitalized in internal medicine departments, 4 (8.7%) patients in ICU, 13 (28.3%) patients in the hemato-oncology ward and 11 (23.9%) patients in the stem cell transplantation ward. Mean age of patients was 62.5±16.8 yr., with 20 (43.5%) males. The mean length of stay before bacteremia occurrence was 29 ± 42.8 days. The presumed sources of bacteremia were respiratory tract (n = 25, 54.5%), vascular catheter (n = 14, 30.5%), urinary tract (n = 2, 4%), and other/unknown sources (n = 5, 11%). The susceptibility of CRAB to colistin was 100%, 7 isolates were susceptible to ampicillin/sulbactam and 4 of 38 tested were susceptible to tigecycline. The overall 7 day mortality in patients with CARB bacteremia was 71.7% (33/46), with an overall 30 day mortality of 93.4% (43/46). Univariable analysis showed that the significant risk factors for 7 day mortality in hemato-oncological patients with CARB bacteremia was higher Sepsis-related Organ Failure Assessment (SOFA) score (Survivors group - median score - 7, IQR 4-10.5, non-survivors group - median score- 13, IQR 10.5-16, p

Description: Introduction Patients with relapsed/refractory acute myeloid leukemia (AML) have a dismal prognosis. Achieving a remission with high-dose chemotherapy followed by allogeneic hematopoietic cell transplantation (alloHCT) remains the only curative approach. However, providing intensive salvage chemotherapy in order to obtain complete remission (CR) before alloHCT may be associated with significant morbidity that may preclude alloHCT. Furthermore, the lag period between the end of salvage chemotherapy and hematologic recovery may allow concomitant leukemic blast cell recovery. In attempt to solve this dilemma, Schmid et al. introduced in 2005 for the first time the sequential conditioning concept consisting of short course of chemotherapy to reduce the leukemic burden, followed shortly by RIC regimen. Aim Assess the feasibility of a transplantation strategy consisting of sequential cytoreductive chemotherapy with fludarabine, cytarabine, and idarubicin (FLAG-IDA) followed sequentially by tailored conditioning regimen and alloHCT (FLAG-IDA HCT) Methods A retrospective analysis of patients treated with the sequential FLAG-IDA HCT strategy in a single center between 01/2014 and 12/2017. Salvage chemotherapy consisted of fludarabine 30mg/m2 (days 1-5), cytarabine 2g/m2 (days 1-5) and idarubicin 12mg/m2 (days 3-5; FLAG-IDA). Dose reduction for cytarabine (1g/m2) and idarubicin (8-10mg/m2) were allowed for older patients and those with cardiac dysfunction, respectively. FLAG-IDA was followed within 3 days by conditioning regimen tailored according to the patient's clinical condition and co-morbidities. Graft versus host (GVHD) prophylaxis consisted of cyclosporine and short course of methotrexate (MTX). In patients with liver toxicity, renal failure, or grade 3-4 mucositis, MTX was replaced by mycophenolate mofetil. Antithymocyte globulin (ATG, Fresenius) was given to patients transplanted from unrelated and mismatched donors. Results 27 patients [median age, 64 years (range, 23 to 73) (3 patients 〉70 years)] received the sequential FLAG-IDA HCT regimen. Most (n=24) patients had AML followed by acute lymphoblastic leukemia, mixed phenotype acute leukemia and myelodysplastic syndrome (1 patient each). 52% (n=14) had primary refractory disease, 37% (n=10) had relapsed disease and 11% (n=3) were treated upfront for adverse-risk AML. All patients had active disease upon treatment initiation and 22% had more than 50% blasts in bone marrow (Table 1). Dose reduction of cytarabine and idarubicin were applied in 48% (n=13) and 26% (n=7) of the patients, respectively. A myeloablative conditioning (MAC), busulfex-based (n=3) or treosulfan-based (n=22), was applied in 25 patients (92%), and 11 (41%) received in-vivo T-cell depletion. 24 patients were transplanted from a matched sibling (n=12) or unrelated (n=12) donor and 3 from a mismatched donor, all but one from peripheral blood stem cell grafts. Median time to neutrophil and platelet engraftment was 12 (range, 8 to 26) and 14 (range, 8 to 68) days, respectively. Six patients (22%) died by day +30, all from infectious complications. Among 21 evaluable patients by day +30, 20 (95%) were in CR with full donor chimerism. With a median follow up of 19 (range, 6 to 52) months, 6 patients are still alive and in CR. Median 1-year OS was 206 days (Figure 1). In total, 21 (77%) patients died: 9 (33%) from relapse, 7 (26%) from infectious complications and 5 (19%) from other causes (acute GVHD, n=3, sarcoma, n=1, late idiopathic neurotoxicity, n=1). Infectious complications were frequent; 32 episodes of clinically documented infections were noted in 18 (67%) patients. These included 25 blood stream infections in 16 patients: bacteremia (n=17) and candidemia (n=3). Grade 2-4 acute GVHD and grade 3-4 acute GVHD by day +100 were documented in 48% and 30% of the patients, respectively. CONCLUSIONS FLAG-IDA HCT is a feasible strategy for relapsed/refractory acute leukemia patients that would have otherwise an extremely dismal prognosis. Yet, this regimen is associated with high early non-relapse mortality. Modifications of this regimen are warranted in order to reduce non-relapse mortality, without compromising the anti-leukemic effect. Disclosures No relevant conflicts of interest to declare.

Description: Background Acute myeloid leukemia (AML) blasts and leukemic stem and progenitor cells typically express higher levels of CD123 than their normal hematopoietic stem cell counterparts, making CD123 an attractive target. Leukemic CD123 expression is associated with poor prognosis, high-risk disease, and increased risk of induction failure (Vergez et al 2011). Single-agent flotetuzumab, an investigational CD123 x CD3 bispecific DART protein, has shown evidence of clinical activity in a Phase 1 study of relapsed/refractory (R/R) acute myeloid leukemia (AML). In this study, flotetuzumab led to T-cell activation which in turn was associated with PD-1 induction on T lymphocytes, enhanced IFNɣ secretion, and upregulation of PD-L1 expression by AML blasts (ASH 2018 Rutella, ASH 2018 Uy). In vitro studies have shown synergistic T-cell mediated cytotoxicity of an AML cell line (KG1A) with flotetuzumab in the presence of PD-1/PD-L1 axis blockade compared to flotetuzumab alone. MGA012, also known as INCMGA00012, is an investigational anti-PD-1 antibody that has shown clinical activity in a Phase 1 study (SITC 2018 Mehnert). We hypothesize that combined checkpoint inhibition with MGA012 together with redirected T‐cell killing of CD123+ cells with flotetuzumab may show enhanced activity over flotetuzumab alone. Methods This is a Phase 1 dose escalation study designed to characterize the safety, tolerability, dose-limiting toxicities, maximum tolerated dose (MTD) or maximum administered dose (if no MTD is defined), pharmacokinetics, and preliminary anti-leukemic activity of flotetuzumab in combination with MGA012, each administered intravenously (IV) in patients with R/R AML. Response evaluation will be determined by modified ELN 2017 criteria. Activity is measured by complete response (CR) (complete remission [CR], or CR with partial hematologic recovery [CRh], or CR with incomplete hematological recovery [CRi], or morphologic leukemia-free state [MLFS]) rate, relapse-free survival, or mortality rate at 1 and 3 months. The impact of flotetuzumab/MGA012 combination on overall survival and event-free survival will be explored. Eligible patients will consist of adults with relapsed or refractory AML (any subtype except acute promyelocytic leukemia) who have exhausted standard of care options. In Induction Cycle 1, patients will be treated with a step-up lead in dose of flotetuzumab, followed by continuous infusion flotetuzumab, starting at week 2 of Cycle 1 and continuing through each 28-day cycle. MGA012 will be administered every two weeks. Depending on response, patients will transition to either consolidation or second induction. Eligible patients who achieve CR/CRh/CRi can receive maintenance MGA012 alone for up to 12 months. Disclosures Wei: AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: AHW is a former employee of the Walter and Eliza Hall Institute and receives a fraction of its royalty stream related to venetoclax, Research Funding, Speakers Bureau; Astellas: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Macrogenics: Honoraria, Membership on an entity's Board of Directors or advisory committees; Genentech: Honoraria, Membership on an entity's Board of Directors or advisory committees; Servier: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astra Zeneca: Honoraria, Research Funding; Janssen: Honoraria. Fong:Novartis: Speakers Bureau; Amgen: Consultancy, Research Funding, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Astellas: Consultancy. Montesinos:Karyopharm: Membership on an entity's Board of Directors or advisory committees, Other: Research support; Janssen: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Research support, Speakers Bureau; Abbvie: Membership on an entity's Board of Directors or advisory committees; Teva: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau; Daiichi Sankyo: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Research support, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Research support, Research Funding, Speakers Bureau. Gil:Jazz Pharmaceuticals: Honoraria; Gilead: Honoraria; Daiichi-Sankyo: Honoraria; Novartis: Honoraria, Research Funding; Pfizer: Honoraria; Abbvie: Honoraria. Perez De Oteyza:Celgene: Speakers Bureau. Rowe:BioSight: Consultancy. Wolach:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Speaker; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Speaker. Sun:MacroGenics, Inc.: Employment, Equity Ownership. Baughman:MacroGenics, Inc.: Employment, Equity Ownership. McNulty:MacroGenics, Inc.: Employment, Equity Ownership. Bonvini:MacroGenics, Inc.: Employment, Equity Ownership. Wigginton:Western Oncolytics: Other: clinical advisory board; MacroGenics, Inc.: Employment, Equity Ownership. Davidson-Moncada:MacroGenics, Inc.: Employment, Equity Ownership.

Description: Mixed-phenotype acute leukemia (MPAL) encompasses a heterogeneous group of rare leukemias in which assigning a single lineage of origin is not possible. A variety of different terms and classification systems have been used historically to describe this entity. MPAL is currently defined by a limited set of lineage-specific markers proposed in the 2008 World Health Organization monograph on classification of tumors of hematopoietic and lymphoid tissues. In adult patients, MPAL is characterized by relative therapeutic resistance that may be attributed in part to the high proportion of patients with adverse cytogenetic abnormalities. No prospective, controlled trials exist to guide therapy. The limited available data suggest that an “acute lymphoblastic leukemia–like” regimen followed by allogeneic stem-cell transplant may be advisable; addition of a tyrosine kinase inhibitor in patients with t(9;22) translocation is recommended. The role of immunophenotypic and genetic markers in guiding chemotherapy choice and postremission strategy, as well as the utility of targeted therapies in non–Ph-positive MPALs is unknown.