Andre C. Schuh

A Requirement for Flk1 in Primitive and Definitive Hematopoiesis and Vasculogenesis

Mouse embryos lacking the receptor tyrosine kinase, Flk1, die without mature endothelial and hematopoietic cells. To investigate the role of Flk1 during vasculogenesis and hematopoiesis, we examined the developmental potential of Flk1-/- embryonic stem cells in chimeras. We show that Flk1 is required cell autonomously for endothelial development. Furthermore, Flk1-/- cells do not contribute to primitive hematopoiesis in chimeric yolk sacs or definitive hematopoiesis in adult chimeras and chimeric fetal livers. We also demonstrate that cells lacking Flk1 are unable to reach the correct location to form blood islands, suggesting that Flk1 is involved in the movement of cells from the posterior primitive streak to the yolk sac and, possibly, to the intraembryonic sites of early hematopoiesis.

International phase 3 study of azacitidine vs conventional care regimens in older patients with newly diagnosed AML with >30% blasts

This multicenter, randomized, open-label, phase 3 trial evaluated azacitidine efficacy and safety vs conventional care regimens (CCRs) in 488 patients age ≥65 years with newly diagnosed acute myeloid leukemia (AML) with >30% bone marrow blasts. Before randomization, a CCR (standard induction chemotherapy, low-dose ara-c, or supportive care only) was preselected for each patient. Patients then were assigned 1:1 to azacitidine (n = 241) or CCR (n = 247). Patients assigned to CCR received their preselected treatment. Median overall survival (OS) was increased with azacitidine vs CCR: 10.4 months (95% confidence interval [CI], 8.0-12.7 months) vs 6.5 months (95% CI, 5.0-8.6 months), respectively (hazard ratio [HR] was 0.85; 95% CI, 0.69-1.03; stratified log-rank P = .1009). One-year survival rates with azacitidine and CCR were 46.5% and 34.2%, respectively (difference, 12.3%; 95% CI, 3.5%-21.0%). A prespecified analysis censoring patients who received AML treatment after discontinuing study drug showed median OS with azacitidine vs CCR was 12.1 months (95% CI, 9.2-14.2 months) vs 6.9 months (95% CI, 5.1-9.6 months; HR, 0.76; 95% CI, 0.60-0.96; stratified log-rank P = .0190). Univariate analysis showed favorable trends for azacitidine compared with CCR across all subgroups defined by baseline demographic and disease features. Adverse events were consistent with the well-established safety profile of azacitidine. Azacitidine may be an important treatment option for this difficult-to-treat AML population. This trial was registered at www.clinicaltrials.gov as #NCT01074047.

Blinatumomab versus Chemotherapy for Advanced Acute Lymphoblastic Leukemia

Background Blinatumomab, a bispecific monoclonal antibody construct that enables CD3‐positive T cells to recognize and eliminate CD19‐positive acute lymphoblastic leukemia (ALL) blasts, was approved for use in patients with relapsed or refractory B‐cell precursor ALL on the basis of single‐group trials that showed efficacy and manageable toxic effects. Methods In this multi‐institutional phase 3 trial, we randomly assigned adults with heavily pretreated B‐cell precursor ALL, in a 2:1 ratio, to receive either blinatumomab or standard‐of‐care chemotherapy. The primary end point was overall survival. Results Of the 405 patients who were randomly assigned to receive blinatumomab (271 patients) or chemotherapy (134 patients), 376 patients received at least one dose. Overall survival was significantly longer in the blinatumomab group than in the chemotherapy group. The median overall survival was 7.7 months in the blinatumomab group and 4.0 months in the chemotherapy group (hazard ratio for death with blinatumomab vs. chemotherapy, 0.71; 95% confidence interval [CI], 0.55 to 0.93; P=0.01). Remission rates within 12 weeks after treatment initiation were significantly higher in the blinatumomab group than in the chemotherapy group, both with respect to complete remission with full hematologic recovery (34% vs. 16%, P<0.001) and with respect to complete remission with full, partial, or incomplete hematologic recovery (44% vs. 25%, P<0.001). Treatment with blinatumomab resulted in a higher rate of event‐free survival than that with chemotherapy (6‐month estimates, 31% vs. 12%; hazard ratio for an event of relapse after achieving a complete remission with full, partial, or incomplete hematologic recovery, or death, 0.55; 95% CI, 0.43 to 0.71; P<0.001), as well as a longer median duration of remission (7.3 vs. 4.6 months). A total of 24% of the patients in each treatment group underwent allogeneic stem‐cell transplantation. Adverse events of grade 3 or higher were reported in 87% of the patients in the blinatumomab group and in 92% of the patients in the chemotherapy group. Conclusions Treatment with blinatumomab resulted in significantly longer overall survival than chemotherapy among adult patients with relapsed or refractory B‐cell precursor ALL. (Funded by Amgen; TOWER ClinicalTrials.gov number, NCT02013167.)

A phase i study of the pan bcl-2FamilyInhibitor obatoclax mesylate in patients with advanced hematologic malignancies

Purpose: The outcome of patients with refractory leukemia and myelodysplasia is poor, and new therapies are needed. The antiapoptotic proteins of the Bcl-2 family are overexpressed in these malignancies and are potential therapeutic targets. Therefore, we conducted a phase I clinical trial of the small-molecule pan-Bcl-2 inhibitor, obatoclax mesylate, in patients with refractory leukemia and myelodysplasia to assess its safety and define its optimal dose. Experimental Design: Forty-four patients with refractory leukemia or myelodysplasia were treated with obatoclax mesylate by continuous intravenous infusion at increasing doses and frequencies. Results: A total of 306 infusions of obatoclax mesylate were administered with a median of 5 infusions per patient. The study drug was well tolerated up to the highest dose planned without dose-limiting toxicity. Grade 1/2 central nervous system symptoms were the most common adverse events attributable to the study drug. One patient with acute myeloid leukemia with mixed lineage leukemia t(9;11) rearrangement achieved a complete remission, which lasted 8 months. Three of 14 patients with myelodysplasia showed hematologic improvement with RBC or platelet transfusion independence. Conclusions: Obatoclax mesylate is well tolerated and these results support its further investigation in patients with leukemia and myelodysplasia.

A 17-gene stemness score for rapid determination of risk in acute leukaemia.

Refractoriness to induction chemotherapy and relapse after achievement of remission are the main obstacles to cure in acute myeloid leukaemia (AML). After standard induction chemotherapy, patients are assigned to different post-remission strategies on the basis of cytogenetic and molecular abnormalities that broadly define adverse, intermediate and favourable risk categories. However, some patients do not respond to induction therapy and another subset will eventually relapse despite the lack of adverse risk factors. There is an urgent need for better biomarkers to identify these high-risk patients before starting induction chemotherapy, to enable testing of alternative induction strategies in clinical trials. The high rate of relapse in AML has been attributed to the persistence of leukaemia stem cells (LSCs), which possess a number of stem cell properties, including quiescence, that are linked to therapy resistance. Here, to develop predictive and/or prognostic biomarkers related to stemness, we generated a list of genes that are differentially expressed between 138 LSC+ and 89 LSC− cell fractions from 78 AML patients validated by xenotransplantation. To extract the core transcriptional components of stemness relevant to clinical outcomes, we performed sparse regression analysis of LSC gene expression against survival in a large training cohort, generating a 17-gene LSC score (LSC17). The LSC17 score was highly prognostic in five independent cohorts comprising patients of diverse AML subtypes (n = 908) and contributed greatly to accurate prediction of initial therapy resistance. Patients with high LSC17 scores had poor outcomes with current treatments including allogeneic stem cell transplantation. The LSC17 score provides clinicians with a rapid and powerful tool to identify AML patients who do not benefit from standard therapy and who should be enrolled in trials evaluating novel upfront or post-remission strategies.

Disease biology rather than age is the most important determinant of survival of patients ≥ 60 years with acute myeloid leukemia treated with uniform intensive therapy

The objectives of the current study were to evaluate the outcome of patients ≥ 60 years with acute myeloid leukemia (AML) treated uniformly with high‐dose daunorubicin containing induction and modified high‐dose cytosine arabinoside containing postremission therapy, and to identify factors predictive of complete disease remission (CR) and survival.

A pilot randomized trial of adjuvant rituximab or placebo for nonsplenectomized patients with immune thrombocytopenia

The benefit of adding rituximab to standard treatment in nonsplenectomized patients with primary immune thrombocytopenia (ITP) is uncertain. We performed a pilot randomized trial to determine the feasibility of recruitment, protocol adherence, and blinding of a larger trial of rituximab versus placebo; and to evaluate the potential efficacy of adjuvant rituximab in ITP. Nonsplenectomized adults with newly diagnosed or relapsed ITP who were receiving standard ITP therapy for a platelet count below 30 × 10(9)/L were randomly allocated to receive 4 weekly infusions of 375 mg/m(2) rituximab or saline placebo. Sixty patients were recruited over 46 months, which was slower than anticipated. Protocol adherence and follow-up targets were achieved, and blinding was successful for research staff but not for patients. After 6 months, there was no difference between rituximab and placebo groups for the composite outcome of any platelet count below 50 × 10(9)/L, significant bleeding or rescue treatment once standard treatment was stopped (21/32 [65.6%] vs 21/26 [80.8%]; relative risk = 0.81, 95% confidence intervals, 0.59%-1.11%). Timely accrual poses a challenge to the conduct of a large randomized trial of rituximab for presplenectomy ITP. No difference in the frequency of the composite outcome was observed in this pilot trial (registered at www.clinicaltrials.gov NCT00372892).

CD109 is expressed on a subpopulation of CD34+ cells enriched in hematopoietic stem and progenitor cells

CD109 is a monomeric cell surface glycoprotein of 170 kD that is expressed on endothelial cells, activated but not resting T-lymphocytes, activated but not resting platelets, leukemic megakaryoblasts, and a subpopulation of bone marrow CD34+ cells. Observing an apparent association between CD109 expression and the megakaryocyte lineage (MK), we sought to determine whether CD109 was expressed on MK progenitors. In fetal bone marrow (FBM), a rich source of MK progenitors, CD109 is expressed on a mean of 11% of CD34- cells. Fluorescence activated cell sorting (FACS) of FBM CD34+ cells into CD109+ and CD109- fractions revealed that the CD34+CD109+ subset contained virtually all assayable MK progenitors, including the colony-forming unit-MK (CFU-MK) and the more primitive burst-forming unit-MK (BFU-MK). The CD34+CD109+ subset also contained all the assayable burst-forming units-erythroid (BFU-E), 90% of the colony-forming units-granulocyte/macrophage (CFU-GM), and all of the more primitive mixed lineage colony-forming units (CFU-mix). In contrast, phenotypic analysis of the CD34+CD109- cells in FBM, adult bone marrow (ABM) and cytokine-mobilized peripheral blood (MPB) demonstrated that this subset comprises lymphoid-committed progenitors, predominantly of the B-cell lineage. CD109 was expressed on the brightest CD34 cells identifiable not only in FBM, but also in ABM and MPB indicating that the most primitive, candidate hematopoietic stem cells (HSC) might also be contained in the CD109+ subset. In long-term marrow cultures of FBM CD34+ cells, all assayable cobblestone area forming cell (CAFC) activity was contained within the CD109+ cell subset. Further phenotypic analysis of the CD34+CD109+ fraction in ABM indicated that this subset included candidate HSCs that stain poorly with CD38, but express Thy-1 (CD90) and AC133 antigens, and efflux the mitochondrial dye Rhodamine 123 (Rho123). When selected CD34+ cells were sorted for CD109 expression and Rho123 staining, virtually all CAFC activity was found in the CD109+ fraction that stained most poorly with Rho123. CD34+ cells were also sorted into Thy-1 CD109+ and Thy-1 CD109+ fractions and virtually all the CAFC activity was found in the Thy-1+CD109+ subset. In contrast, the Thy-1-CD109+ fraction contained most of the short-term colony-forming cell (CFC) activity. CD109, therefore, is an antigen expressed on a subset of CD34+ cells that includes pluripotent HSCs as well as all classes of MK and myelo-erythroid progenitors. In combination with Thy-1, CD109 can be used to identify and separate myelo-erythroid and all classes of MK progenitors from candidate HSCs.

Treatment outcomes following leukemic transformation in Philadelphia-negative myeloproliferative neoplasms

Leukemic transformation (LT) is a rare but fatal complication of Philadelphia-negative myeloproliferative neoplasms (MPNs) for which optimal treatment strategies are not known. At our center, we have adopted a treatment approach for LT where patients within the transplant age group who have a reasonable fitness level are treated with curative intent and offered induction chemotherapy. Subsequently, those who respond and have a suitable donor are considered for allogeneic hematopoietic cell transplantation (HCT). In this study, we evaluated the clinical outcomes of this treatment approach in 75 patients with LT. The 2-year overall survival (OS) from the time of LT was 15%. A total of 39 patients (52%) were treated with curative intent (induction ± HCT) and had a 2-y OS of 26% compared with 3% in those noncuratively treated (P < .0001). In the curative intent group, 18 individuals (46%) achieved complete remission (CR) or CR with incomplete recovery and 12 (31%) reverted to a chronic MPN phase, with 17 patients undergoing HCT. Survival of patients posttransplant was significantly improved compared with those who responded to induction but were not transplanted (2-y OS of 47% vs 15%; P = .03). Thus, induction chemotherapy followed by HCT has the potential for long-term disease control in select patients with LT preceded by a MPN.

Influence of FLT3-Internal Tandem Duplication Allele Burden and White Blood Cell Count on the Outcome in Patients With Intermediate-Risk Karyotype Acute Myeloid Leukemia

In patients with acute myeloid leukemia (AML), testing for fms‐like tyrosine kinase‐3 (FLT3)–internal tandem duplication (FLT3‐ITD) and nucleophosmin‐1 (NPM1) mutations can allow for further prognostic subclassification, but less is known about the effects of FLT3‐ITD allele burden and presenting white blood cell count (WBC) within molecular subgroups.