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Human lymphopoiesis is a dynamic lifelong process that starts in utero 6 weeks postconception. Although fetal B-lymphopoiesis remains poorly defined, it is key to understanding leukemia initiation in early life. Here, we provide a comprehensive analysis of the human fetal B-cell developmental hierarchy. We report the presence in fetal tissues of 2 distinct CD19+ B-progenitors, an adult-type CD10+ve ProB-progenitor and a new CD10-ve PreProB-progenitor, and describe their molecular and functional characteristics. PreProB-progenitors and ProB-progenitors appear early in the first trimester in embryonic liver, followed by a sustained second wave of B-progenitor development in fetal bone marrow (BM), where together they form >40% of the total hematopoietic stem cell/progenitor pool. Almost one-third of fetal B-progenitors are CD10-ve PreProB-progenitors, whereas, by contrast, PreProB-progenitors are almost undetectable (0.53% ± 0.24%) in adult BM. Single-cell transcriptomics and functional assays place fetal PreProB-progenitors upstream of ProB-progenitors, identifying them as the first B-lymphoid–restricted progenitor in human fetal life. Although fetal BM PreProB-progenitors and ProB-progenitors both give rise solely to B-lineage cells, they are transcriptionally distinct. As with their fetal counterparts, adult BM PreProB-progenitors give rise only to B-lineage cells in vitro and express the expected B-lineage gene expression program. However, fetal PreProB-progenitors display a distinct, ontogeny-related gene expression pattern that is not seen in adult PreProB-progenitors, and they share transcriptomic signatures with CD10-ve B-progenitor infant acute lymphoblastic leukemia blast cells. These data identify PreProB-progenitors as the earliest B-lymphoid–restricted progenitor in human fetal life and suggest that this fetal-restricted committed B-progenitor might provide a permissive cellular context for prenatal B-progenitor leukemia initiation.

Human lymphopoiesis is a dynamic lifelong process that starts in utero 6 weeks postconception. Although fetal B-lymphopoiesis remains poorly defined, it is key to understanding leukemia initiation in early life. Here, we provide a comprehensive analysis of the human fetal B-cell developmental hierarchy. We report the presence in fetal tissues of 2 distinct CD19+B-progenitors, an adult-type CD10+ve ProB-progenitor and a new CD10-ve PreProB-progenitor, and describe their molecular and functional characteristics. PreProB-progenitors and ProB-progenitors appear early in the first trimester in embryonic liver, followed by a sustained second wave of B-progenitor development in fetal bone marrow (BM), where together they form >40% of the total hematopoietic stem cell/progenitor pool. Almost one-third of fetal B-progenitors are CD10-ve PreProB-progenitors, whereas, by contrast, PreProB-progenitors are almost undetectable (0.53% ± 0.24%) in adult BM. Single-cell transcriptomics and functional assays place fetal PreProB-progenitors upstream of ProB-progenitors, identifying them as the first B-lymphoid–restricted progenitor in human fetal life. Although fetal BM PreProB-progenitors and ProB-progenitors both give rise solely to B-lineage cells, they are transcriptionally distinct. As with their fetal counterparts, adult BM PreProB-progenitors give rise only to B-lineage cells in vitro and express the expected B-lineage gene expression program. However, fetal PreProB-progenitors display a distinct, ontogeny-related gene expression pattern that is not seen in adult PreProB-progenitors, and they share transcriptomic signatures with CD10-ve B-progenitor infant acute lymphoblastic leukemia blast cells. These data identify PreProB-progenitors as the earliest B-lymphoid–restricted progenitor in human fetal life and suggest that this fetal-restricted committed B-progenitor might provide a permissive cellular context for prenatal B-progenitor leukemia initiation.

Disease relapse is the major cause of treatment failure after allogeneic stem cell transplantation (allo-SCT) in acute myeloid leukemia (AML). To identify AML-associated genes prognostic of AML relapse post–allo-SCT, we resequenced 35 genes in 113 adults at diagnosis, 49 of whom relapsed. Two hundred sixty-two mutations were detected in 102/113 (90%) patients. An increased risk of relapse was observed in patients with mutations in WT1(P= .018), DNMT3A(P= .045), FLT3 ITD(P= .071), and TP53(P= .06), whereas mutations in IDH1were associated with a reduced risk of disease relapse (P= .018). In 29 patients, we additionally compared mutational profiles in bone marrow at diagnosis and relapse to study changes in clonal structure at relapse. In 13/29 patients, mutational profiles altered at relapse. In 9 patients, mutations present at relapse were not detected at diagnosis. In 15 patients, additional available pre–allo-SCT samples demonstrated that mutations identified posttransplant but not at diagnosis were detectable immediately prior to transplant in 2 of 15 patients. Taken together, these observations, if confirmed in larger studies, have the potential to inform the design of novel strategies to reduce posttransplant relapse highlighting the potential importance of post–allo-SCT interventions with a broad antitumor specificity in contrast to targeted therapies based on mutational profile at diagnosis.

Disease relapse is the major cause of treatment failure after allogeneic stem cell transplantation (allo-SCT) in acute myeloid leukemia (AML). To identify AML-associated genes prognostic of AML relapse post–allo-SCT, we resequenced 35 genes in 113 adults at diagnosis, 49 of whom relapsed. Two hundred sixty-two mutations were detected in 102/113 (90%) patients. An increased risk of relapse was observed in patients with mutations in WT1 (P = .018), DNMT3A (P = .045), FLT3 ITD (P = .071), and TP53 (P = .06), whereas mutations in IDH1 were associated with a reduced risk of disease relapse (P = .018). In 29 patients, we additionally compared mutational profiles in bone marrow at diagnosis and relapse to study changes in clonal structure at relapse. In 13/29 patients, mutational profiles altered at relapse. In 9 patients, mutations present at relapse were not detected at diagnosis. In 15 patients, additional available pre–allo-SCT samples demonstrated that mutations identified posttransplant but not at diagnosis were detectable immediately prior to transplant in 2 of 15 patients. Taken together, these observations, if confirmed in larger studies, have the potential to inform the design of novel strategies to reduce posttransplant relapse highlighting the potential importance of post–allo-SCT interventions with a broad antitumor specificity in contrast to targeted therapies based on mutational profile at diagnosis.

Our understanding of the perturbation of normal cellular differentiation hierarchies to create tumor-propagating stem cell populations is incomplete. In human acute myeloid leukemia (AML), current models suggest transformation creates leukemic stem cell (LSC) populations arrested at a progenitor-like stage expressing cell surface CD34. We show that in ∼25% of AML, with a distinct genetic mutation pattern where >98% of cells are CD34−, there are multiple, nonhierarchically arranged CD34+ and CD34− LSC populations. Within CD34− and CD34+ LSC–containing populations, LSC frequencies are similar; there are shared clonal structures and near-identical transcriptional signatures. CD34− LSCs have disordered global transcription profiles, but these profiles are enriched for transcriptional signatures of normal CD34− mature granulocyte–macrophage precursors, downstream of progenitors. But unlike mature precursors, LSCs express multiple normal stem cell transcriptional regulators previously implicated in LSC function. This suggests a new refined model of the relationship between LSCs and normal hemopoiesis in which the nature of genetic/epigenetic changes determines the disordered transcriptional program, resulting in LSC differentiation arrest at stages that are most like either progenitor or precursor stages of hemopoiesis.

Abstract:Through a close reading of several short stories by George Saunders, including “Pastoralia” and “The Semplica Girl Diaries,” this essay reconsiders the uses of pastoral to the representation of precarious work arrangements and a critique of neoliberal ideology. Rooted in the poetry of ancient Greece and Rome, the pastoral literary tradition celebrates the life of rural simplicity and repose, especially as contrasted with courtly sophistication and/or statecraft. Although such basic markers of the pastoral style as idyllic landscape, leisurely atmosphere, and the presence of a rustic country figure would seem frankly to be remote from our contemporary moment (where post-industrial settings exhibit no easy distinction between urban and rural living and technological reach precludes removal from the business of civil society), I argue that for Saunders pastoral is an aesthetic system especially suited to the project of capturing life in a post-globalization world, and the changing nature of the work that sustains it.

Graft-versus-host disease (GVHD) is a significant cause of morbidity and mortality following allogenic haematopoietic stem-cell transplantation and thus the focus of much ongoing research. Despite considerable advances in our understanding of the pathophysiology, diagnosis and predisposing factors for both acute and chronic forms of the disease, a standardised therapeutic strategy is still lacking. There is good evidence for initial treatment of both acute and chronic forms of the disease with corticosteroid therapy. However, the most effective approach to steroid-refractory disease remains controversial, with current practice based mainly on smaller studies and varying considerably between local institutions. Timely diagnosis, multidisciplinary working and good supportive care, including infection prophylaxis, are clearly important in optimizing response and survival in such patients. It is hoped that in the future systematic research strategies and the identification of novel therapeutic targets may improve outcome further. The following review aims to outline some of the existing options for the treatment and management of acute and chronic GVHD.

Children with Down syndrome (DS) up to the age of 4 years are at a 150-fold excess risk of developing myeloid leukemia (ML-DS). Approximately 4%-5% of newborns with DS develop transient myeloproliferative disorder (TMD). Blast cell structure and immunophenotype are similar in TMD and ML-DS. A mutation in the hematopoietic transcription factor GATA1is present in almost all cases. Here, we show that simple techniques detect GATA1mutations in the largest series of TMD (n = 134; 88%) and ML-DS (n = 103; 85%) cases tested. Furthermore, no significant difference in the mutational spectrum between the 2 disorders was seen. Thus, the type of GATA1sequence mutation is not a reliable tool and is not prognostic of which patients with TMD are probable to develop ML-DS.

Children with Down syndrome (DS) up to the age of 4 years are at a 150-fold excess risk of developing myeloid leukemia (ML-DS). Approximately 4%-5% of newborns with DS develop transient myeloproliferative disorder (TMD). Blast cell structure and immunophenotype are similar in TMD and ML-DS. A mutation in the hematopoietic transcription factor GATA1 is present in almost all cases. Here, we show that simple techniques detect GATA1 mutations in the largest series of TMD (n = 134; 88%) and ML-DS (n = 103; 85%) cases tested. Furthermore, no significant difference in the mutational spectrum between the 2 disorders was seen. Thus, the type of GATA1 sequence mutation is not a reliable tool and is not prognostic of which patients with TMD are probable to develop ML-DS.

Myeloid leukemia of Down syndrome (ML-DS) is a tractable human model of acute myeloid leukemia. A preleukemia phase, transient abnormal myelopoiesis (TAM) and silent TAM, occurs in 28% of neonates with Down Syndrome (Roberts et al. Blood 2013). TAM is caused by trisomy 21 and acquired mutations in GATA1that result in a N-terminal truncated protein, GATA1s, in hematopoietic stem and progenitor cells (HSPCs) of fetal origin. ML-DS evolves from TAM by acquisition of additional genetic lesions. The nature of these lesions and the mechanism of transformation are incompletely understood.

Crispino: Scholar Rock: Research Funding; Forma Therapeutics: Research Funding.

Neonates and children with Down Syndrome (DS), with constitutional Trisomy 21 (T21), have a 150-fold increased risk of developing Myeloid Leukaemia (ML-DS), with differentiation arrest of immature megakaryocyte-erythroid cells. Virtually all ML-DS patients have in utero-acquired somatic mutations in the gene encoding the megakaryocyte-erythroid transcription factor GATA1 leading to the production of an 84 amino acid N-terminal truncated form of the GATA1 protein (GATA1s). We, and others, have previously shown that this N-terminal domain is necessary to prevent excessive megakaryocytic proliferation. However, the mechanisms by which GATA1, but not GATA1s, restrains megakaryocyte proliferation are unclear.

Children with Down syndrome (DS) have a high risk of developing a unique form of AML known as myeloid leukaemia of DS (ML-DS) defined by the presence of one or more acquired N-terminal truncating mutations in the hematopoietic transcription factor gene GATA1. ML-DS is confined to children <4 y of age and preceded by a neonatal preleukemic syndrome, Transient Abnormal Myelopoiesis (TAM). Although the same GATA1mutations are present in ML-DS and TAM, indicating they are clonally-linked disorders, chemotherapy is essential to cure ML-DS whereas most cases of TAM spontaneously resolve without treatment.

No relevant conflicts of interest to declare.

Lack of progress in curing AML is likely, in part, to be due to the genetic and functional heterogeneity of AML. ~13 Tier 1 mutations occur per patient sample arrayed in 2-5 clones (CGARN, N Engl J Med, 2013). Not all AML cell populations may be equally chemosensitive; for example, leukemia-propagating leukemic stem cells (LSC) are more chemoresistant. (Ishikawa et al., Nat Biotechnol, 2007). Additionally, the impact of genetic heterogeneity on LSC function is unclear.

No relevant conflicts of interest to declare.

No relevant conflicts of interest to declare.

Abstract 4548

Abstract 4554