Prof Adam Mead MRCP FRCPath

Research Area: Developmental and Stem Cell Biology
Technology Exchange: Biobanking, Cell sorting, Flow cytometry and Transcript profiling
Scientific Themes: Haematology and Developmental Biology & Stem Cells
Keywords: Leukaemia stem cells, Targeted therapies and Myeloid disorders
Web Links:

The major focus of our research programme is towards the identification and genetic modelling of leukaemic and pre-leukaemic stem cells in myeloid malignancies. The aim is to identify the cellular and molecular biology of these key populations of cells which are capable of propagating disease relapse in patients and to understand how these cells might be more effectively targeted and eradicated. In order to achieve this, our research programme is focused on understanding the normal cellular origin of leukaemic stem cells, and to thereby identify the perturbed molecular pathways which result in the generation of preleukaemic clones, and eventually malignant transformation. There are 3 related approaches in this regard:

1. The development of genetically engineered leukaemia models to study the impact of specific mutation(s) on the establishment, evolution and propagation of leukaemic stem cells.

2. The study of leukaemia stem cells in patients with myeloid malignancies throughout their disease course, in order to understand the impact of novel targeted therapies and also to understand the cellular origins of clonal evolution, resistance to therapy and transformation to more aggressive forms of disease. These studies necessitate state of the art single-cell whole-transcriptome analysis of single blood cancer stem cells, a technique which has been established by our group.

3. To understand the clinical and biological consequences of germline genetic abnormalities in humans which predispose to the development of myeloid malignancies later in life.

Name Department Institution Country
Prof Sten Eirik W Jacobsen Nuffield Division of Clinical Laboratory Sciences Oxford University, Weatherall Institute of Molecular Medicine United Kingdom
Prof Paresh Vyas MRCP FRCP FRCPath Nuffield Division of Clinical Laboratory Sciences Oxford University, Weatherall Institute of Molecular Medicine United Kingdom
Prof Claus Nerlov Nuffield Division of Clinical Laboratory Sciences Oxford University, Weatherall Institute of Molecular Medicine United Kingdom
Professor Christopher Yau Wellcome Trust Centre for Human Genetics Oxford University, Henry Wellcome Building of Genomic Medicine United Kingdom
Loughran SJ, Comoglio F, Hamey FK, Giustacchini A, Errami Y, Earp E, Göttgens B, Jacobsen SEW, Mead AJ, Hendrich B, Green AR. 2017. Mbd3/NuRD controls lymphoid cell fate and inhibits tumorigenesis by repressing a B cell transcriptional program. J Exp Med, 214 (10), pp. 3085-3104. | Show Abstract | Read more

Differentiation of lineage-committed cells from multipotent progenitors requires the establishment of accessible chromatin at lineage-specific transcriptional enhancers and promoters, which is mediated by pioneer transcription factors that recruit activating chromatin remodeling complexes. Here we show that the Mbd3/nucleosome remodeling and deacetylation (NuRD) chromatin remodeling complex opposes this transcriptional pioneering during B cell programming of multipotent lymphoid progenitors by restricting chromatin accessibility at B cell enhancers and promoters. Mbd3/NuRD-deficient lymphoid progenitors therefore prematurely activate a B cell transcriptional program and are biased toward overproduction of pro-B cells at the expense of T cell progenitors. The striking reduction in early thymic T cell progenitors results in compensatory hyperproliferation of immature thymocytes and development of T cell lymphoma. Our results reveal that Mbd3/NuRD can regulate multilineage differentiation by constraining the activation of dormant lineage-specific enhancers and promoters. In this way, Mbd3/NuRD protects the multipotency of lymphoid progenitors, preventing B cell-programming transcription factors from prematurely enacting lineage commitment. Mbd3/NuRD therefore controls the fate of lymphoid progenitors, ensuring appropriate production of lineage-committed progeny and suppressing tumor formation.

Harrison CN, Mead AJ, Panchal A, Fox S, Yap C, Gbandi E, Houlton A, Alimam S, Ewing J, Wood M et al. 2017. Ruxolitinib vs best available therapy for ET intolerant or resistant to hydroxycarbamide. Blood, 130 (17), pp. 1889-1897. | Show Abstract | Read more

Treatments for high-risk essential thrombocythemia (ET) address thrombocytosis, disease-related symptoms, as well as risks of thrombosis, hemorrhage, transformation to myelofibrosis, and leukemia. Patients resistant/intolerant to hydroxycarbamide (HC) have a poor outlook. MAJIC (ISRCTN61925716) is a randomized phase 2 trial of ruxolitinib (JAK1/2 inhibitor) vs best available therapy (BAT) in ET and polycythemia vera patients resistant or intolerant to HC. Here, findings of MAJIC-ET are reported, where the modified intention-to-treat population included 58 and 52 patients randomized to receive ruxolitinib or BAT, respectively. There was no evidence of improvement in complete response within 1 year reported in 27 (46.6%) patients treated with ruxolitinib vs 23 (44.2%) with BAT (P = .40). At 2 years, rates of thrombosis, hemorrhage, and transformation were not significantly different; however, some disease-related symptoms improved in patients receiving ruxolitinib relative to BAT. Molecular responses were uncommon; there were 2 complete molecular responses (CMR) and 1 partial molecular response in CALR-positive ruxolitinib-treated patients. Transformation to myelofibrosis occurred in 1 CMR patient, presumably because of the emergence of a different clone, raising questions about the relevance of CMR in ET patients. Grade 3 and 4 anemia occurred in 19% and 0% of ruxolitinib vs 0% (both grades) in the BAT arm, and grade 3 and 4 thrombocytopenia in 5.2% and 1.7% of ruxolitinib vs 0% (both grades) of BAT-treated patients. Rates of discontinuation or treatment switching did not differ between the 2 trial arms. The MAJIC-ET trial suggests that ruxolitinib is not superior to current second-line treatments for ET. This trial was registered at www.isrctn.com as #ISRCTN61925716.

Povinelli BJ, Rodriguez-Meira A, Mead AJ. 2017. Single cell analysis of normal and leukemic hematopoiesis. Mol Aspects Med, | Show Abstract | Read more

The hematopoietic system is well established as a paradigm for the study of cellular hierarchies, their disruption in disease and therapeutic use in regenerative medicine. Traditional approaches to study hematopoiesis involve purification of cell populations based on a small number of surface markers. However, such population-based analysis obscures underlying heterogeneity contained within any phenotypically defined cell population. This heterogeneity can only be resolved through single cell analysis. Recent advances in single cell techniques allow analysis of the genome, transcriptome, epigenome and proteome in single cells at an unprecedented scale. The application of these new single cell methods to investigate the hematopoietic system has led to paradigm shifts in our understanding of cellular heterogeneity in hematopoiesis and how this is disrupted in disease. In this review, we summarize how single cell techniques have been applied to the analysis of hematopoietic stem/progenitor cells in normal and malignant hematopoiesis, with a particular focus on recent advances in single-cell genomics, including how these might be utilized for clinical application.

Mead AJ, Neo WH, Barkas N, Matsuoka S, Giustacchini A, Facchini R, Thongjuea S, Jamieson L, Booth CAG, Fordham N et al. 2017. Niche-mediated depletion of the normal hematopoietic stem cell reservoir by Flt3-ITD-induced myeloproliferation. J Exp Med, 214 (7), pp. 2005-2021. | Show Abstract | Read more

Although previous studies suggested that the expression of FMS-like tyrosine kinase 3 (Flt3) initiates downstream of mouse hematopoietic stem cells (HSCs), FLT3 internal tandem duplications (FLT3 ITDs) have recently been suggested to intrinsically suppress HSCs. Herein, single-cell interrogation found Flt3 mRNA expression to be absent in the large majority of phenotypic HSCs, with a strong negative correlation between Flt3 and HSC-associated gene expression. Flt3-ITD knock-in mice showed reduced numbers of phenotypic HSCs, with an even more severe loss of long-term repopulating HSCs, likely reflecting the presence of non-HSCs within the phenotypic HSC compartment. Competitive transplantation experiments established that Flt3-ITD compromises HSCs through an extrinsically mediated mechanism of disrupting HSC-supporting bone marrow stromal cells, with reduced numbers of endothelial and mesenchymal stromal cells showing increased inflammation-associated gene expression. Tumor necrosis factor (TNF), a cell-extrinsic potent negative regulator of HSCs, was overexpressed in bone marrow niche cells from FLT3-ITD mice, and anti-TNF treatment partially rescued the HSC phenotype. These findings, which establish that Flt3-ITD-driven myeloproliferation results in cell-extrinsic suppression of the normal HSC reservoir, are of relevance for several aspects of acute myeloid leukemia biology.

Giustacchini A, Thongjuea S, Barkas N, Woll PS, Povinelli BJ, Booth CAG, Sopp P, Norfo R, Rodriguez-Meira A, Ashley N et al. 2017. Single-cell transcriptomics uncovers distinct molecular signatures of stem cells in chronic myeloid leukemia. Nat Med, 23 (6), pp. 692-702. | Show Abstract | Read more

Recent advances in single-cell transcriptomics are ideally placed to unravel intratumoral heterogeneity and selective resistance of cancer stem cell (SC) subpopulations to molecularly targeted cancer therapies. However, current single-cell RNA-sequencing approaches lack the sensitivity required to reliably detect somatic mutations. We developed a method that combines high-sensitivity mutation detection with whole-transcriptome analysis of the same single cell. We applied this technique to analyze more than 2,000 SCs from patients with chronic myeloid leukemia (CML) throughout the disease course, revealing heterogeneity of CML-SCs, including the identification of a subgroup of CML-SCs with a distinct molecular signature that selectively persisted during prolonged therapy. Analysis of nonleukemic SCs from patients with CML also provided new insights into cell-extrinsic disruption of hematopoiesis in CML associated with clinical outcome. Furthermore, we used this single-cell approach to identify a blast-crisis-specific SC population, which was also present in a subclone of CML-SCs during the chronic phase in a patient who subsequently developed blast crisis. This approach, which might be broadly applied to any malignancy, illustrates how single-cell analysis can identify subpopulations of therapy-resistant SCs that are not apparent through cell-population analysis.

Mead AJ, Mullally A. 2017. Myeloproliferative neoplasm stem cells. Blood, 129 (12), pp. 1607-1616. | Show Abstract | Read more

Myeloproliferative neoplasms (MPNs) arise in the hematopoietic stem cell (HSC) compartment as a result of the acquisition of somatic mutations in a single HSC that provides a selective advantage to mutant HSC over normal HSC and promotes myeloid differentiation to engender a myeloproliferative phenotype. This population of somatically mutated HSC, which initiates and sustains MPNs, is termed MPN stem cells. In >95% of cases, mutations that drive the development of an MPN phenotype occur in a mutually exclusive manner in 1 of 3 genes: JAK2, CALR, or MPL The thrombopoietin receptor, MPL, is the key cytokine receptor in MPN development, and these mutations all activate MPL-JAK-STAT signaling in MPN stem cells. Despite common biological features, MPNs display diverse disease phenotypes as a result of both constitutional and acquired factors that influence MPN stem cells, and likely also as a result of heterogeneity in the HSC in which MPN-initiating mutations arise. As the MPN clone expands, it exerts cell-extrinsic effects on components of the bone marrow niche that can favor the survival and expansion of MPN stem cells over normal HSC, further sustaining and driving malignant hematopoiesis. Although developed as targeted therapies for MPNs, current JAK2 inhibitors do not preferentially target MPN stem cells, and as a result, rarely induce molecular remissions in MPN patients. As the understanding of the molecular mechanisms underlying the clonal dominance of MPN stem cells advances, this will help facilitate the development of therapies that preferentially target MPN stem cells over normal HSC.

Butt NM, Lambert J, Ali S, Beer PA, Cross NCP, Duncombe A, Ewing J, Harrison CN, Knapper S, McLornan D et al. 2017. Guideline for the investigation and management of eosinophilia British Journal of Haematology, 176 (4), pp. 553-572. | Read more

Harrison CN, McMullin MF, Green AR, Mead AJ. 2017. Equivalence of BCSH and WHO diagnostic criteria for ET. Leukemia, 31 (2), pp. 527-528. | Read more

Mesa RA, Vannucchi AM, Mead A, Egyed M, Szoke A, Suvorov A, Jakucs J, Perkins A, Prasad R, Mayer J et al. 2017. Pacritinib versus best available therapy for the treatment of myelofibrosis irrespective of baseline cytopenias (PERSIST-1): an international, randomised, phase 3 trial The Lancet Haematology, 4 (5), pp. e225-e236. | Show Abstract | Read more

© 2017 Elsevier Ltd Background Available therapies for myelofibrosis can exacerbate cytopenias and are not indicated for patients with severe thrombocytopenia. Pacritinib, which inhibits both JAK2 and FLT3, induced spleen responses with limited myelosuppression in phase 1/2 trials. We aimed to assess the efficacy and safety of pacritinib versus best available therapy in patients with myelofibrosis irrespective of baseline cytopenias. Methods This international, multicentre, randomised, phase 3 trial (PERSIST-1) was done at 67 sites in 12 countries. Patients with higher-risk myelofibrosis (with no exclusions for baseline anaemia or thrombocytopenia) were randomly assigned (2:1) to receive oral pacritinib 400 mg once daily or best available therapy (BAT) excluding JAK2 inhibitors until disease progression or unacceptable toxicity. Randomisation was stratified by risk category, platelet count, and region. Treatment assignments were known to investigators, site personnel, patients, clinical monitors, and pharmacovigilance personnel. The primary endpoint was spleen volume reduction (SVR) of 35% or more from baseline to week 24 in the intention-to-treat population as assessed by blinded, centrally reviewed MRI or CT. We did safety analyses in all randomised patients who received either treatment. Here we present the final data. This trial is registered with ClinicalTrials.gov, number NCT01773187. Findings Between Jan 8, 2013, and Aug 1, 2014, 327 patients were randomly assigned to pacritinib (n=220) or BAT (n=107). Median follow-up was 23·2 months (IQR 14·8–28·7). At week 24, the primary endpoint of SVR of 35% or more was achieved by 42 (19%) patients in the pacritinib group versus five (5%) patients in the BAT group (p=0·0003). 90 patients in the BAT group crossed over to receive pacritinib at a median of 6·3 months (IQR 5·8–6·7). The most common grade 3–4 adverse events through week 24 were anaemia (n=37 [17%]), thrombocytopenia (n=26 [12%] ), and diarrhoea (n=11 [5%]) in the pacritinib group, and anaemia (n=16 [15%] ), thrombocytopenia (n=12 [11%]), dyspnoea (n=3 [3%] ), and hypotension (n=3 [3%]) in the BAT group. The most common serious adverse events that occurred through week 24 were anaemia (10 [5%] ), cardiac failure (5 [2%]), pyrexia (4 [2%] ), and pneumonia (4 [2%]) with pacritinib, and anaemia (5 [5%] ), sepsis (2 [2%]), and dyspnoea (2 [2%] ) with BAT. Deaths due to adverse events were observed in 27 (12%) patients in the pacritinib group and 14 (13%) patients in the BAT group throughout the duration of the study. Interpretation Pacritinib therapy was well tolerated and induced significant and sustained SVR and symptom reduction, even in patients with severe baseline cytopenias. Pacritinib could be a treatment option for patients with myelofibrosis, including those with baseline cytopenias for whom options are particularly limited. Funding CTI BioPharma Corp.

Luis TC, Luc S, Mizukami T, Boukarabila H, Thongjuea S, Woll PS, Azzoni E, Giustacchini A, Lutteropp M, Bouriez-Jones T et al. 2016. Initial seeding of the embryonic thymus by immune-restricted lympho-myeloid progenitors. Nat Immunol, 17 (12), pp. 1424-1435. | Show Abstract | Read more

The final stages of restriction to the T cell lineage occur in the thymus after the entry of thymus-seeding progenitors (TSPs). The identity and lineage potential of TSPs remains unclear. Because the first embryonic TSPs enter a non-vascularized thymic rudiment, we were able to directly image and establish the functional and molecular properties of embryonic thymopoiesis-initiating progenitors (T-IPs) before their entry into the thymus and activation of Notch signaling. T-IPs did not include multipotent stem cells or molecular evidence of T cell-restricted progenitors. Instead, single-cell molecular and functional analysis demonstrated that most fetal T-IPs expressed genes of and had the potential to develop into lymphoid as well as myeloid components of the immune system. Moreover, studies of embryos deficient in the transcriptional regulator RBPJ demonstrated that canonical Notch signaling was not involved in pre-thymic restriction to the T cell lineage or the migration of T-IPs.

Harrison CN, Talpaz M, Mead AJ. 2016. Ruxolitinib is effective in patients with intermediate-1 risk myelofibrosis: a summary of recent evidence Leukemia & Lymphoma, 57 (10), pp. 2259-2267. | Show Abstract | Read more

© 2016 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. Ruxolitinib is the only therapy with an approved indication for myelofibrosis (MF), a myeloproliferative neoplasm associated with progressive bone marrow fibrosis and extramedullary hematopoiesis. Although the pivotal phase 3 COMFORT studies included only patients with intermediate-2 or high-risk MF, the US indication includes all patients with intermediate- or high-risk disease. Data from recent nonrandomized studies confirm that the benefits of ruxolitinib established in the COMFORT studies in terms of spleen size reduction and symptom improvement also extend to patients with intermediate-1 risk MF, who tend to have less advanced disease than patients with higher-risk MF. Given the disease-modifying potential of ruxolitinib therapy, timely initiation of ruxolitinib therapy may not only improve patients’ current clinical status but also lead to better long-term outcomes. The decision of whether or when to initiate ruxolitinib treatment should be based on the expected benefit–risk ratio for each patient, specifically considering potential adverse effects.

Quek L, Otto GW, Garnett C, Lhermitte L, Karamitros D, Stoilova B, Lau I-J, Doondeea J, Usukhbayar B, Kennedy A et al. 2016. Genetically distinct leukemic stem cells in human CD34- acute myeloid leukemia are arrested at a hemopoietic precursor-like stage. J Exp Med, 213 (8), pp. 1513-1535. | Show Abstract | Read more

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.

Drissen R, Buza-Vidas N, Woll P, Thongjuea S, Gambardella A, Giustacchini A, Mancini E, Zriwil A, Lutteropp M, Grover A et al. 2016. Distinct myeloid progenitor-differentiation pathways identified through single-cell RNA sequencing. Nat Immunol, 17 (6), pp. 666-676. | Show Abstract | Read more

According to current models of hematopoiesis, lymphoid-primed multi-potent progenitors (LMPPs) (Lin(-)Sca-1(+)c-Kit(+)CD34(+)Flt3(hi)) and common myeloid progenitors (CMPs) (Lin(-)Sca-1(+)c-Kit(+)CD34(+)CD41(hi)) establish an early branch point for separate lineage-commitment pathways from hematopoietic stem cells, with the notable exception that both pathways are proposed to generate all myeloid innate immune cell types through the same myeloid-restricted pre-granulocyte-macrophage progenitor (pre-GM) (Lin(-)Sca-1(-)c-Kit(+)CD41(-)FcγRII/III(-)CD150(-)CD105(-)). By single-cell transcriptome profiling of pre-GMs, we identified distinct myeloid differentiation pathways: a pathway expressing the gene encoding the transcription factor GATA-1 generated mast cells, eosinophils, megakaryocytes and erythroid cells, and a pathway lacking expression of that gene generated monocytes, neutrophils and lymphocytes. These results identify an early hematopoietic-lineage bifurcation that separates the myeloid lineages before their segregation from other hematopoietic-lineage potential.

Psaila B, Barkas N, Iskander D, Roy A, Anderson S, Ashley N, Caputo VS, Lichtenberg J, Loaiza S, Bodine DM et al. 2016. Single-cell profiling of human megakaryocyte-erythroid progenitors identifies distinct megakaryocyte and erythroid differentiation pathways. Genome Biol, 17 (1), pp. 83. | Show Abstract | Read more

BACKGROUND: Recent advances in single-cell techniques have provided the opportunity to finely dissect cellular heterogeneity within populations previously defined by "bulk" assays and to uncover rare cell types. In human hematopoiesis, megakaryocytes and erythroid cells differentiate from a shared precursor, the megakaryocyte-erythroid progenitor (MEP), which remains poorly defined. RESULTS: To clarify the cellular pathway in erythro-megakaryocyte differentiation, we correlate the surface immunophenotype, transcriptional profile, and differentiation potential of individual MEP cells. Highly purified, single MEP cells were analyzed using index fluorescence-activated cell sorting and parallel targeted transcriptional profiling of the same cells was performed using a specifically designed panel of genes. Differentiation potential was tested in novel, single-cell differentiation assays. Our results demonstrate that immunophenotypic MEP comprise three distinct subpopulations: "Pre-MEP," enriched for erythroid/megakaryocyte progenitors but with residual myeloid differentiation capacity; "E-MEP," strongly biased towards erythroid differentiation; and "MK-MEP," a previously undescribed, rare population of cells that are bipotent but primarily generate megakaryocytic progeny. Therefore, conventionally defined MEP are a mixed population, as a minority give rise to mixed-lineage colonies while the majority of cells are transcriptionally primed to generate exclusively single-lineage output. CONCLUSIONS: Our study clarifies the cellular hierarchy in human megakaryocyte/erythroid lineage commitment and highlights the importance of using a combination of single-cell approaches to dissect cellular heterogeneity and identify rare cell types within a population. We present a novel immunophenotyping strategy that enables the prospective identification of specific intermediate progenitor populations in erythro-megakaryopoiesis, allowing for in-depth study of disorders including inherited cytopenias, myeloproliferative disorders, and erythromegakaryocytic leukemias.

Grover A, Sanjuan-Pla A, Thongjuea S, Carrelha J, Giustacchini A, Gambardella A, Macaulay I, Mancini E, Luis TC, Mead A et al. 2016. Single-cell RNA sequencing reveals molecular and functional platelet bias of aged haematopoietic stem cells. Nat Commun, 7 pp. 11075. | Show Abstract | Read more

Aged haematopoietic stem cells (HSCs) generate more myeloid cells and fewer lymphoid cells compared with young HSCs, contributing to decreased adaptive immunity in aged individuals. However, it is not known how intrinsic changes to HSCs and shifts in the balance between biased HSC subsets each contribute to the altered lineage output. Here, by analysing HSC transcriptomes and HSC function at the single-cell level, we identify increased molecular platelet priming and functional platelet bias as the predominant age-dependent change to HSCs, including a significant increase in a previously unrecognized class of HSCs that exclusively produce platelets. Depletion of HSC platelet programming through loss of the FOG-1 transcription factor is accompanied by increased lymphoid output. Therefore, increased platelet bias may contribute to the age-associated decrease in lymphopoiesis.

Buono M, Facchini R, Matsuoka S, Thongjuea S, Waithe D, Luis TC, Giustacchini A, Besmer P, Mead AJ, Jacobsen SEW, Nerlov C. 2016. A dynamic niche provides Kit ligand in a stage-specific manner to the earliest thymocyte progenitors. Nat Cell Biol, 18 (2), pp. 157-167. | Show Abstract | Read more

Thymic T cell development is initiated from bone-marrow-derived multi potent thymus-seeding progenitors. During the early stages of thymocyte differentiation, progenitors become T cell restricted. However, the cellular environments supporting these critical initial stages of T cell development within the thymic cortex are not known. Here we use the dependence of early, c-Kit-expressing thymic progenitors on Kit ligand (KitL) to show that CD4(-)CD8(-)c-Kit(+)CD25(-) DN1-stage progenitors associate with, and depend on, the membrane-bound form of KitL (mKitL) provided by a cortex-specific KitL-expressing vascular endothelial cell (VEC) population. In contrast, the subsequent CD4(-)CD8(-)c-Kit(+)CD25(+) DN2-stage progenitors associate selectively with cortical thymic epithelial cells (cTECs) and depend on cTEC-presented mKitL. These results show that the dynamic process of early thymic progenitor differentiation is paralleled by migration-dependent change to the supporting niche, and identify VECs as a thymic niche cell, with mKitL as a critical ligand.

Wills QF, Higgs DR, Mead AJ. 2015. Studying epigenomics in single cells: what is feasible and what can we learn? Epigenomics, 7 (8), pp. 1231-1234. | Read more

Wills QF, Mead AJ. 2015. Application of single-cell genomics in cancer: promise and challenges. Hum Mol Genet, 24 (R1), pp. R74-R84. | Show Abstract | Read more

Recent advances in single-cell genomics are opening up unprecedented opportunities to transform cancer genomics. While bulk tissue genomic analysis across large populations of tumour cells has provided key insights into cancer biology, this approach does not provide the resolution that is critical for understanding the interaction between different genetic events within the cellular hierarchy of the tumour during disease initiation, evolution, relapse and metastasis. Single-cell genomic approaches are uniquely placed to definitively unravel complex clonal structures and tissue hierarchies, account for spatiotemporal cell interactions and discover rare cells that drive metastatic disease, drug resistance and disease progression. Here we present five challenges that need to be met for single-cell genomics to fulfil its potential as a routine tool alongside bulk sequencing. These might be thought of as being challenges related to samples (processing and scale for analysis), sensitivity and specificity of mutation detection, sources of heterogeneity (biological and technical), synergies (from data integration) and systems modelling. We discuss these in the context of recent advances in technologies and data modelling, concluding with implications for moving cancer research into the clinic.

Duenas-Perez AB, Mead AJ. 2015. Clinical potential of pacritinib in the treatment of myelofibrosis Therapeutic Advances in Hematology, 6 (4), pp. 186-201. | Show Abstract | Read more

Myelofibrosis (MF) is a myeloid disorder caused by a clonal hematopoietic stem-cell proliferation associated with activation of the Janus kinase (JAK) signal transducer and activator of transcription (STAT) signaling pathways. Patients with MF often develop severe splenomegaly, marked symptom burden and significant cytopenias, with a consequent marked negative impact on quality of life and survival. The management of MF patients has dramatically improved with the development of a group of drugs that inhibit JAK signaling. The first of these agents to be approved was ruxolitinib, a JAK1/JAK2 inhibitor, which has been shown to improve both spleen size and symptoms in patients with MF. However, myelotoxicity, particularly of the platelet lineage, significantly limits the patient population who can benefit from this agent. Thus, there is an unmet need for novel agents with limited myelotoxicity to treat MF. Pacritinib, a JAK2 and FMS-like tyrosine kinase 3 (FLT3) inhibitor, has shown promising results in early phase trials with limited myelotoxicity and clinical responses that are comparable with those seen with ruxolitinib, even in patients with severe thrombocytopenia. Currently there are two large phase III clinical trials of pacritinib in MF, including patients with thrombocytopenia, and those previously treated with ruxolitinib. If the encouraging results observed in early phase clinical trials are confirmed, pacritinib will represent a new and exciting treatment option for patients with MF and particularly patients with significant cytopenias. © 2015, SAGE Publications. All rights reserved.

Cited:

20

Scopus

Reilly JT, Mcmullin MF, Beer PA, Butt N, Conneally E, Duncombe AS, Green AR, Mikhaeel G, Gilleece MH, Knapper S et al. 2014. Use of JAK inhibitors in the management of myelofibrosis: A revision of the British Committee for Standards in Haematology Guidelines for Investigation and Management of Myelofibrosis 2012 British Journal of Haematology, 167 (3), pp. 418-420. | Read more

Harrison CN, Butt N, Campbell P, Conneally E, Drummond M, Green AR, Murrin R, Radia DH, Mead A, Reilly JT et al. 2014. Modification of British committee for standards in haematology diagnostic criteria for essential thrombocythaemia British Journal of Haematology, 167 (3), pp. 421-423. | Read more

Cited:

93

Scopus

Woll PS, Kjällquist U, Chowdhury O, Doolittle H, Wedge DC, Thongjuea S, Erlandsson R, Ngara M, Anderson K, Deng Q et al. 2014. Myelodysplastic syndromes are propagated by rare and distinct human cancer stem cells in vivo Cancer Cell, 25 (6), pp. 794-808. | Show Abstract | Read more

Evidence for distinct human cancer stem cells (CSCs) remains contentious and the degree to which differentcancer cells contribute to propagating malignancies in patients remains unexplored. In low- to intermediate-risk myelodysplastic syndromes (MDS), we establish the existence of rare multipotent MDS stem cells (MDS-SCs), and their hierarchical relationship to lineage-restricted MDS progenitors. All identified somatically acquired genetic lesions were backtracked to distinct MDS-SCs, establishing their distinct MDS-propagating function invivo. In isolated del(5q)-MDS, acquisition of del(5q) preceded diverse recurrent driver mutations. Sequential analysis in del(5q)-MDS revealed genetic evolution in MDS-SCs and MDS-progenitors prior to leukemic transformation. These findings provide definitive evidence for rare human MDS-SCs invivo, with extensive implications for the targeting of the cells required and sufficient for MDS-propagation. © 2014 Elsevier Inc.

Grover A, Mancini E, Moore S, Mead AJ, Atkinson D, Rasmussen KD, O'Carroll D, Jacobsen SEW, Nerlov C. 2014. Erythropoietin guides multipotent hematopoietic progenitor cells toward an erythroid fate. J Exp Med, 211 (2), pp. 181-188. | Show Abstract | Read more

The erythroid stress cytokine erythropoietin (Epo) supports the development of committed erythroid progenitors, but its ability to act on upstream, multipotent cells remains to be established. We observe that high systemic levels of Epo reprogram the transcriptomes of multi- and bipotent hematopoietic stem/progenitor cells in vivo. This induces erythroid lineage bias at all lineage bifurcations known to exist between hematopoietic stem cells (HSCs) and committed erythroid progenitors, leading to increased erythroid and decreased myeloid HSC output. Epo, therefore, has a lineage instructive role in vivo, through suppression of non-erythroid fate options, demonstrating the ability of a cytokine to systematically bias successive lineage choices in favor of the generation of a specific cell type.

Reilly JT, McMullin MF, Beer PA, Butt N, Conneally E, Duncombe AS, Green AR, Mikhaeel G, Gilleece MH, Knapper S et al. 2014. Use of JAK inhibitors in the management of myelofibrosis: a revision of the British Committee for Standards in Haematology Guidelines for Investigation and Management of Myelofibrosis 2012. Br J Haematol, 167 (3), pp. 418-420. | Read more

Harrison CN, Butt N, Campbell P, Conneally E, Drummond M, Green AR, Murrin R, Radia DH, Mead A, Reilly JT et al. 2014. Modification of British Committee for Standards in Haematology diagnostic criteria for essential thrombocythaemia. Br J Haematol, 167 (3), pp. 421-423. | Read more

Cited:

43

Scopus

Böiers C, Carrelha J, Lutteropp M, Luc S, Green JCA, Azzoni E, Woll PS, Mead AJ, Hultquist A, Swiers G et al. 2013. Lymphomyeloid contribution of an immune-restricted progenitor emerging prior to definitive hematopoietic stem cells. Cell stem cell, 13 (5), pp. 535-548. | Show Abstract

In jawed vertebrates, development of an adaptive immune-system is essential for protection of the born organism against otherwise life-threatening pathogens. Myeloid cells of the innate immune system are formed early in development, whereas lymphopoiesis has been suggested to initiate much later, following emergence of definitive hematopoietic stem cells (HSCs). Herein, we demonstrate that the embryonic lymphoid commitment process initiates earlier than previously appreciated, prior to emergence of definitive HSCs, through establishment of a previously unrecognized entirely immune-restricted and lymphoid-primed progenitor. Notably, this immune-restricted progenitor appears to first emerge in the yolk sac and contributes physiologically to the establishment of lymphoid and some myeloid components of the immune-system, establishing the lymphomyeloid lineage restriction process as an early and physiologically important lineage-commitment step in mammalian hematopoiesis. Copyright © 2013 Elsevier Inc. All rights reserved.

Sanjuan-Pla A, Macaulay IC, Jensen CT, Woll PS, Luis TC, Mead A, Moore S, Carella C, Matsuoka S, Bouriez Jones T et al. 2013. Platelet-biased stem cells reside at the apex of the haematopoietic stem-cell hierarchy. Nature, 502 (7470), pp. 232-236. | Show Abstract | Read more

The blood system is maintained by a small pool of haematopoietic stem cells (HSCs), which are required and sufficient for replenishing all human blood cell lineages at millions of cells per second throughout life. Megakaryocytes in the bone marrow are responsible for the continuous production of platelets in the blood, crucial for preventing bleeding--a common and life-threatening side effect of many cancer therapies--and major efforts are focused at identifying the most suitable cellular and molecular targets to enhance platelet production after bone marrow transplantation or chemotherapy. Although it has become clear that distinct HSC subsets exist that are stably biased towards the generation of lymphoid or myeloid blood cells, we are yet to learn whether other types of lineage-biased HSC exist or understand their inter-relationships and how differently lineage-biased HSCs are generated and maintained. The functional relevance of notable phenotypic and molecular similarities between megakaryocytes and bone marrow cells with an HSC cell-surface phenotype remains unclear. Here we identify and prospectively isolate a molecularly and functionally distinct mouse HSC subset primed for platelet-specific gene expression, with enhanced propensity for short- and long-term reconstitution of platelets. Maintenance of platelet-biased HSCs crucially depends on thrombopoietin, the primary extrinsic regulator of platelet development. Platelet-primed HSCs also frequently have a long-term myeloid lineage bias, can self-renew and give rise to lymphoid-biased HSCs. These findings show that HSC subtypes can be organized into a cellular hierarchy, with platelet-primed HSCs at the apex. They also demonstrate that molecular and functional priming for platelet development initiates already in a distinct HSC population. The identification of a platelet-primed HSC population should enable the rational design of therapies enhancing platelet output.

Mead AJ, Constantinescu SN, Jacobsen SE. 2013. Germline counterparts of oncogenic mutations: who gives a JAK?. Oncotarget, 4 (6), pp. 814-815. | Read more

Mead AJ, Chowdhury O, Pecquet C, Dusa A, Woll P, Atkinson D, Burns A, Score J, Rugless M, Clifford R et al. 2013. Impact of isolated germline JAK2V617I mutation on human hematopoiesis. Blood, 121 (20), pp. 4156-4165. | Show Abstract | Read more

The association between somatic JAK2 mutation and myeloproliferative neoplasms (MPNs) is now well established. However, because JAK2 mutations are associated with heterogeneous clinical phenotypes and often occur as secondary genetic events, some aspects of JAK2 mutation biology remain to be understood. We recently described a germline JAK2V617I mutation in a family with hereditary thrombocytosis and herein characterize the hematopoietic and signaling impact of JAK2V617I. Through targeted sequencing of MPN-associated mutations, exome sequencing, and clonality analysis, we demonstrate that JAK2V617I is likely to be the sole driver mutation in JAK2V617I-positive individuals with thrombocytosis. Phenotypic hematopoietic stem cells (HSCs) were increased in the blood and bone marrow of JAK2V617I-positive individuals and were sustained at higher levels than controls after xenotransplantation. In signaling and transcriptional assays, JAK2V617I demonstrated more activity than wild-type JAK2 but substantially less than JAK2V617F. After cytokine stimulation, JAK2V617I resulted in markedly increased downstream signaling compared with wild-type JAK2 and comparable with JAK2V617F. These findings demonstrate that JAK2V617I induces sufficient cytokine hyperresponsiveness in the absence of other molecular events to induce a homogeneous MPN-like phenotype. We also provide evidence that the JAK2V617I mutation may expand the HSC pool, providing insights into both JAK2 mutation biology and MPN disease pathogenesis.

Mead AJ, Kharazi S, Atkinson D, Macaulay I, Pecquet C, Loughran S, Lutteropp M, Woll P, Chowdhury O, Luc S et al. 2013. FLT3-ITDs instruct a myeloid differentiation and transformation bias in lymphomyeloid multipotent progenitors. Cell Rep, 3 (6), pp. 1766-1776. | Show Abstract | Read more

Whether signals mediated via growth factor receptors (GFRs) might influence lineage fate in multipotent progenitors (MPPs) is unclear. We explored this issue in a mouse knockin model of gain-of-function Flt3-ITD mutation because FLT3-ITDs are paradoxically restricted to acute myeloid leukemia even though Flt3 primarily promotes lymphoid development during normal hematopoiesis. When expressed in MPPs, Flt3-ITD collaborated with Runx1 mutation to induce high-penetrance aggressive leukemias that were exclusively of the myeloid phenotype. Flt3-ITDs preferentially expanded MPPs with reduced lymphoid and increased myeloid transcriptional priming while compromising early B and T lymphopoiesis. Flt3-ITD-induced myeloid lineage bias involved upregulation of the transcription factor Pu.1, which is a direct target gene of Stat3, an aberrantly activated target of Flt3-ITDs, further establishing how lineage bias can be inflicted on MPPs through aberrant GFR signaling. Collectively, these findings provide new insights into how oncogenic mutations might subvert the normal process of lineage commitment and dictate the phenotype of resulting malignancies.

Cited:

57

Scopus

Böiers C, Carrelha J, Lutteropp M, Luc S, Green JCA, Azzoni E, Woll PS, Mead AJ, Hultquist A, Swiers G et al. 2013. Lymphomyeloid contribution of an immune-restricted progenitor emerging prior to definitive hematopoietic stem cells. Cell stem cell, 13 (5), pp. 535-548. | Show Abstract

In jawed vertebrates, development of an adaptive immune-system is essential for protection of the born organism against otherwise life-threatening pathogens. Myeloid cells of the innate immune system are formed early in development, whereas lymphopoiesis has been suggested to initiate much later, following emergence of definitive hematopoietic stem cells (HSCs). Herein, we demonstrate that the embryonic lymphoid commitment process initiates earlier than previously appreciated, prior to emergence of definitive HSCs, through establishment of a previously unrecognized entirely immune-restricted and lymphoid-primed progenitor. Notably, this immune-restricted progenitor appears to first emerge in the yolk sac and contributes physiologically to the establishment of lymphoid and some myeloid components of the immune-system, establishing the lymphomyeloid lineage restriction process as an early and physiologically important lineage-commitment step in mammalian hematopoiesis. Copyright © 2013 Elsevier Inc. All rights reserved.

Harrison C, Mesa R, Ross D, Mead A, Keohane C, Gotlib J, Verstovsek S. 2013. Practical management of patients with myelofibrosis receiving ruxolitinib. Expert Rev Hematol, 6 (5), pp. 511-523. | Show Abstract | Read more

Myelofibrosis (MF) is characterized by bone marrow fibrosis, progressive anemia and extramedullary hematopoiesis, primarily manifested as splenomegaly. Patients also experience debilitating constitutional symptoms, including sequelae of splenomegaly, night sweats and fatigue. Ruxolitinib (INC424, INCB18424, Jakafi, Jakavi), a JAK1 and JAK2 inhibitor, was approved in November 2011 by the US FDA for the treatment of intermediate- or high-risk MF, and more recently in Europe and Canada for the treatment of MF-related splenomegaly or symptoms. These approvals were based on data from two randomized Phase III studies: COMFORT-I randomized against placebo, and COMFORT-II randomized against best available therapy. In these studies, ruxolitinib rapidly improved multiple disease manifestations of MF, reducing splenomegaly and improving quality of life of patients and potentially prolonging survival. However, as with other chemotherapies, ruxolitinib therapy is associated with some adverse events, such as anemia and thrombocytopenia. The aims of this article are to provide a brief overview of ruxolitinib therapy, to discuss some common adverse events associated with ruxolitinib therapy and to provide clinical management recommendations to maximize patients' benefit from ruxolitinib.

Eyre T, Schwab CJ, Kinstrie R, McGuire AK, Strefford J, Peniket A, Mead A, Littlewood T, Holyoake TL, Copland M et al. 2012. Episomal amplification of NUP214-ABL1 fusion gene in B-cell acute lymphoblastic leukemia. Blood, 120 (22), pp. 4441-4443. | Read more

Roy A, Cowan G, Mead AJ, Filippi S, Bohn G, Chaidos A, Tunstall O, Chan JKY, Choolani M, Bennett P et al. 2012. Perturbation of fetal liver hematopoietic stem and progenitor cell development by trisomy 21. Proc Natl Acad Sci U S A, 109 (43), pp. 17579-17584. | Show Abstract | Read more

The 40-fold increase in childhood megakaryocyte-erythroid and B-cell leukemia in Down syndrome implicates trisomy 21 (T21) in perturbing fetal hematopoiesis. Here, we show that compared with primary disomic controls, primary T21 fetal liver (FL) hematopoietic stem cells (HSC) and megakaryocyte-erythroid progenitors are markedly increased, whereas granulocyte-macrophage progenitors are reduced. Commensurately, HSC and megakaryocyte-erythroid progenitors show higher clonogenicity, with increased megakaryocyte, megakaryocyte-erythroid, and replatable blast colonies. Biased megakaryocyte-erythroid-primed gene expression was detected as early as the HSC compartment. In lymphopoiesis, T21 FL lymphoid-primed multipotential progenitors and early lymphoid progenitor numbers are maintained, but there was a 10-fold reduction in committed PreproB-lymphoid progenitors and the functional B-cell potential of HSC and early lymphoid progenitor is severely impaired, in tandem with reduced early lymphoid gene expression. The same pattern was seen in all T21 FL samples and no samples had GATA1 mutations. Therefore, T21 itself causes multiple distinct defects in FL myelo- and lymphopoiesis.

Buza-Vidas N, Cismasiu VB, Moore S, Mead AJ, Woll PS, Lutteropp M, Melchiori L, Luc S, Bouriez-Jones T, Atkinson D et al. 2012. Dicer is selectively important for the earliest stages of erythroid development. Blood, 120 (12), pp. 2412-2416. | Show Abstract | Read more

MicroRNAs (miRs) are involved in many aspects of normal and malignant hematopoiesis, including hematopoietic stem cell (HSC) self-renewal, proliferation, and terminal differentiation. However, a role for miRs in the generation of the earliest stages of lineage committed progenitors from HSCs has not been identified. Using Dicer inactivation, we show that the miR complex is not only essential for HSC maintenance but is specifically required for their erythroid programming and subsequent generation of committed erythroid progenitors. In bipotent pre-MegEs, loss of Dicer up-regulated transcription factors preferentially expressed in megakaryocyte progenitors (Gata2 and Zfpm1) and decreased expression of the erythroid-specific Klf1 transcription factor. These results show a specific requirement for Dicer in acquisition of erythroid lineage programming and potential in HSCs and their subsequent erythroid lineage differentiation, and in particular indicate a role for the miR complex in achieving proper balance of lineage-specific transcriptional regulators necessary for HSC multilineage potential to be maintained.

Luc S, Luis TC, Boukarabila H, Macaulay IC, Buza-Vidas N, Bouriez-Jones T, Lutteropp M, Woll PS, Loughran SJ, Mead AJ et al. 2012. The earliest thymic T cell progenitors sustain B cell and myeloid lineage potential. Nat Immunol, 13 (4), pp. 412-419. | Show Abstract | Read more

The stepwise commitment from hematopoietic stem cells in the bone marrow to T lymphocyte-restricted progenitors in the thymus represents a paradigm for understanding the requirement for distinct extrinsic cues during different stages of lineage restriction from multipotent to lineage-restricted progenitors. However, the commitment stage at which progenitors migrate from the bone marrow to the thymus remains unclear. Here we provide functional and molecular evidence at the single-cell level that the earliest progenitors in the neonatal thymus had combined granulocyte-monocyte, T lymphocyte and B lymphocyte lineage potential but not megakaryocyte-erythroid lineage potential. These potentials were identical to those of candidate thymus-seeding progenitors in the bone marrow, which were closely related at the molecular level. Our findings establish the distinct lineage-restriction stage at which the T cell lineage-commitment process transits from the bone marrow to the remote thymus.

Cited:

54

Scopus

Reilly JT, Mcmullin MF, Beer PA, Butt N, Conneally E, Duncombe A, Green AR, Michaeel NG, Gilleece MH, Hall GW et al. 2012. Guideline for the diagnosis and management of myelofibrosis British Journal of Haematology, 158 (4), pp. 453-471. | Show Abstract | Read more

The guideline group regarding the diagnosis and management of myelofibrosis was selected to be representative of UK-based medical experts, together with a contribution from a single expert from the USA. MEDLINE and EMBASE were searched systematically for publications in English from 1966 until August 2011 using a variety of key words. The writing group produced the draft guideline, which was subsequently revised by consensus of the members of the General Haematology and Haemato-oncology Task Forces of the British Committee for Standards in Haematology (BCSH). The guideline was then reviewed by a sounding board of UK haematologists, the BCSH and the British Society for Haematology Committee and comments incorporated where appropriate. The criteria used to state levels and grades of evidence are as outlined in the Procedure for Guidelines commissioned by the BCSH; the 'GRADE' system was used to score strength and quality of evidence. The objective of this guideline is to provide healthcare professionals with clear guidance on the investigation and management of primary myelofibrosis, as well as post-polycythaemic myelofibrosis (post-PV MF) and post-thrombocythemic myelofibrosis (post-ET MF) in both adult and paediatric patients. © 2012 Blackwell Publishing Ltd.

Cited:

36

Scopus

Mclornan DP, Mead AJ, Jackson G, Harrison CN. 2012. Allogeneic Stem Cell Transplantation for Myelofibrosis in 2012 British Journal of Haematology, 157 (4), pp. 413-425. | Show Abstract | Read more

Myelofibrosis (MF) is a heterogeneous disease for which long-term, effective medical therapeutic options are currently limited. The role of allogeneic haematopoietic stem cell transplant (AHSCT) in this population, many of whom are elderly, often provides a challenge with regard to the identification of suitable candidates, timing of transplantation in the disease course and choice of conditioning regimen. This review summarizes key findings from published data concerning AHSCT in MF and attempts to provide a state of the art approach to MF-AHSCT in 2012. In addition, we postulate on how the era of JAK inhibition might impact on transplantation for MF. © 2012 Blackwell Publishing Ltd.

Mead AJ, Rugless MJ, Jacobsen SEW, Schuh A. 2012. Germline JAK2 mutation in a family with hereditary thrombocytosis. N Engl J Med, 366 (10), pp. 967-969. | Read more

Reckzeh K, Bereshchenko O, Mead A, Rehn M, Kharazi S, Jacobsen S-E, Nerlov C, Cammenga J. 2012. Molecular and cellular effects of oncogene cooperation in a genetically accurate AML mouse model LEUKEMIA, 26 (7), pp. 1527-1536. | Show Abstract | Read more

Biallelic CEBPA mutations and FMS-like tyrosine kinase receptor 3 (FLT3) length mutations are frequently identified in human acute myeloid leukemia (AML) with normal cytogenetics. However, the molecular and cellular mechanisms of oncogene cooperation remain unclear because of a lack of disease models. We have generated an AML mouse model using knockin mouse strains to study cooperation of an internal tandem duplication (ITD) mutation in the Flt3 gene with commonly observed CCAAT/enhancer binding protein alpha (C/EBPα) mutations. This study provides evidence that FLT3 ITD cooperates in leukemogenesis by enhancing the generation of leukemia-initiating granulocyte-monocyte progenitors (GMPs) otherwise prevented by a block in differentiation and skewed lineage priming induced by biallelic C/EBPα mutations. These cellular changes are accompanied by an upregulation of hematopoietic stem cell and STAT5 target genes. By gene expression analysis in premalignant populations, we further show a role of FLT3 ITD in activating genes involved in survival/transformation and chemoresistance. Both multipotent progenitors and GMP cells contain the potential to induce AML similar to corresponding cells in human AML samples showing that this model resembles human disease. © 2012 Macmillan Publishers Limited.

Goardon N, Marchi E, Atzberger A, Quek L, Schuh A, Soneji S, Woll P, Mead A, Alford KA, Rout R et al. 2011. Coexistence of LMPP-like and GMP-like leukemia stem cells in acute myeloid leukemia. Cancer Cell, 19 (1), pp. 138-152. | Show Abstract | Read more

The relationships between normal and leukemic stem/progenitor cells are unclear. We show that in ∼80% of primary human CD34+ acute myeloid leukemia (AML), two expanded populations with hemopoietic progenitor immunophenotype coexist in most patients. Both populations have leukemic stem cell (LSC) activity and are hierarchically ordered; one LSC population gives rise to the other. Global gene expression profiling shows the LSC populations are molecularly distinct and resemble normal progenitors but not stem cells. The more mature LSC population most closely mirrors normal granulocyte-macrophage progenitors (GMP) and the immature LSC population a previously uncharacterized progenitor functionally similar to lymphoid-primed multipotential progenitors (LMPPs). This suggests that in most cases primary CD34+ AML is a progenitor disease where LSCs acquire abnormal self-renewal potential.

Kharazi S, Mead AJ, Mansour A, Hultquist A, Böiers C, Luc S, Buza-Vidas N, Ma Z, Ferry H, Atkinson D et al. 2011. Impact of gene dosage, loss of wild-type allele, and FLT3 ligand on Flt3-ITD-induced myeloproliferation. Blood, 118 (13), pp. 3613-3621. | Show Abstract | Read more

Acquisition of homozygous activating growth factor receptor mutations might accelerate cancer progression through a simple gene-dosage effect. Internal tandem duplications (ITDs) of FLT3 occur in approximately 25% cases of acute myeloid leukemia and induce ligand-independent constitutive signaling. Homozygous FLT3-ITDs confer an adverse prognosis and are frequently detected at relapse. Using a mouse knockin model of Flt3-internal tandem duplication (Flt3-ITD)-induced myeloproliferation, we herein demonstrate that the enhanced myeloid phenotype and expansion of granulocyte-monocyte and primitive Lin(-)Sca1(+)c-Kit(+) progenitors in Flt3-ITD homozygous mice can in part be mediated through the loss of the second wild-type allele. Further, whereas autocrine FLT3 ligand production has been implicated in FLT3-ITD myeloid malignancies and resistance to FLT3 inhibitors, we demonstrate here that the mouse Flt3(ITD/ITD) myeloid phenotype is FLT3 ligand-independent.

Tehranchi R, Woll PS, Anderson K, Buza-Vidas N, Mizukami T, Mead AJ, Astrand-Grundström I, Strömbeck B, Horvat A, Ferry H et al. 2010. Persistent malignant stem cells in del(5q) myelodysplasia in remission. N Engl J Med, 363 (11), pp. 1025-1037. | Show Abstract | Read more

BACKGROUND: The in vivo clinical significance of malignant stem cells remains unclear. METHODS: Patients who have the 5q deletion (del[5q]) myelodysplastic syndrome (interstitial deletions involving the long arm of chromosome 5) have complete clinical and cytogenetic remissions in response to lenalidomide treatment, but they often have relapse. To determine whether the persistence of rare but distinct malignant stem cells accounts for such relapses, we examined bone marrow specimens obtained from seven patients with the del(5q) myelodysplastic syndrome who became transfusion-independent while receiving lenalidomide treatment and entered cytogenetic remission. RESULTS: Virtually all CD34+, CD38+ progenitor cells and stem cells that were positive for CD34 and CD90, with undetectable or low CD38 (CD38−/low), had the 5q deletion before treatment. Although lenalidomide efficiently reduced these progenitors in patients in complete remission, a larger fraction of the minor, quiescent, CD34+,CD38-/low, CD90+ del(5q) stem cells as well as functionally defined del(5q) stem cells remained distinctly resistant to lenalidomide. Over time, lenalidomide resistance developed in most of the patients in partial and complete remission, with recurrence or expansion of the del(5q) clone and clinical and cytogenetic progression. CONCLUSIONS: In these patients with the del(5q) myelodysplastic syndrome, we identified rare and phenotypically distinct del(5q) myelodysplastic syndrome stem cells that were also selectively resistant to therapeutic targeting at the time of complete clinical and cytogenetic remission. (Funded by the EuroCancerStemCell Consortium and others.)

Mead AJ, Thomson KJ, Morris EC, Mohamedbhai S, Denovan S, Orti G, Fielding AK, Kottaridis PD, Hough R, Chakraverty R et al. 2010. HLA-mismatched unrelated donors are a viable alternate graft source for allogeneic transplantation following alemtuzumab-based reduced-intensity conditioning. Blood, 115 (25), pp. 5147-5153. | Show Abstract | Read more

The impact of human leukocyte antigen (HLA) mismatch after reduced-intensity conditioning allogeneic hematopoietic stem cell transplantation (RIT) using unrelated donors (UD) is unclear, and may be modulated by T-cell depletion. We therefore examined outcomes of 157 consecutive patients undergoing RIT after uniform conditioning with fludarabine, melphalan, and alemtuzumab (FMC). Donors were 10/10 HLA-matched (MUDs, n = 107) and 6 to 9/10 HLA-matched (MMUDs, n = 50), with no significant differences in baseline characteristics other than increased cytomegalovirus seropositivity in MMUDs. Rates of durable engraftment were high. Graft failure rates (persistent cytopenias with donor chimerism) were similar (8% vs 3%, P = .21), though rejection (recipient chimerism) was more frequent in MMUDs (8% vs 0%, P < .01). There were no significant differences between donors in the incidences of acute graft-versus-host disease (GVHD; 20% vs 22% grade 2-4, respectively, P = .83), chronic extensive GVHD (3-year cumulative incidence [CI] 23% vs 24%, P = .56), or treatment-related mortality (1-year CI 27% vs 27%, P = .96). Furthermore, there was no difference in 3-year overall survival (OS; 53% vs 49%, P = .44). Mismatch occurred at the antigenic level in 40 cases. The outcome in these cases did not differ significantly from the rest of the cohort. We conclude that RIT using HLA-mismatched grafts is a viable option using FMC conditioning.

Mead AJ, Gale RE, Hills RK, Gupta M, Young BD, Burnett AK, Linch DC. 2008. Conflicting data on the prognostic significance of FLT3/TKD mutations in acute myeloid leukemia might be related to the incidence of biallelic disease. Blood, 112 (2), pp. 444-445. | Read more

Mead AJ, Gale RE, Kottaridis PD, Matsuda S, Khwaja A, Linch DC. 2008. Acute myeloid leukaemia blast cells with a tyrosine kinase domain mutation of FLT3 are less sensitive to lestaurtinib than those with a FLT3 internal tandem duplication. Br J Haematol, 141 (4), pp. 454-460. | Show Abstract | Read more

FLT3 tyrosine kinase domain mutations (FLT3/TKDs) are associated with a favourable prognosis in acute myeloid leukaemia (AML), unlike FLT3 internal tandem duplications (FLT3/ITDs) that have a poor prognosis. Whilst FLT3/ITD+ cells are more susceptible to the cytotoxic effects of FLT3 inhibitors than wild type (WT) cells, the sensitivity of FLT3/TKD+ cells to therapeutic agents is unclear, as is the importance of the mutant level. We therefore studied the effect of cytarabine and the FLT3 inhibitor lestaurtinib, either alone or in combination, on in vitro survival of blast cells from 36 cases of AML (14 FLT3/WT, 11 FLT3/ITD+ and 11 FLT3/TKD+). All three groups showed similar sensitivity to the cytotoxic effects of cytarabine but FLT3/ITD mutant level was inversely correlated with cytarabine cytotoxicity (P = 0.04) whereas FLT3/TKD mutant level had no impact. FLT3/TKD+ cells showed a similar response to lestaurtinib as FLT3/WT cells, whereas FLT3/ITD+ cells were more sensitive (P = 0.004). There was no correlation between mutant level and lestaurtinib sensitivity for either FLT3/ITD+ or FLT3/TKD+ cells. Synergistic cytotoxicity of lestaurtinib plus cytarabine was demonstrated in all three groups. These results suggest that FLT3/TKD+ and FLT3/WT cases should not be differentiated when considering patients for treatment with FLT3 inhibitors.

Gale RE, Green C, Allen C, Mead AJ, Burnett AK, Hills RK, Linch DC, Medical Research Council Adult Leukaemia Working Party. 2008. The impact of FLT3 internal tandem duplication mutant level, number, size, and interaction with NPM1 mutations in a large cohort of young adult patients with acute myeloid leukemia. Blood, 111 (5), pp. 2776-2784. | Show Abstract | Read more

An internal tandem duplication in the fms-like tyrosine kinase 3 gene (FLT3/ITD) is associated with poor prognosis in acute myeloid leukemia (AML), but the impact of mutant level, size, and interaction with nucleophosmin 1 (NPM1) mutations remains controversial. We evaluated these characteristics in a large cohort of young adult AML patients. There was a highly significant trend for worsening in relapse risk (RR) and overall survival (OS) with increasing FLT3/ITD mutant level (P < .001 for both), and even in the low level mutant group (1%-24% of total FLT3 alleles), RR was significantly worse than in the FLT3 wild-type (WT) group (P < .001). In multivariate analysis, mutant level was the most powerful prognostic factor for RR. Mutant size and number had no significant impact on outcome. The beneficial impact of an NPM1 mutation on RR and OS was seen in FLT3/ITD(+) as well as FLT3/WT patients; both markers were highly significant independent predictors of outcome (P < .001). Stratification using both markers identified 3 prognostic groups: good (FLT3/ITD(-)NPM1(+)), intermediate (FLT3/ITD(-)NPM1(-) or FLT3/ITD(+)NPM1(+)), and poor (FLT3/ITD(+)NPM1(-)). Patients with high FLT3/ITD mutant level (greater than 50%) or FLT3/ITD(+) in the absence of an NPM1 mutation may be good candidates for more experimental therapeutic approaches.

Mead AJ, Linch DC, Hills RK, Wheatley K, Burnett AK, Gale RE. 2007. FLT3 tyrosine kinase domain mutations are biologically distinct from and have a significantly more favorable prognosis than FLT3 internal tandem duplications in patients with acute myeloid leukemia. Blood, 110 (4), pp. 1262-1270. | Show Abstract | Read more

The prognostic impact of tyrosine kinase domain (TKD) mutations of the fms-like tyrosine kinase-3 (FLT3) gene in acute myeloid leukemia (AML) is currently uncertain. To resolve this issue we screened 1107 young adult nonacute promyelocytic leukemia AML patients with known FLT3 internal tandem duplication (ITD) status for FLT3/TKDs; they were detected in 127 (11%) cases. Mutations were associated with a high white cell count (P =.006) and patients with inv(16) (P = .005) but were infrequent in patients with adverse cytogenetics and secondary AML. Overall survival (OS) at 5 years was 53% and 37% for FLT3/TKD mutant and wild-type patients respectively (odds ratio, 0.72; 95% confidence interval, 0.58 to 0.89; P = .002). For both the cumulative incidence of relapse and OS the difference in outcome between FLT3/ITDs and FLT3/TKDs was highly significant (P < .001). In multivariate analysis, impact of FLT3/TKDs on OS when including all mutant-positive patients was not significant, but patients with high-level mutations (more than 25% mutant) had a significantly improved outcome (P = .004). The novel finding that biologically distinct activating mutations of the same gene can be associated with markedly different clinical outcomes has implications for risk stratification and therapy and is significant to the understanding of chemoresistance in AML.

Mead AJ, Newland AC, Provan D. 2003. Adult idiopathic thrombocytopenic purpura. Hematology, 8 (6), pp. 345-357. | Read more

McGowan S, Eastwood SL, Mead A, Burnet PW, Smith C, Flanigan TP, Harrison PJ. 1996. Hippocampal and cortical G protein (Gs alpha, G(o) alpha and Gi2 alpha) mRNA expression after electroconvulsive shock or lithium carbonate treatment. Eur J Pharmacol, 306 (1-3), pp. 249-255. | Show Abstract | Read more

GTP-binding proteins (G proteins) are heteromers composed of alpha, beta and gamma subunits. The expression of some G protein subunits is altered both by affective disorders and by antidepressant treatments. Here we have studied three G protein alpha subunit mRNAs in the hippocampus and frontoparietal cortex of rats treated with lithium for 14 days or with repeated electroconvulsive shock (five shocks over 10 days). After electroconvulsive shock, the three mRNAs changed differentially in the hippocampus. Specifically, Gs alpha mRNA was decreased in CA3 and CA1, whilst G(o) alpha mRNA was increased in dentate gyrus and Gi2 alpha mRNA was reduced in dentate gyrus and CA3. Lithium carbonate treatment produced a modest, uniform increase in the three mRNAs in dentate gyrus and CA3, and a selective elevation of G(o) alpha mRNA in CA1. Neither treatment altered the G protein mRNAs in the cortex nor cyclophilin mRNA in any region. These data extend the evidence that altered G protein expression is a part of the biochemical response to antidepressant treatments. Differences in the molecular and anatomical pattern of the alterations induced by electroconvulsive shock compared to lithium may contribute to their different therapeutic profiles.

Burnet PW, Mead A, Eastwood SL, Lacey K, Harrison PJ, Sharp T. 1995. Repeated ECS differentially affects rat brain 5-HT1A and 5-HT2A receptor expression. Neuroreport, 6 (6), pp. 901-904. | Show Abstract | Read more

We investigated the effect of electroconvulsive shock (ECS), administered five times over 10 days, on 5-HT1A and 5-HT2A receptor mRNA and binding site densities in the rat brain using in situ hybridization histochemistry and quantitative autoradiography. ECS treatment increased 5-HT1A receptor mRNA abundance and binding site densities in the dentate gyrus, but decreased these parameters in the CA3c layer of the hippocampus. No changes in 5-HT1A receptor mRNA and binding sites occurred in other hippocampal subfields, neocortex or raphe nuclei. Repeated ECS was also found to increase 5-HT2A receptor binding site densities in the neocortex and this was accompanied by a non-significant increase in cortical 5-HT2A receptor mRNA abundance. Our study demonstrates that in the rat, repeated ECS produces anatomically and molecularly discrete effects on 5-HT1A and 5-HT2A receptor gene expression. These changes may be relevant to the therapeutic effect of repeated ECS in depression.

Tapper W, Jones AV, Kralovics R, Harutyunyan AS, Zoi K, Leung W, Godfrey AL, Guglielmelli P, Callaway A, Ward D et al. 2015. Genetic variation at MECOM, TERT, JAK2 and HBS1L-MYB predisposes to myeloproliferative neoplasms. Nat Commun, 6 pp. 6691. | Show Abstract | Read more

Clonal proliferation in myeloproliferative neoplasms (MPN) is driven by somatic mutations in JAK2, CALR or MPL, but the contribution of inherited factors is poorly characterized. Using a three-stage genome-wide association study of 3,437 MPN cases and 10,083 controls, we identify two SNPs with genome-wide significance in JAK2(V617F)-negative MPN: rs12339666 (JAK2; meta-analysis P=1.27 × 10(-10)) and rs2201862 (MECOM; meta-analysis P=1.96 × 10(-9)). Two additional SNPs, rs2736100 (TERT) and rs9376092 (HBS1L/MYB), achieve genome-wide significance when including JAK2(V617F)-positive cases. rs9376092 has a stronger effect in JAK2(V617F)-negative cases with CALR and/or MPL mutations (Breslow-Day P=4.5 × 10(-7)), whereas in JAK2(V617F)-positive cases rs9376092 associates with essential thrombocythemia (ET) rather than polycythemia vera (allelic χ(2) P=7.3 × 10(-7)). Reduced MYB expression, previously linked to development of an ET-like disease in model systems, associates with rs9376092 in normal myeloid cells. These findings demonstrate that multiple germline variants predispose to MPN and link constitutional differences in MYB expression to disease phenotype.

Mead AJ, Neo WH, Barkas N, Matsuoka S, Giustacchini A, Facchini R, Thongjuea S, Jamieson L, Booth CAG, Fordham N et al. 2017. Niche-mediated depletion of the normal hematopoietic stem cell reservoir by Flt3-ITD-induced myeloproliferation. J Exp Med, 214 (7), pp. 2005-2021. | Show Abstract | Read more

Although previous studies suggested that the expression of FMS-like tyrosine kinase 3 (Flt3) initiates downstream of mouse hematopoietic stem cells (HSCs), FLT3 internal tandem duplications (FLT3 ITDs) have recently been suggested to intrinsically suppress HSCs. Herein, single-cell interrogation found Flt3 mRNA expression to be absent in the large majority of phenotypic HSCs, with a strong negative correlation between Flt3 and HSC-associated gene expression. Flt3-ITD knock-in mice showed reduced numbers of phenotypic HSCs, with an even more severe loss of long-term repopulating HSCs, likely reflecting the presence of non-HSCs within the phenotypic HSC compartment. Competitive transplantation experiments established that Flt3-ITD compromises HSCs through an extrinsically mediated mechanism of disrupting HSC-supporting bone marrow stromal cells, with reduced numbers of endothelial and mesenchymal stromal cells showing increased inflammation-associated gene expression. Tumor necrosis factor (TNF), a cell-extrinsic potent negative regulator of HSCs, was overexpressed in bone marrow niche cells from FLT3-ITD mice, and anti-TNF treatment partially rescued the HSC phenotype. These findings, which establish that Flt3-ITD-driven myeloproliferation results in cell-extrinsic suppression of the normal HSC reservoir, are of relevance for several aspects of acute myeloid leukemia biology.

Giustacchini A, Thongjuea S, Barkas N, Woll PS, Povinelli BJ, Booth CAG, Sopp P, Norfo R, Rodriguez-Meira A, Ashley N et al. 2017. Single-cell transcriptomics uncovers distinct molecular signatures of stem cells in chronic myeloid leukemia. Nat Med, 23 (6), pp. 692-702. | Show Abstract | Read more

Recent advances in single-cell transcriptomics are ideally placed to unravel intratumoral heterogeneity and selective resistance of cancer stem cell (SC) subpopulations to molecularly targeted cancer therapies. However, current single-cell RNA-sequencing approaches lack the sensitivity required to reliably detect somatic mutations. We developed a method that combines high-sensitivity mutation detection with whole-transcriptome analysis of the same single cell. We applied this technique to analyze more than 2,000 SCs from patients with chronic myeloid leukemia (CML) throughout the disease course, revealing heterogeneity of CML-SCs, including the identification of a subgroup of CML-SCs with a distinct molecular signature that selectively persisted during prolonged therapy. Analysis of nonleukemic SCs from patients with CML also provided new insights into cell-extrinsic disruption of hematopoiesis in CML associated with clinical outcome. Furthermore, we used this single-cell approach to identify a blast-crisis-specific SC population, which was also present in a subclone of CML-SCs during the chronic phase in a patient who subsequently developed blast crisis. This approach, which might be broadly applied to any malignancy, illustrates how single-cell analysis can identify subpopulations of therapy-resistant SCs that are not apparent through cell-population analysis.

Mead AJ, Mullally A. 2017. Myeloproliferative neoplasm stem cells. Blood, 129 (12), pp. 1607-1616. | Show Abstract | Read more

Myeloproliferative neoplasms (MPNs) arise in the hematopoietic stem cell (HSC) compartment as a result of the acquisition of somatic mutations in a single HSC that provides a selective advantage to mutant HSC over normal HSC and promotes myeloid differentiation to engender a myeloproliferative phenotype. This population of somatically mutated HSC, which initiates and sustains MPNs, is termed MPN stem cells. In >95% of cases, mutations that drive the development of an MPN phenotype occur in a mutually exclusive manner in 1 of 3 genes: JAK2, CALR, or MPL The thrombopoietin receptor, MPL, is the key cytokine receptor in MPN development, and these mutations all activate MPL-JAK-STAT signaling in MPN stem cells. Despite common biological features, MPNs display diverse disease phenotypes as a result of both constitutional and acquired factors that influence MPN stem cells, and likely also as a result of heterogeneity in the HSC in which MPN-initiating mutations arise. As the MPN clone expands, it exerts cell-extrinsic effects on components of the bone marrow niche that can favor the survival and expansion of MPN stem cells over normal HSC, further sustaining and driving malignant hematopoiesis. Although developed as targeted therapies for MPNs, current JAK2 inhibitors do not preferentially target MPN stem cells, and as a result, rarely induce molecular remissions in MPN patients. As the understanding of the molecular mechanisms underlying the clonal dominance of MPN stem cells advances, this will help facilitate the development of therapies that preferentially target MPN stem cells over normal HSC.

Quek L, Otto GW, Garnett C, Lhermitte L, Karamitros D, Stoilova B, Lau I-J, Doondeea J, Usukhbayar B, Kennedy A et al. 2016. Genetically distinct leukemic stem cells in human CD34- acute myeloid leukemia are arrested at a hemopoietic precursor-like stage. J Exp Med, 213 (8), pp. 1513-1535. | Show Abstract | Read more

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.

Psaila B, Barkas N, Iskander D, Roy A, Anderson S, Ashley N, Caputo VS, Lichtenberg J, Loaiza S, Bodine DM et al. 2016. Single-cell profiling of human megakaryocyte-erythroid progenitors identifies distinct megakaryocyte and erythroid differentiation pathways. Genome Biol, 17 (1), pp. 83. | Show Abstract | Read more

BACKGROUND: Recent advances in single-cell techniques have provided the opportunity to finely dissect cellular heterogeneity within populations previously defined by "bulk" assays and to uncover rare cell types. In human hematopoiesis, megakaryocytes and erythroid cells differentiate from a shared precursor, the megakaryocyte-erythroid progenitor (MEP), which remains poorly defined. RESULTS: To clarify the cellular pathway in erythro-megakaryocyte differentiation, we correlate the surface immunophenotype, transcriptional profile, and differentiation potential of individual MEP cells. Highly purified, single MEP cells were analyzed using index fluorescence-activated cell sorting and parallel targeted transcriptional profiling of the same cells was performed using a specifically designed panel of genes. Differentiation potential was tested in novel, single-cell differentiation assays. Our results demonstrate that immunophenotypic MEP comprise three distinct subpopulations: "Pre-MEP," enriched for erythroid/megakaryocyte progenitors but with residual myeloid differentiation capacity; "E-MEP," strongly biased towards erythroid differentiation; and "MK-MEP," a previously undescribed, rare population of cells that are bipotent but primarily generate megakaryocytic progeny. Therefore, conventionally defined MEP are a mixed population, as a minority give rise to mixed-lineage colonies while the majority of cells are transcriptionally primed to generate exclusively single-lineage output. CONCLUSIONS: Our study clarifies the cellular hierarchy in human megakaryocyte/erythroid lineage commitment and highlights the importance of using a combination of single-cell approaches to dissect cellular heterogeneity and identify rare cell types within a population. We present a novel immunophenotyping strategy that enables the prospective identification of specific intermediate progenitor populations in erythro-megakaryopoiesis, allowing for in-depth study of disorders including inherited cytopenias, myeloproliferative disorders, and erythromegakaryocytic leukemias.

Wills QF, Higgs DR, Mead AJ. 2015. Studying epigenomics in single cells: what is feasible and what can we learn? Epigenomics, 7 (8), pp. 1231-1234. | Read more

Wills QF, Mead AJ. 2015. Application of single-cell genomics in cancer: promise and challenges. Hum Mol Genet, 24 (R1), pp. R74-R84. | Show Abstract | Read more

Recent advances in single-cell genomics are opening up unprecedented opportunities to transform cancer genomics. While bulk tissue genomic analysis across large populations of tumour cells has provided key insights into cancer biology, this approach does not provide the resolution that is critical for understanding the interaction between different genetic events within the cellular hierarchy of the tumour during disease initiation, evolution, relapse and metastasis. Single-cell genomic approaches are uniquely placed to definitively unravel complex clonal structures and tissue hierarchies, account for spatiotemporal cell interactions and discover rare cells that drive metastatic disease, drug resistance and disease progression. Here we present five challenges that need to be met for single-cell genomics to fulfil its potential as a routine tool alongside bulk sequencing. These might be thought of as being challenges related to samples (processing and scale for analysis), sensitivity and specificity of mutation detection, sources of heterogeneity (biological and technical), synergies (from data integration) and systems modelling. We discuss these in the context of recent advances in technologies and data modelling, concluding with implications for moving cancer research into the clinic.

Cited:

93

Scopus

Woll PS, Kjällquist U, Chowdhury O, Doolittle H, Wedge DC, Thongjuea S, Erlandsson R, Ngara M, Anderson K, Deng Q et al. 2014. Myelodysplastic syndromes are propagated by rare and distinct human cancer stem cells in vivo Cancer Cell, 25 (6), pp. 794-808. | Show Abstract | Read more

Evidence for distinct human cancer stem cells (CSCs) remains contentious and the degree to which differentcancer cells contribute to propagating malignancies in patients remains unexplored. In low- to intermediate-risk myelodysplastic syndromes (MDS), we establish the existence of rare multipotent MDS stem cells (MDS-SCs), and their hierarchical relationship to lineage-restricted MDS progenitors. All identified somatically acquired genetic lesions were backtracked to distinct MDS-SCs, establishing their distinct MDS-propagating function invivo. In isolated del(5q)-MDS, acquisition of del(5q) preceded diverse recurrent driver mutations. Sequential analysis in del(5q)-MDS revealed genetic evolution in MDS-SCs and MDS-progenitors prior to leukemic transformation. These findings provide definitive evidence for rare human MDS-SCs invivo, with extensive implications for the targeting of the cells required and sufficient for MDS-propagation. © 2014 Elsevier Inc.

Grover A, Mancini E, Moore S, Mead AJ, Atkinson D, Rasmussen KD, O'Carroll D, Jacobsen SEW, Nerlov C. 2014. Erythropoietin guides multipotent hematopoietic progenitor cells toward an erythroid fate. J Exp Med, 211 (2), pp. 181-188. | Show Abstract | Read more

The erythroid stress cytokine erythropoietin (Epo) supports the development of committed erythroid progenitors, but its ability to act on upstream, multipotent cells remains to be established. We observe that high systemic levels of Epo reprogram the transcriptomes of multi- and bipotent hematopoietic stem/progenitor cells in vivo. This induces erythroid lineage bias at all lineage bifurcations known to exist between hematopoietic stem cells (HSCs) and committed erythroid progenitors, leading to increased erythroid and decreased myeloid HSC output. Epo, therefore, has a lineage instructive role in vivo, through suppression of non-erythroid fate options, demonstrating the ability of a cytokine to systematically bias successive lineage choices in favor of the generation of a specific cell type.

Cited:

43

Scopus

Böiers C, Carrelha J, Lutteropp M, Luc S, Green JCA, Azzoni E, Woll PS, Mead AJ, Hultquist A, Swiers G et al. 2013. Lymphomyeloid contribution of an immune-restricted progenitor emerging prior to definitive hematopoietic stem cells. Cell stem cell, 13 (5), pp. 535-548. | Show Abstract

In jawed vertebrates, development of an adaptive immune-system is essential for protection of the born organism against otherwise life-threatening pathogens. Myeloid cells of the innate immune system are formed early in development, whereas lymphopoiesis has been suggested to initiate much later, following emergence of definitive hematopoietic stem cells (HSCs). Herein, we demonstrate that the embryonic lymphoid commitment process initiates earlier than previously appreciated, prior to emergence of definitive HSCs, through establishment of a previously unrecognized entirely immune-restricted and lymphoid-primed progenitor. Notably, this immune-restricted progenitor appears to first emerge in the yolk sac and contributes physiologically to the establishment of lymphoid and some myeloid components of the immune-system, establishing the lymphomyeloid lineage restriction process as an early and physiologically important lineage-commitment step in mammalian hematopoiesis. Copyright © 2013 Elsevier Inc. All rights reserved.

Sanjuan-Pla A, Macaulay IC, Jensen CT, Woll PS, Luis TC, Mead A, Moore S, Carella C, Matsuoka S, Bouriez Jones T et al. 2013. Platelet-biased stem cells reside at the apex of the haematopoietic stem-cell hierarchy. Nature, 502 (7470), pp. 232-236. | Show Abstract | Read more

The blood system is maintained by a small pool of haematopoietic stem cells (HSCs), which are required and sufficient for replenishing all human blood cell lineages at millions of cells per second throughout life. Megakaryocytes in the bone marrow are responsible for the continuous production of platelets in the blood, crucial for preventing bleeding--a common and life-threatening side effect of many cancer therapies--and major efforts are focused at identifying the most suitable cellular and molecular targets to enhance platelet production after bone marrow transplantation or chemotherapy. Although it has become clear that distinct HSC subsets exist that are stably biased towards the generation of lymphoid or myeloid blood cells, we are yet to learn whether other types of lineage-biased HSC exist or understand their inter-relationships and how differently lineage-biased HSCs are generated and maintained. The functional relevance of notable phenotypic and molecular similarities between megakaryocytes and bone marrow cells with an HSC cell-surface phenotype remains unclear. Here we identify and prospectively isolate a molecularly and functionally distinct mouse HSC subset primed for platelet-specific gene expression, with enhanced propensity for short- and long-term reconstitution of platelets. Maintenance of platelet-biased HSCs crucially depends on thrombopoietin, the primary extrinsic regulator of platelet development. Platelet-primed HSCs also frequently have a long-term myeloid lineage bias, can self-renew and give rise to lymphoid-biased HSCs. These findings show that HSC subtypes can be organized into a cellular hierarchy, with platelet-primed HSCs at the apex. They also demonstrate that molecular and functional priming for platelet development initiates already in a distinct HSC population. The identification of a platelet-primed HSC population should enable the rational design of therapies enhancing platelet output.

Mead AJ, Constantinescu SN, Jacobsen SE. 2013. Germline counterparts of oncogenic mutations: who gives a JAK?. Oncotarget, 4 (6), pp. 814-815. | Read more

1570