Integrative single-cell expression and functional studies unravels a sensitization to cytarabine-based chemotherapy through HIF pathway inhibition in AML leukemia stem cells

Relapse remains a major challenge in the clinical management of acute myeloid leukemia (AML) and is driven by rare therapy-resistant leukemia stem cells (LSCs) that reside in specific bone marrow niches. Hypoxia signaling maintains cells in a quiescent and metabolically relaxed state, desensitizing them to chemotherapy. This suggests the hypothesis that hypoxia contributes to the chemoresistance of AML-LSCs and may represent a therapeutic target to sensitize AML-LSCs to chemotherapy. Here, we identify HIFhigh and HIFlow specific AML subgroups (inv(16)/t(8;21) and MLLr, respectively) and provide a comprehensive single-cell expression atlas of 119,000 AML cells and AML-LSCs in paired diagnostic-relapse samples from these molecular subgroups. The HIF/hypoxia pathway signature is attenuated in AML-LSCs compared with more differentiated AML cells but is more expressed than in healthy hematopoietic cells. Importantly, chemical inhibition of HIF cooperates with standard-of-care chemotherapy to impair AML growth and to substantially eliminate AML-LSCs in vitro and in vivo. These findings support the HIF pathway in the stem cell-driven drug resistance of AML and unravel avenues for combinatorial targeted and chemotherapy-based approaches to specifically eliminate AML-LSCs.

Generation of transgene-free hematopoietic stem cells from human induced pluripotent stem cells

Hematopoietic stem cells (HSCs) are the rare cells responsible for the lifelong curative effects of hematopoietic cell (HC) transplantation. The demand for clinical-grade HSCs has increased significantly in recent decades, leading to major difficulties in treating patients. A promising but not yet achieved goal is the generation of HSCs from pluripotent stem cells. Here, we have obtained vector- and stroma-free transplantable HSCs by differentiating human induced pluripotent stem cells (hiPSCs) using an original one-step culture system. After injection into immunocompromised mice, cells derived from hiPSCs settle in the bone marrow and form a robust multilineage hematopoietic population that can be serially transplanted. Single-cell RNA sequencing shows that this repopulating activity is due to a hematopoietic population that is transcriptionally similar to human embryonic aorta-derived HSCs. Overall, our results demonstrate the generation of HSCs from hiPSCs and will help identify key regulators of HSC production during human ontogeny.

Measurable Residual Disease and Fusion Partner Independently Predict Survival and Relapse Risk in Childhood KMT2A-Rearranged Acute Myeloid Leukemia: A Study by the International Berlin-Frankfurt-Münster Study Group

PURPOSE

A previous study by the International Berlin-Frankfurt-Münster Study Group (I-BFM-SG) on childhood KMT2A-rearranged (KMT2A-r) AML demonstrated the prognostic value of the fusion partner. This I-BFM-SG study investigated the value of flow cytometry-based measurable residual disease (flow-MRD) and evaluated the benefit of allogeneic stem-cell transplantation (allo-SCT) in first complete remission (CR1) in this disease.

METHODS

A total of 1,130 children with KMT2A-r AML, diagnosed between January 2005 and December 2016, were assigned to high-risk (n = 402; 35.6%) or non-high-risk (n = 728; 64.4%) fusion partner-based groups. Flow-MRD levels at both end of induction 1 (EOI1) and 2 (EOI2) were available for 456 patients and were considered negative (<0.1%) or positive (≥0.1%). End points were 5-year event-free survival (EFS), cumulative incidence of relapse (CIR), and overall survival (OS).

RESULTS

The high-risk group had inferior EFS (30.3% high risk v 54.0% non-high risk; P < .0001), CIR (59.7% v 35.2%; P < .0001), and OS (49.2% v 70.5%; P < .0001). EOI2 MRD negativity was associated with superior EFS (n = 413; 47.6% MRD negativity v n = 43; 16.3% MRD positivity; P < .0001) and OS (n = 413; 66.0% v n = 43; 27.9%; P < .0001), and showed a trend toward lower CIR (n = 392; 46.1% v n = 26; 65.4%; P = .016). Similar results were obtained for patients with EOI2 MRD negativity within both risk groups, except that within the non-high-risk group, CIR was comparable with that of patients with EOI2 MRD positivity. Allo-SCT in CR1 only reduced CIR (hazard ratio, 0.5 [95% CI, 0.4 to 0.8]; P = .00096) within the high-risk group but did not improve OS. In multivariable analyses, EOI2 MRD positivity and high-risk group were independently associated with inferior EFS, CIR, and OS.

CONCLUSION

EOI2 flow-MRD is an independent prognostic factor and should be included as risk stratification factor in childhood KMT2A-r AML. Treatment approaches other than allo-SCT in CR1 are needed to improve prognosis.

The KMT2A recombinome of acute leukemias in 2023

Chromosomal rearrangements of the human KMT2A/MLL gene are associated with de novo as well as therapy-induced infant, pediatric, and adult acute leukemias. Here, we present the data obtained from 3401 acute leukemia patients that have been analyzed between 2003 and 2022. Genomic breakpoints within the KMT2A gene and the involved translocation partner genes (TPGs) and KMT2A-partial tandem duplications (PTDs) were determined. Including the published data from the literature, a total of 107 in-frame KMT2A gene fusions have been identified so far. Further 16 rearrangements were out-of-frame fusions, 18 patients had no partner gene fused to 5'-KMT2A, two patients had a 5'-KMT2A deletion, and one ETV6::RUNX1 patient had an KMT2A insertion at the breakpoint. The seven most frequent TPGs and PTDs account for more than 90% of all recombinations of the KMT2A, 37 occur recurrently and 63 were identified so far only once. This study provides a comprehensive analysis of the KMT2A recombinome in acute leukemia patients. Besides the scientific gain of information, genomic breakpoint sequences of these patients were used to monitor minimal residual disease (MRD). Thus, this work may be directly translated from the bench to the bedside of patients and meet the clinical needs to improve patient survival.

Characterization of lymphocyte profiles in children with syndromic obesity

BACKGROUND

Little is known about blood lymphocyte subpopulations in children with common (CO) or syndromic (SO) obesity. We aimed to describe the blood lymphocyte profiles of obese children and to search for associations with clinical phenotypes.

METHODS

Main blood lymphocyte subpopulations were analyzed in 159 children with CO and 34 with SO in a retrospective cohort. Phenotypes included obesity history, body mass index (BMI) Z score, percentage fat mass, and inflammatory parameters. Correlations were performed between phenotypes and circulating lymphocyte profiles.

RESULTS

Children with SO had a higher BMI Z score (5.5 ± 1.7 SD) than children with CO (4.7 ± 0.9 SD; p = 0.01). Significant differences were found for lymphocyte counts, including a higher percentage of CD19⁺ B cells (SO = 20.1 ± 6.7 vs. CO = 17.1 ± 6.1%, p = 0.03), despite lower absolute numbers (SO = 0.57 ± 0.20 vs. CO = 0.63 ± 1.9 g/L, p < 0.01). However, no difference in the lymphocyte profile was found between children with SO and those with the most severe CO (BMI Z score ≥ 4.7 SD).

CONCLUSION

Children with SO have altered blood lymphocyte profiles with increased prevalence of CD19⁺ B cells, which is closely linked to the degree of obesity severity and inflammatory markers.

High caspase 3 and vulnerability to dual BCL2 family inhibition define ETO2::GLIS2 pediatric leukemia

Pediatric acute myeloid leukemia expressing the ETO2::GLIS2 fusion oncogene is associated with dismal prognosis. Previous studies have shown that ETO2::GLIS2 can efficiently induce leukemia development associated with strong transcriptional changes but those amenable to pharmacological targeting remained to be identified. By studying an inducible ETO2::GLIS2 cellular model, we uncovered that de novo ETO2::GLIS2 expression in human cells led to increased CASP3 transcription, CASP3 activation, and cell death. Patient-derived ETO2::GLIS2+ leukemic cells expressed both high CASP3 and high BCL2. While BCL2 inhibition partly inhibited ETO2::GLIS2+ leukemic cell proliferation, BH3 profiling revealed that it also sensitized these cells to MCL1 inhibition indicating a functional redundancy between BCL2 and MCL1. We further show that combined inhibition of BCL2 and MCL1 is mandatory to abrogate disease progression using in vivo patient-derived xenograft models. These data reveal that a transcriptional consequence of ETO2::GLIS2 expression includes a positive regulation of the pro-apoptotic CASP3 and associates with a vulnerability to combined targeting of two BCL2 family members providing a novel therapeutic perspective for this aggressive pediatric AML subgroup.

Clonal hematopoiesis driven by chromosome 1q/MDM4 trisomy defines a canonical route toward leukemia in Fanconi anemia

Fanconi anemia (FA) patients experience chromosome instability, yielding hematopoietic stem/progenitor cell (HSPC) exhaustion and predisposition to poor-prognosis myeloid leukemia. Based on a longitudinal cohort of 335 patients, we performed clinical, genomic, and functional studies in 62 patients with clonal evolution. We found a unique pattern of somatic structural variants and mutations that shares features of BRCA-related cancers, the FA-hallmark being unbalanced, microhomology-mediated translocations driving copy-number alterations. Half the patients developed chromosome 1q gain, driving clonal hematopoiesis through MDM4 trisomy downmodulating p53 signaling later followed by secondary acute myeloid lukemia genomic alterations. Functionally, MDM4 triplication conferred greater fitness to murine and human primary FA HSPCs, rescued inflammation-mediated bone marrow failure, and drove clonal dominance in FA mouse models, while targeting MDM4 impaired leukemia cells in vitro and in vivo. Our results identify a linear route toward secondary leukemogenesis whereby early MDM4-driven downregulation of basal p53 activation plays a pivotal role, opening monitoring and therapeutic prospects.

Germline RUNX1 variants in paediatric patients in a French specialised centre

Familial platelet disorder with associated myeloid malignancy (FPD-MM; OMIM 601399) is related to germline RUNX1 mutation. The pathogenicity of RUNX1 variants was initially linked to FPD-MM phenotype, but the discovery of new variants through the expansion of genetic explorations in leukaemia is questioning this assertion. In this study, we add 10 families with germline RUNX1 variant explored at Armand Trousseau Hospital for leukaemia diagnosis or thrombocytopenia, to the 259 described so far. Detailed description of their personal and family history of haematological pathologies allows identifying three phenotypes related to germline RUNX1 variants: thrombocytopenia and/or malignant haematological disease with family history of haematological diseases, thrombocytopenia with no family history of haematological diseases and acute lymphoblastic leukaemia (ALL) with no family history of haematological diseases. In the latter phenotype, ALL characteristics involving RUNX1 suggest the implication of germline variants in the onset of the malignancy.

Biallelic CXCR2 loss-of-function mutations define a distinct congenital neutropenia entity

Not available.

A circulating subset of BRAFV600E -positive cells in infants with high-risk Langerhans cell histiocytosis treated with BRAF inhibitors

BRAF inhibitors are an effective treatment for BRAF^V600E -mutated, risk-organ-positive Langerhans cell histiocytosis (RO⁺ LCH). However, cell-free BRAF^V600E DNA often persists during therapy and recurrence frequently occurs after therapy discontinuation. To identify a pathological reservoir of BRAF^V600E -mutated cells, we studied peripheral blood cells obtained from six infants with RO⁺ multisystem (MS) LCH that received targeted therapy. After cell sorting, the BRAF^V600E mutation was detected in monocytes (n = 5), B lymphocytes (n = 3), T lymphocytes (n = 2), and myeloid and plasmacytoid dendritic cells (n = 2 each). This biomarker may offer an interesting tool for monitoring the effectiveness of new therapeutic approaches for weaning children with RO⁺ LCH from targeted therapy.

Human erythroleukemia genetics and transcriptomes identify master transcription factors as functional disease drivers

Acute erythroleukemia (AEL or acute myeloid leukemia [AML]-M6) is a rare but aggressive hematologic malignancy. Previous studies showed that AEL leukemic cells often carry complex karyotypes and mutations in known AML-associated oncogenes. To better define the underlying molecular mechanisms driving the erythroid phenotype, we studied a series of 33 AEL samples representing 3 genetic AEL subgroups including TP53-mutated, epigenetic regulator-mutated (eg, DNMT3A, TET2, or IDH2), and undefined cases with low mutational burden. We established an erythroid vs myeloid transcriptome-based space in which, independently of the molecular subgroup, the majority of the AEL samples exhibited a unique mapping different from both non-M6 AML and myelodysplastic syndrome samples. Notably, >25% of AEL patients, including in the genetically undefined subgroup, showed aberrant expression of key transcriptional regulators, including SKI, ERG, and ETO2. Ectopic expression of these factors in murine erythroid progenitors blocked in vitro erythroid differentiation and led to immortalization associated with decreased chromatin accessibility at GATA1-binding sites and functional interference with GATA1 activity. In vivo models showed development of lethal erythroid, mixed erythroid/myeloid, or other malignancies depending on the cell population in which AEL-associated alterations were expressed. Collectively, our data indicate that AEL is a molecularly heterogeneous disease with an erythroid identity that results in part from the aberrant activity of key erythroid transcription factors in hematopoietic stem or progenitor cells.

Ontogenic Changes in Hematopoietic Hierarchy Determine Pediatric Specificity and Disease Phenotype in Fusion Oncogene-Driven Myeloid Leukemia

Fusion oncogenes are prevalent in several pediatric cancers, yet little is known about the specific associations between age and phenotype. We observed that fusion oncogenes, such as ETO2-GLIS2, are associated with acute megakaryoblastic or other myeloid leukemia subtypes in an age-dependent manner. Analysis of a novel inducible transgenic mouse model showed that ETO2-GLIS2 expression in fetal hematopoietic stem cells induced rapid megakaryoblastic leukemia whereas expression in adult bone marrow hematopoietic stem cells resulted in a shift toward myeloid transformation with a strikingly delayed in vivo leukemogenic potential. Chromatin accessibility and single-cell transcriptome analyses indicate ontogeny-dependent intrinsic and ETO2-GLIS2-induced differences in the activities of key transcription factors, including ERG, SPI1, GATA1, and CEBPA. Importantly, switching off the fusion oncogene restored terminal differentiation of the leukemic blasts. Together, these data show that aggressiveness and phenotypes in pediatric acute myeloid leukemia result from an ontogeny-related differential susceptibility to transformation by fusion oncogenes. SIGNIFICANCE: This work demonstrates that the clinical phenotype of pediatric acute myeloid leukemia is determined by ontogeny-dependent susceptibility for transformation by oncogenic fusion genes. The phenotype is maintained by potentially reversible alteration of key transcription factors, indicating that targeting of the fusions may overcome the differentiation blockage and revert the leukemic state.See related commentary by Cruz Hernandez and Vyas, p. 1653.This article is highlighted in the In This Issue feature, p. 1631.

Acute megakaryoblastic leukemia (excluding Down syndrome) remains an acute myeloid subgroup with inferior outcome in the French ELAM02 trial

We report the outcome of 27 children with de novo acute megakaryoblastic leukemia (AMKL) (excluding Down syndrome) enrolled in the French multicenter prospective study ELAM02 (2005-2011). There was no difference in gender, initial leukocyte count, CNS involvement, and complete remission rate (88.9%), as compared to other acute myeloid leukemia (AML) subtypes. AMKL patients had a significantly poorer outcome (5-year overall survival 54% [CI 95% 33%-71%] than children with other AML subtypes (5-year overall survival 73% [CI 95% 68%-77%] p = 0.02). Gender, age, CNS leukemia, hyperleukocytosis, complete remission or cytogenetic subgroups were not significant prognostic factors of disease-free survival. AMKL (excluding Down syndrom) remains an AML subgroup with inferior outcome.

The MLL recombinome of acute leukemias in 2017

Chromosomal rearrangements of the human MLL/KMT2A gene are associated with infant, pediatric, adult and therapy-induced acute leukemias. Here we present the data obtained from 2345 acute leukemia patients. Genomic breakpoints within the MLL gene and the involved translocation partner genes (TPGs) were determined and 11 novel TPGs were identified. Thus, a total of 135 different MLL rearrangements have been identified so far, of which 94 TPGs are now characterized at the molecular level. In all, 35 out of these 94 TPGs occur recurrently, but only 9 specific gene fusions account for more than 90% of all illegitimate recombinations of the MLL gene. We observed an age-dependent breakpoint shift with breakpoints localizing within MLL intron 11 associated with acute lymphoblastic leukemia and younger patients, while breakpoints in MLL intron 9 predominate in AML or older patients. The molecular characterization of MLL breakpoints suggests different etiologies in the different age groups and allows the correlation of functional domains of the MLL gene with clinical outcome. This study provides a comprehensive analysis of the MLL recombinome in acute leukemia and demonstrates that the establishment of patient-specific chromosomal fusion sites allows the design of specific PCR primers for minimal residual disease analyses for all patients.

Comprehensive mutational profiling of core binding factor acute myeloid leukemia

Acute myeloid leukemia (AML) with t(8;21) or inv(16) have been recognized as unique entities within AML and are usually reported together as core binding factor AML (CBF-AML). However, there is considerable clinical and biological heterogeneity within this group of diseases, and relapse incidence reaches up to 40%. Moreover, translocations involving CBFs are not sufficient to induce AML on its own and the full spectrum of mutations coexisting with CBF translocations has not been elucidated. To address these issues, we performed extensive mutational analysis by high-throughput sequencing in 215 patients with CBF-AML enrolled in the Phase 3 Trial of Systematic Versus Response-adapted Timed-Sequential Induction in Patients With Core Binding Factor Acute Myeloid Leukemia and Treating Patients with Childhood Acute Myeloid Leukemia with Interleukin-2 trials (age, 1-60 years). Mutations in genes activating tyrosine kinase signaling (including KIT, N/KRAS, and FLT3) were frequent in both subtypes of CBF-AML. In contrast, mutations in genes that regulate chromatin conformation or encode members of the cohesin complex were observed with high frequencies in t(8;21) AML (42% and 18%, respectively), whereas they were nearly absent in inv(16) AML. High KIT mutant allele ratios defined a group of t(8;21) AML patients with poor prognosis, whereas high N/KRAS mutant allele ratios were associated with the lack of KIT or FLT3 mutations and a favorable outcome. In addition, mutations in epigenetic modifying or cohesin genes were associated with a poor prognosis in patients with tyrosine kinase pathway mutations, suggesting synergic cooperation between these events. These data suggest that diverse cooperating mutations may influence CBF-AML pathophysiology as well as clinical behavior and point to potential unique pathogenesis of t(8;21) vs inv(16) AML.

Childhood diagnosis of genetic thrombocytopenia with mutation in the ankyrine repeat domain 26 gene

The most common diagnosis for pediatric thrombocytopenia is immune thrombocytopenia. Nevertheless, in atypical cases, the hypothesis of an inherited thrombocytopenia has to be investigated. We report a series of cases of a newly described entity, genetic thrombocytopenia with mutation in the ankyrine 26 gene, diagnosed from the exploration of five pediatric cases of thrombocytopenia. This entity is characterized by a moderate thrombocytopenia with normal mean platelet volume, and poorly bleeding. Its transmission is autosomal dominant. Final diagnosis is made by sequencing of a short DNA region of ANKRD26 gene. This pathology can be considered as an hematological malignancy predisposition syndrome.

CONCLUSION

We report the first cohort of pediatric patients diagnosed with thrombocytopenia with mutation in the ankyrine 26. The aim is to underline the specificities of this entity in children and bring it to the knowledge of pediatricians who may be in first place to manage these patients.

WHAT IS KNOWN

• Genetic thrombocytopenia with mutation in the ankyrine 26 gene is a recently described entity, which seems to be considered as a predisposition for hematologic malignancies. • The first cohort has been reported in 2011, by Noris et al., in 78 Italian adult patients. What is New: • We describe clinical and biological features of the first pediatric cohort diagnosed with genetic thrombocytopenia with mutation in the ankyrine 26 gene. • It seemed important to consider the pediatric specificities of this entity to enable pediatricians to investigate, diagnose, and manage pediatric patients and their families.

Clinical spectrum and long-term follow-up of 14 cases with G6PC3 mutations from the French Severe Congenital Neutropenia Registry

Background

The purpose of this study was to describe the natural history of severe congenital neutropenia (SCN) in 14 patients with G6PC3 mutations and enrolled in the French SCN registry.

Methods

Among 605 patients included in the French SCN registry, we identified 8 pedigrees that included 14 patients with autosomal recessive G6PC3 mutations.

Results

Median age at the last visit was 22.4 years. All patients had developed various comordibities, including prominent veins (n = 12), cardiac malformations (n = 12), intellectual disability (n = 7), and myopathic syndrome with recurrent painful cramps (n = 1). Three patients developed Crohn’s disease, and five had chronic diarrhea with steatorrhea. Neutropenia was profound (<0.5 × 10⁹/l) in almost all cases at diagnosis and could marginally fluctuate. The bone marrow smears exhibited mild late-stage granulopoeitic defects. One patient developed myelodysplasia followed by acute myelogenous leukemia with translocation (18, 21) at age 14 years, cured by chemotherapy and hematopoietic stem cell transplantation. Four deaths occurred, including one from sepsis at age 5, one from pulmonary late-stage insufficiency at age 19, and two from sudden death, both at age 30 years. A new homozygous mutation (c.249G > A /p.Trp83*) was detected in one pedigree.

Conclusions

Severe congenital neutropenia with autosomal recessive G6PC3 mutations is associated with considerable clinical heterogeneity. This series includes the first described case of malignancy in this neutropenia.

SPRED1, a RAS MAPK pathway inhibitor that causes Legius syndrome, is a tumour suppressor downregulated in paediatric acute myeloblastic leukaemia

Constitutional dominant loss-of-function mutations in the SPRED1 gene cause a rare phenotype referred as neurofibromatosis type 1 (NF1)-like syndrome or Legius syndrome, consisted of multiple café-au-lait macules, axillary freckling, learning disabilities and macrocephaly. SPRED1 is a negative regulator of the RAS MAPK pathway and can interact with neurofibromin, the NF1 gene product. Individuals with NF1 have a higher risk of haematological malignancies. SPRED1 is highly expressed in haematopoietic cells and negatively regulates haematopoiesis. SPRED1 seemed to be a good candidate for leukaemia predisposition or transformation. We performed SPRED1 mutation screening and expression status in 230 paediatric lymphoblastic and acute myeloblastic leukaemias (AMLs). We found a loss-of-function frameshift SPRED1 mutation in a patient with Legius syndrome. In this patient, the leukaemia blasts karyotype showed a SPRED1 loss of heterozygosity, confirming SPRED1 as a tumour suppressor. Our observation confirmed that acute leukaemias are rare complications of the Legius syndrome. Moreover, SPRED1 was significantly decreased at RNA and protein levels in the majority of AMLs at diagnosis compared with normal or paired complete remission bone marrows. SPRED1 decreased expression correlated with genetic features of AML. Our study reveals a new mechanism which contributes to deregulate RAS MAPK pathway in the vast majority of paediatric AMLs.

Human induced pluripotent stem cells can reach complete terminal maturation: in vivo and in vitro evidence in the erythropoietic differentiation model

BACKGROUND

Human induced pluripotent stem cells offer perspectives for cell therapy and research models for diseases. We applied this approach to the normal and pathological erythroid differentiation model by establishing induced pluripotent stem cells from normal and homozygous sickle cell disease donors.

DESIGN AND METHODS

We addressed the question as to whether these cells can reach complete erythroid terminal maturation notably with a complete switch from fetal to adult hemoglobin. Sickle cell disease induced pluripotent stem cells were differentiated in vitro into red blood cells and characterized for their terminal maturation in terms of hemoglobin content, oxygen transport capacity, deformability, sickling and adherence. Nucleated erythroblast populations generated from normal and pathological induced pluripotent stem cells were then injected into non-obese diabetic severe combined immunodeficiency mice to follow the in vivo hemoglobin maturation.

RESULTS

We observed that in vitro erythroid differentiation results in predominance of fetal hemoglobin which rescues the functionality of red blood cells in the pathological model of sickle cell disease. We observed, in vivo, the switch from fetal to adult hemoglobin after infusion of nucleated erythroid precursors derived from either normal or pathological induced pluripotent stem cells into mice.

CONCLUSIONS

These results demonstrate that human induced pluripotent stem cells: i) can achieve complete terminal erythroid maturation, in vitro in terms of nucleus expulsion and in vivo in terms of hemoglobin maturation; and ii) open the way to generation of functionally corrected red blood cells from sickle cell disease induced pluripotent stem cells, without any genetic modification or drug treatment.

Red blood cells from induced pluripotent stem cells: hurdles and developments

PURPOSE OF REVIEW

In the context of chronic blood supply difficulties, generating cultured red blood cells (cRBCs) in vitro after amplification of stem cells makes sense. This review will focus on the recent findings about the generation of erythroid cells from induced pluripotent stem (iPS) cells and deals with the hurdles and next developments that will occur.

RECENT FINDINGS

The most proliferative source of stem cells for generating cRBCs is the cord blood, but this source is limited in terms of hematopoietic stem cells and dependent on donations. Pluripotent stem cells are thus the best candidates and potential sources of cRBCs. Critical advances have led towards the in-vitro production of functional RBCs from iPS cells in the last few years.

SUMMARY

Because iPS cells can proliferate indefinitely and can be selected for a phenotype of interest, they are potential candidates to organize complementary sources of RBCs for transfusion. Proof of concept of generating cRBCs from iPS cells has been performed, but the procedures need to be optimized to lead to clinical application in blood transfusion. Several crucial points remain to be resolved. Notably these include the choice of the initial cell type to generate iPS cells, the method of reprogramming, that is, to ensure the safety of iPS cells as clinical grade, the optimization of erythrocyte differentiation, and the definition of good manufacturing practice (GMP) conditions for industrial production.

Human fetal liver: an in vitro model of erythropoiesis

We previously described the large-scale production of RBCs from hematopoietic stem cells (HSCs) of diverse sources. Our present efforts are focused to produce RBCs thanks to an unlimited source of stem cells. Human embryonic stem (ES) cells or induced pluripotent stem cell (iPS) are the natural candidates. Even if the proof of RBCs production from these sources has been done, their amplification ability is to date not sufficient for a transfusion application. In this work, our protocol of RBC production was applied to HSC isolated from fetal liver (FL) as an intermediate source between embryonic and adult stem cells. We studied the erythroid potential of FL-derived CD34(+) cells. In this in vitro model, maturation that is enucleation reaches a lower level compared to adult sources as observed for embryonic or iP, but, interestingly, they (i) displayed a dramatic in vitro expansion (100-fold more when compared to CB CD34(+)) and (ii) 100% cloning efficiency in hematopoietic progenitor assays after 3 days of erythroid induction, as compared to 10-15% cloning efficiency for adult CD34(+) cells. This work supports the idea that FL remains a model of study and is not a candidate for ex vivo RBCS production for blood transfusion as a direct source of stem cells but could be helpful to understand and enhance proliferation abilities for primitive cells such as ES cells or iPS.

Banking of pluripotent adult stem cells as an unlimited source for red blood cell production: potential applications for alloimmunized patients and rare blood challenges

The transfusion of red blood cells (RBCs) is now considered a well-settled and essential therapy. However, some difficulties and constraints still occur, such as long-term blood product shortage, blood donor population aging, known and yet unknown transfusion-transmitted infectious agents, growing cost of the transfusion supply chain management, and the inescapable blood group polymorphism barrier. Red blood cells can be now cultured in vitro from human hematopoietic, human embryonic, or human-induced pluripotent stem cells (hiPSCs). The highly promising hiPSC technology represents a potentially unlimited source of RBCs and opens the door to the revolutionary development of a new generation of allogeneic transfusion products. Assuming that in vitro large-scale cultured RBC production efficiently operates in the near future, we draw here some futuristic but realistic scenarios regarding potential applications for alloimmunized patients and those with a rare blood group. We retrospectively studied a cohort of 16,486 consecutive alloimmunized patients (10-year period), showing 1 to 7 alloantibodies with 361 different antibody combinations. We showed that only 3 hiPSC clones would be sufficient to match more than 99% of the 16,486 patients in need of RBC transfusions. The study of the French National Registry of People with a Rare Blood Phenotype/Genotype (10-year period) shows that 15 hiPSC clones would cover 100% of the needs in patients of white ancestry. In addition, one single hiPSC clone would meet 73% of the needs in alloimmunized patients with sickle cell disease for whom rare cryopreserved RBC units were required. As a result, we consider that a very limited number of RBC clones would be able to not only provide for the need for most alloimmunized patients and those with a rare blood group but also efficiently allow for a policy for alloimmunization prevention in multiply transfused patients.

A cytometric study of the red blood cells in Gaucher disease reveals their abnormal shape that may be involved in increased erythrophagocytosis

BACKGROUND

Gaucher disease is a sphingolipidosis caused by a deficiency of the enzyme glucocerebrosidase. Macrophages transform into pathogenic Gaucher cells following the phagocytosis of red blood cells (RBCs) and subsequent accumulation of glucosylceramide. Enhanced erythrophagocytosis is one feature of the disease indicating abnormal macrophage-RBC interactions. We hypothesized that the erythrophagocytosis observed in Gaucher disease may be at least partly due to abnormalities in the RBCs themselves.

METHODS

To investigate this hypothesis, we used flow cytometry FSC/SSC to study RBCs sampled from seven patients with Gaucher disease in terms of their shape and the expression of markers of senescence and phagocytosis. Cells from two of the seven patients were evaluated before and 9 months after the start of enzyme-replacement therapy.

RESULTS

Untreated patients were found to have abnormal flow-cytometry profiles suggesting an alteration of Gaucher RBC morphology. Scanning electron microscopy confirmed this finding by revealing many abnormally shaped RBCs. Whereas there was no evidence of desialylation of membrane glycoconjugates or phosphatidylserine exposure, RBC viability (calcein-AM test) and CD47 expression were reduced. These anomalies found in RBCs sampled from two patients before treatment, were no longer present after a 9 month-long enzyme-replacement therapy.

CONCLUSIONS

We report on previously overlooked alterations of Gaucher RBCs that may facilitate erythrophagocytosis in untreated patients. Their potential role in the anemia, the excess of aggregation and rheological anomalies associated with Gaucher disease must now be addressed. RBC anomalies may take part in the abnormal crosstalk between RBCs and macrophages leading to the accumulation of Gaucher cells.

Red blood cell generation from human induced pluripotent stem cells: perspectives for transfusion medicine

BACKGROUND

Ex vivo manufacture of red blood cells from stem cells is a potential means to ensure an adequate and safe supply of blood cell products. Advances in somatic cell reprogramming of human induced pluripotent stem cells have opened the door to generating specific cells for cell therapy. Human induced pluripotent stem cells represent a potentially unlimited source of stem cells for erythroid generation for transfusion medicine.

DESIGN AND METHODS

We characterized the erythroid differentiation and maturation of human induced pluripotent stem cell lines obtained from human fetal (IMR90) and adult fibroblasts (FD-136) compared to those of a human embryonic stem cell line (H1). Our protocol comprises two steps: (i) differentiation of human induced pluripotent stem cells by formation of embryoid bodies with indispensable conditioning in the presence of cytokines and human plasma to obtain early erythroid commitment, and (ii) differentiation/maturation to the stage of cultured red blood cells in the presence of cytokines. The protocol dispenses with major constraints such as an obligatory passage through a hematopoietic progenitor, co-culture on a cellular stroma and use of proteins of animal origin.

RESULTS

We report for the first time the complete differentiation of human induced pluripotent stem cells into definitive erythrocytes capable of maturation up to enucleated red blood cells containing fetal hemoglobin in a functional tetrameric form.

CONCLUSIONS

Red blood cells generated from human induced pluripotent stem cells pave the way for future development of allogeneic transfusion products. This could be done by banking a very limited number of red cell phenotype combinations enabling the safe transfusion of a great number of immunized patients.

Unimpaired terminal erythroid differentiation and preserved enucleation capacity in myelodysplastic 5q(del) clones: a single cell study

BACKGROUND

Anemia is a characteristic of myelodysplastic syndromes, such as the rare 5q- syndrome, but its mechanism remains unclear. In particular, data are lacking on the terminal phase of differentiation of erythroid cells (enucleation) in myelodysplastic syndromes.

DESIGN AND METHODS

We used a previously published culture model to generate mature red blood cells in vitro from human hematopoietic progenitor cells in order to study the pathophysiology of the 5q- syndrome. Our model enables analysis of cell proliferation and differentiation at a single cell level and determination of the enucleation capacity of erythroid precursors.

RESULTS

The erythroid commitment of 5q(del) clones was not altered and their terminal differentiation capacity was preserved since they achieved final erythroid maturation (enucleation stage). The drop in red blood cell production was secondary to the decrease in the erythroid progenitor cell pool and to impaired proliferative capacity. RPS14 gene haploinsufficiency was related to defective erythroid proliferation but not to differentiation capacity.

CONCLUSIONS

The 5q- syndrome should be considered a quantitative rather than qualitative bone marrow defect. This observation might open the way to new therapeutic concepts.

Stem cells--a source of adult red blood cells for transfusion purposes: present and future

We have sufficient knowledge of the biology of hematopoietic stem cells to hope that we might generate human red blood cells in the laboratory. It may soon be possible to produce enough to transfuse "cultured" red blood cells to manufacture human red blood cells from hematopoietic stem cells for transfusion purposes. This article describes progress and the challenges that remain in the search for in vitro generated red blood cells that can be efficiently manufactured in high volumes and given to any recipient.

Stem cell mobilization in idiopathic steroid-sensitive nephrotic syndrome

Steroid-sensitive nephrotic syndrome (SSNS) is classically thought to be a T-cell disorder. The aim of this study was to examine whether or not thymus homeostasis was affected in SSNS. Mature and naive T cell recent thymic emigrants were quantified in the peripheral blood of nephrotic patients and controls. Because the generation of new T cells by the thymus ultimately depends on hematopoietic stem cells, CD34+ cells were also included in the study. Nineteen patients with SSNS during relapse, 13 with SSNS during proteinuria remission, and 18 controls were studied. Cell-surface markers (CD3, CD4, CD8, CD19, CD16, CD56, CD45RA, CD62L, CD34, and CD38) were analyzed by flow cytometric analysis. T-cell rearrangement excision circles (TRECs) were quantified in CD2+ cells by real-time polymerase chain reaction. Stroma cell-derived factor-1 (SDF-1) genotype and metalloproteinase-9 (MMP-9) plasma levels were also determined. Mature T cells (CD4+ and CD8+), circulating naive T cells (CD62L+ and CD3+ CD62L+), and recent thymic emigrants (CD45RA+) as well as TRECs, that measure thymus production, had a similar level in the three groups of patients. Conversely, CD34+ hematopoietic stem cells displayed a two-fold increase in SSNS patients during relapse either compared with controls or SSNS patients at remission. In addition, compared with controls, SSNS patients at remission displayed (1) a decrease in CD19+ cells (B cells) and (2) an increase in CD16CD56+ cells [natural killer (NK) cells]. In conclusion, thymus homeostasis is not significantly affected in nephrotic patients. Hematopoietic stem-cell mobilization at proteinuria relapse, as well as changes in B and NK cells during remission, suggest that SSNS might be due to a general disturbance of hematopoietic and immune cell trafficking.

High WT1 expression after induction therapy predicts high risk of relapse and death in pediatric acute myeloid leukemia

PURPOSE

To determine whether minimal residual disease (MRD) measured by Wilms' tumor gene 1 (WT1) expression is a prognostic marker in pediatric acute myeloid leukemia (AML), we quantified WT1 transcript by real-time quantitative-polymerase chain reaction in 92 AML at diagnosis and during follow-up.

PATIENTS AND METHODS

Patients (median age, 6 years; cytogenetics, favorable 27%, intermediate 59%, poor 13%) were treated between 1995 and 2002 and enrolled in Leucémie aiguë Myéloblastique Enfant (LAME) 89/91, LAME 99 pilot study and Acute Promyelocytic Leukemia French collaborative protocols. With a median follow-up of 26 months, event-free survival was 56% with a standard deviation (SD) of 5% and overall survival of 62.5% with an SD of 6%. WT1 copy number was normalized by TATA box binding protein gene transcripts and expressed as WT1/TBP x 1,000 ratio. Median WT1 ratio in normal patient controls was 12 (range, 0 to 57). A level over two SD than normal bone marrow controls (ie, WT1 ratio > 50), was considered as significant overexpression.

RESULTS

At diagnosis, WT1 overexpression was detected in 78% of patients (72 of 92 patients; median copy ratio, 2231). The WT1 values were significantly higher (P = .01) in favorable cytogenetics and lower (P < .0001) in M5-FAB subtype, 11q23 rearrangements (P < .001), and infants (P = .003) and demonstrate a strong correlation with fusion transcript AML1-ETO, PML-RARalpha expression. After induction treatment, WT1 ratio was analyzed in 46 of 72 patients and found above 50 in nine of 36 patients and five of 25 patients at D35-50 and 3 to 5 months, respectively. WT1 ratio > 50 after induction is an independent prognostic risk factor of relapse (P = .002) and death (P = .02).

CONCLUSION

WT1 quantification is an informative molecular marker for MRD in pediatric AML and is now performed as prospective analysis in ELAM02 protocol.

Molecular response in two children with relapsed acute myeloid leukemia treated with a combination of gemtuzumab ozogamicin and cytarabine

Phase I/II studies of gemtuzumab ozogamicin (GO) in pediatric refractory/relapsed acute myeloid leukemia (AML) have been reported. We present the cases of two children with relapsed AML who were treated with GO plus cytarabine, leading to a decrease of minimal residual disease down to levels not previously obtained. The toxicity profile of this treatment was relatively mild, except for severe but manageable myelosuppression.

Ex vivo generation of fully mature human red blood cells from hematopoietic stem cells

We describe here the large-scale ex vivo production of mature human red blood cells (RBCs) from hematopoietic stem cells of diverse origins. By mimicking the marrow microenvironment through the application of cytokines and coculture on stromal cells, we coupled substantial amplification of CD34(+) stem cells (up to 1.95 x 10(6)-fold) with 100% terminal differentiation into fully mature, functional RBCs. These cells survived in nonobese diabetic/severe combined immunodeficient mice, as do native RBCs. Our system for producing 'cultured RBCs' lends itself to a fundamental analysis of erythropoiesis and provides a simple in vitro model for studying important human viral or parasitic infections that target erythroid cells. Further development of large-scale production of cultured RBCs will have implications for gene therapy, blood transfusion and tropical medicine.

TREM-1, MDL-1, and DAP12 expression is associated with a mature stage of myeloid development

The triggering receptor expressed on myeloid cells (TREM-1) and the myeloid DAP12-associating lectin (MDL-1) are two recently identified receptors which associate non-covalently with DAP12 to form receptor complexes involved in monocytic activation and inflammatory response. In this study, we investigated whether the expression of TREM-1, MDL-1, and DAP12 correlated with myelomonocytic differentiation. Northern and RT-PCR revealed a strong expression of TREM-1, MDL-1, and DAP12 in peripheral blood-derived CD14(+) mature monocytes in contrast to undifferentiated bone marrow CD34(+) stem cells, and in the differentiated versus undifferentiated U937 cells. TREM-1 and MDL-1 RNA expression was also more elevated in adult than fetal tissues and in normal than malignant cells. These findings suggest that the TREM-1/DAP12 and MDL-1/DAP12 signaling pathways are features of mature differentiated myelomonocytic cells. In addition, expression of an alternative mRNA TREM-1 splice variant (TREM-1sv) was detected that might translate into a soluble receptor with potential as a regulator of myeloid activation.

Therapeutic targeting of the MEK/MAPK signal transduction module in acute myeloid leukemia

The mitogen-activated protein kinase (MAPK) pathway regulates growth and survival of many cell types, and its constitutive activation has been implicated in the pathogenesis of a variety of malignancies. In this study we demonstrate that small-molecule MEK inhibitors (PD98059 and PD184352) profoundly impair cell growth and survival of acute myeloid leukemia (AML) cell lines and primary samples with constitutive MAPK activation. These agents abrogate the clonogenicity of leukemic cells but have minimal effects on normal hematopoietic progenitors. MEK blockade also results in sensitization to spontaneous and drug-induced apoptosis. At a molecular level, these effects correlate with modulation of the expression of cyclin-dependent kinase inhibitors (p27(Kip1) and p21(Waf1/CIP1)) and antiapoptotic proteins of the inhibitor of apoptosis proteins (IAP) and Bcl-2 families. Interruption of constitutive MEK/MAPK signaling therefore represents a promising therapeutic strategy in AML.

CFFM4: a new member of the CD20/FcepsilonRIbeta family

Proteins with transmembrane domains are classified in different families based on their structure, amino acid homology, and function. In this study, we report the identification, sequence, and expression profile of a new member of the CD20/FcepsilonRIbeta family, CD20/FcepsilonRIbeta family member 4 (CFFM4). The CFFM4 gene contains seven exons and six introns and is transcribed into an mRNA encoding a 240-amino acid protein with four hydrophobic regions. The CFFM4 protein shares a high degree of homology with the other members of the family, especially in the hydrophobic regions where several amino acids are conserved. However, the CFFM4 protein can be distinguished from the other members of the family based on the length of the second extracellular loop and the absence of an immunoreceptor tyrosine-based activation motif signal. Another distinct characteristic is that CFFM4 mRNA expression is not limited to the hematopoietic lineage. CFFM4 was detected by Northern dot blot in a variety of normal and cancerous tissues. CFFM4 expression was also compared in developmentally early hematopoietic human bone marrow CD34+ stem cells versus peripheral blood-derived CD14+ mature monocytes, in the undifferentiated versus differentiated myelomonocytic U937 cell line, and in acute myelogenous leukemia FAB1 versus FAB5. In each of these systems, cellular myelomonocytic differentiation correlated with an increase in CFFM4 mRNA expression. Such results indicate that CFFM4 is associated with mature cellular function in the monocytic lineage and like CD20 and FcepsilonRIbeta, it may be a component of a receptor complex involved in signal transduction.

Withdrawal of differentiation inhibitory activity/leukemia inhibitory factor up-regulates D-type cyclins and cyclin-dependent kinase inhibitors in mouse embryonic stem cells

The expression of E and D-type cyclins, Cyclin-Dependent Kinase (CDK) 2 and 4, as well as CDK inhibitors p21Cip1 and p27Kip1 were examined during in vitro differentiation of mouse embryonic stem (ES) cells. ES cells cultured in presence of Differentiation Inhibitory Activity/Leukemia Inhibitory Factor (DIA/LIF) express very low levels of cyclin E/CDK2 complexes, p21Cip1 and p27Kip1 CDK inhibitors, while cyclin D/CDK4-associated kinase activity is undetectable. Withdrawal of DIA/LIF, which induces differentiation, results in the progressive up-regulation of all. Up-regulation of D cyclins occurs through an increase in the steady-state levels of mRNA, concomitantly with the activation of Brachyury and Goosecoid, two early markers of mesoderm differentiation. Similarly, cells from the epiblast of the early postimplantation mouse embryo do not express any cyclin D/CDK4 complexes. These are progressively upregulated at gastrulation and early organogenesis. DIA/LIF-stimulated ES cells are not growth-arrested by overexpression of p16Ink4a, a specific inhibitor of CDK4 and CDK6. We propose that the G1/S transition may be regulated by a minimal mechanism in mouse embryonic stem cells. Induction of differentiation triggers the establishment of a more sophisticated mechanism involving both cyclin D/CDK4- and CDK inhibitor-associated control of G1-phase progression.