Age-related alterations in erythroid and granulopoietic progenitors in Diamond-Blackfan anaemia

SATB1 Chromatin Loops Regulate Megakaryocyte/Erythroid Progenitor Expansion by Facilitating HSP70 and GATA1 Induction

Diamond Blackfan anemia (DBA) is an inherited bone marrow failure syndrome associated with severe anemia, congenital malformations, and an increased risk of developing cancer. The chromatin-binding special AT-rich sequence-binding protein-1 (SATB1) is downregulated in megakaryocyte/erythroid progenitors (MEPs) in patients and cell models of DBA, leading to a reduction in MEP expansion. Here we demonstrate that SATB1 expression is required for the upregulation of the critical erythroid factors heat shock protein 70 (HSP70) and GATA1 which accompanies MEP differentiation. SATB1 binding to specific sites surrounding the HSP70 genes promotes chromatin loops that are required for the induction of HSP70, which, in turn, promotes GATA1 induction. This demonstrates that SATB1, although gradually downregulated during myelopoiesis, maintains a biological function in early myeloid progenitors.

An RPS19-edited model for Diamond-Blackfan anemia reveals TP53-dependent impairment of hematopoietic stem cell activity

Diamond-Blackfan anemia (DBA) is a genetic blood disease caused by heterozygous loss-of-function mutations in ribosomal protein (RP) genes, most commonly RPS19. The signature feature of DBA is hypoplastic anemia occurring in infants, although some older patients develop multilineage cytopenias with bone marrow hypocellularity. The mechanism of anemia in DBA is not fully understood and even less is known about the pancytopenia that occurs later in life, in part because patient hematopoietic stem and progenitor cells (HSPCs) are difficult to obtain, and the current experimental models are suboptimal. We modeled DBA by editing healthy human donor CD34+ HSPCs with CRISPR/Cas9 to create RPS19 haploinsufficiency. In vitro differentiation revealed normal myelopoiesis and impaired erythropoiesis, as observed in DBA. After transplantation into immunodeficient mice, bone marrow repopulation by RPS19+/- HSPCs was profoundly reduced, indicating hematopoietic stem cell (HSC) impairment. The erythroid and HSC defects resulting from RPS19 haploinsufficiency were partially corrected by transduction with an RPS19-expressing lentiviral vector or by Cas9 disruption of TP53. Our results define a tractable, biologically relevant experimental model of DBA based on genome editing of primary human HSPCs and they identify an associated HSC defect that emulates the pan-hematopoietic defect of DBA.

Downregulation of SATB1 by miRNAs Reduces Megakaryocyte/Erythroid Progenitor Expansion in pre-clinical models of Diamond Blackfan Anemia

Diamond Blackfan Anemia (DBA) is an inherited bone marrow failure syndrome that is associated with anemia, congenital anomalies, and cancer predisposition. It is categorized as a ribosomopathy, because over 80% or patients have haploinsufficiency of either a small or large subunit-associated ribosomal protein (RP). The erythroid pathology is predominantly due to a block and delay in early committed erythropoiesis with reduced Megakaryocyte/Erythroid Progenitors (MEPs). To understand the molecular pathways leading to pathogenesis of DBA, we performed RNA-seq on mRNA and miRNA from RPS19-deficient human hematopoietic stem and progenitor cells (HSPCs) and compared an existing database documenting transcript fluctuations across stages of early normal erythropoiesis. We determined the chromatin regulator, SATB1 was prematurely downregulated through the coordinated action of upregulated miR-34 and miR-30 during differentiation in ribosomal-insufficiency. Restoration of SATB1 rescued MEP expansion, leading to a modest improvement in erythroid and megakaryocyte expansion in RPS19-insufficiency. However, SATB1 expression did not impact expansion of committed erythroid progenitors, indicating ribosomal insufficiency impacts multiple stages during erythroid differentiation.

Successful gene therapy of Diamond-Blackfan anemia in a mouse model and human CD34+ cord blood hematopoietic stem cells using a clinically applicable lentiviral vector

Diamond-Blackfan anemia (DBA) is an inherited bone marrow failure disorder in which pure red blood cell aplasia is associated with physical malformations and a predisposition to cancer. Twentyfive percent of patients with DBA have mutations in a gene encoding ribosomal protein S19 (RPS19). Our previous proof-of-concept studies demonstrated that DBA phenotype could be successfully treated using lentiviral vectors in Rps19-deficient DBA mice. In our present study, we developed a clinically applicable single gene, self-inactivating lentiviral vector, containing the human RPS19 cDNA driven by the human elongation factor 1αshort promoter, which can be used for clinical gene therapy development for RPS19-deficient DBA. We examined the efficacy and safety of the vector in a Rps19-deficient DBA mouse model and in human primary RPS19- deficient CD34+ cord blood cells. We observed that transduced Rps19-deficient bone marrow cells could reconstitute mice long-term and rescue the bone marrow failure and severe anemia observed in Rps19-deficient mice, with a low risk of mutagenesis and a highly polyclonal insertion site pattern. More importantly, the vector can also rescue impaired erythroid differentiation in human primary RPS19-deficient CD34+ cord blood hematopoietic stem cells. Collectively, our results demonstrate the efficacy and safety of using a clinically applicable lentiviral vector for the successful treatment of Rps19-deficient DBA in a mouse model and in human primary CD34+ cord blood cells. These findings show that this vector can be used to develop clinical gene therapy for RPS19-deficient DBA patients.

An update on the pathogenesis and diagnosis of Diamond-Blackfan anemia

Diamond–Blackfan anemia (DBA) is a rare congenital hypoplastic anemia characterized by a block in erythropoiesis at the progenitor stage, although the exact stage at which this occurs remains to be fully defined. DBA presents primarily during infancy with macrocytic anemia and reticulocytopenia with 50% of cases associated with a variety of congenital malformations. DBA is most frequently due to a sporadic mutation (55%) in genes encoding several different ribosomal proteins, although there are many cases where there is a family history of the disease with varying phenotypes. The erythroid tropism of the disease is still a matter of debate for a disease related to a defect in global ribosome biogenesis. Assessment of biological features in conjunction with genetic testing has increased the accuracy of the diagnosis of DBA. However, in certain cases, it continues to be difficult to firmly establish a diagnosis. This review will focus on the diagnosis of DBA along with a description of new advances in our understanding of the pathophysiology and treatment recommendations for DBA.

Ribosomal and hematopoietic defects in induced pluripotent stem cells derived from Diamond Blackfan anemia patients

Diamond Blackfan anemia (DBA) is a congenital disorder with erythroid (Ery) hypoplasia and tissue morphogenic abnormalities. Most DBA cases are caused by heterozygous null mutations in genes encoding ribosomal proteins. Understanding how haploinsufficiency of these ubiquitous proteins causes DBA is hampered by limited availability of tissues from affected patients. We generated induced pluripotent stem cells (iPSCs) from fibroblasts of DBA patients carrying mutations in RPS19 and RPL5. Compared with controls, DBA fibroblasts formed iPSCs inefficiently, although we obtained 1 stable clone from each fibroblast line. RPS19-mutated iPSCs exhibited defects in 40S (small) ribosomal subunit assembly and production of 18S ribosomal RNA (rRNA). Upon induced differentiation, the mutant clone exhibited globally impaired hematopoiesis, with the Ery lineage affected most profoundly. RPL5-mutated iPSCs exhibited defective 60S (large) ribosomal subunit assembly, accumulation of 12S pre-rRNA, and impaired erythropoiesis. In both mutant iPSC lines, genetic correction of ribosomal protein deficiency via complementary DNA transfer into the "safe harbor" AAVS1 locus alleviated abnormalities in ribosome biogenesis and hematopoiesis. Our studies show that pathological features of DBA are recapitulated by iPSCs, provide a renewable source of cells to model various tissue defects, and demonstrate proof of principle for genetic correction strategies in patient stem cells.

Mice with ribosomal protein S19 deficiency develop bone marrow failure and symptoms like patients with Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is a congenital erythroid hypoplasia caused by a functional haploinsufficiency of genes encoding for ribosomal proteins. Among these genes, ribosomal protein S19 (RPS19) is mutated most frequently. Generation of animal models for diseases like DBA is challenging because the phenotype is highly dependent on the level of RPS19 down-regulation. We report the generation of mouse models for RPS19-deficient DBA using transgenic RNA interference that allows an inducible and graded down-regulation of Rps19. Rps19-deficient mice develop a macrocytic anemia together with leukocytopenia and variable platelet count that with time leads to the exhaustion of hematopoietic stem cells and bone marrow failure. Both RPS19 gene transfer and the loss of p53 rescue the DBA phenotype implying the potential of the models for testing novel therapies. This study demonstrates the feasibility of transgenic RNA interference to generate mouse models for human diseases caused by haploinsufficient expression of a gene.

Diamond-Blackfan anemia, ribosome and erythropoiesis

Diamond-Blackfan anemia is a rare inherited bone marrow failure syndrome (five to seven cases per million live births) characterized by an aregenerative, usually macrocytic anemia with an absence or less than 5% of erythroid precursors (erythroblastopenia) in an otherwise normal bone marrow. The platelet and the white cell counts are usually normal but neutropenia, thrombopenia or thrombocytosis have been noted at diagnosis. In 40 to 50% of DBA patients, congenital abnormalities mostly in the cephalic area and in thumbs and upper limbs have been described. Recent analysis did show a phenotype/genotype correlation. Congenital erythroblastopenia of DBA is the first human disease identified to result from defects in ribosomal biogenesis. The first ribosomal gene involved in DBA, ribosomal protein (RP) gene S19 (RPS19 gene), was identified in 1999. Subsequently, mutations in 12 other RP genes out of a total of 78 RP genes have been identified in DBA. All RP gene mutations described to date are heterozygous and dominant inheritance has been documented in 40 to 45% of affected individuals. As RP mutations are yet to be identified in approximately 50% of DBA cases, it is likely that other yet to be identified genes involved in ribosomal biogenesis or other pathways may be responsible for DBA phenotype.

[Diamond-Blackfan anemia reveals the dark side of ribosome biogenesis]

Diamond-Blackfan anemia (DBA), a rare congenital erythroblastopenia, has recently become a paradigm for a growing set of genetic diseases linked to mutations in genes encoding ribosomal proteins or factors involved in ribosome biogenesis. Recent studies of the structure and the function of ribosomal proteins affected in DBA indicate that their mutation in DBA primarily impacts ribosome biogenesis. Accordingly, cells from DBA patients display anomalies in the maturation of ribosomal RNAs. The explanation of this unexpected link between ribosome biogenesis, a ubiquitous process, and a disease mostly affecting erythroid differentiation may stem in part from the emerging concept of ribosomal stress response, a signaling pathway triggering cell cycle arrest in response to a defect in ribosome synthesis. Future studies of DBA and other diseases related to defects in ribosome biogenesis are likely to rapidly provide important insights into the regulatory mechanisms linking cell cycle progression to this major metabolic pathway.

Diagnosing and treating Diamond Blackfan anaemia: results of an international clinical consensus conference

Diamond Blackfan anaemia (DBA) is a rare, genetically and clinically heterogeneous, inherited red cell aplasia. Classical DBA affects about seven per million live births and presents during the first year of life. However, as mutated genes have been discovered in DBA, non-classical cases with less distinct phenotypes are being described in adults as well as children. In caring for these patients it is often difficult to have a clear understanding of the treatment options and their outcomes because of the lack of complete information on the natural history of the disease. The purpose of this document is to review the criteria for diagnosis, evaluate the available treatment options, including corticosteroid and transfusion therapies and stem cell transplantation, and propose a plan for optimizing patient care. Congenital anomalies, mode of inheritance, cancer predisposition, and pregnancy in DBA are also reviewed. Evidence-based conclusions will be made when possible; however, as in many rare diseases, the data are often anecdotal and the recommendations are based upon the best judgment of experienced clinicians. The recommendations regarding the diagnosis and management described in this report are the result of deliberations and discussions at an international consensus conference.

Recent insights into the pathogenesis of Diamond-Blackfan anaemia

Diamond-Blackfan anaemia (DBA) is a congenital anaemia and broad developmental disease that develops soon after birth. The anaemia is due to failure of erythropoiesis, with normal platelet and myeloid lineages, and it can be managed with steroids, blood transfusions, or stem cell transplantation. Normal erythropoiesis after transplantation shows that the defect is intrinsic to an erythroid precursor. DBA is inherited in about 10-20% of cases, and genetic studies have identified mutations in a ribosomal protein gene, RPS19, in 25% of cases; there is evidence for involvement of at least two other genes. In yeast, RPS19 deletion leads to a block in ribosomal RNA biogenesis. The critical question is how mutations in RPS19 lead to the failure of proliferation and differentiation of erythroid progenitors. While this question has not yet been answered, understanding the biology of DBA may provide insight not only into the defect in erythropoisis, but also into the other developmental abnormalities that are present in about 40% of patients, and into the cancer predisposition that is inherent to DBA.

An RNA interference model of RPS19 deficiency in Diamond-Blackfan anemia recapitulates defective hematopoiesis and rescue by dexamethasone: identification of dexamethasone-responsive genes by microarray

Diamond-Blackfan anemia (DBA), a congenital erythroblastopenia, is a model disease for the study of erythroid differentiation but is poorly understood. RPS19 is the only gene yet to have been associated with DBA, but its relevance to erythroid differentiation is unclear. The molecular basis for the stimulation of erythropoiesis by glucocorticoids in patients with DBA has not been identified. We demonstrate that targeted degradation of the RPS19 transcript, through retroviral expression of short hairpin RNAs (shRNAs), blocks the proliferation and differentiation of erythroid progenitor cells in cultured human CD34(+) cells. Treatment of RPS19-deficient cells with dexamethasone restores erythroid differentiation to normal levels. We investigated the molecular basis of pharmacologic therapies for DBA using oligonucleotide microarrays to survey gene expression in CD34(+) cells treated with combinations of dexamethasone, erythropoietin, stem cell factor, and interleukin-3. Dexamethasone did not alter expression of RPS19 but activated a genetic program that includes a set of key hematopoietic regulatory genes. Genes specific to erythroid progenitor cells were up-regulated by dexamethasone, while genes specific to nonerythroid lineages were down-regulated. Deficiency of RPS19 therefore blocks proliferation of immature erythroid progenitor cells, and dexamethasone activates proliferation of the same cell population through mechanisms independent of RPS19.

Two-phase culture in Diamond Blackfan anemia: localization of erythroid defect

The erythroid defect in Diamond Blackfan anemia (DBA) is known to be intrinsic to the stem cell, but its molecular pathophysiology remains obscure. Using a 2-phase liquid erythroid culture system, we have demonstrated a consistent defect in DBA, regardless of clinical severity, including 3 first-degree relatives with normal hemoglobin levels but increased erythrocyte adenosine deaminase activity. DBA cultures were indistinguishable from controls until the end of erythropoietin (Epo)-free phase 1, but failed to demonstrate the normal synchronized wave of erythroid expansion and terminal differentiation on exposure to Epo. Dexamethasone increased Epo sensitivity of erythroid progenitor cells, and enhanced erythroid expansion in phase 2 in both normal and DBA cultures. In DBA cultures treated with dexamethasone, Epo sensitivity was comparable to normal, but erythroid expansion remained subnormal. In clonogenic phase 2 cultures, the number of colonies did not significantly differ between normal cultures and DBA, in the presence or absence of dexamethasone, and at both low and high Epo concentrations. However, colonies were markedly smaller in DBA under all conditions. This suggests that the Epo-triggered onset of terminal maturation is intact in DBA, and the defect lies down-stream of the Epo receptor, influencing survival and/or proliferation of erythroid progenitors.

Diamond-Blackfan Anaemia: an overview

Diamond Blackfan Anaemia (DBA) is a congenital disease characterised by defective erythroid progenitor maturation. It is usually diagnosed during the first year of life. The main clinical sign is profound isolated normochromic or macrocytic anaemia, with normal numbers and function of the other haemopoietic cells. Reticulocyte counts in patients with DBA are very low. Bone marrow reflects the defective erythropoiesis, showing a very low number of erythropoietic precursors and a reduction of erythroid burst-forming unit progenitor cells. The proliferation and differentiation of the other lineages are normal. More than one-third of patients have malformations, most often involving the upper limbs and head, and the urogenital or cardiovascular systems. However, the link between these malformations and defective erythropoiesis is unclear and a defect in a molecule acting on both early embryonic development and haematopoiesis has been proposed. Whereas most cases are sporadic, inheritance is observed in 10% of patients, with a dominant or, more rarely, recessive pattern. One locus on chromosome 19q13.2 encoding ribosomal protein S19 accounts for a quarter of patients with either the dominant or the sporadic form. Families not linked with this locus have also been described. The diagnosis of DBA may be difficult and differential diagnoses include Fanconi's anaemia and acquired erythroid aplasias. Erythrocyte adenosine deaminase levels are generally high in DBA patients, which may help in the diagnosis, but they are not pathognomic. Corticosteroids are the main treatment option in DBA and these agents induce erythropoiesis in over 60% of patients. Some patients achieve complete remission, which may be either corticosteroid-induced or spontaneous. The increased in vitro erythropoiesis occasionally induced by the addition of specific cytokines, namely interleukin (IL)-3 and stem cell factor (SCF), has suggested their use in vivo. However, few patients have responded to IL-3, whereas SCF administration, though interesting in theory, has not yet been attempted. Patients who do not respond to corticosteroids and those who have to discontinue treatment because of adverse events must rely on long term transfusions, and are thus exposed to all of the associated complications. Bone marrow or cord blood transplantation has been performed in some patients. The former approach is burdened with severe complications and high mortality.

Diamond-Blackfan anaemia

Diamond-Blackfan anaemia (DBA) has had an intellectual allure for decades for clinical and experimental haematologists. The syndrome has a haematological phenotype of early-onset red-cell aplasia but is coupled with a baffling array of pleiotropy. There is discordance with modes of inheritance, physical anomalies, erythropoietic response to corticosteroid therapy, spontaneous 'remissions', and evolution to malignant myeloid transformation and to cancer. The recent discovery of two genes associated with DBA is the entry point for explaining the diversity of the phenotype and for understanding the molecular basis of the syndrome.

Diamond-Blackfan anemia

Diamond Blackfan anemia is a rare congenital hypoplastic anemia that usually presents early in infancy. Congenital anomalies, in particular of the head and upper limbs, are present in about 25% of reported patients. The disease is characterized by a moderate to severe macrocytic anemia, occasional neutropenia or thrombocytosis, a normocellular bone marrow with erythroid hypoplasia, and an increased risk of developing leukemia. Recent genetic studies have led to the identification of mutations in the ribosomal protein RPS19 in approximately 25% of sporadic and familial cases, a second gene on chromosome 8p, and evidence for an additional locus (or loci). The pathogenesis is unknown. The majority of patients respond to prednisone, and often erythropoiesis can be maintained with low doses of the drug. Both remissions and increased resistance to steroid treatment can occur. Patients who do not respond to treatment are usually transfusion dependent, although responses to high dose steroid, androgen, and interleukin-3 have been observed. Bone marrow transplantation can be curative.

Clinical and laboratory evidence for a trilineage haematopoietic defect in patients with refractory Diamond-Blackfan anaemia

Diamond-Blackfan anaemia (DBA) is a constitutional pure red cell aplasia presenting in early childhood. In some patients, neutropenia and/or thrombocytopenia have also been observed during the course of the disease. We have followed 28 patients with steroid-refractory DBA for up to 13 years with serial peripheral blood counts and bone marrow (BM) aspirates and biopsies. In 21/28 (75%) patients, moderate to severe generalized BM hypoplasia developed, with overall cellularities ranging from 0% to 30%. Marrow hypoplasia correlated with the development of neutropenia (9/21; 43%) and/or thrombocytopenia (6/21; 29%) in many patients. No patient had either cytogenetic abnormalities or progressed to acute leukaemia, although one 13-year-old developed marked marrow fibrosis and trilineage dysplasia. We used the in vitro long-term culture-initiating cell (LTC-IC) assay to quantify multilineage, primitive haematopoietic progenitors in a representative subset of these patients. LTC-IC assays showed equivalent frequencies of cobblestone area-forming cells (CAFCs) with a mean of 5.42/10(5) cells +/- 1.9 SD and 6.13/10(5) cells +/- 2.6 SD in nine patients and six normal controls respectively. The average clonogenic cell output per LTC-IC, however, was significantly lower in DBA patients (mean 2.16 +/- 1.2 SD vs. 7. 36 +/- 2.7 SD in normal controls, P = 0.0008). Our results suggest that the underlying defect in patients with severe refractory DBA may not be limited to the erythroid lineage, as was evidenced by the development of pancytopenia, bone marrow hypoplasia and reduced clonogenic cell output in LTC-IC assays.

Long-term bone marrow cultures in Diamond-Blackfan anemia reveal a defect of both granulomacrophage and erythroid progenitors

The hematopoietic defect of Diamond-Blackfan anemia (DBA) results in selective failure of erythropoiesis. Thus far, it is not known whether this defect originates from an intrinsic impediment of hematopoietic progenitors to move forward along the erythroid pathway or to the impaired capacity of the bone marrow (BM) microenvironment to support proliferation and differentiation of hematopoietic cells. Reduced longevity of long-term bone marrow cultures, the most physiologic in vitro system to study the interactions of hematopoietic progenitors and hematopoietic microenvironment, is consistent with a defect of an early hematopoietic progenitor in DBA. However, stromal adherent layers from DBA patients generated in a long-term culture system, the in vitro counterpart of BM microenvironment, did not show evidence of any morphologic, phenotypic, or functional abnormality. Our major finding was an impaired capacity of enriched CD34+ BM cell fraction from DBA patients, cultured in the presence of normal BM stromal cells, to proliferate and differentiate along the erythroid pathway. A similar impairment was observed in some DBA patients along the granulomacrophage pathway. Our result points to an intrinsic defect of a hematopoietic progenitor with bilineage potential that is earlier than previously suspected as a relevant pathogenetic mechanism of the disease. The finding of impaired granulopoiesis in some DBA patients underlines the heterogeneity of this rare disorder.

Clinical value of bone marrow cultures in childhood pure red cell aplasia

PURPOSE

We assessed the value of marrow cultures for defining the pathophysiology, diagnosis, and therapeutic response to immunosuppressive therapy in childhood pure red cell aplasia (PRCA).

PATIENTS AND METHODS

Patients were evaluated either at diagnosis (n = 23) or at the time of treatment failure (n = 2). Twelve patients had transient erythroblastopenia of childhood (TEC), 4 had Diamont-Blackfan anemia (DBA), and 9 had acquired sustained PRCA (A-Su-PRCA). Bone marrow mononuclear cells were cultured with combination of human recombinant (rhu) erythropoietin (EPO), granulocyte monocyte colony stimulating factor (GM-CSF), granulocyte colony stimulating factor (G-CSF), Interleukin 3 (IL-3), either with or without stem cell factor (SCF), and burst forming unit of erythroid (BFU-E) growth was assessed.

RESULTS

The combination of growth factors without SCF failed to induce any erythropoiesis (BFU-E < 10/10(5) mononuclear cells) in 10 patients (2 with TEC, 2 with DBA, and 6 with A-Su-PRCA), although the growth of erythroid colonies was substantially lower in the remaining patients than in controls (45.5 +/- 15.4 versus 91.7 +/- 12.7, p < 0.05). Addition of SCF restored erythropoiesis in all but 6 patients (5 with A-Su-PRCA and 1 with DBA). Five of 6 nonresponders did not respond to any immunomodulating therapy; of the 5, 3 had or developed some evidence of myelodysplasia.

CONCLUSION

Our data indicate that in vitro colony studies might prove to be a useful diagnostic tool, because erythropoiesis' poor response to growth factors, including SCF, may suggest the diagnosis of myelodysplasia. Moreover, it may have predictive value; in cases of PRCA, regardless of etiology, poor growth of erythropoietic colonies may predict refractoriness to immunomodulating therapy.

Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is a rare, congenital, hypoplastic anemia that usually presents in early infancy. Congenital anomalies, particularly of the head and upper limbs, are present in about a quarter of reported patients. The disease is characterized by a moderate-to-severe macrocytic anemia, occasional neutropenia or thrombocytosis, a normocellular bone marrow with erythroid hypoplasia, and an increased risk of developing leukemia. The pathogenesis is unknown. The majority of patients respond to prednisone, and often erythropoiesis can be maintained with low doses of the drug. Both remissions and increased resistance to steroid treatment can occur. Nonresponders usually are transfusion dependent, although responses to high dose steroid, androgen, and interleukin-3 have been observed. Bone marrow transplantation can be curative.

Transient erythrophagocytosis in Diamond-Blackfan anemia

We report on a 4-month-old Japanese infant girl with Diamond-Blackfan anemia (DBA) as shown by congenital macrocytic pure red cell hypoplasia with marked reduction of erythroid precursors in bone marrow, reticulocytopenia, increased fetal hemoglobin, and elevated adenosine deaminase activity in peripheral blood. She responded poorly to conventional doses of corticosteroids, however, with high-dose corticosteroids she responded with reticulocytosis and an elevation of hemoglobin level above 12 g/dL. Erythrophagocytosis was noted during the tapering period of prednisone when her hemoglobin level declined to 7.6 g/dL and reticulocyte level to 0.4%. At that time, the erythrophagocytosis was noted in about 60% of marrow histiocytes. These findings were not observed prior to or during the high dose prednisone therapy. We speculate that one of the causes of pure red cell aplasia and reticulocytopenia in DBA is mediated by erythrophagocytosis.

The use of recombinant SCF protein for rapid determination of c-kit expression in normal and abnormal erythropoiesis

Stem cell factor (SCF) is the ligand for the dimeric c-kit tyrosine kinase receptor. Binding of SCF to c-kit is a crucial element in the developmental stimulus of late stem cells and early progenitor cells. In the erythroid lineage the SCF stimulus is important not only for proliferation and differentiation, but is also known to enhance later haemoglobin production. In an earlier report we described a rapid non-radioactive technique using the extended ester-attached labelled SCF protein itself for detecting c-kit expression in marrow and peripheral blood mononuclear populations. In the present study we have taken this a step further to analyse c-kit expression in developing erythroid cells in vitro, principally using normal donor samples. This was designed for use as a foundation for the comparison of haematological disorders. In this case we tested 4 patients with the congenital disorder of erythropoiesis, Diamond-Blackfan anaemia (DBA), finding that in all cases DBA c-kit expression was elevated over normal, in 1 case as high as 348% of the normal average. This may be indicative of the reduced state of progenitor development in these patients. These results show that the described technique is beneficial for analysis in the stem and progenitor compartment.

Is there a role for interleukin-3 in Diamond-Blackfan anaemia? Results of a European multicentre study

Forty patients (nine adults aged 20-54; 31 children aged 1-17) with Diamond-Blackfan anaemia (DBA) were treated with recombinant human interleukin-3 (IL-3) in a European multicentre compassionate-need study. IL-3 was given as a daily subcutaneous injection at a starting dose of 2.5 micrograms/kg, escalating at day 21 to 5 micrograms/kg, and then to 10 micrograms/kg if there was no response, for a total duration of 12 weeks. Three children achieved a significant response, achieving sustained remissions off all therapy. At the time of entry, one was steroid-responsive and transfusion-independent, and two were transfusion-dependent. Two adults had a transient reduction in transfusion requirements, but could not tolerate the complete course of therapy. Eosinophilia was common; neutrophil and platelet counts were unaffected except in three patients in whom previously noted mild thrombocytopenia was transiently exacerbated. Clinical response to IL-3 did not correlate with in vitro culture results. A comparison of individual patient characteristics of our study with previously reported series confirms earlier impressions that patients who have never achieved significant in vivo erythropoiesis in response to steroids or during a spontaneous remission are highly unlikely to respond to IL-3. In contrast, there may be a 50% chance of a sustained remission, off steroids, in children who are steroid-dependent and transfusion-independent at the time of IL-3 therapy, suggesting a possible role for a short course of IL-3 earlier in the treatment of children with steroid-responsive DBA.

Diamond-Blackfan anaemia: three patterns of in vitro response to haemopoietic growth factors

Culture of bone marrow from patients with Diamond-Blackfan anaemia (DBA) has previously shown a variable progenitor response to growth factor stimulation. An extensive standardized study has now been undertaken to investigate the presence of distinct sub-groups in this disorder. In vitro response of bone marrow progenitors to recombinant human growth factors, including stem cell factor, was examined in 18 DBA patients and five normal donors, assessing BFU-E, CFU-GM and CFU-GEMM development. In 16 of the DBA patients a synergistic response to combinations of growth factors was observed with optimal growth in cultures containing erythropoietin, interleukin-3 and stem cell factor. Growth factor induced erythroid response formed three distinct groups, based on BFU-E numbers: type I (mean age 4.87 years) showed > 70% normal erythroid response; type II (mean age 13.87 years) showed < 70% normal; and type III (mean age 15.29 years) < 5% normal. CFU-GM response also followed the trigrouping. The results suggest more than one pathogenic mechanism for the erythroid failure in DBA, indicating DBA may be composed of more than one distinct disorder, and further suggest the defect in DBA may not be confined to the erythroid series.