Hematopoietic stem cell and progenitor cell mechanisms in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a group of disorders characterized by variable cytopenias and ineffective hematopoiesis. Hematopoietic stem cells (HSCs) and myeloid progenitors in MDS have not been extensively characterized. We transplanted purified human HSCs from MDS samples into immunodeficient mice and show that HSCs are the disease-initiating cells in MDS. We identify a recurrent loss of granulocyte-macrophage progenitors (GMPs) in the bone marrow of low risk MDS patients that can distinguish low risk MDS from clinical mimics, thus providing a simple diagnostic tool. The loss of GMPs is likely due to increased apoptosis and increased phagocytosis, the latter due to the up-regulation of cell surface calreticulin, a prophagocytic marker. Blocking calreticulin on low risk MDS myeloid progenitors rescues them from phagocytosis in vitro. However, in the high-risk refractory anemia with excess blasts (RAEB) stages of MDS, the GMP population is increased in frequency compared with normal, and myeloid progenitors evade phagocytosis due to up-regulation of CD47, an antiphagocytic marker. Blocking CD47 leads to the selective phagocytosis of this population. We propose that MDS HSCs compete with normal HSCs in the patients by increasing their frequency at the expense of normal hematopoiesis, that the loss of MDS myeloid progenitors by programmed cell death and programmed cell removal are, in part, responsible for the cytopenias, and that up-regulation of the “don’t eat me” signal CD47 on MDS myeloid progenitors is an important transition step leading from low risk MDS to high risk MDS and, possibly, to acute myeloid leukemia.     

Engraftment syndrome in children undergoing autologous peripheral blood progenitor cell transplantation

There is limited experience on engraftment syndrome (ES) in children. The present study analyzes the characteristics of ES in pediatric patients undergoing autologous peripheral blood progenitor cells transplantation (PBPCT). From 1993 to 2001, 30 of 156 patients (19.2%) who underwent PBPCT developed ES (skin rash which involved more than 27% of the body surface and temperature >38.3 degrees C with no compatible infectious disease etiology, during neutrophil recovery). Of the 30 patients who developed ES, 20 (66%) developed hypoxia and/or pulmonary infiltrates, seven (23%) had hepatic dysfunction, six (20%) developed renal insufficiency, 16 (53%) showed weight gain and three (10%) experienced transient encephalopathy. Multivariate analysis showed that the only positive predictive factor for developing ES was mobilization with high-dose G-CSF (12 microg/kg twice daily) (RR 3.88, CI 95% 1.73-8.67; P < 0.0005). The overall transplant-related mortality (TRM) was 8.33% and this was significantly higher in the patients who developed ES than in those who did not (23% vs 4.76%; P < 0.0001). We also found a higher morbidity in patients who developed ES, expressed as a statistically significant increase in supportive care (transfusion requirement, parenteral nutrition) and increase in the length of hospital stay. In summary, we have found ES to be the most important cause of morbidity and mortality in children undergoing autologous PBPCT.     

Endothelial cell function in patients with Down's syndrome

Patients with Down's syndrome show an increased pulmonary vascular reactivity that could be due to an impaired vascular endothelial function, which is possibly related to increased oxidative stress. In 8 patients with Down's syndrome and 9 euploid patients of similar age, endothelium-dependent and -independent vasodilation was studied, measuring brachial flow velocity with an intravascular Doppler flow wire. Patients with Down's syndrome showed a significant impairment of endothelial function versus controls. In presence of the antioxidant vitamin C, endothelium-dependent vasodilation in the patients with Down's syndrome was only slightly, but not significantly, improved.     

Cardiovascular malformations in Omani Arab children with Down's syndrome

BACKGROUND AND AIM: Reports from several countries suggest that the prevalence and spectrum of the congenital cardiac malformations seen in the setting of Down's syndrome vary in different ethnic groups and countries, and at different periods in the same country. Data on Arab children are lacking. Our study aimed to fill that void by ascertaining the pattern in Omani Arabs. METHODS: Prospective clinical and echocardiographic evaluation of consecutively recruited Omani children with Down's syndrome. RESULTS: We studied 110 children, aged from one day to 11 years, with a median of 2 months, detecting 76 cardiovascular malformations in 63 (57%) of them. Atrioventricular septal defect, the most prevalent lesion, accounted for 24 (32%) of the 76 defects. Next were atrial septal defects within the oval fossa (29%), patency of the arterial duct (17%), and ventricular septal defect (14%). There were only two cases of Fallot's tetralogy, one each of coarctation of the aorta and right-sided heart, respectively; and none of discordant ventriculo-arterial connections. CONCLUSION: The prevalence of cardiovascular malformations is high, at 57%, in our studied population of Arab children. Overall, 92% of the malformations are defects which are characterized by a left-to-right shunt, and the potential for pulmonary hypertension. These findings underscore the need for early detection and prompt, appropriate care. To achieve this, if feasible, all babies born with Down's syndrome should have echocardiography in the first month of life.     

Hematopoietic cell transplantation for Chediak-Higashi syndrome

We reviewed outcomes after allogeneic hematopoietic cell transplantation (HCT) in 35 children with Chediak-Higashi syndrome (CHS). Twenty-two patients had a history of the life-threatening accelerated phase of CHS before HCT and 11 were in accelerated phase at transplantation. Thirteen patients received their allograft from an human leukocyte antigen (HLA)-matched sibling, 10 from an alternative related donor and 12 from an unrelated donor. Eleven recipients of HLA-matched sibling donor, three recipients of alternative related donor and eight recipients of unrelated donor HCT are alive. With a median follow-up of 6.5 years, the 5-year probability of overall survival is 62%. Mortality was highest in those with accelerated phase disease at transplantation and after alternative related donor HCT. Only four of 11 patients with active disease at transplantation are alive. Seven recipients of alternative related donor HCT had active disease at transplantation and this may have influenced the poor outcome in this group. Although numbers are limited, HCT appears to be effective therapy for correcting and preventing hematologic and immunologic complications of CHS, and an unrelated donor may be a suitable alternative for patients without an HLA-matched sibling. Early referral and transplantation in remission after accelerated phase disease may improve disease-free survival.     

Two new mutations in children affected by partial biotinidase deficiency ascertained by newborn screening

Mutation analysis performed on DNA from 6 Italian patients with partial biotinidase deficiency ascertained by newborn screening allowed the identification of two new mutations, c1211C>T (T404I) and a single base deletion c594delC. All patients were compound heterozygous for the D444H amino acid substitution showing that this mutation is also common in Italian patients affected by partial biotinidase deficiency.     

Congenital cardiac disease in children with Down's syndrome in Guatemala

BACKGROUND: Congenital cardiac disease is the greatest cause of death in patients with Down's syndrome during the first two years of life, with from two-fifths to two-thirds of those with Down's syndrome also having congenital cardiac malformations. The lesions within the heart can be single or multiple. Our objective was to evaluate the frequency and type of such congenital cardiac malformations in patients born with Down's in Guatemala, and to provide baseline information for further research. METHODS: We reviewed all patients with Down's syndrome who underwent a cardiologic screening examination between January, 1997, and December, 2003, in the only department dealing with Paediatric Cardiology in Guatemala. RESULTS: Of the 349 patients reviewed, 189 (54.1 per cent) also had an associated congenital cardiac malformation. The median age at diagnosis was 6 months, with a range from 2 to 13 months. In 152 patients (80.4 per cent), the cardiac lesion was isolated, while 37 patients (19.6 per cent) had multiple defects. The most common single defect was patency of the arterial duct, found in 54 of the 189 patients (28.6 per cent), followed by ventricular septal defect in 27.5 per cent, atrial septal defect in 12.7 per cent, and atrioventricular septal defect with common atrioventricular junction in 9.5 per cent. The most frequent concomitant malformation found co-existing with other congenital cardiac lesions was patency of the arterial duct, found in 17.5 per cent. CONCLUSIONS: As far as we are aware, ours is the first epidemiologic study concerning the frequency and type of congenital cardiac disease found in Guatemalan children with Down's syndrome. The high frequency of patency of the arterial duct, and the differential distribution of the cardiac malformations associated with Down's syndrome among Guatemalan children, differ from what has been reported in the United States of America, Europe, and Asia. This difference warrants further research.     

Hematopoietic stem cell transplantation for severe combined immune deficiency

Hematopoietic stem cell transplantation (HSCT) has been the definitive therapy for severe combined immune deficiency (SCID) since the first successful transplant for SCID in 1968. Improvements in the use of HSCT to treat patients with SCID are continuing. For example, during the last 5 years, the first successful in-utero HSCT, and the first success with gene therapy have occurred in patients with SCID. Debate still continues about the role of pretransplantation therapy for SCID patients, and the biology of post-HSCT immune reconstitution is under investigation.     

Plasma thyrotropin bioactivity in Down's syndrome children with subclinical hypothyroidism

OBJECTIVE: Subclinical hypothyroidism occurs in a number of children with Down's syndrome (DS). The reason for the mildly elevated plasma thyrotropin (TSH) concentrations is not known. The present study investigated whether decreased TSH bioactivity plays a role in this phenomenon. DESIGN: A retrospective study of plasma specimens from DS children with mildly elevated plasma TSH concentrations and thyroid hormone levels within the reference range, using a TSH receptor-adenylate cyclase mediated bioassay. METHODS: Strain JP26 Chinese hamster ovary (CHO) cells, stable transfected with the human TSH receptor, were incubated with unfractionated plasma (1/10 diluted in hypotonic incubation medium) of 10 DS children with subclinical hypothyroidism and nine euthyroid children with insulin-dependent diabetes mellitus as controls. cAMP released in the incubation medium was measured by RIA. Mock-transfected CHO cells were used to correct for non-specific CHO response. WHO Second International Reference Preparation of human TSH was dissolved and diluted in pooled normal human plasma and simultaneously bioassayed to match patient and control results. RESULTS: Plasma TSH levels were slightly increased in DS (mean +/- S.D., 6.5+/-1.3 mU/l, reference range 0.4-4.0 mU/l). Plasma TSH levels for controls (1.3+/-0.4 mU/l) were within the reference range. Plasma thyroid hormone levels in patients and controls were normal, plasma TSH binding inhibitory immunoglobulin and thyroid peroxidase antibodies were negative. cAMP levels (corrected for non-specific CHO response) in DS patients (18.4+/-3.9 pmol/well) and in controls (14.3+/-1.3 pmol/well) did not significantly differ from cAMP levels generated by patient-TSH equivalent TSH standards (16.3+/-0.9 pmol/well). CONCLUSIONS: The present results demonstrate normal TSH bioactivity in plasma of DS children, indicating that subclinical hypothyroidism in these patients is of primary (thyroidal) origin.     

Hematopoietic stem cell and progenitor defects in Sca-1/Ly-6A-null mice

Despite its wide use as a marker for hematopoietic stem cells (HSCs), the function of stem cell antigen-1 (Sca-1) (also known as lymphocyte activation protein-6A [Ly-6A]) in hematopoiesis remains poorly defined. We have previously established that Sca-1(-/-) T cells develop normally, although they are hyperresponsive to antigen. Here, we report detailed analysis of hematopoiesis in Sca-1-deficient animals. The differentiation potential of Sca-1-null bone marrow was determined from examination of the most mature precursors (culture colony-forming units [CFU-Cs]) to less committed progenitors (spleen CFUs [CFU-Ss]) to long-term repopulating HSCs. Sca-1-null mice are mildly thrombocytopenic with a concomitant decrease in megakaryocytes and their precursors. Bone marrow cells derived from Sca-1(-/-) mice also have decreased multipotential granulocyte, erythroid, macrophage, and megakaryocyte CFU (GEMM-CFU) and CFU-S progenitor activity. Competitive repopulation assays demonstrated that Sca-1(-/-) HSCs are at a competitive disadvantage compared with wild-type HSCs. To further analyze the potential of Sca-1(-/-) HSCs, serial transplantations were performed. While secondary repopulations using wild-type bone marrow completely repopulated Sca-1(-/-) mice, Sca-1(-/-) bone marrow failed to rescue one third of lethally irradiated wild-type mice receiving secondary bone marrow transplants from irradiation-induced anemia and contributed poorly to the surviving transplant recipients. These data strongly suggest that Sca-1 is required for regulating HSC self-renewal and the development of committed progenitor cells, megakaryocytes, and platelets. Thus, our studies conclusively demonstrate that Sca-1, in addition to being a marker of HSCs, regulates the developmental program of HSCs and specific progenitor populations.     

康复教育对先天愚型儿童的影响

目的 探讨康复教育对先天愚型儿童的认知、语言、运动、精细动作及社会适应能力的影响.方法 在2003-01～2008-01用0～6岁儿童神经心理发育量表及婴儿-初中生社会适应能力量表对在宁夏儿童福利院生活的15名先天愚型儿童及10名在2003-01之前生活未接受过康复教育的先天愚型儿童进行测试.两组儿童基本情况匹配.结果 2003年之前的未经过康复教育的儿童在认知、语言、运动、精细运动及社会适应能力方面显著低于2003年之后进行康复教育的先天愚型儿童(P＜0.05).结论 接受康复教育的先天愚型儿童各方面的能力明显优于未接受康复训练的先天愚型儿童,在认知、语言、运动、社会适应能力和精细动作与接受康复教育有明显相关性.     

Monoclonal antibody-defined B cell subsets in aging humans and Down's syndrome

Peripheral blood from aging and young humans and patients with Down's syndrome, and from age- and sex-matched controls, was studied for the proportions of surface immunoglobulin (SIg+) bearing and monoclonal antibodies FMC1, and FMC7 defined B lymphocytes and B lymphocyte subsets using fluorescent-activated cell sorter. In aging humans, the proportion of SIg+ and FMC1+ (that detect all B lymphocytes) were comparable to simultaneously studied healthy young controls. However, FMC7+ (that detects a subset of B cells) B cells were significantly (p less than 0.05) increased when compared to young subjects. In aging subjects, the proportions of FMC7+ B cells were comparable to their FMC1+ B cells, whereas in young subjects FMC7+ B cells were a subset of FMC1+ B cells. In Down's syndrome, a phenomenon similar to aging humans was observed, that is the proportions of FMC7+ were increased when compared to age- and sex-matched controls and were comparable to their own FMC1+ B cells. This study demonstrates the abnormality of B lymphocytes in human aging and Down's syndrome. The significance of these findings is discussed.     

Hematopoietic progenitor cell colony growth differentiates chronic myelomonocytic leukemia from reactive monocytosis

In the absence of a cytogenetic abnormality or overt dysplasia, chronic myelomonocytic leukemia (CMML) may be difficult to be distinguished from reactive monocytosis. We have previously described a typical growth pattern in CMML patients, i.e., 'pseudonormal' colonies resembling granulocytic colonies but consisting entirely of monocytic cells when stained. To study the utility of the colony forming unit cell assay (CFU-C) as a diagnostic tool in patients with monocytosis, we analyzed a cohort of 48 consecutive patients referred to our institution with peripheral blood monocytosis. Thirty-six patients fulfilled the WHO criteria for CMML; 12 were diagnosed with reactive monocytosis. Of the patients with CMML, 28 showed pseudonormal growth with or without leukemic cluster growth, another four showed exclusively leukemic growth. None of the patients with reactive monocytosis showed either leukemic or pseudonormal growth. With a specificity of 100% and a sensitivity of 89%, the CFU-C assay has a unique potential to distinguish CMML from reactive monocytosis.