Factors related to allergic transfusion reactions and febrile non-haemolytic transfusion reactions in children.

BACKGROUND AND OBJECTIVES: Allergic transfusion reactions (ATRs) and febrile non-haemolytic transfusion reactions (FNHTRs) are the two major types of transfusion-related adverse reactions (TRARs). Although prestorage leucocyte reduction and diversion of the first aliquot of blood (LR/D) could reduce FNHTRs and bacterial contamination in adult transfusion, ATRs are still problematic. In addition, there is little information about TRARs in paediatric population. MATERIALS AND METHODS: We conducted a single-centre retrospective analysis of all transfusions, except washing products, and TRARs for 153 months to evaluate related factors such as delivery of treatment and the characteristics of recipients. RESULTS: Most TRARs were FNHTRs and/or ATRs in children. In delivering blood products with LR/D, the frequencies of not only FNHTRs but also ATRs were significantly reduced with both platelet concentrates (PCs) and red cell concentrates (RCCs). TRARs of fresh-frozen plasma were infrequent in children. In addition, even after the introduction of LR/D, ATRs were significantly more frequent in patients with primary haematological and malignant diseases who received PCs and RCCs, older patients who received PCs and patients who received frequent RCCs. CONCLUSION: These results suggest that leucocytes or mediators from leucocytes are underlying cause of ATRs in addition to FNHTRs in children. Furthermore, particular characteristics of patients would be other risk factors for ATRs.

Derivation of integration-free iPSCs from a Klinefelter syndrome patient.

PURPOSE: Klinefelter syndrome (KS) (47, XXY) is the most common sex chromosome abnormality in humans. KS is characterized by gynecomastia, tall stature, small testes, low testosterone levels, learning disabilities, and behavioral problems. KS is also associated with infertility due to non-obstructive azoospermia (NOA). The mechanism underlying NOA is still poorly understood, and although there is no current treatment, the use of microdissection testicular sperm extraction (micro-TESE) followed by in vitro fertilization can result in successful conception. The generation of induced pluripotent stem (iPS) cells derived from KS patients may be useful for studying the disease mechanism and identifying novel therapies. METHODS: Cells from a KS patient were transduced with Sendai viral vectors encoding four transcription factors, OCT4, SOX2, KLF4, and C-MYC, and the transduced cells were analyzed for in vitro and in vivo pluripotency. RESULTS: KS patient-derived iPS cells were successfully generated and shown to produce teratomas in the testes of SCID mice. In vitro differentiation of the iPS cells into cardiomyocyte-like cells was confirmed by the presence of clusters of beating cells. CONCLUSIONS: KS patient-derived iPS cells that could differentiate into cardiomyocyte-like cells were established.

Hyperacute graft-versus-host disease: histological assessment of skin biopsy specimens from 19 cases.

BACKGROUND: Hyperacute graft-versus-host disease (GVHD) is defined as GVHD occurring within 14 days after haematopoietic stem-cell transplantation (HSCT). AIM: To evaluate the usefulness of skin biopsy in assessing hyperacute GVHD. METHODS: We examined 19 cases of hyperacute GVHD from a total of 134 consecutive HSCT cases at Shinshu University Hospital between 1999 and 2008. RESULTS: Exanthemas were seen in all patients, which were mainly disseminated maculopapular erythemas, commonly present in acute GVHD as well. Most patients presented with a high fever, and a few had mild hepatic dysfunction and/or diarrhoea. The clinical grade of GVHD was 1-2 in all patients; there were no cases of clinical grades 3-4. The histological findings of skin biopsy were divided into three groups: (i) eight had grade 2 changes, characterized by diffuse vacuolization of basal cells, with dyskeratotic bodies; (ii) five had grade 1 changes, characterized by vacuolization of epidermal basal cells (all these cases were diagnosed as acute GVHD with grade 2 histological changes at subsequent biopsy); (iii) and six had no significant changes (these cases were also diagnosed as acute GVHD with grade 2 (four cases) or grade 1 (one case) histological changes on the second biopsy). Many of the patients developed acute and later chronic GVHD. CONCLUSION: Skin biopsy should be considered when eruption develops after HSCT even before engraftment, especially when other organ involvement is minimal. If the first skin biopsy is inconclusive, follow-up biopsy within a short time is helpful in the diagnosis of hyperacute GVHD.

Engraftment syndrome, but not acute GVHD, younger age, CYP3A5 or MDR1 polymorphisms, increases tacrolimus clearance in pediatric hematopoietic SCT.

We investigated clinical factors that affected the clearance of tacrolimus (FK506) administered by continuous drip infusion to children who had received allogeneic hematopoietic SCT. Blood FK506 levels were measured every day in 27 patients in an attempt to adjust the dose to maintain the target range (10-15 ng/mL). Patients who developed engraftment syndrome (ES) and acute GVHD and patients less than 7 years of age showed a higher FK506 clearance calculated from body weight (BW) for 5 or more consecutive days compared with the control groups. A time-course study showed that the occurrence of ES, but not acute GVHD, was related to increased clearance of FK506. When calculated from body surface area (BSA), a significant increase in FK506 clearance was observed in patients with ES, but not in those less than 7 years of age. FK506 clearance was not influenced by CYP3A5, multidrug resistance 1 or ABCG2 genotypes. None of the clinical parameters affected blood FK506 levels. Determination of the FK506 dose on the basis of frequent monitoring of the blood concentration seems to minimize the serious adverse effects induced by the immunosuppressant. It may be more accurate to dose FK506 according to BSA rather than BW for pediatric patients.

Exercise effects on methylation of ASC gene.

Chronic moderate exercise has been reported to reduce pro-inflammatory cytokines. To analyze the molecular mechanisms by which training exerts these effects, the epigenetic influences of age and exercise on the ASC gene, which is responsible for IL-1beta and IL-18 secretion, were investigated by ASC gene methylation. Further, the relationship between carcinogenesis and exercise, and methylation of the P15 tumor suppressive gene was also analyzed. High-intensity interval walking exercise, consisting of 3 min low-intensity walking at 40% of peak aerobic capacity followed by a 3 min high-intensity walking period above 70% of peak aerobic capacity, was continued for 6 months. Peripheral blood DNA extracts from young control (n=34), older control (n=153), and older exercise (n=230) groups were then analyzed by pyrosequencing for DNA methylation. Methylation of ASC decreased significantly with age (young control vs. older control, p<0.01), which is indicative of an age-dependent increase in ASC expression. Compared to the older control group, the degree of ASC methylation was higher in the older exercise group (older control vs. older exercise: p<0.01), and presumably lower ASC expression. Neither exercise nor age affected the methylation of the P15. In summary, chronic moderate exercise appears to attenuate the age-dependent decrease in ASC methylation, implying suppression of excess pro-inflammatory cytokines through reduction of ASC expression.

MITF-CM, a newly identified isoform of microphthalmia-associated transcription factor, is expressed in cultured mast cells.

The microphthalmia-associated transcription factor (MITF) gene encodes a basic helix-loop-helix and leucin zipper protein. In this study, we identified a novel MITF isoform, MITF-CM, which possesses a unique amino terminus. Exon 1CM is located 84 kb upstream of the exon encoding the B1b domain. MITF-CM was expressed in the human mast cell line HMC-1, the human basophilic cell line KU812, and CB-derived mast cells cultured for 10 weeks as well as bone marrow mononuclear cells. Transient transfection of MITF-CM cDNA in COS-7 cells resulted in the expression of a 64-kDa protein, detected by Western blotting, and nuclear localization of the protein, detected by immunostaining. The transient cotransfection of a luciferase construct under the control of the tyrosinase promoter and MITF-CM cDNA increased luciferase activity threefold. In contrast, none of the MITF isoforms transactivated both the tryptase and chymase gene promoters, indicating differences in the gene transactivation system between humans and mice.

Neurodevelopmental abnormalities associated with severe congenital neutropenia due to the R86X mutation in the HAX1 gene.

OBJECTIVE: Severe congenital neutropenia (SCN), also known as Kostmann syndrome (SCN3, OMIM 610738), includes a variety of haematological disorders caused by different genetic abnormalities. Mutations in ELA2 are most often the cause in autosomal dominant or sporadic forms. Recently, mutations in HAX1 have been identified as the cause of some autosomal recessive forms of SCN, including those present in the original pedigree first reported by Kostmann. We sought to determine the relationship between HAX1 gene mutations and the clinical characteristics of Japanese cases of SCN. METHODS: The genes implicated in SCN (ELA2, HAX1, Gfi-1, WAS, and P14) were analysed in 18 Japanese patients with SCN. The clinical features of these patients were obtained from medical records. Immunoblotting of HAX1 was performed on cell extracts from peripheral blood leucocytes from patients and/or their parents. RESULTS: We found five patients with HAX1 deficiency and 11 patients with mutations in the ELA2 gene. In HAX1 deficiency, a homozygous single base pair substitution (256C>T), which causes the nonsense change R86X, was identified in three affected individuals. Two sibling patients showed a compound heterozygous mutation consisting of a single base pair substitution (256C>T) and a 59 bp deletion at nucleotides 376-434. There was no detectable phenotype in any heterozygous carrier. All patients with HAX1 deficiency had experienced developmental delay. Three patients carrying R86X also suffered from epileptic seizures. In contrast, no SCN patient with heterozygous mutations in the ELA2 gene suffered from any neurodevelopmental abnormality. CONCLUSIONS: These findings suggest that the R86X mutation in the HAX1 gene is an abnormality in Japanese SCN patients with HAX1 deficiency and may lead to neurodevelopmental abnormalities and severe myelopoietic defects.

Evaluation of BacT/Alert 3D SA bottles for accurate detection of Mycobacteremia with special reference to Mycobacterium abscessus.

Bacteremia due to Mycobacterium abscessus, a rapid grower, belonging to the Runyon group IV, occurred in an inpatient with fever of unidentified origin in Shinshu University Hospital. To the best of our knowledge, this is the first documented case of M. abscessus bacteremia in Japan. The organism initially grew on Sheep blood agar plates after terminal-subculturing from the BacT/Alert SA aerobic blood culture bottles with no positive signal, and was subsequently identified as M. abscessus using 16S rRNA sequence analysis. We evaluated the BacT/Alert SA bottles for the detection of Mycobacterium species, with special reference to the rapid growers including M. abscessus by seeding experiments and obtained the following findings: 1) The BacT/Alert system shows the positive sign when the bacterial cell counts reach around 10(6) to 10(7) CFU/ml. 2) The System requires around 6 to 7 days of incubation to obtain a sufficient bacterial growth for the positive signal. 3) The System may result in false negative under the 5-day-culture method recommended by American Society for Microbiology in cases of using automated blood culture systems. 4) So-called the blind- or terminal-subcultures from the bottles are inevitable to perform for precluding the false negative cases.

Dynamic DNA methylation change in the CpG island region of p15 during human myeloid development.

We examined the kenetics of p15 methylation and expression during myeloid development. We treated human cord blood CD34+ cells with either GM-CSF alone or in combination with stem cell factor and followed methylation at this locus using bisulfite genomic sequencing. CD34+ cells were found to be either fully methylated or completely unmethylated at 27 CpG dinucleotide sites in exon 1 and at 18 CpG sites in the promoter region of the p15 gene. A time-course study showed that the percentage of the allelic methylation of p15 CpG island increased to approximately 50% to 60% until 7 days after cytokine stimulation, then decreased to less than 10% after 21 days. The methylation was also observed in bone marrow CD34+ cells exposed to GM-CSF. p15 expression varied inversely with methylation. Expression was negligible or at low levels until 14 days, after which it increased substantially. The frequency of myeloid colony-forming cells in the progeny decreased and myeloid-specific markers increased in the later stages. Based on our observations on cells grown with GM-CSF and 5-aza-2'-deoxycytidine, DNA methylation of the p15 promoter region CpG island appears to be associated with proliferation rather than differentiation of normal human myeloid progenitors.

Expression of apoptosis-associated speck-like protein containing a caspase recruitment domain, a pyrin N-terminal homology domain-containing protein, in normal human tissues.

Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) is a pyrin N-terminal homology domain (PYD)- and caspase recruitment domain (CARD)-containing a proapoptotic molecule. This molecule has also been identified as a target of methylation-induced silencing (TMS)-1. We cloned the ASC cDNA by immunoscreening using an anti-ASC monoclonal antibody. In this study, we determined the binding site of the anti-ASC monoclonal antibody on ASC and analyzed the expression of ASC in normal human tissues. ASC expression was observed in anterior horn cells of the spinal cord, trophoblasts of the placental villi, tubule epithelium of the kidney, seminiferous tubules and Leydig cells of the testis, hepatocytes and interlobular bile ducts of the liver, squamous epithelial cells of the tonsil and skin, hair follicle, sebaceous and eccrine glands of the skin, and peripheral blood leukocytes. In the colon, ASC was detected in mature epithelial cells facing the luminal side rather than immature cells located deeper in the crypts. These observations indicate that high levels of ASC are abundantly expressed in epithelial cells and leukocytes, which are involved in host defense against external pathogens and in well-differentiated cells, the proliferation of which is regulated.

Neutrophil-specific granule deficiency: homozygous recessive inheritance of a frameshift mutation in the gene encoding transcription factor CCAAT/enhancer binding protein--epsilon.

Neutrophil-specific granule deficiency (SGD) is a rare congenital disorder. The neutrophils of individuals with SGD display atypical bi-lobed nuclei, lack expression of all secondary and tertiary granule proteins, and possess defects in chemotaxis, disaggregation, receptor up-regulation, and bactericidal activity, resulting in frequent and severe bacterial infections. Previously, a homozygous mutation in the CCAAT/enhancer binding protein-epsilon (C/EBPepsilon) gene was reported for one case of SGD. To substantiate the role of C/EBPepsilon in the development of SGD and elucidate its mechanism of inheritance, the mutational status of the gene was determined in a second individual. An A-nucleotide insertion in the coding region of the C/EBPepsilon gene was detected. This mutation completely abolished the predicted translation of all C/EBPepsilon isoforms. Microsatellite and nucleotide sequence analyses of the C/EBPepsilon locus in the parents of the proband indicated that the disorder may have resulted from homozygous recessive inheritance of the mutant allele from an ancestor shared by both parents. The mutant C/EBPepsilon(32) protein localized in the cytoplasm rather than the nucleus and was unable to activate transcription. Consistent with this, a significant decrease in the levels of the messenger RNAs (mRNAs) encoding the secondary granule protein human 18-kd cationic antimicrobial protein (hCAP-18)/LL-37 and the primary granule protein bactericidal/permeability-increasing protein were observed in the patient. The hCAP-18 mRNA was induced by overexpression of C/EBPepsilon(32) in the human myeloid leukemia cell line, U937, supporting the hypothesis that C/EBPepsilon is a key regulator of granule gene synthesis. This study strongly implicates mutation of the C/EBPepsilon gene as the primary genetic defect involved in the development of neutrophil SGD and defines its mechanism of inheritance.

24-Oxo metabolites of vitamin D3 analogues: disassociation of their prominent antileukemic effects from their lack of calcium modulation.

The seco-steroid hormone, 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] inhibits proliferation and induces differentiation of malignant cells including those of the hematopoietic system. The 24-oxo metabolite of 1,25(OH)(2)D(3) also has prominent antiproliferative activities against various cancer cells. We chemically synthesized five novel 24-oxo vitamin D(3) analogues and evaluated their abilities both to inhibit clonal growth and induce differentiation of myeloid leukemia cells and to cause hypercalcemia. The 1alpha,25-dihydroxy-16-ene-D(3) [1,25(OH)(2)-16-ene-D(3)] and 1alpha,25-dihydroxy-16-ene-19-nor-D(3) [1,25(OH)(2)-16-ene-19-nor-D(3)] and their 24-oxo metabolites showed greater potency than 1,25(OH)(2)D(3) in their abilities to inhibit clonal proliferation of HL-60, NB4, and U937 leukemic cell lines as measured by methylcellulose soft-gel assay. Their inhibition of clonal growth was irreversible as analyzed by pulse exposure studies. The synthetic analogues also had greater potency than 1,25(OH)(2)D(3) to induce differentiation of HL-60 and NB4 cells as measured by generation of superoxide, nonspecific esterase production, and induction of CD11b and CD14 cell surface antigens and to increase the proportion of these cells in the G(0)-G(1) phase of the cell cycle. For most assays, the 24-oxo metabolite was slightly more potent than the unmodified analogue, and 50% activity was usually found in the nanomolar range. These analogues and their 24-oxo metabolites also inhibited fresh leukemic cell clonal proliferation. Expression of p27(KIP1), a cyclin-dependent kinase inhibitor that plays an important role in blocking the cell cycle, was found by Western blot analysis to be induced by the analogues and their 24-oxo metabolites in both HL-60 and U937 cells, suggesting a possible mechanism by which these analogues inhibit leukemic growth. Notably, the calcemic activity tested by injections of 1alpha,25-dihydroxy-16-ene-24-oxo-19-nor-D(3) in mice was at least 12-fold less than 1alpha,25(OH)(2)-16-ene-19-nor-D(3). Taken together, chemically synthesized 24-oxo metabolites of 1alpha,25(OH)(2)-16-ene-D(3) and 1alpha,25(OH)(2)-16-ene-19-nor-D(3) irreversibly inhibited proliferation and induced differentiation of acute myeloid leukemia cells with minimal toxicity; these compounds may have a role in the maintenance phase of therapy for acute myeloid leukemia.

An increase in circulating mast cell colony-forming cells in asthma.

We compared a potential to generate mast cells among various sources of CD34(+) peripheral blood (PB) cells in the presence of stem cell factor (SCF) with or without thrombopoietin (TPO), using a serum-deprived liquid culture system. From the time course of relative numbers of tryptase-positive and chymase-positive cells in the cultured cells grown by CD34(+) PB cells of nonasthmatic healthy individuals treated with G-CSF, TPO appears to potentiate the SCF-dependent growth of mast cells without influencing the differentiation into mast cell lineage. CD34(+) PB cells from asthmatic patients in a stable condition generated significantly more mast cells under stimulation with SCF alone or SCF+TPO at 6 wk of culture than did steady-state CD34(+) PB cells of normal controls. Single-cell culture studies showed a substantial difference in the number of SCF-responsive or SCF+TPO-responsive mast cell progenitors in CD34(+) PB cells between the two groups. In the presence of TPO, CD34(+) PB cells from asthmatic children could respond to a suboptimal concentration of SCF to a greater extent, compared with the values obtained by those of normal controls. Six-week cultured mast cells of asthmatic subjects had maturation properties (intracellular histamine content and tryptase/chymase enzymatic activities) similar to those derived from mobilized CD34(+) PB cells of nonasthmatic subjects. An increase in a potential of circulating hemopoietic progenitors to differentiate into mast cell lineage may contribute to the recruitment of mast cells toward sites of asthmatic mucosal inflammation.

Genetic and long-term data on a patient with permanent isolated proximal renal tubular acidosis.

UNLABELLED: A 12-year-old girl presented with permanent isolated proximal renal tubular acidosis (pRTA), glaucoma, band keratopathy, mild cataract and short stature. Severe metabolic acidosis was caused by the impairment of bicarbonate reabsorption in the proximal tubules and alkali therapy improved her acidaemia. A homozygous G to A transition at nucleotide 1,678 in the basolateral kidney type Na+/HCO3- (kNBC) cotransporter gene SLC4A4, which is critical in HCO3- resorption in renal proximal tubules, was identified. Her height and height velocity (HV) were very low (-4.0 SD and -4.4 SD, respectively) before alkali treatment, but both improved after initiating alkali therapy at the age of 2 years and 3 months. The patient's body height and HV were 131.5 cm (-2.7 SD) and 4.0 cm (-2.0 SD), respectively at the age of 12 years. CONCLUSION: This case demonstrates that early administration of alkali therapy and sustained correction of acidosis, even if inadequate to correct the metabolic acidosis, can markedly improves growth in permanent isolated proximal renal tubular acidosis.

Thrombopoietin enhances neutrophil production by bone marrow hematopoietic progenitors with the aid of stem cell factor in congenital neutropenia.

We examined the effects of granulocyte colony-stimulating factor (G-CSF), stem cell factor (SCF), and thrombopoietin (TPO), alone or in combination, on the generation of neutrophils by bone marrow (BM) cells from three patients with severe congenital neutropenia (SCN) through the use of a serum-deprived liquid culture system. Synergistic effects of G-CSF and SCF on the neutrophil production by BM CD34+CD38+c-kit+ cells were observed in SCN patients as well as in normal controls. The addition of TPO to the culture containing G-CSF and SCF further augmented the growth of neutrophils in the two groups. Single-cell culture experiments revealed that the three-factor combination caused increases in both the number and size of neutrophil colonies compared with G-CSF + SCF in normal BM cells, whereas only a significant increment in the colony size was observed in SCN patients. Even in the presence of SCF or SCF + TPO, the concentrations of G-CSF necessary for the substantial production of neutrophils by CD34+CD38+c-kit+ cells were higher in two patients compared with the levels obtained by normal control cells. In addition, TPO did not accelerate the maturation of neutrophilic cells supported by G-CSF + SCF. When BM CD34+CD38-c-kit+ cells were targeted, the addition of TPO to the culture containing G-CSF and SCF was required for significant neutrophil colony growth in the two groups. These results suggest that TPO enhances the G-CSF-dependent neutrophil production with the aid of SCF in this disorder.

Retinoic acid is a negative regulator for the differentiation of cord blood-derived human mast cell progenitors.

We examined the effects of retinoids on the human mast cell development using a serum-deprived culture system. When 10-week cultured mast cells derived from CD34(+) cord blood cells were used as target cells, both all-trans retinoic acid (ATRA) and 9-cis RA inhibited the progeny generation under stimulation with stem cell factor (SCF) in a dose-dependent manner (the number of progeny grown by SCF plus RA at 10(-7) mol/L was one tenth of the value obtained by SCF alone). The early steps in mast cell development appear to be less sensitive to RA according to the single CD34(+)c-kit(+) cord blood cell culture study. The optimal concentration of RAs also reduced the histamine concentration in the cultured mast cells (3.00 +/- 0.47 pg per cell in SCF alone, 1.44 +/- 0.18 pg per cell in SCF+ATRA, and 1.41 +/- 0.10 pg per cell in SCF+9-cis RA). RT-PCR analyses showed the expression of RARalpha, RARbeta, RXRalpha, and RXRbeta messenger ribonucleic acid (mRNA) in 10-week cultured mast cells. The addition of an RAR-selective agonist at 10(-10) mol/L to 10(-7) mol/L decreased the number of mast cells grown in SCF, whereas an RXR-selective agonist at up to 10(-8) mol/L was inactive. Among RAR subtype selective retinoids used at 10(-9) mol/L to 10(-7) mol/L, only the RARalpha agonist was equivalent to ATRA at 10(-7) mol/L in its ability to inhibit mast cell growth. Conversely, the addition of excess concentrations of a RARalpha antagonist profoundly counteracted the retinoid-mediated suppressive effects. These results suggest that RA inhibits SCF-dependent differentiation of human mast cell progenitors through a specific receptor. (Blood. 2000;95:2821-2828)

[Lymphocytic infundibuloneurohypophysitis during the first remission in acute lymphoblastic leukemia].

A 15-year-old girl developed acute lymphoblastic leukemia (ALL). The patient was treated according to the 13th protocol of the Tokyo Children's Cancer Study Group, and thereafter remained free of disease. However, at the age of 20, she complained of polyuria, polydipsia and amenorrhea. Hematological or meningeal relapse was ruled out on the basis of clinical and laboratory findings. The plasma concentrations of GH, TSH, LH, FSH, ACTH and ADH were low or below the detectable limits. There was no increase in urine osmolarity after water deprivation. Arginine, LH-RH, TRH and CRH tolerance tests revealed no or low responses of GH, LH/FSH, TSH, and ACTH/cortisol, respectively. Magnetic resonance imaging demonstrated thickening of the pituitary stalk, which was homogeneously enhanced by gadolinium administration. A biopsy specimen showed fibrosis and infiltration of CD8-positive T lymphocytes in a portion of the pituitary stalk, whereas the adenohypophysis was normal. In addition, no leukemic cells were observed in the samples. Thus, a diagnosis of lymphocytic infundibuloneurohyophysitis (LIN) was established. All the symptoms were improved by treatment with hydrocortisone, L-thyroxine, desamino-8-d-arginine vasopressin, estrogen and gestagen. This is the first reported case of ALL complicated by LIN.

Thrombopoietin augments stem cell factor-dependent growth of human mast cells from bone marrow multipotential hematopoietic progenitors.

The effects of thrombopoietin (TPO) and/or stem cell factor (SCF) on the development of human mast cells from CD34(+) bone marrow (BM) cells were investigated using a serum-deprived liquid culture system. Mast cells were identified by measurement of intracellular histamine content, immunocytochemical staining, and flow cytometric analysis. Whereas SCF alone generated only a small number of tryptase+ cells, the addition of TPO to the culture containing SCF resulted in an apparent production of mast cells from 3 weeks until at least 15 weeks. Some of the cells reacted with an antichymase monoclonal antibody as well. Based on the effects of growth factor(s) on a later phase of the mast cell growth, TPO may stimulate an early stage of mast cell development in combination with SCF, whereas subsequent growth seems to be supported by SCF alone. Single-cell culture studies indicated that the CD34(+)CD38(-)c-kit+ cells and CD34(+)CD38(+)c-kit+ cells were responsible for the SCF + TPO-dependent mast cell production. Two-step culture assays clearly showed that mast cells originated from multilineage colony-forming cells that had potential to differentiate into neutrophil/mast cell lineages, neutrophil/macrophage/mast cell lineages, or neutrophil/macrophage/mast cell/erythroid lineages. These results suggest that TPO plays an important role in the development of human mast cells from CD34(+) BM cells in concert with SCF, and provide direct evidence of the differentiation into the mast cell lineage of human multipotential BM-derived progenitors.