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In the present study,we report a new method for enrichment and analysis of fetal CD34+ stem cells after culture in order to determine whether it is feasible for noninvasive prenatal diagnosis. We also determined whether fetal CD34+ stem cells persist in maternal blood after delivery and assessed whether they have an impact on noninvasive prenatal diagnosis of genetic abnormalities. Peripheral blood samples were obtained from 35 pregnant women,13 non-pregnant women who had given birth to male offsprings,12 women who had never been pregnant,and eight pregnant women with male fetuses. CD34+ stem cells were enriched and either cultured for prenatal diagnosis or analyzed with fluorescence in situ hybridization (FISH)/polymerase chain reaction (PCR) to determine peristance in maternal blood. Fetal/maternal cells can be isolated and grown in vitro" to provide enough cells for a more accurate fetal sex or aneuploid prediction than is provided by unenriched and uncultured CD34+ stem cells. The presence of fetal cells in maternal blood samples from mothers who had given birth to male offspring was found in 3 of 13 blood samples. PCR was positive for Y chromosome in one woman who had never been pregnant. Analysis of cultured CD34+ stem cells from mothers with Y PCR positivity did not detect any male cells in any samples. Even if PCR positivity is due to persistence of fetal stem cells from previous pregnancies View Publication

The Cre recombinase (Cre) from bacteriophage P1 is an important tool for genetic engineering in mammalian cells. We constructed lentiviral vectors that efficiently deliver Cre in vitro and in vivo. Surprisingly,we found a significant reduction in proliferation and an accumulation in the G(2)/M phase of Cre-expressing cells. To minimize the toxic effect of Cre,we designed a lentiviral vector that integrates into the host genome,expresses Cre in the target cell,and is subsequently deleted from the genome in a Cre-dependent manner. Thus,the activity of Cre terminates its own expression (self-deleting). We showed efficient modification of target genes in vitro and in the brain after transduction with the self-deleting vectors. In contrast to sustained Cre expression,transient expression of Cre from the self-deleting vector induced significantly less cytotoxicity. Such a self-deleting Cre vector is a promising tool for the induction of conditional gene modifications with minimal Cre toxicity in vivo. View Publication

Reinfusion of ex vivo-expanded autologous megakaryocytes together with a stem cell transplantation may be useful to prevent or reduce the period of chemotherapy-induced thrombocytopenia. In this study,we analyzed several serum-containing and serum-free media to identify the most suitable medium for megakaryocyte expansion. Moreover,two thrombopoietin (Tpo)-mimetic peptides were tested to evaluate whether they could replace Tpo in an expansion protocol. To analyze the effects of different media on megakaryocyte expansion,we used an in vitro liquid culture system. For this purpose,CD34(+) cells were isolated from peripheral blood and cultured for 8 days in the presence of Tpo and interleukin-3 (IL-3). The presence of megakaryocytes was analyzed by flow cytometric analysis after staining for CD41 expression. For our standard culture procedure,megakaryocyte medium (MK medium) supplemented with 10% AB plasma was used. Addition of 5% or 2.5% AB plasma yielded higher numbers of megakaryocytes,implying the presence of inhibitory factors in plasma. However,some plasma components are required for optimal megakaryocyte expansion because addition of less than 1% AB plasma or addition of human serum albumin instead of AB plasma resulted in the formation of lower numbers of megakaryocytes. Two commercially available serum-free media were also tested: Cellgro and Stemspan. If CD34(+) cells were cultured in Cellgro medium similar numbers of megakaryocytes were obtained as when CD34(+) cells were cultured in MK medium supplemented with 10% AB plasma. In MK medium with 2.5% AB plasma,higher numbers of megakaryocytes were cultured than in MK medium supplemented with 10% AB plasma. Therefore,Cellgro medium is not the best alternative medium. In cultures with Stemspan medium,higher numbers of megakaryocytes were obtained compared to MK medium with 10% AB plasma. Stemspan is thus a good alternative for MK medium. Two Tpo-mimetic peptides,AF13948 and PK1M,were tested for their ability to replace Tpo. In cultures with AF13948,comparable numbers of megakaryocytes were obtained as in the presence of Tpo,but in cultures with PK1M the number of megakaryocytes was lower. This study shows that high concentrations of plasma in medium inhibits megakaryocyte formation,but some plasma components are required for optimal megakaryocyte expansion. For an ex vivo expansion protocol,it is worthwhile to test several media,because the number of megakaryocytes differs widely with the medium used. View Publication

Genetic modification of hematopoietic stem cells often results in the expression of foreign proteins in pluripotent progenitor cells and their progeny. However,the potential for products of foreign genes introduced into hematopoietic stem cells to induce host immune responses is not well understood. Gene marking and induction of immune responses to enhanced green fluorescent protein (eGFP) were examined in rhesus macaques that underwent nonmyeloablative irradiation followed by infusions of CD34(+) bone marrow cells transduced with a retroviral vector expressing eGFP. CD34(+) cells were obtained from untreated animals or from animals treated with recombinant human granulocyte colony-stimulating factor (G-CSF) alone or G-CSF and recombinant human stem cell factor. Levels of eGFP-expressing cells detected by flow cytometry peaked at 0.1% to 0.5% of all leukocytes 1 to 4 weeks after transplantation. Proviral DNA was detected in 0% to 17% of bone marrow--derived colony-forming units at periods of 5 to 18 weeks after transplantation. However,5 of 6 animals studied demonstrated a vigorous eGFP-specific cytotoxic T lymphocyte (CTL) response that was associated with a loss of genetically modified cells in peripheral blood,as demonstrated by both flow cytometry and polymerase chain reaction. The eGFP-specific CTL responses were MHC-restricted,mediated by CD8(+) lymphocytes,and directed against multiple epitopes. eGFP-specific CTLs were able to efficiently lyse autologous CD34(+) cells expressing eGFP. Antibody responses to eGFP were detected in 3 of 6 animals. These data document the potential for foreign proteins expressed in CD34(+) hematopoietic cells and their progeny to induce antibody and CTL responses in the setting of a clinically applicable transplantation protocol. (Blood. 2001;97:1951-1959) View Publication

DYRKs are a new subfamily of dual-specificity kinases that was originally discovered on the basis of homology to Yak1,an inhibitor of cell cycle progression in yeast. At present,mDYRK-3 and mDYRK-2 have been cloned,and mDYRK-3 has been characterized with respect to kinase activity,expression among tissues and hematopoietic cells,and possible function during erythropoiesis. In sequence,mDYRK-3 diverges markedly in noncatalytic domains from mDYRK-2 and mDYRK-1a,but is 91.3% identical overall to hDYRK-3. Catalytically,mDYRK-3 readily phosphorylated myelin basic protein (but not histone 2B) and also appeared to autophosphorylate in vitro. Expression of mDYRK-1a,mDYRK-2,and mDYRK-3 was high in testes,but unlike mDYRK1a and mDYRK 2,mDYRK-3 was not expressed at appreciable levels in other tissues examined. Among hematopoietic cells,however,mDYRK-3 expression was selectively elevated in erythroid cell lines and primary pro-erythroid cells. In developmentally synchronized erythroid progenitor cells,expression peaked sharply following exposure to erythropoietin plus stem cell factor (SCF) (but not SCF alone),and in situ hybridizations of sectioned embryos revealed selective expression of mDYRK-3 in fetal liver. Interestingly,antisense oligonucleotides to mDYRK-3 were shown to significantly and specifically enhance colony-forming unit-erythroid colony formation. Thus,it is proposed that mDYRK-3 kinase functions as a lineage-restricted,stage-specific suppressor of red cell development. (Blood. 2001;97:901-910) View Publication

According to the current model of adult hematopoiesis,differentiation of pluripotential hematopoietic stem cells into common myeloid- and lymphoid-committed progenitors establishes an early separation between the myeloid and lymphoid lineages. This report describes a rare and previously unidentified CD45R-CD19+ B cell progenitor population in postnatal bone marrow that can also generate macrophages. In addition to the definition of this B-lineage intermediate,the data indicate that a developmental relationship between the B and macrophage lineages is retained during postnatal hematopoiesis. View Publication

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AC133 antigen is a novel marker for human hematopoietic stem/progenitor cells. In this study,we examined the expression and proliferation potential of AC133(+) cells obtained from steady-state peripheral blood (PB). The proportion of AC133(+) cells in the CD34(+) subpopulation of steady-state PB was significantly lower than that of cord blood (CB),although that of cytokine-mobilized PB was higher than that of CB. The proliferation potential of AC133(+)CD34(+) and AC133(-)CD34(+) cells was examined by colony-forming analysis and analysis of long-term culture-initiating cells (LTC-IC). Although the total number of colony-forming cells was essentially the same in the AC133(+)CD34(+) fraction as in the AC133(-)CD34(+) fraction,the proportion of LTC-IC was much higher in the AC133(+)CD34(+) fraction. Virtually no LTC-IC were detected in the AC133(-)CD34(+) fraction. In addition,the features of the colonies grown from these two fractions were quite different. Approximately 70% of the colonies derived from the AC133(+)CD34(+) fraction were granulocyte-macrophage colonies,whereas more than 90% of the colonies derived from the AC133(-)CD34(+) fraction were erythroid colonies. Furthermore,an ex vivo expansion study observed expansion of colony-forming cells only in the AC133(+)CD34(+) population,and not in the AC133(-)CD34(+) population. These findings suggest that to isolate primitive hematopoietic cells from steady-state PB,selection by AC133 expression is better than selection by CD34 expression. View Publication

Human bone marrow (BM) or mobilized peripheral blood (mPB) CD34(+) cells have been shown to loose their stem cell quality during culture period more easily than those from cord blood (CB). We previously reported that human umbilical CB stem cells could effectively be expanded in the presence of human recombinant cytokines and a newly established murine bone marrow stromal cell line HESS-5. In this study we assessed the efficacy of this xenogeneic coculture system using human BM and mPB CD34(+) cells as materials. We measured the generation of CD34(+)CD38(-) cells and colony-forming units,and assessed severe-combined immunodeficient mouse-repopulating cell (SRC) activity using cells five days after serum-free cytokine-containing culture in the presence or the absence of a direct contact with HESS-5 cells. As compared with the stroma-free culture,the xenogeneic coculture was significantly superior on expansion of CD34(+)CD38(-) cells and colony-forming cells and on maintenance of SRC activity. The PKH26 study demonstrated that cell division was promoted faster in cells cocultured with HESS-5 cells than in cells cultured without HESS-5 cells. These results indicate that HESS-5 supports rapid generation of primitive progenitor cells (PPC) and maintains reconstituting ability of newly generated stem cells during ex vivo culture irrespective of the source of samples. This xenogeneic coculture system will be useful for ex vivo manipulation such as gene transduction to promote cell division and the generation of PPC and to prevent loss of stem cell quality. View Publication

OBJECTIVE: +HOX genes are expressed in the hematopoietic system and increasing data point to their involvement in the control of proliferation and/or differentiation. Genes belonging to the C cluster are preferentially expressed in developing and differentiated lymphoid lineages. However,recent studies demonstrated,by RT-PCR,that the HOXC4 gene is also actively transcribed in the most undifferentiated hematopoietic cells (CD34(+)38(low)) and in more mature myeloid and erythroid progenitors. We evaluated the expression of HOXC4 protein on human CD34(+) cells and the in vitro effect of its overexpression on proliferation and differentiation. MATERIALS AND METHODS: We assessed the expression of HOXC4 on human CD34(+) cells using a polyclonal antibody raised against the C-terminal portion of the protein expressed using the baculovirus system. Overexpression of HOXC4 in human CD34(+) cells was obtained by retroviral gene transfer; its effect on clonogenic (CFU-GM,BFU-E,and CFU-GEMM) and early progenitors (LTC-IC) was evaluated. RESULTS: The HOXC4 protein is indeed expressed in human CD34(+) cells,and its overexpression in human CD34(+) cells increases the proliferation potential of clonogenic and early progenitors. CFU-GM showed a median threefold expansion (range: 1.1-19.4; p textless 0.002) compared with control transduced with the vector alone. The increment of BFU-E was higher (median ninefold,range 2.5-35; p textless 0. 0009) and erythroid colonies presented a larger size with normal morphology. An even more marked effect was observed on LTC-IC (median 13,onefold; range 4.1-102.1,p textless 0.0001). CONCLUSION: We demonstrate that HOXC4 is expressed in CD34(+) cells and that its overexpression induces an in vitro expansion of committed as well as very early hematopoietic progenitors. The most striking effect was obtained on LTC-IC with an expansion of 13.1-fold. The enforced expression of HOXC4 induced a significant increase (p textless 0.009) in the number of erythroid colonies compared with CFU-GM,although without perturbing,at least in vitro,the maturation program of the cells. On the other hand,the effect of the gene overexpression did not induce any skewing in the colony types derived from the myeloid lineage. View Publication

Hematologic malignancies such as acute and chronic myeloid leukemia are characterized by the malignant transformation of immature CD34(+) progenitor cells. Transformation is associated with elevated expression of the Wilm's tumor gene encoded transcription factor (WT1). Here we demonstrate that WT1 can serve as a target for cytotoxic T lymphocytes (CTL) with exquisite specificity for leukemic progenitor cells. HLA-A0201- restricted CTL specific for WT1 kill leukemia cell lines and inhibit colony formation by transformed CD34(+) progenitor cells isolated from patients with chronic myeloid leukemia (CML),whereas colony formation by normal CD34(+) progenitor cells is unaffected. Thus,the tissue-specific transcription factor WT1 is an ideal target for CTL-mediated purging of leukemic progenitor cells in vitro and for antigen-specific therapy of leukemia and other WT1-expressing malignancies in vivo. View Publication