Scientific Resources

The long-term culture-initiating cell (LTC-IC) assay is a physiological approach to the quantitation of primitive human hematopoietic cells. The readout using identification of cobblestone area-forming cells (CAFC) has gained popularity over the LTC-IC readout where cells are subcultured in a colony-forming cell assay. However,comparing the two assays,cord blood (CB) mononuclear cell (MNC) samples were found to contain a higher frequency of CAFC than LTC-IC (126 +/- 83 versus 40 +/- 31 per 10(5) cells,p = 0.0001). Overall,60% of week-5 cobblestones produced by CB MNC were not functional LTC-IC and were classified as false." Separation of CB MNC using immunomagnetic columns showed that false cobblestones were CD34(-)/lineage(+). Purified CD34(+) cells� View Publication

Human T-cell leukemia virus type 1 (HTLV-1) and HTLV-2 are highly related viruses that differ in disease manifestation. HTLV-1 is the etiologic agent of adult T-cell leukemia and lymphoma,an aggressive clonal malignancy of human CD4-bearing T lymphocytes. Infection with HTLV-2 has not been conclusively linked to lymphoproliferative disorders. We previously showed that human hematopoietic progenitor (CD34(+)) cells can be infected by HTLV-1 and that proviral sequences were maintained after differentiation of infected CD34(+) cells in vitro and in vivo. To investigate the role of the Tax oncoprotein of HTLV on hematopoiesis,bicistronic lentiviral vectors were constructed encoding the HTLV-1 or HTLV-2 tax genes (Tax1 and Tax2,respectively) and the green fluorescent protein marker gene. Human hematopoietic progenitor (CD34(+)) cells were infected with lentivirus vectors,and transduced cells were cultured in a semisolid medium permissive for the development of erythroid,myeloid,and primitive progenitor colonies. Tax1-transduced CD34(+) cells displayed a two- to fivefold reduction in the total number of hematopoietic clonogenic colonies that arose in vitro,in contrast to Tax2-transduced cells,which showed no perturbation of hematopoiesis. The ratio of colony types that developed from Tax1-transduced CD34(+) cells remained unaffected,suggesting that Tax1 inhibited the maturation of relatively early,uncommitted hematopoietic stem cells. Since previous reports have linked Tax1 expression with initiation of apoptosis,lentiviral vector-mediated transduction of Tax1 or Tax2 was investigated in CEM and Jurkat T-cell lines. Ectopic expression of either Tax1 or Tax2 failed to induce apoptosis in T-cell lines. These data demonstrate that Tax1 expression perturbs development and maturation of pluripotent hematopoietic progenitor cells,an activity that is not displayed by Tax2,and that the suppression of hematopoiesis is not attributable to induction of apoptosis. Since hematopoietic progenitor cells may serve as a latently infected reservoir for HTLV infection in vivo,the different abilities of HTLV-1 and -2 Tax to suppress hematopoiesis may play a role in the respective clinical outcomes after infection with HTLV-1 or -2. View Publication

We studied the actions of geldanamycin (GA) and herbimycin A (HMA),inhibitors of the chaperone proteins Hsp90 and GRP94,on B chronic lymphocytic leukemia (CLL) cells in vitro. Both drugs induced apoptosis of the majority of CLL isolates studied. Whereas exposure to 4-hour pulses of 30 to 100 nM GA killed normal B lymphocytes and CLL cells with similar dose responses,T lymphocytes from healthy donors as well as those present in the CLL isolates were relatively resistant. GA,but not HMA,showed a modest cytoprotective effect toward CD34+ hematopoietic progenitors from normal bone marrow. The ability of bone marrow progenitors to form hematopoietic colonies was unaffected by pulse exposures to GA. Both GA and HMA synergized with chlorambucil and fludarabine in killing a subset of CLL isolates. GA- and HMA-induced apoptosis was preceded by the up-regulation of the stress-responsive chaperones Hsp70 and BiP. Both ansamycins also resulted in down-regulation of Akt protein kinase,a modulator of cell survival. The relative resistance of T lymphocytes and of CD34+ bone marrow progenitors to GA coupled with its ability to induce apoptosis following brief exposures and to synergize with cytotoxic drugs warrant further investigation of ansamycins as potential therapeutic agents in CLL. View Publication

We previously found that some myeloma cell lines express the heparin-binding epidermal growth factor-like growth factor (HB-EGF) gene. As the proteoglycan syndecan-1 is an HB-EGF coreceptor as well as a hallmark of plasma cell differentiation and a marker of myeloma cells,we studied the role of HB-EGF on myeloma cell growth. The HB-EGF gene was expressed by bone marrow mononuclear cells in 8 of 8 patients with myeloma,particularly by monocytes and stromal cells,but not by purified primary myeloma cells. Six of 9 myeloma cell lines and 9 of 9 purified primary myeloma cells expressed ErbB1 or ErbB4 genes coding for HB-EGF receptor. In the presence of a low interleukin-6 (IL-6) concentration,HB-EGF stimulated the proliferation of the 6 ErbB1+ or ErbB4+ cell lines,through the phosphatidylinositol 3-kinase/AKT (PI-3K/AKT) pathway. A pan-ErbB inhibitor blocked the myeloma cell growth factor activity and the signaling induced by HB-EGF. This inhibitor induced apoptosis of patients'myeloma cells cultured with their tumor environment. It also increased patients' myeloma cell apoptosis induced by an anti-IL-6 antibody or dexamethasone. The ErbB inhibitor had no effect on the interaction between multiple myeloma cells and stromal cells. It was not toxic for nonmyeloma cells present in patients' bone marrow cultures or for the growth of hematopoietic progenitors. Altogether,these data identify ErbB receptors as putative therapeutic targets in multiple myeloma. View Publication

The physiologic function of BUBR1,a key component of the spindle checkpoint,was examined by generating BUBR1-mutant mice. BUBR1(-/-) embryos failed to survive beyond day 8.5 in utero as a result of extensive apoptosis. Whereas BUBR1(+/-) blastocysts grew relatively normally in vitro,BUBR1(-/-) blastocysts exhibited impaired proliferation and atrophied. Adult BUBR1(+/-) mice manifested splenomegaly and abnormal megakaryopoiesis. BUBR1 haploinsufficiency resulted in an increase in the number of splenic megakaryocytes,which was correlated with an increase in megakaryocytic,but a decrease in erythroid,progenitors in bone marrow cells. RNA interference-mediated down-regulation of BUBR1 also caused an increase in polyploidy formation in murine embryonic fibroblast cells and enhanced megakaryopoiesis in bone marrow progenitor cells. However,enhanced megakaryopoiesis in BUBR1(+/-) mice was not correlated with a significant increase in platelets in peripheral blood,which was at least partly due to a defect in the formation of proplatelet-producing megakaryocytes. Together,these results indicate that BUBR1 is essential for early embryonic development and normal hematopoiesis. View Publication

In a patient with refractory anemia with excess blasts (RAEB),a somatic mutation of mitochondrial transfer RNA(Leu(UUR)) was detected in bone marrow cells. Heteroduplex analysis indicated that 40% to 50% of mitochondrial DNA (mtDNA) molecules in the bone marrow (BM) carried the novel G3242A mutation. The proportion of mutant mtDNA was higher in CD34(+) cells than in the unfractionated sample. Surprisingly,the mutation was not detectable by heteroduplex analysis in the peripheral blood (PB). However,PB CD34(+) cells selected by immunomagnetic beads harbored the mutation with a proportion of approximately 50%. In hematopoietic colony assays,CD34(+) cells from BM and PB yielded only colonies with wild-type mtDNA. These results indicate that the mtDNA mutation in CD34(+) cells was associated with a maturation defect. Mitochondrial tRNA mutations impair mitochondrial protein synthesis,thereby causing dysfunction of the mitochondrial respiratory chain. We propose that this effect contributed to ineffective hematopoiesis in our patient. View Publication

In mammals,the continuous production of hematopoietic cells (HCs) is sustained by a small number of hematopoietic stem cells (HSCs) residing in the bone marrow. Early HSC activity arises in the aorta-gonad mesonephros region,within cells localized to the ventral floor of the major blood vessels,suggesting that the first HSCs may be derived from cells capable of giving rise to the hematopoietic system and to the endothelial cells of the vasculature. TIE1 (TIE) and TIE2 (TEK) are related receptor tyrosine kinases with an embryonic expression pattern in endothelial cells,their precursors,and HCs,suggestive of a role in the divergence and function of both lineages. Indeed,gene targeting approaches have shown that TIE1,TIE2,and ligands for TIE2,the angiopoietins,are essential for vascular development and maintenance. To explore possible roles for these receptors in HCs,we have examined the ability of embryonic cells lacking both TIE1 and TIE2 to contribute to developmental and adult hematopoiesis by generating chimeric animals between normal embryonic cells and cells lacking these receptors. We show here that TIE receptors are not required for differentiation and proliferation of definitive hematopoietic lineages in the embryo and fetus; surprisingly,however,these receptors are specifically required during postnatal bone marrow hematopoiesis. View Publication

Germ line mutations in the Adenomatous polyposis coli tumor suppressor gene cause a hereditary form of intestinal tumorigenesis in both mice and man. Here we show that in Apc(Min/+) mice,which carry a heterozygous germ line mutation at codon 850 of Apc,there is progressive loss of immature and mature thymocytes from approximately 80 days of age with complete regression of the thymus by 120 days. In addition,Apc(Min/+) mice show parallel depletion of splenic natural killer (NK) cells,immature B cells,and B progenitor cells in bone marrow due to complete loss of interleukin 7 (IL-7)-dependent B-cell progenitors. Using bone marrow transplantation experiments into wild-type recipients,we have shown that the capacity of transplanted Apc(Min/+) bone marrow cells for T- and B-cell development appears normal. In contrast,although the Apc(Min/+) bone marrow microenvironment supported short-term reconstitution with wild-type bone marrow,Apc(Min/+) animals that received transplants subsequently underwent lymphodepletion. Fibroblast colony-forming unit (CFU-F) colony assays revealed a significant reduction in colony-forming mesenchymal progenitor cells in the bone marrow of Apc(Min/+) mice compared with wild-type animals prior to the onset of lymphodepletion. This suggests that an altered bone marrow microenvironment may account for the selective lymphocyte depletion observed in this model of familial adenomatous polyposis. View Publication

Exposure of murine bone marrow (BM) cells to ionizing radiation (IR; 4 Gy) resulted in textgreater95% inhibition of the frequency of various day types of cobblestone area-forming cells in association with the induction of apoptosis in hematopoietic stem cell alike cells (Lin(-) ScaI(+) c-kit(+) cells; IR: 64.8 +/- 0.4% versus control: 20.4 +/- 0.5%; P textless 0.001) and progenitors (Lin(-) ScaI(-) c-kit(+) cells; IR: 46.2 +/- 1.4% versus control: 7.8 +/- 0.5%; P textless 0.001). Incubation of murine BM cells with busulfan (BU; 30 micro M) for 6 h also inhibited the cobblestone area-forming cell frequency but failed to cause a significant increase in apoptosis in these two types of hematopoietic cells. After 5 weeks of long-term BM cell culture,33% and 72% of hematopoietic cells survived IR- and BU-induced damage,respectively,as compared with control cells,but they could not form colony forming units-granulocyte macrophages. Moreover,these surviving cells expressed an increased level of senescence-associated beta-galactosidase,p16(Ink4a),and p19(Arf). These findings suggest that IR inhibits the function of hematopoietic stem cell alike cells and progenitors primarily by inducing apoptosis,whereas BU does so mainly by inducing premature senescence. In addition,induction of premature senescence in BM hematopoietic cells also contributes to IR-induced inhibition of their hematopoietic function. Interestingly,the induction of hematopoietic cell senescence by IR,but not by BU,was associated with an elevation in p53 and p21(Cip1/Waf1) expression. This suggests that IR induces hematopoietic cell senescence in a p53-p21(Cip1/Waf1)-dependent manner,whereas the induction of senescence by BU bypasses the p53-p21(Cip1/Waf1) pathway. View Publication

Embryonic stem cells can be induced in vitro,by coculture with the stromal line RP.0.10 and a mixture of interleukins 3,6,and 7,to differentiate into T (Joro75+) and B (B-220+) lymphocyte progenitors and other (Thy-1+,PgP-1+,c-kit+,Joro75-,B-220-,F4/80-,Mac-1-) hemopoietic precursors. The progeny of in vitro-induced embryonic stem cells can reconstitute the lymphoid compartments of T- and B-lymphocyte-deficient scid mice and generate mature T and B lymphocytes in sublethally irradiated normal mice. Exogenous cytokines can dramatically alter the developmental fate of embryonic stem cells in culture. The in vitro system described here should facilitate the study of molecular events leading to cell-lineage commitment and to the formation of hemopoietic stem cells and their immediate lymphoid progeny. View Publication

Undifferentiated pluripotent stem cells with flexible developmental potentials are not normally found in peripheral blood. However,such cells have recently been reported to reside in the bone marrow. Herein are reported methods of inducing pluripotency in cells derived from unmobilised adult human peripheral blood. In response to the inclusion of purified CR3/43 monoclonal antibody (mAb) to well-established culture conditions,mononuclear cells (MNC) obtained from a single blood donor are converted into pluripotent haematopoietic,neuronal and cardiomyogenic progenitor stem cells or undifferentiated stem cells. The haematopoietic stem cells are CD34+,clonogenic and have been shown to repopulate non-obese diabetic/severe combined immunodeficient (NOD/SCID) mice. The neuronal precursors transcribe the primitive stem cell markers OCT-4 and nestin,and on maturation,differentially stain positive for neuronal,glial or oligodendrocyte-specific antigens. The cardiomyogenic progenitor stem cells form large bodies of asynchronously beating cells and differentiate into mature cardiomyocytes which transcribe GATA-4. The undifferentiated stem cells do not express haematopoietic-associated markers,are negative for major histocompatibility complex (MHC) class I and II antigens,transcribe high levels of OCT-4 and form embryoid body (EB)-like structures. This induction of stem cell-like plasticity in MNC may have proceeded by a process of retrodifferentiation but,in any case,could have profound clinical and pharmacological implications. Finally,the flexibility and the speed by which a variety of stem cell classes can be generated ex vivo from donor blood could potentially transfer this novel process into a less invasive automated clinical procedure. View Publication

Mice deficient in early B cell factor (EBF) are blocked at the progenitor B cell stage prior to immunoglobulin gene rearrangement. The EBF-dependent block in B cell development occurs near the onset of B-lineage commitment,which raises the possibility that EBF may act instructively to specify the B cell fate from uncommitted,multipotential progenitor cells. To test this hypothesis,we transduced enriched hematopoietic progenitor cells with a retroviral vector that coexpressed EBF and the green fluorescent protein (GFP). Mice reconstituted with EBF-expressing cells showed a near complete absence of T lymphocytes. Spleen and peripheral blood samples were textgreater95 and 90% GFP+EBF+ mature B cells,respectively. Both NK and lymphoid-derived dendritic cells were also significantly reduced compared with control-transplanted mice. These data suggest that EBF can restrict lymphopoiesis to the B cell lineage by blocking development of other lymphoid-derived cell pathways. View Publication