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Expansion of hematopoietic progenitor cells (HPC) ex vivo remains an important focus in fundamental and clinical research. The aim of this study was to determine whether the implementation of such expansion phase in a two-phase culture strategy prior to the induction of megakaryocyte (Mk) differentiation would increase the yield of Mks produced in cultures. Toward this end,we first characterized the functional properties of five cytokine cocktails to be tested in the expansion phase on the growth and differentiation kinetics of CD34+-enriched cells,and on their capacity to expand clonogenic progenitors in cultures. Three of these cocktails were chosen based on their reported ability to induce HPC expansion ex vivo,while the other two represented new cytokine combinations. These analyses revealed that none of the cocktails tested could prevent the differentiation of CD34+ cells and the rapid expansion of lineage-positive cells. Hence,we sought to determine the optimum length of time for the expansion phase that would lead to the best final Mk yields. Despite greater expansion of CD34+ cells and overall cell growth with a longer expansion phase,the optimal length for the expansion phase that provided greater Mk yield at near maximal purity was found to be 5 days. Under such settings,two functionally divergent cocktails were found to significantly increase the final yield of Mks. Surprisingly,these cocktails were either deprived of thrombopoietin or of stem cell factor,two cytokines known to favor megakaryopoiesis and HPC expansion,respectively. Based on these results,a short resource-efficient two-phase culture protocol for the production of Mks near purity (textgreater95%) from human CD34+ CB cells has been established. View Publication

The immune system can act as an extrinsic suppressor of tumors. Therefore,tumor progression depends in part on mechanisms that downmodulate intrinsic immune surveillance. Identifying these inhibitory pathways may provide promising targets to enhance antitumor immunity. Here,we show that Stat3 is constitutively activated in diverse tumor-infiltrating immune cells,and ablating Stat3 in hematopoietic cells triggers an intrinsic immune-surveillance system that inhibits tumor growth and metastasis. We observed a markedly enhanced function of dendritic cells,T cells,natural killer (NK) cells and neutrophils in tumor-bearing mice with Stat3(-/-) hematopoietic cells,and showed that tumor regression requires immune cells. Targeting Stat3 with a small-molecule drug induces T cell- and NK cell-dependent growth inhibition of established tumors otherwise resistant to direct killing by the inhibitor. Our findings show that Stat3 signaling restrains natural tumor immune surveillance and that inhibiting hematopoietic Stat3 in tumor-bearing hosts elicits multicomponent therapeutic antitumor immunity. View Publication

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OVERVIEW: We show the existence of adult human mesenchymal progenitor cells (hMPCs) that can proliferate,in a cytokine-dependent manner,as individual cells in stirred suspension cultures (SSC) while maintaining their ability to form functional differentiated mesenchymal cell types. MATERIALS AND METHODS: Ficolled human bone marrow (BM)-derived cells were grown in SSC (and adherent controls) in the presence and absence of exogenously added cytokines. Phenotypic,gene expression,and functional assays for hematopoietic and nonhematopoietic cell populations were used to kinetically track cell production. Limiting-dilution analysis was used to relate culture-produced cells to input cell populations. RESULTS: Cytokine cocktail influenced total and progenitor cell expansion,as well as the types of cells generated upon plating. Flow cytometric analysis of CD117,CD123,and CD45 expression showed that cytokine supplementation influenced SSC output. The concomitant growth of CD45(+) and CD45(-) cells in the cultures that exhibited the greatest hMPC expansions suggests that the growth of these cells may benefit from interactions with hematopoietic cells. Functional assays demonstrated that the SSC-derived cells (input CFU-O number: 1990+/-377) grown in the presence of SCF+IL-3 resulted,after 21 days,in the generation of a significantly greater number (ptextless0.05) of bone progenitors (33,700+/-8763 CFU-O) than similarly initiated adherent cultures (214+/-75 CFU-O). RT-PCR analysis confirmed that the SSC-derived cells grown in osteogenic conditions express bone-specific genes (Cbfa1/Runx2,bone sialoprotein,and osteocalcin). CONCLUSIONS: Our approach not only provides an alternative strategy to expand adult BM-derived nonhematopoietic progenitor cell numbers in a scalable and controllable bioprocess,but also questions established biological paradigms concerning the properties of connective-tissue stem and progenitor cells. View Publication

The use of induced pluripotent stem cells (iPSCs) as a source of cells for cell-based therapy in regenerative medicine is hampered by the limited efficiency and safety of the reprogramming procedure and the low efficiency of iPSC differentiation to specialized cell types. Evidence suggests that iPSCs retain an epigenetic memory of their parental cells with a possible influence on their differentiation capacity in vitro. We reprogramme three cell types,namely human umbilical cord vein endothelial cells (HUVECs),endothelial progenitor cells (EPCs) and human dermal fibroblasts (HDFs),to iPSCs and compare their hematoendothelial differentiation capacity. HUVECs and EPCs were at least two-fold more efficient in iPSC reprogramming than HDFs. Both HUVEC- and EPC-derived iPSCs exhibited high potentiality toward endothelial cell differentiation compared with HDF-derived iPSCs. However,only HUVEC-derived iPSCs showed efficient differentiation to hematopoietic stem/progenitor cells. Examination of DNA methylation at promoters of hematopoietic and endothelial genes revealed evidence for the existence of epigenetic memory at the endothelial genes but not the hematopoietic genes in iPSCs derived from HUVECs and EPCs indicating that epigenetic memory involves an endothelial differentiation bias. Our findings suggest that endothelial cells and EPCs are better sources for iPSC derivation regarding their reprogramming efficiency and that the somatic cell type used for iPSC generation toward specific cell lineage differentiation is of importance. View Publication

The physical culture parameters have important influences on the proliferation and differentiation fate of hematopoietic stem cells. Recently,we have demonstrated that CD34+ cord blood (CB) cells undergo accelerated and increased megakaryocyte (Mk) differentiation when incubated under mild hyperthermic conditions (i.e.,39 degrees C). In this study,we investigated in detail the impacts of mild hyperthermia on Mk differentiation and maturation,and explored potential mechanisms responsible for these phenomena. Our results demonstrate that the qualitative and quantitative effects on Mk differentiation at 39 degrees C appear rapidly within 7 days,and that early transient culture at 39 degrees C led to even greater Mk yields (ptextless0.03). Surprisingly,cell viability was only found to be significantly reduced in the early stages of culture,suggesting that CB cells are able with time to acclimatize themselves to 39 degrees C. Although mild hyperthermia accelerated differentiation and maturation of CB-derived Mks,it failed to promote their polyploidization further but rather led to a small reduction in the proportion of polyploid Mks (p=0.01). Conversely,gene arrays analysis demonstrated that Mks derived at 39 degrees C have a normal gene expression program consistent with an advanced maturation state. Finally,two independent mechanisms that could account for the accelerated Mk differentiation were investigated. Our results suggest that the accelerated and increased Mk differentiation induced by mild hyperthermia is not mediated by cell-secreted factors but could perhaps be mediated by the increased expression of Mk transcription factors. View Publication

OBJECTIVE: To explore the effects of anti-CD44 monoclonal antibody-IM7 on the in vitro adhesion and migration of chronic myeloid leukemia stem cell (CML-LSC) and its mechanism. METHODS: CD34(+)CD38(-)CD123(+) leukemic stem cells (LSC) from 20 newly-diagnosed chronic myeloid leukemia (CML) patients BM cells and CD34(+)CD38(-) hematopoietic stem cells (HSC) from 20 full-term newborn cord blood cells were isolated with EasySep(TM) magnet beads. The CD44 expression of the LSC and HSC was detected by flow cytometry (FCM),and the adhesion and migration ability of the LSC and HSC pre- and post-incubated with IM7 in vitro by MTT assay and transendothelial migration assay,respectively. RESULTS: (1) After incubated with IM7,the LSC and HSC CD44 expression rates were (86.60 ± 2.10)% vs. (25.40 ± 1.70)% (P textless 0.05),respectively. (2) The adhesive ability of the LSC to endothelial cells was decreased markedly after incubated with IM7,the OD value (A(570)) changing from pre-incubation of (0.62 ± 0.11) to post-incubation of (0.34 ± 0.07),while there was little change of A(570) in the HSC group. (3) The migration ability of the LSC group was inhibited evidently after incubated with IM7,the inhibition rate being 46% ∼ 63%,while little change of that in HSC group was detected. (4) The adhesive ability of the LSC group to marrow stromal cells was decreased markedly after incubated with IM7,while little change was found in that of HSC group. CONCLUSION: The anti-CD44 monoclonal antibody-IM7 can effectively inhibit the adhesion and migration abilities of the LSC in vitro,which might provide a theoretical evidence for targeting therapy. View Publication

The developmental pathway for human megakaryocytes remains unclear and the definition of pure unipotent megakaryocyte progenitor is still controversial. Using single-cell transcriptome analysis,we have identified a cluster of cells within immature hematopoietic stem and progenitor cell populations that specifically express genes related to the megakaryocyte lineage. We used CD41 as a positive marker to identify these cells within the CD34(+)CD38(+)IL-3Rα(dim)CD45RA(-) common myeloid progenitor (CMP) population. These cells lacked erythroid and granulocyte/macrophage potential,but exhibited robust differentiation into the megakaryocyte lineage at a high frequency,both in vivo and in vitro The efficiency and expansion potential of these cells exceeded those of conventional bipotent megakaryocyte/erythrocyte progenitors. Accordingly,the CD41(+) CMP was defined as a unipotent megakaryocyte progenitor (MegP) that is likely to represent the major pathway for human megakaryopoiesis,independent of canonical megakaryocyte-erythroid lineage bifurcation. In the bone marrow of patients with essential thrombocythemia,the MegP population was significantly expanded in the context of a high burden of Janus kinase 2 mutations. Thus,the prospectively isolatable and functionally homogeneous human MegP will be useful for the elucidation of the mechanisms underlying normal and malignant human hematopoiesis. View Publication

Chimeric oncoproteins resulting from fusion of MLL to a wide variety of partnering proteins cause biologically distinctive and clinically aggressive acute leukemias. However,the mechanism of MLL-mediated leukemic transformation is not fully understood. Dot1,the only known histone H3 lysine 79 (H3K79) methyltransferase,has been shown to interact with multiple MLL fusion partners including AF9,ENL,AF10,and AF17. In this study,we utilize a conditional Dot1l deletion model to investigate the role of Dot1 in hematopoietic progenitor cell immortalization by MLL fusion proteins. Western blot and mass spectrometry show that Dot1-deficient cells are depleted of the global H3K79 methylation mark. We find that loss of Dot1 activity attenuates cell viability and colony formation potential of cells immortalized by MLL oncoproteins but not by the leukemic oncoprotein E2a-Pbx1. Although this effect is most pronounced for MLL-AF9,we find that Dot1 contributes to the viability of cells immortalized by other MLL oncoproteins that are not known to directly recruit Dot1. Cells immortalized by MLL fusions also show increased apoptosis,suggesting the involvement of Dot1 in survival pathways. In summary,our data point to a pivotal requirement for Dot1 in MLL fusion protein-mediated leukemogenesis and implicate Dot1 as a potential therapeutic target. View Publication

Imatinib mesylate (IM) induces clinical remissions in chronic-phase chronic myeloid leukemia (CML) patients but IM resistance remains a problem. We recently identified several features of CML CD34(+) stem/progenitor cells expected to confer resistance to BCR-ABL-targeted therapeutics. From a study of 25 initially chronic-phase patients,we now demonstrate that some,but not all,of these parameters correlate with subsequent clinical response to IM therapy. CD34(+) cells from the 14 IM nonresponders demonstrated greater resistance to IM than the 11 IM responders in colony-forming cell assays in vitro (P textless .001) and direct sequencing of cloned transcripts from CD34(+) cells further revealed a higher incidence of BCR-ABL kinase domain mutations in the IM nonresponders (10%-40% vs 0%-20% in IM responders,P textless .003). In contrast,CD34(+) cells from IM nonresponders and IM responders were not distinguished by differences in BCR-ABL or transporter gene expression. Interestingly,one BCR-ABL mutation (V304D),predicted to destabilize the interaction between p210(BCR-ABL) and IM,was detectable in 14 of 20 patients. T315I mutant CD34(+) cells found before IM treatment in 2 of 20 patients examined were preferentially amplified after IM treatment. Thus,2 properties of pretreatment CML stem/progenitor cells correlate with subsequent response to IM therapy. Prospective assessment of these properties may allow improved patient management. View Publication