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Respecifying human iPSC-derived blood cells into highly engraftable hematopoietic stem and progenitor cells with a single factor

ABSTRACT: Purpose: We designed this study to evaluate the feasibility of using only one factor to respecify human induced pluripotent stem cells (iPSCs)-derived blood cells into long-term engraftable hematopoietic stem and progenitor cells (HSPCs). We also parallelly compared iPSC-derived HSPCs (iHSPCs) with primary HSPCs under the same induction and transplantation condition in order to examine the functional equivalency between iHSPCs and bona fide HSPCs. Methods: In vitro derived human iPSC-HSPCs are induced with or without (w/o) doxycycline for the expression of MLL-AF4. In vivo derived bone marrow cells are harvested and FACS-sorted for human populations from primary transplants over nine to sixteen weeks after transplantation. Either iPSC-HSPCs or primary HSPCs, both of which are induced by MLL-AF4, is used for the transplantation experiments. iPSCs are either derived from peripheral blood mobilized CD34+ HSPCs (CD34-iPSC) or mononuclear cells (MN-iPSCs). Normal human CD34+ HSPCs and mononuclear cells are set as control groups. Results: MLL-AF4 can impart HSC and lymphoid potential to iPSC-derived blood cells in vitro, and induction of MLL-AF4 leads to the cellular identity transition from common myeloid progenitors to hematopoietic stem and progenitor cells. MLL-AF4 alone is sufficient to realize the potent engraftment of induced HSPCs (iHSPCs) from iPSCs, and multilineage and long-term hematopoiesis could be observed. Primary HSPCs with the induction of MLL-AF4 could gain significantly enhanced engraftability. During the long-term engraftment period, leukemic mutations with a bias to B-cell leukemia could be found in the iHSPCs and their derivatives. By contrast, MLL-AF4 induced primary HSPCs maintain the normal hematopoiesis without leukemic transformation. Conclusions: Our study has demonstrated for the first time, to our knowledge, that the pluripotency-dependent conversion of somatic cells to long-term engraftable HSPCs can be achieved by using a single factor in a non-integrative way. This study also suggests that iPSC-derived HSPCs are more prone to leukemic mutations during the long-term engraftment period, which provides a necessary caveat of using them in the actual therapies.

ORGANISM(S): Homo sapiens

PROVIDER: GSE103420 | GEO | 2018/01/31

REPOSITORIES: GEO

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Project description:The MLL-AF4 fusion gene is a hallmark genomic aberration in high-risk acute lymphoblastic leukemia in infants. Although it is well-established that MLL-AF4 arises pre-natally during human development, its effects on hematopoietic development in utero remains unexplored. We have created a human-specific in vitro system to study early hemato-endothelial development in MLL-AF4-expressing human embryonic stem cells (hESCs). Differentiation and functional studies as well as clonal analyses and gene expression profiling reveal that expression of MLL-AF4 in hESCs has a phenotypic, functional and gene expression impact. It enhances the specification of hemogenic precursors from hESCs and impairs further hematopoietic commitment of these precursors in favour of the endothelial cell fate. Similar to that reported in cord blood CD34+ hematopoietic stem/progenitor cells (HSPCs), MLL-AF4 expression is not sufficient to transform hESC-derived hematopoietic cells in vitro or in vivo, indicating that additional events may be required to initiate leukemogenesis or that embryonic hematopoiesis is not the appropriate human cellular target for MLL-AF4-mediated leukemogenesis. This work illustrates how hESCs can provide unique insights into human development and further our understanding of how leukemic fusion genes known to arise pre-natally regulate human embryonic hematopoietic specification. MLL is involved in transcriptional regulation and most MLL translocations appear to result in increased expression of Hox genes and hematopoietic genes. We therefore assessed the impact of MLL-AF4 expression on the transcriptome of hESCs. Gene expression profiling performed in MLL-AF4 hESCs revealed that MLL-AF4 preferentially activates transcription. 1826 out of the 3001 genes (61%) expressed were up-regulated in MLL-AF4 hESCs. Human ESC samples were collected during the exponential cell growth phase and stabilized in RNA later. 500 ng of each total RNA sample was labelled with Cy3 using the Quick-Amp Labelling kit and hybridized with the Gene Expression Hybridization kit to a Whole Human Genome Oligo Microarray (Agilent Technologies) following the Manufacturer’s instructions. Each cell line was analyzed as independent duplicates. NEO-expressing (empty lentivector) hESC line was used as the baseline.

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Respecifying human iPSC-derived blood cells into highly engraftable hematopoietic stem and progenitor cells with a single factor

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