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A strategy that expands the resident stem cell pool in the donor BM can help to achieve an improved hematopoietic recovery post transplant. Therefore, we examined whether simvastatin positively regulates steady-state hematopoiesis as well, by treating donor mice with simvastatin for four weeks ( Figure 3A ). Quantification of HSC subsets showed that simvastatin significantly boosted the number of LSK-HSCs, SLAM-LSK-HSCs and LSK-CD34 − (LT-HSCs) in the BM of simvastatin-treated donors ( Figure 3B–E ), without affecting marrow cellularity or hemogram (Online Supplementary Figure S3A–C). Comparable numbers of various progenitors present in the BM of control and simvastatin-treated mice showed that the increased HSC numbers were not related to a block in differentiation (Online Supplementary Figure S3D and E). Cell-cycle analysis of BM cells did not reveal any difference in the cell-cycle status of HSCs, suggesting that HSC expansion in the simvastatin-treated donors were not due to their excessive proliferation (Online Supplementary Figure S3F). CFU assays revealed that marrow cells of simvastatin-treated donors contained a significantly higher number of functional progenitors ( Figures 3F ). Competitive transplants were then performed to assess their engraftment ability. Short-term (4 weeks) ( Figure 3G and Online Supplementary Figure S3G) and long-term (16 weeks) ( Figure 3H ) analyses of donor cells in the recipients’ PB showed that BM cells from simvastatin-treated donors established a significantly higher level of chimerism at both time points and gave rise to a multi-lineage hematopoiesis without introducing any lineage bias ( Figure 3G and H , right panels). Collectively, these results show that simvastatin treatment of non-irradiated mice expands the pool of functionally superior HSCs without inducing any undue myeloproliferation. Immuno-phenotypic analyses of BM cells revealed that simvastatin-treated donors harbored a significantly higher number of osteoblasts and EPCs in their BM ( Figure 3I ). Other niche cells ( Figure 3I ) and CFU-F (Online Supplementary Figure S3H) were not affected by the simvastatin treatment. Commensurate with these data, CD45 − stromal cells sort-purified from simvastatin-treated donors showed significantly increased expression of Sdf-1α, Vegf-A, Ang-1 and Runx-2 mRNA ( Figure 3J ). The increase in Jagged-1-specifc mRNA was only marginal. A small increase in Ppar-γ-specific mRNA by simvastatin suggested that it did not interfere with natural mechanisms involved in the BM adipogenesis ( Figure 3J ). Collectively, these data demonstrate that, under steady-state conditions, simvastatin treatment expands the HSC pool through modulation of the BM niche. Co-infusion of EPCs with HSCs enhances donor cell engraftment. 12 Therefore, in addition to treating transplant recipients, treatment of donors with simvastatin may further enhance engraftment levels due to the presence of higher numbers of HSCs and EPCs in the graft.
Collectively, these data demonstrate that simvastatin treatment of the SCT recipients significantly improved engraftment and expansion of the donor stem cells, and these expanded HSCs showed long-term functionality.
Due to their localization, perivascular cells have been early “hot” candidates for being necessary to maintain HSC homeostasis. Within this population, the best studied cell types are the mesenchymal stromal cells and the C-X-C-motif-chemokine ligand-12 (CXCL-12) abundant reticular cells (CAR), although the latter have been proposed to be a subpopulation of MSCs. 40 The cells are responsible for the retention in the bone marrow, 42,45 the direct supply of soluble and non-soluble factors, 42,44 their capacity to differentiate into other niche cell types such as osteoblasts, adipocytes and chondrocytes, 44-46 as well as the maintenance of HSC quiescence. 47 Some of the functions have been associated to markers such as CD146, 48 CXCL-12, SCF, 43,45,46 platelet derived growth factor receptor (PDGFR)-α and –β 44,49 and Sca-1, 50 stem cell factor (SCF), 43 and CD51. 51,30 Meanwhile, it seems to be clear that mesenchymal stromal cells are the key players among the non-hematopoietic cells in the niche.
The 2016 wave of the Health System Characteristics Survey has been designed following three guiding principles:
- Reduce the data collection burden on countries;
- Facilitate the data collection process and exchange with countries; and
- Shorten the delay to publish collected data
The 2018 data collection, following the same principles, has been made in cooperation with the InterAmerican Development Bank.
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To examine whether the output CD34 + progenitors are functional, we subjected these cells to in vitro functional assays (CFU and LTC-IC). This showed that the 3D-HSCs indeed contained a significantly high number of CFU and LTC-IC units in them (Online Supplementary Figure 1J and K ) confirming that the 3D-cultures contain a significantly high number of functional primitive progenitors.
The authors would like to thank Drs. Shirish Yande, RL Marathe, Prakash Daithankar and Dilip Ghaisas for clinical samples. We would also like to thank Ashwini Atre for image acquisition on confocal microscope, and Hemangini, Pratibha and Swapnil for sample acquisition on flow cytometers. The authors wish to thank the anonymous reviewers for their critical review of the manuscript.