Project description:Haematopoietic stem cells (HSCs) reside in bone marrow (BM) niches where they are maintained to replenish all blood cell lineages throughout life. Among the constituents of the murine HSC niches, various cell types such as CXCL12-abundant reticular (CAR) cells, Nestin-GFP+ perivascular cells, leptin receptor (LepR)+ cells, endothelial cells, osteoblasts, sympathetic nerves, macrophages and megakaryocytes in the BM have been proposed to contribute to HSC niche activity. When niche cells are removed from their natural habitat, the ability to maintain HSCs ex vivo is markedly diminished. Mesenchymal-derived stromal cells (MSCs) identified by Nestin-GFP express high levels of niche factors in vivo, but their expression is downregulated rapidly upon culture, suggesting that alterations in transcriptional rewiring may contribute to the reduced HSC maintenance potential. We found that the enforced expression of 5 genes (Klf7, Ostf1, Xbp1, Irf3 and Irf7) markedly restored HSC niche function in cultured BM-derived MSCs. These revitalized MSCs (rMSCs) exhibited boosted synthesis of HSC niche factors while retaining their mesenchymal lineage differentiation capacity. By contrast to HSCs co-cultured with control MSCs, HSCs expanded with rMSCs showed significantly higher repopulation capacity. To evaluate to what extent rMSCs are reprogrammed toward freshly isolated MSCs, we compared, by RNA-seq analysis, the transcriptome of freshly sorted CD45(-) Ter119(-) CD31(-) Scf-GFP(-) cells, CD45(-) Ter119(-) CD31(-) Scf-GFP(+) cells, rMSCs and control vector-transduced stroma. HSC niche-associated genes were highly expressed in both native Scf-GFP(+) stromal cells and rMSCs compared to the Scf-GFP cell fraction and control MSCs. With the motif analysis of ATAC-seq data, we found that myocyte enhancer factor 2c (Mef2c) is one of the key factor in the revitalization of MSCs. These results suggest that rMSC may provide a promising platform for curative transplantation therapies.

Project description:The occurrence of clonal perturbations and leukemia in patients transplanted with retrovirally-transduced autologous hematopoietic stem and progenitor cells (HSPCs) has stimulated extensive investigation, demonstrating that proviral insertions perturb adjacent proto-oncogene expression. Although enhancer-deleted lentiviruses are less likely to result in insertional oncogenesis, there is evidence that they may perturb transcript splicing, and one patient with a benign clonal expansion of lentivirally-transduced HPSC has been reported. The rhesus macaque model provides an opportunity for informative long-term analysis to ask whether transduction impacts on long-term HSPC properties. We utilized two techniques to examine whether lentivirally-transduced HSPCs from eight rhesus macaques transplanted 1-13.5 years previously are perturbed at a population level, comparing telomere length as a measure of replicative history and gene expression profile of vector positive versus vector negative cells. There were no differences in telomere lengths between sorted GFP+ and GFP- blood cells, suggesting that lentiviral transduction did not globally disrupt replicative patterns. Bone marrow GFP+ and GFP- CD34+ cells showed no differences in gene expression using unsupervised and principal component analysis. These studies did not uncover any global long-term perturbation of proliferation, differentiation, or other important functional parameters of transduced HSPCs in the rhesus macaque model. CD34+ hematopoietic stem and progenitor cells were purified from bone marrow aspirates obtained from 4 rhesus macaques 3-9 years following transplantation with lentivirally-transduced autologous hematopoietic stem and progenitor cells. All lentiviral vectors contained the GFP marker gene. The CD34+ cells from each animal were sorted via flow cytometry into GFP+ and GFP- fractions, and RNA from these cells was used for Affymetrix gene expression analysis as detailed below. There were two samples, GFP+ and GFP-, from each of 4 animals.

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Characterization of transcriptomic changes induced by a gene therapy cell culture protocol to single human bone marrow and mobilized peripheral blood hematopoietic stem and progenitor cells [BM_MPB]

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