Endothelial Cells Promote Expansion of Long-Term Engrafting Marrow Hematopoietic Stem and Progenitor Cells in Primates

Abstract

Successful expansion of bone marrow (BM) hematopoietic stem and progenitor cells (HSPCs) would benefit many HSPC transplantation and gene therapy/editing applications. However, current expansion technologies have been limited by a loss of multipotency and self‐renewal properties ex vivo. We hypothesized that an ex vivo vascular niche would provide prohematopoietic signals to expand HSPCs while maintaining multipotency and self‐renewal. To test this hypothesis, BM autologous CD34+ cells were expanded in endothelial cell (EC) coculture and transplanted in nonhuman primates. CD34+C38− HSPCs cocultured with ECs expanded up to 17‐fold, with a significant increase in hematopoietic colony‐forming activity compared with cells cultured with cytokines alone (colony‐forming unit‐granulocyte‐erythroid‐macrophage‐monocyte; p < .005). BM CD34+ cells that were transduced with green fluorescent protein lentivirus vector and expanded on ECs engrafted long term with multilineage polyclonal reconstitution. Gene marking was observed in granulocytes, lymphocytes, platelets, and erythrocytes. Whole transcriptome analysis indicated that EC coculture altered the expression profile of 75 genes in the BM CD34+ cells without impeding the long‐term engraftment potential. These findings show that an ex vivo vascular niche is an effective platform for expansion of adult BM HSPCs. Stem Cells Translational Medicine 2017;6:864–876

Tissue‐specific endothelial cells: a promising approach for augmentation of soft tissue repair in orthopedics

“…In the original studies, this was shown to occur in a fashion superior to that triggered by human umbilical vein ECs—a classical source of in vitro ECs. Later data showed that clonal expansion of stem cells while maintaining their multipotent phenotype was possible in a BMEC‐rich milieu . The data supported the hypothesis that local microvascular niches of tissues produce optimal complements of soluble factors and signals, in terms of both concentration and temporal expression profile, to stimulate and support local stem cell expansion and differentiation.…”

“…Additionally, so far VVECs have not demonstrated any malignant potential and could be adapted to comply with regulatory clinical guidelines. Thus, these engineered ECs provide an ideal platform for interrogating the angiocrine function of ECs in models of organ regeneration and for translating the proregenerative therapeutic potential of these cells to the clinical setting …”

Blood on the tracks: hematopoietic stem cell-endothelial cell interactions in homing and engraftment

“…E4ORF1 + ECs have been shown to enter a state of replicative senescence and have not demonstrated any malignant potential. A preclinical trial where co-cultured E4ORF1 + EC and HSC were transplanted into irradiated recipients demonstrated enhanced expansion and long-term hematopoietic reconstitution in a nonhuman primate study [105]. This study revealed that E4ORF1 + EC-mediated HSC expansion may be safe and effective in human clinical transplantation and could possibly improve transplant outcomes.…”

Regulation of the hematopoietic stem cell lifecycle by the endothelial niche

“…Maintenance of primary mouse and human ECs without exogenous growth factors or serum allowed us to develop an unbiased EC-HSPC co-culture system, in which the co-culture of mouse HSCs (51) and human umbilical cord blood (UCB) hematopoietic stem and progenitor cells (HSPCs) (117) with ECs resulted in the expansion of bona fide repopulating HSCs which were able to engraft lethally irradiated primary and secondary recipients. This platform’s utility has also been extended to expand engraftable adult BM HSPCs and HSPCs derived from induced pluripotent stem cells (118, 119)*.…”