Humanization of the bone marrow vascular niche to study hematopoietic stem cell and vascular interactionsand function

About This Grant

Hematopoietic stem cells (HSCs) are characterized by their capacity for self-renewal and the generation of all mature hematopoietic cell types within the blood and immune system. The primary objective of this research proposal is to develop novel resources that can provide a cure for a greater number of patients with lifethreatening disorders of the hematopoietic system than is currently feasible. Our goal is to enhance the availability of suitable donors for HSC transplantation (HSCT) and establish novel approaches that minimize the duration of cytopenias, the leading cause of treatment-related mortality. To address this challenge, the current research plan aims to build upon our recent discoveries that the vascular niche provides the instructional cues that enable large-scale expansion of HSCs while preserving their self-renewal capabilities. Utilizing our technologies to isolate and cultivate human primary endothelial cells (ECs), we have established young and aged bone marrow EC (BMEC) primary lines. Our preliminary data indicates that aged BMECs exhibit significantly elevated thrombospondin-1 (THBS1) and co-culture of HSCs with aged BMECs resulted in ex vivo expanded HSCs exhibiting a substantial reduction in long-term engraftment and a myeloid bias. Genetic deletion of Thbs1 or supplementation with a Thbs1 neutralizing antibody restored ex vivo expansion and function comparable to young blood products. Based on these findings, this proposal will determine whether neutralization of Thbs1 can support the function of human blood products and initiate the identification of novel angiocrine factors from a humanized in vivo BM vascular niche that support human HSC and vascular function. To this end, we will employ gold-standard assays to evaluate HSC and vascular function, as well as a novel method to humanize the murine BM vascular niche to investigate whether suppressing Thbs1 can 1) refine current ex vivo human HSC expansion protocols to enhance the quality and quantity of transplantable blood products, 2) develop novel protocols to preserve systemic vascular integrity following myelosuppressive insult, 3) enhance HSC engraftment, and 4) identify novel factors that may serve as potential therapeutic agents to improve hematopoietic and vascular function. The proposed experiments represent a sequential progression of preclinical research, ultimately aiming to investigate the transplantation of expanded long-term repopulating HSCs in patients who may benefit from allogeneic and autologous HSCTs. Successful HSC expansion and improved engraftment will ultimately expand access to HSCT for patients requiring curative HSC replacement. Accomplishing these objectives will ultimately benefit older patients who lack suitable human leukocyte antigen (HLA)-matched sibling or adult unrelated volunteer donors for HSCT, and patients requiring engineered, engraftable HSCs for the correction of genetic disorders, for whom the number of available autologous HSCs is suboptimal.