HEMHOME

Defining regulators of hematopoietic stem cell homing and engraftment

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 Obiettivo del progetto (Objective)

'Transplantation of hematopoietic stem cells (HSC) is a life-saving treatment for many serious diseases. Unfortunately, the procedure is often hampered by insufficient numbers of donor stem cells and attempts to expand HSCs ex vivo prior to transplantation have remained unsuccessful. An important alternative, which significantly would reduce the required number of donor cells, is to enhance the engraftment efficiency of the transplanted HSCs. The aim of this project is to identify factors that regulate homing and adhesion of HSCs using an RNA interference based screening approach. The principle of the approach is to use lentiviral short-hairpin RNA (shRNA) libraries targeted to HSCs to screen for modifiers of cell adhesion. Adhesive interactions with extracellular matrix and surrounding cells, the so-called niche, are essential for HSC biology. Mesenchymal stroma cells (MSCs) will be used as a model for the adhesive interactions in the hematopoietic niche. When seeded on a layer of MSCs, the vast majority of human HSCs remain adherent to the MSCs. These highly adhesive properties of HSCs constitute a baseline for functional selection of shRNAs interfering with adhesion. Large numbers of HSCs will be targeted with pooled shRNA libraries and candidate shRNAs will be retrieved by functional selection of cells with reduced adhesive properties. The method has been standardized using shRNAs targeting the known mediator of cell adhesion, CD29 (β1 integrin). Knock down of CD29 in HSCs dramatically decreased their adhesion to MSCs. Candidate genes from the screens will be characterized for their role in homing and engraftment of HSCs by assays in vitro as well as in vivo through the ability to repopulate bone marrow of immundeficient NOD/SCID mice. Understanding the basic mechanisms that regulate homing and adhesion of HSCs to their niche is essential in order to develop strategies that may enhance the engraftment process in clinical settings.'

Introduzione (Teaser)

Bone marrow transplantation (BMT) is a procedure used for the treatment of blood and bone cancer. EU researchers have investigated how to make the procedure more efficient.

Descrizione progetto (Article)

A significant number of patients who would benefit from BMT or haematopoietic stem cell transplantation (HSCT) cannot receive treatment. Insufficient donor stem cells hampers the procedure. One excellent way to get over this problem is to enhance the engraftment efficiency. Engraftment is when new blood-forming cells start to grow and make healthy blood stem cells.

The 'Defining regulators of hematopoietic stem cell homing and engraftment' (HEMHOME) project has identified new molecules that mediate homing and adhesion of haematopoietic stem and progenitor cells (HSPCs) to their niche in the bone marrow. The microenvironment which interacts with stem cells to regulate cell fate is termed the stem cell niche.

The researchers successfully developed a short hairpin RNA-based screen to isolate possible candidate mediating molecules. Demonstrating feasibility of the approach, the screens detected known regulators of HSPC adhesion.

One promising molecule not previously investigated is cytohesin1 (CYTH1). Successful validation of CYTH1 in HSPC-niche interactions could mean it would be an ideal candidate to modulate the engraftment process in the clinic.

Using interference reflection microscopy in collaboration with the Immunology department in Lund University, the team has investigated exactly how CYTH1 alters the adhesive properties of HSPCs. Highly involved with cell-cell interaction, homing and colonisation, the scientists have looked at CYTH1-integrin activation status. Time-lapse microscopy can analyse movement of HSPCs with CYTH1 using random or shear stress.

Under the umbrella of regenerative medicine, stem cell therapy promises to be a critical element in health care of the future. The HEMHOME project has identified and validated a molecule that could be developed for clinical use in BMT.