Heike Daldrup-Link, Associate Professor at Stanford University School of Medicine, explains that mesenchymal stem cells (MSCs) derived from bone marrow have remarkable potential in cell-based therapy and tissue regeneration.
Transplanted MSCs can help repair damaged joints by promoting generation of bone, cartilage and connective tissue. However, Dr. Daldrup-Link explained that when stem cells are transplanted, they may die and disappear from the transplant site, or fail to differentiate into cartilage.
Consequently, it is necessary to track the stem cells in order to confirm that the transplant has been successful.
In present labeling techniques, stem cells are removed from a donor and cultured with iron oxide solution. The cells labeled with iron oxide are then transplanted into the recipient patient. However, this ex-vivo labeling technique introduces the possibility of contamination of the stem cells between harvest and transplantation.
Ideally, orthopedic surgeons would like stem cells that have been labeled without the need for additional handling before transplantation.
It was proposed that stem cells could be effectively labeled using in vivo by giving an iron supplement to the donor patient intravenously prior to harvesting. Iron oxide, which can be tracked using magnetic resonance imaging (MRI), would be taken up by the donor cells, including the bone marrow stem cells due to be transplanted.
In vivo cell labeling has been successfully performed in rats by researchers at Stanford University School of Medicine. The rats were injected with ferumoxytol, an iron supplement approved for human use, 48 hours before extracting stem cells from bone marrow. The uptake of iron by stem cells was found to be greater after administration of in vivo ferumoxytol than after the conventional ex vivo-labeling technique.
The labeled stem cells were transplanted into knee cartilage defects of seven rats and tracked with MRI for up to a month (Figure 1, Figure 2). Microscopic examination revealed the presence of iron in the labeled stem cells and proved that repair was ongoing in the damaged joints. Thus, in addition to eliminating the risk of contamination from ex vivo labeling procedures, this in vivo labeling also offers instant feedback on the transplanted cells.
Traditional labelling approaches used to assess whether a stem cell graft has been successful necessitates extensive follow up and imaging studies, which can take weeks or even months to complete, yet the stem cells may have died soon after transplantation. In contrast, the in vivo technique allows the cells to be viewed more quickly so it is soon known if the cells have multiplied too much or if they have disappeared from the transplant site.