In Vivo Transfer of Intracellular Labels from Locally Implanted Bone Marrow Stromal Cells to Resident Tissue Macrophages

Abstract

Intracellular labels such as dextran coated superparamagnetic iron oxide nanoparticles (SPION), bromodeoxyuridine (BrdU) or green fluorescent protein (GFP) are frequently used to study the fate of transplanted cells by in vivo magnetic resonance imaging or fluorescent microscopy. Bystander uptake of labeled cells by resident tissue macrophages (TM) can confound the interpretation of the presence of intracellular labels especially during direct implantation of cells, which can result in more than 70% cell death. In this study we determined the percentages of TM that took up SPION, BrdU or GFP from labeled bone marrow stromal cells (BMSCs) that were placed into areas of angiogenesis and inflammation in a mouse model known as Matrigel™ plaque perfusion assay. Cells recovered from digested plaques at various time points were analyzed by fluorescence microscopy and flow cytometry. The analysis of harvested plaques revealed 5% of BrdU+, 5–10% of GFP+ and 5–15% of dextran+ macrophages. The transfer of the label was not dependent on cell dose or viability. Collectively, this study suggests that care should be taken to validate donor origin of cells using an independent marker by histology and to assess transplanted cells for TM markers prior to drawing conclusions about the in vivo behavior of transplanted cells.

In vivo MR detection of fluorine-labeled human MSC using the bSSFP sequence

“…Several studies have pointed out that the signal loss produced by iron-labeled cells can greatly overestimate the presence of the viable transplanted cell population. 29,[42][43][44] The signal void caused by the presence of iron-labeled cells is similar to hypointense signal produced by bone, air, and hemorrhage. This is a major hurdle to the use of MRI to reliably identify iron-labeled cells after their transplantation.…”

“…19 F-labeled cells. This discrepancy is likely related to the fact that bystander cells can be labeled secondarily through the release of labels from dead stem cells; 42 although the bystander cells will contain much lower amounts of the label. Because of the large differences in sensitivity of iron or fluorine signal, iron-labeled bystander cells will still produce signal loss, whereas 19 F-labeled bystander cells may be undetectable.…”

Transplantation of umbilical cord–derived mesenchymal stem cells as a novel strategy to protect the central nervous system: technical aspects, preclinical studies, and clinical perspectives

“…Bromodeoxyuridine, bis-benzimide, and GFP are often used to track transplanted cells in vivo. However, the in vivo transfer of such intracellular labels from locally implanted MSCs to resident macrophages and even neurons and astrocytes has already been demonstrated (89)(90)(91). Therefore, different techniques should be used to validate the donor origin of labeled cells; in particular, the use of an independent histological marker is advised.…”

Pre- and postmortem imaging of transplanted cells

“…The acquisition of PKH and CM-DiI dyes by neighboring cells, mostly tissue macrophages, has been shown, particularly if the labeled cells were dead. 153,154 Although, even if there are no dead cells among the transplanted cell population, the noncovalently bound DiI can dissociate from labeled donor cells and get picked up by the host cells. 155 …”