Thymidine Analogs Are Transferred from Prelabeled Donor to Host Cells in the Central Nervous System After Transplantation: A Word of Caution

Abstract

Thymidine analogs, including bromodeoxyuridine, chlorodeoxyuridine, iododeoxyuridine, and tritiated thymidine, label dividing cells by incorporating into DNA during S phase of cell division and are widely employed to identify cells transplanted into the central nervous system. However, the potential for transfer of thymidine analogs from grafted cells to dividing host cells has not been thoroughly tested. We here demonstrate that graft-derived thymidine analogs can become incorporated into host neural precursors and glia. Large numbers of labeled neurons and glia were found 3-12 weeks after transplantation of thymidine analog-labeled live stem cells, suggesting differentiation of grafted cells. Remarkably, however, similar results were obtained after transplantation of dead cells or labeled fibroblasts. Our findings reveal for the first time that thymidine analog labeling may not be a reliable means of identifying transplanted cells, particularly in highly proliferative environments such as the developing, neurogenic, or injured brain.

Mesenchymal stem cells promote proliferation of endogenous neural stem cells and survival of newborn cells in a rat stroke model

“…However, it is now believed that rapid morphological change to neuron-like cells is due to immediate cytoskeletal rearrangement but not due to the genuine acquisition of neuronal cell fates Neuhuber et al, 2004). In addition, the neuron-like phenotypes of MSCs after transplanted in the brain may be a misinterpretation of the cell-to-cell fusion or reuptake of donor antigen following the ischemic damage (Burns et al, 2006;Coyne et al, 2006 MSCs are known to secrete the many kinds of tropic factors including brain-derived neurotrophic factor (BDNF), VEGF, and nerve growth factor (NGF) (Labouyrie et al, 1999;Kinnaird et al, 2004;Mahmood et al, 2004). Direct infusion of these tropic factors into damaged brain prevents neuronal cell death (Kromer 1987;Hayashi et al, 1998).…”

Radiation-induced brain injury: low-hanging fruit for neuroregeneration

“…57 Interpretation of these data is tricky, since most cells die after transplantation, and BrdU was subsequently found able to be recycled from dead transplanted cells to be taken up by endogenous dividing cells in the area. 10 As such, the apparently poor survival of NSCs in the irradiated hippocampus may have simply reflected the lower rates of endogenous neurogenesis following brain irradiation. 57 Irvine and Blakemore in 2007 grafted early passage neurospheres from an E14 GFP-labeled mouse into the lateral ventricles of mice lesioned with 40 Gy of x-irradiation.…”

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.…”