Abstract
Transplantation of exogenous cells into the injured central nervous system and subsequent examination of how these cells survive, integrate and perform physiological functions within the host environment requires that the cells be clearly identifiable from host cells. As many of the cells used for transplantation studies are derived from cultures of cells indistinguishable from the host using immunochemical approaches, numerous dyes or genetic markers have been devised and used for this purpose. These markers used to label and track these transplanted cells need to be specific, reliable, resistant to leakage or cellular transfer, and remain chemically stable once inside the host to allow long-term tracking. In the current study we compared two labeling methods for long-term tracking of cells following transplantation into the injured rat spinal cord; lentiviral vector transduction with green fluorescent protein (GFP) and DNA in situ hybridization for the Y chromosome after male cell transplantation in female rats. Examination of labeled cells at 12 wk post-injury demonstrated that both labels did not exhibit significant fading or loss of the signal due to instability over time. The visualization procedure for the DNA in situ reaction product was significantly more labor intensive than simple identification of GFP by fluorescent microscopy. Y chromosome positive cells were, however, easier to definitely count for assessment of cell survival than GFP labeled cells, due to the presence of the label as a single point within the nucleus rather than diffuse labeling throughout the entirety of the cell. The limited presence of the signal in Y chromosome positive cells though, made examination of their ability to integrate within the injured spinal cord, migrate and associate with axons impossible without additional immunochemical methods for labeling the entire cell. The combination of immunochemistry with DNA in situ however proved to be unsuccessful with the many antibody combinations tested. In conclusion GFP delivery by lentiviral vectors was far superior to DNA in situ detection of the Y chromosome for labeling of transplanted cells due to its rapid visualization and its applicability to a wide range of assessment techniques.