BACKGROUND: A major technical limitation in preclinical cell replacement 
research is the ability to discriminate between donor and host tissue after 
transplantation. This problem has been lessened by the availability of 
transgenic animals that express "reporter" genes, such as green fluorescent 
protein (GFP).
OBJECTIVE: We determined the usefulness of one such transgenic reporter rat to 
assess the survival of bone marrow-derived rat mesenchymal stem cells (MSCs) 
following direct transplantation into the intact adult brain. We also sought to 
determine if the expression of GFP in the brain affected the survival of the 
MSCs or the host's neuroimmune response to the cells.
METHODS: Rats received intrastriatal injections of sterile transplantation 
medium, 100 000 normal MSCs, or 100 000 GFP-MSCs and were killed humanely 1, 4, 
7, 28, and 42 days posttransplantation for astrocyte and microglial 
immunohistochemical staining.
RESULTS: GFP-MSCs were evident at each examination, although their survival 
declined over time. Graft volume estimates comparing normal and GFP-MSCs 
revealed that GFP expression did not adversely affect the survival of the stem 
cells in the brain. Furthermore, immunostaining for astrocytes and microglia 
revealed that expression of the reporter protein did not affect the 
immunogenicity of the stem cells.
CONCLUSIONS: These data indicate the usefulness of GFP for investigating the 
survival of MSCs following transplantation to the brain. However, the mechanisms 
responsible for the poor survival of the stem cells must be elucidated if these 
cells are to serve cell-based therapies for neurodegenerative disorders.