Low Frequency of Donor-Derived Neuronal, Glia, and Endothelial Cells in the Cerebellum of Patients Undergoing Sex-Mismatched Bone Marrow Transplantation.

Bone marrow-derived hematopoietic stem cells have shown plasticity in nonhematopoietic organs. To date, no consensus exists about the ability of bone marrow-derived stem cells to differentiate into mature neurons and epithelial cells in the brain. Whereas some groups have reported high numbers of epithelial cells of donor origin others have found little or no evidence of transdifferentiation in organs including the brain. These discrepancies result partly from technical difficulties in cell analysis. In this study, triple staining - immunohistochemistry double staining plus fluorescence in situ hybridization (FISH) - was performed on cerebellum autopsy samples from patients with leukemia who had undergone sex-mismatched bone marrow transplantation to determine whether donor-derived hematopoietic stem cells have the potential to differentiate into mature neurons in the recipient’s cerebellum. Thirty thousand to 50,000 neurons, 5,000 to 14,000 glia cells and 7,000 to 10,000 endothelial cells were analyzed for each assay. Tissue sections were treated with different combinations of cell type-specific antibodies, including anti-NeuN/anti-CD45, or anti-GFAP/anti-CD45, or anti-CD31/anti-CD45, in conjunction with FISH analysis of X and Y chromosomes. Donor-derived transdifferentiated cells and donor hematopoietic cells were clearly observed on the same slides. The phenotype of donor-derived transdifferentiated neurons are cells with X⁺Y⁺ chromosome, NeuN⁺ and CD45^- (donor-neuron, see table), the phenotype of a donor-derived transdifferentiated glia is X⁺Y⁺, GFAP⁺ and CD45⁻ (donor-glia), and the phenotype of donor-derived transdifferentiated endothelial cell is X⁺Y⁺, CD31⁺ and CD45⁻ (donor-EC). Four cases were studied including case #4 which had brain injury due to aspergillus and pseudomonas infection. Results are shown in the table. Donor-derived neural, glia, and endothelial cells could be detected at a frequency between one in 1,600 to one in 50,000 cells. The higher frequency of transdifferentiated cells observed in case #4 may be related to brain injury due to aspergillus and pseudomonas infection. Bone marrow from a 31-year old donor (case #1) generated all three types of transdifferentiated cells, while marrow from a 50-year old donor (case #3) did not show any transdifferentiation. While very preliminary, results may suggest the possibility of donor-age related ability to transdifferentiate. This hypothesis requires further investigation. This study provides evidence that donor bone marrow cells can enter the recipient cerebellum and generate donor-derived neurons, glia, and endothelial cells, but the frequency of this event is very low. Brain injury and donor age may influence the frequency of these cells.