Distribution and Differentiation of Donor-Derived Bone Marrow Stem Cells in Various Areas of the Human Brain.
Authors: Wang Rui-Yu , Fuller Gregory N. , McQueen Teresa , Shi Yue-Xi , Champlin Richard E. , Andreeff Michael 
Published: April 2020

Abstract
Hematopoietic stem cells (HSCs) resident in the bone marrow or in circulation, have shown the capacity of transdifferentiation into mature neuronal lineages in the brain (Joanna E et al, Stem Cells 2004, 22:487–500 and Cogle et al, The Lancet, 2004, 363:1432–1437). To determine whether this phenomenon occurs at different frequencies in different regions of the brain, immunohistochemical staining with anti-neuron antibody (brown nuclear localization) and anti-CD45 antibody (leukocyte marker, red cytoplasm localization) combined with fluorescence in situ hybridization (FISH) (chromosome X and Y), were performed on autopsy samples from different regions of the brain of two leukemia patients who had undergone sex-mismatched bone marrow transplantation to identify donor-derived neuron and donor leukocytes. The regions of human brain analyzed included midbrain, cerebellum, hippocampus, olfactory bulbs, medulla, pons, and parietal cortex. The distribution of donor-derived leukocytes and donor-derived transdifferentiated neuron in various regions of the bone marrow transplanted recipient’s brain was analyzed in two cases. Approximately 16,500–45,720 cells (average 32,300 cells) on each tissue section were analyzed. For the deep hypercellular granular layer and molecular layer of cerebellum about 343,000 cells were analyzed. An increased percentage of donor leukocytes was found in the hippocampus in both cases (0.8% in case 1 and 1.4% in case 2). In case 1, an increased percentage of donor leukocytes were also found in the pons (0.9%) and olfactory bulbs (1.2%). Transdifferentiation of donor-derived bone marrow stem cells was determined by enumeration of donor-derived mature neuronal cells as percentage in total chromosome XY - positive cells in each region of the brain. The frequency of donor-derived neurons was between 0.6% to 1.7% in cerebellum (0.6% in case 1 and 0.7% in case 2), medulla (1.6% in case 1 and 1.0% in case 2), hippocampus (0.7% in case 1 and 0.6% in case 2), and olfactory bulbs (0.8% in case 1). We did not find donor-derived transdifferentiated neuronal cells in the medulla, pons and parietal cortex in both cases. To determine whether CD34+ cells or mesenchymal stem cells (MSC) have higher potential to differentiation into mature neurons, CD34+ cells and MSC were cultured in transwells with mouse brain extract, respectively. The expression level of neuron specific gene was analyzed after 4 days using western blotting. The levels in CD34+ cells were 1.14-fold higher than in MSC. No neuron specific gene expression was found in CD34+ cells and MSC. These results suggested that 1) the different frequencies of donor leukocytes in regions indicate that the engraftment of circulated donor cells is different in different regions of the brain. 2) Donor-derived mature neurons were found in regions of the midbrain, cerebellum, hippocampus and olfactory bulbs. No donor-derived neurons were found in medulla, pons, and parietal cortex in the two cases analyzed. 3) CD34+ cells have higher potential to differentiation into neurons than MSC.