Transplanted bone marrow generates new neurons in human brains

Abstract

Adult bone marrow stem cells seem to differentiate into muscle, skin, liver, lung, and neuronal cells in rodents and have been shown to regenerate myocardium, hepatocytes, and skin and gastrointestinal epithelium in humans. Because we have demonstrated previously that transplanted bone marrow cells can enter the brain of mice and differentiate into neurons there, we decided to examine postmortem brain samples from females who had received bone marrow transplants from male donors. The underlying diseases of the patients were lymphocytic leukemia and genetic deficiency of the immune system, and they survived between 1 and 9 months after transplant. We used a combination of immunocytochemistry (utilizing neuron-specific antibodies) and fluorescent in situ hybridization histochemistry to search for Y chromosome-positive cells. In all four patients studied we found cells containing Y chromosomes in several brain regions. Most of them were nonneuronal (endothelial cells and cells in the white matter), but neurons were certainly labeled, especially in the hippocampus and cerebral cortex. The youngest patient (2 years old), who also lived the longest time after transplantation, had the greatest number of donor-derived neurons (7 in 10,000). The distribution of the labeled cells was not homogeneous. There were clusters of Y-positive cells, suggesting that single progenitor cells underwent clonal expansion and differentiation. We conclude that adult human bone marrow cells can enter the brain and generate neurons just as rodent cells do. Perhaps this phenomenon could be exploited to prevent the development or progression of neurodegenerative diseases or to repair tissue damaged by infarction or trauma.

Figures

Figure 1

(A) A 6-μm-thin section from somatosensory cortex of patient 2 demonstrates the presence of the Y chromosome depicted as red dots and viewed through a rhodamine filter. The same field as in A is shown when viewed through the FITC filter to demonstrate the immunostaining for the neuronal marker NeuN in green (B), and the UV filter shows all cell nuclei in blue after staining with 4′,6-diamidino-2-phenylindole, a chromosomal stain (C). (D) The overlay of the three filters, where arrows point to cells that carry all markers, indicating that they derived from the donor bone marrow (Y chromosome-positive) and bear the specific neuronal marker NeuN. Arrowheads point at nonneuronal donor-derived cells. (Scale bars, 10 μm.)

Figure 2

Neuronal markers colocalized with the Y chromosome. Fluorescent microscopic images of neocortex from patients 2 (A–C) and 1 (E) and hippocampus from patients 1 (D) and 3 (F) are shown. The green color represents the immunostaining for neuronal markers Kv2.1 (A–D) and NeuN (E and F), and the Y chromosome is represented by the red fluorescent dots. All cell nuclei are stained with 4′,6-diamidino-2-phenylindole, a chromosomal marker that shows up as blue fluorescence. All images are overlays of the images seen through the three separate filters to show all colors. Arrows point to cells that are labeled with neuronal markers and are also Y chromosome-positive. In the Kv2.1 immunostaining the initial axons of some neurons can also be visualized. (Scale bars, 10 μm.)

Figure 3

Two confocal z series are shown. (A–D) Optical sections (1-μm-thin) of a neocortical neuron from patient 2. (E–F) Optical 1-μm-thin slices of a hippocampal granule cell from patient 1. Both cells are immunostained with the neuronal marker Kv2.1 (green); the Y chromosome is red (CY3-plus), and the nucleus is blue (4′,6-diamidino-2-phenylindole). The arrowheads point to the double-labeled cells. Note that the cell nucleus and the Y chromosome are consistently in the same plane.