blood cells. When bone marrow stem cells (MSCs) are transplanted
in animals depleted of red and white cells, there is
complete reconstitution of the hematopoietic and lymphocytic
system.2 Further study of bone marrow cells identified another
population of stem cells known as mesenchymal or MSCs.
MSCs have been shown in vitro to differentiate in mesenchymal
tissues such as muscle, bone, cartilage, adipose, and
stroma.3–5 In vitro MSC isolation studies have shown that these
cells are a rare population of cells in the bone marrow, accounting
for about 0.001% to 0.01% of nucleated cells and 10-fold
less abundant than HSCs.6