Milieu-adopted in vitro and in vivo differentiation of mesenchymal tissues derived from different adult human CD34-negative progenitor cell clones

Adult mesenchymal stem cells with multilineage differentiation
potentially exist in the bone marrow, but have also been isolated
from the peripheral blood. The differentiation of stem cells after
leaving their niches depends predominately on the local milieu and
its new microenvironment, and is facilitated by soluble factors but
also by the close cell-cell interaction in a three-dimensional
tissue or organ system. We have isolated CD34-negative, mesenchymal
stem cell lines from human bone marrow and peripheral blood and
generated monoclonal cell populations after immortalization with
the SV40 large T-antigen. The cultivation of those adult stem cell
clones in an especially designed in vitro environment, including
self-constructed glass capillaries with defined growth conditions,
leads to the spontaneous establishment of pleomorphic
three-dimensional cell aggregates ( spheroids) from the monoclonal
cell population, which consist of cells with an osteoblast
phenotype and areas of mineralization along with well-vascularized
tissue areas. Modifications of the culture conditions favored areas
of bone-like calcifications. After the transplantation of the at
least partly mineralized human spheroids into different murine soft
tissue sites but also a dorsal skinfold chamber, no further bone
formation could be observed, but angiogenesis and neovessel
formation prevailed instead, enabling the transplanted cells and
cell aggregates to survive. This study provides evidence that even
monoclonal adult human CD34-negative stem cells from the bone
marrow as well as peripheral blood can potentially differentiate
into different mesenchymal tissues depending on the local milieu
and responding to the needs within the microenvironment. Copyright
(C) 2005 S. Karger AG, Basel.