Biomedical Engineering Reference
In-Depth Information
several specific phenotypes, thus suggesting their totipotency which has been
defined as the ability of a cell to form both the embryo and extra-embryonic
membranes and tissues. therefore, pluripotent stem cells, which are able to
transform into cells from all three germ lineages, seem to be the most ideal
candidates for cell therapy-based bone repair. However, since the embryonic
source of pluripotent stem cells for potential therapeutic purposes remains
controversial, researchers have been focussing on the isolation of stem cells
from adult tissues (Ratajczak
et al
., 2008).
Connective tissue progenitors are those heterogeneous populations of
stem and progenitor cells that are found in native tissue and that are capable
of differentiating into one or more connective tissue phenotypes. these
mesenchymal stem or progenitor cells are found in various tissues and show
varying ability to differentiate into specific cell lineages. Indeed, MSCs are
multipotent cells that arise from the mesenchyme during development. they
reside in the bone marrow close to the hematopoietic stem cell niches and are
responsible for maintaining bone marrow homeostasis and for regulating the
maturation of both hematopoietic and non-hematopoietic cells. although it
has been ascertained that MSCs possess an extensive potential to proliferate
and differentiate into osteoblasts and osteocytes, the complete pathway(s)
leading to their differentiation has not yet been clarified. For these reasons,
MSCs are of interest in clinical applications, since they can be easily isolated
from bone marrow aspirates and expanded
in vitro
. When the source of
osteoprogenitors is compromised, cell-based therapies could provide a novel
way to repair bone defects (Heino and Hentunen, 2008). indeed, most of the
available cell-based strategies target the differentiation and tissue regeneration
potential of either local cells or transplanted autologous connective tissue
progenitor cells derived from bone marrow or other tissues (with or without
their expansion in culture) (Patterson
et al
., 2008).
a discrepancy between the data obtained from research studies and clinical
trials highlights the need to identify the type of cells to be used in bone tissue
engineering. Most scientific publications focus on the use of isolated MSCs.
However, many clinical studies have demonstrated the strong osteogenic
potential of fresh harvested total bone marrow. there has been, nevertheless,
little research work on the use of total bone marrow as a source of cells for
bone tissue engineering.
Recent advances in the isolation, expansion and characterisation of human
MSCs have raised the possibility of using them in cell therapies and tissue
engineering for bone reconstruction. it has been demonstrated that hMSCs,
isolated from the bone marrow of healthy adult donors, were minimally
expanded
ex vivo
and pulsed twice toward osteogenic lineage (trombi
et al
.,
2008). However, when the cells were then included into autologous plasma-
derived clots, cell proliferation was sustained under appropriate cell culture
conditions.
