Fetal cells multiply significantly more rapidly and more often in culture.
They can survive at lower oxygen tensions than those tolerated by mature cells and are therefore more resistant to hypoxia during in vitro manipulations.
They also typically lack long extensions and strong intercellular adhesions.
Probably because of all those characteristics, fetal cells tend to display better survival after refrigeration and cryopreservation protocols when compared with adult cells.
Because they are very plastic in their differentiation potential, fetal cells respond better than more mature cells to environmental cues.
Data from fetal myoblasts, osteoblasts, and mesenchymal amniocytes suggest that focused manipulations in culture or in a bioreactor can be designed so as to steer fetal cells into producing enhanced constructs.
Also, at least in part because of their proliferation and differentiation capacities, fetal cells long have been recognized as ideal targets for gene transfers.
Characteristically, fetal mesenchymal stem cells (MSCs) express HLA class 1, but not HLA class 2.
Although the presence of interferon gamma in the growth medium could initiate the intracellular synthesis and cell surface expression of HLA class 2 in these cells, normally neither undifferentiated nor differentiated fetal MSCs induce proliferation of allogenic lymphocytes in mixed cultures.
This indicates that fetal MSCs may not elicit much alloreactive lymphocyte proliferation.
These characteristics suggest that engineered constructs made with fetal cells should be less susceptible to rejection in heterologous applications.
Even xenologous implantations eventually may become viable, as studies suggest that fetal cells also are tolerated better in cross-species transplantations, including in people.
At the same time, however, the expression of major histocompatibility complex antigens in the fetus and, hence, fetal allograft survival in immunocompetent recipients, is age- and tissue-specific.
Fetal cells often produce high levels of angiogenic and trophic factors, which enhance their ability to engraft and grow in vivo.
Interestingly, those factors also can facilitate regeneration of surrounding host tissues.
For example, significant clinical and hematological improvement has been described following fetal liver stem cell transplantation in people, even when there is no clear evidence of engraftment.
These improvements have been attributed to regeneration of autologous hematopoiesis and inhibition of tumor cell growth promoted by the infused cells, through mechanisms that have yet to be determined fully.