Cells, Fetal

ON THE BASIS of National Institutes of Health guidelines, a human fetal stem cell is defined as a cell derived from either a human embryo or a fetus harvested after abortion, whether intentional or incidental. However, this définition fails to highlight the primary difference between embryonic and fetal stem cells. This difference is a question of degree of multipotency. Where the embryonic stem cell is considered to be pluripotent—able to differentiate into any cell type in the human body—most fetal cells are believed to only be multipotent to a limited degree. To put it into layperson's terms, an embryonic stem cell is like the seed of a plant, whereas a fetal cell is a sprout. The seed could grow into any plant type, but the sprout already shows some of the properties of the full—grown plant.

In practical terms, fetal cells typically demonstrate many of the same characteristics of embryonic stem cells. Both cell types are multipotent, albeit to varying degrees; both cell types are able to renew their own populations; and both types are able to proliferate to increase cell number. Therefore, research using fetal stem cells has the potential to achieve many of the same objectives as embryonic stem cell research.

In addition, fetal cells express many of the same cell surface protein markers that can be found on embryonic stem cells, including Notch, CD133, and CD34, though at different concentrations, depending on the source of the fetal cells. Although the immune response to the surface antigens on the fetal cells or embryonic stem cells may be minimal compared to using other cells, patients receiving cell transplants may still require immunosuppression.

There are some advantages to using fetal stem cells in conducting stem cell research. Fetal cells are more robust than many strains of embryonic stem cell, making the culture of fetal cells less difficult. With regard to legal policy, there is wider access and fewer restrictions with fetal cells compared with embryonic cells. A more practical set of concerns solved by fetal cells is the potential for teratoma formation when transplanting embryonic stem cells. Using the more differentiated fetal cells could reduce the risk of teratoma formation and thereby make the usage of stem cells in transplants more practical.

Although culture of fetal cells is typically simpler than culture of embryonic stem cells, there are still several distinct aspects to fetal cell culture that is not common to culture of differentiated cells. Isolation of fetal cells typically involves isolation of the chosen tissue region, followed by culture of whole or lightly dissociated tissue. Following initial cell growth, cells are often dissociated by trypsin or similar chemicals before being replated or frozen.

In some instances, fetal cells can survive without serum; in fact, some fetal lines require culture in defined serum—free mediums for optimum growth of a highly pure population of the desired cell type. Likewise, plating conditions will vary between separate cell types, ranging from simply plating the cells to the use of a three—dimensional polymer scaffold with imbedded proteins. Much like embryonic cells, many fetal lines are able to survive multiple passages without a reduction in the cell's vitality, suggesting that the cells are stable for multiple generations.

...