Our article "A culture system using human foreskin fibroblasts as feeder cells allows production of human embryonic stem cells" describes a new way to culture better-quality human embryonic stem cells (hESC). Until we initiated the derivation of hESC lines using this new system, all lines had been derived using primary cultures of fetal mouse fibroblasts as feeder cells. Feeder cells were needed for non-differentiated growth of hESC. Thinking of use of these cells in human cell transplantation, a contact with mouse cells is totally impossible. The mouse cells contain microbes, such as retroviruses, which can contaminate human hESC cultures, and they also feed the cells with non-human proteins, which are immunogenic.

“Our article was the first step towards safe clinical use of hESC-derived cells.”

We decided to start using postnatal human skin fibroblasts as feeder cells, and chose foreskin fibroblast lines, which can be easily obtained by laboratories culturing human cells. Our first experiments proved successful, and we never needed to use any other feeder cells in the derivation and propagation of our present 29 hESC lines. It is much easier for all laboratories to use these human skin cell lines than killing weekly mouse embryos and make fibroblast lines from them. The quality has been easy to control.

We are working in a laboratory that is located in close contact with a clinical human in vitro fertilization facility. We could not take mice to this human clinical unit. Hence, it was necessary to start thinking of better options. That we wanted to establish hESC lines was a natural consequence of our embryo research project which we already had ongoing in our laboratory.

The only obstacle in the beginning was the negative attitude of some co-workers. But I did not care about such comments as, "You can never succeed using such cells. It will be a waste of embryos," and said that I would test with five embryos. We got two lines from those embryos.

Our culture system using human foreskin fibroblasts was very quickly adopted by many laboratories. Today most of the human hESC lines are cultured on such feeder cells. There are articles in which other authors have shown how much better these human cells support the growth of hESC. When the contamination of all old hESC lines with mouse proteins and viruses became widely known and discussed in the literature around 2005, our feeder system became really widely used.

We and others have been developing even cleaner systems, and we will soon have clinical grade human hESC, which have been totally xeno-free at all stages of derivation and culture. Feeder-free cultures have been developed, but they have not been fully xeno-free, and feeder-free derivation conditions have produced abnormal cells.

Before human hESC derived cells can be used in human cell transplantation, these cells have to meet several safety criteria. They must not contain microbes, which can contaminate human cells and tissue. They should not contain immunogenic non-human proteins, which promote rejection of the cells after transplantation. The cells should be chromosomally normal and contain as small amount of other mutations as possible.

We and several other groups are now developing completely xeno-free new derivation and up-scaling methods in order to obtain safe hESC lines for differentiation for human cell transplantation. It all started with the work published in this article, and since then we have made and published several improvements into the system. Our article was the first step towards safe clinical use of hESC-derived cells.

Dr. Outi Hovatta
Department of Clinical Science, Intervention and Technology
Division of Obstetrics and Gynecology
Karolinska Institute
Stockholm, Sweden