Biologists have had a deep interest in optimizing in vitro cell culture systems since cell culture plays a central role in much of their research. Embryologists have applied these techniques to the in vitro fertilization and culture of human eggs and preimplantation embryos.
One controversial technique for IVF cell culture is the use of “feeder cells” (various cell types from a number of different animal species) to support the development of human embryos in culture. In theory, these co-cultures (feeder layers) enhance the culture medium by releasing (or absorbing) components into (from) it. These components have not been identified but might include metabolites or substrates that are important for embryonic development.
The feeder cells that are used cannot be allowed to proliferate (reproduce to increase their own number) at a normal rate since they would exhaust the media’s substrate (“food”) and acidify this media. Therefore, their own reproduction is usually arrested (by irradiation or other techniques) once a suitable number of cells is achieved.
The type of cells used varies from lab to lab. The beneficial effects that are suggested in the co-culture literature appear to be nonspecific since a very wide range of animal species and tissue types have been used with apparent success. Although cells from many different animal species have been used, some IVF centers only use human cells from one of the embryo’s biological parents since any other cells may introduce harmful viruses or contaminants. In order to use designated fresh human cells there must be (a biologist with) an extremely high level of expertise in cell culture readily available within the IVF lab.
Improved embryo quality (measured by less fragmentation, more blastomeres at transfer, and higher implantation rates) has been reported with the use of co-culture systems. Conflicting reports in the literature demonstrate that there is no improvement in embryo quality or pregnancy rates (in their IVF centers) with the use of (the same) co-culture systems. Certainly any claim that co-culture (universally) improves IVF success rates is unconfirmed at this time (2002).
Many prominant IVF centers do not use co-culture and have among the highest IVF success rates available. It is often thought that within outstanding IVF labs that co-culture is not helpful whereas within suboptimal IVF labs a co-culture system may improve (rescue) culture conditions.