Co-cultures: their relevance to assisted reproduction

Assisted reproductive techniques have contributed significantly to alleviating subfertility in the childless couple. However, the take-home baby rates have been very low throughout the world. One of the contributory causes has been the reduced viability of replaced embryos brought about by suboptimal in vitro conditions. The culture of human embryos in the presence of passaged human tubal ampullary monolayers (co-cultures) is an attractive approach to improving the viability of embryos for assisted reproduction. Seventy per cent of blastocysts can be produced in human ampullary co-culture as compared to 33% in standard culture media. This paper discusses the various roles of human co-cultures in assisted reproduction and provides an opinion as to how the transfer of blastocysts produced via the co-culture system could enhance pregnancy rates. Particular emphasis is placed on human oviductal characteristics, the various co-culture systems, screening of co-cultures for microbes, freezing of ampullary cells, growth factors and embryonic blocks, specificity of co-cultures, sperm hyperactivation in co-culture and pregnancy rates. The first patient on a clinical trial who had four of her oocytes fertilized and grown in human ampullary co-culture and then replaced into her uterus became pregnant. The co-culture system may have tremendous potential in supporting human embryonic growth via embryotrophic factors.