Cocultures in human assisted reproduction. Support of embryos in vitro and their specificity

Assisted reproductive techniques (ART) have contributed tremendously to alleviating infertility in childless couples. However, the "take-home baby" rate for in vitro fertilization (IVF) has been much below the rate for normal fertile couples and for the other tubal procedures such as gamete intrafallopian transfer (GIFT) and tubal embryo transfer (TET). It was therefore speculated that the tubal environment might be playing an important role towards the viability of the embryo and that, in IVF, 4-6 cell stage embryos that were usually replaced directly into the uterus might not be receiving the beneficial effects of the tubal environment. Pronuclear stage human and mouse embryos were thus cocultured with reproductive and other somatic cell types to evaluate the quality of the various cleaving stages and the percentage yield of blastocysts. Human ampullary cell cultures were established in 6 to 7 days and kept alive through one menstrual cycle. Cleavage to the compacted and cavitating stages was achieved in 78% and 69%, respectively, of human embryos cocultured in 24-48 hour human ampullary subcultures as compared to 50% and 33%, respectively, for embryos grown in culture medium alone. The percentages of expanded blastocysts and hatching stages in such cocultures were not significantly different from those of controls. However, human ampullary and cumulus and mouse ampullary and muscle fibroblast cultures supported cleavage and development of mouse embryos up to the hatching stages as well as or better than controls. It thus appears that there is no absolute specificity for a reproductive tract source of cocultured cells and that the beneficial effects of ampullary and cumulus cells are not species-specific. The coculture system also appears to overcome the embryonic blocks of the human and mouse, which may be mediated via growth factors that activate the embryonic genome.