Improvement of human early embryo development in vitro by coculture on monolayers of Vero cells.

Human "spare" embryos, judged unsuitable for freezing because of their poor quality, were cocultured for 5 days on a "Vero" cell layer. These epithelial cells were selected because kidney and genital tract have a common embryologic origin and "Vero" cells are a safe and highly controlled cellular support used for vaccine production. In the control group, the embryos were cultured in culture medium alone (B2 + 15% serum). At the end of the culture, the number of blastocysts was significantly higher in the coculture group: 61% vs. 3%. Moreover, at least half of the blastocysts were expanding and hatching (13/25), with a chronologically normal development. These observations suggest that (1) the coculture system improves human embryonic development; (2) it can rescue early degenerating embryos; (3) beneficial effects of coculture are not strictly genital-tract specific, but rather epithelium dependent. This coculture system could be used for in vitro fertilization to prolong in vitro culture and thus make it possible to transfer embryos at a more appropriate time, to eliminate early-blocked eggs, and to freeze embryos at the blastocyst stage, when freezing procedures are most successful.