Cocultures: a new lead in embryo quality improvement for assisted reproduction.

One of the contributory causes to poor PRs in assisted reproduction has been the decreased viability of transferred embryos and the transfer of four-cell embryos into an environment that naturally would be receptive only to 5-day-old blastocysts. In this paper, we have reviewed our own work and that of others on the role of tubal ampullary cells (cocultures) to mimic the in vivo environment to bring about improved embryo quality and an increased number of blastocysts for replacement in IVF patients. The establishment, maintenance, and behavior of human tubal cell lines is first presented, followed by their use as cocultures for fertilization and cleavage of embryos. The mode of action, specificity, and cryopreservation of ampullary cells are also discussed. The currently available results of pregnancies after cocultures are presented together with future aspects of research that are necessary to refine the coculture system. The ultimate aim is to mimic in vivo conditions in vitro, so that at least the PRs of assisted conception can be parallel to normal fecundity in the human. Therefore, a very attractive future includes the freezing of blastocysts generated from coculture, thawing, and replacing them in natural cycles.