Blastocyst implantation assay: towards the development of a new in vitro model for studying woman-specific blastocyst implantation.

Abstract

Background: Despite the large number of studies on embryo invasion, in vitro models investigating early-implantation phase are limited. The aim of this study was to investigate woman-specific blastocyst implantation through the development of a new in vitro model.

Methods: Human endometrial epithelial cells were purified from endometrial tissue biopsies of women in reproductive age. BeWo cells were used to develop blastocyst surrogate spheroids and Ishikawa cells were used to develop an in vitro spheroids adhesion assay. BeWo-spheroids were co-cultured with endometrial epithelial cells monolayer to assess the endometrial receptivity.

Results: Our BeWo spheroids culture protocol provided us with 3D embryo surrogates that were homogeneous in shape and their dimensions were comparable to blastocysts size after 48h of spheroids culture. Spheroids adhesion rate on Ishikawa cells after three hours co-incubation was 96.3% and there were no significant differences when compared to later time points. This allowed to assess three hours as the optimal time to run the test on primary endometrial epithelial cells. The average adhesion rate on human endometrial epithelial cells was 70.8%.

Conclusions: In this study we developed an in vitro model to mimic the endometrial exposure to the blastocyst in vitro and to evaluate the maternal tissue response in terms of the amount of trophoblastic spheroids able to adhere to endometrial cultures. Our results underline the high variability existing among healthy patients in their endometrial ability to retain the embryo, pointing out the necessity of developing a test aimed at the customization of in vitro fertilization treatments.