Paraffin Embedding and Histological Analyses of Sw71-Spheroids as Human Blastocyst-like Surrogates

Implantation studies are extremely important to solve reproductive problems since about 60% of abortions occur around this period. The 3D in vitro models emerge as closest to the in vivo structures and processes. Here, we constructed trophoblast Sw71-spheroids as implanting human blastocyst–like surrogates (BLS). The model is well-characterized, standardized, validated tool to study extravillous trophoblast (EVT) invasion/migration during implantation. A limitation is that it is a short-living 3D-culture that must be generated de novo. This study aimed to create and embed Sw71-spheroids in paraffin for permanent histological preparations. The main challenges were the micro-size and the preservation of the intact structure. The standardly generated compact and stable Sw71-spheroids were intact, with blastocyst-like morphology. Histological analysis showed preserved cell morphology, shape, and intact periphery of the embedded Sw71-spheroids. These were usable for immunohistochemistry(IHC) and expressed common EVT markers: EpCAM, HLA-C and and HLA-G. Our protocol for spheroid paraffin embedding is suitable for simultaneous histological analyses of several Sw71-spheroids. It might be further optimized to embed migrating/invading Sw71-BLS as snapshots of trophoblast implantation steps in permanent histological preparations for in depth IHC studies.