<em>Ex vivo</em> Culture of Human Placental Explants for the Study of Viral Transmission Across the Maternal-Fetal Interface

The placenta plays a critical role during pregnancy, enabling maternal-fetal exchange while serving as a barrier against pathogens. However, some viruses, including human cytomegalovirus (HCMV) or Zika virus (ZIKV), can cross this barrier and cause congenital infections, leading to severe fetal outcomes such as growth restriction, impairment of brain development, or fetal demise. Understanding how viruses infect and disseminate through the placenta is therefore essential. To investigate viral vertical transmission in a physiologically relevant context, an ex vivo model using human placental explants cultured at the air-liquid interface on gelatin sponges can be used and offers several advantages. Unlike conventional in vitro systems limited to single-cell types, this model preserves the multicellular structure and function of the placental tissue for up to three weeks. This model is compatible with a wide range of upstream experimental applications (histological analyses, RT-qPCR, TUNEL assay, quantification of secreted factors, etc.), making it a robust and accessible platform to study viral replication, immune responses, and placental barrier function under near-physiological conditions.