Reconstitution of the cellular niche requirements for primordial germ cell-like cell progression in humans.

Human primordial germ cell-like cells (hPGCLCs) can be specified from human-induced pluripotent stem cells (hiPSCs), offering a valuable model for human germ cell development. However, further maturation steps of hPGCLCs rely on mouse feeders, or co-culture with mouse gonadal somatic cells. Exposure of hPGCLCs to human cellular niche has not been attempted. Here, we co-cultured female hPGCLCs in two distinct niche compartments. In reconstituted fetal ovary (rOv) culture, human fetal germ cells proliferated and initiated meiosis, while hPGCLCs upregulated gonadal germ cell markers such as DDX4. Additionally, hPGCLCs were supported and matured into migratory hPGCLCs in 3D co-culture with amnion-like cells (AMLCs). Compared to rOv, hPGCLCs in PGCLC/AMLC aggregates were less prone to dedifferentiate. In both niches, stem cell factor (SCF) was crucial for the survival of hPGCLCs. Together, this work underscores that a shift in niche is required for the further germ cell development of hPGCLCs.