Generation of Human Primordial Germ Cell-like Cells at the Surface of Embryoid Bodies from Primed-pluripotency Induced Pluripotent Stem Cells

Primordial germ cells (PGCs) are common precursors of all germline cells. In mouse embryos, a founding population of ~40 PGCs are induced from pluripotent epiblast cells by orchestrated exposures to cytokines, including bone morphogenetic protein 4 (Bmp4). In human embryos, the earliest PGCs have been identified on the endodermal wall of yolk sac around the end of the 3^rd week of gestation, but little is known about the process of human PGC specification and their early development. To circumvent the technical and ethical barriers of studying human embryonic PGCs, surrogate cell culture models have been recently generated from pluripotent stem cells. Here, we describe a 13-day protocol for robust production of human PGC-Like Cells (hPGCLCs). Human induced pluripotent stem cells (hiPSCs) maintained in the primed pluripotency state are incubated in the 4i naïve reprogramming medium for 48 hours, dissociated to single cells, and packed into microwells. Prolonged maintenance of hiPSCs in the naïve pluripotency state causes significant chromosomal aberrations and should be avoided. hiPSCs in the microwells are maintained for an additional 24 hours in the 4i medium to form embryoid bodies (EBs), which are then cultured in low-adherence plasticware under a rocking condition in the hPGCLC induction medium containing a high concentration of recombinant human BMP4. EBs are further cultured for up to 8 days in the rocking, non-adherent condition to obtain maximum yields of hPGCLCs. By immunohistochemistry, hPGCLCs are readily detected as cells strongly expressing OCT4 in almost all EBs exclusively on their surface. When EBs are enzymatically dissociated and subjected to FACS enrichment, hPGCLCs can be collected as CD38+ cells with up to 40-45% yield.