Differentiation of primate primordial germ cell-like cells following transplantation into the adult gonadal niche

A major challenge in stem cell differentiation validation is the availability of bioassays to prove cell types generated in vitro are equivalent to cells in vivo . In the mouse model, differentiation of primordial germ cell-like cells (PGCLCs) from pluripotent cells was validated by transplantation, leading to the generation of spermatogenesis and to the birth of offspring. Here we report the use of xenotransplantation (monkey to mouse) and homologous transplantation (monkey to monkey) to validate our in vitro protocol for differentiating male rhesus macaque PGCLCs (rPGCLCs) from rhesus macaque induced pluripotent stem cells (riPSCs). Specifically, transplantation of aggregates containing rPGCLCs into mouse and nonhuman primate testicles overcomes a major bottleneck in rPGCLC differentiation with the expression of VASA and MAGEA4, but not ENO2. These findings suggest that immature rPGCLCs once transplanted into an adult gonadal niche commit to differentiate towards late PGCs and spermatogonia-like cells but do not complete the conversion into ENO2-positive spermatogonia.