Organ Regeneration: Progress in Organoids and the Challenges of Exploiting Animal Developmental Niches

With the establishment of human pluripotent stem cells (PSCs), organ regeneration research is expected to alleviate the shortage of organs for transplantation. Organ-specific progenitor cells generated from PSCs have the ability to self-assemble and form organoids, which are cell aggregates that mimic organs. Important structural and functional characteristics have been reproduced in various organoids mimicking the brain, kidney, liver, lung, and gastrointestinal tube. Organoids are expected to be applied to elucidate the mechanisms underlying organ development and pathology and promote drug discovery. However, organoid size and maturity are not yet sufficient for transplantation. In addition, kidney organoids require connections to the host urinary tract, which have not yet been established. Other approaches to producing transplantable regenerated human organs from PSCs or progenitor cells include the utilization of the animal organ developmental niche, which is divided into two main categories: blastocyst complementation and fetus organ complementation. High chimera rates have been achieved using xenogeneic animal cells, but there are still hurdles to creating sufficient human organs. In this section, we review the achievement status, challenges, and possible future improvements of organ regeneration research, with a particular focus on the kidney.