Japanese researchers have reported a step toward developing transplantable kidney tissue, showing that multiple embryonic kidney tissues can mature and provide some kidney function after being transplanted into rats.
The study, published in Kidney International in 2025, used metanephroi, embryonic kidney tissues that can develop into nephrons and other kidney structures. Researchers at Jikei University School of Medicine and collaborating institutions combined the tissues with segments of embryonic bladder and connected the grafts to the animals’ urinary tracts.
In rats that had their own kidneys removed, transplantation of 20 metanephroi produced about 50,000 nephrons in vivo. Four of five rats in one survival experiment lived for at least a month after transplantation and urinary reconstruction. The grafts also helped maintain vital functions, including solute clearance, acid-base balance, electrolyte levels and kidney hormone activity.
The researchers found that the transplanted tissues reached a level of structural and molecular maturity comparable to adult kidneys. However, the grafts remained much smaller than normal kidneys and had limited ability to concentrate urine, highlighting important functional shortcomings.
The findings do not mean scientists have created a replacement human kidney. The experiments were conducted in animals and used embryonic kidney tissue rather than a complete organ grown from iPS cells.
Meanwhile, a 2026 review by University of Tokyo researchers said kidney organoids made from human iPS cells are advancing but still face major hurdles, particularly inadequate blood-vessel formation, immature tissue and limited evidence of long-term function. The researchers said improving vascularization and maturation will be critical before such tissues can become viable regenerative treatments.
Together, the findings show progress toward regenerative kidney therapies, but substantial research remains before lab-grown or regenerated kidney tissue could be used routinely in human transplantation.
