Bladder wall transplantation--long-term survival of cells: implications for bioengineering and clinical application

Current bioengineered bladder wall substitutes include acellular scaffolds and grafts seeded with autologous cells. The transplanted cells on a seeded graft may regenerate and/or be replaced by cells of the patient's bladder. This may or may not be advantageous depending upon the underlying pathology. A theoretically perfect bioengineered graft would be intact bladder wall. To determine if such a graft is feasible and to study the cellular changes, we transplanted full-thickness bladder grafts from male inbred rats onto bladders of female syngeneic rats. Bladders were harvested at 1, 3, 6, 12, and 16 months after surgery and evaluated for histologic changes. Cell origin (male donor vs. female host) was determined with fluorescent in situ hybridization with unique probes for rat X and Y chromosomes. Urothelial hyperplasia, inflammation, and increased stromal thickness subsided down to control values by 6 months after surgery. At 16 months, graft muscle demonstrated persistence of male cells. On the other hand, graft urothelium was partially replaced by female host cells with a pattern suggestive of a hematogenous route rather than ingrowth from the host bladder. Bladder wall transplantation is feasible. The slow replacement of the transplanted urothelium and persistence of muscle may imply the same fate for engineered grafts.