Presentations at the American Academy of Pediatrics Section on Urology annual meeting indicate slow, methodical progress in efforts to engineer biologically active tissues.
"We are seeing a steady evolution in tissue engineering," said Anthony Atala, MD, director of the Wake Forest Institute for Regenerative Medicine and chair of urology, Wake Forest University School of Medicine, Winston-Salem, NC. "We are seeing multiple approaches here that will ultimately lead to better clinical deliverables."
The tissue engineering reports presented here were in the form of posters, supporting Dr. Atala's characterization of small, stepwise advances.
Dr. Bertram reported a trial of engineered neobladders versus the cell-free biodegradable scaffold used to grow neobladder and native bladders in dogs that had had a partial cystectomy followed by re-implantation. Only dogs that received the neobladder achieved functional recovery of urodynamic measures and a regenerative tissue response that recapitulated bladder wall structure and function with urodynamic outcomes consistent with normal bladders.
Gold standard comparison
The neobladder is composed of a poly(lactic-co-glycolic acid [PLGA])-based biodegradable mesh scaffold that has been seeded with autologous urothelial and smooth muscle cells. Of the 37 animals in the study group, 16 received neobladders, seven had their native bladders reimplanted, and 14 received the neobladder scaffold alone. Urodynamic and regeneration parameters were compared at baseline and at 1, 3, 6, and 9 months after implantation.
Dogs with autologous bladder implants showed bladder function similar to that of the neobladder dogs in the early months, but urodynamic parameters were unstable. At 9 months, the native bladder group showed a 60% to 75% decrease in urodynamic function from baseline. Dogs that received only a neobladder scaffold showed limited healing and incomplete bladder wall repair.
"We used the natural bladder as the gold standard," Dr. Bertram said. "We made every effort to resect and immediately reimplant the native bladder, but there was still a period of transient ischemia and tissue damage, which we believe affected urodynamic performance. With the neobladder, there was no ischemia, and the body was catalyzed to regenerate all elements of the bladder wall."
The autologous cells seeded on the neobladder scaffold proliferate to form new bladder tissue, Dr. Bertram explained. Unpublished data show that the engineered bladder survives and grows with the host for at least 2 years.
"The neobladder is durable and responds to homeostatic signals for growth," Dr. Bertram said. "The implanted organ size matches that of the natural organ as the animal grows. We can put it into a child and expect it to grow to adult size as the body grows."
Three FDA-guided phase II clinical trials of the neobladder are already under way in the United States, Dr. Bertram told Urology Times. Study populations include children with neurogenic bladder and spina bifida, adults with neurogenic bladder due to spinal cord injuries, and adults with urge incontinence who have failed other therapies.
Stephane Bolduc, MD, pediatric urologist at the Centre Hospitalier Universitaire de Quebec, Canada, discussed another technique to engineer bladder tissue.
His group cultured fibroblasts from autologous skin biopsy to create cellular sheets, which subsequently were layered to form a flexible construct. Urothelial cells obtained from a bladder biopsy were seeded on one side of the construct.
The entire construct was cultured submerged for a week, then partially exposed to air to encourage urothelial cell differentiation. Mechanical tests showed that the construct has a slightly higher uniaxial tensile strength than native bladder tissue has.
"Everybody would like to get away from using bowel tissue to repair the bladder," Dr. Bolduc told Urology Times. "We obtained a mechanically resistant model that is suitable for implantation in the animal model. Earlier constructs had all the strength of a wet tissue."
The next step, Dr. Bolduc said, is to use bladder biopsy to obtain both smooth muscle cells and urothelial cells to create a bladder tissue construct. Not using a scaffold reduces the potential for inflammation, and autologous cells eliminate potential tissue rejection concerns. Dr. Bolduc said his group is planning porcine transplants later this year.
"They have shown that you can grow urothelial cells without a scaffold," Dr. Atala noted. "That's a positive step."