A lab "grown" kidney has been successfully transplanted into a rat and began producing urine, an early research step that may one day lead to replacement organs for humans and will turn organ donations obsolete.

However the study, published in the journal Nature Medicine, showed the engineered kidneys were less effective than natural ones.

But regenerative medicine researchers said the field had huge promise.

Years of research remain before scientists even contemplate testing such a transplant in a person, but the team shared plans to transplant bioengineered pig kidneys into live animals in the coming months to test how well they adapt.

Several labs are competing to develop the most efficient method to produce the most functional organs through such futuristic techniques as 3D printing, which has already yielded a lab-made kidney that works in lab rodents, or through a "bioreactor" that slowly infuses cells onto the rudimentary scaffold of a kidney, as in the latest study.

As many as 10 percent of about of about 100,000 Americans awaiting a kidney transplant as of April 5 will die before getting a transplant, the authors wrote.

"The resulting graft can be transplanted just like a donor kidney," Ott said in a statement. "If this technology can be scaled to human-sized grafts, patients suffering from renal failure who are currently waiting for donor kidneys or who are not transplant candidates could theoretically receive new organs derived from their own cells."

"With a 3D bioprinter, you wouldn't require donor organs," said Dr. Anthony Atala, director of the Institute for Regenerative Medicine at Wake Forest School of Medicine in North Carolina and a pioneer in that technology.

"The printer also lets you be very precise in where the cells go" on and in the scaffold. But he hailed the Massachusetts General Hospital work as "one more study that confirms these technologies are possible."