Although an early step, the feat could bring closer the day when life-saving human organs may be grown in pigs or sheep, the researchers and observers said.
Mice who received transplanted pancreatic tissue in the trial needed only five days of treatment with immunosuppressive drugs to stop their bodies rejecting the foreign matter, the study authors said.
"We found that the diabetic mice were able to normalise their blood glucose levels for over a year after transplantation," said study co-author Hiromitsu Nakauchi of Stanford University.
In the United States alone, more than 76,000 people are waiting for a transplant, said the authors of the study, published in Nature.
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Petri-dish attempts to grow transplantable organs -- which comprise billions of often highly-specialised cells -- have been frustrating.
"Although scientists have begun to master the art of making assemblies of cells that resemble organ precursors in a petri dish, the microscopic size and rudimentary organisation of these organoids is a far cry from that of an adult organ," Harvard University biologist Qiao Zhou, who did not take part in the study, said in a comment published by Nature.
The same team, in 2010, managed to grow a rat pancreas in a mouse.
But the organ grew only to the size of a mouse pancreas, which meant there was not enough tissue for transplant to a rat.
This time, the scientists switched the animals' roles.
They created mouse-rat "chimeras" or hybrids by injecting pluripotent stem cells -- which can become any specialised cell of the body -- into rat embryos.
Almost every organ and tissue of the resulting adults was a mixture of rat and mouse cells, apart from the pancreas which was mainly mouse.