A co-author of a Japanese study that promised a revolutionary way to create stem cells has now called for the headline-grabbing research to be retracted over claims that its data was faulty.
The findings, published by Japanese researcher Haruko Obokata and US-based scientists in the January edition of British journal Nature, outlined a simple and low-tech approach in the quest to grow transplant tissue in the lab.
But it has faced hard questions as the Japanese research institute that sponsored the study launched a probe last month over the credibility of data used to reach the explosive findings.
At issue are allegations that researchers used erroneous image data for the high-profile Nature article.
The Japan-based Riken Institute, which could not be immediately reached Tuesday, had earlier said it was standing by the results for the time being.
Teruhiko Wakayama, a Yamanashi University professor who co-authored the article, said the team's research should be retracted.
"It's hard to believe the findings anymore after so many mistakes in the data," he told broadcaster Nippon Television late Monday.
Nature said it was launching its own investigation.
"Issues relating to this paper have been brought to Nature's attention and we are conducting an on-going investigation," the journal said in an emailed statement.
"We have no further comment at this stage."
However, Hitoshi Niwa, who also contributed to the article, stood by the results despite "minor mistakes" in the data, Japanese media reported.
Another co-author of the study, Charles Vacanti, a tissue engineer at Harvard Medical School and Brigham and Women's Hospital in Boston, told the Wall Street Journal: "Based on the information I have, I see no reason why these papers should be retracted.
"It would be very sad to have such an important paper retracted as a result of peer pressure, when indeed the data and conclusions are honest and valid," he said.
Harvard is also investigating, according to Japanese media reports.
Called stimulus-triggered acquisition of pluripotency (STAP) cells, the innovation was touted as breaking new ground.
Stem cells are primitive cells that, as they grow, differentiate into the various specialised cells that make up the different organs -- the brain, the heart, kidney and so on.
The goal is to create stem cells in the lab and nudge them to grow into these differentiated cells, thus replenishing organs damaged by disease or accident.
The researchers' groundbreaking findings said that white blood cells in newborn mice were returned to a versatile state through a relatively simple process that incubated them in a highly-acidic solution for 25 minutes, followed by a five minute spin in a centrifuge and a week-long immersion in a growth culture.
Until now, only plant cells, and not mammal cells, have been found to reprogramme back to a youthful state through simple environmental factors.