Stem cells that were claimed to be created simply by exposing ordinary cells to stress were probably derived from embryonic stem cells, according to the latest investigation into an ongoing scientific scandal. How that contamination occurred, however, remains an open question.
The investigation was instigated by RIKEN, the Japanese research institution where the original claims were made, and carried out by a committee composed of seven outsiders.
The committee analyzed DNA samples and laboratory records from two teams behind the original papers describing STAP (‘stimulus-triggered acquisition of pluripotency’) cells. Those papers — published in Nature but later retracted — were once heralded as describing a shortcut to producing stem cells: rather than expressing specific genes or carefully transplanting a nucleus from one cell to another, researchers could, it seemed, create stem cells by exposing them to stress, including bathing the cells in acid.
The latest investigation suggests that the STAP findings were merely the result of contamination by embryonic stem cells. Investigators found signs of three separate embryonic stem cell lines. They noted that it is difficult to imagine how contamination by three distinct lines could be accidental, but that they could also not be certain that it was intentional.
“We cannot, therefore, conclude that there was research misconduct in this instance,” the committee wrote. It did, however, find evidence that lead investigator Haruko Obokata, formerly of the RIKEN Center for Developmental Biology in Kobe, had fabricated data for two figures in the original STAP publications.
The committee’s report, released on 26 December, is the latest in a series of damning revelations about the STAP cells originally described in two Nature papers in January 2014. The approach quickly came under scrutiny as other researchers failed to reproduce its results, and as suspicions grew that images in the original papers had been manipulated. In March, another RIKEN investigation found Obokata guilty of scientific misconduct; in July, the STAP papers were retracted and in August another co-author, Yoshiki Sasai, took his own life. Earlier this month, Obokata resigned her position at RIKEN.