The Riken research institute said Wednesday that ongoing efforts to reproduce so-called STAP cells — whose existence was first claimed by scientist Haruko Obokata in the British journal Nature — have failed.

The announcement comes on the heels of a series of scandals that have cast doubt on the veracity of Obokata's claims.

"We're still midway, but there's a possibility that STAP cells don't exist," said Hitoshi Niwa, who leads a research team tasked in April with attempting to reproduce Obokata's original findings.