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