There has been a fourth retraction in the STAP stem cell scandal, according to Retraction Watch.
In 2014, researchers from the US and Japan reported in Nature on a way to generate embryonic-like stem cells just by exposing cells to a strong stimulus. But scientists quickly found flaws in the work, which led to the papers' retraction and to findings of research misconduct by the first author, Riken's Haruko Obokata, who later resigned. A Riken investigation noted that the findings may have been due to contamination and two Nature papers later found the approach was not robust or reproducible. A third STAP-related paper was retracted from Nature Protocols in 2016, Retraction Watch notes.
In addition to Obokata's resignation, Ryoji Noyori, who was the president of Riken, also stepped down from his post amid the fallout of the scandal. Yoshiki Sasai, one of the co-authors on the papers who was not implicated in the research misconduct, died by suicide.
A fourth paper, which was published in Tissue Engineering Part A in 2011, has now been retracted, according to Retraction Watch. It adds that the senior author, Harvard University's Charles Vacanti, requested the retraction following an investigation by the school. According to the retraction notice, this move built on a correction that had been made to the paper due to issues with a figure.