WASHINGTON A U.S. researcher who co-authored controversial papers on stem cell development will quit his post at Brigham and Womens Hospital in Boston on Sept. 1, the institution said Tuesday.

Charles Vacanti, chairman of the hospitals Department of Anesthesiology, Preoperative and Pain Medicine, was involved in the publication by a Japanese institution of two theses on so-called STAP cells whose credibility came into question earlier this year.

Vacanti, known as a mentor of Haruko Obokata at the Japanese government-affiliate Riken institute who is a key author of the papers, will remain on faculty, the Boston hospital said.

Following a one-year sabbatical Vacanti intends to focus his energies on regenerative medicine and mentoring the next generation of anesthesiologists, the hospital said.

It remains unknown if his latest step is linked with the STAP cell controversy.

According to a U.S.-based expert on regenerative medicine, Vacanti of Harvard Medical School is believed to have written an email informing his colleagues and others of his intention to resign from the post.

Paul Knoepfler, associate professor at the University of Californias Davis School of Medicine, released Vacantis email on his blog on Monday.

It is with somewhat mixed emotions that I share with you my decision to step down, it reads.

Vacanti did not mention whether his decision has to do with his involvement in the papers on STAP cells that were published in the British science journal Nature in January and retracted in July after critical errors were found.

I plan to take a one-year sabbatical to contemplate my future goals, redirect my efforts and spend time doing some of the things that I enjoy most, the email says.

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