It has been a crazy week for stem cell research. After the high of a Nobel prize for Japan's Shinya Yamanaka, the pioneer of cellular reprogramming, events took an alarming and surreal turn when a little-known compatriot Hisashi Moriguchi claimed to have already run a clinical trial in which similarly reprogrammed cells were injected into people.

But Moriguchi's claims quickly unravelled. "I have not found a single person to say anything concrete indicating that this has really happened," says Paul Knoepfler, a stem cell researcher at the University of California, Davis, who tracked the unfolding story on his blog.

In a poster presented at a meeting of the New York Stem Cell Foundation, Moriguchi who claimed to work at Harvard Medical School and the University of Tokyo described results from a trial in which cardiac muscle cells were grown from induced pluripotent stem (iPS) cells, and transplanted into six US patients with severe heart failure.

The Yomiuri Shimbun newspaper Japan's biggest splashed the story, based on an interview with Moriguchi, who claimed he had received ethical approval from Harvard Medical School's Institutional Review Board (IRB).

This was surprising, given the safety concerns that surround iPS cells adult cells that have been reprogrammed to an embryonic state. Support for the claim quickly disintegrated: within hours, Harvard released a statement noting that Moriguchi had no current affiliation with the university, nor any ethical approval to run a clinical trial.

Moriguchi's poster describing the clinical trial was taken down after the New York Stem Cell Foundation learned of Harvard's statement but a summary was published on Knoepfler's blog. This suggested an improvement of 41.5 per cent in "ejection fraction" a measure of heart output in patients whose hearts were injected with iPS-derived cells, compared to 4.1 per cent in a placebo group.

That would have been an astonishing claim, says Michael Laflamme at the University of Washington in Seattle, who is working to develop cell therapies for heart attack: "I'm not aware of any clinical trial that reported anything of this magnitude."

Indeed, similar studies involving adult stem cells have typically found improvements of less than 5 per cent (European Journal of Hearth Failure, doi.org/crq5k6).

Moriguchi did not respond to emails from New Scientist. But on Saturday he admitted to reporters that for five of the patients he was actually describing "planned" procedures. Still, Moriguchi maintained that he had transplanted cells into one patient at an unidentified hospital in Boston.

New Scientist's enquiries raise further questions about Moriguchi's work. In papers published earlier this year, he described experiments on freezing human ovarian tissue (Scientific Reports, doi.org/jht), and a remarkable claim to be able to eliminate liver tumour cells using a reprogramming technique (Scientific Reports, doi.org/jhv). Both gave Harvard and University of Tokyo affiliations, and claimed ethical approval from each institution.

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Claim of first human stem cell trial unravels