TOKYO, Oct. 12 (Kyodo) — Doubts kept growing Friday about a Japanese researcher's claim to have conducted the first clinical application of induced pluripotent stem cell technology, for which Kyoto University professor Shinya Yamanaka on Monday was jointly awarded this year's Nobel Prize in Physiology or Medicine.

Hisashi Moriguchi, who claimed to be a visiting lecturer at Harvard University, said Wednesday he transplanted cardiac muscle cells developed from iPS cells into six heart-failure patients at Massachusetts General Hospital in Boston.

On Thursday, however, Harvard University said it and the hospital never authorized any such clinical studies by Moriguchi, adding more than a decade has passed since Moriguchi worked at the hospital.

Moriguchi "was a visiting fellow at Massachusetts General Hospital from 1999-2000, and has not been associated with MGH or Harvard since that time," the university said.

In Tokyo on Friday, science minister Makiko Tanaka expressed concern over the potential damage to basic research should Moriguchi's claims prove bogus.

"It is regrettable because (such a scandal) would have significant repercussions on researchers who have been studying seriously," said Tanaka, Japan's minister for education, culture, sports, science and technology.

Noting she does not yet know all the facts of the case, Tanaka expressed disbelief such a hoax could occur if that is what has happened.

"I wonder how this kind of thing happened. It is a matter of grave concern if any criminality is involved," Tanaka said.

Moriguchi said Wednesday he was part of a team of researchers that developed heart muscle cells from iPS stem cells, which were produced from patients' livers. He said those muscle cells were then transplanted to six heart-failure patients in the United States.

Moriguchi's claim to have already conducted clinical trials involving iPS stem cells was made just two days after Yamanaka, a Japanese researcher at Kyoto University, was awarded this year's Nobel Prize in medicine along with Britain's John Gurdon for their work that led to development of iPS stem cells.

Yamanaka told reporters Friday he cannot comment on the alleged work of Moriguchi until he actually reads Moriguchi's report about the clinical trial.

Yamanaka also said his work to put his scientific breakthrough into practical use will proceed.

"We are preparing to apply (multipurpose cells) to patients after confirming safety and effectiveness. We hope to promote our research and development...without being affected by such news reports (about Moriguchi)," Yamanaka said.