Apologetic but resolute in the face of intense international scrutiny of her stem cell research, Haruko Obokata stood by her claim Wednesday that she had discovered so-called STAP cells.

Appearing at a news conference at an Osaka hotel accompanied by her lawyers, the 30-year-old researcher at the government-backed Riken institute denied allegations that she falsified or fabricated data presented in research papers published in the British science journal Nature in January.

“I sincerely apologize for suspicions raised over my research papers and the enormous trouble caused to Riken, co-authors of the papers and many others due to my carelessness, sloppiness and immaturity,” she said. “I think my mistakes were incredibly (immature) in the eyes of many researchers.

“But these mistakes do not affect the conclusions of my paper, and above all, the experiments have been solidly conducted and the data (proving STAP cells) exist.”

Wednesday’s news conference, jam-packed with hundreds of journalists and TV crews, marked Obokata’s first public appearance since Jan. 28, when she announced in Kobe that a team of Japanese and U.S. researchers led by her discovered STAP (stimulus-triggered acquisition pluripotency) cells.

In an announcement that turned Obokata into a celebrity overnight, the researchers claimed they had succeeded in reprogramming adult cells of mice into pluripotent cells by simply soaking them in mildly acidic liquid.

Obokata said she had wanted to answer some of the questions raised by critics at a much earlier timing, including the criticism that no third-party researchers have been able to replicate STAP cells. But she was dissuaded by Riken from making public statements, she said.

Obokata expressed confidence that other scientists would succeed in reproducing the cells, only if they acquired “the little know-how.”

She added that she herself has succeeded in producing STAP cells “more than 200 times,” sometimes in the presence of other researchers at various labs she worked for.

She stressed she will not retract the paper in question. “A retraction would mean announcing to the world that the results of my research have been completely false,” she said.

On Tuesday, she filed an appeal with Riken, protesting the findings of its investigative committee, which on April 1 pronounced her guilty of two instances of misconduct of the six allegations they examined.

The investigative panel, headed by Riken’s Shunsuke Ishii, found fabricated and falsified data in one of the two STAP papers published in Nature, of which Obokata was the lead author. The committee has refused to confirm or refute the existence of STAP cells.

In the meantime, the institute has independently begun to attempt to replicate the cells, a process expected to take about a year.

The panel labeled as a “fabrication” an image used in one of the papers that “closely resembled” one in her doctoral thesis for Waseda University, though the Riken-sponsored experiments were conducted under different conditions.

The panel also found that her manipulation of an image from a lab test to add contrast was an act of “falsification.”

But Obokata has maintained these were simple errors, not acts done “out of malicious intent.”

According to Riken’s internal regulations, “mistakes made without malice” do not constitute research misconduct.

Obokata also complained in her appeal that she was not given enough opportunity to make a rebuttal, saying the investigative panel interviewed her only once.

Riken will soon decide whether to re-examine the case against her. The reinvestigation will likely be carried out by the same committee that has found her guilty of misconduct. The committee will report the results of its probe within “around 50 days,” according to Riken regulations.

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