Haruko Obokata's research papers made her an instant star in Japan. Kyodo News/Associated Press

The scientific journal Nature has retracted two landmark research studies that offered a surprisingly easy way to make master stem cells for treating disease.

In January, researchers from the Riken Center for Development Biology in Kobe, Japan, published two studies that described how specialized cells could be changed into an embryonic-like state simply by stressing them a bit.

The approach offered a simple way for making fresh, patient-specific master stem cells—those that can become all other tissues in the body and are therefore useful for tissue transplantation and for treating maladies.

Nature said it had now retracted the papers because of misrepresented data and other flaws that undermined their conclusions.

Haruko Obokata during a news conference in Osaka, Japan, earlier this year. European Pressphoto Agency

The papers attracted world-wide attention and made the lead researcher, Haruko Obokata, an instant star in Japan. Dr. Obokata and her colleagues said they had stressed blood cells by dipping them into a low-acid environment, which changed them into an embryonic-like state.

The new cells were dubbed STAP, or stimulus-acquired acquisition of pluripotency. At the time, even Dr. Obokata acknowledged that the transformation was "surprising," because such cellular changes typically require genetic manipulation.

The story quickly unraveled. Within days outside scientists had spotted errors in the figures and apparent instances of plagiarism in the description of methods used. More than a dozen labs tried to duplicate the efforts and failed.

Riken launched an investigation and pinpointed a host of problems in the way the experiments were done. In April, it found Dr. Obokata guilty of misconduct. Dr. Obokata couldn't be reached for comment on Wednesday.

In one of their two retractions published in Nature, Dr. Obokata and her co-authors—including her former mentor, Charles Vacanti of Harvard Medical School and Brigham and Women's Hospital—acknowledged that major errors undermined their findings.

"These multiple errors impair the credibility of the study as a whole and we are unable to say without doubt whether the [STAP] phenomenon is real," the authors said.

A representative for Nature said the journal had been "insufficiently thorough in the number and extent of checks" related to images submitted by authors.

In an editorial published alongside the latest retractions, Nature said that neither its editors nor the referees who examined the STAP papers before publication could have detected the many faults. The journal acknowledged that the episode had highlighted some flaws in its procedures.

"We—research funders, research practitioners, institutions and journals—need to put quality assurance and laboratory professionalism ever higher on our agendas, to ensure that the money entrusted by governments isn't squandered, and that citizens' trust in science isn't betrayed."

Write to Gautam Naik at gautam.naik@wsj.com