Seven laboratories have confirmed that a type of stem cell said to have been discovered by a Japanese scientist in now-retracted papers could not be reproduced, despite over 100 attempts, according to research published Wednesday.

The British science journal Nature said the reanalysis of so-called STAP cells “provides a strong example of the self-correcting nature of science.”

The journal printed papers in January 2014 in which a little-known scientist of Japan’s Riken research institute, Haruko Obokata, among other scientists, revealed the discovery of a type of cell they said was capable of forming any type of mouse tissues.

According to Nature, the seven laboratories were based in the United States, China, the Netherlands and Israel, including Harvard Medical School, to which professor Charles Vacanti, co-author of the disgraced papers on the STAP cell discovery, belongs.

The laboratories tried to generate STAP cells following the methods promoted by Obokata and Vacanti by applying multiple kinds of stress to spleen and lung cells of mice, for example.

They conducted 133 experiments for the purpose, but all ended in failure, their papers said.

The journal said that “all of the claimed STAP cell lines were contaminated with embryonic stem cells,” and that the contamination affected the results.

The Japanese institute, which already retracted the controversial papers, also said in Nature’s latest edition that what was touted as STAP cells originated from embryonic stem cells.

A researcher who led the Harvard laboratory team suggested its participation in the bid to reproduce STAP cells had nothing to do with a potential decision by the school regarding the fate of Vacanti.

“It is not related to any official Harvard inquiry,” George Daley, professor in the school’s Children’s Hospital Boston, said.

The other laboratories involved included those affiliated with Erasmus Medical Center, the Weizmann Institute of Science and Peking University.