Aseries of questions and suspicions have challenged the validity of a scientific paper that reported that body cells taken from mice could be reprogrammed into stem cells — immature cells that can develop into all types of body tissues — by simply exposing them to low-pH (acidic) liquids.

The paper, published in Nature magazine on Jan. 29 by a group of scientists led by Dr. Haruko Obokata at the government-backed Riken’s Center for Developmental Biology in Kobe, attracted global attention as a groundbreaking stem cell study.

Riken must carry out a rigorous investigation, then issue a report that squarely answers each question and suspicion.

In the paper, Obokata and 13 other co-authors, including scientists at Harvard University and the Riken center, said they had soaked lymph corpuscle taken from 7-day-old mice in mildly acidic liquids for about 30 minutes, cultured a few cells that survived, then transplanted them into mice. They said they found that the cells developed into nerve and muscle tissues. They named this new way of reprogramming adult cells into pluripotent cells “stimulus-triggered acquisition of pluripotency,” or STAP.

Since February, though, doubts have been raised about the paper. One problem is that other scientists have not been able to produce STAP cells when they replicated the experiment. A scientific discovery may be declared false if other scientists cannot reach the same conclusion after repeating an original experiment. Riken disclosed steps to produce STAP cells only on March 5.

Questions and suspicions were also raised about graphics and sentences used in the paper. The most crucial of these is the claim that photographs that appeared in Nature magazine closely resemble photos that Obokata used in her Ph.D. dissertation submitted to Waseda University 2011.

The latter photos showed differentiation of a cell produced through a method different from the STAP method. The photos in Nature show that a STAP cell can grow into various cell types. If the photos that ran in the magazine and those used in Obokata’s Ph.D. dissertation are identical, it means that photos having nothing to do with a STAP cell were used to illustrate its pluripotency.

After learning of the two sets of photos, Teruhiko Wakayama, co-author of the STAP cell paper and professor at Yamanashi University, said Monday that something was wrong with the key point of the claimed discovery and called for retraction of the paper.

Some scientists say that sufficient proof has not been made concerning the paper’s basic story that a STAP cell was produced from lymph corpuscle. But Charles Vacanti, a Harvard University professor who co-authored the paper, said, “Some mistakes were made, but they don’t affect the conclusions.”

Riken has the duty to give convincing answers to the questions and suspicions. It should find out whether photos were reused and data manipulated. If so, Riken must determine whether they were done by mistake or deliberately.

If Riken thinks that the conclusions are not affected despite mistakes or data manipulation, it needs to re-enact the production of STAP cells in an environment free of manipulation.

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