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It is an explanation that stem-cell scientist Rudolf Jaenisch of the Massachusetts of Technology in Cambridge, who was part of the replication efforts, suggested in April 2014 to Nature’s news team, although he did not have evidence at the time to support it.
One lingering question is how these embryonic stem cells and trophoblast stem cells came to replace purported STAP cells when the experiments were done. Cross-contamination — accidental contamination of one cell culture by another type of cell — is a well-known problem in biology. But multiple independent contamination events would be necessary to explain the mistakes in the STAP paper data.
