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A question of contamination
To help to resolve the first question, seven teams in four countries tried to replicate the procedure under various conditions1. The teams’ work amounted to 133 attempts to produce STAP cells, all of which failed.
One of the teams, led by researchers at Harvard Medical School, worked with one of the original STAP co-authors at the laboratory where the STAP research project began. In cells engineered to express a fluorescent protein when a gene related to pluripotency was expressed — supposed to be a sign of conversion to a 'STAP state' — they did find some fluorescence. But further testing showed this to be an artefact — a phenomenon in which cells can naturally emit light, known as autofluorescence1. The six other groups also observed autofluorescence and no evidence of STAP conversion.
