Stimulus-triggered acquisition of pluripotency (STAP) was a proposed method of generating pluripotent stem cells by subjecting ordinary cells to certain types of stress, such as the application of a bacterial toxin, submersion in a weak acid, or physical trauma. The technique gained prominence in January 2014 when research by Haruko Obokata et al. was published in Nature. Over the following months, all scientists who tried to duplicate her results failed, and suspicion arose that Obokata's results were due to error or fraud. An investigation by her employer, RIKEN, was launched. On April 1, 2014, RIKEN concluded that Obokata had falsified data to obtain her results. On June 4, 2014, Obokata agreed to retract the papers. On August 5, 2014, Yoshiki Sasai—Obokata's supervisor at RIKEN and one of the coauthors on the STAP cell papers—was found dead at a RIKEN facility after an apparent suicide by hanging. STAP would have been a radically simpler method of stem cell generation than previously researched methods as it requires neither nuclear transfer nor the introduction of transcription factors. Overview Haruko Obokata claimed that STAP cells were produced by exposing CD45+ murine spleen cells to certain stresses including an acidic medium with a pH of 5.7 for half an hour. Following this treatment, the cells were verified to be pluripotent by observing increasing levels of Oct-4 (a transcription factor expressed in embryonic stem cells) over the following week using an Oct4-GFP transgene. On average only 25% of cells survived the acid treatment, but over 50% of those that survived converted to Oct4-GFP+CD45− pluripotent cells. The researchers also claimed that treatment with bacterial toxins or physical stress were conducive to the acquisition of pluripotent markers. STAP cells injected into mouse embryos grew into a variety of tissues and organs found throughout the body. According to the researchers, the chimaeric mice "[appeared] to be healthy, fertile, and normal" after one-to-two years of observation. Additionally, these mice produced healthy offspring, thereby demonstrating germline transmission which is "a strict criterion for pluripotency as well as genetic and epigenetic normality." STAP cells were supposedly able to differentiate into placental cells, meaning they would be more potent than embryonic stem cells or induced pluripotent stem cells (iPS). It was not clear why ordinary cells do not convert into stem cells when subjected to similar stimuli under ordinary conditions, such as acidity in the body; Obokata et al. suggested that in vivo