A group of researchers believed that subjecting tissues to trauma could give ordinary cells stem-cell-like properties. Illustration by Chad Hagen

Yoshiki Sasai was known as “the brainmaker.” One of Japan’s foremost developmental biologists, he made discoveries that illuminated the formation of the embryonic nervous system, and, using stem cells, he grew the optic cup, parts of the cerebral cortex, and the rudiments of a cerebellum. Calm and precise in the lab, Sasai was cultivated and erudite outside it, with a reputation as a gracious host who escorted visiting colleagues to onsen spas and prepared sushi for lab parties. “There are not too many people in our field who like to discuss Goethe,” Christof Niehrs, a prominent biologist, told me. “His talks were exquisite. He was a perfectionist in whatever he did.”

In 2000, during a period of explosive growth in his field, Sasai helped found the Center for Developmental Biology, a branch of the prestigious, government-funded research institute Riken. C.D.B., based in Kobe, was staffed with ambitious scientists who, freed from teaching obligations and equipped with sophisticated laboratories, were expected to make significant discoveries, and publish them illustriously. At this, too, Sasai excelled, announcing his discoveries in major journals such as Nature and Cell, and keeping the center’s laboratories well funded by skillfully marketing their achievements. “He understood how to push the science,” Ken Cho, a friend and colleague of Sasai’s, told me. “He had that sixth sense.”

Several years ago, Sasai began to collaborate on a novel stem-cell technology being developed at C.D.B. The idea was so simple as to be heretical: ordinary cells could be turned into stem cells by subjecting them to profound stress. Few cells could survive the abuse, but those which did emerged transformed, apparently able to make any cell in the body. Sasai named the cells STAP, for stimulus-triggered acquisition of pluripotency.

Sasai and his colleagues announced STAP in January of 2014, in two simultaneous papers in Nature, the British journal that first published Watson and Crick’s double-helix model of DNA. The findings were exhilarating, suggesting an innate regenerative mechanism in the body. Austin Smith, a stem-cell scientist at the University of Cambridge, wrote a companion piece, touting the cells’ “unusually broad developmental potency.” Here, theoretically, was a never-ending supply of super-versatile custom stem cells, free of ethical baggage. By 2020, according to the consulting firm Frost & Sullivan, stem-cell therapies will be a forty-billion-dollar global industry. STAP seemed to be a bridge to long-held goals of patient-specific drug development, advanced disease modelling, and, ultimately, the ability to regenerate body parts without the risk of immune-system rejection. Sasai compared STAP to Copernicus’s reorganization of the cosmos. A financial windfall, if not a Nobel Prize, might await its discoverers.

The revolutionary behind the work was Haruko Obokata, a thirty-year-old postdoctoral researcher who was the first author on both papers. With the publications, Obokata—a stylish, self-possessed beauty, uncommonly adept at maneuvering in the mostly male world of Japanese science—was hailed as a maverick. “A brilliant new star has emerged in the science world,” an editorial in the Asahi Shimbun read. “This is a major discovery that could rewrite science textbooks.” As an outsider—young, female, and not an established stem-cell biologist—Obokata, the newspapers argued, was unhindered by conventional notions of what cells can and cannot do. Her fresh perspective, coupled with dogged work and natural genius, had conspired to create one of the great scientific breakthroughs of the twenty-first century.

The promises of stem-cell research lie at the core of human desires—to understand our origins and to cheat death—and there is a great deal of money and prestige at stake. It is a ruthlessly competitive field, susceptible to fantasy and correspondingly sensitive to bunglers. Human embryonic stem cells were first cultured in 1998; nearly twenty years later, basic assumptions about cell behavior are still routinely overturned. Andrew McMahon, a top researcher at the Broad Center for Regenerative Medicine and Stem Cell Research, at the University of Southern California, told me, “It’s not unusual to see something and not be able to explain it.” In reporting results, researchers must often craft a narrative to make sense of mysterious phenomena. What to ignore and what to privilege—that discernment can be the difference between brilliance and quackery, and between fame and obscurity.

Five months after publication, both STAP papers were retracted, under intense scrutiny and growing doubt about their validity. By that point, Riken had cited Obokata for research misconduct and charged her mentors with “heavy responsibility”; one of those mentors had implicated her in a fraud; she had been hospitalized for depression; a co-author had suffered a stress-related stroke; and an outside committee had recommended that Riken dismantle C.D.B.

Sasai may have felt the anguish most profoundly. Distracted in the lab, he seemed frail and diminished, and was being treated by a psychiatrist. Then, in August, 2014, a security guard found him hanged from a handrail in a stairwell at C.D.B., his shoes placed neatly on the steps. In an obituary, Edward De Robertis, who had been Sasai’s mentor at the University of California, Los Angeles, wrote, “Yoshiki was a man of rectitude and a scientist of high personal integrity.” De Robertis did not refer to STAP: the name was by then unmentionable. Talking to me on the phone, De Robertis said ruefully, “He got trapped.”

Thoroughly discredited, Obokata went into hiding for more than a year. At the end of January, though, after I had tried for months to reach her, she sent me a letter, her first engagement with a member of the media since the scandal. Soon afterward, she published a memoir in Japan, strenuously arguing that she had been misunderstood. “I feel a strong sense of responsibility for the STAP papers,” she wrote to me. “However, I want you to know I never wrote those papers to deceive anyone.” She insisted that STAP was real.

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It seemed that Sasai, too, never lost faith in the discovery, or in Obokata. According to the Japan Times, he left a note for her, which said, “Be sure to reproduce STAP cells.”

The idea behind STAP originated in Boston about fifteen years ago, in the lab of Charles Vacanti, who recently retired as the chairman of the anesthesiology department at Brigham and Women’s Hospital. Vacanti is in his mid-sixties, tall and stoop-shouldered, with short gray hair and an amiable tendency to credit his achievements to good luck. (His bad luck he attributes to ego and naïveté.) A lifelong tinkerer, and one of eight siblings, he spent his adolescence taking apart old cars with his brothers; he now has a collection that includes seventeen vintage motorcycles, most of which he restored himself. Vacanti’s father was a professor of dentistry, and his brothers Jay, Martin, and Frank are also physicians.

Chuck, as Vacanti is known, approaches his work with the trouble-shooter’s willingness to take a flyer. “If you don’t say something really stupid once in a while, you aren’t really pushing the envelope,” he says. In the late eighties, he was working at Mass General; his brother Jay, a liver-transplant surgeon at Children’s Hospital and a pioneer of tissue engineering, was struggling to grow a liver from cells seeded on a scaffold. Bored by the prospect of anesthesiology research, Chuck asked Jay if he could pitch in. He began to tinker, sometimes to outlandish effect, and often with a keen instinct for publicity. In the mid-nineties, he released a picture of a mouse with what appeared to be a human ear growing from its back. “Earmouse”—made by inserting an ear-shaped scaffold seeded with cow cells under the skin of a live mouse—became a sensational meme at the dawn of Internet Bizarre. Oprah covered it; Jay Leno called Chuck in the operating room. Later, after engineering a trachea for a fourteen-year-old girl with a life-threatening tumor, Chuck made a guest appearance on “Grey’s Anatomy.”