John D. Gearhart (1943─2020)

John Gearhart, the developmental biologist who first derived human pluripotent stem cells from primordial germ cells, died on 27 May. He was 77. The discovery of one type of human pluripotent stem cell, along with the contemporaneous discovery of another type of human pluripotent stem cell by James Thomson, made it possible to grow human stem cells in a petri dish that could, in principle, develop into any body tissue. The implications for stem cell–based therapeutics were profound, as were concerns that biologists were going a step too far. John tackled the issues head on, speaking with the public, politicians, and the press with patience and determination. John spent his early years on a family farm in Pennsylvania's Allegheny Mountains. After his father passed away when John was 6, he was sent to a boarding school for orphans in Philadelphia. He obtained a B.S. in biology in 1964 from Pennsylvania State University and studied lilacs at the University of New Hampshire, earning an M.S. in genetics in 1966. He expanded his repertoire by studying Drosophila genetics at Cornell University in Ithaca, New York, earning his Ph.D. in 1970. As a postdoc in the lab of embryologist Beatrice Mintz, a pioneer in the development of mouse chimeras and transgenics, John began his work in the field of study that he would continue for the rest of his life. He took a professor position at the University of Maryland School of Medicine and then at Johns Hopkins University in Baltimore, Maryland, where he later became director of multiple research programs. John was a founding member of the International Society for Stem Cell Research. In 2008, he became a professor at the University of Pennsylvania School of Medicine and director of the school's Institute for Regenerative Medicine. The 1960s, when John began his career, were a golden time for mammalian embryology. Studies of odd testicular tumors (teratomas and teratocarcinomas) and their pluripotent stem cells, known as embryonal carcinoma cells, provided models for embryogenesis. The development of monoclonal antibodies to embryonal carcinoma cells allowed characterization and isolation of specific cell types. As a newly minted assistant professor, John initially focused on mouse genetic models of intellectual disability, but he later realized the need to generate human cells to better understand the condition. John's research was among many studies that led to the push for developing normal pluripotent stem cell lines. Biologists Martin Evans and Gail Martin made strides toward the goal when they independently succeeded in deriving the cells from peri-implantation mouse embryos. Biologist Brigid Hogan and I (P.J.D.) then demonstrated that pluripotent stem cells, called embryonic germ cells, could be formed from primordial germ cells in mice, suggesting a different way to make human stem cells. John, along with others attempting to develop human stem cells, had to obtain access to elusive human material and overcome the fear that developing such cells could evoke negative reactions. Motivated by the potential for such a discovery to shed light on conditions such as Down syndrome, John had no hesitation in moving forward. In 1998, he led the team that successfully developed human embryonic germ cells. With an intuitive understanding of the implications of stem cell research, John began asking questions about the ethical and moral issues involved even before his groundbreaking discovery. Once his landmark paper was published, he made the momentous career decision to step out of the lab and into the public sphere to talk to the world about the power and potential of stem cells. The remarkable span of topics John studied during his training was reflected in his ability to explain, discuss, and debate the issues from multiple perspectives. For years, he devoted himself to educating the public about what stem cells could and could not do. He made more than 100 trips to Washington, D.C., to lobby elected officials to fund their ethical use. John served as an important and rare example of a scientist dedicating his life to public service. He inspired many others in the stem cell field to do the same, arguing that it is our responsibility as scientists to explain the work to the public who funds it and to inform and educate those tasked with regulating it. John was guided by the classic medical dictum “first, do no harm.” His highest priority was making sure that potential clinical applications of pluripotent stem cells would be safe for patients. Yet his advocacy came at a personal risk. He received death threats and needed police protection during some of his first trips to the Capitol. John had a warm and welcoming presence and was generous in sharing research credit. He had a mischievous sense of humor and would roar with laughter as he told stories of pranks he pulled on fellow students in his university days. John and I (P.J.D.) collaborated prior to, and as colleagues at, Johns Hopkins. A friend and mentor, he was always excited to discuss research, and he encouraged me to join him in engaging the public and their representatives. I (K.S.Z.) worked most closely with John when I began at the Institute for Regenerative Medicine in 2009. I was humbled by his relentless advocacy for the stem cell field. He never missed a chance to strengthen it and expand its reach. John Gearhart was a generous, thoughtful person who left an indelible mark both on the stem cell field and on how science is communicated to the public. John was also a devoted father who would light up when talking about his two daughters. Despite his monumental contributions to research and science advocacy, we think he would like to be remembered as a man who cared about his treasured children. John showed that no matter what your scientific accomplishments, some things in life are more important.