Stanley Paul Leibo (1937–2014): scientist, mentor and friend

On Tuesday, March 25, 2014, the world lost Stanley Leibo to cancer. Stanley was a pioneer and scientific giant in the field of cryobiology. To legions of his friends, colleagues, collaborators, and students throughout the world, his death is an immense professional and personal loss. He was predeceased by his wife Bette and is survived by his daughter Beth of Austin, Texas, and by his son Jonathan of San Diego, California.

Stanley was born in Pawtucket, Rhode Island, USA, on April 8, 1937. He attended high school in Providence, and then received a Bachelor of Arts degree (1959) from Brown University, followed by an M.Sc. (1961) from the University of Vermont, and M.A. (1962) and Ph.D. (1963) from Princeton University. As part of his graduate training, he joined Peter Mazur at the Oak Ridge National Laboratory in Tennessee in 1962 to begin his life-long career of the study of cryopreservation of living organisms. In 1972, David Whittingham, a noted embryologist, travelled to Oak Ridge to collaborate with Stanley and Peter Mazur to attempt to cryopreserve mouse embryos. They succeeded in doing so, resulting in the birth of the first mammalian offspring from frozen–thawed embryos. The report of their efforts () is a landmark publication in mammalian biology.

In 1981, Stanley joined Rio Vista International in San Antonio, Texas as Vice President, Research and Development. While there, he developed and perfected methods for the cryopreservation of cattle embryos, including a one-step procedure for thawing and transfer. These accomplishments revolutionized animal breeding because it became possible to store and disseminate the genetic traits of elite females, especially for international export. By Stanley’s own estimate, over 10 million calves have been born from frozen–thawed embryos. Of particular interest during his time in San Antonio was the setting in which he worked: Rio Vista was a functional Texas cattle ranch. True, it included a well-equipped laboratory dedicated to bovine embryo cryopreservation and transfer (and one that subsequently attracted William F. Rall as a fellow staff scientist and collaborator) but it was a working ranch, nonetheless, situated in a rural setting to the west of San Antonio, miles from the nearest academic institution or comprehensive science library. Stanley’s solution was simple – he brought the academic world to the ranch and took it upon himself to contact all local universities, the medical school and graduate school at the University of Texas Health Science Center, the San Antonio Zoo and every veterinarian engaged in embryo transfer within a three county area. An invitation was made to all interested parties to meet on Friday afternoon, once a month, at Rio Vista to discuss any aspect of reproduction and cryobiology that the group desired. Those discussions invariably continued well past sunset and were legendary. Stanley was an organizer and artful moderator of all things embryological.

Stanley moved to the Baylor College of Medicine, Houston, Texas in 1988 to pursue fundamental studies of cryobiology, culminating in a collaboration with Robert McWilliams and William Gibbons that defined fundamental osmotic responses of both mouse and human ova to a variety of sugars, both mono- and disaccharides (). In 1991, Keith Betteridge attracted Stanley to join the Animal Biotechnology Embryo Laboratory (ABEL) at the University of Guelph where he resumed his work on cattle embryos, continued his work on mouse embryos, and developed methods for the cryopreservation of mouse sperm. Upon Keith’s retirement, Stanley became the Director of ABEL. In 1998, Stanley was awarded the Doris Zemurray Stone Chair in Reproductive Biology at the University of New Orleans (UNO) with a co-appointment to the Audubon Institute Center for Research of Endangered Species. He remained at the University of New Orleans until his death, and his work there included studies aimed toward the preservation of endangered species.

Stanley’s publications include 100 refereed publications, 23 book chapters, 70 refereed abstracts, and over 100 other conference proceeding and abstracts. He participated in 183 scientific meetings, many as an invited keynote speaker. He also held two patents on methods and apparatus for embryo transfer. In addition to his work with mouse and cattle embryos, his publications include studies of bacteriophage; catfish sperm; cattle sperm, fetal ovarian germ cells, oocytes, fibroblasts (for cloning), and red blood cells; cheetah sperm; Chinese hamster cells; dog sperm, oocytes, and fibroblasts; cat spermatogonial stem cells, sperm, ovarian tissue, ovarian follicles, oocytes, and embryos; Drosophila melanogaster embryos; hamster oocytes; horse ovarian tissue and embryos; human sperm, oocytes, and embryos; mouse bone marrow stem cells, sperm, and oocytes; pig embryos; rabbit zygotes; red alga Chromoprotein phycoerythrin; Rhesus monkey sperm, ovarian tissue, and oocytes; and sheep sperm and embryos. In addition to investigating low temperature phenomena across systematic kingdoms and phyla throughout his career, Stanley remained engaged in the longitudinal evolution of cryobiological applications to the reproductive biology of animals and humans. From the fundamental proof of principle in 1972, he subsequently described improvements to warming protocols following equilibrium cooling, evaluated the effects of various non-permeating and permeating cryoprotectant additives, studied the effects of rate phenomena upon bovine embryo cryopreservation and investigated novel platforms and processes facilitating successful vitrification of bovine oocytes. His collaborations with Masashige Kuwayama of Japan were instrumental in advancing human oocyte vitrification to the status it currently enjoys in human assisted reproductive technology. His work with the cryopreservation of the spermatozoa of mice and a variety of domestic animals species is likewise considered landmark.

Stanley was a member of nine professional and scientific societies. He served as President for the Society for Cryobiology from 1985 to 1987 and as a member of the Board of Governors from 1989 to 1995. In addition, he was President of the International Embryo Transfer Society from 1989 to 1990, serving on the Board of Governors from 1990 to 1991. His fundamental contributions to our understanding of low temperature biology, plus his altruism to fellow scientists and students alike, were recognized by his peers in the form of several prestigious awards. In 1996, he became an Honorary Life Member of the American Embryo Transfer Association. In 2005, he was elected Fellow of the Society for Cryobiology, an honorary appointment “to recognize exemplary contributions to the discipline of cryobiology and service to the Society”. The following year he was the Spallanzani Lecturer at the 10th International Symposium on Spermatology held in Madrid, Spain. In January 2009, his universal contributions to animal reproductive biology were acknowledged when he was awarded the Pioneer Award by the International Embryo Transfer Society.

Stanley was an editorial board member for eight journals, and reviewed papers for 15 others. He also reviewed 39 grant applications for major funding agencies. He directed 12 graduate students, and supervised the work of 16 post-doctoral fellows and visiting scientists. He taught five different courses at the University of Guelph, and 18 at the University of New Orleans. Stanley will be awarded the University of New Orleans College of Sciences Undergraduate Teaching Award posthumously. Equally important, he disseminated his expertise as a faculty member in 18 different training programmes. Among these, he taught the Jackson Laboratory Course on Mouse Embryo Cryopreservation 37 times.

Stanley’s contribution to cryobiology and reproductive biology can only be described as enormous and awe-inspiring. has been cited almost 900 times, including 11 citations this year. However, while the direct effects of Stanley’s work may be appreciated from his publications and from the citations of those publications, the secondary, indirect effects, are much more far-reaching, and, unfortunately, largely immeasurable. Because of his work, millions of mouse embryos have been frozen for research purposes, comprising untold numbers of unique genetic strains. How many diseases will be cured or eased by molecular and genetic studies using those embryos? What scientific and economic advances will be made in animal breeding because of his work on cattle embryos? How many species will be saved from extinction because he led the way to the cryopreservation of the germplasm of exotic species? How many human families will be created from frozen embryos? It is both sad and wonderful that many of those advances have and will be made by and for people who don’t know that Stanley Leibo made them possible.

Given his visionary nature, it was only fitting that he was identified by the U.S. National Institutes of Health as an advisory committee member to consider “Achieving High Throughput Repositories for Biomedical Germplasm Preservation” in 2007. By contrast, although Stanley saw biology as the unique continuum it is, he never saw himself as unique or a visionary. For those of us lucky enough to have known Stanley, his creative genius and scientific accomplishments were equaled by his warm and sharing personality. Stanley was both a gentleman in the classic sense, and a gentle man. He took his work very seriously but he never took himself seriously. He was always willing to share his expertise and knowledge with anyone who asked. No one could make a short story long like Stanley could, but his tangents and mental perambulations were always instructive and never boring. In many ways is difficult to separate what Stanley did from how he treated others. In our deep sadness at his loss, we console ourselves that we had the privilege to have known him.

Although perhaps unusual, we include Figure 1 as a testament to his memory. To our recollection, Stanley never discussed his science without referring to a drawing or a graph. The graph shows the proportion of live births from frozen human IVF embryos as a proportion of live births from all IVF embryos in the United States from 1996 to 2011 (data taken from http://www.cdc.gov/art/ARTReports.htm). From 2000 to 2011, that proportion has increased from 12% to 27%. It is becoming increasingly clear that transferring frozen embryos is better than transferring fresh embryos, and so that proportion will continue to increase, perhaps to near 100%. In fact, in Japan, the proportion of live births from frozen IVF embryos is already over 65% (). One can say that Stanley not only contributed to the practice of human assisted reproductive technology, but also made a major contribution to its improvement.

Our sympathies to his family and to all who knew him. A great man is gone, but he will live on forever.