By Cheryl Lancaster, University of Durham
“Today, it is widely held that Stevens’s [sic] lucky break and all his science thereafter went a long way toward launching the field of stem cell biology.” (Parson 2004, 26)
Teratomas – tumours of the testes or ovaries – can develop several tissue types in various stages of differentiation, including hair, teeth and muscle, for example. These tumours were therefore identified as potentially useful in studying early development (given the ethical & technical difficulties in examining development in the actual foetus).
In the 1950s, Leroy Stevens, working at The Roscoe B Jackson Memorial Laboratory (JAX), identified an inbred strain of mice particularly prone to developing testicular teratomas, and, alongside Don Varnum (a technician working in Stevens’ laboratory), developed these ‘strain 129’ mice to study these tumours.
“We killed it, and looked at the testes, and they had strange things inside.” (Varnum, speaking to Ricki Lewis; Lewis 2001, 132)
Stevens and his colleagues observed that, when transplanted, tumour formation continued. Stevens believed that this was due to ‘pluripotent embryonal cells’ (Stevens and Little 1954).
Barry Pierce, a recent medical graduate specialising in pathology, has since suggested that he became interested in teratomas when he was unable to treat a young patient with a testicular teratoma (Pierce 1993). This led him to Frank Dixon, who had published an article on testicular teratomas in adults (Dixon and Moore 1952). Pierce joined Dixon (by then Professor of Pathology at the University of Pittsburgh) in 1955, which included a period working with Stevens at JAX. Here, Pierce developed ‘embryoid bodies’ (Stevens, 1960).
To maintain tumour cells, Stevens would inject them into the peritoneal cavity (a fluid-filled space between the skin and the gut) of mice. However, he and Pierce observed that these produced embryoid bodies – clusters of cells that appear extremely similar to the normal developing embryo. The maintenance of teratoma cells in ascites tumours would allow the cells to be moved to laboratories around the world, and many of those interested in studying the embryo would obtain teratoma cells from Stevens and JAX in this way.
As had been proposed fifty years earlier (Azkanazy 1907), Dixon and Pierce suggested that the formation of embryoid bodies must have been due to the presence of a stem cell population (Pierce and Dixon 1959a; Pierce and Dixon 1959b). Individual teratoma cells, left for longer periods in the peritoneal cavity, could develop tumours containing a variety of cell types. Taking this work a stage further, Pierce worked alongside Lewis Kleinsmith to isolate individual teratoma cells, and transplant them into otherwise healthy mice. In total, eleven tissue types were observed (Kleinsmith and Pierce 1964).
The Nobel prize-winning biologist Martin Evans was told about Stevens’ teratomas as a young researcher. The teratoma cells seemed ideal for his research into studying genes in development – they would grow quickly, and produce a variety of cell types. Stevens sent Evans (then at University College London) mice containing the ascites tumours, which Evans developed into cell lines – cells that could be grown in dishes in the laboratory (Evans 1972). Gail Martin (an American cell biologist relocating to England with her husband) began work with Evans soon after, and helped to isolate the stem cells of these cultures (Martin and Evans 1974), which could be induced to become various other cell types (Martin and Evans 1975a; Martin and Evans 1975b). Martin suggested that there was little difference between these embryonal carcinoma cells (ECCs) and embryonic cells:
“There are at least two possible ways in which embryonal carcinoma cells could arise from their progenitor cell types. First, some malignant change occurs in the progenitor cell types. Second, that embryonal carcinoma cells are normal undifferentiated embryonic cells (or primordial germ cells) which behave abnormally because they are not in their normal environment” (Martin 1975, 240).
Using her skills in cell biology, Martin worked on injecting ECCs into developing mouse blastocysts (clusters of cells that form at the beginning of embryo formation). When injected into surrogate mice, these embryos developed normally. Live births were achieved, and some tissues of these mice were found to have developed from the injected teratoma cells. Martin also observed that if a normal blastocyst was transplanted elsewhere in the body, teratomas would form. Using the techniques she had learned manipulating these blastocysts, Martin attempted to ‘split’ the blastocyst and grow the isolated cells from it in culture. Martin found that the cells isolated from the blastocyst could be cultured. These were mouse embryonic stem cells, grown in the laboratory for the first time.
During this period, Martin Evans moved to Cambridge University, where he met Matthew Kaufman working in the Anatomy Department. Kaufman and Evans collected unfertilised eggs from strain 129 mice, and activated them to develop embryos without being fertilised; these eggs were then transferred to surrogate mice. After 4-5 days, the blastocysts were removed and grown in the laboratory. Evans and Kaufman named the cells they had isolated after themselves (‘EK cells’), which were tested and defined as ‘pluripotential embryo-derived’ cells (Kaufman et al. 1984, 75); Evans later also stated that these were likely to be the same cells Martin had isolated in 1980.
This short story then clearly demonstrates how research into a rare tumour eventually allowed the isolation of embryonic stem cells. The techniques and expertise required were not available prior to 1980; it was with considerable certainty that biologists accepted that the first cells of the developing embryo must be both pluripotent and self-replicating (i.e. stem cells), however it was not until the pioneering work of Martin Evans and Gail Martin that isolation and culture of these cells became a reality.
Cheryl Lancaster is a researcher in the Centre for the History of Medicine and Disease at the University of Durham. This blog post is based on the paper , “How tetratomas became embryonic stem cells: an example of interdisciplinary knowledge production“ which she is due to give at iCHSTM as part of symposium T153, “New Themes and approaches in science studies -Interdisciplinarity” on Thursday 25th July
You can follow Cheryl on Twitter @Stem_Cell_Hist
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