Originally, Stevens' work focused on studying the harmful health impacts of cigarette paper because of tobacco company grant to C.C. Little, the founder of The Jackson Laboratory.[4] However, in 1958 he examined a large testicular tumor on a mouse from the 129 strain and noticed it was composed of many kinds of tissues, including muscle, skin, bone, and hair.[4] Over time, Stevens observed that these tumors, known as teratocarcinomas or teratomas, produced not only this variety of tissue types but also groups of undifferentiated cells with the capacity to grow into a wide range of tissue types. In 1970, Stevens noticed that the cell populations he was studying that gave rise to teratomas were very similar to the cells of very early embryos.[5] Stevens called these cell types "pluripotentembryonic stem cells." In order to study this phenomenon, Stevens selectively bred strain 129 to select for the teratoma tendency. Normally, such cancers are very rare but in Stevens’ new mouse strain, they were present in 1 out of every 10 mice.[6]Beatrice Mintz and Karl Illmensee, visited Stevens to learn his techniques and use his 129 mice bred for a high rate of teratomas and used these techniques to demonstrate that the embryonic stem cells could develop not only into teratomas but also into full organisms.[7] This work was foundational in the field of embryonic stem cells and stem cell research.
Stevens' later studies focused on developing mouse models for the testing of chemotherapeutic drugs. and retired from the Laboratory in 1989.[1][2] In 2015, at the age of 94, he died of congestive respiratory failure.[1]
^Stevens, Leroy C. (March 1970). "The development of transplantable teratocarcinomas from intratesticular grafts of pre- and postimplantation mouse embryos". Developmental Biology. 21 (3): 364–382. doi:10.1016/0012-1606(70)90130-2. PMID5436899.
