Leroy C. Stevens

Leroy C. Stevens (1920–2015) was a scientist at The Jackson Laboratory acknowledged as an early pioneer of embryonic stem cell research. When he returned to the US, he completed his Ph.D. in embryology from the University of Rochester in 1952 studying under Johannes Holtfreter. He subsequently joined The Jackson Laboratory as a postdoctoral laboratory Fellow in 1953. 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. Stevens called these cell types "pluripotent embryonic 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. 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. 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.