The character of Ester Rivers is partially based off of Eunice Rivers who both had similar roles in the Tuskegee Experiments. Unlike the film where she is temporarily fired due to budget constraints, in real life she was one of the few (arguably the only) medical staff professional who worked on the experiments for its entire 40 year run. Furthermore, she was promoted past her nursing position, something that is only hinted at in the film.
The character of Quentin Smith is partially based off of Taliaferro Clark who both had similar roles in the Tuskegee Experiments. In the movie he is portrayed as a young up and coming prodigal medic whereas in real life he was already established by the time he came to help out with the Tuskegee Experiments. Furthermore, he was ruined after the experiments because of what he did whereas the film shows no indication of what happened to him after the experiments.
The characters of John Kent and Eugene Bellsen are both partially based off of Eugene Dibble who had similar roles in the Tuskegee Experiments.
The character of Lewis Shaw is partially based off of Herman Shaw who both had similar roles in the Tuskegee Experiments. In real life he managed to survive the experiments and died in 2000 whereas in the film he dies during the experiments are taking place.
The character of John Kent is partially based off of John Heller who both had similar roles in the Tuskegee Experiments. The main difference between them is the fact that in the film he portrayed as an African-American male in his 30's while in real life he was a Caucasian-American male in his late 40's to Early 50's when the experiments began.