David Phillip Vetter was born with X-linked severe combined immunodeficiency disorder, or X-SCID, and spent most of his life in an isolated sterile bubble to stay alive. X-SCID is a genetic disorder that causes a deficiency of protective immune cells that fight infections, which increases susceptibility to disease. Vetter’s weakened immune system meant that he would die if he encountered any bacteria, viruses, or other germs, so his doctors placed him in a sterile isolator, a plastic bubble that prevented germs from entering. Vetter was thus a germ-free human, meaning he developed in the absence of germ exposure. He grew up in his sterile isolator, earning him the nickname “Bubble Boy,” and lived there until his death in 1984 at age twelve. Researchers frequently studied Vetter’s development because he was one of the first individuals with X-SCID to survive over a year after birth. As one of the first germ-free humans, Vetter provided an opportunity for researchers to study what happens when a human develops without germs and his cells helped them determine the genetic cause of X-SCID.