Dr. William T. Shearer, right, and Dr. Ralph D. Feiginfield field questions at a new conference about the death of David Vetter, the "Bubble Boy," in Houston, Texas, Feb. 23, 1984. (AP Photo/Ed ...

The death of Houston's famed "Bubble Boy" — the boy without an immune system — made headlines around the world. And it helped pave the way for a treatment that could save Sebastian's life.

Big Boy, all 1.2 million pounds of it, came rolling into Houston Friday afternoon. The four-cylinder steam engine was built in 1941, and is the last of 25 similar models still in existence.