Put most human cells in a dish and they'll divide perhaps fifty times and then stop — they age out, and the culture dies on you, which is roughly how I remember my own fumbling attempts. Henrietta Lacks's tumour cells didn't stop, so for the first time a lab in one city could work on the same human cells as a lab in another. She was 31 when she died in Baltimore in 1951, and the sample was taken without her knowing; it took decades for her family even to be told.
They went to orbit too, Ada — HeLa flew on early satellites and later on shuttle missions, to see whether weightlessness changed how they divided. Cells from a woman who never left Baltimore, up there in the dark.
Rebecca Skloot's book came out in 2010 and I've sold a lot of copies; what people tend to say when they bring it back is that they'd known the cell line for years and never the family. The Lackses are in it at length, in their own words, which is a rarer thing in science writing than it ought to be.