In early 1951, a poor black tobacco farmer named Henrietta Lacks went to a hospital in the US city of Baltimore with acute abdominal pain. She would die eight months later of cervical cancer, aged 31.
"I had seen probably 1,000 patients with cancer of the cervix," Howard Jones, the first physician to see her at the Johns Hopkins Hospital, later wrote. The tumour that Lacks had was different, though, he said - as big as a 25-cent piece and purple and soft, not hard like most cervical tumours.
Sixty-five years ago, in February 1951, Jones took a tissue sample from the tumour and gave it to the laboratory run by his colleague Dr George Gey and Gey's wife and research assistant, Margaret.
They placed it in a petri dish medium of chicken plasma, bovine embryo extract and human placental cord serum, and put the dish in a refrigerator, expecting the tissue to soon die, because no one had grown human cells in the laboratory for more than a few weeks.
But the cells - which Margaret Gey labelled "HeLa," for "Henrietta Lacks" - kept multiplying. Their number doubled overnight. Soon there were millions of them.
"This is a major landmark in the history of research," said Elisabeth Schwarz, a biologist at the German Cancer Research Centre (DKFZ) in Heidelberg. "It was a scientific sensation."
Extensive medical research on human cells was now possible for the first time. George Gey sent HeLa freely to laboratories around the world, where scientists combined the cells with those of mice and chickens and analyzed the effects of cancer, polio and AIDS on them.
Soon HeLa was being used for research in molecular biology and cell biology too. It has never died out. The cell line from Henrietta Lacks became standard in every laboratory and remains so to this day.
And despite the hundreds of other human cell lines now available to researchers, HeLa is one of the most coveted, Schwarz said.
"HeLa cells grow very unproblematically and are extremely robust," she noted. "A cell divides in 24 hours - in other cell lines it takes much longer."
Scientists still don't know exactly why HeLa cells are so vigorous - so much so, in fact, that they sometimes attack and overrun other cell lines, rendering them useless for research.
Harald zur Hausen, the DKFZ's scientific director from 1983 to 2003, detected the human papillomavirus types HPV16 and HPV18 in the HeLa line.
This immediately raised the question whether the virus's DNA played an important role in the development of cervical tumours, said Schwarz, who was zur Hausen's assistant at the time. After years of research beginning in the 1970s, he concluded that it did.
An HPV vaccine was approved in 2006, and zur Hausen received the Nobel Prize in Medicine two years later.
As for Henrietta Lacks, no one had even asked her consent to use her tissue sample. It was standard practice at the time to just take such things as of right, writes science journalist Rebecca Skloot in her book The Immortality of Henrietta Lacks.
Her children - she was a mother of five - only found out some 20 years later that cells from their mother were still living, which was a shock particularly for her daughter Deborah.
"Deborah’s family tended toward preaching, faith healings, and sometimes voodoo. She grew up in a black neighbourhood that was one of the poorest and most dangerous in the country," Skloot said. "Deborah believed Henrietta’s spirit lived on in her cells."
The children say they have never received any money for their mother's role in helping to combat cervical cancer, and that public acknowledgement of that role has come slowly.
Several years ago, a commemorative plaque was placed in the Virginia cemetery where Lacks is thought to be buried. In 2011 she was posthumously awarded an honorary doctorate in public service by Morgan State University in Baltimore.
"The story of Henrietta Lacks gave the impetus for asking consent before human material is used for research purposes," Schwarz said.