that holds the keys to understanding cancer, virology, and genetics.

Luckily for us,

such a thing exists in the form of trillions upon trillions

of human lab-grown cells called HeLa.

Let's take a step back for a second.

Scientists grow human cells in the lab to study how they function,

understand how diseases develop,

and test new treatments without endangering patients.

To make sure that they can repeat these experiments over and over,

and compare the results with other scientists,

they need huge populations of identical cells

that can duplicate themselves faithfully for years,

but until 1951, all human cell lines that researchers tried to grow

had died after a few days.

Then a John Hopkins scientist named George Gey

received a sample of a strange looking tumor:

dark purple, shiny, jelly-like.

This sample was special.

Some of its cells just kept dividing,

and dividing,

and dividing.

When individual cells died,

generations of copies took their place and thrived.

The result was an endless source of identical cells that's still around today.

The very first immortal human cell line.

Gey labeled it "HeLa" after the patient with the unusual tumor, Henrietta Lacks.

Born on a tobacco farm in Virginia,

she lived in Baltimore with her husband and five children.

She died of aggressive cervical cancer

a few months after her tumorous cells were harvested,

and she never knew about them.

So what's so special about the cells from Henrietta Lacks

that lets them survive when other cell lines die?

The short answer is we don't entirely know.

Normal human cells have built-in control mechanisms.

They can divide about 50 times before they self destruct

in a process called apoptosis.

This prevents the propagation of genetic errors

that creep in after repeated rounds of division.

But cancer cells ignore these signals, dividing indefinitely

and crowding out normal cells.

Still, most cell lines eventually die off, especially outside the human body.

Not HeLa, though, and that's the part we can't yet explain.

Regardless, when Dr. Gey realized he had the first immortal line of human cells,

he sent samples to labs all over the world.

Soon the world's first cell production facility

was churning out 6 trillion HeLa cells a week,

and scientists put them to work in an ethically problematic way,

building careers and fortunes off of Henrietta's cells

without her or her family's consent, or even knowledge until decades later.

The polio epidemic was at its peak in the early 50s.

HeLa cells, which easily took up and replicated the virus,

allowed Jonas Salk to test his vaccine.

They've been used to study diseases,

including measles,

mumps,

HIV,

and ebola.

We know that human cells have 46 chromosomes

because a scientist working with HeLa discovered a chemcial

that makes chromosomes visible.

HeLa cells themselves actually have around 80 highly mutated chromosomes.

HeLa cells were the first to be cloned.

They've traveled to outer space.

Telomerase,

an enzyme that helps cancer cells evade destruction by repairing their DNA,

was discovered first in HeLa cells.

In an interesting turn of fate,

thanks to HeLa, we know that cervical cancer can be caused by a virus called HPV

and now there's a vaccine.

HeLa-fueled discoveries have filled thousands of scientific papers,

and that number is probably even higher than anyone knows.

HeLa cells are so resilient that they can travel on almost any surface:

a lab worker's hand,

a piece of dust,

invading cultures of other cells and taking over like weeds,

countless cures, patents and discoveries all made thanks to Henrieta Lacks.