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Old 13 May 2011, 09:13 PM
evidenceguy
 
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Default 50 million tons of HeLa cells?

I've recently seen a lot of references to a questionable idea presented by Rebecca Skloot in her otherwise excellent book, "The Immortal Life of Henrietta Lacks". Ms Skloot states that if you could take all the cells cultured from the HeLa cell line and pile them onto a scale they would weigh 50 million metric tons, which is as much as 100 Empire State Buildings. ("HeLa" refers to a cell line taken from the late Henrietta Lacks, an African American woman who had a sample of a tumor removed without her consent in 1951. These cells were then cultured and became the first "immortal" cell line.)

Although I don't want to nit-pick about a very well written and important book this figure of 50 million tons has been repeated over and over again, and it seems to be backed up by only one email that Ms Skloot received from a prominent scientist named Leonard Hayflick, who made a statement that, I think, Ms Skloot simply misinterpreted. And from here the idea took on a life of its own, and became more and more authoritative as it was repeated over and over again.

This is a quote from the "notes" section of Ms Skloot's book, which she uses to back up the 50 million tons figure.

"The estimate of the possible weight of HeLa cells comes from Leonard Hayflick, who calculated the greatest possible weight potential of a normal human cell strain as 20 million metric tons and says HeLa’s potential would be “infinitely greater” since it’s not bound by the Hayflick limit. As Hayflick wrote to me in an email: “If we were to grow HeLa for just 50 population doublings it would yield 50 million metric tons if all the cells were saved. Clearly that is impractical to do.” "

Notice that nothing Hayflick says here implies that he was trying to make an estimate of the number of HeLa cells that have actually been grown.

The "Hayflick limit" that Ms Skloot refers to is based on the observation that normal, non-cancerous cells can only reproduce about 50 times before they lose the ability to reproduce further. And when Hayflick refers to the astounding output that would result from 50 population doublings he is talking about the strangely counter-intuitive result of a geometric progression.

For example, if I had a chess board and I offered to give someone 1 penny for the first square on the board, and two pennies for the second square, and four pennies for the third square, and then 8 pennies, 16 pennies, 32 pennies, etc, by the time I reached the last square on the board I would owe vastly more money than exists in the world. And the same is true if someone doubles the number of cells in a culture, and then doubles it again, and again, etc. Even if they start with only a fraction of a gram, say the weight of 2 or 3 grains of rice, and then they double this 50 times they will end up with tens of millions of tons of rice, or HeLa cells, or whatever. But of course it would be absurd to actually do this in the real world, and that's why Hayflick says, "Clearly that is impractical to do.” (Which is a huge understatement.)

But I don't think Ms Skloot understood this, and instead she assumed that Hayflick was making an estimate of the number of HeLa cells have actually been grown, or that he was showing how "easy" it would be to produce 50 million tons of HeLa cells, or whatever. I'm just not sure what she was thinking. But the result is that this virtually made up figure is now being repeated all over the internet and tv-land. And you can't really disagree with it because there are thousands of "references" that "back it up," and because it is undeniably true that vast amounts of HeLa cells have actually been grown - so who's to say that it isn't enough to fill 100 Empire State Buildings with 50 trillion petri dishes full of cells?!

I don't know if this fits the Snopes criteria for an urban legend, but I thought I would throw it out anyway.

If you're interested here's a link to a discussion I started at "Reddit/ Ask Science." http://www.reddit.com/r/askscience/c...ve_been_grown/ (The results were inconclusive, with one scientist agreeing with my criticism and one disagreeing.)

I would be interested to hear what anyone thinks about this.
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Old 22 May 2011, 11:19 AM
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Quote:
Originally Posted by evidenceguy View Post
"The estimate of the possible weight of HeLa cells comes from Leonard Hayflick, who calculated the greatest possible weight potential of a normal human cell strain as 20 million metric tons and says HeLa’s potential would be “infinitely greater” since it’s not bound by the Hayflick limit. As Hayflick wrote to me in an email: “If we were to grow HeLa for just 50 population doublings it would yield 50 million metric tons if all the cells were saved. Clearly that is impractical to do.” "
Thanks for posting that, Evidence Guy. Sounds like everything you'd need to discredit the idea that there are 50 million tons of HeLa cells is right there in Skloot's own note: It's just an example of how many there theoretically could be after a given amount of duplication.
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