# How many generations of cells could now exist from a single sample taken in 1972?March 6, 2012 11:51 AM   Subscribe

If a sample of cells was taken in 1972, reproduced in laboratory by cell division to create a cell line used in science today based originally on the sample, what "generation" of cell would be used today, and how far back in history BC/E would a comparable human generation be? Is that even calculable?

HEK293 is in the news, a sampling taken from an aborted fetus in ~1972 (who presumably would have been aborted anyway and discarded) that created a cell line called HEK293 that is used in science labs around the country today.

If we were to say, "that would be like calling you the same person as your great-great-great(1.0x10^z)-grandfather," what might that number be? Would it not be absurdly astronomical?
posted by Quarter Pincher to Science & Nature (12 answers total)

Well, it's not really like saying that, it's like saying that even though you had an entirely different set of skin cells when you were born than you do right now, you are still the same person. Or that your blood is made up of none of the cells that were there 6 months ago, but is still your blood, and was still your blood 6 months ago. Our cells divide all the time, but that doesn't make us a new person every time one of our cells divide, that's not how it works -- some of our cells divide as or more often than this line does (though some do much slower).

That said, this article says that the cell division rate is 24-36 hours, so assuming you started with 1 cell, and did not affect any of the cells with temperature changes of any sort, or with other agents that change the rate, or did anything else to them but let them sit in an ideal environment... there were 350,640 hours between 1/1/1972 and 1/1/2012, and that's 11,688 periods of 30 hours (halfway in between that cell division rate), so, you know, that's how many generations of daughter cells there might have been, but the analogy doesn't really make much sense.
posted by brainmouse at 12:01 PM on March 6, 2012

I can't answer the question directly, but will point out that the vast majority of commercially available cell lines are stored frozen to keep passage numbers as low as possible. Grow up a bunch, freeze at early passage number, clone and sell the remaining, use the frozen cells as backup stock. If anything goes wrong with what you are selling, you thaw out one of the early aliquots and start over.

So it isn't like the cells are alive and growing the entire time. Just when more is needed.
posted by caution live frogs at 12:04 PM on March 6, 2012 [3 favorites]

Hmm... Half a million years, give or take? Assuming the cells divide about once per day for 40 years and that a human generation is 30 years long.

(I should note that whatever cells are being used today have not gone through that many generations. Typical numbers for cell lines would be more like 100-200 passages, and being super-generous wouldn't be more than 1000 generations. Too much genetic drift, otherwise.)
posted by tchemgrrl at 12:05 PM on March 6, 2012

It's at home and I'm at work, but The Immortal Life of Henrietta Lacks goes through some of these exact calculations for you. Check it out.
posted by gerryblog at 12:31 PM on March 6, 2012 [3 favorites]

HEK293 has a doubling time of approximately 34 hours. From 1972 to 2012 is 40 years or 14,610 days. 14610*(24/34) gives about 10,313 generations.
posted by exogenous at 12:48 PM on March 6, 2012 [1 favorite]

On the other hand, if it was continuously passaged since then, the line would have hit the Hayflick limit a looong time ago.

I have some HEK293T cells that I inherited at "P9," and I'm down to one tube of P10 and a bunch of P12s sitting in freezing media in a vapour-phase liquid nitrogen tank.

I'm not sure what the actual passage number would be if you ordered some HEK cells from ATCC today.
posted by porpoise at 12:56 PM on March 6, 2012 [2 favorites]

Immortalized cells lines like HEK293 cancer cells aren't subject to the Hayflick limit (this is also noted in the Wiki article). When I did mammalian cell culture with HEK293, we never bothered counting their passage number and didn't have any problems in that regard.
posted by exogenous at 1:24 PM on March 6, 2012

exogenous - I've had issues with higher passage number cells. Depends on what you use them for, I guess. I do a lot of imaging and there are definite morphological changes once you get into the upper 20's along with lower transfection efficiency (or more likely, higher variability between cells to express stuff driven by different promoters). They become unreliable.

Could they continue to grow indefinitely? I haven't tried. The culture loses its usefulness to me long before P30. Trypsin, media, and tissue culture plates (I re-use them for 3 passages before transferring to a fresh plate) all cost money.
posted by porpoise at 8:17 PM on March 6, 2012

Whatever the number is for HEK293, it will be even greater for HeLa, which has had a 20 year head start. I think it was the HeLa cell line that was first used to demonstrate that replicative senesence doesn't apply for immortalized cell lines. They still change with time, of course, which is how we get the different strains of cell line and why, as caution live frogs points out, we freeze and thaw cell lines to minimise genetic drift.

Thus, although it's pretty much impossible to actually work out how many generations have occurred for a given cell line (unless you've got 40+ years of really, really good bookkeeping), the upper limit will be around 10,000 (exogenous' answer). Since a short-yet-reasonable human generation could be considered as 20 years, this takes you to 200,000 years BCE for the "human equivalence" part of your question. That was about the time anatomically modern humans originated in Africa.

While we're no the topic of serially passaging, I would like to point out that Albert Calmette and Camille GuĂ©rin serially passaged their strain of tubercle bacillus for 13 years before producing the BCG strain. Needless to say, it underwent a lot of change during this time!
posted by kisch mokusch at 3:05 AM on March 7, 2012

Oh, to clarify, a passage is typically around 4-5 (ish) doublings, so a P30 batch of HEK293 cells are about 120-150+ divisions from when the cell line was originally shipped out (after who knows how many original divisions).

So, immortalized cell lines definitely exceed the conventional Hayflick limit, but are still subject to senescence.
posted by porpoise at 8:15 AM on March 7, 2012

So, immortalized cell lines definitely exceed the conventional Hayflick limit, but are still subject to senescence.

Are you still speaking from your own experience, or can you point to some literature that says that immortalized cell lines inevitably become senescent? Because you seem to be saying several different things in this thread.

My understanding is that immortalized cells will divide without limit so long as culture conditions are maintained. (Though as others have said, a line isolated and identified in 19xx has not necessarily been grown continuously since then---it may have spent some time frozen and thus not proliferating.)
posted by Mapes at 10:33 AM on March 7, 2012

As an aside, you might be interested in Richard Lenskis work. He has deliberately evolving E. coli for over 50,000 generations - see the counter on this page.
posted by scodger at 11:34 AM on March 7, 2012

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