The Differentiator

JangoCell Science Updates to Enlighten and Entertain

Not all passages are created equal. Part 2.

The Differentiator JangoCell Science Updates to Enlighten and Entertain Not all passages are created equal. Part 2: Double, double, toil and trouble. A big challenge for consumers of commercially available cell products is finding cells that will continue to proliferate or expand after purchase so that they can continue to be used for experimentation, therefore researchers often look for the lowest passage number possible [1-3]. However, as a customer you have no idea how many population doublings your purchased cells may have gone through before they arrive in your laboratory based simply on passage number. Are you sure that the cells labeled as “passage 1” have gone through fewer population doublings than cells labeled as “passage 2”? Manufacturers may be calling a population of cells “passage 1” even though they have gone through a significant portion of their useful doubling potential before they get to your bench. This begs the question, is passage number still the best metric for determining which cells to purchase for your experiment? As we discussed in Part 1 of this series, When to Start the Clock, some commercial manufacturers wait to designate passage zero until after cells have been isolated from primary tissues, which means that they are excluding several population doublings in their calculations of cellular age. While important, the proper timing for designation of passage zero is not the only determinative factor in assessing the accurate age of commercially purchased cells. Other factors impact how many times a population of cells has doubled before they get to your lab, which in turn impacts how long they will continue to proliferate and can reliably be used for experimentation. Think about the step-by-step process involved in passaging cells. Every time a cell divides into two daughter cells, it is called ‘doubling.’ When a total population of

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Not all passages are created equal. Part 1.

The Differentiator JangoCell Science Updates to Enlighten and Entertain Not all passages are created equal. Part 1: When to start the clock. Imagine you’re a researcher shopping for cells for your next experiment. You intend to expand these cells in culture. What do you look for when comparing cells from different commercial suppliers? We’re willing to bet that “passage number” is among your criteria to determine the best cell line for your purposes, and that you would prefer a cell line at the lowest possible passage. Luckily, your putative cell suppliers are selling all of their products at “passage 1” or “passage 2.” Depending on cell type, you might even find some products advertising “passage 0.” You must feel relieved knowing that senescence of these cells is a long way away. But wait. How can so many commercial suppliers produce so many cells at passage 1, when we know the cells would have been expanded after isolation in large enough quantities to be ready to sell? Do you know whether a “passage 1” cell line has undergone fewer population doublings than a “passage 2” cell line? Are you confident that all commercial cell suppliers even count passages in the same way? That you’re comparing apples to apples? A close examination of product descriptions for competing cell merchants makes it clear that there are some stark differences in advertised passage numbers. Many resources establish the “standard” definition of passage number and how to calculate it for cell cultures [1-3]. Such standards, however, are not sufficient to guarantee that you, the consumer, have enough information to judge different cell lines using passage number alone. For instance, there is no clear indication as to when cells should be labeled as “passage 0” when coming from primary tissues, nor how many prior population doublings

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