Stem cell mistaken identity: who are you?

One of the biggest issues in the world of cellular medicine and also in cellular research is one of mistaken identity.

I’m talking about scientists, doctors, or others thinking that their cells are one type (say type X) when in reality the cells are something else (say type Y).

Or maybe the cells are some mixture of types X and Y.

If you as a scientist talk to your cells (yes, scientists really do this sometimes), you might quote rock group The Who and ask the cells, “Who are you?”

Some cells such as retinal pigmented epithelial cells (RPEs) or beating cardiac myocytes are hard to mistake as anything else because their appearance is so distinctive, but for many cell types things are not so clear. For most cell types, a cell is a cell is a cell at least in terms of how they look. Sure, there can be subtle differences apparent to the trained eye (e.g. I’ve been looking at cells in culture for about 25 years now), but often it is tough to tell when looking at millions of cells by light microscopy no matter who is looking.

In addition, you might have in your culture say 80-90% RPEs, myocytes or neurons (whatever your desired cell type might be), but hidden away in there might be other cell types that both you and (if you are doing clinical work) your patients do not want to be there.

You can do various things to try to maintain purity or get rid of heterogenous cell types such as clonal selection or doing flow sorting, but nothing is going to help deal with common problems such as culture cross-contamination, starting with cells that are heterogeneous to begin with, or differentiating a starting pure population of stem cells, a process that in most cases leads to much cellular diversity. From lab to lab and clinic to clinic, how different lab staff isolate and handle cells in distinct ways also can lead to unexpected cell types showing up.

If you are a cell biologist you might be confident that the cells that you are studying are one type when in fact they could be something else or again a mixture. Mistaken cell identity or contaminated cells are a growing concern.

This also gets at the larger question of how we know (or think we know) the identity of cells.

Appearance under the scope? Staining for markers? FACS for markers? Genomic and/or transcriptomic analysis? Functional behavior?

All of the above?

Cell cultures also change over time so even if you start out with the perfect culture after a week or two they will have changed. An important approach is to not grow your cells for too long or they will acquire mutations and changes in function.

Perhaps one of the other most important things to do is not work with multiple cell types in a tissue culture hood simultaneously. There may be more pressure to do that in a predatory clinical lab focused on profit.  If you are working with stem cells you can also

You could end up spending most of your budget just being sure you have the right and most pure cells without evening getting to the point of studying their functions or using them clinically, whatever your goal may be. There has to be a happy middle ground, which today probably means devoting at least relatively more time and resources to being aware of your cells than you have in the past. Genetic tools may be helpful in that regard.

Cases of mistaken cellular identity are probably more common than we all think and they are really bad for both science and cellular medicine.