How to Determine Cell Viability and Vitality
Many physicians and patients get pitched on amniotic and cord “stem cell” products based on a document that purports to show that these cells are “viable”. However, there’s much more to the story than a simple viability percentage. You need to know a lot more to determine if cells are vital and healthy.
What Is Cell Viability and Cell Vitality?
Viability simply means the percentage of cells that are living. Viability is not the same thing as cell vitality, so it doesn’t reveal the full story of a cell’s health. Let’s use you as an analogy for cells. Since you are reading this right now, you would be counted as alive, or viable, in a live/dead test. However, so would the guy at your local hospital in the ICU on his deathbed. In addition, that same live/dead test would count the 90-year-old across the street with severe Alzheimer’s and who can barely walk as viable. You get the point, viability doesn’t equal health.
How to Determine Cell Viability and Vitality
There are four assays that need to be performed to determine viability and vitality:
- Simple viability
- Cell proliferation
- Cell function
While the simple viability assay is the test you most often see, it’s important to understand that all four tests must be done to properly determine not just cell viability or live cells, but also vitality or healthy cells.
Simple Viability Assay
The most common type of simple viability assay is called a “dye exclusion” test. Cells that are living have an intact membrane. Cells that are dead have a damaged membrane that is not intact. When dye (e.g., trypan blue, eosin, or propidium) is added to a bunch of cells, the living cells will exclude, or not take up, the dye due to their intact and functional membrane. The dead cells will take up the dye because their membrane is not intact.
Cells also have a process called apoptosis, which means they’re dying but not dead yet. In apoptotic cells, the membrane is still intact, so they typically don’t take up the dye in dye exclusion tests and are counted as viable cells in a simple cell viability assay.
Consider a high school wrestler in the ER with a fractured arm and an unconscious guy upstairs in ICU who’s nearing his final breath. For one of them, life goes on; for the other, death is imminent. In both cases, however, they are currently alive. However, an apoptosis test can differentiate that the guy in the ICU shouldn’t be counted as healthy.
The apoptosis assay, uses an “I’m dying” marker. How? Using flow cytometry is a technology that measures whether a fluorescent marker attaches to the surface of a cell at a specific receptor. In this case, the molecule used is usually Annexin that binds to a phosphatidylserine molecule (the ‘I’m dying marker). The Annexin has a fluorescent dye on it that will light up when it passes through the LASER light in the flow cytometer.
So credible cell viability and health studies always include measuring the level of dying or apoptotic cells as well as the number of viable cells via flow cytometry. If we only use the simple viability assay, we won’t get a clear picture of which viable cells are truly healthy and which are dying. Somehow, amniotic and cord blood tissue manufacturers always manage to skip this test.
Cell Proliferation Assay
The cell proliferation assay is another essential test for viability and vitality. It involves growing the cells in culture to see if they form colonies and propagate. Live, viable, healthy cells will thrive during this test, while dead and apoptotic cells will not grow or reproduce. This is a very simple and inexpensive test to perform that doesn’t require specialized equipment, so there is absolutely no reason to skip this test. However, just like the apoptosis assay, it’s almost never performed by amniotic and cord tissue vendors.
Cell Function Assay
Finally, for stem cells, a functional assay is needed. And this is usually via a trilineage differentiation test for mesenchymal stem cells (MSCs) to make sure that they can still function and differentiate (i.e., become osteoblasts, adipocytes, and chondrocytes). This makes sure that cells that can grow haven’t been damaged and can still carry out one of their important key tasks.
The upshot? As you can see, there’s a lot more to know about cell health than just simple viability. Yet somehow, we never seem to see a complete test of cell viability and vitality from amniotic and cord blood tissue vendors. Why? That is, of course, the right question be asking. The IOF asked this question and found that it couldn’t reproduce the viability numbers being reported. In addition, in the four amniotic and one cord blood samples it has tested, everything died and wasn’t able to propagate. Hence, don’t accept simple viability as proof that the cells you’re being sold will live to do some good for your patients.