Why we need chemically defined cell culture media

Let me tell you what’s driving your FBS batch-to-batch variation; it’s similar to how bear serum varies between summer and winter months (yep, see the comments for that absolute gem of a study).

At first glance, “batch variation” sounds like a QC problem but most biologists will know FBS variability comes down to its animal-derived nature.

FBS is essentially a biological snapshot of fetal physiology at a specific point in gestation. The fetal blood is pooled, essentially in an attempt to somewhat standardize the FBS.

What scientists might not know, is pooling can help mitigate shifts due to:

🐮 Fetal age: As fetuses mature, albumin levels increase, immunoglobulins rise, and lipid profiles shift. Pooling smooths this out to an extent.

🐮 Stress at harvest: Cortisol and catecholamine spikes in mama cow alter glucose, lactate, and metabolic profiles. Pooling dilutes these acute stress-related changes.

Pooling does not (particularly) help mitigate changes due to

🐮 Maternal diet: Micronutrients, fatty acids, and trace minerals pass directly from mama to fetus.

🐮 Seasonality: Pasture quality, climate, and feed composition change micronutrients, hormones, and fatty acids in serum. FBS collected in winter is measurably different from summer (like bears!).

🐮 Geography: Soil composition, water mineral content, and regional feed practices influence trace elements, metal-binding proteins, and vitamin levels found in serum.

And this is why you’ll see differences in cells cultured using FBS from South America versus the US versus Europe versus New Zealand.
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We spent years developing an animal-free replacement for FBS that doesn’t have batch-to-batch variation. To do that, we had to benchmark against FBS - multiple batches of FBS.

It’s tough to establish a baseline of “this is what good looks like” when your standard is intrinsically variable. For balance, we worked with ~6 FBS batches. As an extreme example, one batch straight up did not grow our AD-MSCs.

This is why scientists batch-test and stockpile FBS to ensure consistency across a series of experiments. Once a given batch of FBS is gone, it’s impossible to precisely replicate the mix of proteins, lipids, metabolites and trace elements.

This is also why — where feasible, because it certainly isn’t always feasible (yet) — growing cells in chemically defined media is a good move for scientific reproducibility.

Interesting science below if you want to dive deeper, including that study in which mouse cells were cultured with bear serum from summer versus winter, aka hibernation season.


https://pubmed.ncbi.nlm.nih.gov/34336951/ - Winter/Summer bear serum, and how it maybe can be used to identify helpful therapeutic agents

https://pubmed.ncbi.nlm.nih.gov/39617443/ - Selenium variation in FBS from different geographies....and the result on cells.

https://pubmed.ncbi.nlm.nih.gov/29196597/ - Impact of different batches of FBS on cells

https://pubmed.ncbi.nlm.nih.gov/1153408/ - An older paper, in which different FBS batches were quantitatively profiled