Human blood is limited in availability, and would be phenomenally expensive as well as having the reproducibility problems you mentioned. We use FBS (fœtal bovine serum) as a substitute. It's routinely added to culture media such as MEM and DMEM; 10% v/v is typical. This is still pretty expensive though, as well as having ethical concerns (the extraction process is horrific).

It's also still rather unrealistic. Most cells aren't directly exposed to blood plasma and all of its proteins. They are perfused by interstitial fluid which is blood plasma filtered through the capillaries.

One of the goals of some of the more modern media (as in this article) is to supplement every known necessary component of blood plasma to avoid the need for any animal-derived sera, and to make the media completely defined and standardised. This isn't new; people were doing this over a decade back when I was working on my PhD. However, the number of components in blood plasma makes this difficult, if not intractable. Most of these new media had a small amount of FBS (≤1%) to make up for the unknown components. That notwithstanding, the efforts to better understand the exact requirements are laudable. However, proving that all the needed components are present and in the correct concentrations is difficult if not impossible, since it might appear to work while causing some subtle physiological change. We might have to settle for "appears to be good enough for all common cell types". But even that would be a huge improvement upon the status quo.

Working with human blood introduces also a non negligible risk for the workers. You can't pick hepatitis from a zebra fish.

> Human blood is limited in availability, and would be phenomenally expensive

Just wait until researchers realize where to obtain human blood for free...

You're looking awfully pale today Steven!

You joke, but I work in a pharmaceutical company, and we have a program specifically for employees to donate blood for research purposes. It's complicated so that the donors and researchers are blinded to where the blood comes from and who it goes to.

On top of what others said, adding human samples increases the degree of regulations rightfully. Accidentally coming in contact with these reagents means a visit to the lab to confirm you didn't get any blood borne disease

Blood contains immune system elements which would likely reject cancer samples from a different donor. Having to obtain blood and cancer sample from the same donor would complicate things quite a bit.

In addition, it doesn't seem as though they are able to recycle the medium. Frequently draining and refilling with fresh blood seems rather wasteful.

The immune cells are trivial to remove; a few minutes in a centrifuge is all that is required. Even antibodies can be separated out pretty easily (though I haven't done it myself). The problem is the quantity and quality of the product. And blood alone isn't sufficient; it doesn't contain enough glucose and other metabolites to sustain cells for long (since it's continuously circulating and levels are maintained by the body, which isn't true for a culture flask).