Believer scientist working with cells for cultivated meat
May 31, 2023
May 31, 2023

What Are Immortalized Cells and Why Do We Use Them?


Cultivated meat is real meat grown from animal cells without having to raise or slaughter animals. The key ingredient in this innovative food category is real animal cells, which proliferate into biomass that is used to make cultivated chicken, lamb and other types of meat. Typically, the cells used to make cultivated meat are immortalized cells — cells that proliferate indefinitely.

For curious consumers and others interested in better understanding how cultivated meat is made, we're explaining what immortalized cells are, why they are crucial for the production of cultivated meat, different ways cultivated meat companies can source them, and common misconceptions about them.

Cell Culture 101: Primary Cells vs. Immortal Cells

First, a necessary primer on the difference between primary cells and immortal cells. Primary cells are taken directly from animals — whether for research or to make cultivated meat — and can grow for just a few days in a controlled environment, such as a bioreactor. Immortal cells are cells which can be induced or propagated from primary cells, which are able to grow forever without limit. Here's a closer look:

Primary Cells

Primary cells are isolated directly from a living animal. This provides scientists with a small sample of cells; enough to line the bottom of a small cell culture dish. These original cells are known as primary cells and are essentially identical to cells inside of an animal's body.

If provided with the right environmental conditions and "fed" with a nutrient-rich growth media, these primary cells will proliferate, just as they do inside an animal. But even in optimal conditions, most cells will only undergo a certain number of divisions before undergoing senescence, aging and dying.

Believer Meat, discovered a process that allows animal cells to evade senescence and, therefore, proliferate indefinitely. Once these immortal cells were established, they guaranteed an infinite supply of the building blocks of meat. 

Immortal Cells

Immortal cells are populations of cells that do not reach senescence or age. The cells continue to proliferate, growing and dividing, indefinitely. These cells can provide researchers — or cultivated meat makers, like us — with an indefinite supply of animal cells.

Advantages of Immortalized Cells in Cultivated Meat

To understand why cultivated meat companies need immortalized cells, it's helpful to imagine a tiny sample of cells under a microscope. Consider how many times those microscopic cells must multiply to create enough biomass to make a single chicken strip. Now imagine how much proliferation must take place to create millions of pounds of meat. 

For cultivated meat to eventually be widely available and accessible to consumers, the industry needs a constant supply of animal cells. Clearly, primary cells with limited expansion capabilities are not the most practical cells to use.

One very impractical workaround is to continuously isolate new primary cells from donor animals. But besides being a very expensive way to maintain a supply of cells, this method needlessly ties animals to the cultivated meat-making process. The more efficient and animal-friendly way to produce big batches of animal cells, therefore, is to establish immortal cells that proliferate indefinitely.

Methods for Establishing Immortal Cells

How can cells be "immortalized" or prevented from reaching senescence? There are three main methods used in the world of cultivated meat.

Isolating Naturally Immortal Cells

Stem cells are naturally immortal, an attractive characteristic for cultivated meat companies looking for a constant supply of cells. They can also differentiate types of cells such as muscle and fat. However, stem cells are expensive to grow and are extremely unstable. Tiny changes in the growth environment causes stem cells to differentiate and stop being immortal. 

Immortalization Through Genetic Modification

The most common way to immortalize cells is to genetically modify them to bypass senescence. This can be done by infecting cells with viruses or inserting pieces of DNA that contain genes that make cells immortal. While some companies may rely on genetic modification, this is not how we immortalize cells at Believer Meats.

Spontaneous Immortalization

Believer Meats developed a process to select cells that naturally immortalize, we call this process spontaneous immortalization. When cells grow in our controlled environment, they compete with their neighbors. Naturally, the fastest growing cells overtake the culture, while cells undergoing senescence age and die. After a hundred generations, an immortal population of cells emerges from the culture. These cells do not undergo senescence or age.    

Believer's immortal chicken cells, for example, were established more than three years ago from a small sample of primary chicken cells obtained the ability to proliferate forever, and continue to do so for over 1,000 generations to date. Over the last few years, we've gained deep expertise in spontaneously immortalizing cells and now have immortal chicken, ovine, and beef cells that we use — and will use for years to come — to make our meat. 

The Big C: Why Cultivated Meat Cells Are Not Cancer Cells

Outside of the world of science, an average person might associate the concept of cellular immortality with cancer. However, cancer is a distinctly different process than the one used to create immortal cells for cultured meat. 

How Do Believer Meat’s Immortalized Cells Differ from Cancer Cells 

Cancer cells have very well defined hallmarks. Cancer cells lack the ability to repair their DNA from damage. Cancer cells' genetic material is unstable. Cancer cells can form tumors and invade tissues in the body. 

Believer Meat’s immortal cells are different. Our cells retain their ability to repair their DNA from damage. Our cells are genetically stable and have maintained that stability for over 1,000 generations. And finally, our cells can’t form tumors or invade tissues in the body. 

How do we know this? Because our scientists and their collaborators at the Hebrew University of Jerusalem ran a plethora of tests that were published in a high profile peer-reviewed paper in the prestigious journal Nature Food. In short, we found that our immortalized cells cannot form tumors, that they repair broken DNA very well, and lack any cancer-related mutations. 

Why People Cannot Get Cancer From Cells Used in Cultivated Meat

Both independent experts and scientists at Believer Meats make clear that there is no way humans could get cancer from animal cells used to make cultivated meat — or even from eating an actual animal that had cancer. Here's what some experts have said on this topic:

  • Lucas Smith, an assistant professor in the College of Biological Sciences and School of Medicine at the University of California-Davis told USA Today that it would be “virtually impossible” for someone to get cancer even if they ate meat from an animal with cancer, and that we "know much more about the genetic makeup of cultivated meat cells than what we currently ingest from traditional meat."
  • Robert Weinberg, a renowned Massachusetts Institute of Technology biologist and cancer researcher, told Bloomberg that “it’s essentially impossible for a cell from one species to gain a foothold in the tissues of another species...So even if one were to take highly malignant cells from a cow and drink them, I don’t see what the problem would be.” 
  • Our own scientists explain that cells used to make our meat would be "very dead" before they ever reached a consumer (as a result of the freezing and high temperature extrusion process our products go through). But even if they weren't dead, consumers could "take cells directly from our bioreactor and eat them with a spoon" and still rest assured that they'd be safe. 

What to Know About Immortalized Cells And Cultivated Meat

The bottom line: immortalized cells are essential for the production of cultivated meat. Whether they are genetically modified or spontaneously immortalized (like our cells), these ever-proliferating cells provide companies with an endless supply of real animal biomass — the key building block of our products. 

We've demonstrated through rigorous peer-reviewed research that the cells Believer Meats use for cultured meat production are not related to cancer. And even under some extremely unlikely scenarios, scientists around the world agree that people could safely eat cultured meat.

More importantly, the immortalized cells proliferating in our facilities today hold the potential to feed people around the world for many years to come and to save an untold number of animals from slaughter.

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