The production of cultured meat will require stable cell lines from multiple different species to be successful, reports FoodNavigator.

Potential Barriers

A review in Nature Food explored the use of stem cells in cultured meat, examining the best stem cells for the job as well as potential barriers.

Stem cells, according to the UK National Health Service, are the basic building blocks of life, foundational cells that transform (differentiate) into other cells in their native organism. Therefore, they provide a key opportunity for cultured meat producers as they are flexible and can be used in a wide variety of ways.

Using stem cells that create the major cellular components of meat, such as myofibers, adipocytes, and fibroblasts, is an efficient way for cultured meat producers to proliferate their product as well as efficiently replicate the taste of traditionally slaughtered animals.

"A defining feature of stem cells is that they can become other cells," said Lucas Robert Smith, one of the study's authors, to FoodNavigator. "With beef, for example, the goal is to have cow stem cells that can transform into muscle or fat cells. This will impact the proteins and fats present in the cells that give the meat its familiar flavor."

Texture and Fat

When developing cultured meats, it's crucial to reproduce the texture of traditional animal meat (texture has been shown to be a key concern for consumers). "Meat texture is complex and involves interactions between multiple cells," Smith told us. "One of the critical components is the dominant protein of the extracellular matrix, collagen.

"While many cells produce collagen in muscle fibroblasts, fibroadipogenic progenitors play a major role in collagen production and organizing collagen in ways that influence texture."

Fat is also a key component of cultured meat. "Additionally, fibroadipogenic progenitors can be differentiated into adipose cells upon adipogenic induction," Smith told us.

"Intramuscular fat, also known as marbling in pork and beef, comes from these fibroadipogenic progenitors.

Other potential sources of cells for cultured fat cells include stem cells derived from fat and mature dedifferentiated adipocytes. Both have strong in vitro adipogenic potential and can be easily differentiated into adipose cells when grown in adipogenic environments."

Proliferation

Of course, for stem cells to be effective in developing any quantity of cultured meat, they need to be able to proliferate. While doubling is typical for stem cells, some cells are better at it than others.

"Cell doubling within a 24-hour time frame is typical for cells cultivated in a nutrient-rich growth environment," Smith told us. "Embryonic stem cells rapidly divide during development, and doubling times of 16-20 hours are achievable.

There have been reports of mouse embryonic stem cells dividing every 4-5 hours while maintaining pluripotency, the ability to become any cell type. Creating culture conditions and cell lines that optimize doubling times while maintaining cellular functions will be important for cultured meat production."

When stem cells become immortalized, they are even more efficient at proliferation because they can retain the key qualities of stem cells while doubling.

"Immortalized stem cells can undergo indefinite doubling, all while retaining their stem cell qualities to become other differentiated cell types, such as muscle. Often, reaching 100 doublings is used as a practical way to assess whether a cell is immortalized. There are various immortalization methods to achieve this."

Improving Immortalization

Researchers are still working on ways to immortalize stem cells, but there are some barriers, Smith told us. "Cells have checkpoints before passing through the cell cycle to duplicate. One limiting factor is telomeres at the end of chromosomes that shorten with each doubling and limit the potential for doubling.

One strategy to combat this is to add telomere-lengthening enzymes to cells to bypass this limit. It's also possible to introduce signals to bypass cell cycle checkpoint crossings. Another strategy is to put cells under stress, forcing some cells to adapt, become immortalized, and then can be selected."

Some of the best stem cells for proliferation also come with barriers to efficient production. Pluripotent stem cells (PSC) can renew indefinitely and can become nearly any type of cell relevant to cultured meat. They "resemble cells found in embryos during early developmental stages," Smith told us.

However, while this "makes them a desirable source for cultured meat, it also means that more steps are needed to produce specialized muscle or adipose cells. At this time, efficient and consistent differentiation of PSCs into meat progenitor cells is still a barrier to using PSCs."

One potential way to overcome such obstacles presented by individual stem cells is genetic modification. "The cells used dictate the ability to proliferate, determine the cell type, as well as the media conditions required for each type. Genetic modification of stem cells has the potential to overcome each of these obstacles," Smith told us.

"Genetic modification can produce immortalized cells, can control differentiation into muscle or adipose components, and can grow without expensive additives. However, further research is needed to make these possible using genetic engineering."

Differentiation and Ethical FBS

When stem cells differentiate, they develop into specific cells that have a function within an animal organism. This process is vital for cultured meat development.

One of the key aids in this regard is fetal bovine serum (FBS), as it provides key nutrients and growth factors to cells. However, FBS is derived from cow fetuses (though these fetuses are not specifically sacrificed for FBS), posing a challenge to the vegan status of cultured meat when used.

FBS "has been a critical component of cell culture media for many decades," Smith told us. "Its use has allowed scientists to make incredible progress in cell culture techniques and forms the foundation of our current understanding of how cells and tissues function.

"Although these advances allow us to think today about making meat in the lab, it is important to consider alternatives that use strategies that do not contain animal-derived components (except for cells) and do not require or minimize the sacrifice of animals.

"FBS is a costly component of growth media. There are serum-free formulations on the cell culture market, but they are just as expensive. The field is actively seeking ways to culture cells without serum."

Regulation

Of course, the use of such technology will need to be regulated. Cutting-edge research almost always presents risks, and cultured meat developed through stem cells is no exception.

"For any food product, safety is the fundamental priority," Smith told us. "Although the manufacturing, processing, and preparation of cultured meat are different from conventional meat, risk-based food safety principles remain the same.

"Each company will need to establish science-based approaches to identify, characterize, and control microbial, chemical, and physical hazards in the manufacturing process. These control strategies will need to be validated, verified, and approved by regulatory agencies.

In addition, nutritional claims and food product labels must be truthful and not misleading."

Source: Nature Food 'Stem cell-based strategies and challenges for production of cultivated meat’ Published on: 16 October 2023 Doi: https://doi.org/10.1038/s43016-023-00857-z Authors: T. C. Jara, K. Park, P. Vahmani, A. L. Van Eenennaam, L. R. Smith & A. C. Denicol