Contributors: Jocelyn Drasdauskis, Diane Jeon, Matt Kingston, Chris Fetterly
A look back at the history of cell culture
At the beginning of the 1900s, cell culture as a science was still in its infancy. Researchers such as Burrows and Harrison were able to culture primary animal cells using various concoctions of animal blood and serum. However, these lab experiments were limited in both scope and scale and were not standardised to any degree. 
It wasn’t until the 1950s that cell culture began in earnest when a Johns Hopkins researcher named Dr. Gey received a unique tumour sample from a patient. With this sample, a new immortalised cell line was created: HeLa.  HeLa cells were derived from the cancer patient named Henrietta Lacks, and as is unfortunately the case with many early scientific discoveries, there are ethical issues with how they came to be. After a short battle with cervical cancer, Henrietta passed away and she would never know the significant impact her cells came to have on the scientific community. HeLa cells were spread globally to research labs, eventually even sold by commercial companies, all without the consent or knowledge of her family. 
With these miraculously easy-to-culture cells, Dr. Gey also gave his colleagues a recipe for cell culture media using chicken blood in addition to his instructions on how to culture the cells. Over time, as cell culture research began to grow from the knowledge gained from HeLa, new companies took over media formulation and production, and the science of growing cells in the lab became more standardised. In 1958, the properties of fetal bovine serum (FBS) were highlighted by Theodore Puck. In his experiments, Puck discovered that this serum could culture very minute samples of normal cells from human tissue biopsies, and as HeLa and other cultured cells were immortalised, this was a revolutionary finding. Puck hypothesised that if researchers did further studies they would be able to culture both primary and immortalised cells with FBS, and so started its use as a cell culture silver bullet. The benefit of FBS over other serums and substitutes was that it contains approximately 1800 proteins and over 4000 metabolites in addition to its pH buffering capacity, so it optimally supported cell growth.  In addition, not only could one culture HeLa cells with this serum, but just about any other cell type as well—fish cells, primary human cells, Chinese hamster ovary (CHO) cells, and more. All of these can grow in various plain basal media as long as they are supplemented with FBS.
FBS, food, and fighting climate change
Despite its wide applicability, FBS poses ethical issues in that its source, as the name implies, is unborn fetal calves. Harvested from pregnant cows during slaughter in dairy or meat industries, FBS is commonly obtained by way of cardiac puncture, and without anaesthesia. This “protein cocktail”, though effective, creates a messy problem for cell culture scientists.
Outside the lab, our planet is heating up at an alarming rate. In our hunt for solutions to combat climate change, scientists look to our food supply, meat in particular, as it is one of the major sources of carbon emissions and greenhouse gases (GHGs). 
Animal farming is a large source of GHGs for several reasons including but not limited to:
- The animals themselves produce emissions. In the case of cows, methane is produced, a GHG 70 times more potent than CO2
- Industrialised animal rearing concentrates animals in specific locations, rendering local ecosystems unable to deal with the waste and forcing infrastructure to ship food in and meat out
- Land use changes have swapped carbon sequestering ecosystems for methane producing farmland 
- Animals convert feed to protein very inefficiently
These inefficiencies combined with a preference for premium cuts of meat have led to an overall low-efficiency and high-GHG system that only feeds a relatively small number of humans.  For example, the average steer weighing over 1200 pounds will yield about 500 lbs of meat after processing which provides enough calories to feed just one person for three-quarters of the year.  The US saw 14.7 million head of beef cattle in 2021, which could provide enough calories to feed just 3% of their population while emitting 3 billion pounds of methane. 
Despite many advances in plant-based meat alternatives, the slow uptake of these products by the market suggests that they may not be a complete substitute as many in the population will not abstain from meat despite easy access to alternatives.  Scientists have recognized this consumer preference and came up with another potential solution to our dependence on animal-derived meat for protein: cellular agriculture, or cell ag. By growing animal cells in bioreactors, in a process that is similar to the one we use to create beer and other fermented foods, cell ag companies can drastically reduce the carbon impact of our food production system, while producing a product that consumers want. 
Therein lies the rub: how can this industry sustainably grow enough cells for human consumption using the same bovine-derived sera that cell culture science has relied on for so long? The short answer is, it can’t. An industry that is championing novel, sustainable, and ethically aligned food cannot use FBS for its standard method of cell-based production. We must then come up with a new solution: serum-free chemically defined media.
Understanding serum-free media for cell ag
Growing cells without serum isn’t an entirely new concept, though pharmaceutical companies and scientists have been doing it for years as it can be difficult to predictably experiment with a complex mixture. . This research was mostly done using small batches of media or with extraordinary budgets, so cost was often not an issue, but this will not be the case for emerging cell ag companies that are revolutionising the food chain. Researchers and cellular agriculture companies are then faced with having to create new formulations for serum-free media that consider both the cost and sustainability of materials going into the recipes.
The basic ingredients being added to the basal media vary but are usually comprised of several growth factors, amino acids, sugars, and proteins. Growth factors are generally considered by the cellular agriculture industry to be one of the most problematic of growth media components.  Growth factors are signalling molecules that promote cell viability and proliferation—a critical requirement for producing enough cells to feed the globe. The problematic aspect of these molecules is the nature of their production and overall cost: traditional growth factors are made in bioreactors similar to what cell ag hopes to grow the food cells in, and they are prohibitively expensive. As cellular agriculture creates new media formulations that check all the boxes of cost, sustainability, and ethics, the industry will find a large impact in tackling the growth factors that go into it.
A fly solution
Fortunately, the minds of the globe are coming together to solve these problems and are discovering new and revolutionary ways to make growth factors that are cost-effective, sustainable, and aren’t constrained by limited bioreactor supply chains. Some companies are using filamentous fungi or plants to grow these proteins and escape legacy production paradigms. Our strategy has been to replace the tank entirely, with fruit flies. We at Future Fields think the humble fruit fly combined with synthetic biotechnology can help solve the growth factor dilemma. Rearing fruit flies has many advantages as they do not require bioreactors, require little water and food, and are incredibly efficient and cost-effective to scale. Acting as nature’s ‘bioreactor’, our fly-based EntoEngine™ can express the recombinant proteins required to grow cells, all within a circular economy framework. Cell ag companies seeking a serum-free media formulation which is devoid of traditional animal agriculture processes can use these growth factors and improve their triple bottom line—i.e. people, profit, and the planet.
When building scientific innovations for humanity and the planet, we must take a good long look at the processes and infrastructure that brought us to today. Are there areas for improvement? Can we make things greener, cleaner, and fairer? The accelerating cell ag industry is at a critical point of creating a standard for the companies to follow and must ensure that their production methods are just as sustainable and ethical as their product. Let us consider the lessons from history and fully lean into feeding the planet sustainably, one serum-free solution at a time.
- Rodríguez-Hernández, C. O., S. E. Torres-García, C. Olvera-Sandoval, F. Y. Ramírez-Castillo, A. L. Muro, F. J. Avelar-Gonzalez, and A. L. Guerrero-Barrera. "Cell culture: history, development and prospects." Int J Curr Res Aca Rev 2, no. 12 (2014): 188-200.
Skloot, Rebecca. The immortal life of Henrietta Lacks. Broadway Paperbacks, 2017.
Chelladurai, Karthikeyan Subbiahanadar, Jackson Durairaj Selvan Christyraj, Kamarajan Rajagopalan, Beryl Vedha Yesudhason, Saravanakumar Venkatachalam, Manikandan Mohan, Niranjan Chellathurai Vasantha, and Johnson Retnaraj Samuel Selvan Christyraj. "Alternative to FBS in animal cell culture-An overview and future perspective." Heliyon 7, no. 8 (2021): e07686.
- Koneswaran, Gowri, and Danielle Nierenberg. "Global farm animal production and global warming: impacting and mitigating climate change." Environmental health perspectives 116, no. 5 (2008): 578-582
Statham, Jonathan, Martin Green, James Husband, and Jon Huxley. "Climate change and cattle farming." In Practice 39, no. 1 (2017): 10-19.
Collier, Elizabeth S., Lisa-Maria Oberrauter, Anne Normann, Cecilia Norman, Marlene Svensson, Jun Niimi, and Penny Bergman. "Identifying barriers to decreasing meat consumption and increasing acceptance of meat substitutes among Swedish consumers." Appetite 167 (2021): 105643.
Jönsson, Erik. "On breweries and bioreactors: Probing the “present futures” of cellular agriculture." Transactions of the Institute of British Geographers 45, no. 4 (2020): 921-936.
- Barnes, David. "Hormonally defined, serum-free media for epithelial cells in culture." In Tissue Culture of Epithelial Cells, pp. 235-253. Springer, Boston, MA, 1985.