stilllifephotographer / Claudia Totir / Getty / Katie Martin / The Atlantic

The inconvenient truth about breastfeeding is that breasts are, invariably, attached to a person. A person who could get too sick to breastfeed. A person who might have to go back to work within two weeks of giving birth, because U.S. law does not mandate paid leave. A person who might have no place to pump at work, despite a law that does actually mandate such a room. For understandable and frustrating reasons, many mothers who want to breastfeed—who have internalized years of hearing “Breast is best”—simply cannot.

Enter: a bioreactor of lactating human breast cells.

A small start-up called Biomilq recently announced it has managed to grow human mammary cells that make at least two of the most common components of breast milk: a protein called casein and a sugar called lactose. This is the first step, the company hopes, to making human milk outside the human body.

Breast milk is of course far, far more complex than just casein and lactose. It is made up of at least hundreds of different components: a multitude of proteins, fats, and sugars, but also antibodies, hormones, and beneficial bacteria. Biomilq’s founders, Leila Strickland and Michelle Egger, say that they seek to eventually make milk that is “nutritionally” but not necessarily “immunologically” close to breast milk. Experts I spoke with said that mammary cells in a bioreactor simply could not replicate the full complexity and benefits of breast milk. One researcher laughed at the idea.

Biomilq does seem to be onto something though, at least culturally. Since the postwar days of doctors pushing formula as the superior “scientific” option, the conventional and medical wisdom has swung in the opposite direction—to the point where women often feel guilty for being unable to breastfeed. “There’s just a feeling of failure: I can’t do this for my child. This is really important,” said Maryanne Perrin, a breast-milk researcher at the University of North Carolina at Greensboro, who has studied women trying to buy breast milk online for their children. “I heard a lot of anxiety in the voices and comments,” she added. In other words, there is definitely a demand for human breast milk.

The idea for Biomilq, in fact, came out of Strickland’s own struggles to breastfeed as a new mom. Her son had trouble latching after he was born, and she wasn’t making enough milk. “During those months of life, my whole world revolved around whether or not my body would produce enough of this food,” she says. She wished for an option that was not formula. Strickland has a background in cell biology, so she naturally wondered: What about breast cells?

In 2013, she began growing mammary cells in a tiny lab space in North Carolina, and in 2019, she met Egger, a student at Duke’s business school and a former food scientist at General Mills, who had worked on products such as Go-Gurt. They officially launched Biomilq late last year to make lab-grown human milk—or as they prefer to call it, “cultured breastmilk.” Another start-up based in Singapore, TurtleTree Labs, recently announced it is trying to re-create cow and human milk with cells as well.

Human milk is currently available for sale, but it is not easy to buy. Officially, parents can go to a milk bank to buy donated breast milk that has been screened and pasteurized—but this requires a doctor’s prescription and can go for a hefty $4 or $5 an ounce to cover processing costs. (Milk banks also prioritize donor milk for sick or preterm infants in the hospital, for whom cow-based formula is particularly prone to causing a serious gut disease called necrotizing enterocolitis.) Unofficially, parents can go on Facebook or Craigslist or another online marketplace where women share or sell extra breast milk. These markets are cheaper and more convenient, but they’re also unregulated. Donors largely follow the honor system for disclosing medications and other health information. Meanwhile, formula is cheap, safe, and widely available in grocery stores. Biomilq promises to combine the “nutrition of breastmilk” with the “practicality of formula.”

It’s hard to say, at this nascent stage, exactly how still-hypothetical breast milk made by cells in a bioreactor would compare with formula. The cultured human-milk proteins could be more suitable in a baby’s gut than dairy proteins, and sugars specific to human milk could help feed a baby’s new gut microbes.

But milk from cells in a bioreactor would still be missing some key components of true breast milk—for the simple reason that the components of breast milk don’t come from the breast alone. Natalie Shenker, a breast-milk researcher at Imperial College London, enumerated some examples: Antibodies, which transfer immunity against pathogens from mother to baby, come from the mother’s own immune cells in her blood. Hormones, which may shape the baby’s brain and behavior, from her endocrine system. Fats, which make up a substantial portion of the calories in milk, from her diet and own stored fatty tissue. (Biomilq suggests that these fats could be supplemented in cultured cells.) Beneficial bacteria that help populate the baby’s gut come from the mother’s own microbiome. The whole body is responsible for the production of what we call breast milk.  

The exact cocktail of protein, sugar, fats, antibodies, hormones, and bacteria in breast milk can change from day to day and even hour to hour. It can change in response to the baby’s needs. One hypothesis suggests that a sick baby can communicate via “retrograde milk flow”—more memorably termed “baby spit backwash”—to change the composition of breast milk to help the baby fight off disease. Breast milk is complex and dynamic. Perrin said she applauds any efforts to improve infant nutrition, but “to re-create breast milk in a test tube, I think we’re just so far away from that.”

Growing enough mammary cells to make any milk at scale is also a huge technical challenge. These cells require expensive nutrients and are incredibly prone to contamination from bacteria. The recent interest in lab-grown meat has prompted a number of companies to work on these problems, but breast milk is likely to face higher scrutiny, deservedly so, because it is for babies. Shenker, who is familiar with the challenges of growing mammary cells from her own research, wondered whether re-creating milk was the best use of resources. Why go through the expensive, unproven process of growing cells to make milk in a bioreactor, she asked, when we already know how to get actual milk—nutritionally complete—from a donor? The problem is not a lack of breast milk on Earth, but a lack of access and distribution.

When I contacted breast-milk researchers to ask about lab-grown breast milk, they ended up changing the topic to barriers faced by women who want to breastfeed. “A lot of moms aren’t getting the support they need,” said Meghan Azad, a breast-milk researcher at the University of Manitoba. Breastfeeding takes skill, which was lost for a generation when formula was dominant. It takes workplaces that give women the time and flexibility to breastfeed or pump. And it takes a culture that doesn’t shame women for breastfeeding in public. And although society makes it hard for women to breastfeed, it also tells them that “Breast is best.” The result is a nearly impossible set of expectations.

The appeal of Biomilq is that it’s supposed to close the gap—that frustrating space between what mothers are expected to do and what most can realistically do. “We’re done making trade-offs between our baby’s health, our wellbeing, and the environment,” the company’s website proclaims. But it also puts the company in the position of both touting the benefits of breastfeeding … and telling women it’s okay not to breastfeed. Egger says Biomilq is not about replacing breastfeeding, but supplementing it. “If women can breastfeed even part of the time, they should be wholeheartedly supported in doing that,” she says. “We just see this as an opportunity for them to actually continue to enable that process and not having to feel guilt or shame or frustration.” She draws a particular contrast with formula companies, which have used aggressive tactics to get into hospitals and influence breastfeeding recommendations. Over the course of the 20th century, these standardized cans of formula often came to replace the highly personalized breast milk of mothers.

The irony is that if human milk from cells, as a concept, really does take off one day, the more successful it is, the more likely it is to become formula 2.0: another practical, standardized, and commercial product. In fact, formula companies are already adding sugars called “human milk oligosaccharides” to their products, to sell formula that they can say is closer to breast milk.

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