Fecal Transplants Show Promise Against Severe Peanut Allergy
For the roughly 33 million Americans living with severe food allergies, even trace exposure to something like peanuts can turn dangerous within minutes. Existing treatments can raise a person’s tolerance somewhat, but the protection usually disappears the moment treatment stops. A small new clinical trial from Boston Children’s Hospital points toward something different: borrowing gut bacteria from someone without allergies to help reset the immune system’s response to food.
Borrowing Bacteria From a Healthy Gut
The trial, led by Dr. Rima Rachid, director of the Food Allergy Program and the Allergen Immunotherapy Program at Boston Children’s Hospital, along with Dr. Talal Chatila, director of translational immunology, tested fecal microbiota transplantation, or FMT, in adults with severe peanut allergies. The findings were published in the journal Science Translational Medicine.
The approach builds on earlier laboratory work from Rachid and Chatila’s team, which found that transferring stool samples from allergic infants into allergy-prone mice triggered anaphylaxis, while stool from healthy, non-allergic infants protected the mice from allergic reactions. That earlier research identified a specific set of “good” bacterial strains in healthy infant guts that appeared responsible for the protective effect.
What the Human Trial Found
For the new trial, researchers transferred these protective bacterial strains from healthy donors into ten young adults with severe, trace-reactive peanut allergies, delivered as frozen, encapsulated “poop pills.” After a single treatment of 36 capsules taken over the course of a few hours, three of the ten participants showed improved peanut tolerance when tested four months later, able to eat multiple peanuts without reacting.
In a second phase, participants received a course of antibiotics before their fecal transplant, intended to clear out competing native gut bacteria so the donor strains could establish themselves more easily. Three of five participants in this group improved, tolerating more than four peanuts before reacting, a result suggesting the antibiotic pretreatment may have made the bacterial transfer more effective.
“These results were very encouraging,” said Rachid. “A single fecal microbiota transplant led to a significant increase in the threshold of reactivity to peanut at both one month and four months after treatment, showing that the effect was prolonged.”
Bile Acids as a Possible Mechanism
To understand why the treatment worked for some participants and not others, the researchers analyzed blood samples and found that people who responded to the therapy had higher levels of certain bile salts than those who did not respond. Bile salts are produced in the liver, stored in the gallbladder, and released into the small intestine to help digest fat.
The donor bacteria appeared to be more efficient at metabolizing these bile salts than the bacteria already present in the allergic participants’ guts. In further experiments, the team found that this bile salt metabolism increased levels of immune regulatory cells known to protect against allergic reactions.
“Food allergy reflects a failure of oral tolerance, the process by which the gut immune system learns to accept food, and what this study shows is that the right bacteria can help restore that process, working through bile acid metabolites to promote the immune cells that enforce tolerance,” said Chatila. “Knowing how the bacteria restore tolerance to food in allergic individuals allows us to optimize the therapy for more effective outcomes.”
Why Existing Treatments Fall Short
Current options for peanut allergy, including certain antibody medications and gradual oral exposure therapy, can raise a person’s tolerance threshold, but that protection typically fades once treatment stops. Patients on these therapies must also remain vigilant, since allergic reactions can still occur even while following the prescribed regimen.
“People with food allergies want freedom from constant anxiety and extreme vigilance and to not have to be on guard for potentially dangerous exposures every time they leave the house,” Rachid said. “Patients don’t want therapies that have to be taken indefinitely and instead are looking for a permanent disease modification or cure.”
What Comes Next
This was a small, early-phase trial, and the researchers are careful to note that larger studies are needed before fecal transplantation could become a standard food allergy treatment. Rachid is now leading a follow-up study testing the approach in teenagers, using a purified, concentrated version of the therapy developed in collaboration with Dr. Alexander Khoruts of the University of Minnesota. Unlike the original capsules, this newer formulation can be stored in a home refrigerator, potentially allowing patients to take it under medical supervision without repeated clinic visits. A third ongoing study is examining whether combining this newer formulation with peanut oral immunotherapy improves results further.
“Larger studies of fecal and microbiota transplantation are now essential to confirm these findings, identify the patients most likely to benefit, and discover beneficial bacteria that could be developed into targeted probiotic therapies for food allergy,” Rachid said.
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