Biologic drugs have opened the door to treating diseases that were once considered difficult or impossible to treat. However, unlike small molecule drugs, biologics require intravenous or subcutaneous delivery because they would otherwise degrade if they passed through the upper gastrointestinal tract. “We don’t have a good way of delivering those orally,” said Zachary Baker, a graduate student in biological sciences at Virginia Tech. “We wanted to find a way to improve upon the current oral delivery mechanisms.” 

To make that happen, Baker and other researchers led by microbiologist Bryan Hsu and immunologist Liwu Li at Virginia Tech are beginning to forge a path towards oral biologic drugs that can produce therapeutic proteins directly in the human gut (1). Currently, biopharma grows microbes in large fermenters to produce biologic drugs, but Hsu pointed out that it doesn’t have to be that way. “We are our own bacterial fermenter in our gut. All we need to do is introduce the genetic material there,” he said.

Their work relies on bacteriophages, viruses that infect bacteria to replicate and then burst out from the bacteria to release their progeny. By introducing a gene for a biologic drug into the phage, they could then deliver the phage orally where it subsequently hijacks a bacterium’s resources to produce the biologic in the gut. Phages can persist in the gut for over a year, making them ideal for long-term expression of therapeutics (2).

Laurent Debarbieux, a molecular microbiologist at the Pasteur Institute who was not involved in the study, said that this was “quite an interesting concept.”

Hsu’s team began by introducing a green fluorescent protein gene into the phage genome so that they could visually track protein production once inside the gut. Then they gave the phage to mice orally and imaged their guts four days later. They found that the green fluorescent protein ended up in the mucosal lining of the gut. “That got us really excited,” said Hsu. “That's where the protein will be produced … right where we need it to be.”

Next, they used two mouse models to more closely show how their system would work to deliver disease-relevant proteins. In one model, they focused on producing the serine protease inhibitor B1a (SERPINB1a) protein, which regulates an enzyme involved in the gastrointestinal disease ulcerative colitis. When they used phages to deliver the SERPINB1a  gene into gut bacteria, they saw that mice treated with the phage had lower enzyme activity and had gained more weight compared to mice that didn’t receive the gene via the phage.

In another mouse model, they tested the phage’s ability to introduce ClpB, a protein that plays a role in reducing weight gain in mouse models of obesity (3). The team fed mice a high-fat diet and then introduced the CLPB  gene via phage. Afterwards, they saw that these mice reduced their food consumption.

Both of these proof-of-concept experiments suggested that protein drugs that need to act within the gut could be produced by bacteria that have been infected by phages in the lower gastrointestinal tract, avoiding degradation by the stomach. “The next challenge, which is something we'll be looking at into the future, is: How do we get those proteins that are produced in the gut and get them absorbed into the body?” said Hsu. The researchers mentioned in their publication that this could be done by altering the physicochemical properties of the drug so that it could cross the intestinal lining.

Phage, for a long time, had been thought of as purely an antimicrobial.
- Zachary Baker, Virginia Tech

Debarbieux noted other avenues for further research, pointing out that while Hsu’s team showed that expression of the protein was completely distributed along the gut, it could be possible to limit protein production to specific locations by targeting bacteria that predominantly reside in one area of the gut but not others. Situations that could call for more specialized targeting include producing proteins in places of localized inflammation or near tumors. In addition, Debarbieux said that it’s important to have ways to turn off phage activity.

“Phage, for a long time, had been thought of as purely an antimicrobial,” said Baker. “What we're hoping to do with this research is to expand upon that … and repurpose it and use it as a tool for something different.”

References

1. Baker, Z.R. et al.  Sustained in situ protein production and release in the mammalian gut by an engineered bacteriophage. Nat Biotechnol  (2025).
2. Minot S. et al. Rapid evolution of the human gut virome. PNAS 110, 12450-12455 (2013).
3. Legrand, R. et al.  Commensal Hafnia alvei strain reduces food intake and fat mass in obese mice—a new potential probiotic for appetite and body weight management. Int J Obes  44, 1041–1051 (2020).