Genetically modified hookworms produce and deliver therapeutics

Hookworms, intestinal parasites that infect hundreds of millions of people in under-resourced tropical regions around the globe, have evolved to survive inside the human gut for years, secreting molecules that enable coexistence with their hosts. Now, researchers at Washington University School of Medicine in St. Louis have harnessed that biological mechanism for potential human benefit, engineering a hookworm to produce and deliver a drug within a living host.

In a new study, the team reports the first successful genetic modification of the human hookworm. It was designed to produce an antibody that neutralizes tetrodotoxin, a deadly neurotoxin produced by pufferfish and other marine animals. After colonizing an animal host with the modified hookworms, the parasites produced the antitoxin and secreted it into the bloodstream, partially inactivating the toxin. The findings are published in Nature Communications.

The work demonstrates that this drug production and delivery approach could be a long-term solution to any number of medical needs, from chronic conditions requiring continuous drug treatment to exposure to toxins in remote locations without medical care available.

"The hookworm has spent millions of years perfecting how to assure long-term survival inside a human host and how to get molecules out of its body and into ours," said senior author Makedonka Mitreva, Ph.D., the Gordon R. Miller Professor at the John T. Milliken Department of Medicine's Division of Infectious Diseases at WashU Medicine. "We asked: What if we could add one more molecule to the roughly 1,000 things the worm already secretes, something therapeutically useful to people? This study shows that's not just a concept. It works."

A parasite that delivers

Hookworms have already been studied as treatments for inflammatory bowel diseases such as ulcerative colitis, based on evidence that the anti-inflammatory molecules the worms secrete can dampen the immune responses that drive those conditions. Mitreva's team set out to build on that foundation by engineering the worm to secrete a therapeutic of the researchers' choosing, rather than relying solely on what the parasite produces naturally.

The appeal of hookworms as a long-term drug production and delivery platform stems from a quirk of their biology. When a person is infected with a controlled number of hookworm larvae, which can be administered orally as a pill or through the skin like a lotion, the worms migrate to the small intestine and take up residence, often for years. Because they cannot multiply inside the host, the number of worms stays fixed, and the infection remains controlled. If the infection ever needs to be cleared, a single dose of an oral antiparasitic drug eliminates the hookworms within 24 hours.

Although natural hookworm infection may cause only mild digestive symptoms in healthy adults, chronic infection with large numbers of hookworms can be dangerous for children, pregnant people and malnourished or otherwise vulnerable individuals, leading to anemia, poor growth and development, pregnancy complications, and—in extreme untreated cases—heart problems or death. This underscores the importance of keeping the infection strictly controlled for therapeutic use, Mitreva noted, which is possible because of the worms' inability to reproduce without spending part of their life cycle in soil.

The antibody selected for this proof-of-concept study neutralizes tetrodotoxin, a paralyzing and potentially lethal toxin with no antidote. The project presented significant technical hurdles: gene-editing tools that work in other organisms had not been adapted for hookworms, and no one had previously achieved stable genetic modification in the species.

To adapt hookworms for therapeutic use, Mitreva and her team drew on more than two decades of hookworm genomics research conducted at WashU Medicine. This depth of data helped them understand the organism's biology from the cellular to the genetic level, allowing them to locate a viable site in the genome to insert the new gene carrying instructions for making the new antitoxin. Critically, they had to ensure that the insertion wouldn't disrupt surrounding gene activity and would prompt the worm to secrete the antitoxin out into the host.

The effort was successful. Blood collected from hamsters infected with Mitreva's genetically modified hookworms partially neutralized tetrodotoxin, whereas blood from animals infected with unmodified worms had no neutralizing capability.

From proof-of-concept to broader platform

Mitreva noted that the level of neutralization achieved in this initial study, while significant, likely represents only a fraction of what the platform can ultimately deliver.

Several components of what she calls a "configurable chassis" are still being optimized to increase the amount of therapeutic protein produced and secreted. Because the worm resides in the gut and a substantial portion of what it secretes remains there, rather than entering the bloodstream, the researchers expect that concentrations of therapeutic molecules in the intestine may be substantially higher than what was detected in circulation in this study, making the platform suitable for gut-directed therapies.

"What we demonstrated here is that the concept works end to end—you can insert a gene, the worm produces the protein, the protein gets out of the worm, and it is functionally active in the host," Mitreva said. "From that starting point, we can optimize the platform and think carefully about which diseases stand to benefit most from a delivery system that is continuous, targeted and long-lasting. That's a fundamentally different kind of pharmaceutical biofactory platform, and we think it opens possibilities that are very hard to achieve with any other platform."

Gut inflammatory diseases, including Crohn's disease and ulcerative colitis, and food allergies are among the conditions Mitreva sees as strong candidates for future development. Diseases requiring small but sustained therapeutic concentrations, where compliance with repeated injections or infusions is a barrier, may also be well-suited to the platform.

Future studies will need to conduct rigorous safety evaluations before human use. Mitreva noted that biocontainment strategies, such as engineering the worms to be unable to produce eggs, are under consideration to protect hosts and their environments as the platform advances.