WASHINGTON – Research on standardized microbiome-based therapies designed to prevent the recurrence of Clostridioides difficile infection (CDI) is moving “with a lot of momentum,” according to one expert, and modulation of the gut microbiome may even enhance responses to immunotherapy and/or abrogate toxicity, according to another.
Several products for prevention of CDI recurrence are poised for either phase 3 trials or upcoming Food and Drug Administration approval, Sahil Khanna, MBBS, MS, professor of medicine, gastroenterology, and hepatology at the Mayo Clinic in Rochester, Minn., reported at the annual Gut Microbiota for Health World Summit.
Jennifer A. Wargo, MD, MMSc, of the University of Texas MD Anderson Cancer Center, Houston, described her investigations of microbiome modulation’s role in cancer treatment. “I used to say yes [we can do this] somewhat enthusiastically without data, but now we have data to support this,” she said at the meeting, sponsored by the American Gastroenterological Association and the European Society for Neurogastroenterology and Motility. “The answer now is totally yes.”
New approaches for CDI
“Based on how the field is moving, we might be able to [offer our patients] earlier microbiome restoration” than is currently afforded with fecal microbiota transplantation (FMT), he said. “Right now the [Food and Drug Administration] and our clinical guidelines say we should do FMT after three or more episodes [of CDI] – that’s heartbreaking for patients.”
Several of the microbiome-based therapies under investigation – including two poised for phase 3 trials – have shown efficacy after a second episode of CDI, and one of these two has also had positive results after one episode of CDI in patients 65 at older, a group at particularly high risk of recurrence, said Dr. Khanna.
The value of standardized, mostly pill-form microbiome therapies has been heightened during the pandemic. “We’ve been doing conventional FMT for recurrent C. difficile for over a decade now, and it’s probably the most effective treatment we have,” said Colleen R. Kelly, MD, associate professor of medicine at Brown University, Providence, R.I., and moderator of the session on microbiota-based therapies.
Prepandemic “it got really hard, with issues of identifying donors, and quality control and safety ... And then when COVID hit the stool banks shut down,” she said in an interview after the meeting. With stool testing for SARS-CoV-2 now in place, some stool is again available, “but it made me realize how fragile our current system is,” Dr. Kelly said. “The fact that companies are putting these products through the FDA pipeline and investigating them in rigorous, scientific randomized controlled trials is really good for the field.”
The products vary in composition; some are live multi-strain biotherapeutics derived from donor stool, for instance, while others are defined live bacterial consortia not from stool. Most are oral formulations, given one or multiple times, that do not require any bowel preparation.
One of the products most advanced in the pipeline, RBX2660 (Rebiotix, Ferring Pharmaceuticals) is stool derived and rectally administered. In phase 3 research, 70.5% of patients who received one active enema after having had two or more CDI recurrences and standard-of-care antibiotic treatment had no additional recurrence at 8 weeks compared to 58.1% in the placebo group, Dr. Khanna said.
The other product with positive phase 3 results, SER-109 (Seres Therapeutics), is a donor stool-derived oral formulation of purified Firmicutes spores that is administered after bowel prep. In results published earlier this year, the percentage of patients with recurrence of CDI up to 8 weeks after standard antibiotic treatment was 12% in the SER-109 group and 40% in the placebo group.
Patients in this trial were required to have had three episodes of CDI, and interestingly, Dr. Khanna said, the diagnosis of CDI was made only by toxin enzyme immunoassay (EIA). Earlier phase 2 research, which allowed either toxin EIA or polymerase chain reaction testing for the diagnosis of CDI (as other trials have done), produced negative results, leading investigators to surmise that some of the included patients had been colonized with C. difficile rather than being actively infected, Dr. Khanna said.
Researchers of these trials are documenting not only resolution of CDI but what they believe are positive shifts in the gut microbiota after microbiome-based therapy, he said. For instance, a phase 1 trial he led of the product RBX7455 (Rebiotix, Ferring Pharmaceuticals) – an oral capsule of lyophilized stool-based bacteria that can be kept for several days at room temperature – showed increases in Bacteroidia and Clostridia.
And other trials’ analyses of microbiome engraftment have demonstrated that “you can restore [species] even when these bacteria aren’t [included in the therapy],” he noted. “As the milieu of the gut improves, species that were not detected start coming back up.”
Asked about rates of efficacy in the trials’ placebo arms, Dr. Khanna said that “we’ve become smarter with our antibiotic regimens ... the placebo response rate is the response to newer guideline-based therapies.”
In addition to CDI, microbiome-based therapies are being studied, mostly in phase 1 research, for indications such as Crohn’s disease, ulcerative colitis, autism spectrum disorder, hepatitis B, and hepatic encephalopathy, Dr. Khanna noted.
Dr. Kelly, whose own research has focused on FMT for CDI, said she anticipates an expansion of research into other indications once products to prevent CDI recurrence are on the market. “There have been a couple of promising ulcerative colitis trials that haven’t gone anywhere clinically yet,” she said in the interview. “But will we now identify patients with UC who may be more sensitive to microbial manipulation, for whom we can use these microbial therapies along with a biologic?”
Some of her patients with IBD and CDI who are treated with FMT have not only had their CDI eradicated but have subsequently seen improvements in their IBD, she noted.
The role of traditional FMT and of stool banks will likely change in the future with new standardized oral microbiome-based therapies that can be approved and regulated by the FDA, she said. However, “we think the stool banks will still have some value,” she said, certainly for clinical research and probably for some treatment purposes as well. Regarding new therapies, “I just really hope they’re affordable,” she said.