Can Fecal Transplants Enhance Immunotherapy? New Evidence and Cautions

A trio of new studies, published simultaneously in February in Nature Medicine, add to growing evidence that manipulating the gut microbiome may enhance responses to immunotherapy in selected patients with cancer.

In these small, early-phase studies involving patients with metastatic renal cell carcinoma (RCC), non-small cell lung cancer (NSCLC), and melanoma receiving immune checkpoint inhibitor (ICI) therapy, fecal microbiota transplantation (FMT) was associated with objective response rates that compared favorably with historical or prespecified benchmarks.

The idea that microbiome modulation via FMT “can augment immunotherapy efficacy is probably a good one and these studies certainly support that hypothesis,” said Diwakar Davar, MD, assistant professor of medicine and an oncologist/hematologist at the University of Pittsburgh, Pennsylvania, who wasn’t part of the new work.While “an intriguing approach and certainly worthy of further evaluation,” Davar cautioned that the latest studies are not robust enough to answer the question conclusively.

Although ICIs have improved outcomes for patients with melanoma, NSCLC, and RCC, many patients still do not respond or eventually develop resistance. A growing body of evidence suggests that the gut microbiome can influence the effectiveness of ICI therapy. However, much of this evidence comes from preclinical studies showing that modulating the microbiome via FMT can alter responses to immunotherapy, along with small proof-of-concept human studies — predominantly in melanoma — suggesting this approach may help overcome primary or acquired resistance to anti-PD-1 therapy.

The new studies aimed to build on this foundation by exploring whether FMT could improve ICI responses and clinical outcomes in patients with NSCLC, melanoma, and RCC.

In the phase 2, open-label FMT-LUMINate trial, researchers tested a healthy-donor FMT delivered as oral capsules before patients began immunotherapy. FMT capsules were produced using 80-100 g of feces per dose from screened healthy donors, and patients consumed 30-40 capsules while under supervision. The study included 20 patients with NSCLC and high PD-L1 tumor expression receiving FMT before standard first-line pembrolizumab monotherapy and 20 patients with cutaneous melanoma receiving FMT before ipilimumab plus nivolumab.

In the NSCLC cohort, 16 patients (80%) achieved an objective response. The 80% objective response rate exceeded the prespecified efficacy threshold of 64% and was higher than previously described historical data, which ranged from 39% to 46%, the study team noted.

In the melanoma cohort, FMT before nivolumab and ipilimumab yielded an objective response rate of 75%, also exceeding the historical expected response rates of 50% to 58% among patients receiving this ICI combination.

In patients with NSCLC, no grade 3 or higher adverse events were reported. However, grade 3 or higher adverse events were reported in 13 (65%) patients in the melanoma group, suggesting a potentially accelerated onset of immune-related adverse events. Researchers also observed a higher-than-expected frequency of myocarditis in melanoma patients (15%). These toxicities clustered among patients who had FMT donors enriched in Prevotella spp, highlighting the importance of donor selection for future trials, the researchers explained.

The team plans to assess the potential of FMT to overcome primary resistance to ICI as part of the phase 2 CanBiome2 randomized trial, which aims to enroll 128 patients.

The RCC Data

The other two studies focused on FMT in patients with metastatic RCC. In the phase 1 PERFORM study, 20 treatment-naive patients with metastatic RCC added encapsulated healthy-donor FMT to standard ICI-based regimens — most commonly ipilimumab plus nivolumab, with some patients receiving pembrolizumab plus axitinib or pembrolizumab plus lenvatinib.

The primary endpoint was safety defined by the incidence and severity of immune-related adverse events. The safety endpoint was met; 50% of patients (10 of 20) experienced grade 3 immune-related adverse events, and there were no serious FMT-related toxicities and no grade 4 or 5 events.

Among 18 evaluable patients, nine (50%) achieved an objective response, including two who had complete responses (11%). Notably, most treatment responders did not develop any grade 3 or higher immune-related adverse events, the researchers reported.

Finally, in the phase 2a TACITO trial, 45 patients with treatment-naive metastatic RCC were randomly allocated to receive donor FMT or placebo FMT. Patients received three administrations over 6 months — first via colonoscopy then as capsulized doses, alongside pembrolizumab plus axitinib.

The primary endpoint of 12-month progression-free survival narrowly missed statistical significance — 70% vs 41% (P = .053) — but suggested a benefit in the donor FMT group.

“We need more than 1 year to appreciate statistical significance in terms of progression-free survival,” study investigator Gianluca Ianiro, MD, PhD, with Catholic University of the Sacred Heart, Rome, told Medscape Medical News.

As for secondary endpoints, median progression-free survival was significantly longer with donor FMT (24.0 vs 9.0 months; hazard ratio, 0.50; P = .035) and the objective response rate was higher with donor FMT (52% vs 32%).

Why Might FMT Boost ICI Response?

Conceptually, FMT is intended to reshape the gut ecosystem in ways that favor antitumor immunity, and possibly reduce immune dysregulation.

Across these new studies, the mechanistic story is moving beyond the idea that more diversity is good and toward a model that suggests a benefit to removing or suppressing taxa associated with resistance or inflammatory toxicity.

For example, in the TACITO trial, microbiome analysis confirmed that acquisition or loss of specific bacterial strains was associated with 12-month progression-free survival.

Additionally, results of the FMT-LUMINate trial hinted that the therapeutic benefit of FMT may be driven by eliminating harmful bacteria present at baseline, most notably Enterocloster, Clostridium and Streptococcus spp.

“This bacterial depletion was associated with a favorable immunometabolic milieu,” the FMT-LUMINate researchers wrote. Additionally, the results suggest that “failure to eliminate baseline deleterious taxa may sustain an immunosuppressive metabolic and systemic immune milieu that compromises ICI responses.”

Is FMT Ready for Prime Time?

Ianiro told Medscape Medical News he “definitely” thinks microbiome modulation could eventually become part of standard immunotherapy regimens.

Although the “signal” of benefit is clearly there, Davar cautioned that it’s too early to justify routine, off-trial use of FMT specifically to improve ICI response.

“These remain small, proof-of-concept studies. They are not adequately powered trials of fecal transplants and multiple different covariates haven’t been considered,” Davar said.

The study researchers noted that issues around donor selection and availability, dosing schedules, product standardization, and safety risk stratification need to be resolved.

For example, TACITO’s real-world experience shows logistics can matter. Delays occurred due to capsule unavailability and other scheduling barriers, which led to late dosing and missed or shifted treatments in some patients.

That’s a reminder that scaling FMT for oncology would require robust manufacturing, distribution, and time-sensitive coordination with ICI start dates.

More broadly, “whether FMT is the most suitable method of essentially changing the gut microbiome remains unclear,” explained Davar, who suggested that engineered microbiome therapeutics or tailored therapies may be a preferable, more scalable and tailored long-term solution.

Overall, does this new research provide impetus to develop stool banks? “Probably not,” Davar said.

But is it a call for interested parties to think about clinical trials and experimental products that could influence the gut microbiome? “Those are all probably good ideas,” he said.

The PERFORM, TACITO and FMT-LUMINate trials had no commercial funding. Saman Maleki Vareki, PhD, of the PERFORM trial, is a cofounder of LND Therapeutics Inc and has submitted a US patent application related to FMT donor screening. Ianiro has received personal fees for acting as a speaker for Biocodex and Illumina and for acting as a consultant/advisor for Ferring Therapeutics. Arielle Elkrief, MD, of the FMT-LUMINate trial, has received honoraria from AstraZeneca, Merck, Bristol Myers Squibb, and EMD Serono; consulting fees from EverImmune, NECBio, and Sanofi-Pasteur; and is an inventor on a patent regarding the microbiome and immunotherapy response. Davar had no relevant disclosures.

A version of this article first appeared on Medscape.com.