In the fall of 2020, Hassane M. Zarour, MD, and colleagues began to pore over raw data from their
Dr. Hassane M. Zarour
Preclinical mouse studies have demonstrated that the gut microbiota could influence the response of tumors to anti–PD-1 immunotherapy, but FMT had not been previously evaluated in human patients with malignant melanoma whose disease persisted or progressed after medical therapy. Only 30%-40% of melanoma patients respond to anti–PD-1 immunotherapy, so the researchers’ sense of anticipation was palpable. “It’s a high-risk, high-reward study, so you never know,” Dr. Zarour, a dermatologist and immunologist who is coleader of the melanoma program at the University of Pittsburgh Medical Center’s Hillman Cancer Center, said in an interview.
For the study, which was funded by the National Institutes of Health and published in Science, Dr. Zarour and a team of colleagues, including Diwakar Davar, MD, a medical oncologist/hematologist at UPMC and Giorgio Trinchieri, MD, head of the cancer immunology section at the National Cancer Institute, enrolled 16 patients with advanced melanoma whose disease had persisted or progressed with anti-PD-1 drugs; donors were 7 patients with advanced melanoma who had responded to pembrolizumab, 4 with a complete response and 3 with a partial response, with a median progression-free survival of 56 months.
After donors and patients underwent serial stool sampling and studies to stamp out the potential for transmitting infectious agents, the researchers administered the donor-derived FMT to patients via colonoscopy every 14 days for 3 weeks, followed by pembrolizumab. To their delight, 6 of the 15 evaluable recipients responded to treatment, with a reduction in tumor or long-term disease stabilization. Moreover, responders also showed increased abundance of taxa that were previously associated with response to immunotherapy, increased activation of CD8+ T cells, and decreased frequency of interleukin-8–expressing myeloid cells.
“This opens new doors for the future,” Dr. Zarour said. “It’s very encouraging, but I don’t want to overstate the data. It’s a small, nonrandomized trial, but one has to keep in mind that people were skeptical about this work; they didn’t think FMT would work. Now we see many people coming into the field to investigate the role of the microbiome as a therapeutic tool, which is great.”
Dr. Teri Greiling
Teri Greiling, MD, characterized the finding as a key development in understanding the microbiome’s potential to influence the course of melanoma and other diseases. “What’s emerging over the last decade of research is that our immune system has a close, back-and-forth relationship with our microbiota,” said Dr. Greiling, associate professor of dermatology at Oregon Health & Science University, Portland. “From day 1 of birth, we’re colonized by microbes that train our immune system how to function. In response, your immune system keeps those microbes in check and shapes which ones are allowed to colonize, and which ones are a target for attack. Thus, inflammatory responses are generated. Similarly, the goal of immunotherapy is to activate the immune system to fight cancer. This study shows that the immune system continues to need the colonizing microbes in our body to function optimally.”
Immunotherapy with checkpoint inhibitors was not an option for malignant melanoma patients until 2011, she noted, so the potential for FMT to further improve outcomes is welcome news for patients and their families. “We went from a less than 5% chance of survival with metastatic melanoma to now, with the right combination of checkpoint inhibitors, we’re up over 50%, which is amazing in a decade,” Dr. Greiling said. “Still, we’re losing half of our patients. If [FMT provides] a 30% improvement over that, that would be great, but it’s hard to extrapolate from such small numbers.”