Positive results in an Israeli study
Results from a similar, smaller phase 1 trial of 2 FMT donors and 10 recipients with metastatic melanoma who had progressed on anti-PD-1 therapy, from the Ella Lemelbaum Institute for Immuno-Oncology at Sheba Medical Center in Tel HaShomer, Israel, yielded similar results. The FMT protocol in this study included colonoscopy and oral stool capsules, followed by the reintroduction of anti–PD-1 therapy with nivolumab. The two FMT donors had previously been treated with anti–PD-1 monotherapy for metastatic melanoma and had achieved a clinical response for at least 1 year. Of the 10 FMT recipients, 1 had a complete response and 2 had a partial response.
Dr. Erez Baruch
“We expected changes in the immune system but did not expect that 3 out of the 10 patients in our study would be turned from nonresponders to responders,” the study’s lead author, Erez N. Baruch, MD, PhD, told this news organization. “Since this was a first-in-human study, we were aiming to assess safety and not clinical responses. [We found] that microbiota modulation can change the immune infiltration within melanoma tumors and by this affect response to immunotherapy.”
Dr. Baruch, an internal medicine resident in the physician-scientist track program at the University of Texas, Houston, said that the findings create a potential new therapeutic paradigm, or a new “playing ground” for drug development that can support existing immunotherapies. “It is important for dermatologists to understand that disruptions of the gut microbiota, mainly by antibiotics, may be harmful to melanoma patients,” he said. “Antibiotics in cancer patients should be used judiciously but of course should not be avoided when there’s an indication.”
As for next steps, Dr. Zarour and colleagues are recruiting more patients to boost their sample size and conducting sequential analysis of the microbiome of study participants “to better determine what the good and bad bugs are,” he said. “There are so many variables, including diet and geography. We need more data.” The hope is to develop a “microbiome signature” to identify patients likely to respond to FMT, and maybe one day, a probiotic capsule that patients take to optimize their response to immunotherapy.
“We don’t want to say that the microbiome is responsible for everything, but it’s responsible for some of the response and some of the resistance to treatment,” Dr. Zarour said. “So, we want to identify what candidate nonresponders are more likely to respond to FMT and be able to stick the right stool in the donor. This goes to better education of the microbiome signature. We are working hard on that.”
Dr. Baruch added that performing FMT for melanoma patients requires tight collaborations between oncologists, dermatologists, GI, and infectious disease experts. “These usually can be done in the setting of large cancer centers and will probably not be available in any hospital,” he said. “This is why understanding the mechanisms and developing an FMT-like drug is important. We are focusing on studying the mechanisms behind the clinical effect in order to develop a drug with an FMT-like effect without the safety and logistic issues related to FMTs.”
Dr. Tamia A. Harris-Tyron
Tamia A. Harris-Tryon, MD, PhD, whose lab at the University of Texas Southwestern Medical Center at Dallas is studying how diet and the microbiota impact skin immunity, underscored the importance of evaluating the characteristics of the diet of patients as trials of FMT in melanoma patients carry on. “We know that the diet impacts the repertoire of microbes that colonize the gut,” said Dr. Harris-Tryon, assistant professor in the department of dermatology at the medical center. “The diet of the recipient likely has an impact” on the success of donor FMT.
She also noted that other skin conditions have been linked to a disrupted gut microbiome, such as psoriasis. “Given the safety of FMT in both of these studies, trials of FMT in psoriasis and other systemic skin conditions should be considered,” she said.
According to Dr. Zarour, mounting data from separate studies show that some gut microbiota play a role in adverse events experienced by melanoma patients on immunotherapy. “That is very important, especially with combination therapy,” he said. “There are also microbes involved in resistance to treatment, so the idea would be to identify these microbes.”
Studies raise more questions
In the opinion of Dr. Greiling, results from these two studies raise more questions than they answer. “The big question ... is why and how does FMT work, and how can we make the response better?” she said. “Is there one particular gene product from one microbe that is the key magic ingredient, and we can harness this as a drug? More likely it’s a complex interplay between multiple bacterial species needed to direct the immune response. Is there a group of microbes that is the same from person to person, or is it more complex?”
Then there are pending regulatory concerns. “We know that FMT works for [Clostridioides] difficile colitis but it’s not officially [Food and Drug Administration] approved,” Dr. Greiling said. “The FDA is really struggling with how to approve or regulate using bacteria as a drug. Where is that crossover? That inhibits things moving forward, for good reason. You want to balance safety with live microbes.”
The UPMC clinical trial was supported by Merck. Dr. Zarour disclosed that he is supported by grants from the National Cancer Institute and the James W. and Frances G. McGlothlin Chair in Melanoma Immunotherapy Research at UPMC. The Israeli study was funded by the Ella Lemelbaum Institute for Immuno-Oncology. Dr. Baruch was supported by the Allen Berg Fund for Excellence in Immuno-Oncology Research. Dr. Greiling and Dr. Harris-Tryon reported having no relevant financial disclosures.