Microbiome Modifiers and Cancer Immunotherapy - Seerave & MVIF Symposium
The gut microbiome is a modifiable determinant of response to immune checkpoint inhibitors, yet it remains one of the most underrecognised variables in immuno-oncology practice. Multiple lines of evidence including a soon-to-be published meta-analysis of 116 cohorts and nearly 98,000 cancer patients has established a significant association between antibiotic exposure and worse survival outcomes, with the sharpest impact seen in patients exposed immediately before ICI initiation. As approximately 30% of ICI-treated patients receive antibiotics and immunotherapy indications continue to expand, being able to define ways of rationalising the use of microbiome-modifiers holds significant benefit for patients.
Antibiotics are not the only variable in play. Diet, co-medications such as proton pump inhibitors, and other microbiome modifiers further shape how patients respond to treatment. Coordinated strategies to address these factors at scale remain lacking.
This symposium brings together researchers, clinicians, and innovators to share recent advances and results of their work. In partnership with the Microbiome Virtual International Forum (MVIF), the Seerave Foundation convenes a global community to advance a shared oncology-microbiome agenda, spanning antibiotic stewardship, microbiome-centred interventions, and emerging immunotherapies including CAR-T with a focused aim: translating evidence into actionable clinical recommendations that improve patient outcomes.
The symposium is held across two sessions, Atlantic and Pacific, with distinct speaker programmes in each session.
Atlantic Event
Introduction: Seerave Foundation & MVIF
1. Gut dysbiosis and immunoresistance in oncology
By Prof. Laurence Zitvogel, Institut Gustave Roussy, France
Evidence from the past decade demonstrates that gut dysbiosis is a potentially modifiable contributor to immunotherapy resistance in cancer, creating a need to incorporate patients’ gut microbial ecology into both oncological research and clinical care. We review gut microbial signatures associated with treatment response across cancer types and evaluate stool- and blood-based biomarkers of dysbiosis, including microbial metabolites, host inflammatory signatures, and composite tools such as TOPOSCORE that aim to characterise individual gut ecology. We then consider how these biomarkers could be integrated into clinical research and practice. Combined with medical history and lifestyle factors, gut microbial biomarkers may help identify patients most likely to benefit from microbiota-centred interventions and improve treatment outcomes. Clinical translation will require prospective validation and standardisation of trial design, sample collection and processing, analytical methods, and reporting. These advances could enable more precise, microbiome-informed strategies for overcoming immunotherapy resistance in cancer.
Session One: The role of antibiotic stewardship in Cancer Immunotherapy
2. Antibiotics, gut microbiome, and cancer immunotherapy
By Gianluca Ianiro, Fondazione Policlinico A. Gemelli, Rome, Italy
3. Microbiome from bench-to-bedside in 2026 and beyond
By Dr. Arielle Elkrief, CHUM, Université de Montréal, Canada
4. FLR-101, an engineered probiotic medical food for the management of antibiotic perturbations to the gut microbiome
By Dr. Andres Cubillos Ruiz & Dr. Raphael Gayet, Florey Biosciences, USA
Session Two: Beyond antibiotics: Diet, PPIs and Polypharmacy as clinically relevant drivers of cancer-related dysbiosis or modulator of cancer Immunotherapy?
5. Diet as a Microbiome Modifier: Ecological Considerations for Its Use Alongside Cancer Immunotherapy
By Prof. Dr. Jens Walter, APC Microbiome Institute and University College Cork, Ireland
Diet is a measurable modulator of the gut microbiome, but its effects are context-dependent, individualized, and constrained by microbial ecology. Plant-forward diets and targeted substrates such as fibre and prebiotics can induce substantial shifts in specific taxa, yet cohort-wide effects on overall community composition are often modest compared with dominant inter-individual differences. Diversity is also an imperfect marker of benefit, particularly in cancer patients whose microbiomes may already be disrupted by disease, treatment, and antibiotics. This talk will discuss what diet can realistically achieve as a microbiome modifier, using an ecological perspective that distinguishes taxonomic change, community-level constraints, and microbial function. I will argue that the most clinically relevant effects of diet may lie less in broadly “remodelling” the microbiome and more in shaping microbial metabolism, including short-chain fatty acids, tryptophan-derived metabolites, bile acids, and other pathways that plausibly connect diet, the microbiome, and immune function. The presentation will highlight opportunities, misconceptions, and key evidence gaps for dietary strategies alongside cancer immunotherapy.
6. Proton Pump Inhibitors and the Microbiome
By Prof. Rinse Weersma, University Medical Center Groningen, The Netherlands
Proton Pump Inhibitors are widely used in the population, frequently for non-evidence based indications. Increasingly they are implicated in unfavourable changes in the microbiome composition driven by "oralization" of the fecal microbiome. There is emerging evidence that the use of PPIs is associated with decreased efficacy of ICI and CAR-T treatment, potentially driven by these microbiome changes. We will discuss this and other topics around PPI use in the presenation. Is it time for PPI-stewardship?
7. Recent studies of roles of other medications (PPIs, SSRIs, benzodiazepines, OTC, probiotics) and response to immunotherapy: what should the clinician know?
By Dr. Bertrand Routy, Centre Hospitalier de l’Université de Montréal, Canada
Review the data on the impact of co-medication on microbiome composition and clinical outcome.
8. Disruption score and its impact
By Martin Jack Blaser, Rutgers, The State University of New Jersey, USA
Pacific Event
Introduction: Seerave Foundation & MVIF
1. Targeting the microbiome to promote health and end cancer
By Prof. Jennifer Wargo, The University of Texas MD Anderson Cancer Center, USA
Cancer immunotherapy has transformed oncology by reactivating the immune system’s ability to recognize and eliminate cancer cells. However, many patients still do not respond, and treatment-related toxicity remains a major challenge. In this talk, Dr. Jennifer Wargo will discuss how the human microbiome shapes immunity, cancer biology, and response to therapy.
Drawing on foundational concepts in immune activation and checkpoint blockade, the presentation will highlight emerging evidence that microbes within tumors, the gut, and other body sites can influence carcinogenesis, treatment response, and overall physiology. Dr. Wargo will review studies showing that the gut microbiome differs between patients who respond and do not respond to immunotherapy, and that microbiome-targeted approaches may help improve outcomes. Emphasis will be placed on diet and dietary fiber, including evidence that fiber-fermenting gut bacteria and sufficient dietary fiber intake are associated with improved response to immune checkpoint blockade.
The talk will also explore the broader potential of microbiome monitoring and modulation as a new pillar of cancer care, that may support treatment, interception, prevention, toxicity and long-term health. As part of the presentation, Dr. Wargo will share a preview of early findings from ongoing, unpublished clinical trials, offering a glimpse into how microbiome-directed strategies may be translated into future cancer care. By connecting cancer immunology, microbiome science, diet, lifestyle, and prevention, Dr. Wargo will outline a vision for targeting the microbiome to promote health and help end cancer.
Session One: What can the solid tumor field learn from a decade of hematological oncology
2. Preclinical and clinical assessments: The impact of the gut microbiome on CAR T cells
By Dr. Melody Smith, Stanford University School of Medicine, USA
3. Microbiome from bench-to-bedside in 2026 and beyond
By Dr. Arielle Elkrief, CHUM, Université de Montréal, Canada
4. FLR-101, an engineered probiotic medical food for the management of antibiotic perturbations to the gut microbiome
By Dr. Andres Cubillos & Raphaël Gayetz, Florey Biosciences, USA
Session two: Can diet/nutrition be leveraged to enhance cancer Immunotherapy?
5. Diet, the microbiome and solid tumor treatment response: State of the evidence
By Dr. Jennifer McQuade, Seerave Foundation
The gut microbiome is a critical determinant of response, resistance, and toxicity to immune checkpoint inhibitors (ICI), and diet represents one of the most powerful and modifiable influences on microbial composition and function. This talk reviews the current state of evidence linking dietary patterns and specific dietary components to immunotherapy outcomes in solid tumors — from preclinical data establishing mechanistic links between diet, pro-ICI microbial taxa, and microbiome-derived metabolites, to observational and interventional clinical data from trials testing high-fiber and prebiotic dietary strategies in patients undergoing immunotherapy. The functional consequences of diet-driven shifts in microbiome composition, including changes in microbial metabolite output and immune crosstalk, will be highlighted as key mediators of treatment response.
6. The Molecular Language of Food: A New Frontier for Human Biology and Therapeutic Discovery
By Dr. Selena Ahmed (American Heart Association) & Dr. Nile Nair (Harvard University and American Heart Association)
Food contains thousands of biologically active molecules that influence human biology. The Periodic Table of Food Initiative (PTFI) is a global collaboration creating the world's largest standardized molecular atlas of edible biodiversity through harmonized multi-omics methods and open-access data. This presentation will explore how PTFI enables therapeutic discovery by linking food-derived molecules to biological pathways. Applications include bioactivity-informed meal design through the Swap It Smart platform, predictive modeling of food–biology interactions, and experimental and clinical validation to advance precision nutrition, biomarker discovery, and therapeutic innovation.
7. Regulatory Pathways for Medical Foods
By Lisa Navarro & Carly Pavia, Ramboll (Americas)