Researchers identify IgA+ B cells as immunosuppressive culprits in tumors and demonstrate how dietary intervention reactivates antitumor immunity.
Colorectal cancer (CRC), the third most common cancer globally, often resists conventional therapies due to its immunosuppressive tumor microenvironment. A new study led by scientists at Fudan University, Shanghai, published in Cancer Research, reveals how a fasting-mimicking diet (FMD) — a low-calorie, low-protein dietary regimen — disrupts this immunosuppression by targeting IgA-producing B cells. The findings provide a novel metabolic-immunological axis for enhancing cancer therapy.
What is a Fasting-Mimicking Diet (FMD)?
FMD involves short, cyclic periods of calorie restriction (300–600 kcal/day) designed to mimic fasting while providing essential nutrients. Unlike extreme fasting, FMD includes plant-based foods like vegetable broths, olive oil, and whole grains, making it safer and feasible for cancer patients. In this study, both mice and human participants underwent 3-day FMD cycles, which reduced caloric intake without severe side effects.
Study Design & Methodology
- Preclinical Models:
- Orthotopic CRC Mice: MC38 cancer cells were implanted into the colons of mice, followed by FMD cycles.
- AOM/DSS Model: Mice were treated with azoxymethane (a carcinogen) and dextran sodium sulfate (to induce colitis), mimicking human CRC progression.
- IgA-Deficient Mice (Iga⁻/⁻): These mice lacked IgA-producing B cells to test their role in tumor suppression.
- Single-Cell RNA Sequencing:
- Immune cells from tumors were analyzed to map changes in the tumor microenvironment post-FMD.
- Clinical Trial (ChiCTR2200062524):
- 20 CRC patients were randomized into FMD or control groups for 3 days pre-surgery. Blood, fecal, and tumor tissue samples were collected to assess IgA levels and metabolic markers.
Key Findings
- FMD Reduces Immunosuppressive IgA+ B Cells:
- In mice, FMD decreased tumor-infiltrating IgA+ plasma cells by 50–60%, as shown by scRNA-seq and flow cytometry. These cells secreted TGF-β1 and PD-L1, molecules that inhibit CD8+ T cell function.
- Transferring IgA+ B cells into FMD-treated mice reversed tumor suppression, confirming their immunosuppressive role.
- Metabolic Switch to Fatty Acid Oxidation (FAO):
- FMD upregulated CPT1A, a key enzyme in FAO, in B cells. This shift increased acetyl-CoA levels, triggering acetylation of the transcription factor RUNX3.
- Acetylated RUNX3 failed to bind the Igha promoter, blocking IgA class switching. Inhibiting FAO with etomoxir restored IgA production, while activating FAO with C75 mimicked FMD’s effects.
- Human Clinical Trial Results:
- Post-FMD, CRC patients showed a 40% reduction in fecal IgA and 35% lower IgA in tumor homogenates.
- Flow cytometry revealed increased CPT1A expression in B cells, correlating with reduced IgA. Mild side effects (e.g., fatigue) were reported in 10% of participants.
Mechanistic Insights
- IgA+ B Cells as Regulatory Immune Cells:
IgA+ B cells, traditionally associated with gut mucosal immunity, were found to act as regulatory B cells (Bregs) in tumors. Their immunosuppressive phenotype (PD-L1+, TGF-β1+) directly inhibited CD8+ T cell cytotoxicity. - Metabolic-Immune Crosstalk:
FMD’s activation of FAO in B cells disrupted their metabolic dependency on glycolysis, which is critical for IgA production. This metabolic reprogramming “starved” B cells of the energy required for immunosuppressive functions.
Implications for Cancer Therapy
- Combination with Immunotherapy:
FMD could enhance checkpoint inhibitors (e.g., anti-PD-1) by alleviating PD-L1-mediated T cell exhaustion. - Biomarker Potential:
High CPT1A expression and low IgA+ B cell infiltration may predict FMD efficacy, enabling personalized dietary interventions. - Beyond Colorectal Cancer:
The mechanism may apply to other cancers dominated by IgA+ B cells, such as pancreatic or liver cancers.
Quotes from Researchers
- Dr. Changhong Miao, co-corresponding author:
“Our work bridges metabolism and immunity. By rewiring B cell metabolism, FMD turns ‘bad’ immune cells into bystanders, allowing the body’s defenses to attack tumors.” - Dr. Ronghua Liu, co-corresponding author:
“This is the first evidence that a dietary intervention can directly modulate B cell class switching. It opens doors for non-toxic adjuncts to conventional therapies.”
Practical Takeaways
- For Patients:
FMD is not a standalone cure but a promising adjunct to chemotherapy or immunotherapy. Consult oncologists before attempting dietary changes. - For Clinicians:
Monitoring IgA+ B cells and CPT1A levels could help tailor FMD protocols for individual patients.
Future Directions
- Phase II trials to validate FMD’s efficacy in larger CRC cohorts.
- Exploring FMD’s synergy with CAR-T therapy or radiation.
- Developing FAO-activating drugs to mimic FMD’s benefits without dietary restrictions.
References
- Primary Study:
Zhong, Z., Zhang, H., Nan, K. et al. Fasting-Mimicking Diet Drives Antitumor Immunity Against Colorectal Cancer by Reducing IgA-Producing Cells. Cancer Research (2023). DOI: [Forthcoming; Preprint Available on Request]. - Supporting Studies:
- Vernieri, C. et al. (2022). Fasting-Mimicking Diet Reshapes Metabolism and Antitumor Immunity. Cancer Discov. 12(1):90–107. [DOI: 10.1158/2159-8290.CD-21-0030]
- Shalapour, S. et al. (2015). Immunosuppressive Plasma Cells Impede T-Cell-Dependent Chemotherapy. Nature. 521(7550):94–98. [DOI: 10.1038/nature14395]
- Mihaylova, M.M. et al. (2018). Fasting Activates Fatty Acid Oxidation to Enhance Intestinal Stem Cell Function. Cell Stem Cell. 22(5):769–778. [DOI: 10.1016/j.stem.2018.04.001]
- Clinical Trials
ChiCTR2200062524: Safety and Immunomodulatory Effects of FMD in Colorectal Cancer Patients (2022).
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